Seiji Ueda

Hemodialysis Impairs Endothelial Function via Oxidative Stress : Effects of Vitamin E-Coated Dialyzer

BACKGROUND Patients who undergo hemodialysis experience accelerated atherosclerosis and premature death. Recent evidence suggests that endothelial dysfunction proceeds to and exacerbates atherosclerosis. It remains unknown whether hemodialysis per se causes endothelial dysfunction. METHODS AND RESULTS We evaluated endothelial function estimated by flow-mediated vasodilation during reactive hyperemia using high-resolution ultrasound Doppler echocardiography before and after a single session in patients on maintenance hemodialysis. Several studies have shown that the imbalance between pro-oxidant and antioxidant activities in hemodialyzed patients results in high oxidative stress, which causes lipid peroxidation and endothelial injury. Accordingly, we investigated the effects of antioxidative modification during hemodialysis on endothelial function using a vitamin E-coated cellulose membrane dialyzer. Nonspecific endothelium-independent vasodilation was measured after administration of a sublingual glyceryl trinitrate spray (0.3 mg). A single session of hemodialysis by noncoated dialyzer impaired flow-mediated vasodilation (P<0.05) associated with increased plasma levels of oxidized LDL (P<0.05), an index of oxidative stress. Hemodialysis by vitamin E-coated membrane prevented dialysis-induced endothelial dysfunction and increases in oxidized LDL. Plasma levels of oxidized LDL were inversely correlated with the magnitudes of flow-mediated vasodilation (r=-0.53, P< 0.001). Hemodialysis by noncoated or vitamin E-coated membrane did not affect glyceryl trinitrate-induced endothelium-independent vasodilation. CONCLUSIONS Our findings indicate that hemodialysis per se impairs endothelial function, possibly by increasing oxidative stress.

Advanced Glycation End-Products Attenuate Human Mesenchymal Stem Cells and Prevent Cognate Differentiation Into Adipose Tissue, Cartilage, and Bone†‡

The impact of AGEs on human MSCs was studied. AGEs inhibited the proliferation of MSCs, induced apoptosis, and prevented cognate differentiation into adipose tissue, cartilage, and bone, suggesting a deleterious effect of AGEs in the pathogenesis of musculoskeletal disorders in aged and diabetic patients.

Tetrahydrobiopterin restores endothelial function in long-term smokers

OBJECTIVES We sought to test whether tetrahydrobiopterin (BH4) supplementation improves nitric oxide (NO) bioactivity in smokers. BACKGROUND In smokers, endothelium-derived NO bioactivity is impaired. BH4 is an essential cofactor of NO synthase, and its deficiency decreases NO bioactivity. METHODS Sapropterin hydrochloride, an active analogue of BH4 (2 mg/kg body weight), was administered orally to healthy male smokers and age-matched nonsmokers. Before and 3 and 24 h after sapropterin, we measured plasma levels of BH4 and examined flow-mediated vasodilation (FMV) of the brachial artery by high resolution ultrasonography, a noninvasive test of endothelial function. RESULTS Basal plasma levels of BH4 were not different between smokers and nonsmokers. Sapropterin administration increased plasma levels of BH4 by threefold at 3 h, which returned to the baseline at 24 h. Before sapropterin, FMV was significantly smaller in smokers (p = 0.0002). Sapropterin significantly augmented endothelium-dependent vasodilation in smokers, but did not affect it in nonsmokers (p = 0.001 by analysis of variance [ANOVA]). Coadministration of N(G)-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor (20 micromol), into the brachial artery completely abolished the vasodilatory effects of sapropterin (p = 0.002 by ANOVA). Endothelium-independent vasodilation by glyceryl trinitrate was not different between smokers and nonsmokers and was not altered by BH4. CONCLUSIONS We demonstrated that BH4 supplementation improved bioactivity of endothelium-derived NO in smokers. These observations strongly suggest that decreased NO-dependent vasodilation in smokers could be related to reduced bioactivity of BH4.

Role of advanced glycation end products (AGEs) and oxidative stress in vascular complications in diabetes.

BACKGROUND A non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules, whose process has been known to progress at an accelerated rate under hyperglycemic and/or oxidative stress conditions. Over a course of days to weeks, early glycation products undergo further reactions such as rearrangements and dehydration to become irreversibly cross-linked, fluorescent protein derivatives termed advanced glycation end products (AGEs). SCOPE OF REVIEW In this paper, we review the role of AGE-oxidative stress axis and its therapeutic interventions in vascular complications in diabetes. MAJOR CONCLUSIONS AGEs elicit oxidative stress generation and subsequently cause inflammatory and thrombogenic reactions in various types of cells via interaction with a receptor for AGEs (RAGE), thereby being involved in vascular complications in diabetes. In addition, mitochondrial superoxide generation has been shown to play an important role in the formation and accumulation of AGEs under diabetic conditions. Further, we have recently found that a pathophysiological crosstalk between AGE-RAGE axis and renin-angiotensin system (RAS) could contribute to the progression of vascular damage in diabetes. GENERAL SIGNIFICANCE These observations suggest that inhibition of AGE-RAGE-oxidative stress axis or blockade of its interaction with RAS is a novel therapeutic strategy for preventing vascular complications in diabetes.

