Insight into the practical models for prediciting the essential role of the cytochrome P450-mediated biotransformation in emodin-associated hepatotoxicity

Emodin is widely present in Chinese herbs with broad application prospects, however, the conflicting reports of its hepatotoxicity have created a concern. It was therefore aimed to develop practical models to elucidate the outcome of CYP450 biotransformation on emodin. HepG2 and rat liver microsomes (RLM) coculture system was first utilized for prediction. It was found that emodin (35 μM)-mediated cytotoxicity was alleviated only when the cofactor of CYP450 NADPH (1 mM) was present. Similarly, both the pan-CYP450 inhibitor 1-aminobenzotriazole (ABT) (2 mM) and the heat-inactivated liver microsomes completely abolished the protective effect of RLM (0.75 mg/mL). Consistently, ABT significantly increased the toxicity of emodin in primary rat liver cells. Along similar lines, only the monohydroxylation metabolite M3 that accounted for neglectable amount of the whole metabolites showed similar toxicity to emodin, both M1 and M2 exhibited far less toxcity than emodin in THLE-2 cells. In vivo study further supported that ABT (50 mg/kg, s.c.) aggravated the hepatotoxicity of emodin (80 mg/kg, i.p.) on mice, as emodin treatment only mediated slight increase of liver index and histological score likely due to the metabolic detoxication of emodin, whereas ABT co-administration resulted in severe liver injury as reflected by the dramatic increase of the liver index value, serum ALT and AST levels, and histopathological score. Moreover, it was explored that ROS generation together with the electrophilicity of emodin contributed to its hepatotoxicity. These findings not only provided a clear evidence of the metabolic detoxification of emodin, but also shed a light on the hepatotoxic mechanisms of emodin, which would lay a solid foundation for the rational application of emodin in the future.