Pioglitazone lowers systemic asymmetric dimethylarginine by inducing dimethylarginine dimethylaminohydrolase in rats

Ex vivo gene transferring of human dimethylarginine dimethylaminohydrolase-2 improved endothelial dysfunction in diabetic rat aortas and high glucose-treated endothelial cells

OBJECTIVES

Elevated level of asymmetric dimethylarginine (ADMA) is an independent risk factor for endothelial dysfunction. Dimethylarginine dimethylaminohydrolase (DDAH) is the key enzyme responsible for the degradation of endogenous ADMA. The purposes of this study were to determine whether suppressed DDAH2 expression would implicate in endothelial dysfunction associated with diabetes mellitus and further to investigate whether adenovirus-mediated DDAH2 gene overexpression could improve the hyperglycemia-induced endothelial dysfunction.

METHODS

Diabetic model was induced by intraperitoneal injection of streptozotocin to male Sprague-Dawley rats. Recombinant adenoviral vector encoding human DDAH2 gene driven by a cytomegalovirus promoter was constructed to overexpress hDDAH2 gene in isolated rat aortas and endothelial cells. Changes in DDHA/ADMA/nitric oxide (NO) pathway in diabetic rats and high glucose-treated endothelial cells were examined.

RESULTS

DDAH2 expression was distinctly suppressed, which was accompanied by inhibited DDAH activity and impaired endothelium-dependent relaxation in aortas, and elevated ADMA concentrations in serum of diabetic rats compared to control rats. Suppressions of DDAH2 expression and DDAH activity, accumulation of ADMA, and inhibition of NO synthesis were observed in high glucose-treated endothelial cells. DDAH2 overexpression not only improved endothelial dysfunction in diabetic aortas but also attenuated hyperglycemia-induced changes in DDAH/ADMA//NO pathway in endothelial cells.

CONCLUSION

These results indicate that suppression of DDAH2 expression contributes to hyperglycemia-induced endothelial dysfunction, which can be improved by DDAH2 overexpression. This study suggests that targeted modulation of DDAH2 gene in vascular endothelium may be a novel approach for the treatment of endothelial dysfunction in diabetes mellitus.

The effects of thiazolidinediones on blood pressure levels – A systematic review

Insulin resistance has been proposed to be the underlying disorder of the so-called metabolic or insulin resistance syndrome, which represents the clustering in the same individual of several cardiovascular risk factors, such as type 2 diabetes mellitus, hypertension, abdominal obesity, elevated triglycerides and low high-density lipoprotein-cholesterol. As far as the connection of insulin resistance and compensatory hyperinsulinaemia with hypertension is concerned, a number of mechanisms possibly linking these disturbances have been described, such as activation of sympathetic nervous system, enhancement of renal sodium reabsorption, or impairment of endothelium-dependent vasodilatation. Thiazolidinediones (TZDs) constitute a class of oral antihyperglycaemic agents that act by decreasing insulin resistance, and apart from their action on glycaemic control, they have been also reported to exert beneficial effects on other parameters of the metabolic syndrome. In particular, during recent years a considerable number of animal and human studies have shown that the use of TZDs was associated with usually small but significant reductions of blood pressure (BP) levels. Since a possible beneficial action of these compounds on BP could be of particular value for patients with the metabolic syndrome, this review aimed to summarize and evaluate the literature data in the field, derived either from studies that just examined BP levels among other parameters or from studies that were specifically designed to determine the effect of a TZD on BP.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

15-Deoxy-Delta-Prostaglandin J(2) Upregulates the Expression of LPS-Induced IL-8/CXCL8 mRNA in Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats

Background

15d-PGJ₂ has been known to act as an anti-inflammatory agent and has anti-hypertensive effects. As a result of these properties, we examined the effect of 15d-PGJ₂ on the LPS-induced IL-8/CXCL8 mRNA expression in VSMCs from SHR.

