Stefanie M. Bode-Böger

Plasma concentration of asymmetrical dimethylarginine and mortality in patients with end-stage renal disease: a prospective study

BACKGROUNDnThe plasma concentration of asymmetrical dimethylarginine (ADMA), an inhibitor of nitric-oxide synthase, which has been linked to endothelial dysfunction and atherosclerosis in the general population, is raised in patients with end-stage renal disease and could contribute to the high cardiovascular risk in patients with chronic renal failure. We investigated the relation between cardiovascular risk factors and plasma ADMA concentration in a cohort of haemodialysis patients (n=225), and tested the predictive power of ADMA for mortality and cardiovascular outcomes.nnnMETHODSnPatients had standard dialysis three times a week. We accurately recorded cardiovascular events over a mean follow-up of 33.4 months (SD 14.6); these events were reviewed by a panel of physicians. We identified correlates of plasma ADMA by univariate and multivariate analyses.nnnFINDINGSnOn univariate analysis, ADMA concentration in plasma was directly related to concentrations of fibrinogen and L-arginine in plasma, duration of dialysis treatment, and serum cholesterol concentration, and was inversely related to serum albumin concentration. On multivariate analysis, only plasma fibrinogen (p=0.0001) and serum albumin (p=0.04) concentrations were independently related to plasma ADMA concentration (multiple r=0.44, p=0.0001). 83 patients died, 53 (64%) by cardiovascular causes. In a Coxs proportional-hazards model, plasma ADMA ranked as the second factor predicting overall mortality (hazard ratio 1.26, 95% Cl 1.11-1.41, p=0.0001) and cardiovascular events (1.17, 1.04-1.33, p=0.008).nnnINTERPRETATIONnIn haemodialysis patients, plasma ADMA is a strong and independent predictor of overall mortality and cardiovascular outcome. These findings lend support to the hypothesis that accumulation of ADMA is an important risk factor for cardiovascular disease in chronic renal failure.

LDL Cholesterol Upregulates Synthesis of Asymmetrical Dimethylarginine in Human Endothelial Cells: Involvement of S-Adenosylmethionine–Dependent Methyltransferases

Asymmetrical dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor. It is formed by protein arginine N-methyltransferases (PRMTs), which utilize S-adenosylmethionine as methyl group donor. ADMA plasma concentration is elevated in hypercholesterolemia, leading to endothelial dysfunction and producing proatherogenic changes of endothelial cell function. Four different isoforms of human PRMTs have been identified. Because the release of ADMA from human endothelial cells is increased in the presence of native or oxidized LDL cholesterol, we investigated the potential involvement of PRMT activity and gene expression in this effect. We found that the production of ADMA by human endothelial cells is upregulated in the presence of methionine or homocysteine and inhibited by either of the methyltransferase inhibitors S-adenosylhomocysteine, adenosine dialdehyde, or cycloleucine. This effect is specific for ADMA but not symmetrical dimethylarginine. The upregulation of ADMA release by native and oxidized LDL is abolished by S-adenosylhomocysteine and by the antioxidant pyrrollidine dithiocarbamate. Furthermore, a methyl-(14)C label is transferred from S-adenosylmethionine to ADMA but not symmetrical dimethylarginine, in human endothelial cells. The expression of PRMTs is upregulated in the presence of native or oxidized LDL. Our data suggest that the production of ADMA by human endothelial cells is regulated by S-adenosylmethionine-dependent methyltransferases. This activity is upregulated by LDL cholesterol, which may be due in part to the enhanced gene expression of PRMTs. In concentrations reached by stimulation of methyltransferases (5 to 50 micromol/L), ADMA significantly inhibited the formation of (15)N-nitrite from L-[guanidino-(15)N(2)]arginine. These findings suggest a novel mechanism by which ADMA concentration is elevated in hypercholesterolemia, leading to endothelial dysfunction and atherosclerosis.

Asymmetric Dimethylarginine and Progression of Chronic Kidney Disease: The Mild to Moderate Kidney Disease Study

