The function of this website is to provide a single place to access relevant Arginine research studies. Where possible we have included full text of the studies.
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Randomized, Double-Blind, Placebo-Controlled Study of Supplemental Oral L-Arginine in Patients With Heart Failure
Thomas S. Rector, PhD; Alan J. Bank, MD; Kathleen A. Mullen, RN; Linda K. Tschumperlin, RN; Ronald Sih, MD; Kamalesh Pillai, MD; Spencer H. Kubo, MD
From the Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis.
Correspondence to Thomas S. Rector, PhD, Box 508 UMHC, University of Minnesota Medical School, 420 Delaware St SE, Minneapolis, MN 55455.
Background Patients with heart failure have reduced peripheral blood flow at rest, during exercise, and in response to endothelium-dependent vasodilators. Nitric oxide formed from L-arginine metabolism in endothelial cells contributes to regulation of blood flow under these conditions. A randomized, double-blind crossover study design was used to determine whether supplemental oralL-arginine can augment peripheral blood flow and improve functional status in patients with moderate to severe heart failure.
Methods and Results Fifteen subjects were given 6 weeks of oral L-argininehydrochloride (5.6 to 12.6 g/d) and 6 weeks of matched placebo capsules in random sequence. Compared with placebo, supplemental oral L-argininesignificantly increased forearm blood flow during forearm exercise, on average from 5.1±2.8 to 6.6±3.4 mL·min-1·dL-1 (P<.05). Furthermore, functional status was significantly better on L-arginine compared with placebo, as indicated by increased distances during a 6-minute walk test (390±91 versus 422±86 m,P<.05) and lower scores on the Living With Heart Failure questionnaire (55±28 versus 42±26, P<.05). Oral L-arginine also improved arterial compliance from 1.99±0.38 to 2.36±0.30 mL/mm Hg (P<.001) and reduced circulating levels of endothelin from 1.9±1.1 to 1.5±1.1 pmol/L (P<.05).
Conclusions Supplemental oral L-arginine had beneficial effects in patients with heart failure. Further studies are needed to confirm the therapeutic potential of supplemental oral L-arginine and to identify mechanisms of action in patients with heart failure.
Impaired L-Arginine Transport and Endothelial Function in Hypertensive and Genetically Predisposed Normotensive Subjects
- Markus P. Schlaich, MD;
- Melinda M. Parnell, PhD;
- Belinda A. Ahlers, PhD;
- Samara Finch, BSc;
- Tanneale Marshall, BSc;
- Wei-Zheng Zhang, PhD;
- David M. Kaye, MD, PhD
From the Wynn Department of Metabolic Cardiology, Baker Heart Research Institute, Melbourne, Victoria, Australia.
- Correspondence to Dr David Kaye, Wynn Department of Metabolic Cardiology, Baker Heart Research Institute, PO Box 6492, St Kilda Rd Central, Melbourne, Victoria 8008, Australia. E-mail email@example.com
Background— Impaired endothelium-dependent NO-mediated vasodilation is a key feature of essential hypertension and may precede the increase in blood pressure. We investigated whether transport of the NO precursor L-arginine is related to decreased endothelial function.
Methods and Results— Radiotracer kinetics ([3H]L-arginine) were used to measure forearm and peripheral blood mononuclear cell arginine uptake in hypertensive subjects (n=12) and in 2 groups of healthy volunteers with (n=15) and without (n=15) a family history of hypertension. In conjunction, forearm blood flow responses to acetylcholine and sodium nitroprusside were measured before and after a supplemental intra-arterial infusion of L-arginine. In vivo and in vitro measures of L-arginine transport were substantially reduced in the essential hypertension and positive family history groups compared with the negative family history group; however, no difference was detected in peripheral blood mononuclear cell mRNA or protein expression levels for the cationic amino acid transporter CAT-1. Plasma concentrations of L-arginine and NG,NG′-dimethylarginine (ADMA) did not differ between groups. L-Arginine supplementation improved the response to acetylcholine only in subjects with essential hypertension and positive family history.
Conclusions— Similar to their hypertensive counterparts, normotensive individuals at high risk for the development of hypertension are characterized by impaired L-arginine transport, which may represent the link between a defective L-arginine/NO pathway and the onset of essential hypertension. The observed transport defect is not due to apparent alterations in CAT-1 expression or elevated endogenous ADMA.
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L-Arginine Prevents Xanthoma Development and Inhibits Atherosclerosis in LDL Receptor Knockout Mice
Walif Aji, MD; Stefano Ravalli, MD; Matthias Szabolcs, MD; Xian-cheng Jiang, PhD; Robert R. Sciacca, Eng ScD; Robert E. Michler, MD; Paul J. Cannon, MD
the Departments of Medicine (W.A., S.R., X.J., R.R.S., P.J.C.), Surgery (R.E.M.), and Pathology (M.S.), Columbia University College of Physicians and Surgeons, New York, NY.
Correspondence to Paul J. Cannon, MD, Department of Medicine, Division of Cardiology, Columbia University, 630 W 168th St, New York, NY 10032.
Background The potential antiatherosclerotic actions of NO were investigated in four groups of mice (n=10 per group) lacking functional LDL receptor genes, an animal model of familial hypercholesterolemia. Group 1 was fed a regular chow diet. Groups 2 through 4 were fed a 1.25% high-cholesterol diet. In addition, group 3 received supplemental L-arginine and group 4 received L-arginine and Nω-nitro-L-arginine (L-NA), an inhibitor of NO synthase (NOS).
Methods and Results Animals were killed at 6 months; aortas were stained with oil red O for planimetry and with antibodies against constitutive and inducible NOSs. Plasma cholesterol was markedly increased in the animals receiving the high-cholesterol diet. Xanthomas appeared in all mice fed the high-cholesterol diet alone but not in those receiving L-arginine. Aortic atherosclerosis was present in all mice on the high-cholesterol diet. The mean atherosclerotic lesion area was reduced significantly (P<.01) in the cholesterol-fed mice given L-arginine compared with those receiving the high-cholesterol diet alone. The mean atherosclerotic lesion area was significantly larger (P<.01) in cholesterol-fed mice receiving L-arginine + L-NA than in those on the high-cholesterol diet alone. Within the atherosclerotic plaques, endothelial cells immunoreacted for endothelial cell NOS; macrophages, foam cells, and smooth muscle cells immunostained strongly for inducible NOS and nitrotyrosine residues.
Conclusions The data indicate that L-arginine prevents xanthoma formation and reduces atherosclerosis in LDL receptor knockout mice fed a high-cholesterol diet. The abrogation of the beneficial effects of L-arginine by L-NA suggests that the antiatherosclerotic actions of L-arginine are mediated by NOS. The data suggest that L-arginine may be beneficial in familial hypercholesterolemia.
Long-term L-Arginine Supplementation Improves Small-Vessel Coronary Endothelial Function in Humans
Amir Lerman, MD; John C. Burnett, Jr, MD; Stuart T. Higano, MD; Linda J. McKinley, RN; ; David R. Holmes, Jr, MD
From the Department of Internal Medicine and Division of Cardiovascular Diseases, Mayo Clinic and Foundation, Rochester, Minn.
Correspondence to Amir Lerman, MD, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN 55905. E-mail firstname.lastname@example.org
Background—Coronary endothelial dysfunction is characterized by an imbalance between endothelium-derived vasodilating and vasoconstricting factors and coronary vasoconstriction in response to the endothelium-dependent vasodilator acetylcholine. Thus, the present double-blind, randomized study was designed to test the hypothesis that long-term, 6-month supplementation of L-arginine, the precursor of the endothelium-derived vasodilator NO, reverses coronary endothelial dysfunction to acetylcholine in humans with nonobstructive coronary artery disease.
Methods and Results—Twenty-six patients without significant coronary artery disease on coronary angiography and intravascular ultrasound were blindly randomized to either oral L-arginine or placebo, 3 g TID. Endothelium-dependent coronary blood flow reserve to acetylcholine (10-6 to 10-4 mol/L) was assessed at baseline and after 6 months of therapy. There was no difference between the two study groups in clinical characteristics or in the coronary blood flow in the response to acetylcholine at baseline. After 6 months, the coronary blood flow in response to acetylcholine in the subjects who were taking L-arginine increased compared with the placebo group (149±20% versus 6±9%, P<0.05). This was associated with a decrease in plasma endothelin concentrations and an improvement in patients' symptoms scores in the L-arginine treatment group compared with the placebo group.
Conclusions—Long-term oral L-arginine supplementation for 6 months in humans improves coronary small-vessel endothelial function in association with a significant improvement in symptoms and a decrease in plasma endothelin concentrations. This study proposes a role for L-arginine as a therapeutic option for patients with coronary endothelial dysfunction and nonobstructive coronary artery disease.
Full Study PDF: PDF
Effect of L-arginine or L-citrulline oral supplementation on blood pressure and right ventricular function in heart failure patients with preserved ejection fraction
source = http://www.ncbi.nlm.nih.gov/pubmed/21154265
The effect of L-arginine and L-citrulline on blood pressure and right ventricular function in heart failure patients with preserved ejection fraction (HFpEF) is unknown. We have therefore evaluated, in a randomized clinical trial, the effect of these aminoacids in chronic outstanding and stable patients with HFpEF.
METHODS AND RESULTS:
All patients underwent an echocardiogram and radioisotopic ventriculography rest/exercise, and were randomized in a consecutive manner to the L-arginine group (n = 15; 8 g/day); and thecitrulline malate group (n = 15; 3 g/day). The duration of follow-up was two months. The principal echocardiographic finding was a statistically significant decrease in pulmonary artery pressure in the L-arginine (56.3 ± 10 vs 44 ± 16.5 mm Hg, p < 0.05) and the citrulline (56.67 ± 7.96 vs 47.67 ± 8.59 mm Hg, p < 0.05) groups. Duration on treadmill and right ventricular ejection fraction post exercise increased, while diastolic and systolic artery pressure decreased significantly in both groups. There were no other statistically significant differences between the groups.
Administration of L-arginine and citrulline to patients with HFpEF improved right ventricular function by increasing right ventricular ejection fraction, and probably decreasing systolic pulmonary artery pressure.
Insulin resistance in obesity and metabolic syndrome: is there a connection with platelet l-arginine transport?
Departamento de Farmacologia e Psicobiologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil.
Assumpção CR, Brunini TM, Pereira NR, Godoy-Matos AF, Siqueira MA, Mann GE, Mendes-Ribeiro AC.
Nitric oxide (NO) is a short-lived gaseous messenger with multiple physiological functions including regulation of blood flow, platelet adhesion and aggregation inhibition. NO synthases (NOS) catalyze the conversion of cationic amino acid L-arginine in L-citrulline and NO. Despite an increasing prevalence of obesity and metabolic syndrome (MetS) in the last decades, the exact mechanisms involved in the pathogenesis and cardiovascular complications are not fully understood. We have examined the effects of obesity and MetS on the L-arginine-NO-cGMP pathway in platelets from a population of adolescents.
A total of twenty six adolescent patients (13 with obesity and 13 with MetS) and healthy volunteers (n=14) participated in this study. Transport of L-arginine, NO synthase (NOS) activity and cGMP content in platelets were analyzed. Moreover, platelet function, plasma levels of L-arginine, metabolic and clinical markers were investigated in these patients and controls.
L-arginine transport (pmol/10(9) cells/min) in platelets via system y(+)L was diminished in obese subjects (20.8±4.7, n=10) and MetS patients (18.4±3.8, n=10) compared to controls (52.3±14.8, n=10). The y(+)L transport system correlated negatively to insulin levels and Homeostasis Model Assessment of Insulin Resistance (HOMA IR) index. No differences in NOS activity and cGMP content were found among the groups. Moreover, plasma levels of L-arginine were not affected by obesity or MetS.
Our study provides the first evidence that obesity and MetS lead to a dysfunction of L-arginine influx, which negatively correlates to insulin resistance. These findings could be a premature marker of futurecardiovascular complications during adulthood.
The role of ADMA and arginine in the failing heart and its vasculature.
Visser M, Paulus WJ, Vermeulen MA, Richir MC, Davids M, Wisselink W, de Mol BA, van Leeuwen PA.
Department of Surgery, VU University Medical Center, Amsterdam, The Netherlands
Eur J Heart Fail. 2010 Dec;12(12):1274-81. Epub 2010 Oct 5.
Nitric oxide (NO) is formed from arginine by the enzyme nitric oxide synthase (NOS). Asymmetric dimethylarginine (ADMA) can inhibit NO production by competing with arginine for NOS binding. Therefore, the net amount of NO might be indicated by the arginine/ADMA ratio. In turn, arginine can be metabolized by the enzyme arginase, and ADMA by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). While ADMA has been implicated as a cardiovascular risk factor, arginine supplementation has been indicated as a treatment in cardiac diseases.
