Activation of AhR-NQO1 Signaling Pathway Protects Against Alcohol-Induced Liver Injury by Improving Redox Balance

BACKGROUND & AIMS: Aryl hydrocarbon receptor (AhR) is a liver-enriched xenobiotic receptor that plays important role in detoxification response in liver. This study aimed to investigate how AhR signaling may impact the pathogenesis of alcohol-related liver disease (ALD). METHODS: Chronic alcohol feeding animal studies were conducted with mouse models of hepatocyte-specific AhR knockout (AhR(Δhep)) and NAD(P)H quinone dehydrogenase 1 (NQO1) overexpression, and dietary supplementation of the AhR ligand indole-3-carbinol. Cell studies were conducted to define the causal role of AhR and NQO1 in regulation of redox balance and apoptosis. RESULTS: Chronic alcohol consumption induced AhR activation and nuclear enrichment of NQO1 in hepatocytes of both alcoholic hepatitis patients and ALD mice. AhR deficiency exacerbated alcohol-induced liver injury, along with reduction of NQO1. Consistently, in vitro studies demonstrated that NQO1 expression was dependent on AhR. However, alcohol-induced NQO1 nuclear translocation was triggered by decreased cellular oxidized nicotinamide adenine dinucleotide (NAD(+))-to-NADH ratio, rather than by AhR activation. Furthermore, both in vitro and in vivo overexpression NQO1 prevented alcohol-induced hepatic NAD(+) depletion, thereby enhancing activities of NAD(+)-dependent enzymes and reversing alcohol-induced liver injury. In addition, therapeutic targeting of AhR in the liver with dietary indole-3-carbinol supplementation efficiently reversed alcoholic liver injury by AhR-NQO1 signaling activation. CONCLUSIONS: This study demonstrated that AhR activation is a protective response to counteract alcohol-induced hepatic NAD(+) depletion through induction of NQO1, and targeting the hepatic AhR-NQO1 pathway may serve as a novel therapeutic approach for ALD.