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

Phosphorylation of Nonmuscle Myosin Light Chain Promotes Endothelial Injury in Hyperlipidemic Rats Through a Mechanism Involving Downregulation of Dimethylarginine Dimethylaminohydrolase 2

Suppression of dimethylarginine dimethylaminohydrolase (DDAH) activation is related to endothelial dysfunction in hyperlipidemia, and nonmuscle myosin regulatory light chain (nmMLC₂₀) has been show to exert transcriptional function in regulation of gene expression. This study aims to explore whether the suppression of DDAH activation promotes endothelial injury under the condition of hyperlipidemia and whether nmMLC₂₀ can regulate DDAH expression in a phosphorylation-dependent manner. The rats were fed with high-fat diet for 8 weeks to establish a hyperlipidemic model, which showed an increase in plasma lipids and endothelial injury, accompanied by an elevation in myosin light chain kinase (MLCK) activity, phosphorylated nmMLC₂₀ (p-nmMLC₂₀) level, and asymmetric dimethylarginine (ADMA) content as well as a reduction in DDAH2 expression, DDAH activity, and nitric oxide (NO) content. Next, human umbilical vein endothelial cells (HUVECs) were incubated with oxidized low-density lipoprotein (ox-LDL; 100 μg/mL) for 24 hours to establish a cellular injury model in vitro. Consistent with the finding in vivo, ox-LDL induced HUVECs injury (apoptosis and necrosis) concomitant with an increase in MLCK activity, p-nmMLC₂₀ level (in total or nuclear proteins), and ADMA content as well as a reduction in DDAH2 expression, DDAH activity, and NO content; these phenomena were attenuated by MLCK inhibitor. Either in hyperlipidemic rats or in ox-LDL-treated HUVECs, there was not significant change in DDAH1 expression. Based on these observations, we conclude that the suppression of DDAH2 expression might account for, at least partially, the vascular endothelial dysfunction in hyperlipidemia, and nmMLC₂₀ plays a role in suppression of DDAH2 expression in a phosphorylation-dependent manner.

Long-term subarachnoid haemorrhage survivors still die due to cerebrovascular causes

OBJECTIVE

Subarachnoid haemorrhage (SAH) is associated with sympathetic nervous activation and inflammation. SAH could therefore theoretically be a risk factor for development of cardiovascular disease. The aim of this study was to investigate whether long-term (≥1 year) SAH survivors had an increased risk of death due to cardiovascular causes.

MATERIAL & METHODS

SAH patients ≥18 years treated at Umeå University Hospital between 1986 and 2006 were eligible for inclusion. Deceased patients were identified in the Swedish population register. Death certificates from long-term SAH survivors and causes of death in the general population were obtained from the National Board of Health and Welfare, Sweden. The prevalence of comorbidities at the time of SAH was compared with the distribution of cardiovascular risk factors in the northern Sweden MONICA (Multinational Monitoring of Trends and Determinants in Cardiovascular Disease) health survey. Analyses were stratified for age and sex.

RESULTS

In the SAH patients, the median year of SAH was 1992 and the median year of death was 2001. The MONICA survey in 1994 and the distribution of deaths in the general population in 2001 were used for comparison. Long-term SAH survivors had, compared to the general population, a significantly increased risk for death due to cerebrovascular disease (P < 0.0001), but not for death due to cardiovascular disease. Hypertension was more common in SAH patients compared to survey participants (P < 0.01).

CONCLUSION

Cerebrovascular causes of death were significantly more common in long-term survivors after SAH compared to the general population.

Impact of eNOS-Dependent Oxidative Stress on Endothelial Function and Neointima Formation

AIMS

Vascular oxidative stress generated by endothelial NO synthase (eNOS) was observed in experimental and clinical cardiovascular disease, but its relative importance for vascular pathologies is unclear. We investigated the impact of eNOS-dependent vascular oxidative stress on endothelial function and on neointimal hyperplasia.

RESULTS

A dimer-destabilized mutant of bovine eNOS where cysteine 101 was replaced by alanine was cloned and introduced into an eNOS-deficient mouse strain (eNOS-KO) in an endothelial-specific manner. Destabilization of mutant eNOS in cells and eNOS-KO was confirmed by the reduced dimer/monomer ratio. Purified mutant eNOS and transfected cells generated less citrulline and NO, respectively, while superoxide generation was enhanced. In eNOS-KO, introduction of mutant eNOS caused a 2.3-3.7-fold increase in superoxide and peroxynitrite formation in the aorta and myocardium. This was completely blunted by an NOS inhibitor. Nevertheless, expression of mutant eNOS in eNOS-KO completely restored maximal aortic endothelium-dependent relaxation to acetylcholine. Neointimal hyperplasia induced by carotid binding was much larger in eNOS-KO than in mutant eNOS-KO and C57BL/6, while the latter strains showed comparable hyperplasia. Likewise, vascular remodeling was blunted in eNOS-KO only.

INNOVATION

Our results provide the first in vivo evidence that eNOS-dependent oxidative stress is unlikely to be an initial cause of impaired endothelium-dependent vasodilation and/or a pathologic factor promoting intimal hyperplasia. These findings highlight the importance of other sources of vascular oxidative stress in cardiovascular disease.

CONCLUSION

eNOS-dependent oxidative stress is unlikely to induce functional vascular damage as long as concomitant generation of NO is preserved. This underlines the importance of current and new therapeutic strategies in improving endothelial NO generation.

Atrial Fibrillation Is Associated with a Marker of Endothelial Function and Oxidative Stress in Patients with Acute Myocardial Infarction

Background

Atrial fibrillation (AF), whether silent or symptomatic, is a frequent and severe complication of acute myocardial infarction (AMI). Asymmetric dimethylarginine (ADMA), an endogenous eNOS inhibitor, is a risk factor for endothelial dysfunction. We addressed the relationship between ADMA plasma levels and AF occurrence in AMI.

Methods

273 patients hospitalized for AMI were included. Continuous electrocardiographic monitoring (CEM) ≥48 hours was recorded and ADMA was measured by High Performance Liquid Chromatography on admission blood sample.

