Metformin ameliorates acetaminophen hepatotoxicity via Gadd45β-dependent regulation of JNK signaling in mice

Background & Aims Acetaminophen (APAP) overdose is a leading cause of drug-induced acute liver failure. Prolonged c-Jun N-terminal kinase (JNK) activation plays a central role in APAP-induced liver injury and growth arrest, and DNA damage-inducible 45 beta (Gadd45β) is known to inhibit JNK phosphorylation. Metformin has recently been shown to have hepatoprotective effects. The aim of the present study is to investigate whether metformin mitigates APAP-induced hepatotoxicity and to ascertain the molecular basis of this effect. Methods We used APAP- and/or metformin-treated Gadd45β knockout (KO) mice and wild type (WT) C57BL/6J control mice. Primary mouse hepatocytes were isolated from WT and Gadd45β KO mice were used for in vitro study. Results Metformin pretreatment protected against APAP toxicity with decreased liver damage, and inhibited APAP-induced prolonged hepatic JNK phosphorylation in WT mice. Gadd45β expression was increased after APAP treatment, and the expression of Gadd45β was further enhanced by metformin. The effects of metformin on APAP-induced liver injury and JNK phosphorylation were abolished in Gadd45β KO mice. Notably, subtoxic doses of APAP caused cell death and sustained JNK phosphorylation in Gadd45β-deficient primary hepatocytes. In parallel, APAP increased mortality, severe liver injury, and JNK activation in Gadd45β KO mice. Interestingly, metformin administered after APAP treatment protected against APAP-evoked hepatotoxicity in WT mice, but not in Gadd45β KO mice. Conclusions This study is the first to demonstrate that metformin shows protective and therapeutic effects against APAP overdose-evoked hepatotoxicity via Gadd45β-dependent JNK regulation. Metformin would be a promising therapeutic strategy for treatment of APAP overdose. Acetaminophen (APAP) overdose is a leading cause of drug-induced acute liver failure. Prolonged c-Jun N-terminal kinase (JNK) activation plays a central role in APAP-induced liver injury and growth arrest, and DNA damage-inducible 45 beta (Gadd45β) is known to inhibit JNK phosphorylation. Metformin has recently been shown to have hepatoprotective effects. The aim of the present study is to investigate whether metformin mitigates APAP-induced hepatotoxicity and to ascertain the molecular basis of this effect. We used APAP- and/or metformin-treated Gadd45β knockout (KO) mice and wild type (WT) C57BL/6J control mice. Primary mouse hepatocytes were isolated from WT and Gadd45β KO mice were used for in vitro study. Metformin pretreatment protected against APAP toxicity with decreased liver damage, and inhibited APAP-induced prolonged hepatic JNK phosphorylation in WT mice. Gadd45β expression was increased after APAP treatment, and the expression of Gadd45β was further enhanced by metformin. The effects of metformin on APAP-induced liver injury and JNK phosphorylation were abolished in Gadd45β KO mice. Notably, subtoxic doses of APAP caused cell death and sustained JNK phosphorylation in Gadd45β-deficient primary hepatocytes. In parallel, APAP increased mortality, severe liver injury, and JNK activation in Gadd45β KO mice. Interestingly, metformin administered after APAP treatment protected against APAP-evoked hepatotoxicity in WT mice, but not in Gadd45β KO mice. This study is the first to demonstrate that metformin shows protective and therapeutic effects against APAP overdose-evoked hepatotoxicity via Gadd45β-dependent JNK regulation. Metformin would be a promising therapeutic strategy for treatment of APAP overdose.