The non-steroidal
antiandrogen flutamide is widely used for treatment of
prostatic cancer, but causes side effects, including cholestatic
hepatitis and
fulminant hepatitis. We investigated the pathogenesis of
flutamide-induced cholestatic
hepatitis, focusing on the
bile salt export pump (BSEP; ABCB11), which exports
bile salts to the bile. We examined the inhibitory effects of
flutamide and its active metabolite,
hydroxyflutamide, on the transport of
taurocholic acid (TCA) by membrane vesicles derived from hBSEP-expressing Sf9 cells.
Flutamide inhibited the transport of TCA by hBSEP (IC50 value, about 50 microM), while
hydroxyflutamide had no effect at up to 100 microM. When
flutamide was administered to rats as a single oral dose of 100 mg/kg, the biliary excretion rate of bolus-injected [3H]TCA was decreased and the liver tissue concentration of
flutamide exceeded 50 microM. Repeated doses of
flutamide for 5 d (10 mg/kg/d) also decreased the biliary excretion rate of bolus-injected [3H]TCA. In this case, the liver tissue concentration of
flutamide was below 0.1 microM. In both cases, no change in the
mRNA level of rat Bsep was detected by RT-PCR. These results suggest that
flutamide itself, but not its major metabolite, may cause
cholestasis by inhibiting BSEP-mediated
bile salt excretion.