Results

The incidence of silent and symptomatic AF was 39(14%) and 29 (11%), respectively. AF patients were markedly older than patients without AF (≈ 20 y). There was a trend towards higher ADMA levels in patients with symptomatic AF than in patients with silent AF or no AF (0.53 vs 0.49 and 0.49 μmol/L, respectively, p = 0.18,). After matching on age, we found that patients with symptomatic AF had a higher heart rate on admission and a higher rate of patients with LV dysfunction (28% vs. 3%, p = 0.025). Patients who developed symptomatic AF had a higher ADMA level than patients without AF (0.53 vs. 0.43 μmol/L; p = 0.001). Multivariate logistic regression analysis to estimate symptomatic AF occurrence showed that ADMA was independently associated with symptomatic AF (OR: 2.46 [1.21–5.00], p = 0.013) beyond history of AF, LVEF<40% and elevated HR.

Conclusion

We show that high ADMA level is associated with the occurrence of AF. Although no causative role can be concluded from our observational study, our work further supports the hypothesis that endothelial dysfunction is involved in the pathogenesis of AF in AMI.

Assessment of serum asymmetric dimethylarginine levels and left ventricular diastolic function in patients with ankylosing spondylitis

AIM

To assess left ventricular diastolic functions and serum dimethylarginine (ADMA) concentrations, as well as the effect of different treatment strategies on ADMA concentrations and diastolic function parameters, in patients with ankylosing spondylitis (AS).

METHOD

Sixty AS patients and 40 control subjects without classical cardiovascular (CV) risk factors were included in the study. Baseline clinical and echocardiographic variables were obtained. C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and ADMA levels were measured. Spinal mobility, disease activity and functional status were assessed using Bath Ankylosing Spondylitis Metrology Index, Bath Ankylosing Spondylitis Disease Activity Index and Bath Ankylosing Spondylitis Functional Index.

RESULTS

CRP, ESR and ADMA levels were significantly higher in the AS group as compared to the control group. Two (5%) control subjects and six (10%) AS patients met the criteria for left ventricular diastolic dysfunction (DD) on conventional Doppler echocardiography, but the difference was not statistically significant (P = 0.36). However, using tissue Doppler imaging, 12 (20%) patients in the AS group and three (8%) subjects in the control group were diagnosed with left ventricular DD (P = 0.08). The anti-tumor necrosis factor (TNF)-α group, conventional therapy group and control group were compared in terms of ADMA, CRP, ESR levels and echocardiographic parameters. ADMA levels were significantly lower in anti-TNF-α group as compared to the conventional therapy group (P < 0.001). In the control group, ADMA levels were significantly lower than both treatment groups (P < 0.001).

CONCLUSION

Increased ADMA levels reveal impaired nitric oxide metabolism in a relatively young group of patients with AS, who have no classical CV risk factors. Anti-TNF-α may have beneficial effect on endothelial function in AS patients by reducing ADMA levels.

Exercise-induced vasodilation in healthy males: A marker of reduced endothelial function

OBJECTIVES

Reduced arterial vasodilatatory capacity is a marker of coronary heart disease. The aim was to investigate if the difference between the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers.

DESIGN

Post-ischemic hyperemia after 5 min of arterial occlusion was examined before and after a bicycle test with strain-gauge plethysmography (measuring peak reactive hyperemia in the forearm) and peripheral arterial tonometry (PAT hyperemia ratio: measuring pulse waves in the index finger relative to the contra-lateral index finger) in 30 healthy males. A low PAT hyperemia ratio or a low peak reactive hyperemia reflects endothelial dysfunction. Inflammatory and endothelial biomarkers were assessed.

RESULTS

A low peak reactive hyperemia and a low PAT hyperemia ratio before the bicycle test was associated with a high percentage increase in peak reactive hyperemia after exercise (r = - 0.68, p < 0.001; r = - 0.35, p = 0.06, respectively). Asymmetric dimethylarginine and interleukin-10 were associated with the percentage increase in peak reactive hyperemia in multiple linear regression analyses (β: 165 (confidence interval [CI], 34-296), p = 0.02; β: 19 (CI, - 0.5-39), p = 0.06, respectively).

CONCLUSIONS

The difference in the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers in healthy males.

Asymmetric dimethylarginine in somatically healthy schizophrenia patients treated with atypical antipsychotics: a case-control study

BACKGROUND

Schizophrenia is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of the nitric oxide synthase, and the L-arginine:ADMA ratio are markers of endothelial dysfunction that predict mortality and adverse outcome in a range of cardiovascular disorders. Increased ADMA levels may also lead to increased oxidative stress. We hypothesized that ADMA and the L-arginine:ADMA ratio are increased in somatically healthy schizophrenia patients treated with atypical antipsychotics (AAP), and that the ADMA and the L-arginine: ADMA ratio are positively correlated to measures of oxidative stress.

METHODS

We included 40 schizophrenia patients treated with AAP, but without somatic disease or drug abuse, and 40 healthy controls. Plasma concentrations of ADMA and L-arginine were determined by high-performance liquid chromatography. Data were related to markers of systemic oxidative stress on DNA, RNA and lipids, as well as measures of medication load, duration of disease and current symptomatology.

RESULTS

Plasma ADMA and the L-arginine:ADMA ratio did not differ between schizophrenia patients and controls. Furthermore, ADMA and the L-arginine:ADMA ratio showed no correlations with oxidative stress markers, medication load, or Positive and Negative Syndrome Scale scores.

CONCLUSIONS

Schizophrenia and treatment with AAP was not associated with increased levels of plasma ADMA or the L-arginine:ADMA ratio. Furthermore, plasma levels of ADMA were not associated with levels of systemic oxidative stress in vivo.

