Reduced urinary excretion of nitric oxide metabolites and increased plasma levels of asymmetric dimethylarginine in men with essential hypertension

Effect of iloprost on plasma asymmetric dimethylarginine and plasma and platelet serotonin in patients with peripheral arterial occlusive disease

BACKGROUND

Iloprost, a prostacyclin analogue, is used in the treatment of peripheral arterial occlusive disease at Leriche-Fontaine stages III-IV, through intravenous infusion for at least 21 days. Recently, iloprost has been shown to be safe and effective in critical limb ischemia patients when administered per 7 days. We investigated in patients at Leriche-Fontaine stages III-IV the effect of 1-week treatment with iloprost on plasma asymmetric dimethylarginine (ADMA), plasma and platelet serotonin, and on clinical response.

METHODS AND RESULTS

Twenty-four critical limb ischemia patients (16 men and 8 women, mean age 76+/-9.7 years) were included in the study and treated with intravenous iloprost (titrated from 0.5 up to 1.5 ng/kg/min) for 16 h a day for seven consecutive days. Blood samples were drawn before infusion on days 1, 4 and 8 of treatment, under the same conditions. Clinical assessment was performed by clinical evaluation, ankle/brachial pressure index and treadmill exercise test. During treatment with iloprost patients clinically improved and plasma levels of ADMA significantly decreased (p<0.001). We also observed a significant increase of serotonin (p<0.01) in platelets and a significant decrease of serotonin (p<0.001) in plasma. Similar variations of ADMA and serotonin were found in two subgroups of patients, diabetics and non-diabetics.

CONCLUSIONS

One-week treatment with iloprost in critical limb ischemia patients induced changes of peripheral markers of endothelial dysfunction and atherosclerosis, such as ADMA and serotonin, associated to a clinical improvement.

ADMA, proteinuria, and insulin resistance in non-diabetic stage I chronic kidney disease

The rationale of this study is based on the fact that, both proteinuria and elevated asymmetric dimethyl arginine (ADMA) levels have been linked to the progression of vascular disease. Currently, there is not enough knowledge about any association between the levels of proteinuria and ADMA levels. Seventy-eight non-diabetic patients (42 men, 36 women, mean age of 26.1+/-5.2 years) with proteinuria having normal glomerular filtration rate were enrolled along with 38 healthy subjects (20 men, 18 women, mean age of 26.9+/-5.9 years). Proteinuria was below 3.5 g/day in 40 patients and above 3.5 g/day in 38 patients. Both groups had similar age, gender, and body mass index distributions. Serum ADMA, symmetric dimethyl arginine (SDMA), immunoreactive insulin, and high sensitivity C reactive protein (hsCRP) levels were measured. Insulin resistance was determined by homeostasis model assessment (HOMA). Serum ADMA, SDMA, insulin, hsCRP levels, and HOMA indexes were significantly higher in patients than in healthy control subjects. The above parameters were higher in the nephrotic range proteinuria group when compared to patients having protein levels below 3.5 g/day. There were significant correlations between the levels of proteinuria and the above parameters. According to the regression analysis, levels of proteinuria and hsCRP were significant determinants of serum ADMA levels. Our results indicate that, independent of other risk factors, ADMA is directly associated with proteinuria. Further studies are recommended to find out whether elevated ADMA levels are implicated in the high cardiovascular risk of proteinuric nephropathies.

Pharmacological Effects of Xanthones as Cardiovascular Protective Agents

Many epidemiological studies indicate that consumption of dietary polyphenolic compounds is beneficial in the prevention of cardiovascular diseases. Xanthones are a class of polyphenolic compounds that commonly occur in plants and have been shown to have extensive biological and pharmacological activities. Recently, the pharmacological properties of xanthones in the cardiovascular system have attracted great interest. Xanthones and xanthone derivatives have been shown to have beneficial effects on some cardiovascular diseases, including ischemic heart disease, atherosclerosis, hypertension and thrombosis. The protective effects of xanthones in the cardiovascular system may be due to their antioxidant, antiinflammatory, platelet aggregation inhibitory, antithrombotic and/or vasorelaxant activities. In particular, the antagonism of endogenous nitric oxide synthase inhibitors by xanthones may represent the basis for improved endothelial function and for reduction of events associated with atherosclerosis.

Asymmetric dimethylarginine and hemodynamic regulation in middle-aged men

The goal of this study was to evaluate the role of asymmetric dimethylarginine (ADMA) in the regulation of hemodynamic functions in hypertensive men. It has been suggested that ADMA, as an endogenous nitric oxide synthase inhibitor, is linked to hypertension and vascular reactivity. Sixty-seven men aged 51.1 years (range, 45-55 years) were studied. Plasma ADMA and symmetric dimethylarginine were determined by high-performance liquid chromatography-tandem mass spectrometry. Blood pressure (BP) was measured by 24-hour ambulatory recordings and casual measurements. Hemodynamic regulation was assessed by noninvasive methods. The nitric oxide production was estimated based on plasma nitrate (NO(3)(-)) determination. Results showed that plasma arginine derivatives or l-arginine/ADMA ratio was not associated with BP values observed during 24-hour monitoring or in casual measurements. Systemic vascular resistance, pulse wave velocity, or cardiac output was not associated with plasma ADMA or plasma NO(3)(-) levels. No association was found between plasma ADMA and NO(3)(-) either. Interestingly, subjects on antihypertensive treatment had lower plasma ADMA concentrations than nontreated subjects (0.30+/-0.08 and 0.36+/-0.11 micromol/L, respectively, P=.04) despite higher BP values. In conclusion, these results suggest that plasma ADMA does not have a determinative role in the regulation of hemodynamic functions in Finnish middle-aged men.

Effect of acute inhibition of nitric oxide synthesis by l-NAME on cardiovascular responses following peripheral autonomic blockade in rabbits

The pressor and chronotropic responses to acute inhibition of nitric oxide synthase enzyme by N(G)-nitro-L-arginine methyl ester (L-NAME) were studied in anaesthetized rabbits with intact autonomic nervous system (ANS) activity. Also, they were investigated when administration of L-NAME was preceded by peripheral autonomic blockade. Autonomic blockade had different forms: ganglionic (hexamethonium-induced), post-ganglionic beta-adrenergic blockade (propranolol induced), parasympathetic blockade (atropine induced), and complete autonomic blockade by coadministration of hexamethonium and atropine simultaneously. L-NAME injected intravenously (10 mg/kg) in animals with intact and blocked autonomic activity induced a pressor response. This pressor response was accompanied by bradycardia in rabbits with either intact autonomic activity or hexamethonium-induced ganglionic blockade. L-NAME exerted no effect on heart rate in animals with beta-adrenergic blockade or parasympathetic blockade. In rabbits with complete autonomic blockade, L-NAME evoked tachycardia. These experiments indicate that L-NAME-induced hypertension is not relying only on ANS. Also, L-NAME-induced tachycardia in rabbits treated with atropine plus hexamethonium suggests other humoral mechanisms that may be involved in the L-NAME induced chronotropic response.

Plasma levels of asymmetric dimethylarginine (ADMA) are related to intima-media thickness of the carotid artery: an epidemiological study

Asymmetric dimethylarginine (ADMA) is a circulating endogenous nitric oxide (NO) synthase inhibitor. It has been reported that plasma levels of ADMA are related to intima-media thickness (IMT) in small numbers. We investigated this issue in a large number of subjects without overt cerebro-cardiovascular diseases. A total of 712 subjects (305 men and 407 women; age, 62.6+/-11.2 years) received a health examination in 1999 in a farming community. We measured blood pressure (BP), blood chemistries, and fasting plasma total ADMA levels. IMT of the common carotid artery was determined with the use of duplex ultrasonography as an index of atherosclerosis. Uni- and multi-variate analyses for determinants of IMT were performed. For the total population, the mean ADMA level was 0.50 micromol/l. By the use of multiple stepwise regression analysis, IMT was significantly associated with ADMA (p<0.01), age (p<0.001), and systolic BP (p<0.001). Furthermore, when IMT was analyzed across the ADMA tertiles after adjustments for age, sex, and other confounders, analysis of co-variance showed a significant (p<0.001) and linear association between IMT and ADMA levels. In conclusion, our study indicates that plasma level of ADMA is a strong and independent determinant of IMT of the carotid artery in the large number of subjects without overt cerebro-cardiovascular diseases.