This review discusses the roles of ADMA and arginine in the failing heart and its vasculature. Furthermore, it proposes nutritional therapies to improve NO availability.
The effect of L-arginine and citrulline on endothelial function in patients in heart failure with preserved ejection fraction.
Orea-Tejeda A, Orozco-Gutiérrez JJ, Castillo-Martínez L, Keirns-Davies C, Montano-Hernández P, Vázquez-Díaz O, Valdespino-Trejo A, Infante O, Martínez-Memije R.
Heart Failure Clinic, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, Mexico.
Cardiol J. 2010;17(5):464-70.
To evaluate the effect of the amino acids L-arginine and citrulline on endothelial function in patients in stable diastolic and right heart failure using photoplethysmography.
Thirty patients from the Heart Failure Clinic of the Instituto Nacional de Ciencias Médicas y Nutrición "Salvador Zubirán" underwent photoplethysmography using the hyperemia technique. Index finger flow was assessed at baseline and after ischemia every 30 s by maximum amplitude time (MAT), total time of the curve (TT) and the index of the two (MAT/TT < 30 = normal) before and after the administration of L-arginine (8 g/day in two doses, n = 15) or citrulline (3 g/day in one dose, n = 15) for 60 days in addition to optimal pharmacological treatment.
There were no statistically significant differences between the two groups at baseline. After the intervention, the MAT/TT index of all patients normalized in each evaluation period with statistically significant differences. Basal L-arginine group = 38.75 ± 11.52, final 23.32 ± 6.08, p = 0.007 and basal citrulline group = 41.4 ± 13.47, final 23.65 ± 6.74, p = 0.007 at 60-90 s. Post-ischemia: basal L-arginine 36.60 ± 11.51, final 18.81 ± 15.13, p = 0.004 and basal citrulline = 49.51 ± 15.17, final 27.13 ± 7.87, p = 0.003.
The administration of L-arginine and citrulline has a beneficial effect on endothelial function as shown by the normalized MAT/TT index. It probably improves systemic and pulmonary hemodynamics, which could help in the treatment of diastolic heart failure.
Effects of L-citrulline (watermelon supplementation) on aortic blood pressure and wave reflection in individuals with prehypertension: a pilot study.
Figueroa A, Sanchez-Gonzalez MA, Perkins-Veazie PM, Arjmandi BH.
Department of Nutrition, Food and Exercise Sciences, Florida State University, Tallahassee, USA. email@example.com
Am J Hypertens. 2011 Jan;24(1):40-4. Epub 2010 Jul 8.
Oral L-citrulline is efficiently converted to L-arginine, the precursor for endothelial nitric oxide (NO) synthesis. Oral L-arginine supplementation reduces brachial blood pressure (BP). We evaluated the effects of watermelon supplementation on aortic BP and arterial function in individuals with prehypertension.
Heart rate (HR), brachial systolic BP (bSBP), brachial pulse pressure (bPP), aortic SBP (aSBP), aortic PP (aPP), augmentation index (AIx), AIx adjusted for HR of 75 beats/min (AIx@75), amplitude of the first (P1) and second (P2) systolic peaks, reflection time (Tr), and carotid-femoral pulse wave velocity (PWV) were evaluated in the supine position in nine subjects (four men/five women, age 54 ± 3 years) with prehypertension (134/77 ± 5/3 mm Hg). Subjects were randomly assigned to 6 weeks of watermelon supplementation (L-citrulline/L arginine, 2.7 g/1.3 g/day) or placebo followed by a 4-week washout period and then crossover.
There was a significant treatment effect (change in the value of watermelon minus placebo from baseline to 6 weeks) on bPP (-8 ± 3 mm Hg, P < 0.05), aSBP (-7 ± 2 mm Hg, P < 0.05), aPP (-6 ± 2 mm Hg, P < 0.01), AIx (-6 ± 3%, P < 0.05), AIx@75 (-4 ± 2%, P < 0.05), and P2 (-2 ± 1 mm Hg, P < 0.05). There was no significant treatment effect (P > 0.05) on bSBP, brachial diastolic BP (DBP), aortic DBP, Tr, P1, HR, and carotid-femoral PWV.
This pilot study shows that watermelon supplementation improves aortic hemodynamics through a decrease in the amplitude of the reflected wave in individuals with prehypertension.
Oral L-citrulline supplementation attenuates blood pressure response to cold pressor test in young men.
Figueroa A, Trivino JA, Sanchez-Gonzalez MA, Vicil F.
Department of Nutrition, Food and Exercise Sciences, College of Human Sciences, Florida State University, Tallahassee, Florida, USA. firstname.lastname@example.org
Am J Hypertens. 2010 Jan;23(1):12-6. Epub 2009 Oct 22.
Oral L-citrulline is efficiently converted to L-arginine, which has been shown to decrease brachial blood pressure (BP) at rest and during the cold pressor test (CPT). However, aortic BP may better reflectcardiovascular risk than brachial BP. The purpose of this study was to test the hypothesis that oral L-citrulline supplementation attenuates brachial BP and aortic hemodynamic responses to CPT.
Brachial BP, aortic BP, stroke volume (SV), and wave reflection at rest and during CPT were evaluated in 17 young (21.6 +/- 0.9 years) normotensive men. Subjects were randomly assigned to 4 weeks of oral L-citrulline (6 g/day) or placebo in a crossover design. Hemodynamic responses to CPT were reevaluated after each treatment.
During CPT, there were significant (P < 0.05) increases in brachial and aortic BP [systolic (SBP), diastolic (DBP), and pulse pressure (PP)], augmentation index (AIx), SV, and a decrease in transit time of the reflected wave (Tr) from baseline. Compared to placebo, oral L-citrulline treatment decreased (P < 0.05) brachial SBP (-6 +/- 11 mm Hg), aortic SBP (-4 +/- 10 mm Hg), and aortic PP (-3 +/- 6 mm Hg) during CPT but not at rest. There was an inverse correlation (r = -0.40, P < 0.05) between changes in aortic SBP and Tr during CPT after L-citrulline supplementation.
We conclude that oral L-citrulline supplementation attenuates the brachial SBP, aortic SBP, and aortic PP responses to CPT in young normotensive men. Increased wave reflection time contributes to the reduction in aortic SBP response to CPT.
Diminished global arginine bioavailability and increased arginine catabolism as metabolic profile of increased cardiovascular risk.
Tang WH, Wang Z, Cho L, Brennan DM, Hazen SL.
Center for Cardiovascular Diagnostics and Prevention, Department of Cell Biology, Lerner Research Institute, Cleveland, OH, USA. email@example.com
J Am Coll Cardiol. 2009 Jun 2;53(22):2061-7.
We hypothesized that an integrated assessment of arginine with its catabolic products might better predict cardiovascular risks than arginine levels alone.
Arginine is the sole nitrogen source for nitric oxide (NO) synthesis. The major catabolic products of arginine are ornithine and citrulline.
Plasma levels of free arginine, ornithine, citrulline, and the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) were measured with liquid chromatography coupled with tandem mass spectrometry. We examined the relationship of global arginine bioavailability ratio (GABR) (defined as arginine/[ornithine + citrulline]) versus arginine and its catabolic metabolites to prevalence of significantly obstructive coronary artery disease (CAD) and incidence of major adverse cardiovascular events (MACE) (death, myocardial infarction, stroke) over a 3-year follow-up in 1,010 subjects undergoing elective cardiac catheterization.
Patients with significantly obstructive CAD had significantly lower GABR (median [interquartile range]: 1.06 [0.75 to 1.31] vs. 1.27 [0.96 to 1.73], p < 0.001) and arginine levels [mean: 68 +/- 20 micromol/l vs. 74 +/- 24 micromol/l, p < 0.001) than those without significantly obstructive CAD. After adjusting for Framingham risk score, C-reactive protein, and renal function, lower GABR (but not arginine levels) and higher citrulline levels remained significantly associated with both the prevalence of significantly obstructive CAD (adjusted odds ratio: 3.93, p < 0.001, and 5.98, p < 0.001, respectively) and 3-year risk for the incidence of MACE (adjusted hazard ratio: 1.98, p = 0.025, and 2.40, p = 0.01, respectively) and remained significant after adjusting for ADMA.
GABR might serve as a more comprehensive concept of reduced NO synthetic capacity compared with systemic arginine levels. Diminished GABR and high citrulline levels are associated with both development of significantly obstructive atherosclerotic CAD and heightened long-term risk for MACE.
|Arginine metabolism and nutrition in growth, health and disease.
Wu G, Bazer FW, Davis TA, Kim SW, Li P, Marc Rhoads J, Carey Satterfield M, Smith SB, Spencer TE, Yin Y.
Department of Animal Science, Texas A&M University, College Station, TX 77843, USA. firstname.lastname@example.org
Amino Acids. 2009 May;37(1):153-68. Epub 2008 Nov 23.
L-Arginine (Arg) is synthesised from glutamine, glutamate, and proline via the intestinal-renal axis in humans and most other mammals (including pigs, sheep and rats). Arg degradation occurs via multiple pathways that are initiated by arginase, nitric-oxide synthase, Arg:glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine, and agmatine with each having enormous biological importance. Arg is also required for the detoxification of ammonia, which is an extremely toxic substance for the central nervous system. There is compelling evidence that Arg regulates interorgan metabolism of energy substrates and the function of multiple organs. The results of both experimental and clinical studies indicate that Arg is a nutritionally essential amino acid (AA) for spermatogenesis, embryonic survival, fetal and neonatal growth, as well as maintenance of vascular tone and hemodynamics.
Moreover, a growing body of evidence clearly indicates that dietary supplementation or intravenous administration of Arg is beneficial in improving reproductive, cardiovascular, pulmonary, renal, gastrointestinal, liver and immune functions, as well as facilitating wound healing, enhancing insulin sensitivity, and maintaining tissue integrity. Additionally, Arg or L-citrulline may provide novel and effective therapies for obesity, diabetes, and the metabolic syndrome. The effect of Arg in treating many developmental and health problems is unique among AAs, and offers great promise for improved health and wellbeing of humans and animals.
Platelet nitric oxide signalling in heart failure: role of oxidative stress.
Shah A, Passacquale G, Gkaliagkousi E, Ritter J, Ferro A.
Department of Clinical Pharmacology, Cardiovascular Division, School of Medicine, King's College London, UK.
Cardiovasc Res. 2011 Sep 1;91(4):625-31. Epub 2011 Apr 18.
Heart failure is associated with deficient endothelial nitric oxide (NO) production as well as increased oxidative stress and accelerated NO degradation. The aim of this study was to evaluate platelet NO biosynthesis and superoxide anion (O(2)(-)) production in patients with heart failure.
METHODS AND RESULTS:
In platelets from patients with heart failure due to idiopathic dilated cardiomyopathy (n= 16) and healthy control subjects (n= 23), NO synthase (NOS) activity was evaluated by L-[(3)H]-arginine to l-[(3)H]-citrulline conversion, cGMP was determined by radioimmunoassay, vasodilator-stimulated phosphoprotein (VASP: total and serine-239-phosphorylated) was assessed by western blotting, and O(2)(-) production and O(2)(-) scavenging capacity were measured by pholasin-enhanced chemiluminescence. In platelets from patients with heart failure, basal NOS activity was higher than in those from controls; furthermore, whereas platelet NOS activity increased as expected in response to albuterol or collagen in controls, no increase occurred in platelets from heart failure subjects. Despite this, basal intraplatelet NO-attributable cGMP was lower inheart failure than in control subjects, as was serine-239 phosphorylation of VASP, suggesting a decrease in bioactive NO. Platelets from heart failure subjects exhibited higher basal and collagen-stimulated O(2)(-) production and impaired O(2)(-) scavenging capacity, resulting in higher oxidative stress, consistent with the observed decrease in bioactive NO.
In heart failure, despite activation of NOS, platelets produce less bioactive NO, probably as a result of NO scavenging due to increased O(2)(-) production. This functional defect in the platelet l-arginine/NO/guanylyl cyclase pathway could contribute to the platelet activation observed in heart failure.
L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance.
Bailey SJ, Winyard PG, Vanhatalo A, Blackwell JR, Dimenna FJ, Wilkerson DP, Jones AM.
It has recently been reported that dietary nitrate supplementation which increases plasma nitrite concentration, a biomarker of nitric oxide (NO) availability, improves exercise efficiency and exercise tolerance in healthy humans. We hypothesised that dietary supplementation with L-arginine, the substrate for nitric oxide synthase (NOS), would elicit similar responses. In a double-blind, crossover study, nine healthy males (aged 19-38 years) consumed a 500 mL beverage containing 6 g of L-arginine (ARG) or a placebo beverage (PLA), and completed a series of 'step' moderate-intensity and severe-intensity exercise bouts 1 h post-ingestion.