Plasma asymmetric and symmetric dimethylarginine in a rat model of endothelial dysfunction induced by acute hyperhomocysteinemia

Hyperhomocysteinemia induces vascular endothelial dysfunction, an early hallmark of atherogenesis. While higher levels of circulating asymmetric dimethylarginine (ADMA) and symmetric dimethyl arginine (SDMA), endogenous inhibitors of nitric oxide synthesis, have been associated with increased cardiovascular risk, the role that ADMA and SDMA play in the initiation of hyperhomocysteinemia-induced endothelial dysfunction remains still controversial. In the present study, we studied the changes of circulating ADMA and SDMA in a rat model of acutely hyperhomocysteinemia-induced endothelial dysfunction. In healthy rats, endothelium-related vascular reactivity (measured as acetylcholine-induced transient decrease in mean arterial blood pressure), plasma ADMA and SDMA, total plasma homocysteine (tHcy), cysteine and glutathione were measured before and 2, 4 and 6 h after methionine loading or vehicle. mRNA expression of hepatic dimethylarginine dimethylaminohydrolase-1 (DDAH1), a key protein responsible for ADMA metabolism, was measured 6 h after the methionine loading or the vehicle. Expectedly, methionine load induced a sustained increase in tHcy (up to 54.9 ± 1.9 µM) and a 30 % decrease in vascular reactivity compared to the baseline values. Plasma ADMA and SDMA decreased transiently after the methionine load. Hepatic mRNA expression of DDAH1, cathepsin D, and ubiquitin were significantly lower 6 h after the methionine load than after the vehicle. The absence of an elevation of circulating ADMA and SDMA in this model suggests that endothelial dysfunction induced by acute hyperhomocysteinemia cannot be explained by an up-regulation of protein arginine methyltransferases or a down-regulation of DDAH1. In experimental endothelial dysfunction induced by acute hyperhomocysteinemia, down-regulation of the proteasome is likely to dampen the release of ADMA and SDMA in the circulation.

Asymmetric dimethylarginine is negatively correlated with hyperglycemia in children

Asymmetric dimethylarginine (ADMA) is a nonselective nitric oxide (NO) synthase inhibitor associated with cardiovascular and metabolic disorders. In several prospective and cross-sectional studies, ADMA has evolved as a marker of cardiovascular risk. However, there is limited information on this serum marker in young people, particularly in those with obesity, type 1 diabetes (DM1) and type 2 diabetes (DM2). We investigated ADMA concentrations in children and adolescents with hyperglycemia as compared with healthy age- and sex-matched individuals. The subjects were 21 simple obesity [male 13, female 8; aged 11.7±4.3 years], 18 with DM1 [male 4, female 14; aged 12.9±4.2 years, duration of disease 3.4±2.1 years], 10 with DM2 [male 5, female 5; aged 13.9±3.4 years, duration of disease 2.8±1.4 years] and 21 controls [male 12, female 9; aged 11.1±2.7 years]. ADMA levels were analyzed in a cross-sectional study. Concentrations of serum ADMA were determined using an enzyme-linked immunosorbent assay. Circulating levels of ADMA were significantly lower in subjects with DM1, DM2 or obesity. In all subjects, ADMA levels were inversely correlated with glycated hemoglobin A1c concentrations (r=-0.401, p=0.0003) and serum glucose levels (r=-0.341, p=0.0023). Low circulating ADMA levels are directly associated with glucose levels, suggesting that ADMA production is suppressed in childhood in order to compensate and protect vasculopathy due to hyperglycemia.

Genome-wide association study of L-arginine and dimethylarginines reveals novel metabolic pathway for symmetric dimethylarginine

BACKGROUND

Dimethylarginines (DMA) interfere with nitric oxide formation by inhibiting nitric oxide synthase (asymmetrical DMA [ADMA]) and l-arginine uptake into the cell (ADMA and symmetrical DMA [SDMA]). In prospective clinical studies, ADMA has been characterized as a cardiovascular risk marker, whereas SDMA is a novel marker for renal function and associated with all-cause mortality after ischemic stroke. The aim of the current study was to characterize the environmental and genetic contributions to interindividual variability of these biomarkers.

METHODS AND RESULTS

This study comprised a genome-wide association analysis of 3 well-characterized population-based cohorts (Framingham Heart Study [FHS; n=2992], Gutenberg Health Study [GHS; n=4354], and Multinational Monitoring of Trends and Determinants in Cardiovascular Disease Study [MONICA]/Cooperative Health Research in the Augsburg Area, Augsburg, Bavaria, Germany [KORA] F3 [n=581]) and identified replicated loci (DDAH1, MED23, Arg1, and AGXT2) associated with the interindividual variability in ADMA, l-arginine, and SDMA. Experimental in silico and in vitro studies confirmed functional significance of the identified AGXT2 variants. Clinical outcome analysis in 384 patients of the Leeds stroke study demonstrated an association between increased plasma levels of SDMA, AGXT2 variants, and various cardiometabolic risk factors. AGXT2 variants were not associated with poststroke survival in the Leeds study or were they associated with incident stroke in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium.

CONCLUSIONS

These genome-wide association study support the importance of DDAH1 and MED23/Arg1 in regulating ADMA and l-arginine metabolism, respectively, and identify a novel regulatory renal pathway for SDMA by AGXT2. AGXT2 variants might explain part of the pathogenic link between SDMA, renal function, and outcome. An association between AGXT2 variants and stroke is unclear and warrants further investigation.

Endothelial dysfunction in conduit arteries and in microcirculation. Novel therapeutic approaches

The vascular endothelium not only is a single monolayer of cells between the vessel lumen and the intimal wall, but also plays an important role by controlling vascular function and structure mainly via the production of nitric oxide (NO). The so called "cardiovascular risk factors" are associated with endothelial dysfunction, that reduces NO bioavailability, increases oxidative stress, and promotes inflammation contributing therefore to the development of atherosclerosis. The significant role of endothelial dysfunction in the development of atherosclerosis emphasizes the need for efficient therapeutic interventions. During the last years statins, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists, antioxidants, beta-blockers and insulin sensitizers have been evaluated for their ability to restore endothelial function (Briasoulis et al., 2012). As there is not a straightforward relationship between therapeutic interventions and improvement of endothelial function but rather a complicated interrelationship between multiple cellular and sub-cellular targets, research has been focused on the understanding of the underlying mechanisms. Moreover, the development of novel diagnostic invasive and non-invasive methods has allowed the early detection of endothelial dysfunction expanding the role of therapeutic interventions and our knowledge. In the current review we present the available data concerning the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function with a view to understand the multiple targets of therapeutic interventions. Finally we focus on the classic and novel therapeutic approaches aiming to improve endothelial dysfunction and the underlying mechanisms.