Methods

Effect and action mechanism of 15d-PGJ₂ on the expression of LPS-induced IL-8/CXCL8 mRNA in VSMCs from SHR and WKY were examined by using real-time polymerase chain reaction, electrophoretic mobility shift assay for NF-κB avtivity, Western blotting analysis for ERK and p38 phosphorylation and flow cytometry for NAD(P)H oxidase activity.

Results

15d-PGJ₂ decreased the expression of LPS-induced IL-8/CXCL8 mRNA in WKY VSMCs, but increased the expression of LPS-induced IL-8/CXCL8 mRNA in SHR VSMCs. The upregulatory effect of 15d-PGJ₂ in SHR VSMCs was mediated through PPARγ, and dependent on NF-κB activation and ERK phosphorylation. However, inhibition of the p38 signaling pathway augmented the upregulatory effect of 15d-PGJ₂ on LPS-induced IL-8/CXCL8 mRNA. A NAD(P)H oxidase inhibitor inhibited the upregulatory effect of 15d-PGJ₂ on LPS-induced IL-8/CXCL8 mRNA expression in SHR VSMCs, and an increase in NAD(P)H oxidase activity was detected in SHR VSMCs treated with 15d-PGJ₂/LPS.

Conclusion

Our results indicate that the upregulatory effect of 15d-PGJ₂ on LPS-induced IL-8/CXCL8 expression in SHR VSMCs is mediated through the PPARγ and ERK pathway, and may be related to NAD(P)H oxidase activity. However, p38 inactivation may also play an important role in 15d-PGJ₂/LPS-induced IL-8/CXCL8 expression in SHR VSMCs.

ADMA, cardiovascular disease and diabetes

The endogenous competitive nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is an emerging risk marker for future cardiovascular events. Elevated ADMA concentrations have been described in patients with an adverse cardiovascular risk profile. Recently, various studies investigated the independent role of ADMA as a cardiovascular risk predictor in several patient cohorts. In addition, ADMA might not only be a risk marker but also a causative factor for cardiovascular disease. This review summarizes the literature on the relationship between ADMA, cardiovascular disease and diabetes.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.

Nitric oxide upregulates dimethylarginine dimethylaminohydrolase-2 via cyclic GMP induction in endothelial cells

Dimethylarginine dimethylaminohydrolase (DDAH) is an enzyme that metabolizes asymmetrical N(G),N(G)-dimethyl-L-arginine (ADMA) and N(G)-monomethyl-L-arginine (MMA), which are competitive endogenous inhibitors of NO synthase. However, it remains unknown whether NO itself influences DDAH activity and/or ADMA/MMA contents to regulate NO generation via a biofeedback mechanism. The present study was designed to examine the effects of NO on intracellular ADMA and MMA contents and DDAH gene expression levels and enzymatic activities in cultured rat aortic endothelial cells. The NO donors SNAP and NOR3 did not influence DDAH-1 expression but increased DDAH-2 mRNA and protein levels in concentration-dependent manners. SNAP upregulated DDAH enzymatic activity and reduced the MMA and ADMA contents but did not affect the symmetrical N(G),N'(G)-dimethyl-L-arginine and L-arginine levels, thereby negating a mediatory role for system y(+) in ADMA/MMA downregulation. The cGMP agonists 8-bromo-cGMP and C-type natriuretic peptide also stimulated DDAH-2 gene and protein expression levels and DDAH activity and increased the amount of nitrite/nitrate released into the culture supernatants. SNAP-induced DDAH-2 gene expression and DDAH activity were significantly inhibited by a protein kinase G inhibitor, KT5823, and a soluble guanylate cyclase inhibitor, ODQ, suggesting a mediatory role for cGMP in NO-induced DDAH-2 expression. Suppression of DDAH-2 mRNA using small interfering RNA technology abrogated NO-induced DDAH-2 expression. These data demonstrate that NO acts on endothelial cells to induce DDAH-2 expression via a cGMP-mediated process to reduce ADMA/MMA. Thus, the DDAH-2-ADMA/MMA-endothelial NO synthase regulatory pathway and NO-induced cGMP constitute a positive feedback loop that ultimately serves to maintain NO levels in the endothelial environment.

