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 (AhRΔhep) 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.