No effect of B vitamins on ADMA levels in patients at increased cardiovascular risk

OBJECTIVE

Asymmetric dimethylarginine (ADMA) is a recently identified potent cardiovascular risk factor. ADMA levels are increased in hyperhomocysteinaemia and the metabolism of ADMA is linked with that of homocysteine in several ways. Treatment with B vitamins effectively reduces homocysteine levels, but studies investigating the effect on ADMA levels are scarce and show conflicting results. In this study we evaluated the effect of treatment with B vitamins on ADMA levels in two high cardiovascular risk populations.

METHODS

In study I, 110 siblings of patients with clinical atherosclerotic disease and postmethionine hyperhomocysteinaemia were treated with 5 mg of folic acid and 250 mg of pyridoxine or placebo, and were analysed after 1 year. In study II, 41 patients with type 2 diabetes and mild hyperhomocysteinaemia were analysed after 6 months treatment with 5 mg of folic acid or placebo.

RESULTS

A correlation between baseline homocysteine and ADMA levels was found, which was partly due to confounding by renal function. Homocysteine levels decreased by 43% in study I and by 28% in study II. In both studies, treatment with B vitamins had no effect at all on ADMA, arginine/ADMA ratio and SDMA levels. This result was confirmed in multiple linear regression analyses with adjustment for baseline values and gender.

CONCLUSIONS

Our studies indicate that B vitamins, despite causing a substantial reduction in plasma homocysteine levels, have no beneficial effect on ADMA levels.

Amino acids, arginase and nitric oxide in vascular health

1. Nitric oxide (NO) plays a fundamental role in the vasculature because of its diverse influence in vascular protection, including its well-reported antiproliferative, anti-inflammatory, antithrombotic and vasodilator effects. In many vascular disease states, NO production is reduced as a result of endothelial dysfunction, in part caused by a decrease in substrate (L-arginine) availability. 2. The role of L-arginine and other amino acids important in nitrogen balance has been re-examined in the context of their effects on vascular health. The metabolism of L-arginine is complex because it is involved in a plethora of other pathways, such as urea, creatine and agmatine production. L-Arginine supplementation in patients with vascular disease is well reported to benefit patients therapeutically because of its effect on both NO-dependent and -independent mechanisms. 3. L-Arginine availability depends on the flux of other amino acids in the body, including L-glutamine, L-glutamate, L-ornithine, L-citrulline and L-lysine. The role of L-methionine and homocystine and their effect on NO also play an influential role in the body. 4. Recent data suggest that the key enzyme involved in the L-arginine-urea cycle, arginase, is coexpressed in NO-producing cells in the vasculature. In the present review, we examine the potential role of arginase as a therapeutic target for vascular health.

Asymmetric dimethylarginine (ADMA) as a risk marker for stroke and TIA in a Swedish population

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, has been shown to be involved in the pathogenesis of atherosclerosis. The present study was initiated to investigate the role of ADMA as a risk marker of acute cerebrovascular disease (CVD). We examined 363 CVD patients and 48 controls. The ADMA concentration (mean+/-S.D., mumol/L) in controls was 0.50 +/- 0.06. Compared to controls, increased concentrations of ADMA were observed in cardio-embolic infarction (0.55 +/- 0.08; p < 0.001; n = 71), and TIA (0.54 +/-0 .05; p < 0.001; n = 31), but not in non-cardio-embolic infarction (0.51 +/- 0.07; p = 0.56; n = 239) and haemorrhagic stroke (0.51 +/- 0.11; p = 0.77; n = 22). In multivariate logistic regression models, CVD increased across quartiles of ADMA in all subgroups, but this association was only significant in the TIA group (odds ratio for highest versus lowest quartile 13.1; 95% CI: 2.9-58.6; p trend 0.001) A decreased arginine/ADMA ratio was significantly associated with CVD in the entire study population (p < 0.01). Our results indicate that ADMA is a weak independent marker for acute stroke and a strong marker for TIA and that relative arginine deficiency, measured as the l-arginine/ADMA ratio, is present in acute CVD.

Asymmetric dimethylarginine (ADMA): a cardiovascular and renal risk factor on the move

The endogenous inhibitor of the nitric oxide synthase, asymmetric dimethylarginine (ADMA), by reducing nitric oxide (NO) availability, may trigger pro-atherogenic effects. A high plasma concentration of this substance has been associated to intima-media thickening, left ventricular hypertrophy and all-cause and cardiovascular mortality in patients with end-stage renal disease, and to coronary events in males in the general population. Recent studies show that ADMA predicts renal disease progression and death in patients with moderate to severe renal insufficiency. ADMA may be at the crossroad of the atherosclerosis process and may represent an important factor in the high risk associated with renal insufficiency.

Effect of vasoconstrictor coupling factor 6 on gene expression profile in human vascular endothelial cells: enhanced release of asymmetric dimethylarginine

BACKGROUND

Coupling factor 6 (CF6), a component of ATP synthase, inhibits phospholipase A2 and induces vasoconstriction. However, because arachidonic acid acts in the widespread fields of vascular biology, CF6 might exert profound effects in addition to vasoconstriction. We investigated the effect of CF6 on the gene expression profile in human umbilical vein endothelial cells.

METHODS AND RESULTS

The increased gene expression after 24-h exposure to CF6 at 10 mol/l, assessed by cDNA microarray (n = 3), included neuregulin-1 (1.84 +/- 0.07 fold compared with control, P < 0.05) and relaxin-1 (1.74 +/- 0.20, P < 0.05), both relating to congestive heart failure, urokinase type plasminogen activator receptor (1.77 +/- 0.24, P = 0.06) and estrogen receptor beta (1.74 +/- 0.36, P = 0.08), both relating to vascular inflammation and cell infiltration, and protein arginine methyltransferase (PRMT-1; 1.73 +/- 0.20, P < 0.05). Out of these genes, the enzyme relating to the synthesis (PRMT-1) of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), was further examined concomitantly with the degradation enzyme, dimethylarginine dimethylaminohydrolase 2 (DDAH-2). The ratio of PRMT-1 to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA, measured by real-time quantitative reverse transcription-polymerase chain reaction, was increased by 9 +/- 2% (n = 10, P < 0.01) at 48 h after CF6 at 10 mol/l, whereas the ratio of DDAH-2 to GAPDH was decreased by 12 +/- 2% (n = 8, P < 0.01). DDAH-2 protein and activity were decreased by 28 +/- 5% (n = 5, P < 0.01) and 19 +/- 2% (n = 6, P < 0.01) by CF6, respectively. ADMA release was enhanced by 20 +/- 8% and NOS activity was decreased by 13 +/- 1% (both n = 8, P < 0.05) by CF6.

CONCLUSIONS

CF6 changes the gene expression profile to be proatherogenic and functions as a novel stimulator for ADMA release by enhancing its synthesis and suppressing its degradation.

Fast and Efficient Determination of Arginine, Symmetric Dimethylarginine, and Asymmetric Dimethylarginine in Biological Fluids by Hydrophilic-Interaction Liquid Chromatography–Electrospray Tandem Mass Spectrometry

Background: Nitric oxide is synthesized from the amino acid Arg by the enzyme endothelial nitric oxide synthase, which is competitively inhibited by the arginine metabolite asymmetric dimethylarginine (ADMA). In this way, increased concentrations of ADMA lead to reduced nitric oxide production associated with a range of cardiac diseases. Research in this field requires the measurement of Arg and of ADMA and its closely related substance, symmetric dimethylarginine (SDMA).

Methods: We quantified Arg, ADMA, and SDMA in human plasma, human urine, and cell culture supernatant by HPLC–electrospray tandem mass spectrometry. Sample preparation required only protein precipitation. Separation was by liquid chromatography on a 150 × 3 mm silica column with an isocratic mobile phase consisting of water–acetonitrile–trifluoroacetic acid–propionic acid (10:90:0.025:1 by volume). The chromatographic run time was 7 min.

Results: The chromatograms were interference-free in all matrices. In the low-concentration quality-control samples, the interassay CVs in plasma were 4.7% for Arg, 7.7% for ADMA, and 4.9% for SDMA. Similar values were obtained in urine and cell culture supernatants. The calibration functions were linear and covered the ranges of healthy and pathologic samples.

Conclusion: The new method requires neither derivatization nor complete chromatographic separation between ADMA and SDMA for quantification of the 3 metabolites, has calibration functions that are independent of the sample matrix, and provides measured concentrations that agree with those reported in the literature.

Effect of fenofibrate on the level of asymmetric dimethylarginine in individuals with hypertriglyceridemia

OBJECTIVE

To test whether treatment with fenofibrate decreases asymmetric dimethylarginine (ADMA) level in hypertriglyceridemic individuals.

