Effects of glutathione and cysteine on pyrrolizidine alkaloid-induced hepatotoxicity and DNA adduct formation in rat primary hepatocytes

Abstract

Pyrrolizidine alkaloids (PAs) are hepatotoxic, genotoxic, and carcinogenic phytochemicals. Upon metabolic activation, PAs produce dehydropyrrolizidine alkaloids (dehydro-PAs) as reactive primary pyrrolic metabolites. Dehydro-PAs are unstable, facilely hydrolyzed to (±)−6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP). Both dehydro-PAs and DHP are capable of binding to cellular DNA and proteins to form DHP-DNA and DHP-protein adducts leading to tumorigenicity and cytotoxicity. We recently determined that the reaction of dehydro-PAs with glutathione and cysteine generated 7-glutathione-DHP (7-GS-DHP) and 7-cysteine-DHP, respectively which can also bind to DNA to produce DHP-DNA adducts. In this study, we determined the effects of glutathione and cysteine on the induction of hepatocytotoxicity and the formation of DHP-DNA adducts in primary hepatocytes cultured with riddelliine and monocrotaline. We found that both glutathione and cysteine can drastically reduce hepatotoxicity while the levels of DHP-DNA adduct formation are slightly affected.

Keywords:

• Pyrrolizidine alkaloid
• glutathione
• cysteine
• DHP
• 7-GS-DHP

Acknowledgments

This research was supported in part by appointments (X.H.) to the Postgraduate Research Program at the NCTR administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and the FDA. This article is not an official U.S. Food and Drug Administration (FDA) guidance or policy statement. No official support or endorsement by the U.S. FDA is intended or should be inferred. The authors declare no competing financial interest.