Pioglitazone enhances the antihypertensive and renoprotective effects of candesartan in Zucker obese rats fed a high-protein diet

The metabolic syndrome is a risk factor for the development of chronic kidney disease. Angiotensin II type 1 receptor blockers (ARBs) and thiazolidinediones (TZDs) provide renovascular protection, probably in the metabolic syndrome. However, the effect of both agents administered together in patients with metabolic syndrome remains to be determined. The aim of this study was to assess the effects of ARB plus TZD combination therapy in Zucker obese rats fed a high-protein diet, an animal model of metabolic syndrome and renal injury. Zucker obese rats were fed a high-protein diet (OHP; n=6), a high-protein diet containing candesartan, an ARB (OHP+C; n=6), or a high-protein diet containing both candesartan and pioglitazone (OHP+CP; n=6) for 12 weeks. Systolic blood pressure and urinary protein excretion were measured throughout the study, and renal histology and immunohistochemistry were assessed at 12 weeks. OHP rats developed hypertension (157+/-4 mmHg) and proteinuria (178+/-44 mg/d), and these conditions were significantly ameliorated by candesartan (to 143+/-3 mmHg and 84+/-25 mg/d, respectively). Pioglitazone enhanced the antihypertensive and anti-proteinuric effects of candesartan (121+/-3 mmHg, 16+/-8 mg/d, respectively). Histologically, candesartan ameliorated glomerulosclerosis, podocyte injury, interstitial fibrosis and monocyte/macrophage infiltration into the tubulointerstitium in the kidneys of OHP rats. Pioglitazone abrogated residual interstitial fibrosis in the kidneys of OHP+C rats. Our results suggested that pioglitazone augmented the antihypertensive, anti-proteinuric and possibly renal anti-fibrotic actions of candesartan in Zucker obese rats fed a high-protein diet. The combination therapy of ARB and TZD may protect against renal injury in patients with metabolic syndrome.

An antiproliferative BMP-2/PPARgamma/apoE axis in human and murine SMCs and its role in pulmonary hypertension

Loss-of-function mutations in bone morphogenetic protein receptor II (BMP-RII) are linked to pulmonary arterial hypertension (PAH); the ligand for BMP-RII, BMP-2, is a negative regulator of SMC growth. Here, we report an interplay between PPARgamma and its transcriptional target apoE downstream of BMP-2 signaling. BMP-2/BMP-RII signaling prevented PDGF-BB-induced proliferation of human and murine pulmonary artery SMCs (PASMCs) by decreasing nuclear phospho-ERK and inducing DNA binding of PPARgamma that is independent of Smad1/5/8 phosphorylation. Both BMP-2 and a PPARgamma agonist stimulated production and secretion of apoE by SMCs. Using a variety of methods, including short hairpin RNAi in human PASMCs, PAH patient-derived BMP-RII mutant PASMCs, a PPARgamma antagonist, and PASMCs isolated from PPARgamma- and apoE-deficient mice, we demonstrated that the antiproliferative effect of BMP-2 was BMP-RII, PPARgamma, and apoE dependent. Furthermore, we created mice with targeted deletion of PPARgamma in SMCs and showed that they spontaneously developed PAH, as indicated by elevated RV systolic pressure, RV hypertrophy, and increased muscularization of the distal pulmonary arteries. Thus, PPARgamma-mediated events could protect against PAH, and PPARgamma agonists may reverse PAH in patients with or without BMP-RII dysfunction.

