Hepatocellular bioactivation and cytotoxicity of the synthetic endoperoxide antimalarial arteflene

Abstract

Arteflene is a synthetic endoperoxide antimalarial. Its peroxide bridge undergoes iron(II)-mediated reduction in vitro which yields a carbon-centered cyclohexyl radical and a mixture of cis- and trans-α,β-unsaturated ketones (enones). The enones are biliary metabolites in rats and therefore surrogate markers of bioactivation. Arteflene is reported to be more cytotoxic to primary rat hepatocytes than some non-endoperoxide antimalarials. Hepatic metabolism of arteflene was investigated in recirculating isolated perfused rat livers, and the drug’s metabolism and cytotoxicity were compared using hepatocytes from male rats. Both preparations metabolized [ 14 C ]arteflene to cis- and trans-[ 14 C ]enone, 8-hydroxyarteflene glucuronide and an unassigned isomeric glucuronide. During a 2 h liver perfusion, the cis- and trans-enones recovered in bile represented 8.1±3.4 and 11.3±4.6% (mean±S.D., N=6), respectively, of the [ 14 C ]arteflene (52 μM) added to the perfusate. After a 3 h incubation of [ 14 C ]arteflene (10 μM) with hepatocytes in suspension, the cis- and trans-enones comprised, respectively, 14.8±7.1 and 2.1±1.0% ( N=4) of the recovered radioactivity; the corresponding data for cultured hepatocytes being 18.6±6.9 and 3.3±2.2%. Arteflene was significantly ( P<0.05) toxic to isolated hepatocytes with reference to extramitochondrial reductase activity (tetrazolium reduction) but not enzyme leakage when the cells were exposed to drug concentrations ≥50 μM for 24 h. Cellular glutathione was depleted under these conditions. Therefore arteflene was acutely cytotoxic, though only at relatively high concentrations, when it was metabolized via a pathway which generates carbon-centered radicals.