Plasma [nitrite] was significantly greater following L-arginine consumption compared to placebo (ARG: 331 +/- 198 vs. PLA: 159 +/- 102 nM; P<0.05) and systolic blood pressure was significantly reduced (ARG: 123 +/- 3 vs. PLA: 131 +/- 5 mmHg; P<0.01). The steady-state VO(2) during moderate-intensity exercise was reduced by 7% in the ARG condition (ARG: 1.48 +/- 0.12 vs. PLA: 1.59 +/- 0.14 L*min(-1); P<0.05). During severe-intensity exercise, the VO(2) slow component amplitude was reduced (ARG: 0.58 +/- 0.23 vs. PLA: 0.76 +/- 0.29 L*min(-1); P<0.05) and the time-to-exhaustion was extended (ARG: 707 +/- 232 s vs. PLA: 562 +/- 145 s; P<0.05) following ARG.
In conclusion, similar to the effects of increased dietary nitrate intake, elevating NO bioavailability through dietary L-arginine supplementation reduced the O(2) cost of moderate-intensity exercise and blunted the VO(2) slow component and extended the time-to-exhaustion during severe-intensity exercise.
PMID: 20724562 [PubMed - as supplied by publisher]
Supplementation of L-arginine along with regular therapy may be beneficial to the patients of ischemic myocardial syndromes
Oxid Med Cell Longev. 2009 Sep-Oct;2(4):231-7.
Oral administration of L-arginine in patients with angina or following myocardial infarction may be protective by increasing plasma superoxide dismutase and total thiols with reduction in serum cholesterol and xanthine oxidase.
Tripathi P, Chandra M, Misra MK.
Department of Biochemistry, Lucknow University, Lucknow, India.Abstract
Administration of L-arginine has been shown to control ischemic injury by producing nitric oxide which dilates the vessels and thus maintains proper blood flow to the myocardium. In the present study attempt has been made to determine whether oral administration of L-arginine has any effect on oxidant/ antioxidant homeostasis in ischemic myocardial patients [represented by the patients of acute angina (AA) and acute myocardial infarction (MI)]. L-arginine has antioxidant and antiapoptotic properties, decreases endothelin-1 expression and improves endothelial function, thereby controlling oxidative injury caused during myocardial ischemic syndrome. Effect of L-arginine administration on the status of free radical scavenging enzymes, pro-oxidant enzyme and antioxidants viz. total thiols, carbonyl content and plasma ascorbic acid levels in the patients has been evaluated. We have observed that L-arginine administration (three grams per day for 15 days) resulted in increased activity of free radical scavenging enzyme superoxide dismutase (SOD) and increase in the levels of total thiols (T-SH) and ascorbic acid with concomitant decrease in lipid per-oxidation, carbonyl content, serum cholesterol and the activity of proxidant enzyme, xanthine oxidase (XO).
These findings suggest that the supplementation of L-arginine along with regular therapy may be beneficial to the patients of ischemic myocardial syndromes.
PMID: 20716909 [PubMed - in process]PMCID: PMC2763261
Aspirin and clopidogrel (Plavix) treatment impair nitric oxide biosynthesis by platelets.
O'Kane PD, Reebye V, Ji Y, Stratton P, Jackson G, Ferro A.
Department of Clinical Pharmacology, Cardiovascular Division, 3.07 Franklin-Wilkins Building, King's College London, 150 Stamford Street, London SE1 9NH, UK.
J Mol Cell Cardiol. 2008 Aug;45(2):223-9. Epub 2008 Jul 7.
Aspirin and clopidogrel (Plavix) are used therapeutically for their anti-platelet effects. We examined the effects of aspirin and clopidogrel on basal and beta-adrenoceptor (beta-AR)-mediated platelet nitric oxide (NO) synthesis in healthy subjects and patients with coronary heart disease (CHD). Healthy subjects (n=19) were randomized in a double-blind cross-over manner to receive aspirin or clopidogrel, each at 75 mg daily, for 14 days. Patients (n=17) of similar age with CHD, taking aspirin, were randomized double-blind to either continue on aspirin 75 mg daily or to receive clopidogrel 75 mg daily for 14 days. NO synthase (NOS) activity was measured from l-[(3)H]arginine to l-[(3)H]citrulline conversion, and cGMP was determined by radioimmunoassay, in platelets basally and following incubation with isoproterenol or albuterol (each at 10(-5) mol/L).
In healthy subjects, aspirin did not affect basal NOS activity or cGMP in platelets, but suppressed the normal increase in both by isoproterenol and albuterol. Clopidogrel suppressed platelet NOS activity and cGMP both basally and in response to beta-AR agonists. In platelets from CHD patients, clopidogrel suppressed basal and beta-AR-stimulated NOS activity and cGMP as compared with aspirin. Platelet NOS activity and cGMP were lower in CHD subjects pre-randomization compared with healthy subjects both pre-randomization and post-aspirin.
We conclude that chronic aspirin treatment suppresses beta-AR-stimulated but not basal platelet NO synthesis, as previously described, whereas chronic clopidogrel (Plavix) treatment suppresses both, with resultant functional consequences. Moreover, CHD may itself be associated with decreased platelet NO biosynthesis.
[PubMed - indexed for MEDLINE]
L-arginine plasma levels and severity of idiopathic pulmonary arterial hypertension.
Beyer J, Kolditz M, Ewert R, Rubens C, Opitz C, Schellong S, Hoeffken G, Halank M.
University Clinic Dresden, Medical Clinic III, Dept. of Vascular Medicine, Germany. Beyer.Jan@uniklinikum-dresden.de
Vasa. 2008 Feb;37(1):61-7.
Idiopathic pulmonary arterial hypertension (iPAH) is a rare disease of unknown aetiology characterized by a poor prognosis. Impairment of nitric oxide (NO) synthesis or NO-induced vasorelaxation has been suspected to play a role in the development of iPAH. This study was performed to investigate possible correlations between the plasma levels of the NO-related aminoacids L-arginine, L-citrulline and N-hydroxy-L-arginine (L-NHA) and the severity of iPAH.
In twelve iPAH patients hemodynamics were measured by right heart catheterization, and plasma levels of L-arginine, L-citrulline and L-NHA were determined in blood samples from the pulmonary artery, peripheral artery and peripheral vein by high-performance liquid chromatography analysis. In eight of twelve patients a six minute walk test was performed.
Plasma levels of L-arginine strongly correlated to right atrial pressure, cardiac output, cardiac index, mixed-venous oxygen saturation, six minute walk data and NYHA functional class at all sites of blood sampling (p < 0.05).
The results suggest a possible role of the NO precursor L-arginine in the pathogenesis of iPAH.
[PubMed - indexed for MEDLINE]
Obesity reduces the bioavailability of nitric oxide in juveniles.
Gruber HJ, Mayer C, Mangge H, Fauler G, Grandits N, Wilders-Truschnig M.
Clinical Institute of Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria. email@example.com
Int J Obes (Lond). 2008 May;32(5):826-31. Epub 2008 Jan 15.
There is growing evidence that nitric oxide (NO) is critically involved in obesity and its clinical consequences like cardiovascular disease, hypertension and diabetes. We hypothesize that NO is already involved in the pathophysiology of juvenile obesity. We here determined the role of NO, its metabolites arginine and citrulline in obese and normal weight children.
We investigated 57 obese and 57 normal weight age- and gender-matched juveniles. Various clinical parameters as well as body measurements and intima media thickness were determined.
Obese juveniles revealed highly significant alterations in the NO pathway. NOX and citrulline were decreased in obese compared to normal weight juveniles and negatively correlated with body weight. Argininewas increased in obese juveniles and positively correlated with body weight. We found a significant negative correlation between NOX and oxidized low-density lipoprotein. Analysis of gamma-aminobutyric acid (GABA) revealed correlations with the NO pathway as NOX and citrulline were negatively correlated with GABA and arginine showed a positive correlation.
We show here that NO and its metabolites arginine and citrulline are already involved in juvenile obesity that may contribute to atherogenesis via reduced bioavailability of NO. Moreover, we identify GABA as a new parameter in the mechanism of obesity-related NO reduction.
[PubMed - indexed for MEDLINE]
Dysregulated Arginine Metabolism, Hemolysis-Associated Pulmonary Hypertension, and Mortality in Sickle Cell Disease
- Claudia R. Morris, MD;
- Gregory J. Kato, MD;
- Mirjana Poljakovic, PhD;
- Xunde Wang, PhD;
- William C. Blackwelder, PhD;
- Vandana Sachdev, MD;
- Stanley L. Hazen, MD, PhD;
- Elliott P. Vichinsky, MD;
- Sidney M. Morris, Jr, PhD;
- Mark T. Gladwin, MD
[+] Author Affiliations
Author Affiliations: Departments of Emergency Medicine (Dr C. Morris) and Hematology-Oncology (Dr Vichinsky), Children’s Hospital & Research Center at Oakland, Oakland, Calif; Vascular Therapeutics Section, Cardiovascular Branch, National Heart, Lung, and Blood Institute (Drs Kato, Wang, and Gladwin), Critical Care Medicine Department, Clinical Center (Drs Kato, Wang, Blackwelder, and Gladwin), and Echocardiography Laboratory (Dr Sachdev), National Institutes of Health, Bethesda, Md; Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, Pa (Drs Poljakovic and S. Morris); and Center for Cardiovascular Diagnostics and Prevention, Departments of Cell Biology and Cardiovascular Medicine, Cleveland Clinic Foundation, Cleveland, Ohio (Dr Hazen).
- Corresponding Author: Claudia R. Morris, MD, Department of Emergency Medicine, Children’@s Hospital & Research Center at Oakland, 747 52nd St, Oakland, CA 94609 (firstname.lastname@example.org).
Context Sickle cell disease is characterized by a state of nitric oxide resistance and limited bioavailability of L-arginine, the substrate for nitric oxide synthesis. We hypothesized that increased arginase activity and dysregulated argininemetabolism contribute to endothelial dysfunction, pulmonary hypertension, and patient outcomes.
Objective To explore the role of arginase in sickle cell disease pathogenesis, pulmonary hypertension, and mortality.
Design Plasma amino acid levels, plasma and erythrocyte arginase activities, and pulmonary hypertension status as measured by Doppler echocardiogram were prospectively obtained in outpatients with sickle cell disease. Patients were followed up for survival up to 49 months.
Setting Urban tertiary care center and community clinics in the United States between February 2001 and March 2005.
Participants Two hundred twenty-eight patients with sickle cell disease, aged 18 to 74 years, and 36 control participants.
Main Outcome Measures Plasma amino acid levels, plasma and erythrocyte arginase activities, diagnosis of pulmonary hypertension, and mortality.
Results Plasma arginase activity was significantly elevated in patients with sickle cell disease, with highest activity found in patients with secondary pulmonary hypertension. Arginase activity correlated with the arginine-ornithine ratio, and lower ratios were associated with greater severity of pulmonary hypertension and with mortality in this population (risk ratio, 2.5; 95% confidence interval [CI], 1.2-5.2; P = .006). Global arginine bioavailability, characterized by the ratio of arginine to ornithine plus citrulline, was also strongly associated with mortality (risk ratio, 3.6; 95% CI, 1.5-8.3; P<.001). Increased plasma arginase activity was correlated with increased intravascular hemolytic rate and, to a lesser extent, with markers of inflammation and soluble adhesion molecule levels.
Conclusions These data support a novel mechanism of disease in which hemolysis contributes to reduced nitric oxide bioavailability and endothelial dysfunction via release of erythrocyte arginase, which limits argininebioavailability, and release of erythrocyte hemoglobin, which scavenges nitric oxide. The ratios of arginine to ornithine and arginine to ornithine plus citrulline are independently associated with pulmonary hypertension and increased mortality in patients with sickle cell disease.
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How to fail an Arginine study.
This study has several problems. First they used
L-arginine hydrochloride, a form of L-Arginine known to be harmful. Second the protocal was 3 grams 3 times a day. Arginine only lasts 30 minutes and it's comepletely gone in the body. By using L-Citruline with L-Arginine the effect ability of L-Arginine to produce Nitric oxide is increased up to 36 hours. So by limiting the study to just Arginine and spacing the dose they completely negated Arginine's ability to produce Nitric Oxide. In addition, by limiting the dose to 3 grams they further mitigated the effect of Arginine. The ground breaking Arginine study that won the Noble Prize in 1998 demonstrated that the dose has to be at least 5 grams.
I have also included a reply to this article from 2 of the participants.
