Fasting augments pyrrolizidine alkaloid-induced hepatotoxicity.

Pyrrolizidine alkaloids (PAs) are phytotoxins widely present in various natural products and foodstuffs. The present study aims to investigate the effects of fasting on PA-induced hepatotoxicity and the underlying biochemical mechanisms. The results of hepatotoxic study showed that 15-h overnight fasting significantly exacerbated the hepatotoxicity of retrorsine (RTS, a representative toxic PA) in fasted rats compared to fed rats, as indicated by remarkably elevated plasma ALT and bilirubin levels and obvious liver histological changes. Further toxicokinetic studies revealed that fasting significantly enhanced cytochromes P450 enzymes (CYPs)-mediated metabolic activation of RTS leading to increased formation of pyrrole-protein adducts and thus decreased the in vivo exposure and excretion of both parent RTS and its N-oxide metabolite. Metabolic studies demonstrated that fasting induced enzyme activities of CYP1A2, CYP2B6 and CYP2E1 that participated in catalyzing RTS to its reactive pyrrolic metabolites. Moreover, fasting also dramatically decreased hepatic glutathione (GSH) content, which restricted the detoxification of GSH by neutralizing the reactive pyrrolic metabolite of RTS, further contributing to the enhanced hepatotoxicity. The present findings may have an impact on future PA toxicity tests with different dietary styles and/or risk assessment of metabolite-mediated toxins by considering the profound effects of fasting.