METHODS

In the present study, 45 subjects with hypertriglyceridemia were recruited to receive treatment with fenofibrate (200 mg/d). Serum concentrations of ADMA, malondialdehyde (MDA), nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) were measured. Endothelial function assessed by flow-mediated dilation (FMD) of the brachial artery was performed.

RESULTS

Compared with control, serum levels of ADMA (0.47+/-0.05 micromol/L in control and 0.62+/-0.28 micromol/L in hypertriglyceridemic patients, P<0.01), MDA and TNF-alpha were markedly elevated, and the level of NO was significantly reduced, concomitantly with impaired endothelium-dependent vasodilation in individuals with hypertriglyceridemia. 8-week treatment with fenofibrate significantly reduced the elevated levels of ADMA (0.53+/-0.12 micromol/L, P<0.01), MDA and TNF-alpha, attenuated the decreased level of NO and improved endothelial function.

CONCLUSIONS

These results suggest that the beneficial effect of fenofibrate on the endothelium in hypertriglyceridemic individuals may be related to reduction of ADMA level.

Asymmetric dimethylarginine is associated with macrovascular disease and total homocysteine in patients with type 2 diabetes

BACKGROUND

The endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and total homocysteine (tHcy) are elevated in patients at increased cardiovascular risk. Patients with type 2 diabetes (T2DM) have higher incidence of macrovascular disease than the general population. Recent reports suggest a relationship between tHcy and ADMA. To evaluate the connection between ADMA and tHcy and macrovascular disease, we determined both risk factors in T2DM patients with and without macrovascular disease.

SUBJECTS AND METHODS

Plasma concentrations of ADMA and tHcy were cross-sectionally determined in 136 T2DM patients. Fifty-five patients had macrovascular disease defined by history of stroke, myocardial infarction, coronary heart disease or peripheral arterial occlusive disease. Logistic regression analysis was performed to examine the relationship between macrovascular disease and these risk factors. Potential confounders were identified by significant Spearman rank correlation coefficients.

RESULTS

In unadjusted models ADMA (per 0.1 micromol/l) and tHcy (per 5 micromol/l) were both significantly related to macrovascular disease (OR=1.63, 95% CI: 1.21-2.19 and OR=1.49, 95% CI: 1.04-2.14). In multivariate models, ADMA was significantly associated with macrovascular disease independent of l-arginine, albumin excretion rate, tHcy and glomerular filtration rate (GFR; OR=1.53, 95% CI: 1.04-2.26). The connection between tHcy and macrovascular disease was not independent of diastolic blood pressure, age, ADMA or GFR. Linear regression analyses revealed that ADMA, GFR and low-density lipoprotein cholesterol were independent predictors for tHcy.

CONCLUSION

ADMA is associated with macrovascular disease independent of tHcy and traditional cardiovascular risk factors in patients with T2DM.

Asymmetric dimethylarginine (ADMA): a novel risk marker in cardiovascular medicine and beyond

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), an endogenous messenger molecule formed in healthy vascular endothelium from the amino acid precursor L-arginine. Endothelial dysfunction is caused by various cardiovascular risk factors, metabolic diseases, and systemic or local inflammation. One mechanism that explains the occurrence of endothelial dysfunction is the presence of elevated blood levels of asymmetric dimethylarginine (ADMA)--an L-arginine analogue that inhibits NO formation and thereby can impair vascular function. Supplementation with L-arginine has been shown to restore vascular function and to improve the clinical symptoms of various diseases associated with vascular dysfunction.

Increased circulating concentrations of asymmetric dimethylarginine (ADMA) in white coat hypertension

Elevated plasma levels of the endogenous nitric oxide (NO) synthase inhibitor asymmetric dimethylarginine (ADMA) contribute to endothelial dysfunction and seem to be a predictor for cardiovascular mortality. Elevated ADMA plasma concentrations have been demonstrated in patients with hypertension. However, the plasma concentrations of ADMA in white coat hypertension (WCH) has not been previously studied. The aim of this study was to evaluate ADMA in WCH and compare with normotensive (NT) and hypertensive (HT) patients. We also evaluated the relation between ADMA and NO in these three groups. For this purpose, 34 NT, 34 white coat hypertensive (clinical hypertension and ambulatory daytime blood pressure <135/85 mmHg) and 34 HT patients were recruited in this study. The subjects were matched for age, gender, body mass index (BMI) and the patients with smoking habit, dyslipidaemia and diabetes mellitus were excluded. The ADMA levels were determined by high performance liquid chromatography. Plasma ADMA levels were significantly higher in WCH group than in the NT group (3.21+/-0.49 micromol/l vs 2.84+/-0.58 micromol/l, P=0.046). It was significantly higher in the HT group than in the NTs (4.24+/-0.38 micromol/l, P<0.001). There was also a significant difference between the HT and WCH groups (P<0.001). The WCH subjects had significantly higher levels of NO than the HTs (41.68+/-2.23 vs 32.18+/-2.68 micromol/l; P<0.001) and significantly lower values than the NTs (48.24+/-4.29 micromol/l; P<0.001). In WCH and HT group, there was a negative correlation between ADMA and NO (r=-0.515, P=0.003 and r=-0.389, P=0.034, respectively). In NT subjects, there was no correlation between these two parameters (r=-0.287, P=0.124). The correlation between ADMA and NO was stronger in WCH group than in HT group. Although NO levels in HT patients were lower than WCHs and ADMA levels were higher in HT patients than WCHs, the negative correlation of these two parameters were more pronounced in WCH group. Decreased NO and increased ADMA levels in WCH may indicate endothelial dysfunction. Our data indicate also that WCH represent an intermediate group between NT and HT when endothelial dysfunction is concerned.

Targeting endothelial dysfunction in hypertensive subjects

The endothelium is a favourite early target of cardiovascular risk factors and cardiovascular diseases like hypertension. This key role of the endothelium results from its capacity to respond to numerous autocrine and paracrine stimuli and to mechanical factors like shear stress but also from the pathophysiological consequences of endothelial dysfunction on vasomotor tone, arterial stiffness, arterial remodelling, and inflammation, all of which are factors that play a critical role in atherosclerosis and target-organ damage. In hypertension, endothelial dysfunction has been shown at the level of both resistance and conduit arteries and mainly results from an increase in nitric oxide (NO) degradation by interaction between NO and superoxide anions, while in experimental models of hypertension a decrease in NO production can also be observed. The fact that forearm endothelial dysfunction is a marker of future cardiovascular events in patients with hypertension stresses the importance of the clinical evaluation of endothelial function and of the evaluation of the effects of the different antihypertensive drug classes on this parameter. In this context, many studies have demonstrated that angiotensin-converting enzyme inhibitors, the perindopril-indapamide combination, and angiotensin II type I receptor (AT1) blockers improve endothelium-dependent vasodilatation partly independently of arterial pressure. Both their antioxidant effects and the stimulation of the release of NO are involved in their beneficial effects. For calcium antagonists, only the recent drugs have been shown to improve endothelial function with a simultaneous improvement in several markers of oxidative stress. Finally, beta-blockers classically do not affect endothelial function. Only nebivolol, a beta-blocker with NO donor properties, has been shown to improve endothelial function, but this effect results from the increase in NO and not from the beta-blocking properties of the drug.

Body size, but neither age nor asymptomatic mitral regurgitation, influences plasma concentrations of dimethylarginines in dogs

Asymmetric dimethylarginine (ADMA) is a marker of various cardiovascular diseases in man. The aim of the present study was to test if Cavalier King Charles Spaniels (CKCS) with varying degrees of mitral regurgitation (MR) had increased plasma concentration of ADMA and furthermore, characterize the plasma level of ADMA and symmetric dimethylarginine (SDMA) in normal dogs. Seventy-six dogs were included (44 CKCS and 32 dogs of other breeds). The CKCS had various degrees of MR, whereas the remaining dogs had either no or minimal MR. Apart from cardiac murmurs, no dogs showed signs of cardiac or systematic disease. The degree of MR had no significant influence on ADMA (P = 0.33). Body weight was directly associated with ADMA (P = 0.0004) and creatinine was directly associated with SDMA (P<0.0001). Furthermore, the plasma concentration of ADMA was three to four times higher than found in healthy humans.

