Peripheral alcohol metabolism dictates ethanol consumption and drinking microstructure in mice.

BACKGROUND

Ethanol metabolism is intimately linked with the physiological and behavioral aspects of ethanol consumption. Ethanol is mainly oxidized by alcohol dehydrogenase (ADH) to acetaldehyde and further to acetate via aldehyde dehydrogenases (ALDHs). Understanding how ethanol and its metabolites work together to initiate and drive continued ethanol consumption is crucial for identifying interventions for alcohol use disorder (AUD). Therefore, the goal of our study was to determine how ADH1, which is mainly peripherally expressed and metabolizes >90% of ingested ethanol, modulates ethanol metabolite distribution and downstream behaviors.

METHODS

Ethanol consumption in drinking-in-the-dark (DID) and two-bottle choice (2BC) drinking paradigms, ethanol metabolite concentrations, and lickometry were assessed after ADH1 inhibition and/or in Adh1-knockout (Adh1 KO) mice.

RESULTS

We found that Adh1 KO mice of both sexes exhibited decreased ethanol consumption and preference compared with wild-type (WT) mice in DID and 2BC. ADH1 inhibitor fomepizole (4-MP) also significantly decreased normal and sweetened ethanol consumption in DID studies. Measurement of ethanol and its metabolites revealed that ethanol was increased at 1 h but not 15 min, peripheral acetaldehyde was slightly decreased at both timepoints, and ethanol-induced increases in acetate were abolished after ethanol administration in Adh1 KO mice compared with controls. Similarly, ethanol accumulation as a function of consumption was 2-fold higher in Adh1 KO or 4-MP-treated mice compared with controls. We then used lickometry to determine how this perturbation in ethanol metabolism affects drinking microstructure. Adh1 KO mice consume most of their ethanol in the first 30 min, like WT mice, but display altered temporal shifts in drinking behaviors and do not form normal bout structures, resulting in lower ethanol consumption.

CONCLUSIONS

Our study demonstrates that ADH1-mediated ethanol metabolism is a key determinant of ethanol consumption, highlighting a fundamental knowledge gap regarding how ethanol and its metabolites drive ethanol consumption.