Myeloperoxidase-Mediated Metabolic Activation of Aristolochic Acid I Aggravates Liver Injury Under Inflammatory Conditions

This study aimed to characterize the roles of inflammation and myeloperoxidase (MPO) in aristolochic acid I (AAI)-induced liver injury and to identify the resulting reactive metabolites. We found that acetaminophen-induced inflammation exacerbated AAI hepatotoxicity in mice and increased hepatic AAI-related protein adduction. While Mpo-knockout mice exhibited attenuated liver injury and fewer AAI-protein adduction. Further investigation revealed that MPO mediates the metabolic activation of AAI, specifically its metabolite aristolactam I (ALI). An ALI-chloride (ALI-Cl) intermediate was identified in both ALI/leukocyte incubations and ALI/hypochlorous acid incubations. ALI-Cl exhibited chemical reactivity toward N-acetylcysteine (NAC) and cysteine, forming ALI-NAC or ALI-cysteine conjugates when ALI was incubated with leukocytes. Additionally, ALI-Cl also reacted with sulfhydryl groups on cysteine residues of cellular protein in leukocytes. After enzymatic hydrolysis, the resultant ALI-cysteine adduct matched that identified in the liver digests of AAI-exposed mice. This study facilitates the understanding of the mechanisms underlying AAI toxicity under inflammatory conditions.