Incidence of all-cause and cardiovascular mortality predicted by symmetric dimethylarginine in the population-based study of health in pomerania

Background

L-Arginine and its dimethylated derivatives asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) have been associated with cardiovascular (CV) and all-cause mortality in populations at risk. The present study aimed to investigate the prognostic value of L-arginine and its derivatives in the general population.

Methods and Results

We evaluated 3,952 individuals (1,936 men and 2,016 women) aged 20–81 (median (IQR) 51 (37; 64) years) from the population-based Study of Health in Pomerania (SHIP). Associations of continuous [per standard deviation (SD) increase] and categorized (age- and sex-specific tertiles) serum L-arginine, ADMA, and SDMA concentrations with all-cause and cause-specific mortality were analysed. During a median (IQR) follow-up period of 10.1 (9.3; 10.8) years (38,476 person-years), 426 deaths (10.8%) were observed, including 139 CV deaths (3.5%), and 150 cancer deaths (3.8%). After multivariable adjustment, we revealed a positive association of SDMA with all-cause [hazard ratio (HR) per SD increase: 1.16, 95% confidence interval (CI): 1.07–1.25] and CV mortality [HR: 1.19, 95% CI: 1.05–1.35]. In contrast, we did not observe any association of SDMA with cancer mortality. Neither L-arginine nor ADMA were associated with all-cause or CV mortality.

Conclusion

SDMA, but not ADMA, is an independent predictor of all-cause and CV mortality in a large population-based cohort of European ancestry.

ADMA/SDMA in elderly subjects with asymptomatic carotid atherosclerosis: values and site-specific association

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor known as a mediator of endothelial dysfunction and atherosclerosis. Circulating ADMA levels are correlated with cardiovascular risk factors such as hypercholesterolemia, arterial hypertension, diabetes mellitus, hyperhomocysteinemia, age and smoking. We assessed the relationship between ADMA values and site-specific association of asymptomatic carotid atherosclerosis (intima-media thickness (CIMT) and plaque) in elderly subjects. One hundred and eighty subjects underwent a complete history and physical examination, determination of serum chemistries and ADMA levels, and carotid ultrasound investigation (CUI). All subjects had no acute or chronic symptoms of carotid atherosclerosis. Statistical analyses showed that high plasma levels of ADMA/SDMA were positively correlated to carotid atherosclerosis (CIMT and plaque) (p < 0.001), with significant site-specific association. Total cholesterol, low density lipoprotein cholesterol, triglycerides and C-reactive protein plasma concentrations were significantly associated with asymptomatic carotid atherosclerosis (p < 0.001). High serum concentrations of ADMA and SDMA were associated with carotid atherosclerotic lesions as measured by CIMT ad plaque and may represent a new marker of asymptomatic carotid atherosclerosis in elderly subjects.

Increased circulatory asymmetric dimethylarginine and multiple organ failure: bile duct ligation in rat as a model

Bile duct ligation (BDL)-treated rats exhibit cholestasis, increased systemic oxidative stress, and liver fibrosis, which ultimately lead to liver cirrhosis. Asymmetric dimethylarginine (ADMA) is a competitive inhibitor of nitric oxide synthase that can decrease the synthesis of nitric oxide. BDL rats have higher plasma and hepatic ADMA levels, which may be due to increased hepatic protein arginine methyltransferase-1 and decreased dimethylarginine dimethylaminohydrolase expression. BDL rats also exhibit renal and brain damage characterized by increased tissue ADMA concentrations. The increased plasma ADMA levels and multiple organ damages seen here are also observed following multiple organ failures associated with critical illness. This review discusses the dysregulation of ADMA in major organs in BDL rats and the role of increased ADMA in multiple organ damages.

Determination of asymmetric Nα-acetyldimethylarginine in humans: a phase II metabolite of asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is produced by protein methylation, a common mechanism of posttranslational protein modification. Elevated levels of ADMA lead to impaired endothelial nitric oxide production and subsequently to a range of cardiovascular and other diseases related to decreased nitric oxide production. Knowledge of the elimination pathways of ADMA and the possibility of influencing them is therefore of major clinical interest. One of these pathways is the N-acetylation and subsequent renal elimination of ADMA in the form of asymmetric Nα-acetyldimethylarginine (Ac-ADMA). In this work, we describe the first method to quantitatively determine Ac-ADMA in human plasma and urine. Ac-ADMA was separated by HPLC on a porous graphitic carbon column and selectively analyzed by tandem mass spectrometry. Ac-ADMA and the internal standard D7-Ac-ADMA were synthesized in-house. Precision and accuracy of the method were better than 5% in plasma and urine quality control samples. First results obtained with this method in samples of healthy volunteers showed plasma levels of 0.643±0.454 nmol/L and urine levels of 152.7±76.7 nmol/L or 13.0±8.9 nmol/mmol creatinine. The method is a suitable tool for investigating this currently mostly neglected ADMA elimination pathway.

Biomarkers for pediatric pulmonary arterial hypertension - a call to collaborate

Therapeutic approaches in pediatric pulmonary arterial hypertension (PAH) are based primarily on clinician experience, in contrast to the evidence-based approach in adults with pulmonary hypertension. There is a clear and present need for non-invasive and objective biomarkers to guide the accurate diagnosis, treatment, and prognosis of this disease in children. The multifaceted spectrum of disease, clinical presentation, and association with other diseases makes this a formidable challenge. However, as more progress is being made in the understanding and management of adult PAH, the potential to apply this knowledge to children has never been greater. This review explores the state of the art with regard to non-invasive biomarkers in PAH, with an eye toward those adult PAH biomarkers potentially suitable for application in pediatric PAH.

