AT1-receptor blockade with irbesartan improves peripheral but not coronary endothelial dysfunction in patients with stable coronary artery disease

Endothelium as a Therapeutic Target in Diabetes Mellitus: From Basic Mechanisms to Clinical Practice

Endothelium plays an essential role in human homeostasis by regulating arterial blood pressure, distributing nutrients and hormones as well as providing a smooth surface that modulates coagulation, fibrinolysis and inflammation. Endothelial dysfunction is present in Diabetes Mellitus (DM) and contributes to the development and progression of macrovascular disease, while it is also associated with most of the microvascular complications such as diabetic retinopathy, nephropathy and neuropathy. Hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia are the main factors involved in the pathogenesis of endothelial dysfunction. Regarding antidiabetic medication, metformin, gliclazide, pioglitazone, exenatide and dapagliflozin exert a beneficial effect on Endothelial Function (EF); glimepiride and glibenclamide, dipeptidyl peptidase-4 inhibitors and liraglutide have a neutral effect, while studies examining the effect of insulin analogues, empagliflozin and canagliflozin on EF are limited. In terms of lipid-lowering medication, statins improve EF in subjects with DM, while data from short-term trials suggest that fenofibrate improves EF; ezetimibe also improves EF but further studies are required in people with DM. The effect of acetylsalicylic acid on EF is dose-dependent and lower doses improve EF while higher ones do not. Clopidogrel improves EF, but more studies in subjects with DM are required. Furthermore, angiotensin- converting-enzyme inhibitors /angiotensin II receptor blockers improve EF. Phosphodiesterase type 5 inhibitors improve EF locally in the corpus cavernosum. Finally, cilostazol exerts favorable effect on EF, nevertheless, more data in people with DM are required.

Coronary Artery Disease and Endothelial Dysfunction: Novel Diagnostic and Therapeutic Approaches

Coronary artery disease is the leading cause of morbidity and mortality worldwide. The most common pathophysiologic substrate is atherosclerosis which is an inflammatory procedure that starts at childhood and develops throughout life. Endothelial dysfunction is associated with the initiation and progression of atherosclerosis and is characterized by the impaired production of nitric oxide. In general, endothelial dysfunction is linked to poor cardiovascular prognosis and different methods, both invasive and non-invasive, have been developed for its evaluation. Ultrasound evaluation of flow mediated dilatation of the branchial artery is the most commonly used method to assessed endothelial function while intracoronary administration of vasoactive agents may be also be used to test directly endothelial properties of the coronary vasculature. Endothelial dysfunction has also been the subject of therapeutic interventions. This review article summarizes the knowledge about evaluation of endothelial function in acute coronary syndromes and stable coronary artery disease and demonstrates the current therapeutic approaches against endothelial dysfunction.

Hydration Status and Cardiovascular Function

Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin–angiotensin–aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.

Angiotensin receptor blockers & endothelial dysfunction: Possible correlation & therapeutic implications

The endothelium is one of the most important constituents of vascular homeostasis, which is achieved through continual and balanced production of different relaxing and contractile factors. When there is a pathological disturbance in release of these products, endothelial dysfunction (ED) will probably occur. ED is considered to be the initial step in the development of atherosclerosis. This pathological activation and inadequate functioning of endothelial cells was shown to be to some extent a reversible process, which all together resulted in increased interest in investigation of different beneficial treatment options. To this point, the pharmacological approach, including for example, the use of angiotensin-converting enzyme inhibitors or statins, was clearly shown to be effective in the improvement of ED. One of many critical issues underlying ED represents instability in the balance between nitric oxide and angiotensin II (Ang II) production. Considering that Ang II was confirmed to be important for the development of ED, the aim of this review article was to summarize the findings of up to date clinical studies associated with therapeutic application of angiotensin receptor blockers and improvement in ED. In addition, it was of interest to review the pleiotropic actions of angiotensin receptor blockers linked to the improvement of ED. The prospective, randomized, double-blind, placebo or active-controlled clinical trials were identified and selected for the final evaluation.

