Oral administration of both tetrahydrobiopterin and L-arginine prevents endothelial dysfunction in rats with chronic renal failure.

We examined the mechanism of endothelial dysfunction in chronic renal failure (CRF), with reference to NO synthase. CRF was induced by 5/6 nephrectomy in rats. Either L-arginine (1.25 g/L in drinking water), tetrahydrobiopterin (BH4, 10 mg/kg per day in food), or a combination of the 2 were orally administered to CRF rats for 9 weeks. CRF rats showed elevation of systolic blood pressure compared with sham-operated rats. Endothelium-dependent relaxation induced by acetylcholine or A23187 in the isolated aorta was significantly reduced, and in vitro treatment with L-arginine, BH4, or superoxide dismutase restored the relaxation. Aortic segments from CRF rats showed significantly higher superoxide production in response to A23187, which was inhibited by L-NAME. Plasma concentrations of asymmetric dimethylarginine and symmetric dimethylarginine were higher in CRF rats. These changes in CRF rats were totally or partially decreased by L-arginine or BH4 supplementation in vivo. Interestingly, the combined treatment showed additive effects in certain parameters. These results suggest that vascular disorders in CRF rats may be partly due to NOS uncoupling caused by a relative deficiency of BH4 and partially due to accumulation of endogenous inhibitors of NOS and L-arginine uptake, resulting in the decrease of NO production and the increase of reactive oxygen species.

Involvement of activation of NADPH oxidase and extracellular signal-regulated kinase (ERK) in renal cell injury induced by zinc.

Zinc is employed as a supplement; however, zinc-related nephropathy is not generally known. In this study, we investigated zinc-induced renal cell injury using a pig kidney-derived cultured renal epithelial cell line, LLC-PK(1), with proximal kidney tubule-like features, and examined the involvement of free radicals and extracellular signal-regulated kinase (ERK) in the cell injury. The LLC-PK(1) cells showed early uptake of zinc (30 microM), and the release of lactate dehydrogenase (LDH), an index of cell injury, was observed 24 hr after uptake. Three hours after zinc exposure, generation of reactive oxygen species (ROS) was increased. An antioxidant, N, N'-diphenyl-p-phenylenediamine (DPPD), inhibited a zinc-related increase in ROS generation and zinc-induced renal cell injury. An NADPH oxidase inhibitor, diphenyleneiodonium (DPI), inhibited a zinc-related increase in ROS generation and cell injury. We investigated translocation from the cytosol fraction of the p67(phox) subunit, which is involved in the activation of NADPH oxidase, to the membrane fraction, and translocation was induced 3 hr after zinc exposure. We examined the involvement of ERK1/2 in the deterioration of zinc-induced renal cell injury, and the association between ERK1/2 and an increase in ROS generation. Six hours after zinc exposure, the activation (phosphorylation) of ERK1/2 was observed. An antioxidant, DPPD, inhibited the zinc-related activation of ERK1/2. An MAPK/ERK kinase (MEK1/2) inhibitor, U0126, almost completely inhibited zinc-related cell injury (the release of LDH), but did not influence ROS generation. These results suggest that early intracellular uptake of zinc by LLC-PK(1) cells causes the activation of NADPH oxidase, and that ROS generation by the activation of the enzyme leads to the deterioration of renal cell injury via the activation of ERK1/2.

Chronotoxicity of nedaplatin in rats.

Chronotoxicologic profiles of nedaplatin, a platinum compound, were evaluated in rats maintained under a 12 light/12 dark cycle with light from 07:00h to 19:00 h. Nedaplatin (5 mg/kg) was injected intravenously, once a week for 5 weeks at 08:00h or 20:00h. The suppression of body weight gain and reduction of creatinine clearance were significantly greater with the 20:00h than 08:00h treatment. Accumulation of nedaplatin in the renal cortex and bone marrow were also greater with 20:00 h treatment. There were significant relationships between the nedaplatin content in the kidney and bone marrow and degree of injury to each. These results suggest that the nedaplatin-induced toxicity depends on its dosing-time, and it is greater with treatment at 20:00 h, during the active phase. The dosing-time dependency in the accumulation of nedaplatin in the tissue of the organs might be involved in this chronotoxicologic phenomenon.