EFFECT OF ENZYME-INDUCTION ON SANDIMMUN (CYCLOSPORINE-A) BIOTRANSFORMATION AND HEPATOTOXICITY IN CULTURED RAT HEPATOCYTES AND INVIVO

This study was designed to examine the relationship between the extent of Sandimmun® (cyclosporin A, SIM) metabolism and SIM-induced hepatotoxicity both in vivo and in primary cultures of rat hepatocytes. Firstly, SIM (50 mg/kg p.o.) was administered daily to male Wistar rats for 10 days with or without co-administration of Aroclor 1254. SIM-induced hepatotoxicity appeared after 4 days of treatment and was enhanced after 10 administrations of SIM. Total plasma proteins were decreased and hyperbilirubinemia as well as increased levels of plasma bile salts were prominent. Aroclor 1254 stimulated total hepatic cytochrome P-450 3.7-fold, and markedly increased the rate of SIM metabolism and plasma elimination as determined by both HPLC and RIA techniques. However, this induction did not change the degree of SIM-induced hepatotoxicity. Secondly, short-term cultures of hepatocytes obtained from normal rats and from rats pretreated with either Aroclor 1254 or dexamethasone, a specific inducer of the cytochrome P-450 III gene family responsible for the formation of the primary SIM metabolites M1, M17 and M21, were incubated with various concentrations of SIM for up to 17 hr. At 1 μM SIM, both inducers greatly increased the rate of SIM metabolism in vitro, producing, however, different metabolite patterns. In the hepatocyte cultures, SIM inhibited the incorporation of amino acids into proteins. In addition, a small fraction of [3H]-labeled SIM was covalently bound to hepatocellular macromolecules. Although the fraction of covalently bound SIM was markedly increased in cells from dexamethasone-treated rats, the degree of inhibition of hepatocellular protein synthesis was not changed in cells from induced rats. In contrast to SIM-induced nephrotoxicity, these results suggest that increased rates of SIM biotransformation by inducers of drug metabolism are not associated with an attenuation of hepatotoxicity both in vivo and in vitro. © 1989.