Novel Pathophysiological Mechanisms in Hypertension

Hypertension is the most common disease affecting humans and imparts a significant cardiovascular and renal risk to patients. Extensive research over the past few decades has enhanced our understanding of the underlying mechanisms in hypertension. However, in most instances, the cause of hypertension in a given patient continues to remain elusive. Nevertheless, achieving aggressive blood pressure goals significantly reduces cardiovascular morbidity and mortality, as demonstrated in the recently concluded SPRINT trial. Since a large proportion of patients still fail to achieve blood pressure goals, knowledge of novel pathophysiologic mechanisms and mechanism based treatment strategies is crucial. The following chapter will review the novel pathophysiological mechanisms in hypertension, with a focus on role of immunity, inflammation and vascular endothelial homeostasis. The therapeutic implications of these mechanisms will be discussed where applicable.

Effect of Angiotensin Receptor Blockers on Flow-Mediated Vasodilation: A Meta-Analysis of Randomized Controlled Trials

Background: In a meta-analysis, we investigated the effects of angiotensin receptor blockers (ARBs) in comparison to placebo or other classes of antihypertensive drugs on endothelial function, which was measured by brachial flow-mediated vasodilation (FMD). Methods: We searched for randomized controlled trials that compared ARBs with placebo or other classes of antihypertensive drugs in improving FMD. A random-effect model was used to compute pooled estimates. Results: In 13 trials (n = 529), ARBs were more efficacious in improving brachial FMD than placebo [pooled weighted mean change difference (WMD) 1.34%, 95% CI, 0.93-1.75%, p < 0.001]. In 15 trials (n = 918), treatment with ARBs had a significant effect on brachial FMD when compared with other antihypertensive drugs (pooled WMD 0.59%, 95% CI, 0.20-0.98%, p = 0.003 with significant heterogeneity). ARBs were also more efficacious in improving brachial FMD than calcium channel blockers (CCBs; pooled WMD 1.61%, 95% CI, 0.72-2.49%, p < 0.001) but not the other classes of drugs (p ≥ 0.072). Conclusions: This meta-analysis shows that ARBs improve brachial FMD, a marker of endothelial function, and that they are superior to placebo and CCBs. There was no significant difference in the effect on brachial FMD between ARBs and the other antihypertensive drugs.

Selective Serotonin Reuptake Inhibitors and Night Sweats in a Primary Care Population

Objective

Several small published case reports have suggested that selective serotonin reuptake inhibitors (SSRIs) can cause night sweats. The purpose of this study was to investigate this possibility further and to explore possible associations between night sweats and other commonly prescribed medications.

Design

Cross-sectional, secondary data analysis.

Setting

Data were obtained during the Oklahoma Longitudinal Assessment of the Health Outcomes of Mature Adults, a longitudinal cohort study carried out in the Oklahoma Physicians Resource/Research Network.

Participants

413 adult primary care patients aged 65–94 years.

Interventions

Current regular use of one of 35 classes of medication.

Main Outcome Measures

At least moderate night sweats during the prior month.

Results

A total of 38 (9.2 %) reported night sweats. Age, gender, body mass index, and total number of medications taken regularly were not associated with night sweats. After adjusting for age and gender, SSRIs (odds ratio [OR] 3.01; 95 % confidence interval [CI] 1.26–7.19), angiotensin receptor blockers (ARBs) (OR 3.44; 95 % CI 1.36–8.69), and thyroid hormone supplements (OR 2.53; 95 % CI 1.24–5.15) were the only classes of medications associated with night sweats.

Conclusions

Use of SSRIs may well be associated with night sweats in older patients. Associations found between night sweats and ARBs and thyroid supplements warrant further study.

Anti-platelet therapy with clopidogrel prevents endothelial dysfunction and vascular remodeling in aortas from hypertensive rats