Molecular Mechanism for Elevation of Asymmetric Dimethylarginine and Its Role for Hypertension in Chronic Kidney Disease

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase. ADMA is generated by protein methyltransferase (PRMT) and is metabolized mainly by dimethylarginine dimethylaminohydrolase (DDAH). ADMA levels are reported to increase in patients with chronic kidney disease (CKD), thereby playing a role in the pathogenesis of accelerated atherosclerosis in this population. However, the precise mechanism underlying ADMA accumulation in these patients is not fully understood. This study investigated the molecular mechanism for the elevation of ADMA levels in CKD, using a rat remnant kidney model that represents progressive CKD. After male Sprague-Dawley rats underwent baseline measurement of BP and renal function, 5/6 subtotal nephrectomy (5/6Nx) and 4/6 nephrectomy were performed. Plasma and urinary levels of ADMA and symmetric dimethylarginine, an inert isomer of ADMA, were measured by HPLC. Expression levels of PRMT genes and DDAH proteins were analyzed by semiquantitative reverse transcription-PCR and Western blotting, respectively. Plasma ADMA levels were elevated in the Nx groups in proportion to the degree of nephrectomy despite marked increases in renal clearance of ADMA. In contrast, renal clearance of symmetric dimethylarginine was decreased and its plasma levels were increased in the Nx groups. Furthermore, both liver and kidney gene expression of PRMT was increased, whereas DDAH protein expression was decreased in the 5/6Nx group. Plasma ADMA levels were correlated with systolic BP levels. Moreover, adenovirus-mediated DDAH gene transfer into the 5/6Nx rats prevented the elevation of BP levels, which was associated with the reduction of plasma and urinary ADMA levels. The results presented here suggest that decreased DDAH levels as well as increased PRMT gene expression could cause the elevation of plasma ADMA levels, thereby eliciting hypertension in CKD. Substitution of DDAH protein or enhancement of its activity may become a novel therapeutic strategy for the treatment of hypertension-related vascular injury in CKD.

Molecular mechanisms of diabetic nephropathy and its therapeutic intervention.

Diabetic nephropathy is a leading cause of end-stage renal failure, which could account for disabilities and high mortality rates in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and hemodynamic factors, which activate common pathways that lead to renal damage. Recent large landmark clinical studies have shown that intensive glucose control reduces the risk of the development and progression of diabetic nephropathy, and the blockade renin-angiotensin system (RAS) is also an important target for both metabolic and hemodynamic derangements in diabetic nephropathy. However, diabetic nephropathy remains the leading cause of end-stage renal failure in developed countries. Therefore, to develop novel therapeutic strategies that specifically target diabetic nephropathy may be helpful for most patients with diabetes. High glucose, via various mechanisms such as increased production of oxidative stress and advanced glycation end products (AGEs), and activation of the RAS and protein kinase C (PKC), elicits vascular inflammation and alters gene expression of growth factors and cytokines, thereby it might be involved in the development and progression of diabetic nephropathy. This article summarizes the molecular mechanisms of diabetic nephropathy and the potential therapeutic interventions that may prevent this devastating disorder even in the presence of hyperglycemia, control of which is often difficult with current therapeutic options.

Agents that block advanced glycation end product (AGE)-RAGE (receptor for AGEs)-oxidative stress system: a novel therapeutic strategy for diabetic vascular complications

Background: Diabetic vascular complications are leading causes of acquired blindness, end-stage renal failure, a variety of neuropathies, and accelerated atherosclerosis, which together could account for disabilities and high mortality rates in patients with diabetes. Since there is accumulating evidence that the advanced glycation end product (AGE)–RAGE (receptor for AGEs)–oxidative stress axis is involved in diabetic vascular complications, inhibition of the AGE–RAGE system may be a promising target for therapeutic intervention in these devastating disorders. Objective: In this review, we discuss several types of agent that may be able to inhibit the AGE–RAGE–oxidative stress system, and their therapeutic implications in vascular complications in diabetes. Methods: We have analyzed currently available scientific literature in the field of AGE–RAGE to create a comprehensive review on novel therapeutic agents for vascular complications in diabetes. Results/conclusion: Inhibition of AGE formation, blockade of the AGE–RAGE interaction, and suppression of RAGE expression or its downstream pathways may be novel therapeutic strategies for the treatment of vascular complications in diabetes.

