BIOCHEMICAL MECHANISMS UNDERLYING CYCLOSPORINE-INDUCED NEPHROTOXICITY EFFECT OF CONCOMITANT ADMINISTRATION OF PREDNISOLONE

Biochemical mechanisms underlying cyclosporine (CsA)-induced nephrotoxicity and the effect of concomitant administration of prednisolone (Pr) on the nephrotoxicity were studied. Male Wistar rats were treated with the vehicles used for CsA and Pr administration (group 1), Pr alone (group 2), CsA alone (group 3), or CsA plus Pr (group 4), respectively. The dose of CsA was 5 mg/kg/day, i.p. for the initial 7 days, and was decreased to 2.5 mg/kg/day i.p. thereafter. The dose of Pr was always maintained at one-tenth of that of CsA. At 10, 30, and 90 days after the initiation of these treatments, blood urea nitrogen (BUN) and serum levels of creatinine and CsA were determined. The syntheses of DNA, RNA, and protein, Na+, K+-adenosine triphosphate (ATP)ase activity, and ATP content were measured using homogenates of the renal cortex obtained from each experimental group. At an early stage (at 10 and 30 days) of CsA administration, the impairment of renal function and inhibition of the synthesis of DNA and RNA appeared in groups 3 and 4. The magnitude of these changes was found to be greater in group 3 (CsA alone) than in group 4 (CsA plus Pr). Group 3 also showed a significant reduction of Na+, K+-ATPase activity as well as ultrastructural abnormalities. At a later stage (at 90 days), however, such differences in nephrotoxicity between groups 3 and 4 were not detected. These results strongly suggest that inhibition of the synthesis of DNA and RNA and the activity of enzymes related to the functions of cell membrane, such as Na+, K+-ATPase, may be involved in the occurrence of CsA-induced nephrotoxicity. The present results also suggest that the concomitant administration of Pr with CsA may reduce the nephrotoxicity of CsA at early stages of CsA administration, but this preventive effect of Pr may disappear if the administration of CsA is prolonged.