The aim was to investigate the beneficial effects of clopidogrel in thoracic aorta function and structure and to characterize if P2Y₁₂ receptors contribute to these effects. Male Sprague Dawley rats were infused with angiotensin II [(Ang II) 60 ng.min⁻¹, 14 days] or saline (control rats) and were simultaneously treated with clopidogrel (10 mg.kg⁻¹.day⁻¹) or vehicle. After 14 days, systolic blood pressure (mmHg) was similar in Ang II-hypertensive rats treated with clopidogrel or vehicle (199±9 vs. 190±11, respectively). Systolic blood pressure in control rats was not altered by clopidogrel treatment (128±1 vs. vehicle, 134±2). Endothelium-dependent relaxation induced by 2-MeS-ADP was decreased in aortas from vehicle-treated Ang II-hypertensive rats, compared to vehicle-treated control rats. This response was elicited via activation of P2Y₁ and P2Y₁₂ receptors. In the presence of L-NAME and indomethacin, 2-MeS-ADP induced contraction and this response was augmented in vehicle-treated Ang II-hypertensive rats, compared to vehicle-treated control rats. The contraction to 2-MeS-ADP was evoked by P2Y₁₃ and P2Y₁₂ receptor activation. Clopidogrel-treatment did not normalize relaxation or contractile responses induced by 2-MeS-ADP in aortas from Ang II-hypertensive rats. P2Y₁ and P2Y₁₂ protein expression was increased, whereas P2Y₁₃ receptor expression was reduced in aorta from vehicle-treated Ang II-hypertensive rats. Endothelium-dependent relaxation upon acetylcholine-stimulation was reduced in vehicle-treated Ang II-hypertensive rats, and clopidogrel treatment was effective in improving endothelial function. Clopidogrel also prevented vascular remodeling, evidenced by augmented media thickness in aortas from Ang II-hypertensive rats. Clopidogrel has beneficial effects on the aortic endothelium of Ang II-hypertensive rats, but its effects do not seem to be directly related to the presence of P2Y₁₂ receptors in this vessel.

Angiotensin II receptor blockers improve peripheral endothelial function: a meta-analysis of randomized controlled trials

OBJECTIVE(S)

Several studies have assessed the effect of angiotensin II receptor blockers (ARBs) on peripheral endothelial dysfunction as measured by flow-mediated vasodilatation (FMD), a widely-used indicator for endothelial function. We conducted a meta-analysis to investigate the effect in comparison to placebo or no treatment and other antihypertensives.

METHODS

MEDLINE, Cochrane library and EMBASE were searched to September 2013 for randomized controlled trials (RCTs) that assessed the effect of ARBs versus placebo or no treatment and other antihypertensives (angiotensin-converting enzyme inhibitors (ACEIs), calcium channel blockers (CCBs), β-blockers, diuretics) by forearm FMD. Furthermore, we also use meta-regression to analyze the relationship between the endothelial function and the duration of ARBs treatments.

RESULTS

In 11 trials including 590 patients, ARBs (n = 315) significantly improved FMD (1.36%, 95% confidence internal [CI]:1.28 to 1.44) versus placebo or no treatment (n = 275). In 16 trials that included 1028 patients, ARBs (n = 486) had a significant effect (0.59%, 95% CI: 0.25 to 0.94) on FMD when compared with other antihypertensives (n = 542). In 8 trials, ARBs (n = 174) had no significant effect (-0.14%, 95% CI: -0.32 to 0.03) compared with ACEI (n = 173). Compared with others, the benefits of ARBs, respectively, were 1.67% (95% CI: 0.65 to 0.93) in 7 trials with CCBs, 0.79% (95% CI: 0.42 to 1.01) with β-blockers in 3 trials and 0.9% (95% CI: 0.77 to 1.03) with diuretics in 3 trials. Importantly, we found ARBs were less effective in a long time span (95% CI: -1.990 to -0.622) than the first 6 months (95% CI: -0.484 to 0.360).

CONCLUSIONS

This study shows that ARBs improve peripheral endothelial function and are superior to CCBs, β-blockers and diuretics. However, the effect couldn't be maintained for a long time. In addition, there was no significant difference between ARBs and ACEI.

Changes in cardiopulmonary reserve and peripheral arterial function concomitantly with subclinical inflammation and oxidative stress in patients with heart failure with preserved ejection fraction