Asymmetric dimethylarginine may be a missing link between cardiovascular disease and chronic kidney disease

Decreased nitric oxide (NO) production and/or impaired NO bioavailability may occur in patients with chronic kidney disease (CKD), and could contribute to the elevation of blood pressure, cardiovascular disease (CVD) and the progression of renal injury in these patients. However, the underlying molecular mechanisms for reduced NO action in patients with CKD remains to be elucidated. Asymmetric dimethylarginine (ADMA) is a naturally occurring L-arginine analogue found in plasma and various types of tissues, acting as an endogenous NO synthase inhibitor in vivo. Further, plasma level of ADMA is elevated in patients with CKD and found to be a strong biomarker or predictor for future cardiovascular events. In addition, plasma level of ADMA could predict the progression of renal injury in these patients as well. These findings suggest that elevation of ADMA may be a missing link between CVD and CKD. In this review, we discuss the molecular mechanisms for the elevation of ADMA and its pathophysiological role for CVD in high-risk patients, especially focusing on patients with CKD.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists attenuate the profibrotic response induced by TGF-beta1 in renal interstitial fibroblasts

BACKGROUND

Studies have shown that peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists could ameliorate renal fibrotic lesions in both diabetic nephropathy and nondiabetic chronic kidney diseases. In order to elucidate the antifibrotic mechanism of PPAR-gamma agonists, we investigated the effects of PPAR-gamma activation on TGF-beta1-induced renal interstitial fibroblasts.

METHODS

In rat renal interstitial fibroblasts (NRK/49F), the mRNA expression of TGF-beta1-induced alpha-smooth muscle actin (alpha-SMA), connective tissue growth factor (CTGF), fibronectin (FN) and collagen type III (Col III) were observed by reverse transcriptase-polymerase chain reaction (RT-PCR). The protein expressions of FN and Smads were observed by Western blot.

RESULTS

In NRK/49F, TGF-beta1 enhanced CTGF, FN and Col III mRNA expression in a dose- and time-dependent manner. alpha-SMA, CTGF, FN and Col III mRNA and FN protein expression in 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2)-troglitazone- and ciglitazone-pretreated groups, respectively, were significantly decreased compared with the TGF-beta1-stimulated group. TGF-beta1 (5 ng/mL) enhanced p-Smad2/3 protein expression in a time-dependent manner. Compared with the TGF-beta1-stimulated group, p-Smad2/3 protein induced by TGF-beta1 in PPAR-gamma agonists-pretreated groups significantly decreased with no statistical difference amongst the three pretreated groups.

CONCLUSION

PPAR-gamma agonists could inhibit TGF-beta1-induced renal fibroblast activation, CTGF expression and ECM synthesis through abrogating the TGF-beta1/Smads signaling pathway.

Antiproteinuric and anti-inflammatory effects of thiazolidinedione

Type 2 diabetes is the most common cause of chronic renal failure worldwide. Only a few oral antidiabetic drugs can be used for treating type 2 diabetes in patients with renal failure. Among them is thiazolidinedione, which is the agonist of peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma receptors are expressed in many tissues including the kidney. Recently, beneficial effects of PPAR-gamma agonists on several aspects related to renal function have been reported. These drugs have been shown to have favourable haemodynamic and anti-inflammatory effects on the kidneys. On the other hand, there is a rising concern on the association between thiazolidinedione treatment and the risk of cardiovascular disease. In the present paper, we review the recent studies that evaluated these potential effects of thiazolidinedione in patients with kidney diseases.

Pioglitazone, a thiazolidinedione derivative, attenuates left ventricular hypertrophy and fibrosis in salt-sensitive hypertension

