Liver molecular networks associated with drinking behavior in nonhuman primates

Consumed ethanol is primarily metabolized by the liver, with resulting products of ethanol metabolism, acetaldehyde and salsolinol that influence brain activity and alcohol drinking behavior. Alcohol consumption in humans is highly heritable with numerous associated genetic variants. Functional variants in the ADH and ALDH genes influence liver alcohol metabolism but only account for a small percentage of variance in consumption. We hypothesized that variation in hepatic molecular networks during the induction phase, where animals consume identical amounts of alcohol, predicted variation in drinking behavior during subsequent ad libitum access in nonhuman primates (NHPs).

We studied male rhesus macaques at baseline and during the uniform consumption phase that became discordant at the later ad libitum phase. The study design increased the likelihood of identifying functional molecular differences between light drinkers (LD) and very heavy drinkers (VHD) before animals exhibited differences in drinking behavior. We analyzed liver biopsies, provided by the Monkey Alcohol and Tissue Research Resource (MATRR), collected at baseline and after 3 months of uniform consumption, using multiomic and histologic methods.

We found hepatic molecular pathways and networks differed between LD and VHD at baseline and in response to identical consumption. Notably, Sirtuin Signaling and a MYC-regulated network were significantly enriched for differentially abundant molecules in both LD and VHD response to uniform alcohol consumption. Potential epigenomic mechanisms regulating response to alcohol consumption were significantly different with LD response primarily through microRNAs, and VHD primarily through DNA methylation. Histological analysis of liver biopsies showed no liver pathologies in either group.

Our findings of differences in molecular networks prior to alcohol consumption suggest genetic variation contributes to drinking phenotypes, and differences in molecular response to uniform alcohol consumption suggest epigenetic mechanisms regulating liver networks also contribute to the development and progression of drinking phenotypes in NHP.