Multiple endogenous aldehydes amplify acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury is a leading cause of liver injury cases in some Western countries. Although APAP hepatotoxicity is well-documented, the precise mechanisms underlying its pathogenesis remain incompletely understood. This study investigates the role of endogenous aldehydes in exacerbating APAP-induced liver injury through covalent modification of hepatic proteins. Here, 74 free biogenic aldehydes were identified in the mouse liver following APAP administration. Among these, 47 aldehydes exhibited the ability to covalently bind to hepatic proteins, with 29 being reported in the liver for the first time. Protein adducts of 29 aldehydes peaked at 2-3 h post-APAP treatment. Inhibition of APAP metabolic activation using the CYP2E1 inhibitor 4-methylpyrazole significantly reduced aldehyde-mediated protein adduction. Furthermore, activation of aldehyde dehydrogenase-2 by Alda-1 and the nucleophilic trapping reagent N-acetyl-l-lysine attenuated both protein adduction by aldehydes and APAP-induced liver injury. Notably, these biogenic aldehydes demonstrated intrinsic hepatotoxicity, with their combined effects leading to liver injury through additive covalent protein modifications. Additionally, aldehydes induced c-Jun amino-terminal kinase phosphorylation, further amplifying APAP-induced liver damage. In conclusion, our findings reveal that endogenous aldehydes triggered by the reactive metabolite of APAP amplify liver damage through "additive effects" on covalent protein modification. This study provides novel insights into the mechanisms of APAP hepatotoxicity and highlights potential therapeutic targets for mitigating liver injury.