"We disagree with the characterization of the mortality rates in our study. In planning the study, we estimated a 10% mortality risk over 6 months in patients aged 60 years and older based on review of the literature.3-4 The mortality in our study was lower than anticipated:"
L-Arginine Therapy in Acute Myocardial Infarction
The Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) Randomized Clinical Trial
- Steven P. Schulman, MD;
- Lewis C. Becker, MD;
- David A. Kass, MD;
- Hunter C. Champion, MD, PhD;
- Michael L. Terrin, MD;
- Sandra Forman, MA;
- Kavita V. Ernst, MD;
- Mark D. Kelemen, MD;
- Susan N. Townsend, RN, BS;
- Anne Capriotti;
- Joshua M. Hare, MD;
- Gary Gerstenblith, MD
[+] Author Affiliations
Author Affiliations: Division of Cardiology (Drs Schulman, Becker, Kass, Champion, Ernst, Kelemen, Hare, and Gerstenblith and Mss Townsend and Capriotti), Johns Hopkins Medical Institutions, and Maryland Medical Research Institute (Dr Terrin and Ms Forman), Baltimore. Dr Terrin is now at the Department of Epidemiology and Dr Kelemen is at the Division of Cardiology, University of Maryland School of Medicine, Baltimore, and Dr Ernst is now at the Division of Cardiology, Stanford School of Medicine, Stanford, Calif.
- Corresponding Author: Steven P. Schulman, MD, Halstead 500, Johns Hopkins Hospital, Baltimore, MD 21287 (email@example.com).
Context The amino acid L-arginine is a substrate for nitric oxide synthase and is increasingly used as a health supplement. Prior studies suggest thatL-arginine has the potential to reduce vascular stiffness.
Objective To determine whether the addition of L-arginine to standard postinfarction therapy reduces vascular stiffness and improves ejection fraction over 6-month follow-up in patients following acute ST-segment elevation myocardial infarction.
Design and Setting Single-center, randomized, double-blind, placebo-controlled trial with enrollment from February 2002 to June 2004.
Patients A total of 153 patients following a first ST-segment elevation myocardial infarction were enrolled; 77 patients were 60 years or older.
Intervention Patients were randomly assigned to receive L-arginine (goal dose of 3 g 3 times a day) or matching placebo for 6 months.
Main Outcome Measures Change in gated blood pool–derived ejection fraction over 6 months in patients 60 years or older randomized to receive L-argininecompared with those assigned to receive placebo. Secondary outcomes included change in ejection fraction in all patients enrolled, change in noninvasive measures of vascular stiffness, and clinical events.
Results Baseline characteristics, vascular stiffness measurements, and left ventricular function were similar between participants randomized to receive placebo or L-arginine. The mean (SD) age was 60 (13.6) years; of the participants, 104 (68%) were men. There was no significant change from baseline to 6 months in the vascular stiffness measurements or left ventricular ejection fraction in either of the 2 groups, including those 60 years or older and the entire study group. However, 6 participants (8.6%) in the L-arginine group died during the 6-month study period vs none in the placebo group (P = .01). Because of the safety concerns, the data and safety monitoring committee closed enrollment.
Conclusions L-Arginine, when added to standard postinfarction therapies, does not improve vascular stiffness measurements or ejection fraction and may be associated with higher postinfarction mortality. L-Arginine should not be recommended following acute myocardial infarction.
Clinical Trial Registration ClinicalTrials.gov Identifier: NCT00051376
Arginine Therapy for Acute Myocardial Infarction—Reply
- Gary Gerstenblith, MD
[+] Author Affiliations
Division of Cardiology
Johns Hopkins University School of Medicine
In Reply: Drs Abumrad and Barbul note that prestudy and 6-month plasmaarginine levels were similar in the placebo and active therapy groups. Although poor adherence is one possible explanation, pill counts at 1 month, 3 months, and 6 months indicate otherwise. We suggested that in this cohort with normal baseline arginine levels, up-regulation of enzymes responsible for argininecatabolism, as described by Morris1 and Castillo et al,2 is a more likely mechanism. The product we used was L-arginine hydrochloride, produced with a good manufacturing practice label.
We disagree with the characterization of the mortality rates in our study. In planning the study, we estimated a 10% mortality risk over 6 months in patients aged 60 years and older based on review of the literature.3-4 The mortality in our study was lower than anticipated: 7.8% over 6 months in those patients aged 60 years …
From Critical Care Medicine
Sepsis: An Arginine Deficiency State?
Posted: 10/27/2004; Crit Care Med. 2004;32(10) © 2004 Lippincott Williams & Wilkins
Abstract and Introduction
Objective: Sepsis is a major health problem considering its significant morbidity and mortality rate. The amino acid l-arginine has recently received substantial attention in relation to human sepsis. However, knowledge of arginine metabolism during sepsis is limited. Therefore, we reviewed the current knowledge about arginine metabolism in sepsis.
Data Source: This review summarizes the literature on arginine metabolism both in general and in relation to sepsis. Moreover, arginine-related therapies are reviewed and discussed, which includes therapies of both nitric oxide (NO) and arginine administration and therapies directed toward inhibition of NO.
Data: In sepsis, protein breakdown is increased, which is a key process to maintain arginine delivery, because both endogenous de novo production from citrulline and food intake are reduced. Arginine catabolism, on the other hand, is markedly increased by enhanced use of arginine in the arginase and NO pathways. As a result, lowered plasma arginine levels are usually found. Clinical symptoms of sepsis that are related to changes in arginine metabolism are mainly related to hemodynamic alterations and diminished microcirculation. NO administration and arginine supplementation as a monotherapy demonstrated beneficial effects, whereas nonselective NO synthase inhibition seemed not to be beneficial, and selective NO synthase 2 inhibition was not beneficial overall.
Conclusions: Because sepsis has all the characteristics of an arginine-deficiency state, we hypothesise that arginine supplementation is a logical option in the treatment of sepsis. This is supported by substantial experimental and clinical data on NO donors and NO inhibitors. However, further evidence is required to prove our hypothesis.
Sepsis is defined as a systemic response to an infection.[1,2] It is a major health problem because of its significant morbidity and overall mortality rate of about 30% and generally requires intensive care treatment.Considerable efforts have been undertaken to understand the pathogenesis of sepsis and to improve its therapeutic modalities. The amino acid arginine has recently received substantial attention in relation to human sepsis. However, from this discussion it became clear that knowledge of arginine metabolism during sepsis is limited. Moreover, therapeutic interventions based on both stimulation and inhibition of arginine metabolism have produced seemingly contradictory results. Therefore, we will review the current knowledge about arginine metabolism in sepsis, which indicates that sepsis is an arginine-deficiency state. This hypothesis regarding sepsis as an arginine deficient disease makes arginine supplementation a logical option in the treatment of sepsis.
Arginine Availability in Sepsis
In septic patients, plasma and intracellular muscle arginine levels were found to be markedly decreased compared with control values of healthy subjects or control hospital patients,[34-36] although other amino acids besides arginine may also decrease, and a decrease may also exist in nonseptic, stressed patients ( Table 1X ). An additional important factor is that plasma arginine concentrations were found to be significantly lower in those patients who died of sepsis compared with patients surviving sepsis. In well-controlled animal models of sepsis, induction of sepsis decreased the total blood amino acid concentration, including arginine.[38,39]
Reduced arginine levels in sepsis suggest that arginine metabolism has changed or transport across the cell membrane is increased. Plasma arginine production, which is the total production of arginine from protein breakdown and from de novo synthesis, was not different between pediatric septic patients and healthy adults or between adult septic patients and nonseptic intensive care unit controls. However, arginine production during endotoxemia in pigs was increased, mainly from muscle protein breakdown. In particular, the intestinal-renal pathway resulting in de novo arginine synthesis from citrulline has been considered as the primary pathway responsible for maintenance of the plasma arginine level.[12,13,32,41] We recently observed a diminished de novoarginine synthesis in septic patients when compared with healthy adults and with nonseptic intensive care unit patients with moderate inflammation, in line with lowered plasma arginine level in the septic patients. This may point to lack of adaptation to the enhanced arginine need in sepsis, which is normally through up-regulation of endogenous arginine production, and may be due to lack of citrulline[9,36] or renal failure.
Exogenous daily arginine supply by nutritional intake is normally about 5-6 grams,[43,44] which is still a substantial amount compared with the endogenous daily arginine production of about 15-20 gram.[14,45] Because septic patients are often not fed during their initial stay in the intensive care unit, arginine supply relies completely on endogenous arginine synthesis. The importance of endogenous arginine synthesis is also demonstrated by the normal physiologic adaptation to a low-protein diet. It has been suggested that large amounts of arginine are then metabolized into citrulline in the small bowel to bypass the liver, and citrulline is subsequently converted back to arginine in the kidney.[12,22] This saves arginine from being converted to urea and therefore being wasted. However, even when septic patients are fed, arginine availability may still be compromised due to impaired intestinal absorption or impaired intestinal function through citrulline production when nutrition is given enterally.
In conclusion, diminished endogenous de novo production of arginine is probably an important factor that reduces the availability of arginine in sepsis. This may be worsened by reduced arginine intake and increased arginine catabolism, as is discussed in detail in the next paragraph.
The Role of ADMA and Arginine in the Failing Heart and its Vasculature
Posted: 01/27/2011; Eur J Heart Fail. 2010;12(12):1274-1281. © 2010 Oxford University Press
Abstract and Introduction
Nitric oxide (NO) is formed from arginine by the enzyme nitric oxide synthase (NOS). Asymmetric dimethylarginine (ADMA) can inhibit NO production by competing with arginine for NOS binding. Therefore, the net amount of NO might be indicated by the arginine/ADMA ratio. In turn, arginine can be metabolized by the enzyme arginase, and ADMA by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). While ADMA has been implicated as a cardiovascular risk factor, arginine supplementation has been indicated as a treatment in cardiac diseases. This review discusses the roles of ADMA and arginine in the failing heart and its vasculature. Furthermore, it proposes nutritional therapies to improve NO availability.
Nitric oxide (NO) is a prominent compound in the heart and its vasculature and plays an intriguing role in the physiology of this organ. In the coronary vasculature, NO is involved in vasodilatation, down regulation of cellular adhesion molecules, inhibition of platelet aggregation, vascular proliferation, and angiogenesis. In cardiomyocytes, the actions of NO are more complex as it can induce different, and sometimes opposing effects on cardiac functioning such as triggering apoptosis and improving left ventricular function.
Nitric oxide is formed from the amino acid arginine by the enzyme nitric oxide synthase (NOS), simultaneously with citrulline. Three different isoforms of NOS are known: neuronal NOS (nNOS or NOS1), endothelial NOS (eNOS or NOS3), and inducible NOS (iNOS or NOS2). Arginine is a semi-essential amino acid, meaning that under healthy conditions, endogenous arginine production is adequate for metabolic needs, but under stress conditions, when arginine is excessively catabolized by the enzyme arginase, dietary intake of this amino acid is required.
The production of NO can be disturbed by NOS inhibitors, such as asymmetric dimethylarginine (ADMA). As a consequence, ADMA has been indicated as a new marker of cardiovascular risk. Asymmetric dimethylarginine can either be excreted by the kidneys or metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Since ADMA inhibits NO production by competing with arginine for NOS binding, the net amount of NO production might be indicated by the ratio between substrate and inhibitor: the arginine/ADMA ratio. Therefore, the detrimental effect of ADMA might be inhibited by increasing the concentration of arginine or the concentration of its precursors, citrulline and glutamine, which would increase the arginine/ADMA ratio and thereby might reverse the competitive inhibition of NOS by ADMA. In this review, we focus on the role of ADMA and arginine in the failing heart and its vasculature. Furthermore, we will discuss therapies to reduce the deleterious effects of ADMA, especially that of arginine and its precursor's citrulline and glutamine.
Asymmetric Dimethylarginine Metabolism
There are two compounds that can inhibit NOS, N-monomethyL-arginine (NMMA) and ADMA, which both reduce NO synthesis by competing with arginine for NOS binding. N-monomethy L-arginine concentrations in plasma, however, are much lower compared with plasma ADMA concentrations. N-monomethy L-arginine is formed when protein-incorporated arginine is methylated by the enzymes protein arginine methyltransferases (PRMT)-1 or PRMT-2 (Figure 1). Protein arginine methyltransferases-1 can subsequently methylate NMMA, resulting in the formation of ADMA, whereas PRMT-2 can methylate NMMA into symmetric dimethylarginine (SDMA). After proteolysis, the methylated arginines are released as unbound forms in the cytosol where NMMA and ADMA are able to inhibit NOS. In contrast to ADMA, SDMA is not able to inhibit NOS. All methylated arginines are released from the cell into the circulation, via system y+-carriers of the cationic amino acid transporter (CAT) family, from which they can be taken up by other cells that use the same transporters. Cationic amino acid transporters also facilitate the transport of arginine across the cell membrane. All methylated arginine metabolites are considered to interfere with NO synthesis indirectly, because the methylated arginine analogues compete with arginine for transport via CAT. However, because SDMA lacks NOS inhibitory activity and only small amounts of NMMA are found in the plasma, ADMA is considered to be the major inhibitor of NO availability. Asymmetric dimethylarginine is excreted into the urine for <20%. The major part of the NOS inhibitor is cleared by the enzymes DDAH-1 and DDAH-2 resulting in the formation of citrulline and dimethylamine. Both the expression and the activity of DDAH seem to be regulated by NO through feedback mechanisms.
