Commensal Gut Microbiota Modulates the Susceptibility to Acetaminophen-Induced Hepatotoxicity

Overdose of acetaminophen (APAP) can cause severe hepatotoxicity. APAP-induced hepatotoxicity exhibits large inter-individual variability and the risk factor(s) for the susceptibility remain unclear. Human body harbors trillions of bacteria in the gut which have huge impact on host physiology.Therefore, we hypothesized that differential gut microbiota modulate APAP-induced hepatotoxicity and can be a potential risk factor for APAP hepatotoxicity In chapter 1, we summarize the mechanism of APAP-induced hepatotoxicity and previous studies which suggest the role of gut microbiota in APAP metabolism and/or APAP hepatotoxicity. In Chapter 2, our findings which suggest the role of gut microbiota in modulating the susceptibility to APAP toxicity and underlying mechanism are described. C57BL/6 mice from different vendors, Jackson (JAX) or Taconic (TAC), showed different response to APAP hepatotoxicity where TAC mice developed higher toxicity which disappeared upon cohousing. Transplantation of cecum materials collected from JAX or TAC mice to germ free (GF) mice recapitulated difference in APAP hepatotoxicity observed in JAX and TAC mice. Using unbiased metabolomics profiling with portal vein serum and liver tissues and in vitro toxicity screening test with mouse primary hepatocytes, we identified a gut microbiota-derived metabolite, 3-phenylpropionate (PPA) whose levels were higher in cecum and serum from mice harboring JAX gut microbiota, reduced APAP hepatotoxicity. Supplementation of PPA in drinking water alleviated APAP hepatotoxicity in vivo. To determine underlying mechanism of PPA mediated protection against APAP hepatotoxicity, we performed time course experiments using mice treated with PPA or normal water and found that PPA decreased CYP2E1 protein expression, a major drug metabolizing enzyme responsible for bioactivation of APAP to NAPQI, a toxic metabolite which consequently led to low bioactivation of APAP to NAPQI (a critical initiating step for APAP hepatotoxicity). Mice with JAX gut microbiota which increases PPA level in the host also exhibited lower CYP2E1 protein expression and activity of NAPQI formation. This suggest that JAX gut microbiota reduces APAP hepatotoxicity by increasing PPA level in the host which decreases CYP2E1 protein expression and thus NAPQI formation. Findings from this study demonstrated gut microbiota-liver interaction mediated by a gut bacteria-derived metabolite in modulating APAP hepatotoxicity.