Safingol [(2S,3S)-2-amino-1,3-octadecanediol], a
sphingosine analog that inhibits
protein kinase C, was developed to treat
dermatoses and
cancer. Preclinical toxicology studies performed to assess the effects of
safingol showed that 6 weeks of dermal application over 10% of body surface area caused dose-dependent increases in serum
enzymes and hepatic histopathological changes associated with liver damage in female rats. Liver toxicity was not seen in male rats at the same doses. Plasma
safingol concentrations were similar in male and female rats following topical exposure. The underlying mechanism(s) for the sex differences in toxicity in rats were examined using isolated hepatocytes. An in vitro model of male versus female differences in
safingol.HCl-induced hepatotoxicity was established using a
suspension/culture technique. Concentrations of
safingol.HCl which produced cytolethality in 50% of the hepatocytes were 125 and 48 microM for male and female rat hepatocytes, respectively. Cytolethality was time-, concentration-, and cell number-dependent. Inhibition of
cytochrome P450 in vitro with
1-phenylimidazole increased
safingol.HCl-induced cytolethality in male but not female hepatocytes, suggesting that male rat hepatocytes have a
cytochrome p450 isoenzyme which metabolizes
safingol.HCl to an inactive metabolite thus reducing hepatotoxicity. Furthermore, in vivo pretreatment 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 either lack or have a reduced constitutive level of a
cytochrome P450 isoenzyme that metabolizes
safingol to a nontoxic metabolite. In addition,
safingol produced hepatocyte cell death without
inflammation in vivo, and a "ladder-like" DNA fragmentation pattern in vitro, consistent with an apoptotic mechanism of cell death.