Purpose. The effect of AST-120, an oral adsorbent, on oxidative stress in the systemic circulation in chronic renal failure (CRF) was examined and the potential role of indoxyl sulfate (IS), an uremic toxin adsorbed by AST-120, in inducing the formation of reactive oxygen species (ROS) in the vascular system was studied, in vitro and in vivo. Materials and methods. The level of oxidized albumin, a marker for oxidative stress in the systemic circulation was determined by HPLC, as previously reported. The mRNA levels of TGF-b 1 and Oat1 were measured by quantitative RT-PCR. The IS induced ROS generation in cultured human umbilical vein endothelial cells (HUVECs) was estimated using a fluorescence microplate reader.Results. An increase in the ratio of oxidized to unoxidized albumin was determined using 5/6 nephrectomized rats (CRF rats) compared to a control group. The ratio was significantly reduced in the group that received AST-120 of 4 weeks, suggesting that AST-120 inhibits oxidative stress in CRF. An anti-oxidative effect of AST-120 was also observed in CRF rats with a similar renal function. The ratio of oxidized albumin was correlated with serum IS levels in vivo. The same relationship was also observed in CRF rats with the continued administration of IS. In addition, IS dramatically increased the generation of ROS in both a dose-and time-dependent manner in HUVEC, suggesting that accumulated IS may play an important role in enhancing intravascular oxidative stress. Conclusion. We propose that AST-120 reduces IS concentrations in the blood that induces ROS production in endothelial cells, thereby inhibiting the subsequent occurrence of oxidative stress in the systemic circulation in renal failure.

a b s t r a c tThe effect of the uremic solute indoxyl sulfate (IS) on scavenging superoxide anion radicals (O ÅÀ 2 ) generated from both the xanthine/xanthine oxidase (X/XO) system and activated neutrophils was investigated by electron paramagnetic resonance spectroscopy, combined with 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide (EMPO). The findings show that the presence of normalphysiological serum concentrations of IS (0.1-10 lM) resulted in decreased formation of EMPOsuperoxide adduct without affecting XO activity. Furthermore, IS showed scavenging activity against cell-derived O ÅÀ 2 generated from activated neutrophils. In addition, IS also eliminated hydroxyl radicals. These findings suggest that IS acts as a novel endogenous antioxidant under normal-physiological conditions. Ó

The effect of olmesartan, an inverse angiotensin II type 1 receptor blocker (ARB), on oxidative stress in hemodialysis (HD) patients is not fully understood, and has not been widely investigated in vitro or in vivo.

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure (BP). It has recently been revealed that the elevated levels of RAS are associated with various organ impairments. Thus, an angiotensin II receptor blocker (ARB) and an angiotensin converting enzyme inhibitor (ACEI) are effective for treating hypertension and show protective effects for the heart or kidney. For example, in a clinical trial in which the effect of ARB valsartan and calcium channel blocker (CCB) amlodipine were compared in patients with diabetes, valsartan was found to decrease the urinary albumin excretion rate to a greater extent than CCB, while BP was reduced to the same level.1) Consequently, RAS antagonists may exert a renal protective effect that is independent of its antihypertensive effect, and may be involved in reducing of the levels of oxidative stress. In fact, contrary to CCB, ARB improved endothelium-dependent coronary dilation in hypertensive patients independent of BP reduction. These beneficial effects on coronary vasomotion might be a result of the antioxidant properties of ARBs. 2)Olmesartan medoxomil, a prodrug that is converted into the active metabolite olmesartan has recently been developed in association with ARB.3,4) Miyata et al. reported that the antioxidant effects of olmesartan were greater than any other ARBs in an in vitro study. 5) We recently reported, in an in vitro study, that clinical concentrations of olmesartan exert antioxidant properties. This was further confirmed in a clinical trial for hemodialysis (HD) patients as well.6) We also reported that the antioxidant effects of olmesartan might be independent of its BP lowering ability. To develop a better understanding of the antioxidant effect of olmesartan in vivo, relationships between the antioxidant activity of olmesartan and pharmacological effects, such as renoprotective or BP lowering effects, were examined using the 5/6 nephrectomy rat. MATERIALS AND METHODS MaterialsOlmesartan was obtained from the DaiichiSankyo Pharmaceutical Co., Ltd. (Tokyo, Japan). All other chemicals were of the highest grade available from commercial sources.Animals and Treatment Male Wister rats were purchased from Seac Yoshitomi, Ltd. (Fukuoka, Japan). The experimental protocol was inspected and approved by the Animal Care and Use Committee of School of Medicine, Kumamoto University and the law and notification of the Japanese government prior to commencement of the study. Fiveweek-old male rats weighing 140-150 g were subjected to a 5/6 nephrectomy, as previously described. 7,8) Six weeks after the operation, the treated rats showed increased plasma concentrations of creatinine (Ͼ1.0 mg/dl), and reduced levels of creatinine clearance (1.12 approximately 1.24 ml/min). Agematched Sham-operated rats were used for comparison. These rats were divided into three groups as follows: (a) untreated nephrectomized group (nϭ4-6). (b) Olmesartan (10 mg/kg/d) treated nephrectomized group (nϭ4-6). (c) Sham-operated rats (nϭ4-6). All of the rats received s...