WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• L-Arginine is a semiessential amino acid that is converted to nitric oxide (NO) by NO synthase (NOS).• NO improves endothelial function by elevating cyclic guanosine monophosphate.• However, oral L-arginine treatment in humans is hampered by extensive metabolism. WHAT THIS STUDY ADDS• Oral L-citrulline supplementation raises plasma L-arginine concentration and augments NO-dependent signalling in a dose-dependent manner.• L-Citrulline may thus be an alternative to L-arginine in patients with impaired NOS activity. AIMSOral L-arginine supplementation has been used in several studies to improve endothelium-dependent, nitric oxide (NO)-mediated vasodilation. L-Arginine treatment is hampered by extensive presystemic elimination due to intestinal arginase activity. In contrast, L-citrulline is readily absorbed and at least in part converted to L-arginine. The aim of our study was to assess this metabolic conversion and its subsequent pharmacodynamic effects. METHODSIn a double-blind, randomized, placebo-controlled cross-over study, 20 healthy volunteers received six different dosing regimes of placebo, citrulline, and arginine. Pharmacokinetic parameters (Cmax, Tmax, Cmin, AUC) were calculated after 1 week of oral supplementation. The ratio of plasma L-arginine over asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase (arginine/ADMA ratio), urinary cyclic guanosine monophosphate (cGMP) and nitrate excretion rates, and flow-mediated vasodilation (FMD) was measured to assess pharmacodynamic effects. RESULTSL-Citrulline dose-dependently increased AUC and Cmax of plasma L-arginine concentration more effectively than L-arginine (P < 0.01). The highest dose of citrulline (3 g bid) increased the Cmin of plasma L-arginine and improved the L-arginine/ADMA ratio from 186 Ϯ 8 (baseline) to 278 Ϯ 14 [P < 0.01, 95% confidence interval (CI) 66, 121]. Moreover, urinary nitrate and cGMP were increased from 92 Ϯ 10 to 125 Ϯ 15 mmol mmol -1 creatinine (P = 0.01, 95% CI 8, 58) and from 38 Ϯ 3.3 to 50 Ϯ 6.7 nmol mmol -1 creatinine (P = 0.04, 95% CI 0.4, 24), respectively. No treatment improved FMD over baseline. However, pooled analysis of all FMD data revealed a correlation between the increase of arginine/ADMA ratio and improvement of FMD. CONCLUSIONOur data show for the first time that oral L-citrulline supplementation raises plasma L-arginine concentration and augments NO-dependent signalling in a dose-dependent manner.

Background-Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, induces endothelial dysfunction. Although elevated ADMA has been associated with an increased risk of cardiovascular disease events and death in referral samples, the prognostic significance of ADMA in the community has not been adequately evaluated. Methods and Results-We related plasma ADMA, L-arginine (Arg), and the ratio of Arg to ADMA to the incidence of cardiovascular disease (fatal or nonfatal myocardial infarction, coronary insufficiency, angina pectoris, stroke or transient ischemic attack, intermittent claudication, or heart failure) and death in 3320 Framingham Offspring Study participants (1769 women; mean age, 59 years). Over a follow-up period of 10.9 years, 281 individuals of 2956 free of cardiovascular disease at baseline developed incident cardiovascular disease, and 285 participants died. In multivariable models adjusting for established risk factors and other biomarkers (B-type natriuretic peptide, renin, homocysteine, urine albumin excretion, and C-reactive protein), ADMA and the ratio of Arg to ADMA were significantly associated with all-cause mortality (adjusted-hazard ratio [HR] per 1-SD increment, 1.21; 95% CI, 1.07 to 1.37; and HR per 1-SD increment, 0.80; 95% CI, 0.69 to 0.93, respectively), whereas Arg was not (HR per 1-SD increment, 0.89; 95% CI, 0.77 to 1.02). We noted effect modification by diabetes status; ADMA was associated with death in individuals without diabetes (adjusted HR per 1-SD increment, 1.30; 95% CI, 1.13 to 1.50) but not in individuals with diabetes (adjusted HR per 1-SD increment, 0.85; 95% CI, 0.62 to 1.16). ADMA, Arg, and the ratio of Arg to ADMA were not associated with cardiovascular disease incidence (PϾ0.10). Conclusions-In our large community-based sample, ADMA was significantly associated with all-cause mortality, particularly in nondiabetic individuals. (Circulation. 2009;119:1592-1600.)

Background-Oxidative stress is involved in the pathophysiology of atherosclerosis, diabetes mellitus, hypertension, obesity, and cigarette smoking, all of these being risk factors for coronary heart disease (CHD). We tested the hypothesis that risk factors of CHD are associated with abundant systemic oxidative stress. Methods and Results-We conducted a case-control study with 93 CHD patients and 93 control subjects frequencymatched by age and sex. Urinary excretion of the F 2 -isoprostane 8-iso-prostaglandin (PG) F 2␣ and its major urinary metabolite, 2,3-dinor-5,6-dihydro-8-iso-PGF 2␣ , were measured by gas chromatography-tandem mass spectrometry. Body mass index, systolic blood pressure, and C-reactive protein were elevated in CHD patients (PϽ0.01). Urinary 8-iso-PGF 2␣ and 2,3-dinor-5,6-dihydro-8-iso-PGF 2␣ also differed, from 77 (interquartile range, 61-101) to 139 (93-231) pmol/mmol creatinine and from 120 (91-151) to 193 (140 -275) pmol/mmol in control subjects and case subjects, respectively (PϽ0.001). 8-iso-PGF 2␣ and its metabolite were highly correlated (Spearman's ϭ0.664, PϽ0.001). HDL cholesterol was diminished in CHD patients (PϽ0.001). All of these characteristics predicted CHD in univariate analysis. In a multivariate model, the odds ratios were increased only for 8-iso-PGF 2␣ (Ն131 pmol/mmol, PϽ0.001) and C-reactive protein (Ͼ3 mg/L, PϽ0.01), ie, by 30.8 (95% CI, 7.7-124) and 7.2 (1.9 -27.6), respectively. 8-iso-PGF 2␣ was found to be a novel marker in addition to known risk factors of CHD, ie, diabetes mellitus, hypercholesterolemia, hypertension, and smoking. Urinary excretion of 8-iso-PGF 2␣ correlated with the number of risk factors for all subjects (PϽ0.001 for trend). Conclusions-8-iso-PGF

The main finding in this study is that in essential hypertensives the L-arginine and endogenous inhibitor of nitric oxide synthase, ADMA, are inversely related to endothelial function.

Abstract:The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endotheliumderived factors mediating NO-independent pathways is evaluated.

Overall, this study indicates that raised plasma concentration of ADMA is associated to concentric LVH and LV dysfunction. Intervention studies are needed to see whether the link between ADMA and concentric LVH remodeling and LV dysfunction is a causal one.

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