Trimethylamine N‐oxide exacerbates acetaminophen‐induced liver injury by interfering with macrophage‐mediated liver regeneration

Acetaminophen (APAP)‐induced acute liver injury (AILI) is the most frequent cause of acute liver failure in developed countries. Trimethylamine N‐oxide (TMAO) is a metabolite derived from the gut microbiota and is relatively high in the circulation of the elderly, individuals with diabetes, and heart disease. Herein, we showed that TMAO exacerbates APAP hepatotoxicity. It is possible that delayed liver repair and regeneration that resulted from reduced macrophage accumulation was responsible for this combined hepatotoxicity. Moreover, matrix metalloproteinase 12 (Mmp12), expressed predominantly by macrophages, were reduced by TMAO in vitro and in vivo. This led to the inhibition of macrophage migration and a subsequent decrease in the recruitment of proresolving macrophages to the necrosis area. Furthermore, the administration of recombinant Mmp12 mitigated the enhanced hepatotoxicity in mice cotreated with TMAO and APAP. Overall, this study indicates that TMAO exacerbates APAP‐induced hepatotoxicity by hindering macrophage‐mediated liver repair, which might stem from the inhibition of Mmp12. These findings imply that liver damage in patients with high levels of circulating TMAO may be more severe in AILI and should exercise caution when treating with NAC. When taken as an overdose, APAP was transformed to N‐acetyl‐para‐benzo‐quinone Imine (NAPQI), which causes hepatocytes necrosis. This leads to activation of resident hepatic macrophages (Kupffer cells). Activated Kupffer cells and hepatocytes secrete a variety of proinflammatory cytokines and chemokines, such as CCL2/MCP1(chemokine C‐C motif ligand 2) and CX3CL1 (C‐X3‐C motif chemokine ligand 1), leading to sterile inflammation and leukocyte infiltration. At the late phase of APAP‐induced liver injury, macrophages undergo phenotypic and functional transition for effective liver regeneration. These reparative macrophages secrete anti‐inflammatory cytokines and protease to facilitate proper repair. Matrix metalloproteinase 12 (Mmp12), a protease involved in macrophage migration, also have a crucial role in regulating the resolution of inflammation. Trimethylamine N‐oxide (TMAO), a metabolite derived from the gut microbiota, exerts a negative influence on macrophages migration in vitro and in vivo by inhibiting Mmp12 expression. Decreased macrophage recruitment leads to retarded liver regeneration and enhanced hepatotoxicity in APAP‐induced liver injury after TMAO intervention. Accordingly, increased synthe