Dietary arginine is absorbed in the small intestine and is taken up from the circulation by CAT into the liver, kidney, and endothelial cells. Besides dietary intake, arginine availability depends on endogenous release through protein degradation, on synthesis from citrulline by the enzymes argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL), and the conversion of glutamine into citrulline, which can be converted into arginine in the kidney (Figure 1).
Arginine can be incorporated into proteins by the enzyme arginyl-tRNA synthetase (ATS) or can be used as a substrate in four metabolic pathways (Figure 1). First, arginine can be converted into agmatine by arginine decarboxylase (ADC). The second metabolic pathway is creatine synthesis by the conversion of arginine by arginine glycine amidinotransferase (AGAT) to guanidinoacetic acid, which is converted to creatine. Creatine is converted into creatine phosphate, which is an important form of stored energy in (cardiac) muscle tissue. The third pathway is the conversion of arginine into NO and citrulline facilitated by NOS. Nitric oxide can subsequently diffuse into the vascular smooth muscle layer resulting in cGMP-mediated relaxation and vasodilation. Although the concentration of arginine in endothelial cells is higher than necessary to saturate NOS, it has been shown that increased extracellular arginine can be taken up by endothelial cells and can contribute to NO production, a phenomenon called 'the arginine paradox'. The arginine/ADMA ratio might play a role in this paradox since this ratio reflects the amount of substrate (arginine) relative to inhibitor of NOS (ADMA), which can be considered as a better indicator of NO production than ADMA or arginine concentration separately. The last metabolic pathway of arginine is its conversion into urea and ornithine by the enzyme arginase. Two isoforms of arginase are known: type I metabolizes arginine in the cytosol, whereas type II is active in the mitochondria. Ornithine can be converted into polyamines by the enzyme ornithine decarboxylase (ODC) and into proline and glutamate by ornithine aminotransferase (OAT).
Asymmetric Dimethylarginine in the Failing Heart and its Vasculature
Since ADMA has been shown to inhibit NO synthesis its role in cardiac, and especially (coronary) vascular dysfunction has been investigated extensively. Elevated ADMA levels have been found in a variety of cardiac diseases (Table 1). More importantly, ADMA is indicated to have prognostic capacities for disease progression and mortality in heart failure patients (Figure 2), in critically ill patients,and in the community. Furthermore, ADMA infusion has been shown to impair relaxation of coronary arteries, induce myocardial remodelling, deteriorate cardiac function, and cause myocardial ischaemia (Table 2). Together with low arginine levels (as induced by arginase infusion), ADMA infusion further deteriorated stroke volume and cardiac output in rats. The detrimental effects of ADMA on the heart and subsequent outcome might be explained by disturbed NO synthesis. Nevertheless, NOS inhibitors have been proposed as a treatment for the overproduction of NO in sepsis and cardiogenic shock. The underlying hypothesis is that the increased production of NO by iNOS in shock contributes to hypotension and multiple organ dysfunction. However, results of several randomized trials investigating NOS inhibitors are conflicting. In cardiogenic shock patients, NOS inhibition resulted in a modest increase in mean arterial pressure and reduced mortality rate. In contrast, in a large clinical trial, another NOS inhibitor increased the mortality rate of septic shock patients. Mortality and adverse events in the treatment group were associated with cardiovascular death and haemodynamic dysfunction, including heart failure and decreased cardiac output. In addition, administration of NOS inhibitors reduced coronary flow and induced local ischaemia in endotoxin-treated rat hearts. These effects can probably be explained by microvascular pathology due to inhibition of eNOS, which can ultimately result in myocardial dysfunction. Therefore, non-selective inhibition of NOS cannot be recommended in the critically ill patient.
Overall, many studies have shown that ADMA can induce detrimental effects (Tables 1 and 2). These unfavourable actions are primarily the result of diminished NO availability, resulting in disturbed vasodilatation and anti-thrombotic, anti-inflammatory, and anti-apoptotic actions that overall might induce cardiac dysfunction (Figure 2). Furthermore, ADMA is able to uncouple NOS after which NOS becomes a source of superoxide radicals instead of producing NO (Figure 3). Asymmetric dimethylarginine infusion has been shown to increase superoxide production (Table 2). The increase in production of reactive oxygen species after NOS uncoupling can inhibit DDAH activity and can lead to oxidation of cellular components in cardiomyocytes, such as proteins critical for excitation–contraction coupling. It can also lead to increased susceptibility of cardiomyocytes to cell death, which can finally lead to cardiac dysfunction.
The increased plasma ADMA levels seen in several diseases of the heart and its vasculature might be explained by either increased intracellular production and/or decreased excretion from the plasma. However, PRMT-1 expression was unchanged in the hearts of dogs with congestive heart failure. Altered expression of CAT, which transports ADMA across the cell membrane, is also doubtful since both reductions and increases in CAT expression have been found in heart failure patients.[14,15] Another explanation might be found in high ADMA levels resulting from impaired renal function, which is often seen in heart failure patients. However, in patients with coronary artery disease, ADMA correlated negatively with glomerular filtration rate (eGFR, used as indicator for renal function), whereas in patients with acute myocardial infarction, a relationship between ADMA and eGFR was not present. Finally, increased ADMA levels can be the result of reduced DDAH activity and/or expression. Since ADMA catabolism is mainly regulated by DDAH, it can be hypothesized that a reduction in DDAH induction is the main contributing factor to elevated ADMA levels in cardiac dysfunction.
It has been estimated that DDAH metabolizes >80% of the ~300 µmol of ADMA that is generated daily in humans. Furthermore, complete malfunction of DDAH can lead to a daily increase in plasma ADMA concentrations of ~5 µmol/L. Indeed, DDAH activity and expression were reduced in dogs with congestive heart failure and atrial fibrillation. The results of murine studies suggest that DDAH has healing capacities, as its expression and activity increased after ischaemia and reperfusion, and overexpression of the enzyme reduced reperfusion injury. In the infarcted rat heart, the increased levels and activity of both DDAH-1 and DDAH-2 were associated with a retained arginine/ADMA ratio. Therefore, DDAH may provide local regulation of ADMA and subsequent NO synthesis, specifically in cells that play a role in the healing process after myocardial infarction. This explanation is in line with results from a study in human umbilical vein endothelial cells (HUVECs) in which DDAH-2 upregulation was associated with an increase in vascular endothelial growth factor expression, which stimulated angiogenesis and enhanced vessel tube formation. Overall, these studies imply the ability of DDAH to locally regulate ADMA concentrations and the concomitant NO synthesis in the heart. Studies are now needed to investigate whether this mechanism of DDAH metabolism is also applicable in the human heart.
As it is clear that ADMA can induce deleterious effects in the heart and its vasculature, treatments are needed that can reduce ADMA levels or alter its metabolism. Studies that have investigated such treatments used either pharmacological therapies such as cardiovascular drugs, or non-pharmacological therapies such as invasive procedures and nutritional interventions. Pharmacological studies focusing on lowering ADMA levels in cardiac diseases show promising results (Table 3). However, the mechanisms by which these treatments reduce ADMA levels are still not fully understood. The expression and/or activity of DDAH are probably upregulated. Indeed, beta-blockers reduced ADMA levels via an increase in DDAH-2 expression and activity in HUVECs.Furthermore, all-trans-retinoic acid and insulin stimulated DDAH expression and activity which resulted in decreased ADMA levels in murine endothelial cells and HUVECs, respectively. A possible mechanism might be that these treatments lower oxidative stress which preserves DDAH activity and reduces accumulation of ADMA. Unfortunately, to the best of our knowledge, there are no studies investigating DDAH induction or PRMT inhibition in the normal or diseased heart. Interestingly, ADMA levels are reduced in patients after invasive procedures such as percutaneous coronary intervention and coronary artery bypass grafting (CABG) (Table 3). Of the nutritional interventions, the amino acid arginine is the most extensively investigated nutrient, which can lower plasma ADMA levels by reversing its competitive inhibition of NOS.
Arginine in the Failing Heart and its Vasculature
Arginine and Arginase
As stated previously, plasma arginine levels can be low under conditions of stress, for example following surgery, when this amino acid is excessively catabolized by arginase. Here, the catabolized arginine is no longer available to NOS, hence subsequent NO synthesis by NOS is diminished. As a result, the actions of NO on the heart and its vasculature are disturbed, and superoxide might be produced, which can be harmful for cardiac functioning. Moreover, the polyamines and proline formed after arginase catabolism might be implicated in the development of coronary vascular lesions and subsequent cardiac dysfunctioning. However, the effect of low plasma arginine levels on heart function and blood flow remains unclear when considering the conflicting results of studies performed by our group.[6,27,28] Prins et al. found paradoxical changes after arginase infusion in rats: blood flow to the heart increased while vascular resistance in the heart decreased. In a second rat study, Prins et al. found both unchanged heart rate and stroke volume after arginase infusion. Only after lipopolysaccharide infusion, low arginine levels resulted in higher heart rates and lower stroke volumes, which together maintained cardiac output. Richir et al. infused both arginase and ADMA in rats, which decreased cardiac output and stroke volume. The ratio between the levels of arginine and ADMA probably plays a role in these contradictory results, as this ratio might be a better indicator of NO availability and concomitant haemodynamic and cardiac function than arginine or ADMA concentration alone. For example, when ADMA levels are high, NO synthesis might still be possible when arginine levels are sufficiently high to dislocate ADMA and serve as a substrate for NOS. This hypothesis is supported by the recently reported positive correlation between the arginine/ADMA ratio and cardiac output in critically ill patients.
Studies investigating the impact of arginine on cardiomyocytes are scarce. One in vitro study simulated ischaemia followed by reoxygenation with arginine in myocardial biopsies of patients undergoing CABG surgery. In this study, arginine significantly decreased lactate dehydrogenase leakage but had no effect on viability or oxygen consumption. In another study, pre-anoxic treatment with arginine in a human ventricular heart cell model protected against cellular injury in a dose–dependent way. Additionally, arginine treatment during reoxygenation protected heart cells from low-volume anoxia injury and increased NO production.
In contrast, many clinical trials have been performed in which the effect of arginine administration, either given by infusion or orally, on cardiac and especially vascular function, has been investigated (extended discussion). In healthy volunteers, intravenous arginine infusion significantly reduced systolic and diastolic blood pressure, and increased heart rate, and plasma catecholamine levels. In endotoxin-treated rat hearts, arginine infusion increased coronary blood flow and restored perfusion in ischaemic areas. Furthermore, arginine infusion potentiated the paracrine myocardial contractile effects of receptor-mediated coronary endothelium stimulation in transplant recipients. In summary, the results from other cardiovascular studies using arginine infusion are generally consistent with respect to the beneficial effects of this amino acid on cardiovascular function.
However, the results from cardiovascular studies where oral arginine supplementation was used are not fully consistent. Most of these studies have shown positive or no effects. A possible explanation might be that arginine plasma concentrations have to be elevated above the physiological concentration range in order to induce acute vasodilator effects. Furthermore, it has been proposed that acute arginine supplementation has more effect on NO bioavailability than long-term arginine administration. This might explain, for example, the lack of effect of long-term arginine treatment on ventricular remodelling and heart failure and quality of life in hypertensive rats and in patients with chronic systolic heart failure, respectively. Conversely, in one study increased mortality rates were found in the patient group that received oral arginine after acute myocardial infarction. However, this effect was most probably not an effect of arginine supplementation as plasma arginine levels were not raised in patients that died, and four of the six deaths in the arginine group were almost certainly not related to the amino acid.
In inflammatory states arginine supplementation is more complicated, as more than one study has demonstrated increased mortality rates while administering arginine in critically ill patients. The negative results might be explained by both the involved NOS isoform and the arginine/ADMA ratio. For instance in shock, an arginine-induced excess in NO production by iNOS might be deleterious, as it might lead to detrimental vasodilation and to increased formation of peroxynitrite leading to cellular damage. On the other hand, an increase in NO facilitated by eNOS is of vital importance as it can mediate microvascular vasodilatation. Hence, NO availability needs to be perfectly balanced. Therefore, the effect of arginine supplementation might be influenced by the presence of ADMA. Furthermore, as the arginine/ADMA ratio is in part dependent on the activities of its degrading enzymes arginase and DDAH, the activities of these enzymes might also influence the effect of arginine supplementation.