Comparision of Effects of Rosuvastatin Versus Atorvastatin Treatment on Plasma Levels of Asymmetric Dimethylarginine in Patients With Hyperlipidemia Having Coronary Artery Disease

Elevated plasma levels of asymmetric dimethylarginine (ADMA) are prevalent in patients with hypercholesterolemia and coronary artery disease. A total of 83 patients with hypercholesterolemia and angiographically documented mild coronary artery stenosis were randomized to rosuvastatin treatment (20 mg) or atorvastatin treatment (40 mg) once daily for 6 weeks after a 4-week dietary lead-in phase. Both statins decreased total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglyceride levels effectively. Only rosuvastatin increased high-density lipoprotein cholesterol (HDL-C) levels. Both rosuvastatin and atorvastatin decreased plasma ADMA levels; rosuvastatin had a significantly greater effect. The reduction in ADMA levels were correlated with the reduction in TC and LDL-C levels as well as LDL-C–HDL-C ratio. Treatment with rosuvastatin or atorvastatin in patients with hyperlipidemia with mild coronary artery stenosis may lead to a decrease in ADMA levels, which may contribute to improved endothelial function.

Aortic valve calcification in chronic kidney disease

Several clinical studies reported an increased prevalence and accelerated progression of aortic valve calcification among patients with end-stage renal disease when compared with subjects with normal kidney function. Recently, mechanisms of calcific valve degeneration have been further elucidated and many of the pathways involved could be amplified in patients with decreased renal function. In particular, calcium-phosphate balance, MGP metabolism, OPG/RANK/RANKL triad, fetuin-A mineral complexes and FGF-23/Klotho axis have been shown to be impaired among patients with advanced chronic kidney disease and could play a role during vascular/valve calcification. The scope of the present review is to summarize the clinical data and the pathophysiological mechanisms potentially involved in the link between renal function decline and the progression of aortic valve disease.

Elevated asymmetric dimethylarginine levels predict short- and long-term mortality risk in critically ill patients

OBJECTIVE

Serum concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, may contribute to endothelial dysfunction and organ failure in sepsis. We aimed at investigating ADMA levels as a potential diagnostic or prognostic biomarker in critically ill patients.

METHODS

Two hundred fifty-five patients (164 with sepsis, 91 without sepsis) were studied prospectively upon admission to the medical intensive care unit (ICU) and on day 7, in comparison to 78 healthy controls. ADMA serum concentrations were correlated with clinical data and extensive laboratory parameters. Patients' survival was followed up for up to 3 years.

RESULTS

ADMA serum levels were significantly elevated in critically ill patients at admission compared to controls. ADMA levels did not differ between patients with or without sepsis, but were closely related to hepatic and renal dysfunction, metabolism and clinical scores of disease severity. ADMA levels further increased during the first week of ICU treatment. ADMA serum levels at admission were an independent prognostic biomarker in critically ill patients not only for short-term mortality at the ICU, but also for unfavorable long-term survival.

CONCLUSION

Serum ADMA concentrations are significantly elevated in critically ill patients, associated with organ failure and related to short- and long-term mortality risk.

Plasma asymmetric dimethylarginine and adverse events in patients with atrial fibrillation referred for coronary angiogram

OBJECTIVES

Elevated plasma levels of asymmetric dimethylarginine (ADMA) have been reported to be associated with endothelial dysfunction, inflammation, and oxidative stress in multiple cardiovascular diseases. This study aimed to investigate whether ADMA was a predictor of clinical outcomes in atrial fibrillation (AF).

METHODS AND RESULTS

From 2006-2009, 990 individuals were referred to our institution for coronary angiography. Among these patients, 141 subjects with a diagnosis of AF, including 52 paroxysmal AF (PAF) and 89 non-paroxysmal AF (non-PAF) patients, were identified as the study population. Plasma ADMA levels were measured. An adverse event was defined as the occurrence of ischemic stroke or cardiovascular death. The ADMA levels were higher in AF than non-AF patients (0.50 ± 0.13 versus 0.45 ± 0.07 µmol/L; p<0.001). Besides, non-PAF patients had higher ADMA levels than PAF patients (0.52 ± 0.15 versus 0.48 ± 0.08 µmol/L; p<0.001). During the follow-up of 30.7±14.4 months, 21 patients (14.9%) experienced adverse events, including cardiovascular death in 7 patients and ischemic stroke in 14. ADMA level, CHA2DS2-VASc score, and left atrial diameter were independent predictors of adverse events in the multivariate analysis. At a cutoff-value of 0.55 µmol/L, the Kaplan-Meier survival analysis showed that patients with a high ADMA level had a higher event rate during the follow-up period.

CONCLUSIONS

A higher level of ADMA was a risk factor of adverse events in AF patients, which was independent from the CHA2DS2-VASc score. It deserves to further study whether ADMA could potentially refine the clinical risk stratification in AF.

Early-pregnancy asymmetric dimethylarginine (ADMA) levels in women prone to develop recurrent hypertension

OBJECTIVE

To evaluate early-pregnancy levels of ADMA (asymmetric dimethylarginine) in recurrent hypertensive pregnancy.

STUDY DESIGN

In this retrospective observational study, blood samples from 35 normotensive women with a previous hypertensive pregnancy were obtained preconceptionally and at 12, 16 and 20weeks in their next pregnancy. We assessed ADMA, symmetric dimethylarginine (SDMA), l-arginine and l-citrulline. We analyzed differences in longitudinal patterns between normotensive (NT, n=18) and recurrent hypertensive (HT, n=17) pregnancies by linear mixed models, with a sub-analysis for preeclampsia (PE, n=6).

MAIN OUTCOME MEASURES

ADMA, SDMA, l-arginine and l-citrulline.