Pioglitazone lowers systemic asymmetric dimethylarginine by inducing dimethylarginine dimethylaminohydrolase in rats

Peroxisome proliferator activated receptor-gamma (PPARgamma) ligands increase nitric oxide (NO) production and reduce systemic blood pressure. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor degraded by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), which has two isoforms, DDAH-I and -II. In order to elucidate the mechanism whereby PPARgamma ligands affect NO metabolism, their effects on the DDAH-ADMA pathway were investigated. Six-week-old male Wister-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were maintained with or without pioglitazone (PIO), a PPARgamma ligand. After 4 weeks, serum ADMA levels and urinary daily NO excretion were analyzed. Tissue DDAH expression was examined by real-time polymerase chain reaction (PCR), immunoblotting, and immunohistochemistry. The results showed that PIO decreased serum ADMA and increased urinary NO excretion in both WKY and SHR. Also in both strains, the expression level of DDAH-II in the kidney was increased at transcriptional levels, although the DDAH-I level was unaffected. PIO lowered blood pressure in SHR, but not in WKY. We also demonstrated that PIO induced DDAH-II protein expression in Marbin-Dubin Canine Kidney (MDCK) cells, a renal tubular cell line. In conclusion, a PPARgamma ligand was here found to increase NO production partly by upregulating tissue DDAH-II expression and decreasing systemic ADMA levels. This mechanism constitutes a direct action on renal tubular cells, but is less likely to be responsible for the blood pressure-lowering effects of PPARgamma ligands. Since ADMA is one of the risk factors for cardiovascular events, this study provides compelling evidence that PPARgamma ligands have the potential for reducing cardiovascular risks.

Dimethylarginine dimethylaminohydrolase overexpression suppresses graft coronary artery disease

BACKGROUND

Graft coronary artery disease (GCAD) is the leading cause of death after the first year of heart transplantation. The reduced bioavailability of endothelium-derived nitric oxide (NO) may play a role in endothelial vasodilator dysfunction and the structural changes that are characteristic of GCAD. A potential contributor to endothelial pathobiology is asymmetric dimethylarginine (ADMA), an endogenous NO synthase inhibitor. We hypothesized that lowering ADMA concentrations by dimethylarginine dimethylaminohydrolase (DDAH) overexpression in the recipient might suppress GCAD and long-term immune responses in murine cardiac allografts.

METHODS AND RESULTS

In one series, donor hearts of C-H-2(bm12)KhEg (H-2(bm12)) wild-type (WT) mice were heterotopically transplanted into C57BL/6 (H-2b) transgenic mice overexpressing human DDAH-I or WT littermates and procured after 4 hours of reperfusion (WT and DDAH-I recipients, n=6 each). In a second series, donor hearts were transplanted into DDAH-I-transgenic or WT mice and procured 30 days after transplantation (n=7 each). In DDAH-I recipients, plasma ADMA concentrations were lower, in association with reduced myocardial generation of superoxide anion (WT versus DDAH-I, 465.7+/-79.8 versus 173.4+/-32.3 micromol.L(-1).mg(-1).h(-1); P=0.02), inflammatory cytokines, adhesion molecules, and chemokines. GCAD was markedly reduced in cardiac allografts of DDAH-I-transgenic recipients as assessed by luminal narrowing (WT versus DDAH, 79+/-2% versus 33+/-7%; P<0.01), intima-media ratio (WT versus DDAH, 1.1+/-0.1 versus 0.5+/-0.1; P<0.01), and the percentage of diseased vessels (WT versus DDAH, 100+/-0% versus 62+/-10%; P<0.01).

CONCLUSIONS

Overexpression of DDAH-I attenuated oxidative stress, inflammatory cytokines, and GCAD in murine cardiac allografts. The effect of DDAH overexpression may be mediated by its reduction of plasma and tissue ADMA concentrations.

Asymmetrical dimethylarginine plasma clearance persists after acute total nephrectomy in rats

Elevated plasma concentrations of symmetrical dimethylarginine (SDMA) and asymmetrical dimethylarginine (ADMA) are repeatedly associated with kidney failure. Both ADMA and SDMA can be excreted in urine. We tested whether renal excretion is necessary for acute, short-term maintenance of plasma ADMA and SDMA. Sprague-Dawley rats underwent sham operation, bilateral nephrectomy (NPX), ureteral ligation, or ureteral section under isoflurane anesthesia. Tail-snip blood samples (250 microl) were taken before and at 6- or 12-h intervals for 72 h after operation. Plasma clearance was assessed in intact and NPX rats. High-performance liquid chromatography determined SDMA and ADMA concentrations. Sodium, potassium, creatinine, blood urea nitrogen (BUN), and body weight were also measured. Forty-eight hours after NPX, SDMA increased 25 times (0.23 +/- 0.03 to 5.68 +/- 0.30 microM), whereas ADMA decreased (1.17 +/- 0.08 to 0.73 +/- 0.08 microM) by 38%. Creatinine and BUN increased, paralleling SDMA. Sham-operated animals showed no significant changes. Increased SDMA confirms continuous systemic production of SDMA and its obligatory renal excretion, much like creatinine. In contrast, decreased plasma ADMA suggests that acute total NPX either reduced systemic ADMA formation and/or systemic hydrolysis of ADMA increased 48-h post-NPX. However, plasma clearance of ADMA appeared unchanged 48 h after NPX. We conclude that renal excretory function is needed for SDMA elimination but not needed for acute, short-term ADMA elimination in that systemic hydrolysis is fully capable of clearing plasma ADMA.

Asymmetric dimethylarginine and the risk of cardiovascular events and death in patients with coronary artery disease: results from the AtheroGene Study

As a competitive inhibitor of endothelial nitric oxide synthase, asymmetric dimethylarginine (ADMA) has been related to atherosclerotic disease. Little is known about the prognostic impact of baseline ADMA determination. In a prospective cohort of 1908 patients with coronary artery disease, we assessed baseline serum concentration of ADMA in 1874 consecutive patients with coronary artery disease. One hundred fourteen individuals developed the primary end point of death from cardiovascular causes or nonfatal myocardial infarction during a mean follow-up of 2.6+/-1.2 years. Median concentrations of ADMA levels were higher among individuals who subsequently developed the primary end point than among those who did not (0.70 versus 0.63 micromol/L; P<0.001). The risk of future cardiovascular event was associated with increasing thirds of baseline ADMA (P for trend, <0.001) such that individuals in the highest third at entry had a hazard ratio 2.48 times higher than those in the lowest third (95% confidence interval, 1.52 to 4.06; P<0.001). This relationship remained nearly unchanged after adjustment for most potential confounders. Prediction models that simultaneously incorporated ADMA, B-type natriuretic peptide, C-reactive protein, and creatinine in addition to traditional risk factors revealed B-type natriuretic peptide (hazard ratio, 1.96; 95% confidence interval, 1.3 to 3.0; P=0.002) and ADMA (hazard ratio, 1.90; 95% confidence interval, 1.3 to 2.8; P=0.001) as the strongest risk predictors. High levels of baseline ADMA independently predict future cardiovascular risk. ADMA has prognostic value beyond traditional risk factors and novel biomarkers and might guide therapeutic strategies.

Asymmetric Dimethylarginine, L-Arginine, and Endothelial Dysfunction in Essential Hypertension

OBJECTIVES

We investigated the relationship between ADMA plasma levels and endothelium-dependent vasodilation in 36 never-treated essential hypertensives and in 8 normotensive healthy subjects.

BACKGROUND

It has been demonstrated that endothelium-dependent vasodilatation is impaired in essential hypertension. The potential contribution of asymmetric dimethylarginine (ADMA) to endothelial dysfunction of hypertensive humans has received poor attention.

METHODS

Endothelial function was measured during intra-arterial infusion of acetylcholine (ACh), alone and during co-infusion of L-arginine, and sodium nitroprusside at increasing doses. Concentrations of ADMA and L-arginine in plasma were measured by high-performance liquid chromatography.

RESULTS

Hypertensive subjects had significantly higher ADMA and L-arginine plasma concentrations than normotensive healthy controls; ACh-stimulated forearm blood flow (FBF) was significantly reduced in hypertensive subjects in comparison to normotensive control subjects (p < 0.0001). Intra-arterial coinfusion of L-arginine induced a further significant enhancement in ACh-stimulated vasodilation in hypertensive patients. In these, ADMA was strongly and inversely associated with the peak increase in FBF. In a multivariate model, only ADMA and L-arginine were independent correlates, accounting for 33.9% and 8.9% of the variability in the peak FBF response to ACh (p < 0.0001), respectively.

CONCLUSIONS

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.