Background. Changes in cardiopulmonary reserve and biomarkers related to wall stress, inflammation, and oxidative stress concomitantly with the evaluation of peripheral arterial blood flow have not been investigated in patients with heart failure with preserved ejection fraction (HFpEF) compared with healthy subjects (CTL). Methods and Results. Eighteen HFpEF patients and 14 CTL were recruited. Plasma levels of inflammatory and oxidative stress biomarkers were measured at rest. Brain natriuretic peptide (BNP) was measured at rest and peak exercise. Cardiopulmonary reserve was assessed using an exercise protocol with gas exchange analyses. Peripheral arterial blood flow was determined by strain gauge plethysmography. Peak VO₂ (12.0 ± 0.4 versus 19.1 ± 1.1 mL/min/kg, P < 0.001) and oxygen uptake efficiency slope (1.55 ± 0.12 versus 2.06 ± 0.14, P < 0.05) were significantly decreased in HFpEF patients compared with CTL. BNP at rest and following stress, C-reactive-protein, interleukin-6, and TBARS were significantly elevated in HFpEF. Both basal and posthyperemic arterial blood flow were not significantly different between the HFpEF patients and CTL. Conclusions. HFpEF exhibits a severe reduction in cardiopulmonary reserve and oxygen uptake efficiency concomitantly with an elevation in a broad spectrum of biomarkers confirming an inflammatory and prooxidative status in patients with HFpEF.

Diagnosis and treatment of endothelial dysfunction in cardiovascular disease

Vascular endothelial dysfunction reflected by reduced nitric oxide (NO) availability is certainly the causative factor or promoting mechanism of arteriosclerosis. It is necessary to detect endothelial dysfunction at an early stage using appropriate methods, and to choose a treatment for the recovery of endothelial function. There are nonpharmacological and pharmacological therapies to attain endothelial repair. The former includes body weight reduction, aerobic exercise, and restriction of salt intake, while the latter includes the use of renin-angiotensin system inhibitors, calcium antagonists, some types of beta blockers, statins, erythropoietin, tetrahydrobiopterin, and antioxidants. These therapies are intended to increase NO synthase activity and NO release, inhibit NO degradation, and enhance the activity of endothelial progenitor cells.

Prospective, randomized, single-blind comparison of effects of 6 months of treatment with telmisartan versus enalapril on high-molecular-weight adiponectin concentrations in patients with coronary artery disease

BACKGROUND

High-molecular-weight (HMW) adiponectin has important antiatherosclerotic properties.

OBJECTIVES

This study compared circulating HMW adiponectin concentrations and other parameters between patients with coronary artery disease (CAD) and participants without CAD. We investigated whether treatment with statins and either telmisartan or enalapril might affect HMW adiponectin and other parameters in patients with CAD. Finally, adiponectin concentrations were compared after 6 months of treatment between CAD patients with versus without cardiac events.

METHODS

Consecutive patients with stable CAD admitted to our hospital (Iwate Medical University School of Medicine, Iwate, Japan) for percutaneous coronary intervention (PCI) and stent implantation and with no previous treatment with renin-angiotensin system blockers or statins were recruited. Patients with CAD who met all eligibility criteria were randomly assigned using computer-generated numbers in a 1:1 ratio to receive telmisartan (40 mg/d) or enalapril (5 mg/d) for 6 months. In addition, all patients with CAD were treated with atorvastatin (10 mg/d). The patients without CAD received no treatment with telmisartan, enalapril, or atorvastatin. Plasma concentrations of total and HMW adiponectin were measured using a highly sensitive ELISA system before PCI or drug treatment (ie, baseline) and after 6 months of treatment. In addition, high-sensitivity C-reactive protein (hs-CRP) and homeostasis model assessment of insulin resistance (HOMA-IR) were measured. To evaluate cardiac events, follow-up coronary angiography was performed at least 6 months after PCI.

