SEX-DIFFERENCES IN RAT HEPATIC CYTOLETHALITY OF THE PROTEIN-KINASE INHIBITOR SAFINGOL - ROLE OF BIOTRANSFORMATION

Safingol [(2S,3S)-2-amino-1,3-octadecanediol], a sphingosine analog th at inhibits protein kinase C, was developed to treat dermatoses and ca ncer. Preclinical toxicology studies performed to assess the effects o f safingol showed that 6 weeks of dermal application over 10% of body surface area caused dose-dependent increases in serum enzymes and hepa tic histopathological changes associated with liver damage in female r ats, Liver toxicity was not seen in male rats at the same doses. Plasm a safingol concentrations were similar in male and female rats followi ng topical exposure. The underlying mechanism(s) for the sex differenc es in toxicity in rats were examined using isolated hepatocytes. An in vitro model of male versus female differences in safingol . HCl-induc ed hepatotoxicity was established using a suspension/culture technique , Concentrations of safingol . HCl which produced cytolethality in 50% of the hepatocytes were 125 and 48 mu M for male and female rat hepat ocytes, respectively, Cytolethality was time-, concentration-, and cel l number-dependent. Inhibition of cytochrome P450 in vitro with 1-phen ylimidazole increased safingol . HCl-induced cytolethality in male but not female hepatocytes, suggesting that male rat hepatocytes have a c ytochrome P450 isoenzyme which metabolizes safingol . HCl to an inacti ve metabolite thus reducing hepatotoxicity, Furthermore, in vivo pretr eatment with the CYP4A-inducing agent, clofibrate, protected both male and female hepatocytes from cytolethality. The results of this study indicate that the sex differences seen in hepatotoxicity could be due to differences in biotransformation such that female rat hepatocytes e ither lack or have a reduced constitutive level of a cytochrome P450 i soenzyme that metabolizes safingol to a nontoxic metabolite. In additi on, safingol produced hepatocyte cell death without inflammation in vi vo, and a ''ladder-like'' DNA fragmentation pattern in vitro, consiste nt with an apoptotic mechanism of cell death. (C) 1996 Academic Press, Inc.