Pathophysiological basis for the prophylaxis of preeclampsia through early supplementation with antioxidant vitamins

Preeclampsia (PE) is a multisystem disorder that remains a major cause of maternal and foetal morbidity and death. To date, no treatment has been found that prevents the development of the disease. Endothelial dysfunction is considered to underlie its clinical manifestations, such as maternal hypertension, proteinuria, and edema; however, the precise biochemical pathways involved remain unclear. A current hypothesis invokes the occurrence of oxidative stress as pathogenically important, as suggested by the fact that in PE, the placental and circulating levels of lipid peroxidation products (F2-isoprostanes and malondialdehyde [MDA]) are increased and endothelial cells are activated. A potential mechanism for endothelial dysfunction may occur via nuclear transcription factor kappa B (NF-kappaB) activation by oxidative stress. Alternatively, the idea that the antiangiogenic placental soluble fms-like tyrosine kinase 1 factor (sFlt1) is involved in the pathogenesis of this disease is just emerging; however, other pathophysiological events seem to precede its increased production. This review is focused on evidence providing a pathophysiological basis for the beneficial effect of early antioxidant therapy in the prevention of PE, mainly supported by the biological effects of vitamins C and E.

Reduced L-arginine level and decreased placental eNOS activity in preeclampsia

Nitric oxide is produced enzymatically by the nitric oxide synthase (NOS), which converts L-arginine in the presence of oxygen to L-citrulline and NO. Moreover, it has been reported that asymmetric dimethylarginine (ADMA) acts as is an endogenous inhibitor of endothelial NOS (eNOS) by competing with the enzyme for L-arginine. In this study, we measured L-arginine and ADMA in normal and preeclamptic women, and also investigated the association between the Glu298Asp eNOS gene polymorphism and preeclampsia. Finally, we assessed eNOS expression levels in the placentas of both normal and preeclamptic patients, using Western blot and immunohistochemistry. L-arginine levels were found to be significantly lower in the preeclamptic women than in the normal pregnant women (p=0.02) but there were no significant differences in ADMA levels between the normal and preeclamptic women. We also determined there to be no association between the Glu298Asp eNOS gene and preeclampsia. With regard to placental eNOS expression, we detected a lower degree of eNOS expression in the preeclamptic syncytiotrophoblasts than in the normal syncytiotrophoblasts. We suggest that reduced L-arginine levels, rather than increased ADMA levels, contribute to the development of preeclampsia, and also that decreased placental eNOS expression constitutes a characteristic finding in preeclamptic placentas.

Accumulated endogenous nitric oxide synthase inhibitors, enhanced arginase activity, attenuated dimethylarginine dimethylaminohydrolase activity and intimal hyperplasia in premenopausal human uterine arteries

The present study was designed to investigate the involvement of nitric oxide synthase (NOS), endogenous NOS inhibitors, arginase, which shares L-arginine as a common substrate with NOS, and dimethylarginine dimethylaminohydrolase (DDAH) as a metabolizing enzyme of NOS inhibitors in the occurrence of intimal hyperplasia in premenopausal human uterine arteries. Fifty-two uterine arteries were obtained from 52 patients undergoing total hysterectomy with an informed consent for the present study. All specimens were assessed histologically and the intima:media ratio (%) was evaluated as an index of intimal hyperplasia. Nineteen specimens were found to be histologically normal (intima:media ratio=16.1+/-0.8%), whereas remaining 33 specimens were categorized as intimal hyperplasia (intima:media ratio=34.4+/-1.5%). The intimal hyperplasia was associated with the impaired cyclic GMP production without change in endothelial NOS activity per se, accumulation of endogenous NOS inhibitors in endothelial cells, attenuated DDAH activity in endothelial cells and enhanced arginase activity in endothelial cells and smooth muscle layer. These findings suggest that the impaired cyclic GMP production as a marker of NO production is possibly due to the accumulated endogenous NOS inhibitors and enhanced arginase activity, which, in turn, closely relates to the occurrence of intimal hyperplasia, and that the impaired DDAH activity would result in the accumulation of endogenous NOS inhibitors in endothelial cells. Because of the enhanced arginase activity in endothelial cells and smooth muscle layer, the accelerated polyamine biosynthetic pathway may be implicated in the occurrence of intimal hyperplasia in premenopausal human uterine arteries.

NITRIC OXIDE and SYMPATHETIC NERVE ACTIVITY IN THE CONTROL OF BLOOD PRESSURE

1. Endothelial dysfunction marked by impairment in the release of nitric oxide (NO) is seen very early in the development of hypertension and is considered important in mediating the impaired vascular tone evident in essential hypertensive patients. 2. Recently, a hypothesis has emerged that NO acting as a neurotransmitter in the brain can modulate levels of sympathetic nerve activity and thereby blood pressure. The NO inhibition model of hypertension has been used to explore the possibility that a decrease in levels of NO can cause an increase in levels of sympathetic nerve activity that can mediate the hypertension. 3. In the present review, we examine the literature regarding the role of NO in setting the mean level of sympathetic nerve activity and blood pressure. Although the acute effects of NO inhibition are well understood, the chronic interaction between the sympathetic nervous system and NO has only been investigated using indirect measures of sympathetic nerve activity, such as ganglionic blockade. This has led to inconsistent results regarding the role of NO in modulating sympathetic nerve activity chronically. 4. Some of the conflicting results may be explained by differences in the 'background' levels of angiotensin (Ang) II. Evidence suggests that NO may interact with AngII and baroreceptor afferent inputs in the central nervous system to set the mean level of sympathetic nerve activity. 5. We suggest chronic NO inhibition can increase sympathetic nerve activity if baroreceptor input is intact and AngII levels are elevated. Although studies exploring the actions of NO or AngII in isolation are useful for gathering initial information, future studies should focus on their interactions and their role in setting the long-term levels of sympathetic activity and blood pressure.

Elevation of asymmetric dimethylarginine in patients with unstable angina and recurrent cardiovascular events

AIMS

We investigated the role of asymmetric dimethylarginine (ADMA) for clinical outcome of patients with unstable angina.

METHODS AND RESULTS

Forty-five patients with stable angina, 36 patients with unstable angina, and 40 healthy controls were included in this study. Coronary artery disease (CAD) patients were prospectively followed for 1 year. ADMA levels were measured at baseline and after 6 weeks using a validated ELISA. Baseline ADMA concentration in controls was significantly lower than in patients with CAD (0.59+/-0.23 vs. 0.76+/-0.17 micromol/L; P<0.001). Patients with unstable angina had significantly higher baseline ADMA levels than patients with stable angina (0.82+/-0.18 vs. 0.73+/-0.15 micromol/L; P=0.01). There was a significant reduction of ADMA levels at 6 weeks after percutaneous coronary intervention (PCI) in patients with unstable angina who experienced no recurrent cardiovascular event (from 0.81+/-0.14 to 0.73+/-0.19 micromol/L; P<0.05). In contrast, patients with unstable angina who had an event showed no significant decrease in ADMA at 6 weeks. Actuarial survival analysis showed a significantly higher event rate in patients with persistently elevated ADMA plasma concentrations.

CONCLUSION

ADMA is significantly elevated in patients with unstable angina. A reduced ADMA level at 6 weeks after PCI may indicate a decreased risk of recurrent cardiovascular events.

Determination of NG,NG-dimethyl-L-arginine, an endogenous NO synthase inhibitor, by gas chromatography-mass spectrometry

A fully validated gas chromatographic-mass spectrometric (GC-MS) method for the accurate and precise quantification of NG,NG-dimethyl-L-arginine (asymmetric dimethylarginine, ADMA), an endogenous inhibitor of the NO synthase, in cell culture supernatants and in small volumes of plasma is described. ADMA was concentrated by solid phase extraction and converted to its methyl ester pentafluoropropionic amide derivative. The derivatives were analyzed without any further purification. Using gas chromatography-chemical ionization mass spectrometry, fragment ions at m/z 634 and m/z 640 were obtained for ADMA and for NG,NG-[2H6]-dimethyl-L-arginine ([2H6]-ADMA) as internal standard, respectively. [2H6]-ADMA was synthesized by reaction of L-ornithine fastened at bromcyan-agarose with dimethylamine. The limit of detection of the method was 2 fmol, while the limit of quantitation for cell culture supernatants was 0.05 microM. The method was validated in a concentration range of 0-1.2 microM in cell culture medium and 0-2 microM in 50 microl aliquots of human plasma. The precision was > or =97% and the accuracy was determined to be > or =94%. This method is fast, rugged and an alternative to high performance liquid chromatography (HPLC) analysis of ADMA in cell culture supernatants and small volumes of human plasma.

Circulating ADMA concentrations are elevated in hypopituitary adults with and without growth hormone deficiency

BACKGROUND

Cardiovascular mortality is increased in patients with hypopituitarism. Elevated concentrations of the endogenous NO synthase antagonist asymmetrical dimethylarginine (ADMA) may be related to the development of atherosclerosis and are associated with cardiovascular risk. We studied the concentrations of ADMA in hypopituitary patients with and without growth hormone deficiency (GHD) and in healthy subjects.

