In an attempt to define the role of the pineal secretory melatonin and an analogue, 6-hydroxymelatonin (6-OHM), in limiting oxidative stress, the present study investigated the cisplatin (CP)-induced alteration in the renal antioxidant system and nephroprotection with the two indolamines. Melatonin (5 mg/kg), 6-OHM (5 mg/kg), or an equal volume of saline were administered intraperitoneally (i.p.) to male Sprague Dawley rats 30 min prior to an i.p. injection of CP (7 mg/kg). After CP treatment, the animals each received indolamine or saline every day and were sacrificed 3 or 5 days later and plasma as well as kidney were collected. Both plasma creatinine and blood urea nitrogen increased significantly following CP administration alone; these values decreased significantly with melatonin co-treatment of CP-treated rats. In the kidney, CP decreased the levels of GSH (reduced glutathione)/GSSG (oxidized glutathione) ratio, an index directly related to oxidative stress. When animals were treated with melatonin, the reduction in the GSH/GSSG ratio was prevented. Treatment of CP-enhanced lipid peroxidation in the kidney was again prevented in animals treated with melatonin. The activity of the antioxidant enzyme, glutathione peroxidase (GSH-Px), decreased as a result of CP administration, which was restored to control levels with melatonin co-treatment. Upon histological analysis, damage to the proximal tubular cells was seen in the kidneys of CP-treated rats; these changes were prevented by melatonin treatment. 6-OHM has been shown to have some antioxidative capacity, however, the protective effects of 6-OHM against CP-induced nephrotoxicity were less than those of melatonin. The residual platinum concentration in the kidney of melatonin co-treated rats was significantly lower than that of rats treated with CP alone. It is concluded that administration of CP imposes a severe oxidative stress to renal tissue and melatonin confers protection against the oxidative damage associated with CP. This mechanism may be reasonably attributed to its radical scavenging activity, to its GSH-Px activating property, and/or to its regulatory activity for renal function.

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The ability of ebselen, which exhibits glutathione peroxidase (GSH-Px)-like activity, to prevent cisplatin (CDDP)-induced nephrotoxicity was examined in rats. CDDP (6 mg/kg [20 micromol/kg] body weight) was injected intraperitoneally. In subgroups, daily ebselen doses of 2.75 (10 micromol), 5.5 (20 micromol), or 11.0 mg (40 micromol)/kg body weight were administrated orally 1 hour prior to CDDP treatment. Treatment with CDDP alone resulted in significantly increased plasma creatinine (Cr) and blood urea nitrogen (BUN) levels. Repeated administration of 5.5 and 11.0 mg/kg ebselen prevented the CDDP-induced elevation of plasma Cr and BUN levels and protected against kidney damage. Relative to controls, rat that received CDDP treatment displayed a decreased ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), an indicator directly related to oxidative stress, and elevated malondialdehyde (MDA) levels in the kidney. In comparison with controls, activity of GSH-Px activity, which antioxidant enzyme, was also reduced in the kidney of rats treated with CDDP. Repeated administration of 5.5 or 11.0 mg/kg ebselen prevented CDDP-induced alteration of GSH/GSSG ratios, MDA levels, and GSH-Px activity; however, no protection against CDDP was observed with administration of 2.75 mg/kg ebselen. Effective protection of CDDP-induced nephrotoxicity with ebselen was observed only when the molar amount of each daily ebselen treatment equaled or exceeded

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