CYCLOSPORINE-A-INDUCED OXIDATIVE STRESS IN RAT HEPATOCYTES

In man the immunosuppressive drug Cyclosporine A (CsA) has been used s uccessfully in organ transplantation and in the treatment of autoimmun e disorders. The drug, however, causes side effects which occur mainly in the kidney but also in the liver. The mechanisms leading to the he patic side effects are not yet fully understood. Because reactive oxyg en production is a common mechanism of drug toxicity, the goal of this study was to evaluate whether CsA induces oxidative stress in rat liv er cells. In primary rat hepatocyte 20-h cultures, CsA caused a concen tration-dependent increase of free reactive oxygen species, thiobarbit uric acid reactive substances, loss of protein thiols and decrease of molar ratios of glutathione and glutathione disulfide in the range of 0 to 50 mu M CsA. The weakening or enforcement of the cellular glutath ione state by the glutathione synthesis inhibitor buthionine sulfoximi ne or the glutathione disulfide-reducing agent dithiothreitol either i ncreased or inhibited the CsA cytotoxicity, as determined by lactate d ehydrogenase release. CsA also decreased the level of endogenous antio xidant ascorbic acid and increased its oxidation product dehydroascorb ic acid. Supplementation of the cell cultures with ascorbic acid signi ficantly reduced the CsA toxicity. The antioxidant lpha-tocopherol-pol yethylene-glycol-1000-succinate partly decreased CsA-mediated reactive oxygen species formation, totally decreased thiobarbituric acid react ive substances formation, prevented the loss of protein-bound sulfhydr yl groups and in addition totally inhibited the CsA cytotoxicity. The present data provide good evidence that oxidative stress is part of th e mechanism by which CsA causes toxicity in rat liver cells.