MATERIALS AND METHODS

Plasma from 44 patients with hypopituitarism with (n = 30) and without GHD (n = 14) and from 25 age- and sex-matched healthy controls was taken for analysis of L-arginine, ADMA, symmetrical dimethylarginine (SDMA) and clinical parameters. Further plasma from 10 hypopituitary patients was examined before and after treatment with 9 g of oral L-arginine for 14 days.

RESULTS

Asymmetrical dimethylarginine was significantly higher in the hypopituitary patients than in the controls (0.63 +/- 0.12 vs. 0.51 +/- 0.15 micromol L(-1); P < 0.005). L-arginine and the L-arginine/ADMA ratios were lower in the subjects with hypopituitarism (53 +/- 18 vs. 90 +/- 29 micromol L(-1) and 87 +/- 31 vs. 185 +/- 59; both P < 0.0001). Symmetrical dimethylarginine was comparable between the patients and the controls. L-arginine and dimethylarginines were associated with 2-h stimulated glucose levels in a glucose tolerance test (r = 0.33; P < 0.05), but not other cardiovascular risk factors. Oral L-arginine supplementation normalized the reduced L-arginine/ADMA ratio in the hypopituitary patients.

CONCLUSION

Asymmetrical dimethylarginine is elevated in patients with hypopituitarism independent of GHD and traditional risk factors. This might contribute to the increased cardiovascular morbidity in hypopituitary patients.

Asymmetric dimethylarginine (ADMA): the silent transition from an 'uraemic toxin' to a global cardiovascular risk molecule

Endothelial dysfunction as a result of reduced bioavailability of nitric oxide (NO) plays a central role in the process of atherosclerotic vascular disease. In endothelial cells NO is synthesized from the amino acid l-arginine by the action of the NO synthase (NOS), which can be blocked by endogenous inhibitors such as asymmetric dimethylarginine (ADMA). Acute systemic administration of ADMA to healthy subjects significantly reduces NO generation, and causes an increase in systemic vascular resistance and blood pressure. Increased plasma ADMA levels as a result of reduced renal excretion have been associated with atherosclerotic complications in patients with terminal renal failure. However, a significant relationship between ADMA and traditional cardiovascular risk factors such as advanced age, high blood pressure and serum LDL-cholesterol, has been documented even in individuals without manifest renal dysfunction. As a consequence, the metabolism of ADMA by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) has come into the focus of cardiovascular research. It has been proposed that dysregulation of DDAH with consecutive increase in plasma ADMA concentration and chronic NOS inhibition is a common pathophysiological pathway in numerous clinical conditions. Thus, ADMA has emerged as a potential mediator of atherosclerotic complications in patients with coronary heart disease, peripheral vascular disease, stroke, etc., being the culprit and not only an innocent biochemical marker of the atherosclerotic disease process.

Hypothesis: Uric acid, nephron number, and the pathogenesis of essential hypertension

BACKGROUND

Essential hypertension affects more than 25% of the world's population. Genetic, physiologic, and epidemiologic studies provide clues to its origins, but a clear understanding has been elusive. Recent experimental and clinical studies have implicated uric acid in the onset of essential hypertension.

METHODS

In a retrospective chart review, we identified 95 children with confirmed, new onset hypertension, and evaluated the cause of hypertension and parental history of hypertension, birth weight, and serum uric acid. In an open-label, cross-over trial we treated 5 children with confirmed essential hypertension with allopurinol as single treatment agent, and screened for change in blood pressure by casual and ambulatory methods. In tissue culture experiments, we evaluated the effect of uric acid on glomerular endothelial cell function.

RESULTS

Elevation of serum uric acid is related to the onset of essential hypertension in children, reduced birth weight, and endothelial dysfunction. Normalization of uric acid appears to ameliorate new onset essential hypertension.

CONCLUSION

These findings, combined with animal model data, support the hypothesis that uric acid has a key role in the pathogenesis of early onset essential hypertension, and may unify some of the disparate theories of the origins of essential hypertension.

Elevated levels of asymmetric dimethylarginine (ADMA) as a marker of cardiovascular disease and mortality

The endothelium plays a crucial role in the maintenance of vascular tone and structure by releasing the endothelium-derived vasoactive mediator, nitric oxide (NO). NO is formed in healthy vascular endothelium from the amino acid precursor L-arginine. Endothelial dysfunction is caused by various cardiovascular risk factors, metabolic diseases, and systemic or local inflammation. One mechanism that explains the occurrence of endothelial dysfunction is the presence of elevated blood levels of asymmetric dimethylarginine (ADMA) – an L-arginine analogue that inhibits NO formation and thereby can impair vascular function. Accumulating evidence from prospective clinical studies suggests that elevated plasma or serum levels of ADMA are associated with an increased risk of major adverse cardiovascular events. This article gives an updated overview of the currently available literature on ADMA and cardiovascular disease from prospective clinical trials. Recently, advances have been made in the development of analytical methods that are reliable and fast enough to allow determination of ADMA in clinical routine.

Relationship between obesity, smoking, and the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine

We investigated the levels of asymmetric dimethylarginine (ADMA), an important endogenous inhibitor of nitric oxide (NO), as related to metabolic risk factors known to contribute to atherosclerotic disease. Dimethylarginines were analysed in a cross-sectional study of 563 elderly high-risk men (70 +/- 6 years). ADMA and the l-arginine/ADMA (l-arg/ADMA) ratio were highly significantly correlated with several metabolic risk factors. However, only the association with body mass index (BMI) remained significant after adjustment for inter-related variables. When analyzing the results according to being overweight or not, ADMA levels were independently significantly higher (P = .05) and the L-arg/ADMA ratios were significantly lower (P < .008) in individuals with high BMI (> or =26 kg/m(2), median value) as compared with subjects with low BMI. ADMA levels were furthermore significantly lower (P = .037) and L-arginine and the l-arg/ADMA ratios were significantly higher (P = .004 and P = .001, respectively) in smokers compared with nonsmokers, the latter being independent of other risk factors. The strong relationship found between BMI and plasma levels of ADMA and the l-arg/ADMA ratio indicate a link to endothelial dysfunction in overweight subjects. The beneficial dimethylarginine profile observed in smokers in this elderly population is not easily explainable and should be further investigated.

Diminished L-arginine bioavailability in hypertension

L-Arginine is the precursor of NO (nitric oxide), a key endogenous mediator involved in endothelium-dependent vascular relaxation and platelet function. Although the concentration of intracellular L-arginine is well above the Km for NO synthesis, in many cells and pathological conditions the transport of L-arginine is essential for NO production (L-arginine paradox). The present study was designed to investigate the modulation of L-arginine/NO pathway in systemic arterial hypertension. Transport of L-arginine into RBCs (red blood cells) and platelets, NOS (NO synthase) activity and amino acid profiles in plasma were analysed in hypertensive patients and in an animal model of hypertension. Influx of L-arginine into RBCs was mediated by the cationic amino acid transport systems y+ and y+L, whereas, in platelets, influx was mediated only via system y+L. Chromatographic analyses revealed higher plasma levels of L-arginine in hypertensive patients (175+/-19 micromol/l) compared with control subjects (137+/-8 micromol/l). L-Arginine transport via system y+L, but not y+, was significantly reduced in RBCs from hypertensive patients (60+/-7 micromol.l(-1).cells(-1).h(-1); n=16) compared with controls (90+/-17 micromol.l(-1).cells(-1).h(-1); n=18). In human platelets, the Vmax for L-arginine transport via system y+L was 86+/-17 pmol.10(9) cells(-1).min(-1) in controls compared with 36+/-9 pmol.10(9) cells(-1).min(-1) in hypertensive patients (n=10; P<0.05). Basal NOS activity was decreased in platelets from hypertensive patients (0.12+/-0.02 pmol/10(8) cells; n=8) compared with controls (0.22+/-0.01 pmol/10(8) cells; n=8; P<0.05). Studies with spontaneously hypertensive rats demonstrated that transport of L-arginine via system y+L was also inhibited in RBCs. Our findings provide the first evidence that hypertension is associated with an inhibition of L-arginine transport via system y+L in both humans and animals, with reduced availability of L-arginine limiting NO synthesis in blood cells.