Therefore, besides the arginine/ADMA ratio, future studies should explore the profile of arginase and DDAH in both blood plasma and cardiac tissue of patients with cardiac dysfunction. The results of these studies could then be used to find out which patient profiles might benefit from arginine supplementation. Given the potential risks of arginine supplementation in inflammatory states, this intervention should first be performed in an experimental setting with and without concomitant iNOS inhibition. Second, the effect of normal nutrition, which itself contains small amounts of arginine, on arginine and ADMA metabolism in the heart, should be investigated. Subsequently, studies can investigate the effect of arginine supplementation or ADMA removal directly or indirectly by influencing arginase and DDAH in cardiac diseases.
Citrulline and Glutamine Therapy
Another method for upregulating the arginine/ADMA ratio is by increasing the concentration of the arginine precursors, citrulline or glutamine. These compounds may influence the competitive inhibition of NOS.
The maintenance of high plasma arginine concentrations may be problematic because of its catabolism by arginase. The effectiveness of arginine therapy might be reduced in several cardiovascular disorders in which intestinal and cytosolic arginase expression and activity are enhanced. In contrast to arginine, citrulline is not metabolized in the intestine or liver and it does not induce tissue arginase, it even inhibits its activity. Citrulline is largely absorbed and metabolized by the kidney, where it can be converted into arginine. For these reasons, administration of citrulline might be an alternative way to improve cardiac functioning in diseases that are associated with arginine deficiency or increased arginase activity.
Compared with the high number of studies investigating the effect of arginine, only a few investigators have studied the effect of citrulline supplementation on heart function. In healthy volunteers, administration of oral citrulline augmented NO-dependent signalling. Oral citrulline supplementation increased plasma concentrations of both citrulline and arginine in children undergoing cardiopulmonary bypass surgery and reduced post-operative pulmonary hypertension.
Although these limited results might suggest citrulline supplementation as a promising method in diseases of the heart, more studies are needed to support the use of citrulline administration. Furthermore, it should be taken into account that arginine obtained by synthesis of citrulline is calculated to represent 78% of the whole-body plasma citrulline turnover, whereas only 11% of the whole-body plasma flux of arginine is obtained by de novo synthesis of arginine from citrulline.
Glutamine is a precursor of citrulline, which in turn is mainly metabolized to arginine in the kidney. This might make supplementation of glutamine a more physiological way to produce arginine.
In a rat model, increased plasma arginine levels obtained from a glutamine-enriched enteral diet induced an increase in splanchnic blood flow. However, the mean daily urinary nitrate excretion in this study did not differ between groups, suggesting that NO production did not play a role in the vasodilatory responses of glutamine. Other studies have shown inhibitory effects of glutamine on endothelial NO synthesis. In contrast to NO production by the constitutive NOS isoforms, glutamine seems to be required for NO production by iNOS. This might explain why optimal plasma glutamine levels are needed for optimal NO synthesis by iNOS, particularly in conditions such as sepsis and infection, which is underlined by several studies that have shown valuable effects of glutamine as an immunological form of nutrition. These studies further suggest that supplementation of glutamine might be more beneficial in disease states of immunological impairment, whereas glutamine might be less advantageous in the failing heart and its vasculature.
Summary and Conclusion
By inhibiting NOS, ADMA affects the correct functioning of the heart; studies have shown that ADMA is involved in vasoconstriction, cardiac remodelling, fibrosis, disturbance of angiogenesis and cardiac performance, myocardial ischaemia, and even mortality. These results show that ADMA is not only a risk factor for cardiovascular disease, but also an indicator of outcome in patients with cardiac dysfunction. The elevated ADMA levels shown in cardiac disorders are thought to be the result of diminished activity and/or expression of its metabolizing enzyme DDAH. Upregulation of DDAH has been shown to reduce ADMA with a concomitant increase in NO production resulting in beneficial effects for the heart and its vasculature. As ADMA competes with arginine for NOS binding, the net amount of NO might not only depend on ADMA levels but also on arginine concentrations, which can be reflected by the arginine/ADMA ratio.
Arginine levels can be insufficient under catabolic conditions in which arginase catalyses arginine. Interestingly, increased extracellular arginine can be taken up by endothelial cells and can contribute to NO synthesis. Therefore, arginine supplementation, especially by infusion, seems beneficial under conditions of cardiac dysfunction without inflammation. The impact of the arginine precursors citrulline and glutamine is less apparent. More research is needed to investigate the ability of nutritional therapies to increase the arginine/ADMA ratio directly or indirectly via its degrading enzymes arginase and DDAH, respectively, which might enhance NO availability with a concomitant improvement in cardiac function.
Effect of Oral L-arginine Supplementation on Blood Pressure
A Meta-analysis of Randomized, Double-blind, Placebo-controlled Trials
Posted: 12/29/2011; American Heart Journal. 2011;162(6):959-965. © 2011 Mosby, Inc.
Abstract and Introduction
Background Previous studies suggest that L-arginine, an amino acid and a substrate of nitric oxide synthase, may have blood pressure (BP)-lowering effect. Because some studies were performed with limited number of patients with hypertension and therefore limited statistical power with sometimes inconsistent results, we aimed to examine the effect of oral L-arginine supplementation on BP by conducting a meta-analysis of randomized, double-blind, placebo-controlled trials.
Methods PubMed, Cochrane Central Register of Controlled Trials, and the ClinicalTrials.gov databases were searched through June 2011 to identify randomized, double-blind, placebo-controlled trials of oral L-arginine supplementation on BP in humans. We also reviewed reference lists of obtained articles. Either a fixed-effects or, in the presence of heterogeneity, a random-effects model was used to calculate the combined treatment effect.
Results We included 11 randomized, double-blind, placebo-controlled trials involving 387 participants with oral L-arginine intervention ranging from 4 to 24 g/d. Compared with placebo, L-arginine intervention significantly lowered systolic BP by 5.39 mm Hg (95% CI −8.54 to −2.25, P = .001) and diastolic BP by 2.66 mm Hg (95% CI −3.77 to −1.54, P < .001). Sensitivity analyses restricted to trials with a duration of 4 weeks or longer and to trials in which participants did not use antihypertensive medications yielded similar results. Meta-regression analysis suggested an inverse, though insignificant (P = .13), relation between baseline systolic BP and net change in systolic BP.
Conclusions This meta-analysis provides further evidence that oral L-arginine supplementation significantly lowers both systolic and diastolic BP.
Hypertension is a huge public health burden, affecting approximately one billion individuals worldwide. It has been widely believed that lifestyle and dietary factors play an important role in the development of hypertension. This view has been reinforced by studies such as the DASH which demonstrates that a diet rich in vegetables, fruits, and low-fat dairy foods and low in saturated and total fat can substantially lower blood pressure (BP).Moreover, the DASH diet contains more protein than the control diet, and arginine-rich protein has been hypothesized to contribute to the BP-lowering effect of this diet.
L-Arginine, a semi-essential amino acid, is the natural substrate for nitric oxide (NO) synthase and responsible for the production of the endothelium-derived relaxing factor NO, which is involved in a wide variety of regulatory mechanisms of the cardiovascular system. This property led to the hypothesis that L-arginine may have BP-lowering effect. It is attractive to lower BP and prevent hypertension through effective lifestyle modification, particularly dietary supplements in persons with prehypertension, given the lack of evidence that antihypertensive drugs reduce cardiovascular morbidity and mortality in this population. During the past decades, a number of clinical trials have been carried out to evaluate the role of L-arginine in BP regulation. However, the sample size of these trials was small, the quality varied from low to high, and the results were inconsistent. We therefore aimed to examine the effect of oral L-arginine supplementation on BP by conducting a meta-analysis of randomized, double-blind, placebo-controlled trials.
We attempted to follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines in the report of this meta-analysis. We searched PubMed, Cochrane Central Register of Controlled Trials, and the ClinicalTrials.gov databases through June 2011 for relevant studies, using terms of "arginine" and "L-arginine" in combination with "blood pressure" and "hypertension." Our search was limited to randomized controlled trials of oral L-arginine supplementation in humans. In addition, we systemically searched the reference lists of obtained articles. No attempt was made to identify unpublished studies.
Studies were included if they: (1) were randomized, double-blind, placebo-controlled trials; (2) used oral L-arginine supplementation as intervention; and (3) reported the net changes of BP and the associated standard deviations (or data to calculate them). Studies were excluded if they: (1) had a short duration of intervention (<1 week); (2) had L-arginine administered by infusion; (3) were single-blind or open-label; (4) used L-arginine as part of intervention; (5) or lacked a concurrent placebo-controlled group.
We recorded study characteristics as follows: first author's last name, publication year; design details, including whether parallel or crossover; study duration; number of participants; antihypertensive medication use; daily dose of L-arginine treatment; and adverse effects. Participant characteristics including health status, mean age, and baseline BP were also recorded. Further, we assess the methodological quality of each included trial using the Jadad scale, which assigned scores for reported randomization, blinding, and withdrawals. Two of the authors independently performed the literature search, data extraction, and bias assessment, with disagreements resolved by discussion.
For parallel trials, the net changes were calculated by the difference (intervention minus control) of the changes (final values minus baseline values) of the mean values. For cross-over trials, the net changes were calculated as the difference of mean values at the end of the intervention and control periods. Where necessary, standard errors, CIs, and P values were converted to standard deviations for the analysis. Standard deviations for changes from baseline in each group were obtained. If not specified, we computed the missing standard deviations using the method proposed by Follmann et al in which a correlation coefficient of 0.5 was assumed.
The homogeneity of the effect size among studies was tested using the Q test at the P < .10 level of significance. We also calculated the I2 statistic,[8,9] a quantitative measure of inconsistency across studies. An I2 value > 50% was considered to indicate substantial heterogeneity between trials. Either a fixed-effects or, in the presence of heterogeneity, a random-effects model was used to calculate the combined effect size. We did not conduct subgroup analysis because of the small number of included studies. Rather, we performed sensitivity analyses to explore potential sources of heterogeneity across studies and to test the robustness of the results based on various criteria regarding the magnitude of BP reduction, the duration of intervention, and the use of antihypertensive medication. We also investigated the influence of a single study on the overall effect estimate by omitting one study in each turn. Furthermore, we conducted meta-regression analyses to assess whether BP reductions were related to study or subject characteristics, including L-arginine dose, intervention duration, and baseline BP levels. Potential publication bias was assessed by Begg's test and Egger's test at the P < .10 level of significance. All analyses were performed using STATA version 11.0 (StataCorp, College Station, TX). P < .05 was considered statistically significant, except where otherwise specified.
The study was sponsored by Nestec Ltd, Vevey, Switzerland. No other extramural funding was used to support this work.
Characteristics of the Studies
We identified 11 studies[12–22] that fully met the inclusion criteria for this meta-analysis. A flow chart of literature search and study selection is presented in Figure 1. The characteristics of the selected trials are presented in Table I. The included trials were published between 1996 and 2010. The sample size varied from 12 to 79, reaching a total of 387. All trials were randomized, double-blind, and placebo-controlled, of which 9 trials were parallel-designed and 2 had a crossover design. Five trials[16,18,20–22] had BP as a primary outcome. The duration of intervention lasted from 2 to 24 weeks, with a median of 4 weeks. Dose of L-arginine varied from 4 to 24 g/day, with a median of 9 g/day. Information on adverse effects of L-arginine intervention was available in 6 trials. Characteristics of participants enrolled in these trials varied across studies. Of note, two trials[18,22] were conducted in pregnant women with hypertension, and another trial presented results separately by hypertension status. Few of the remaining trials specified hypertension status, and most included participants were normotensive as indicated by mean BP levels at baseline.
Effect of L-arginine on BP
The net changes and corresponding 95% CIs for systolic and diastolic BP in each trial, and overall, are presented in Figure 2 and Figure 3. Compared with placebo, oral L-arginine intervention was associated with an average net change ranging from −23.0 to 2.8 mm Hg for systolic BP and from −11.0 to 1.0 mm Hg for diastolic BP. Most trials showed an intervention-related trend toward BP reductions, but only a few reached statistical significance. The combined effect size of L-arginine on systolic BP was −5.39 mm Hg (95% CI −8.54 to -2.25, P = .001), and substantial heterogeneity was observed (P < .001, I2 = 73.3%). For diastolic BP, the combined effect size was -2.66 mm Hg (95% CI −3.77 to −1.54, P < .001), with little evidence of heterogeneity (P = .12, I2 = 34.4%). Neither Begg's test nor Egger's test provided evidence of publication bias regarding effect of L-arginine on systolic or diastolic BP (all P > .30).