Pigment epithelium-derived factor (PEDF) blocks angiotensin II signaling in endothelial cells via suppression of NADPH oxidase: a novel anti-oxidative mechanism of PEDF

Angiotensin II (Ang II), the dominant effector of the renin–angiotensin system, regulates numerous inflammatory–proliferative responses in vascular wall cells and is thus involved in atherosclerosis. We have previously shown that pigment epithelium-derived factor (PEDF) inhibits advanced glycation end-product-induced pericyte apoptosis, thereby exerting beneficial effects on diabetic retinopathy. However, a role for PEDF in vascular inflammation and atherosclerosis remains to be elucidated. In this study, we have examined whether PEDF inhibits the Ang-II-induced endothelial cell (EC) activation in vitro and the way that it might achieve this effect. Ang II significantly induced redox-sensitive transcriptional factor NF-κB activation and subsequent monocyte chemoattractant protein-1 expression in human umbilical vein ECs (HUVEC), both of which were completely inhibited by PEDF or the anti-oxidant N-acetylcysteine. PEDF or diphenylene iodonium, an inhibitor of NADPH oxidase, inhibited Ang-II-induced intracellular reactive oxygen species (ROS) generation in HUVEC. Furthermore, PEDF inhibited Ang-II-induced up-regulation of mRNA levels of p22phox, Nox4, and gp91phox/Nox2, which are membrane components of NADPH oxidase, and its enzymatic activity in HUVEC. Antisense, but not sense, DNAs against p22phox, Nox4, or gp91phox/Nox2 were found significantly to inhibit Ang-II-induced ROS generation in HUVEC. These results demonstrate that PEDF inhibits Ang-II-induced EC activation by suppressing NADPH-oxidase-mediated ROS generation and that PEDF may play a protective role in the development and progression of atherosclerosis.

Role of AGEs in Diabetic Nephropathy

Diabetic nephropathy is the most common cause of end-stage renal disease in the world, and accounts for a significant increase in morbidity and mortality in patients with diabetes. Therapeutic options such as strict blood pressure and/or glycemic control are effective for preventing the development and progression of diabetic nephropathy, but the number of diabetic patients on hemodialysis is still increasing. Therefore, a novel therapeutic strategy that could halt the progression of diabetic nephropathy should be developed. Advanced glycation end products (AGEs) are heterogeneous cross-linked sugar-derived proteins which could accumulate in glomerular basement membrane, mesangial cells, endothelial cells, and podocytes in patients with diabetes and/or end-stage renal failure. AGEs are thought to be involved in the pathogenesis of diabetic nephropathy via multifactorial mechanisms such as oxidative stress generation and overproduction of various growth factors and cytokines. Further, recently, the cross-talk between AGEs and the renin-angiotensin system (RAS) has been proposed to participate in diabetic nephropathy. In addition, activation of the RAS elicits ROS generation and subsequently stimulates growth factor and cytokine production by kidney cells as well. These observations suggest that combination therapy with inhibitors of the RAS and blockers of the AGEs formation and/or their downstream pathway may be a novel therapeutic option for preventing diabetic nephropathy. In this paper, we review the role of AGEs and their receptor system in the pathogenesis of diabetic nephropathy. We further discuss here the cross-talk between AGEs and the RAS in the development and progression of diabetic nephropathy.

Dimethylarginine Dimethylaminohydrolase Prevents Progression of Renal Dysfunction by Inhibiting Loss of Peritubular Capillaries and Tubulointerstitial Fibrosis in a Rat Model of Chronic Kidney Disease

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). It was recently reported that reduced DDAH expression could contribute to ADMA accumulation and subsequent elevation of BP in an experimental model of chronic kidney disease (CKD). ADMA is a strong predictor of the progression of CKD as well. However, a role for the ADMA-DDAH in the pathogenesis of CKD remains to be elucidated. This study investigated the effects of DDAH-elicited ADMA lowering on renal function and pathology in a rat remnant kidney model. Four weeks after five-sixths subtotal nephrectomy (Nx), the rats were given tail-vein injections of recombinant adenovirus vector encoding DDAH-I (Adv-DDAH) or control vector expressing bacterial beta-galactosidase (Adv-LZ) or orally administered 20 mg/kg per d hydralazine (Hyz), which served as a BP control model. In comparison with Adv-LZ or Hyz administration, Adv-DDAH decreased plasma levels of ADMA and inhibited the deterioration of renal dysfunction. Plasma levels of ADMA were associated with decreased number of peritubular capillaries, increased tubulointerstitial fibrosis, and proteinuria levels in Nx rats. These changes were progressed in Adv-LZ-or Hyz-treated Nx rats, which were ameliorated by DDAH overexpression. In addition, semiquantitative reverse transcriptase-PCR and immunohistochemistry for TGF-beta revealed that Adv-DDAH inhibited upregulation of TGF-beta expression in Nx rats. These data suggest that ADMA may be involved in peritubular capillary loss and tubulointerstitial fibrosis, thereby contributing to the progression of CKD. Substitution of DDAH protein or enhancement of its activity may become a novel therapeutic strategy for the treatment of CKD.