RESULTS

Pre-pregnant SDMA and l-citrulline were lower in HT. At 12weeks, ADMA and ADMA/SDMA ratio correlated inversely with PAPP-A and β-hCG, respectively. In both groups, ADMA-related compounds changed inconsistently with advancing (mid-trimester) pregnancy, although in HT, l-arginine tended to decrease between 16 and 20weeks, a decline consistent in PE.

CONCLUSION

These data support a modest role for ADMA and related metabolites in the pathogenesis of hypertensive pregnancy.

A comparison of the association between glomerular filtration and L-arginine status in HIV-infected and uninfected African men: the SAfrEIC study

Hypertension, a major risk factor for cardiovascular disease worldwide, is increasing significantly in urbanised South Africans. Impaired glomerular filtration is a potential contributor to hypertension. Although HIV infection is widespread, little is known regarding its contribution to diminished estimated glomerular filtration rate (eGFR) and, in turn, hypertension in Africans. We compared eGFRs and cardiovascular profiles of newly identified HIV infected African men (N=53) not yet undergoing anti-retroviral therapy, and uninfected African men of similar age and anthropometry. The aim of the study was to determine whether eGFR is diminished in treatment naive HIV infected individuals and whether eGFR is associated with a potential modulator of hypertension, namely serum L-arginine. Cardiovascular risk factor profiles of HIV infected and uninfected men were similar. In men with healthy eGFRs >90 ml min(-1) per 1.73 m(2), eGFR was significantly lower with HIV infection (114 (90; 147)) compared with that in uninfected men: (120 (91; 168)), P=0.043. Despite the absence of clinically-diagnosed renal dysfunction, eGFR associated significantly with serum L-arginine only in HIV infected men (R(2)=0.277, β=-0.299, P=0.034), whereas L-arginine did not stay in the model for uninfected men. This difference suggests that the fate of L-arginine as a substrate for nitric oxide generation may be altered in HIV infected individuals. Subsequently this is likely to escalate endothelial dysfunction, contributing to later hypertension and cardiovascular disease. Our findings show that while glomerular filtration rate is not associated with L-arginine in uninfected men, it is diminished and significantly negatively associated with serum L-arginine in HIV infected men.

Biological significance of a thyroid hormone-regulated secretome

The thyroid hormone, 3,3,5-triiodo-L-thyronine (T3), modulates several physiological processes, including cellular growth, differentiation, metabolism and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Several intracellular and extracellular protein candidates are regulated by T3. Moreover, T3-regulated secreted proteins participate in physiological processes or cellular transformation. T3 has been employed as a marker in several disorders, such as cardiovascular disorder in chronic kidney disease, as well as diseases of the liver, immune system, endocrine hormone metabolism and coronary artery. Our group subsequently showed that T3 regulates several tumor-related secretory proteins, leading to cancer progression via alterations in extracellular matrix proteases and tumor-associated signaling pathways in hepatocellular carcinomas. Therefore, elucidation of T3/thyroid hormone receptor-regulated secretory proteins and their underlying mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a detailed summary on the known secretory proteins regulated by T3 and their physiological significance. This article is part of a Special Issue entitled: An Updated Secretome.

Effects of asymmetric dimethylarginine on inflammatory cytokines (TNF-α, IL-6 and IL-10) in rats

This study is intended to examine the effects of administration of asymmetric dimethylarginine (ADMA) on the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-10. A total of 30 Wistar adult albino rats were used. Group I was administrated ( n = 10) with 1 mg/kg/day of ADMA, group II ( n = 10) was administrated with 2 mg/kg/day of ADMA and the control group was administrated ( n = 10) with 0.9% sodium chloride. ADMA was intraperitoneally administrated for 7 days. The serum levels of IL-6, TNF-α and IL-10 were measured. There was a significant decrease in the levels of TNF-α, IL-6 and IL-10 in group I compared with that of the control group ( p < 0.001 ). There was also a significant decrease in the levels of IL-10 in group II compared with that of the control group ( p < 0.05) but the increase was much more distinct in the levels of IL-6 and TNF-α ( p < 0.001). When comparing the groups by the doses given, no difference between the levels of IL-6 and IL-10 in groups I and II ( p > 0.05) was observed; the levels of TNF-α in group II were significantly lower than those of group I (p < 0.05). A significant decrease in the serum levels of inflammatory cytokines IL-6, TNF-α and IL-10, after administration of 1 mg/kg/day and 2 mg/kg/day of ADMA, indicates that ADMA has an effect on inflammation. Increase in ADMA levels in the rats shows that the effects of inflammatory cytokines were suppressed.

Probing AGXT2 enzyme activity in mouse tissue by applying stable isotope-labeled asymmetric dimethyl arginine as substrate

Asymmetric dimethylarginine (ADMA) is a metabolite of the amino acid L-arginine. It competitively inhibits the enzymatic production of the cell-signaling substance nitric oxide. Therefore, increased levels of ADMA are associated with a range of cardiovascular and other diseases. ADMA is biologically eliminated by direct renal excretion and hydrolysis by the enzyme DDAH. Recently, a further elimination pathway via the transamination by the enzyme AGXT2 to α-keto-δ-(N(G),N(G)-dimethylguanidino)valeric acid (DMGV) has come into the focus of biological research. In this work, we describe an assay for the AGXT2 activity in mouse liver and kidney tissue. It is based on the transformation of isotope-labeled ADMA-d(6) to DMGV-d(6). The quantification of the DMGV-d(6) produced by this reaction in tissue homogenate samples was accomplished by chromatographic separation on a porous graphitic carbon column and tandem mass spectrometric detection. DMGV-d(6) with the deuterium labels in different molecular positions was used as internal standard. The overall production rates of DMGV-d(6) in mice were 195.37 pmol/min/mg total protein in liver and 85.21 pmol/min/mg total protein in kidney tissue, with coefficients of variation of 6.31% and 11.25%, respectively. This method can be applied as a tool for the characterization of the ADMA elimination by the AGXT2 pathway.