To explore potential sources of heterogeneity across studies of oral L-arginine supplementation on systolic BP and to test robustness of the results, we performed sensitivity analyses. After excluding two trials[14,17] that showed large systolic BP reductions in response to L-arginine intervention, there was no heterogeneity (P = .59,I2 = 0%), and the combined effect size was −3.34 mm Hg (95% CI −4.93 to −1.86, P < .001). Restricting analysis to 8 trials with a duration of 4 weeks or longer did not change the overall BP estimates (systolic BP −3.96 mm Hg, 95% CI −5.68 to −2.24; diastolic BP -2.62 mm Hg, 95% CI −4.11 to −1.14). Restricting analysis to 7 trials in which participants did not use antihypertensive medications yielded similar results (systolic BP −3.92 mm Hg, 95% CI −6.47 to −1.37; diastolic BP −2.50 mm Hg, 95% CI −3.75 to −1.25). Additional analyses examining the influence of an individual trial on the combined effect size by omitting one trial in each turn yielded a range from −3.66 (95% CI −5.54 to −1.78) to −5.92 mm Hg (95% CI −9.33 to −2.51) for systolic BP and a range from −2.40 (95% CI −3.55 to −1.26) to −3.20 mm Hg (95% CI −4.68 to −1.73) for diastolic BP. None of the individual studies appeared to have appreciable impacts on the overall combined effect sizes.
We next performed meta-regression analyses to assess whether BP reductions were related to L-arginine dose, intervention duration, or baseline BP levels. None of these covariates had significant impacts on the combined effect sizes (Table II). However, there was a trend toward greater reductions in systolic BP among subjects with higher systolic BP at baseline .
This meta-analysis of randomized, double-blind, placebo-controlled trials brought evidence that oral L-arginine supplementation, compared with placebo, significantly lowered systolic BP by 5.39 mm Hg (95% CI −8.54 to −2.25) and diastolic BP by 2.66 mm Hg (95% CI −3.77 to −1.54).
The magnitudes of the BP reductions in response to L-arginine supplementation in this meta-analysis are moderate but detectable. It should be noted that most participants included in these studies were normotensive, a category in which there may be less room for improving. In fact, one trial 20 that performed separate analysis according to hypertension status showed greater BP reductions in hypertensive participants than in normotensive ones (systolic BP: −5.6 vs −1.8 mm Hg, diastolic BP: −3.8 vs −1.8 mm Hg). It would be useful to perform stratified analysis by hypertension status, but the small number of trials conducted in hypertensive subjects[18,20,22] precluded such analysis. Yet our meta-regression analysis suggested an inverse, although not significant (P = .13), relation between baseline systolic BP and net change in systolic BP. It is therefore possible that L-arginine supplementation could exert larger BP-lowering effect in those with high BP. Given the inherent limitations of meta-regression analysis, this finding should be regarded as hypothesis-generating and need to be verified in future studies.
The observed heterogeneity among trials of L-arginine on systolic BP appeared to be due to 2 trials[14,17] that showed large BP reductions. After exclusion of these two trials, heterogeneity disappeared, and the combined effect size did not substantially change and remained significant. In one trial, both treatment and control groups were submitted to a low-caloric diet and exercise training program, and L-arginine supplementation combined with lifestyle modification and dietary therapy may have led to the pronounced BP reductions. For another trial, the disparate results were likely due to chance as the sample size was rather small (n = 12). In addition, all the participants enrolled in these 2 trials[14,17] were type 2 diabetic patients.
Several mechanisms may be responsible for the beneficial effect of L-arginine on BP. As a substrate for NO synthase, L-arginine may exhibit antihypertensive activities by augmenting the production of NO in endothelium and improving its bioavailability in vascular smooth muscle cells, which are essential to maintain vascular homeostasis.[23,24] A recent meta-analysis suggests that oral L-arginine supplementation is effective at improving endothelial cell function in individuals with endothelial dysfunction. In addition, L-arginine has been shown to improve insulin resistance,[14,26] which plays an important role in the etiology of hypertension associated with metabolic syndrome.[27,28]
It is also worth mentioning the "L-arginine paradox" that exogenous L-arginine supplementation improves NO-mediated biological effects despite high endogenous concentration of L-arginine. One possible explanation may be related to asymmetric dimethylarginine (ADMA). ADMA is an endogenous inhibitor of NO synthase and has been shown to reduce the sensitivity of NO synthase to L-arginine.[23,24,30] There is also considerable evidence that ADMA modulates endothelial NO synthase activity within the concentration range found in patients with vascular disease.[23,24,29] Overcoming the inhibition of NO synthase by ADMA may therefore underlie the beneficial effects of L-arginine supplementation on BP.
Our study had stringent inclusion and exclusion criteria. All included studies were randomized, double-blind, placebo-controlled trials, which minimized biases and suggested a high internal validity. We excluded studies[32,33] using L-arginine supplementation as part of intervention, and hence the BP-lowering effect was mainly attributable to L-arginine supplementation. We were able to detect the potential sources of heterogeneity among studies with the use of sensitivity analyses. In addition, results of sensitivity analyses supported the robustness of the findings.
However, the results of this meta-analysis should be interpreted with caution because of several limitations. First, the sample sizes of individual trials were relatively small, which limited the capacity of randomization to minimize the potential influences of confounding factors. For example, in one trial more participants in the placebo group used antihypertensive medication than those in the L-arginine group (45% vs 24%), and this imbalance may have obscured the effect of L-arginine on BP. Nevertheless, restricting analysis to trials in absence of antihypertensive medication use did not change the overall BP estimates. Second, the validity of our meta-analysis depended upon the quality of the individual studies. Although all studies were randomized and double-blind, allocation concealment, quality of randomization, and details of withdrawals were not always reported. In addition, information on the adverse effects of L-arginine supplementation was available in a few studies. Third, the included studies had a short duration, with the majority shorter than 3 months. Therefore, the effect of L-arginine supplementation on BP as well as its safety in long term is uncertain. Fourth, only 11 studies were eligible for this meta-analysis. Most of them were conducted in patients with specific diseases and disorders, such as gestational hypertension, type 2 diabetes, and hypercholesterolemia, which may have limited the generalization of the findings. Finally, as with any meta-analyses, publication bias may affect the results. Although formal statistical tests[10,11] did not detect evidence of this bias in our meta-analysis, the power of these tests were limited due to the small number of studies.
In conclusion, this meta-analysis of randomized, double-blind, placebo-controlled trials provides evidence that oralL-arginine supplementation significantly lowers both systolic and diastolic BP. Large-scale, long-term randomized controlled trials are warranted to confirm the BP-lowering effect of L-arginine supplementation, in particular among the hypertensive populations. While it is premature to recommend L-arginine supplementation to treat and control hypertension, adopting a healthy diet that contains L-arginine–rich foods such as fish, soy, whole grains, beans, and nuts may contribute to hypertension prevention.
Arginine Supplements May Help Treat Pulmonary Hypertension in Sickle Cell Disease
June 30, 2003 — Arginine supplements may be a new treatment for pulmonary hypertension in sickle cell disease patients, according to the results of a small trial published in the July 1 issue of theAmerican Journal of Respiratory and Critical Care Medicine.
"Pulmonary hypertension is a life-threatening complication of sickle cell disease," write Claudia R. Morris, MD, from Children's Hospital Oakland in California, and colleagues. "L-Arginine is the nitrogen donor for synthesis of nitric oxide, a potent vasodilator that is deficient during times of sickle cell crisis. This deficiency may play a role in pulmonary hypertension."
Because arginase hydrolyzes arginine to ornithine and urea, it may compete with nitric oxide synthase, leading to decreased nitric oxide production. Inhaled nitric oxide therapy has improved pulmonary hypertension in sickle cell disease, and other studies suggest that arginine therapy may be helpful in primary and secondary pulmonary hypertension.
After five days of oral arginine therapy, 10 patients with pulmonary hypertension and sickle cell disease had a 15.2% mean reduction in estimated pulmonary artery systolic pressure (63.9 ± 13 to 54.2 ± 12 mm Hg; P = .002). Arginase activity nearly doubled ( P = .07) in patients with pulmonary hypertension, which may limit arginine bioavailability. The authors also suggest that elevated arginase activity may contribute to the pathogenesis of pulmonary hypertension in sickle cell disease.
Study limitations include lack of cardiac catheterization, uncontrolled design, and small sample size.
"With limited treatment options and a high mortality rate for patients with sickle cell disease who develop pulmonary hypertension, arginine is a promising new therapy that warrants further investigation," the authors write. "Arginine is a well tolerated, nontoxic nutritional supplement with few side effects."
Am J Respir Crit Care Med. 2003;168:63-69
Reviewed by Gary D. Vogin, MD
Ageing and endothelial dysfunction
- P.M. Vanhoutte *
Institut de Recherches Internationales Servier (IRIS), Courbevoie, France
- *Correspondence: Paul M. Vanhoutte, IRIS, 6 place des Pléiades, 92415 Courbevoie Cedex, France.
Although the available information is limited, a survey of the literature concerning the effect of ageing on endothelium-dependent responses in animal blood vessels suggests that the release of endothelium-derived relaxing factors (nitric oxide and endothelium-derived hyperpolarizing factor) is reduced, whereas that of endothelium-derived vasoconstrictor prostanoids is augmented. The very few in vitro data on isolated human blood vessels and a number of studies conducted in intact people concur with the animal data. Taken in conjunction, these findings suggest that ageing is accompanied by progressive endothelial dysfunction, which sets the scene for development of atherosclerosis.
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The ageing endothelium, cardiovascular risk and disease in man.
Department of Internal Medicine, University of Pisa, Via Roma 67, 56100 Pisa, Italy.
Ageing is a major risk factor for cardiovascular disease, not only because there is a process of vascular ageing per se but also because ageing increases the time of exposure to other cardiovascular risk factors. Endothelial dysfunction is now considered an early and important mechanism that predisposes to atherothrombotic damage and thus contributes to the occurrence of cardiovascular events. The normal endothelium exerts a major vascular-protecting role by secreting substances, the most important of which is nitric oxide (NO). In disease conditions (such as the presence of cardiovascular risk factors), activation of endothelial cells can lead to the production and release of contracting factors, which counteract the beneficial effects of NO, and reactive oxygen species (ROS), which cause NO breakdown. Besides the opposite effects on vascular tone, NO and endothelium-derived contracting factors also respectively inhibit and activate several other mechanisms that are involved in the pathogenesis of atherothrombosis. Moreover, endothelial dysfunction is associated with vascular subclinical damage and, importantly, an increasing body of evidence strongly suggests that it might be an independent predictor for the risk of future cardiovascular events. Like the other traditional risk factors, ageing has been demonstrated to be associated with progressive impairment of endothelial function, in both conduit arteries and resistance vessels, mainly because of an increased production of ROS.
Therefore, it is conceivable that endothelial dysfunction plays a major role in predisposing to age-related increased cardiovascular risk in the elderly.
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- [PubMed - indexed for MEDLINE]
Supplement: 6th Amino Acid Assessment Workshop: SESSION 3
Adverse Gastrointestinal Effects of Arginine and Related Amino Acids1,2
George K. Grimble*
Department of Food Biosciences, University of Reading, Whiteknights, Reading RG6 6AP, UK
* To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
Oral supplements of arginine and citrulline increase local nitric oxide (NO) production in the small intestine and this may be harmful under certain circumstances. Gastrointestinal toxicity was therefore reviewed with respect to the intestinal physiology of arginine, citrulline, ornithine, and cystine (which shares the same transporter) and the many clinical trials of supplements of the dibasic amino acids or N-acetylcysteine (NAC). The human intestinal dibasic amino acid transport system has high affinity and low capacity. L-Arginine (but not lysine, ornithine, or D-arginine) induces water and electrolyte secretion that is mediated by NO, which acts as an absorbagogue at low levels and as a secretagogue at high levels. The action of many laxatives is NO mediated and there are reports of diarrhea following oral administration of arginine or ornithine. The clinical data cover a wide span of arginine intakes from 3 g/d to >100 g/d, but the standard of reporting adverse effects (e.g. nausea, vomiting, and diarrhea) was variable. Single doses of 3–6 g rarely provoked side effects and healthy athletes appeared to be more susceptible than diabetic patients to gastrointestinal symptoms at individual doses >9 g. This may relate to an effect of disease on gastrointestinal motility and pharmacokinetics. Most side effects of arginine and NAC occurred at single doses of >9 g in adults (>140 mg/kg) often when part of a daily regime of ∼>30 g/d (>174 mmol/d). In the case of arginine, this compares with the laxative threshold of the nonabsorbed disaccharide alcohol, lactitol (74 g or 194 mmol). Adverse effects seemed dependent on the dosage regime and disappeared if divided doses were ingested (unlike lactitol). Large single doses of poorly absorbed amino acids seem to provoke diarrhea. More research is needed to refine dosage strategies that reduce this phenomenon. It is suggested that dipeptide forms of arginine may meet this criterion.
