Cytochrome P450 Enzyme-Mediated Bioactivation as an Underlying Mechanism of Columbin-Induced Hepatotoxicity.

Columbin, a furanoid compound, is the major bioactive ingredient of Tinospora sagittata (Oliv.) Gagnep, a traditional Chinese medicine that has been reported to cause liver injury in clinic. The aim of this study was to investigate the hepatotoxicity caused by columbin and the underlying mechanism. Our results indicated that columbin could result in the increase of mice serum ALT and AST after orally treated with columbin in a dose-dependent manner, as well as local spotty necrosis in the liver of mice treated with columbin. No hepatotoxicity was observed in mice treated with the same dose of tetrahydro-columbin. Pretreated with ketoconazole prevented the animal from columbin-induced hepatotoxicity. Further study suggested that bioactivation of furan ring played an indispensable role in columbin-caused hepatotoxicity. In vitro and in vivo metabolism studies demonstrated that columbin could be metabolized into cis-butene-1, 4-dial (BDA), which was readily to react with GSH and NAL to form stable nucleophile adducts. Ketoconazole displayed strong inhibitory effect on the generation of cyclic mono-GSH conjugates (M4 and M5) both in vitro and in vivo. Further recombinant human CYP450 screening demonstrated CYP3A4 was the major enzyme responsible for columbin bioactivation. The present study demonstrated that columbin was hepatotoxic and CYP3A4-mediated bioactivation of furan ring would serve as an underlying mechanism for columbin-induced hepatotoxicity.