Thiazolidinediones, which stimulate peroxisome proliferator-activated receptor gamma, have been shown to prevent cardiovascular injury. However, little is known about their effects on salt-sensitive hypertension. We thus investigated whether or not pioglitazone affects left ventricular (LV) hypertrophy in Dahl salt-sensitive rats, then compared its effects to those of an angiotensin II receptor blocker, candesartan. Rats were used at 16 weeks of age after they had been fed either a low-salt (0.3%; DSL) or high-salt (8%; DSH) diet for 10 weeks; some of the DSH rats were treated with pioglitazone (10 mg/kg/day) or candesartan (4 mg/kg/day). Both drugs decreased the elevated blood pressure in DSH rats, although it was still higher than in DSL rats. Both drugs decreased plasma insulin levels, but neither affected plasma glucose levels. The thiobarbituric acid reactive substance level in the LV was decreased by both drugs. LV hypertrophy evaluated by echocardiography in DSH rats was nearly normalized by both drugs, whereas only candesartan decreased LV diameter. In histological analysis, both drugs ameliorated LV fibrosis and myocardial cell hypertrophy. Both drugs decreased elevated gene expression levels of transforming growth factor-beta1 and collagen type I, although the pioglitazone action was slightly modest. The metalloproteinase activity was increased in DSH rats, but both drugs decreased this level. Taken together, these findings indicate that pioglitazone reduced LV hypertrophy and fibrosis in salt-sensitive hypertension. Improvement in blood pressure, insulin level, and oxidative stress may be associated with this beneficial action of pioglitazone.

Effect of telmisartan on nitric oxide--asymmetrical dimethylarginine system: role of angiotensin II type 1 receptor gamma and peroxisome proliferator activated receptor gamma signaling during endothelial aging

Telmisartan, in addition to blocking angiotensin (Ang) II type 1 receptor (AT(1)R), activates peroxisome proliferator activated receptor gamma (PPARgamma) signaling that interferes with nitric oxide (NO) system. Because aging of endothelial cells (ECs) is hallmarked by a reduction in NO synthesis, we hypothesized that telmisartan increases NO formation by regulated asymmetrical dimethylarginine (ADMA)-dimethylarginine dimethylaminohydrolase (DDAH)-system through blocking AT(1)R and activating PPARgamma signaling. To test this hypothesis, ECs were cultured with telmisartan, eprosartan, Ang II, and GW9662 (PPARgamma antagonist) until the twelfth passage. During the process of aging, PPARgamma protein expression decreased significantly, whereas the expression of AT(1)R increased. Telmisartan reversed these effects and dose-dependently decreased reactive oxygen species and 8-iso-prostaglandin (PG) F(2alpha) formation. This effect was associated with an upregulated activity and protein expression of DDAH, accompanied by a decrease in ADMA concentration, an increase in NO metabolites, and delayed senescence. Blockade of PPARgamma signaling by GW9662 or PPARgamma small-interference RNA prevented the effect of telmisartan on ADMA-DDAH-NO system. Coincubation with Ang II did not affect the effect of telmisartan-delayed senescence, whereas Ang II itself accelerated endothelial aging. Moreover, AT(1)R blocker eprosartan that did not influence PPARgamma protein expression had no effect on ADMA system and senescence. We have demonstrated that telmisartan mainly by activating PPARgamma signaling can alter the catabolism and release of ADMA as an important cardiovascular risk factor. We therefore propose that telmisartan translationally and posttranslationally upregulated DDAH expression via activation of PPARgamma signaling, causing ADMA to diminish and increase NO synthesis sufficient to delay senescence.

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.

Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction

CONTEXT

Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation.

OBJECTIVE

We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans.

DESIGN AND SETTING

We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital.

PATIENTS AND INTERVENTIONS

Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations.

MAIN OUTCOME MEASURES

Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion.

RESULTS

Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline).

CONCLUSIONS

Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.

