Acetaminophen can induce liver injury with variable clinical outcome. We show that acetaminophen-induced hepatotoxicity is potentiated by activation of the transcription factor aryl hydrocarbon receptor (Ahr). Therefore, varying exposition to activating Ahr ligands might explain individual sensitivity to acetaminophen.BACKGROUND & AIMS: Acetaminophen (APAP)-induced liver injury is one of the most common causes of acute liver failure, however, a clear definition of sensitizing risk factors is lacking. Here, we investigated the role of the ligand-activated transcription factor aryl hydrocarbon receptor (Ahr) in APAP-induced liver injury. We hypothesized that Ahr, which integrates environmental, dietary, microbial and metabolic signals into complex cellular transcriptional programs, might act as a rheostat for APAP-toxicity. METHODS: Wildtype or conditional Ahr knockout mice lacking Ahr in hepatocytes (Alb D/DAhr ) or myeloid cells (LysM D/DAhr ) were treated with the specific Ahr ligand 2-(1'H-indole-3'carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) together with APAP.RESULTS: Ahr activation by ITE, which by itself was non-toxic, exacerbated APAP-induced hepatotoxicity compared to vehicletreated controls, causing 80% vs. 0% mortality after administration of a normally sublethal APAP overdose. Of note, Ahr activation induced hepatocyte death even at APAP doses within the therapeutic range. Aggravated liver injury was associated with significant neutrophil infiltration; however, lack of Ahr in myeloid cells did not protect LysM D/DAhr mice from exacerbated APAP hepatotoxicity. In contrast, Alb D/DAhr mice were largely protected from ITE-induced aggravated liver damage, indicating that Ahr activation in hepatocytes, but not in myeloid cells, was instrumental for disease exacerbation. Mechanistically, Ahr activation fueled hepatic accumulation of toxic APAP metabolites by up-regulating expression of the APAPmetabolizing enzyme Cyp1a2, a direct Ahr downstream target.CONCLUSIONS: Ahr activation in hepatocytes potentiates APAP-induced hepatotoxicity. Thus, individual exposition to environmental Ahr ligands might explain individual sensitivity to hyperacute liver failure.
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