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- Felipe Vadillo-Ortega, professor1,
- Otilia Perichart-Perera, titular researcher2,
- Salvador Espino, associate professor of obstetrics and gynaecology2,
- Marco Antonio Avila-Vergara, associate professor of obstetrics and gynaecology3,
- Isabel Ibarra, associate professor4,
- Roberto Ahued, professor of obstetrics and gynaecology2,
- Myrna Godines, associate professor of obstetrics and gynaecology1,
- Samuel Parry, associate professor and chief of division of maternal-fetal medicine5,
- George Macones, Mitchell and Elaine Yanow professor and head of obstetrics and gynaceology56,
- Jerome F Strauss, professor of obstetrics and gynaecology and dean of School of Medicine7
- Correspondence to: F Vadillo-Ortega email@example.com
Objective To test the hypothesis that a relative deficiency in L-arginine, the substrate for synthesis of the vasodilatory gas nitric oxide, may be associated with the development of pre-eclampsia in a population at high risk.
Design Randomised, blinded, placebo controlled clinical trial.
Setting Tertiary public hospital in Mexico City.
Participants Pregnant women with a history of a previous pregnancy complicated by pre-eclampsia, or pre-eclampsia in a first degree relative, and deemed to be at increased risk of recurrence of the disease were studied from week 14-32 of gestation and followed until delivery.
Interventions Supplementation with a medical food—bars containing L-arginine plus antioxidant vitamins, antioxidant vitamins alone, or placebo—during pregnancy.
Main outcome measure Development of pre-eclampsia/eclampsia.
Results 222 women were allocated to the placebo group, 228 received L-arginine plus antioxidant vitamins, and 222 received antioxidant vitamins alone. Women had 4-8 prenatal visits while receiving the bars. The incidence of pre-eclampsia was reduced significantly (χ2=19.41; P<0.001) in women randomised to L-arginine plus antioxidant vitamins compared with placebo (absolute risk reduction 0.17 (95% confidence interval 0.12 to 0.21). Antioxidant vitamins alone showed an observed benefit, but this effect was not statistically significant compared with placebo (χ2=3.76; P=0.052; absolute risk reduction 0.07, 0.005 to 0.15). L-arginine plus antioxidant vitamins compared with antioxidant vitamins alone resulted in a significant effect (P=0.004; absolute risk reduction 0.09, 0.05 to 0.14).
Conclusions Supplementation during pregnancy with a medical food containing L-arginine and antioxidant vitamins reduced the incidence of pre-eclampsia in a population at high risk of the condition. Antioxidant vitamins alone did not have a protective effect for prevention of pre-eclampsia. Supplementation with L-arginine plus antioxidant vitamins needs to be evaluated in a low risk population to determine the generalisability of the protective effect, and the relative contributions of L-arginine and antioxidant vitamins to the observed effects of the combined treatment need to be determined.
Trial registration Clinical trials NCT00469846.
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© 2010 American Society for Nutrition
L-Arginine supplementation improves exercise capacity after a heart transplant1,2,3
- Stéphane Doutreleau,
- Olivier Rouyer,
- Paola Di Marco,
- Evelyne Lonsdorfer,
- Ruddy Richard,
- François Piquard, and
- Bernard Geny
1From the Medicine Faculty Physiology Institute, Strasbourg, France (SD, OR, PDM, EL, RR, FP, and BG), and the Physiology Department, Nouvel Hôpital Civil, Strasbourg, France (SD, OR, PDM, EL, RR, and BG).
↵2 L-arginine was supplied by Novartis, France.
↵3 Address correspondence to S Doutreleau, Nouvel Hôpital Civil, 1 Place de l'hôpital, 67000 Strasbourg, France. E-mail: firstname.lastname@example.org.
Background: Endothelial dysfunction is associated with the decreased exercise capacity observed in heart-transplant (HTx) recipients. L-Arginine supplementation (LAS) stimulates the nitric oxide (NO) pathway and restores endothelial function.
Objective: We compared exercise capacity in healthy subjects and HTx patients and investigated whether chronic LAS might improve exercise capacity and NO/endothelin balance after an HTx.
Design: Clinical, echocardiographic, and exercise characteristics were measured in 11 control subjects and 22 HTx recipients. In a prospective, double-blind study, the 22 HTx recipients performed a 6-min exercise [6-min-walk test (6MWT)] and a maximal bicycle exercise test before and after a 6-wk period of placebo intake or LAS. Endothelial function was measured by analyzing blood NO metabolites, endothelin, and the resulting NO/endothelin balance.
Results: Exercise capacity decreased after transplantation. Unlike with the placebo intake, 6 wk of LAS improved quality of life in HTx recipients (mean ± SEM Minnesota Score: from 15.3 ± 1.3 to 10.6 ± 1.1; P < 0.001) and their submaximal exercise capacity. The distance walked during the 6MWT increased (from 525 ± 20 to 580 ± 20 m; P = 0.002), and the ventilatory threshold during the incremental test was delayed by 1.2 min (P = 0.01). Central factors such as resting stroke volume, systolic pulmonary arterial pressure, cardiac systolodiastolic functions, and heart-rate reserve were not modified, but LAS significantly increased the NO:endothelin ratio (from 2.49 ± 0.38 to 3.31 ± 0.39;P = 0.03).
Conclusion: Oral LAS may be a useful adjuvant therapeutic to improve quality of life and exercise tolerance in HTx recipients.
Received April 3, 2009.
Accepted February 2, 2010.
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Characteristics and function of cardiac mitochondrial nitric oxide synthase
We used laser scanning confocal microscopy in combination with the nitric oxide (NO)-sensitive fluorescent dye DAF-2 and the reactive oxygen species (ROS)-sensitive dyes CM-H2DCF and MitoSOX Red to characterize NO and ROS production by mitochondrial NO synthase (mtNOS) in permeabilized cat ventricular myocytes. Stimulation of mitochondrial Ca2+ uptake by exposure to different cytoplasmic Ca2+ concentrations ([Ca2+]i = 1, 2 and 5 μM) resulted in a dose-dependent increase of NO production by mitochondria when L-arginine, a substrate for mtNOS, was present. Collapsing the mitochondrial membrane potential with the protonophore FCCP or blocking the mitochondrial Ca2+uniporter with Ru360 as well as blocking the respiratory chain with rotenone or antimycin A in combination with oligomycin inhibited mitochondrial NO production. In the absence of L-arginine, mitochondrial NO production during stimulation of Ca2+ uptake was significantly decreased, but accompanied by increase in mitochondrial ROS production. Inhibition of mitochondrial arginase to limit L-arginine availability resulted in 50% inhibition of Ca2+-induced ROS production. Both mitochondrial NO and ROS production were blocked by the nNOS inhibitor (4S)-N-(4-amino-5[aminoethyl]aminopentyl)-N′-nitroguanidine and the calmodulin antagonist W-7, while the eNOS inhibitor L-N5-(1-iminoethyl)ornithine (L-NIO) or iNOS inhibitor N-(3-aminomethyl)benzylacetamidine, 2HCl (1400W) had no effect. The superoxide dismutase mimetic and peroxynitrite scavenger MnTBAP abolished Ca2+-induced ROS generation and increased NO production threefold, suggesting that in the absence of MnTBAP either formation of superoxide radicals suppressed NO production or part of the formed NO was transformed quickly to peroxynitrite. In the absence of L-arginine, mitochondrial Ca2+ uptake induced opening of the mitochondrial permeability transition pore (PTP), which was blocked by the PTP inhibitor cyclosporin A and MnTBAP, and reversed by L-arginine supplementation. In the presence of the mtNOS cofactor (6R)-5,6,7,8,-tetrahydrobiopterin (BH4; 100 μM) mitochondrial ROS generation and PTP opening decreased while mitochondrial NO generation slightly increased.
These data demonstrate that mitochondrial Ca2+ uptake activates mtNOS and leads to NO-mediated protection against opening of the mitochondrial PTP, provided sufficient availability of L-arginine and BH4.
In conclusion, our data show the importance of L-arginine and BH4 for cardioprotection via regulation of mitochondrial oxidative stress and modulation of PTP opening by mtNOS.
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(Received 23 October 2008; accepted after revision 15 December 2008; first published online 22 December 2008)
© 2008 American Society for Nutrition
Increase in fasting vascular endothelial function after short-term oral L-arginine is effective when baseline flow-mediated dilation is low: a meta-analysis of randomized controlled trials 123
- Yongyi Bai,
- Lan Sun,
- Tao Yang,
- Kai Sun,
- Jingzhou Chen, and
- Rutai Hui
1From the Key Laboratory for Clinical Cardiovascular Genetics & Sino-German Laboratory for Molecular Medicine, Cardiovascular Institute & FuWai Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China (YB, TY, KS, JC, and RH); the Hypertension Division, Cardiovascular Institute & FuWai Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China (YB and RH); and the National Center for Pharmaceutical Screening, Institute of Materia Medica Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China (LS).
↵2 Supported by grant no. 2006CB503805 from the Ministry of Science and Technology of China (to RH).
↵3 Address requests for reprints and correspondence to R Hui, Cardiovascular Institute & FuWai Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, 167 Beilishilu, Beijing 100037, PR China. E-mail: email@example.com.
Background: Previous trials suggest that oral L-arginine administration affects endothelial function. However, most of these studies were small, the conclusions were inconsistent, and the precise effects are therefore debatable.
Objective: The objective was to assess the effect of oral L-arginine supplementation on endothelial function, as measured with the use of fasting flow-mediated dilation (FMD).
Design: We conducted a meta-analysis of randomized, placebo-controlled L-arginine supplementation trials that evaluated endothelial function. Trials were identified in PubMed, Cochrane Library, Embase, reviews, and reference lists of relevant papers. The weighted mean difference (WMD) was calculated for net changes in FMD by using random-effect models. Previously defined subgroup analyses and meta-regression analyses were performed to explore the influence of study characteristics.
Results: Thirteen trials were included and evaluated. Because there was only one long-term study, we focused on short-term effects of L-arginine (12 studies, 492 participants). In an overall pooled estimate, L-arginine significantly increased FMD (WMD: 1.98%; 95% CI: 0.47, 3.48; P = 0.01). Meta-regression analysis indicated that the baseline FMD was inversely related to effect size (regression coefficient = −0.55; 95% CI: −1.00, −0.1; P = 0.016). A subgroup analysis suggested that L-arginine supplementation significantly increased FMD when the baseline FMD levels were <7% (WMD: 2.56%; 95% CI: 0.87, 4.25; P = 0.003), but had no effect on FMD when baseline FMD was >7% (WMD: −0.27%; 95% CI: −1.52, 0.97; P = 0.67).
Conclusion: Short-term oral L-arginine is effective at improving the fasting vascular endothelial function when the baseline FMD is low.
Received June 16, 2008.
Accepted October 19, 2008.
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Plasma arginine concentrations are reduced in cancer patients: evidence forarginine deficiency?1,2,3
Yvonne LJ Vissers, Cornelis HC Dejong, Yvette C Luiking, Kenneth CH Fearon, Maarten F von Meyenfeldt and Nicolaas EP Deutz
1 From the Departments of Surgery, Nutrition, and Toxicology, Research Institute Maastricht, Maastricht University, and University Hospital Maastricht, Maastricht, Netherlands (YLJV, YCL, CHCD, MFvM, and NEPD), and the Royal Infirmary, Edinburgh, United Kingdom (CHCD and KCHF)
Background: The disturbances leading to cancer cachexia remain to be unraveled. Preliminary evidence suggests that arginine availability in cancer is reduced. However, no valid data are available on plasma arginine concentrations in cancer patients.
Objective: We aimed to determine whether there is evidence for disturbedarginine metabolism in cancer.
Design: We measured plasma arginine concentrations postabsorptively in patients with various types of tumors, hypothesizing that arginineconcentrations would be lower than those in age- and sex-matched control subjects. Patients with localized tumors with a range of metabolic implications were studied: breast cancer (no weight loss), colonic cancer (sometimes weight loss), and pancreatic cancer (usually weight loss). Plasma amino acid concentrations were measured by HPLC.
Results: Plasma arginine concentrations were lower in patients with cancer (breast cancer: 80 ± 3 compared with 103 ± 9 µmol/L; colonic cancer: 80 ± 3 compared with 96 ± 7 µmol/L; pancreatic cancer: 76 ± 5 compared with 99 ± 7 µmol/L; P < 0.05 versus respective age- and sex-matched control subjects), irrespective of tumor type, weight loss, tumor stage, or body mass index (correlations with P > 0.05).
Conclusions: Malignant tumors associated with various degrees of metabolic derangements are all associated with decreased plasma arginine concentrations, even without weight loss. This suggests that decreased arginine availability is a specific feature of the presence of cancer. These disturbances in argininemetabolism could contribute to the cascade of metabolic events leading to cancer cachexia.
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