Elevated homocysteine and asymmetric dimethyl arginine levels in pulmonary hypertension associated with congenital heart disease

Pulmonary arterial hypertension (PAH) is a major cause of morbidity and mortality among patients with congenital heart disease (CHD). This study was designed to determine biomarker levels in patients with PAH associated with CHD (PAH-CHD) and CHD patients without PAH and to investigate the relationship of these potential biomarkers with hemodynamic findings. In this prospective single-center study, patients with CHD were analyzed according to the presence or absence of PAH and compared with healthy control subjects. Cardiac catheterization and echocardiographs were performed. Plasma homocysteine, asymmetric dimethyl arginine (ADMA), and nitric oxide (NO) levels were determined by enzyme-linked immunosorbent assay. Homocysteine and ADMA levels were higher in the PAH-CHD group (n = 30) than among CHD patients with left-to-right shunting but no PAH (n = 20; P < 0.001) and healthy control subjects (n = 20; P < 0.001). There was no difference in NO levels. Cyanotic PAH-CHD patients had significantly higher homocysteine than acyanotic patients in the same group. No correlation was shown between echocardiographic/hemodynamic parameters and homocysteine, ADMA, and NO levels. Homocysteine and ADMA levels are increased in patients with PAH-CHD. These parameters have the potential to be used as biomarkers in the diagnosis and follow-up evaluation of patients with PAH-CHD. However, large, multicentered prospective studies are required to facilitate routine use of these biologic markers in the clinical setting.

Asymmetric dimethylarginine, endothelial dysfunction and renal disease

l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review.

New directions in cardiovascular risk assessment: the role of secondary risk stratification markers

Cardiovascular disease (CVD) risk screening is performed by multivariate methods relying on calculators derived from the Framingham study, other epidemiological studies or primary care records. However, it only identifies 70% of individuals at risk for CVD events and there has been interest in adding other risk factors to improve its predictive capacity. The addition of a family history of premature CVD is well established and there is evidence for adding lipoprotein (a) in some populations and possibly C-reactive protein may be suitable for general use in CVD risk assessment. Most new biochemical and imaging markers have been assessed in the context of improving risk classification in intermediate-risk groups rather than in the general population. There is evidence that N-terminal pro-B-type natriuretic peptide and coronary artery calcium score add significantly to risk prediction. The data for carotid intima-media thickness, ankle-brachial index are less strong and high sensitivity troponins look promising, but have had only limited data to date. Large scale meta-analyses ideally of pooled primary patient data will be required to determine the best additional markers to add to conventional risk prediction and in what groups to apply them.

L-arginine infusion during resuscitation for hemorrhagic shock: impact and mechanism

BACKGROUND

Our previous work showed a survival advantage with L-arginine (L-Arg) pretreatment in a swine model of severe hemorrhagic shock. This study was designed to evaluating whether the benefit is sustained when L-Arg is given during resuscitation and whether the mechanism is mediated by enzymatic activation of nitric oxide (NO) synthesis.

METHODS

Adult rats (n = 30) underwent 40% blood volume loss and were resuscitated with saline (3 shed blood volume). Animals were divided into five treatment groups of six animals each: (1) Sham, (2) Control (resuscitation alone), (3) L-Arg (300 mg/kg)with resuscitation, (4) L-Arg + L-nitroarginine methyl ester pretreatment, and (5) D-arginine (300 mg/kg) with resuscitation.Animals were observed for 240 minutes postresuscitation or until death. Hemodynamic, metabolic, histologic, and survival outcomes were measured.

RESULTS

Administration of L-Arg after hemorrhage and before resuscitation significantly improved outcomes, relative to the control group.The L-Arg infusion improved terminal arterial pressures, lowered lactate, improved small bowel histologic signs of reperfusion injury, and increased survival (p < 0.05). Endpoints of the L-Arg group were similar to the Sham group. The benefits of L-Arg infusion were abolished or attenuated when animals were pretreated with L-nitro arginine methyl ester and potentiated with D-arginine, suggesting a NO-specific mechanism of L-Arg. Finally, severe shock and resuscitation injury significantly elevated circulating asymmetric dimethylarginine levels, which are potent competitive inhibitors of NO synthetase.

CONCLUSION

L-Arg infusion during resuscitation offers a significant functional, metabolic, and survival benefit after severe hemorrhagic shock.The mechanism seems to be by activation of NO synthesis with its attendant benefits to local perfusion and inflammation after global reperfusion.

NOX1, 2, 4, 5: counting out oxidative stress

For decades, oxidative stress has been discussed as a key mechanism of endothelial dysfunction and cardiovascular disease. However, attempts to validate and exploit this hypothesis clinically by supplementing antioxidants have failed. Nevertheless, this does not disprove the oxidative stress hypothesis. As a certain degree of reactive oxygen species (ROS) formation appears to be physiological and beneficial. To reduce oxidative stress therapeutically, two alternative approaches are being developed. One is the repair of key signalling components that are compromised by oxidative stress. These include uncoupled endothelial nitric oxide (NO) synthase and oxidized/heme-free NO receptor soluble guanylate cyclase. A second approach is to identify and effectively inhibit the relevant source(s) of ROS in a given disease condition. A highly likely target in this context is the family of NADPH oxidases. Animal models, including NOX knockout mice and new pharmacological inhibitors of NADPH oxidases have opened up a new era of oxidative stress research and have paved the way for new cardiovascular therapies.

Severely decreased activity of placental dimethylarginine dimethylaminohydrolase in pre-eclampsia

OBJECTIVES

Asymmetric dimethylarginine (ADMA) is a key regulator of nitric oxide production. Elevations of ADMA have previously been associated with endothelial dysfunction in pre-eclamptic women. ADMA is degraded mainly by dimethylarginine dimethylaminohydrolase (DDAH), which is also expressed in placental tissue. Therefore, we measured placental DDAH expression and activity in pre-eclampsia and normal pregnancies in order to determine whether impairment of this enzyme in the pre-eclamptic placenta could contribute to elevations of ADMA levels in these women.