Gut and liver handling of asymmetric and symmetric dimethylarginine in the rat under basal conditions and during endotoxemia

INTRODUCTION/AIM

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase enzymes, whereas symmetric dimethylarginine (SDMA) competes with arginine transport. Although both dimethylarginines may be important regulators of the arginine-NO pathway, their metabolism is largely unknown. In previous studies, evidence was found for the liver in the metabolism of dimethylarginines. We aimed to investigate dimethylarginine handling of the gut and the liver in detail under basal conditions and during endotoxemia.

METHODS

Twenty-one male Wistar rats were used for this study. Endotoxemia was induced by lipopolysaccharide (LPS) infusion (8 mg/kg). Blood flow was measured using radiolabeled microspheres according to the reference sample method. Concentration of dimethylarginines were measured by high-performance liquid chromatography. The combination of arteriovenous concentration difference and organ blood flow allowed calculation of net organ fluxes and fractional extraction (FE) rates.

RESULTS

Arterial plasma concentration of ADMA was lower in LPS rats, in contrast to a higher SDMA concentration. For the gut, net release of ADMA was found, which was higher in LPS rats. In contrast, for the gut, net uptake of SDMA was found, which was lower in LPS rats. For the liver, a high net uptake of ADMA was found in both groups, while FE was significantly increased in LPS rats. Hepatic handling of SDMA was negligible.

CONCLUSION

The liver plays an important role in eliminating ADMA from the circulation and endotoxemia stimulates this capacity. In contrast to the liver, the gut releases ADMA. Endotoxemia results in a reduced systemic ADMA concentration.

Asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, explains the "L-arginine paradox" and acts as a novel cardiovascular risk factor

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO). Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of NO synthase. ADMA inhibits vascular NO production in concentrations found in pathophysiological conditions; ADMA also causes local vasoconstriction when it is infused intraarterially. Thus, elevated ADMA levels may explain the "L-arginine paradox," i.e., the observation that supplementation with exogenous L-arginine improves NO-mediated vascular functions in vivo, although its baseline plasma concentration is about 25-fold higher than the Michaelis-Menten constant K(m) of the isolated, purified endothelial NO synthase in vitro. The biochemical and physiological pathways related to ADMA are well understood: Dimethylarginines are the result of degradation of methylated proteins; the methyl group is derived from S-adenosylmethionine. Both ADMA and its regioisomer, symmetric dimethylarginine, are eliminated from the body by renal excretion, whereas only ADMA is metabolized via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). DDAH activity and/or expression may therefore contribute to the pathogenesis of endothelial dysfunction in various diseases. Plasma ADMA levels are increased in humans with hypercholesterolemia, atherosclerosis, hypertension, chronic renal failure, and chronic heart failure. Increased ADMA levels are associated with reduced NO synthesis as assessed by impaired endothelium-dependent vasodilation. In several prospective and cross-sectional studies, ADMA evolved as a marker of cardiovascular risk. With increasing knowledge of the role of ADMA in the pathogenesis of cardiovascular disease, ADMA is becoming a goal for pharmacotherapeutic interventions. Among other potential strategies that are currently being tested, administration of L-arginine has been shown to improve endothelium-dependent vascular functions in subjects with high ADMA levels. Finally, ADMA has gained clinical importance recently because several studies have shown that ADMA is an independent cardiovascular risk factor.

Effect of fenofibrate on LDL-induced endothelial dysfunction in rats

Previous investigations have demonstrated that asymmetric dimethylarginine (ADMA) is an important factor contributing to endothelial dysfunction, and that fenofibrate has a protective effect on the endothelium in hyperlipidaemic patients. In the present study in rats treated with native low-density lipoprotein (nLDL), we addressed the question of whether the beneficial effect of fenofibrate on endothelial cells is related to reduction of the ADMA concentration. A single injection of nLDL (4 mg/kg, 48 h) markedly reduced endothelium-dependent relaxation in response to acetylcholine and the plasma level of nitrite/nitrate and increased the plasma concentrations of ADMA, malonyldialdehyde (MDA) and tumour necrosis factor-alpha (TNF-alpha). Treatment with fenofibrate (30 or 100 mg/kg) significantly reduced the inhibition of vasodilator responses to acetylcholine, decreased the elevated levels of ADMA, MDA and TNF-alpha, and enhanced the decreased level of nitrite/nitrate in the rats treated with LDL. These results suggest that the protective effect of fenofibrate on endothelial cells in rats treated with LDL may be related to the reduction of ADMA concentration.

Demethylbellidifolin preserves endothelial function by reduction of the endogenous nitric oxide synthase inhibitor level

The present study examined the anti-oxidation and protective effects of demethylbellidifolin (DMB), a xanthone compound extracted from swertia davidi Franch, on endothelium. The relationship between the protective effects of DMB on endothelium and the level of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, was also determined in the present study. DMB significantly inhibited Cu(2+)-induced low-density lipoprotein (LDL) oxidation and scavenged DPPH radicals. DMB significantly attenuated the inhibition of endothelium-dependent vasodilator responses, induced by lysophosphatidycholine (LPC) in vitro and LDL in vivo, and increased release of lactate dehydrogenase induced by LDL in cultured endothelial cells. DMB significantly attenuated the increased concentration of malondialdehyde and ADMA, and the decreased level of nitric oxide induced by LDL in vivo and in cultured endothelial cells. DMB also significantly reduced the decreased activity of dimethylarginine dimethylaminohydrolase (DDAH) induced by LDL in cultured endothelial cells. In summary, the present results suggest that DMB protects endothelial damage induced by LPC in vitro and LDL in vivo or in endothelial cells, and the protective effect of DMB on the endothelium is related to reduction of ADMA concentration via an increase of DDAH activity by inhibition of lipid peroxidation.

Dietary composition as a determinant of plasma asymmetric dimethylarginine in subjects with mild hypercholesterolemia

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor that participates in the regulation of vasodilatory function and is also linked to hypertension, whereas its stereoisomere, symmetric dimethylarginine (SDMA), is biologically inactive. Dietary components influence vascular functions and a high-fat meal seems to increase postprandial plasma ADMA levels. However, it has not been published whether diet influences plasma ADMA levels. In this study, we investigated the impact of diet on plasma ADMA and SDMA levels. Thirty-four mildly hypercholesterolemic, otherwise healthy women (n = 14) and men (n = 20) with a mean age of 46.2 years (range, 35 to 62 years) participated in the study. The subjects were examined twice at intervals of 2 months. Seven-day food records were used to analyze diet and alcohol intake. ADMA was measured by using high-performance liquid chromatography (HPLC)-tandem mass spectrometry. In a multivariate analysis (R2 = 0.20, P < .002), low amount of energy received from carbohydrates (r = -0.31, P = .009) and high plasma triglycerides (r = 0.30, P = .01) were predictors of high ADMA plasma levels. Alcohol drinkers had higher plasma ADMA concentrations than abstainers (0.50 +/- 0.13 v 0.42 +/- 0.11 micromol/L, P = .04). Plasma ADMA correlated with systolic (r = 0.60, P = .005) and diastolic blood pressure (r = 0.53, P = .02) in abstainers but not in alcohol drinkers. Plasma SDMA was not associated with any dietary components or with blood pressure. In conclusion, a high amount of dietary carbohydrates is strongly associated with low levels of plasma ADMA. Concentration of ADMA in plasma seems to be higher in alcohol drinkers than in abstainers.

Plasma concentration of coupling factor 6 and cardiovascular events in patients with end-stage renal disease

BACKGROUND

Plasma asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is an independent predictor of overall mortality and cardiovascular outcome in hemodialysis patients. However, not only ADMA but also traditional risk factors account for only part of the high cardiovascular morbidity and mortality in these patients. We investigated cross-sectionally the association between coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis, and cardiovascular events in 95 hemodialysis patients.

METHODS

Plasma CF6 level was measured by radioimmunoassay, whereas plasma ADMA level by high-performance liquid chromatography (HPLC).

RESULTS

Plasma levels of CF6 and ADMA were threefold higher in hemodialysis patients than in control individuals, and there was a positive correlation between these two compounds (r=0.25, P < 0.05). Plasma CF6 level was positively correlated with serum creatinine level (r=0.36, P < 0.01) and was reduced after dialysis (P < 0.05). Plasma CF6 and ADMA levels were both higher in hemodialysis patients complicating ischemic heart disease (myocardial infarction and/or angina) than in those free of cardiovascular events. In a multiple regression model, plasma CF6 level (r=0.24, P=0.023) and ADMA level (r=0.26, P=0.023) were independently related to the occurrence of ischemic heart disease in hemodialysis patients.