The past, presence and future of ADMA in nephrology

Kakimoto and Akazawa, first isolated and identified asymmetric dimethylarginine (ADMA) from human urine in 1970. They speculated that ADMA, and its structural isomer symmetrical dimethylarginine (SDMA), "may be important for the study of various pathological states". It took 22 years before this hypothesis materialized in form of the seminal paper by Vallance et al. who advanced the idea that ADMA accumulation may be a cardiovascular risk factor in chronic kidney disease (CKD). In the last 15 years the relationship between ADMA and adverse cardiovascular outcomes has been thoroughly investigated in more than 600 published reports. These studies have shown that ADMA does not only correlate with traditional and non-traditional risk factors but also, independently of other risk factors, is strongly associated with clinical measures of cardiovascular burden such as intima-media thickness (IMT) of the carotid artery and left ventricular mass. Furthermore, cohort studies in both the general population and the dialysis population demonstrated a strong and independent link between ADMA, all-cause mortality and cardiovascular events. Last but not least, ADMA predicts the progression of CKD. This burgeoning body experimental and clinical studies form a fairly coherent framework indicating that ADMA is not only a marker but also a potent mediator of endothelial dysfunction and atherosclerosis as well as a solid predictor of mortality in selected patient populations. This article reviews the role of ADMA as a marker and mediator in cardiovascular disease in the setting of CKD and summarizes the effect of different renal replacement therapies as well as the effect on ADMA levels of commonly used drugs in nephrology. We conclude with remarks on the usefulness of ADMA as a marker in the clinical setting as well as for emerging therapeutic strategies.

Role of nitric oxide-producing and -degrading pathways in coronary endothelial dysfunction in chronic kidney disease

Cardiovascular events are accelerated in chronic kidney disease (CKD). Although deranged nitric oxide (NO) pathways and asymmetric dimethylarginine (ADMA) cause endothelial dysfunction, no direct evidence for coronary artery endothelial dysfunction in CKD has been documented. CKD was induced in male dogs by heminephrectomy (1/2Nx) or five-sixths nephrectomy (5/6Nx). After 4 wk, renal ablation reduced GFR (control 76 [54 to 85]; 1/2Nx 38 [29 to 47]; 5/6Nx 15 [12 to 46] ml/min) and elevated plasma ADMA (control 1.88 [1.68 to 2.54]; 1/2Nx 2.51 [2.11 to 3.55]; 5/6Nx 3.84 [2.16 to 3.95] micromol/L). Coronary circulatory responses to acetylcholine revealed marked increases in coronary blood flow in control group (83 +/- 17% increment) but blunted responses in 1/2Nx (34 +/- 8% increment) and 5/6Nx (20 +/- 4% increment). The acetylcholine-induced changes in epicardial arteriolar diameter, using needle-lens probe charge-coupled device videomicroscopy, showed similar results. The responsiveness to sodium nitroprusside did not differ among three groups. Plasma nitrite/nitrate levels decreased in 1/2Nx and 5/6Nx, and the mRNA expressions of dimethylarginine dimethylaminohydrolase-II (DDAH-II), ADMA-degrading enzyme, and endothelial NO synthase (eNOS) in coronary arteries were downregulated in 1/2Nx and 5/6Nx. Finally, 4-wk treatment with all-trans retinoic acid restored the impaired endothelium-dependent vasodilation and reversed the expression of eNOS but not DDAH-II. Coronary endothelial function is impaired in the early stage of CKD. The dysfunction is attributed to the downregulation of eNOS and/or DDAH-II in coronary arteries. Furthermore, the manipulation of NO pathways may constitute a therapeutic strategy for the prevention of coronary dysfunction in CKD.

Comparison of the Effects of Pioglitazone and Metformin on Insulin Resistance and Hormonal Markers in Patients with Impaired Glucose Tolerance and Early Diabetes

