Cysteine-Based Protein Covalent Binding and Hepatotoxicity Induced by Emodin

Emodin (EMD) is a major ingredient of Polygonum multiflorum Thunb. (PMT), which has shown adverse liver reactions. Despite multiple pharmacological activities, EMD is reported to show various toxicities. Our early study demonstrated the reactivity of EMD to glutathione. This study aimed to determine the covalent interaction of hepatic protein with EMD and the correlation of the protein modification with hepatotoxicity induced by EMD. EMD-derived protein adduction was detected in an incubation mixture containing mouse liver homogenates and EMD. Such protein adduction was also observed in hepatic protein obtained from mice exposed to EMD. The protein covalent binding occurred in time- and dose-dependent manners. Pre-treatment of l-buthionine-sulfoximine significantly potentiated EMD-induced adduction and hepatotoxicity caused by EMD and lipopolysaccharide co-treatment. As expected, EMD-derived protein modification was observed in mouse primary hepatocytes treated with EMD. The increase in EMD exposure concentration intensified EMD-derived protein adduction and increased EMD-induced cell death. The susceptibility of hepatocytes to EMD cytotoxicity and the intensity of EMD-induced protein adduction were attenuated by the co-treatment of hepatocytes with N-acetyl cysteine. A good association of protein modification with hepatotoxicity induced by EMD was illustrated, which facilitates the understanding of the mechanism of hepatotoxicity induced by EMD.