CONCLUSION

CF6 is a novel risk factor for ischemic heart disease in end-stage renal disease (ESRD). Synergism of this peptide and ADMA might contribute to its occurrence presumably by inhibition of prostacyclin and nitric oxide production. A prospective study is needed to evaluate this issue more precisely.

Effect of rosuvastatin on plasma levels of asymmetric dimethylarginine in patients with hypercholesterolemia

Elevated plasma levels of asymmetric dimethylarginine (ADMA) have been associated with attenuated endothelium-dependent vasodilation in hypercholesterolemic patients. However, whether lowering of plasma cholesterol concentration by hydroxymethylglutaryl coenzyme A reductase inhibitors (statins) can reduce plasma ADMA levels is still not clear. This study was a multicenter, randomized, double-blind, placebo-controlled design including 46 patients with elevated low-density lipoprotein cholesterol levels. Patients were randomized into 2 groups: rosuvastatin 10 mg/day and placebo for 6 weeks. Plasma levels of ADMA, 8-isoprostane (as a marker of oxidative stress), homocysteine, and high-sensitivity C-reactive protein were measured at baseline and 6 weeks later. Endothelial function assessed by flow-mediated vasodilation of the brachial artery was performed in 11 patients in the rosuvastatin group and in 12 in the placebo group. Baseline characteristics of both groups were similar, and the plasma ADMA levels were significantly correlated with 8-isoprostane (r = 0.388, p = 0.008). After 6 weeks of treatment, plasma ADMA levels were significantly reduced in the rosuvastatin group (from 0.60 +/- 0.19 to 0.49 +/- 0.10 micromol/L, p <0.001). Increases in flow-mediated vasodilation were positively correlated with reductions in plasma levels of ADMA (p = 0.017) and low-density lipoprotein cholesterol (p <0.001). Thus, our findings suggest that treatment with rosuvastatin in patients with hypercholesterolemia may lead to a significant reduction in plasma ADMA levels, which appear to be related to the improvement in endothelial function by rosuvastatin.

Asymmetric dimethylarginine produces vascular lesions in endothelial nitric oxide synthase-deficient mice: involvement of renin-angiotensin system and oxidative stress

OBJECTIVE

Asymmetric dimethylarginine (ADMA) is widely believed to be an endogenous nitric oxide synthase (eNOS) inhibitor. However, in this study, we examined our hypothesis that the long-term vascular effects of ADMA are not mediated by inhibition of endothelial NO synthesis.

METHODS AND RESULTS

ADMA was infused in wild-type and eNOS-knockout (KO) mice by osmotic minipump for 4 weeks. In wild-type mice, long-term treatment with ADMA caused significant coronary microvascular lesions. Importantly, in eNOS-KO mice, treatment with ADMA also caused an extent of coronary microvascular lesions that was comparable to that in wild-type mice. These vascular effects of ADMA were not prevented by supplementation of l-arginine, and vascular NO production was not reduced by ADMA treatment. Treatment with ADMA caused upregulation of angiotensin-converting enzyme (ACE) and an increase in superoxide production that were comparable in both strains and that were abolished by simultaneous treatment with temocapril (ACE inhibitor) or olmesartan (AT(1) receptor antagonist), which simultaneously suppressed vascular lesion formation.

CONCLUSIONS

These results provide the first direct evidence that the long-term vascular effects of ADMA are not solely mediated by simple inhibition of endothelial NO synthesis. Direct upregulation of ACE and increased oxidative stress through AT(1) receptor appear to be involved in the long-term vascular effects of ADMA in vivo. This study demonstrates that asymmetrical dimethylarginine (ADMA) causes arteriosclerotic coronary lesions in mice in vivo through mechanisms other than simple inhibition of endothelial NO synthesis. Our findings should contribute to a better understanding of the pathophysiological role of ADMA in arteriosclerosis.

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in patients with chronic kidney diseases

BACKGROUND

NO synthesis is inhibited by the dimethylarginine (DMA) ADMA, which accumulates, similar to SDMA, in the plasma of patients suffering from chronic renal failure (CRF). ADMA and possibly SDMA contribute to hypertension and atherosclerosis in patients with chronic renal disease: ADMA inhibits directly eNOS, whereas SDMA competes with the NO precursor arginine for uptake into the cells.

METHODS

In 26 control persons and 221 patients with kidney diseases of different stage as were CRF, end stage renal disease (ESRD), and patients after renal transplantation (RT), the plasma concentrations of ADMA (c(ADMA)), SDMA (c(SDMA)) and 20 endogenous amino acids (AA) were measured by HPLC and correlated to blood pressure, cardiac events, endothelial dysfunction, and diabetes mellitus.

RESULTS

Both ADMA (1.04+/-0.04 vs. 0.66+/-0.04 microM) and SDMA (2.69+/-0.12 vs. 0.49+/-0.03 microM) were significantly (p<0.001) elevated in all patients compared to healthy controls, whereas arginine concentration (51.4+/-2.3 vs. 76.0+/-5.2 microM) was decreased in dependence on the degree of kidney disease. In RT patients, SDMA levels were significantly decreased, but c(ADMA) remained enhanced. A strong correlation was found between SDMA and both serum urea and creatinine in CRF and RT patients. A linear correlation was found between ADMA and cholesterol concentrations in RT patients. Hypertension in CRF was accompanied by a further increase in the concentration of DMAs. There was no relation between DMAs and the occurrence of peripheral arterial occlusive disease or cerebrovascular diseases. In patients with cardiac diseases, c(SDMA) was additionally increased only in the CRF group.

CONCLUSIONS

In patients with chronic kidney disease, c(ADMA) and c(SDMA) are significantly increased but cardiovascular diseases are evidently not correlated to changes in DMA concentrations in this group of patients.

Increased (E)-4-hydroxy-2-nonenal and asymmetric dimethylarginine concentrations and decreased nitric oxide concentrations in the plasma of patients with major depression

BACKGROUND

(E)-4-Hydroxy-2-nonenal (HNE) is a highly electrophilic end-product of lipid peroxidation. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (NOS). ADMA is metabolised by dimethylarginine dimethylaminohydrolase (DDAH). DDAH contains a nucleophilic cysteine residue in its active site. There is an increase in lipid peroxidation in major depression. Major depression is associated with the development of coronary heart disease (CHD) and greatly increases morbidity and mortality. There is an increase in circulating ADMA in CHD and vascular risk factors.

OBJECTIVES

To determine plasma HNE, ADME and nitric oxide (NO) concentrations in patients with major depression compared to normal volunteers and to examine the effect of HNE on ADMA formation and DDAH activity in cultured endothelial cells.

METHODS

The study was conducted in 25 patients with major depression (DSM-IV criteria) and 25 healthy control subjects. Plasma concentrations of HNE were determined as the O-pentafluorylbenzyl oxime using capillary column GC-MS and deuterated HNE as the internal standard; ADME by LC-MS-MS using 13C6-L-arginine as the internal standard; and NO by GC-MS following reduction to nitrate and nitrite and derivatisation to the pentafluorobenzyl derivative using [15N]nitrate and [15N]nitrite as the internal standards. Human umbilical vein endothelial cells were incubated in serum-free medium in the presence of HNE. The concentration of ADMA in the medium was determined by LC-MS-MS. DDAH activity was determined by measuring L-citrulline in endothelial cell lysates using LC-MS.

RESULTS

There was a significant increase in the plasma concentration of HNE (P<0.0001) and ADMA (P<0.0002) in patients with major depression. There was a significant decrease in the plasma concentration of NO (P<0.0001). A significant positive correlation was found between the plasma concentrations of HNE and ADMA (r=0.63, P<0.0001). A significant negative correlation was detected between the plasma concentrations of ADMA and NO (r=-0.595, P<0.0001). HNE significantly increased ADMA formation (P<0.0001) and significantly decreased DDAH activity (P<0.0001) in cultured endothelial cells. The effects of HNE on DDAH activity were significantly attenuated by the addition of glutathione (P<0.0001).

LIMITATIONS

No allowance was made for the phase of the menstrual cycle which could influence plasma nitric oxide concentrations.

CONCLUSIONS

There is an increase in circulating HNE in major depression. HNE inactivates the cysteine residue in the active site of endothelial DDAH leading to the accumulation of ADMA in the circulation. The ADMA then decreases the production of eNOS. This could reduce the amount of NO diffusing from cerebral blood vessels to nearby neurons and influence the release of neurotransmitters. ADMA also constricts cerebral blood vessels and may contribute to the decreased regional perfusion in major depression. The accumulation of ADMA could explain the increased risk of CHD in major depression. The preservation of DDAH activity and the reduction of ADMA accumulation may represent a novel therapeutic approach to the treatment of major depression.