Reduced bioavailability of nitric oxide (NO) is thought to play an important role in progression of renal damage. The hypothesis that the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) is involved in progression of kidney disease was tested. Plasma ADMA concentrations and other putative progression factors were assessed in 227 relatively young patients (45.7 +/- 12.6 yr) with nondiabetic kidney diseases and mild to moderate renal failure. Progression assessed as doubling of serum creatinine and/or renal replacement therapy was evaluated prospectively. Baseline plasma ADMA concentrations in renal patients correlated significantly with serum creatinine (r = 0.595), GFR (r = -0.591), age (r = 0.281), and proteinuria (r = 0.184; all P < 0.01). Patients who reached an end point during follow-up were significantly older (P < 0.05) and had significantly higher creatinine, ADMA, and parathyroid hormone blood concentrations and protein excretion rates at baseline, whereas GFR and hemoglobin were significantly lower (all P < 0.01). Cox regression analysis revealed baseline serum creatinine (odds ratio 2.00; 95% confidence interval [CI] 1.61 to 2.49; P < 0.001) and ADMA (odds ratio 1.47; 95% CI 1.12 to 1.93 for an increment of 0.1 mumol/L; P < 0.006) as independent predictors of disease progression. In patients with ADMA levels above median, progression was significantly faster (P < 0.0001), and their mean follow-up time to a progression end point was 52.8 mo (95% CI 46.9 to 58.8) as compared with 71.6 mo (95% CI 66.2 to 76.9) in patients with ADMA levels below the median. The endogenous NO synthase inhibitor ADMA is significantly associated with progression of nondiabetic kidney diseases. Lowering plasma ADMA concentrations may be a novel therapeutic target to prevent progressive renal impairment.

Restoring vascular nitric oxide formation by l-arginine improves the symptoms of intermittent claudication in patients with peripheral arterial occlusive disease

BACKGROUNDnAdministration of L-arginine improves nitric oxide (NO) formation and endothelium-dependent vasodilation in atherosclerotic patients.nnnOBJECTIVESnWe investigated in this double-blind, controlled study whether prolonged intermittent infusion therapy with L-arginine improves the clinical symptoms of patients with intermittent claudication, as compared with the endothelium-independent vasodilator prostaglandin E1, and control patients.nnnMETHODSnThirty-nine patients with intermittent claudication were randomly assigned to receive 2 x 8 g L-arginine/day, or 2 x 40 microg prostaglandin E1 (PGE1)/day or no hemodynamically active treatment, for 3 weeks. The pain-free and absolute walking distances were assessed on a walking treadmill at 3 km/h, 12% slope, and NO-mediated, flow-induced vasodilation of the femoral artery was assessed by ultrasonography at baseline, at 1, 2 and 3 weeks of therapy and 6 weeks after the end of treatment. Urinary nitrate and cyclic guanosine-3, 5-monophosphate (GMP) were assessed as indices of endogenous NO production.nnnRESULTSnL-Arginine improved the pain-free walking distance by 230+/-63% and the absolute walking distance by 155+/-48% (each p < 0.05). Prostaglandin E1 improved both parameters by 209+/-63% and 144+/-28%, respectively (each p < 0.05), whereas control patients experienced no significant change. L-Arginine therapy also improved endothelium-dependent vasodilation in the femoral artery, whereas PGE1 had no such effect. There was a significant linear correlation between the L-arginine/asymmetric dimethylarginine (ADMA) ratio and the pain-free walking distance at baseline (r=0.359, p < 0.03). L-Arginine treatment elevated the plasma L-arginine/ADMA ratio and increased urinary nitrate and cyclic GMP excretion rates, indicating normalized endogenous NO formation. Prostaglandin E1 therapy had no significant effect on any of these parameters. Symptom scores assessed on a visual analog scale increased from 3.51+/-0.18 to 83+/-0.4 (L-arginine) and 7.0+/-0.5 (PGE1; each p < 0.05), but did not significantly change in the control group (4.3+/-0.4).nnnCONCLUSIONSnRestoring NO formation and endothelium-dependent vasodilation by L-arginine improves the clinical symptoms of intermittent claudication in patients with peripheral arterial occlusive disease.

Supplementation of hypercholesterolaemic rabbits with L-arginine reduces the vascular release of superoxide anions and restores NO production

L-arginine, the precursor of endogenous nitric oxide (NO), has been shown to enhance endothelial function and to reduce intimal plaque area in cholesterol (Chol)-fed rabbits. We have studied endogenous NO production in such animals in vitro (endothelium-dependent relaxations) and in vivo (assessed by urinary NO3- excretion) before and during chronic oral administration of L-arginine and inhibitor of NO synthesis, L-NAME. Vascular superoxide anion (O2-) production of aortic rings was measured under basal conditions and following exposure to phorbol-myristate-acetate (PMA). Cholesterol feeding reduced endothelium-dependent relaxations and decreased urinary NO3- excretion. These effects were potentiated by administration of L-NAME. L-arginine partly restored endothelium-dependent relaxations and increased NO3- excretion. PMA-stimulated O2- production was increased in aortic rings from rabbits given cholesterol ( +159 +/- 28%; mean +/- S.E.M.) or cholesterol + L-NAME ( +149 +/- 37%) as compared with controls ( -22 +/- 7%). In rabbits given cholesterol + L-arginine, O2- production was decreased to control levels ( +14 +/- 17%; P < 0.05). We conclude that the systemic synthesis of NO is impaired in cholesterol-fed rabbits, as indicated by the decreased urinary excretion of NO3-. Enhanced O2- production may further contribute to the decreased biological activity of NO in hypercholesterolaemia. L-arginine restores endothelial function in hypercholesterolaemia by enhancing NO production and by protecting NO from early breakdown by O2-.