Impaired glucose tolerance (IGT) is associated with cardiovascular risk factors, but the effects of pioglitazone and metformin on IGT are not well described. We tested the hypothesis that each drug would exhibit antiatherogenic and anti-inflammatory effects in subjects with IGT and early diabetes. The study design was a prospective, randomized, open label, cross-over study. Blood tests, including a 75-g oral glucose tolerance test (OGTT), were performed at baseline and after each treatment. Pioglitazone 15 mg/day or metformin 500-750 mg/day was given for 3 months. Biochemical markers to assess insulin resistance as well as lipid, inflammatory, neurohumoral, and hemostatic factors were included. Twenty-five subjects (17 male, 8 female; age [mean+/-SD]: 61+/-9 years; 84% hypertensive) completed the protocol. Of 25 subjects, 14 were diagnosed as IGT and 11 as diabetes with 75-g OGTT. Pioglitazone significantly reduced fasting glucose (p<0.05), and homeostasis model assessment of insulin resistance (HOMA-IR) (p<0.05) and metformin (p<0.01) reduced cholesterol. Both drugs significantly reduced aldosterone (both p<0.05) and von Willebrand factor (vWF) (both p<0.05). Plasma adiponectin was increased only by pioglitazone (p<0.001). Neither drug affected BP levels. In conclusion, pioglitazone was superior to metformin for the improvement of insulin resistance and adiponectin, and both drugs were equally effective in reducing vWF and aldosterone in subjects with IGT and early diabetes. Early intervention with pioglitazone or metformin therapy may reduce the incidence of future cardiovascular disease in subjects with impaired glucose tolerance or early diabetes.

Asymmetric dimethylarginine: a new player in the pathogenesis of renal disease?

PURPOSE OF REVIEW

This review summarizes current knowledge on asymmetric dimethylarginine, renal function in health and disease, and renal disease progression and examines interventions that may modify the plasma concentration of this methylarginine.

RECENT FINDINGS

Nitric oxide deficiency may occur in patients with chronic kidney disease and may contribute to accelerate progression of chronic kidney disease, hypertension and cardiovascular complications. An increase of endogenous nitric oxide inhibitors like asymmetric dimethylarginine seems to play a major role in this process. The kidneys are crucial in both, in re-absorbing and generating L-arginine as well as in eliminating asymmetric dimethylarginine primarily by the enzyme dimethylarginine dimethylaminohydrolase and to a minor degree by urinary excretion. Asymmetric dimethylarginine accumulation predicts both accelerated renal function loss and death in patients with chronic kidney disease and incident cardiovascular complications in patients with end stage renal disease.

SUMMARY

Asymmetric dimethylarginine is a new risk factor potentially implicated in the progression of renal insufficiency and in the high rate of cardiovascular complications of patients with chronic kidney disease.

The Clinical Significance of Asymmetric Dimethylarginine

In 1992, asymmetrical dimethylarginine (ADMA) was first described as an endogenous inhibitor of the arginine-nitric oxide (NO) pathway. From then, its role in regulating NO production has attracted increasing attention. Nowadays, ADMA is regarded as a novel cardiovascular risk factor. The role of the kidney and the liver in the metabolism of ADMA has been extensively studied and both organs have proven to play a key role in the elimination of ADMA. Although the liver removes ADMA exclusively via degradation by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), the kidney uses both metabolic degradation via DDAH and urinary excretion to eliminate ADMA. Modulating activity and/or expression of DDAH is still under research and may be a potential therapeutic approach to influence ADMA plasma levels. Interestingly, next to its association with cardiovascular disease, ADMA also seems to play a role in other clinical conditions, such as critical illness, hepatic failure, and preeclampsia. To elucidate the clinical significance of ADMA in these conditions, the field of research must be enlarged.

Improvement of hypertension and vascular dysfunction by hydroxyhydroquinone-free coffee in a genetic model of hypertension

Chlorogenic acid, a polyphenol found in coffee, has antihypertensive actions, but epidemiologic data on the effects of coffee on blood pressure are controversial. Specific coffee components that inhibit the hypotensive effect of chlorogenic acid and the physiologic mechanisms underlying the effects of coffee without these components were investigated. One component, hydroxyhydroquinone (HHQ), inhibited the hypotensive effects of chlorogenic acid in spontaneously hypertensive rats (SHR). The attenuation of hypertension by HHQ-free coffee was associated with nitric oxide, the suppression of mRNA expression of NAD(P)H oxidase, and the improvement in endothelium-dependent vasodilation in the aorta. Thus, HHQ-free coffee might regulate vascular tone by improving the bioavailability of nitric oxide in SHR.