RESULTS

This study included 70 patients with stable CAD (mean [SD] age, 65.8 [10.9] years; male/female ratio, 55/15) and 25 participants with normal results on coronary angiography (non-CAD) (mean age, 63.5 [11.2] years; male/female ratio, 20/5). Baseline concentrations (mean [SD]) of HMW adiponectin were significantly lower in the CAD group than in the non-CAD group (2.0 [0.3] vs 9.2 [0.5] microg/mL; P < 0.01). The ratio of HMW to total adiponectin was also lower in the CAD group than in the non-CAD group (0.37 [0.02] vs 0.53 [0.02]; P < 0.01). Baseline concentrations of HMW adiponectin were negatively correlated with hs-CRP (r = -0.60) and HOMA-IR (r = -0.30) in patients with CAD. After 6 months of treatment, the telmisartan group showed significantly increased HMW adiponectin concentrations and HMW/total adiponectin ratio (HMW, 3.7 [0.7] vs 2.1 [0.5] microg/mL; P < 0.01 vs baseline; HMW/total, 0.44 [0.02] vs 0.39 [0.02]; P < 0.05 vs baseline), whereas HOMA-IR was significantly decreased (2.86 [1.93] vs 3.39 [1.77]; P < 0.05 vs baseline). HOMA-IR at follow-up was significantly lower in the telmisartan group than in the enalapril group (2.86 [1.93] vs 3.64 [1.45]; P < 0.05). In contrast, treatment with enalapril was not associated with any significant changes in total or HMW adiponectin concentrations, HMW/total adiponectin ratio, or HOMA-IR. Both the telmisartan and the enalapril groups showed significant decreases in hs-CRP after 6 months (P < 0.05 vs baseline). After 6 months of treatment with either telmisartan or enalapril, HMW adiponectin concentrations were 0.7 (0.2) microg/mL with cardiac events versus 3.2 (0.4) microg/mL without (P < 0.05); HMW/total concentrations were 0.25 (0.03) with cardiac events versus 0.43 (0.01) without (P < 0.01). In contrast, hs-CRP concentrations were higher in patients with cardiac events than in those without cardiac events (2.42 [0.52] vs 1.86 [0.45] log10 microg/dL; P < 0.01).

CONCLUSION

This study found that treatment with telmisartan and statins (but not enalapril and statins) was associated with a significant increase in HMW adiponectin concentrations and a decrease in insulin resistance in these patients with CAD.

Vascular and metabolic effects of angiotensin II receptor blockers

Angiotensin II receptor blockers (ARBs) are widely used in patients with hypertension, heart failure and type 2 diabetes mellitus (T2DM). Several large clinical trials have demonstrated that these agents are effective in reducing cardiovascular mortality and morbidity. These benefits are partly independent of the degree of blood pressure reduction and most likely related to ARBs' anti-inflammatory, metabolic and vascular effects. Clinical studies showed that the anti-inflammatory effect of ARBs could be related to the dosage and/or the length of the treatment. In large clinical trials, ARBs have inconsistently reduced the risk of new-onset T2DM. Among ARBs, only losartan significantly reduced serum uric acid levels. Moreover, it has been demonstrated that ARBs improve endothelial dysfunction in patients with hypertension and/or coronary artery disease (CAD), while all but one of the studies proved that these agents could usually, after 6-12 months of therapy, induce regression of vascular hypertrophy in hypertensive patients. These positive effects could be relevant to vascular protection and, together with the blood pressure reduction, constitute the background of the improved outcome observed in clinical studies on mortality and/or morbidity in hypertensive, high-risk and CAD patients. The clinical significance of the different potency of ARBs needs to be investigated further in specific and adequately powered trials.

Endothelial effects of antihypertensive treatment: focus on irbesartan

The endothelium is characterized by a wide range of important homeostatic functions. It participates in the control of hemostasis, blood coagulation and fibrinolysis, platelet and leukocyte interactions with the vessel wall, regulation of vascular tone, and of blood pressure. Many crucial vasoactive endogenous compounds are produced by the endothelial cells to control the functions of vascular smooth muscle cells and of circulating blood cells. These complex systems determine a fine equilibrium which regulates the vascular tone. Impairments in endothelium-dependent vasodilation lead to the so called endothelial dysfunction. Endothelial dysfunction is then characterized by unbalanced concentrations of vasodilating and vasoconstricting factors, the most important being represented by nitric oxide (NO) and angiotensin II (AT II). High angiotensin-converting enzyme (ACE) activity leads to increased AT II generation, reduced NO levels with subsequent vasoconstriction. The net acute effect results in contraction of vascular smooth muscle cells and reduced lumen diameter. Furthermore, when increased ACE activity is chronically sustained, increase in growth, proliferation and differentiation of the vascular smooth muscle cells takes place; at the same time, a decrease in the anti-proliferative action by NO, a decrease in fibinolysis and an increase in platelets aggregation may be observed. AT II is then involved not only in the regulation of blood pressure, but also in vascular inflammation, permeability, smooth muscle cells remodelling, and oxidative stress which in turn lead to atherosclerosis and increased cardiovascular risk. Given the pivotal role exerted by AT II in contributing to alteration of endothelial function, treatment with ACE inhibitors or angiotensin receptor blockers (ARBs) may be of particular interest to restore a physiological activity of endothelial cells. In this view, the blockade of the renin-angiotensin system (RAS), has been shown to positively affect the endothelial function, beyond the antihypertensive action displayed by these compounds. In this review, attention has been specifically focused on an ARB, irbesartan, to examine its effects on endothelial function.

