Targeting liver aldehyde dehydrogenase-2 prevents heavy but not moderate alcohol drinking

Abstract

Significance It is generally accepted that ethanol and its metabolite acetaldehyde are primarily metabolized in the liver via the alcohol dehydrogenase and the aldehyde dehydrogenase-2 (ALDH2), respectively. However, by using tissue-specific Aldh2 knockout mice, we demonstrated that the liver ALDH2 is only responsible for approximately half of circulating acetaldehyde clearance after acute alcohol intake. Thus, cumulative ALDH2 activity from multiple organs may contribute to circulating acetaldehyde clearance. The present study shows that, although the liver ALDH2 only partially contributes to acetaldehyde clearance, genetic deletion or knockdown of the liver Aldh2 decreases excessive but not light to moderate alcohol drinking. Our results suggest that liver-specific ALDH2 inhibition may be an effective strategy for the treatment of alcohol user disorder with excessive drinking. Aldehyde dehydrogenase 2 (ALDH2), a key enzyme for detoxification the ethanol metabolite acetaldehyde, is recognized as a promising therapeutic target to treat alcohol use disorders (AUDs). Disulfiram, a potent ALDH2 inhibitor, is an approved drug for the treatment of AUD but has clinical limitations due to its side effects. This study aims to elucidate the relative contribution of different organs in acetaldehyde clearance through ALDH2 by using global- (Aldh2−/−) and tissue-specific Aldh2-deficient mice, and to examine whether liver-specific ALDH2 inhibition can prevent alcohol-seeking behavior. Aldh2−/− mice showed markedly higher acetaldehyde concentrations than wild-type (WT) mice after acute ethanol gavage. Acetaldehyde levels in hepatocyte-specific Aldh2 knockout (Aldh2Hep−/−) mice were significantly higher than those in WT mice post gavage, but did not reach the levels observed in Aldh2−/− mice. Energy expenditure and motility were dramatically dampened in Aldh2−/− mice, but moderately decreased in Aldh2Hep−/− mice compared to controls. In the 2-bottle paradigm and the drinking-in-the-dark model, Aldh2−/− mice drank negligible volumes from ethanol-containing bottles, whereas Aldh2Hep−/− mice showed reduced alcohol preference at high but not low alcohol concentrations. Glial cell- or neuron-specific Aldh2 deficiency did not affect voluntary alcohol consumption. Finally, specific liver Aldh2 knockdown via injection of shAldh2 markedly decreased alcohol preference. In conclusion, although the liver is the major organ responsible for acetaldehyde metabolism, a cumulative effect of ALDH2 from other organs likely also contributes to systemic acetaldehyde clearance. Liver-targeted ALDH2 inhibition can decrease heavy drinking without affecting moderate drinking, providing molecular basis for hepatic ALDH2 targeting/editing for the treatment of AUD.