Endogenous nitric oxide synthase inhibitors are responsible for the L-arginine paradox.

L‐Arginine, the substrate of nitric oxide (NO) synthases (NOSs), is found in the mammalian organism at concentrations by far exceeding K M values of these enzymes. Therefore, additional L‐arginine should not enhance NO formation. In vivo, however, increasing L‐arginine concentration in plasma has been shown repeatedly to increase NO production. This phenomenon has been named the L‐arginine paradox; it has found no satisfactory explanation so far. In the present work, evidence for the hypothesis that the endogenous NOS inhibitors methylarginines, asymmetric dimethylarginine being the most powerful (IC50 1.5 μM), are responsible for the L‐arginine paradox is presented.

ADMA and oxidative stress are responsible for endothelial dysfunction in hyperhomocyst(e)inemia: effects of L-arginine and B vitamins.

OBJECTIVESnHyperhomocyst(e)inemia is a risk factor for atherosclerotic vascular disease, and it is associated with endothelial dysfunction. Mechanisms responsible for endothelial dysfunction in hyperhomocyst(e)inemia may involve impaired bioavailability of NO, possibly secondary to accumulation of the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) and increased oxidative stress. We investigated whether oral treatment with B vitamins or L-arginine normalizes endothelium-dependent, flow-dependent vasodilation (FDD) in patients with peripheral arterial occlusive disease (PAOD) and hyperhomocyst(e)inemia.nnnMETHODSn27 patients with PAOD and hyperhomocyst(e)inemia were assigned to oral treatment with combined B vitamins (folate, 10 mg; vitamin B-12, 200 microg; vitamin B-6, 20 mg/day), L-arginine (24 g/day) or placebo, for 8 weeks in a double-blind fashion. FDD was determined by high-resolution ultrasound in the radial artery.nnnRESULTSnVitamin B supplementation significantly lowered plasma homocyst(e)ine concentration from 15.8+/-1.8 to 8.7+/-1.1 micromol/l (P<0.01). However, B vitamins had no significant effect on FDD (baseline, 7.8+/-0.7%, B vitamins, 8.3+/-0.9%, placebo 8.9+/-0.7%; P=n.s.). In contrast, L-arginine treatment did not affect homocyst(e)ine levels, but significantly improved FDD (10.2+/-0.2%), probably by antagonizing the impact of elevated ADMA concentration (3.8+/-0.3 micromol/l) and reducing the oxidative stress by lowering urinary 8-iso-prostaglandin F(2alpha) (baseline, 76.3+/-7.1 vs. 62.7+/-8.3 pmol/mmol creatinine after 8 weeks).nnnCONCLUSIONSnOral supplementation with combined B vitamins during 8 weeks does not improve endothelium-dependent vasodilation in PAOD patients with hyperhomocyst(e)inemia, whereas L-arginine significantly improved endothelial function in these patients. Thus, accumulation of ADMA and increased oxidative stress may underlie endothelial dysfunction under hyperhomocyst(e)inemic conditions. These findings may have importance for evaluation of homocyst(e)ine-lowering therapy.

Elevation of asymmetrical dimethylarginine may mediate endothelial dysfunction during experimental hyperhomocyst(e)inaemia in humans.

Hyperhomocyst(e)inaemia is associated with endothelial dysfunction in animals and humans. Mechanisms responsible for endothelial dysfunction in hyperhomocyst(e)inaemia are poorly understood, but may involve impaired bioavailability of endothelium-derived nitric oxide (NO). We hypothesized that acute elevation of homocyst(e)ine by oral methionine loading may stimulate the formation of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, due to a transmethylation reaction during the formation of homocyst(e)ine from methionine. We studied nine healthy human subjects (five males, four females) aged 29+/-2 years. Flow-mediated vasodilation (FMD) in the brachial artery (endothelium-dependent) and vasodilation induced by nitroglycerine (endothelium-independent) were measured with high-resolution ultrasound before and 8 h after oral methionine (100 mg/kg in cranberry juice) or placebo (cranberry juice), on separate days and in random order. Plasma homocyst(e)ine and ADMA concentrations were measured by specific HPLC methods. After a methionine bolus, elevation of homocyst(e)ine (28.4+/-3.5 micromol/l) was associated with an increased plasma concentration of ADMA (2.03+/-0.18 micromol/l) and reduced FMD (1.54+/-0.92%). Placebo had no effect on these parameters. There was a significant inverse linear relationship between ADMA concentration and FMD (r=-0.49; P<0.05), which was stronger than the relationship between the homocyst(e)ine concentration and FMD (r=-0.36; not significant). We conclude that acute elevation of the homocyst(e)ine concentration impairs vascular endothelial function by a mechanism in which an elevated concentration of ADMA may be involved. This finding may have importance for understanding the mechanism(s) leading to homocyst(e)ine-associated vascular disease, and its potential treatment.