STUDY DESIGN

ADMA plasma levels were measured by LC-MS/MS in 18 pre-eclamptic patients and 28 controls. Placental DDAH activity was determined by measuring the degradation of [(2)H(6)]-labeled ADMA in tissue homogenates from placental biopsies in 15 women with pre-eclampsia and 16 controls. Placental mRNA expression of DDAH 1, DDAH 2, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and protein-arginine methyltransferase 1 (PRMT1) was determined in tissue biopsies by RT-PCR.

RESULTS

Placental DDAH activity was almost undetectable in pre-eclampsia, and it was significantly higher in controls. ADMA plasma levels were higher in pre-eclampsia as compared to normal pregnancies (0.51±0.15μmol/l vs. 0.42±0.07μmol/l; p=0.005), and the difference between maternal and fetal ADMA levels (feto-maternal ADMA gradient) was lower in pre-eclampsia (0.63±0.20μmol/l vs. 0.80±0.18μmol/l; p=0.02). Furthermore, mRNA expression levels of DDAH 2 were significantly lower in pre-eclamptic women (p=0.04), while PRMT1 expression levels were the same. In pre-eclampsia, we found only weak correlations between maternal ADMA levels and DDAH 1 (r=-0.41; p=0.22) and DDAH 2 expressions (r=-0.45; p=0.17) but a slightly stronger correlation between DDAH 2 expression and feto-maternal ADMA gradient (r=0.60; p=0.07).

CONCLUSION

Decreased DDAH activity in the pre-eclamptic placenta might contribute to elevated ADMA levels in these patients.

Asymmetric dimethylarginine in young people with Type 1 diabetes: a paradoxical association with HbA(1c)

AIMS

Asymmetric dimethylarginine (ADMA) is an independent risk factor for cardiovascular disease and its concentrations are increased in several diseases, including diabetes. However, there is limited information on this plasma marker in young people, particularly in those with Type 1 diabetes. The aim of the present study was therefore to perform a longitudinal evaluation of plasma ADMA and of its determinants in young people with childhood-onset Type 1 diabetes.

METHODS

For measurement of ADMA using mass spectrometry, 1018 longitudinal stored blood samples were available from 330 young people with Type 1 diabetes followed in the Oxford Regional Prospective Study. Additional data concerning annual assessments of HbA(1c) , height, weight, insulin dose and three early morning urine samples for measurement of the albumin/creatinine ratio were available.

RESULTS

ADMA levels were significantly higher in males than in females (mean ± SD: 0.477 ± 0.090 vs. 0.460 ± 0.089 μmol/l, P=0.002) and declined with chronological age (estimate ± SE: -0.0106 ± 0.0008, P<0.001). A significant inverse association was detected between ADMA and HbA(1c) (estimate ± SE:-0.0113 ± 0.001, P<0.001). ADMA levels were lower in subjects developing microalbuminuria (mean ± SD: 0.455 ± 0.093 vs. 0.476 ± 0.087 μmol/l, P=0.001) than in subjects with normoalbuminuria, but this difference disappeared after adjusting for HbA(1c) .

CONCLUSIONS

In this longitudinal study, ADMA concentrations decreased with age and were significantly higher in males and lower in subjects developing microalbuminuria. These associations were largely explained by a paradoxical negative association between HbA(1c) and ADMA. We suggest that chronic hyperglycaemia might down-regulate mechanisms implicated in ADMA production or stimulate its metabolism confounding short-term associations with complications risk.

Relationships between serum levels of thyroid hormones and serum concentrations of asymmetric dimethylarginine (ADMA) and N-terminal-pro-B-type natriuretic peptide (NT-proBNP) in patients with Graves' disease

Endothelial dysfunction as well as abnormal thyroid hormone levels may be responsible for increased cardiovascular risk in Graves' disease (GD). Asymmetric dimethylarginine (ADMA) and N-terminal-pro-B-type natriuretic peptide (NT-proBNP) are new markers of endothelial and myocardial dysfunction, respectively. The purpose of this study was to investigate the relationship among the serum levels of ADMA, NT-proBNP, and thyroid hormones in GD patients. This was a cross-sectional investigation conducted in a university teaching hospital. Two hundred and thirty-nine GD (Female: 182, Male: 57) patients and 81 normal controls were enrolled in this study. Serum levels of ADMA were positively related with FT3 (r = 0.584, P < 0.001), FT4 (r = 0.551, P < 0.001), and TRAb levels (r = 0.502, P < 0.001). Serum NT-proBNP levels were positively associated with FT3 (r = 0.243, P < 0.001) and FT4 levels (r = 0.274, P < 0.001), as well as heart rate (r = 0.271, P < 0.03). The elevation of serum ADMA and NT-proBNP levels were also observed in patients with controlled hyperthyroidism. It is thus concluded that serum ADMA and NT-proBNP levels were increased in GD patients. Future studies may determine the usefulness of these two biomarkers to detect early signs of endothelial dysfunction, vascular stiffness, and fluid volume in GD patients.

Cellular hypomethylation is associated with impaired nitric oxide production by cultured human endothelial cells

Hyperhomocysteinemia (HHcy) is a risk factor for vascular disease, but the underlying mechanisms remain incompletely defined. Reduced bioavailability of nitric oxide (NO) is a principal manifestation of underlying endothelial dysfunction, which is an initial event in vascular disease. Inhibition of cellular methylation reactions by S-adenosylhomocysteine (AdoHcy), which accumulates during HHcy, has been suggested to contribute to vascular dysfunction. However, thus far, the effect of intracellular AdoHcy accumulation on NO bioavailability has not yet been fully substantiated by experimental evidence. The present study was carried out to evaluate whether disturbances in cellular methylation status affect NO production by cultured human endothelial cells. Here, we show that a hypomethylating environment, induced by the accumulation of AdoHcy, impairs NO production. Consistent with this finding, we observed decreased eNOS expression and activity, but, by contrast, enhanced NOS3 transcription. Taken together, our data support the existence of regulatory post-transcriptional mechanisms modulated by cellular methylation potential leading to impaired NO production by cultured human endothelial cells. As such, our conclusions may have implications for the HHcy-mediated reductions in NO bioavailability and endothelial dysfunction.