Pathophysiology, diagnosis and prognostic implications of endothelial dysfunction

Endothelial dysfunction (ED) in the setting of cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, chronic smoking as well as in patients with heart failure has been shown to be at least in part dependent on the production of reactive oxygen species (ROS) such as superoxide and the subsequent decrease in vascular bioavailability of nitric oxide (NO). Methods to quantify endothelial dysfunction include forearm plethysmography, flow-dependent dilation of the brachial artery, finger-pulse plethysmography, pulse curve analysis, and quantitative coronary angiography after intracoronary administration of the endothelium-dependent vasodilator acetylcholine. Superoxide sources include the NADPH oxidase, xanthine oxidase, and mitochondria. Superoxide produced by the NADPH oxidase may react with NO released by the endothelial nitric oxide synthase (eNOS) thereby generating peroxynitrite (ONOO-), leading to eNOS uncoupling and therefore eNOS-mediated superoxide production. The present review will discuss current concepts of how to assess endothelial function, prognostic implications of ED, mechanisms underlying ED with focus on oxidative stress and circulating biomarkers, which have been proposed to indicate endothelial dysfunction and/or damage, respectively.

Role of asymmetric dimethylarginine for angiotensin II-induced target organ damage in mice

The aim of the present study was to investigate the role of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and its degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH) in angiotensin II (ANG II)-induced hypertension and target organ damage in mice. Mice transgenic for the human DDAH1 gene (TG) and wild-type (WT) mice (each, n = 28) were treated with 1.0 microg kg(-1) min(-1) ANG II, 3.0 microg kg(-1) min(-1) ANG II, or phosphate-buffered saline over 4 wk via osmotic minipumps. Blood pressure, as measured by tail cuff, was elevated to the same degree in TG and WT mice. Plasma levels of ADMA were lower in TG than WT mice and were not affected after 4 wk by either dose of ANG II in both TG and WT animals. Oxidative stress within the wall of the aorta, measured by fluorescence microscopy using the dye dihydroethidium, was significantly reduced in TG mice. ANG II-induced glomerulosclerosis was similar between WT and TG mice, whereas renal interstitial fibrosis was significantly reduced in TG compared with WT animals. Renal mRNA expression of protein arginine methyltransferase (PRMT)1 and DDAH2 increased during the infusion of ANG II, whereas PRMT3 and endogenous mouse DDAH1 expression remained unaltered. Chronic infusion of ANG II in mice has no effect on the plasma levels of ADMA after 4 wk. However, an overexpression of DDAH1 alleviates ANG II-induced renal interstitial fibrosis and vascular oxidative stress, suggesting a blood pressure-independent effect of ADMA on ANG II-induced target organ damage.

Asymmetrical dimethylarginine in renal disease: limits of variation or variation limits? A systematic review

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is increasingly recognized as a putative biomarker in cardiovascular and renal disease. Elevated plasma levels of ADMA are the consequence of increased synthesis, reduced renal clearance or reduced enzymatic degradation. Based upon the metabolic fate the highest plasma concentrations of ADMA have been reported in patients with renal failure in whom this molecule accumulates. However, the range of published ADMA levels in patients with chronic renal failure as well as in patients with end-stage renal failure undergoing maintenance hemodialysis, peritoneal dialysis or kidney transplant recipients is widely scattered and overlaps with the levels reported in healthy individuals. This wide distribution can in part be explained by different bioanalytical techniques and the lack of standardization of such assays. This review summarizes available literature on ADMA in patients with kidney disease and stresses the urgent need for a consensus regarding reference values for different analytical methods in order to appreciate the prognostic significance of elevated ADMA levels. At present, one cannot advocate this molecule for risk assessment or individual patient prognosis in the clinical work-up of patients with renal impairment.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.