Dietary l-arginine and α-tocopherol reduce vascular oxidative stress and preserve endothelial function in hypercholesterolemic rabbits via different mechanisms

Vascular oxidative stress brought about by superoxide radicals and oxidized low-density lipoproteins (oxLDL) is a major factor contributing to decreased NO-dependent vasodilator function in hypercholesterolemia and atherosclerosis. We investigated whether chronic administration of L-arginine (2% in drinking water) or of alpha-tocopherol (300 mg/day) improves endothelium-dependent vasodilator function and systemic NO production, reduces vascular oxidative stress, and reduces the progression of atherosclerosis in cholesterol-fed rabbits with pre-existing hypercholesterolemia. Systemic NO production was assessed as urinary nitrate excretion; oxidative stress was measured by urinary 8-iso-PGF2alpha excretion in vivo, by lucigenin-enhanced chemiluminescence of isolated aortic rings ex vivo, and by copper-mediated LDL oxidation in vitro. Endothelium-dependent relaxation was almost completely abrogated in cholesterol-fed rabbits. Urinary nitrate excretion was reduced by 46+/-10%, and 8-iso-PGF2alpha excretion was increased by 61+/-18% as compared to controls (each P <0.05). Vascular superoxide radical release stimulated by PMA ex vivo was increased by 273+/-93% in this group, and the lag time of LDL oxidation was reduced by 35+/-6% (each P <0.05). Treatment with L-arginine and alpha-tocopherol reduced intimal lesion formation (by 68+/-6 and 4+/-11%, respectively; P <0.05) and improved endothelium-dependent relaxation. Both treatments also normalized urinary 8-iso-PGF2alpha excretion. L-Arginine increased urinary nitrate excretion by 43+/-13% (P <0.05) and reduced superoxide radical release by isolated aortic rings to control levels, which was unaffected by vitamin E treatment. By contrast, vitamin E dramatically increased the resistance of isolated LDL to copper-mediated oxidation in vitro by 178+/-7% (P <0.05), which was only marginally prolonged by L-arginine. Intimal thickening was reduced by both treatments. We conclude that both L-arginine and alpha-tocopherol reduce the progression of atherosclerotic plaques in cholesterol-fed rabbits. However, while L-arginine increases NO formation and reduces superoxide release, alpha-tocopherol antagonizes mainly oxLDL-related events in atherogenesis. Thus, both treatments reduce urinary isoprostane excretion and improve endothelium-dependent vasodilation via different mechanisms.

Endothelium-dependent vasodilation is independent of the plasma L-arginine/ADMA ratio in men with stable angina - Lack of effect of oral L-arginine on endothelial function, oxidative stress and exercise performance

OBJECTIVESnThis study was designed to determine the effect of two weeks treatment with L-arginine on the ratio of plasma L-arginine to asymmetric dimethylarginine (ADMA), oxidative stress, endothelium-dependent vasodilatation to acetylcholine, exercise performance and heart rate variability in men with stable angina.nnnBACKGROUNDnThe ratio of plasma L-arginine:ADMA has been proposed as a determinant of endothelium-dependent dilation; dietary supplementation with L-arginine has been shown to improve endothelium-dependent vasodilation and symptoms in some conditions.nnnMETHODSnMen (n = 40) with stable angina, at least one epicardial coronary artery with a stenosis >50% and a positive exercise test were randomized to receive L-arginine (15 g daily) or placebo for two weeks according to a double-blind parallel-group design. Plasma L-arginine, ADMA, 8-epi-prostaglandin F2alpha (a marker of oxidative stress) and forearm vasodilator responses to brachial artery infusion of nitroprusside and acetylcholine (+/-L-arginine) were measured. A standard Bruce protocol exercise test was performed before and at the end of the treatment period.nnnRESULTSnPlasma L-arginine increased after oral L-arginine, whereas ADMA remained unchanged, leading to an increase in the L-arginine/ADMA ratio of 62 +/- 11% (mean +/- SE, p < 0.01). Despite a significant enhancement in acetylcholine response by intra-arterial L-arginine at baseline, this response remained unchanged after oral L-arginine. Measures of oxidative stress and exercise performance after L-arginine/placebo were similar in placebo and active groups.nnnCONCLUSIONSnIn men with stable angina, an increase in plasma L-arginine/ADMA ratio after two weeks oral supplementation with L-arginine is not associated with an improvement in endothelium-dependent vasodilatation, oxidative stress or exercise performance.