The effects of ethanol and tributyrin on Alzheimer's disease pathogenesis in 3×Tg-AD mice.

Alzheimer’s disease (AD) is a complex progressive neurodegenerative dementia with clinical hallmarks of amyloid-β plaques, hyper-phosphorylated tau in neurofibrillary tangles (NFTs), and neurodegeneration. Chronic, excessive alcohol consumption is associated with an increased risk for developing AD and other dementias. Both AD and chronic alcohol consumption are associated with dysbiosis in the gut microbiome (GM) characterized by a significant loss of beneficial butyrate-producing bacteria within the Firmicutes phylum. Previous studies demonstrate that chronic alcohol consumption accelerates AD pathogenesis in the 3×Tg-AD mouse model and that oral tributyrin (TB) supplementation in 3×Tg-AD mice reduces age-associated GM dysbiosis and AD-associated neurobehavioral deficits and neuropathology. Similarly, TB supplementation reduces EtOH-associated pathogenic changes to the GM in C57BL6 mice. Therefore, we hypothesize that chronic alcohol consumption will accelerate AD-associated GM dysbiosis and neurobehavioral deficits in 3×Tg-AD mice and TB supplementation will reduce EtOH-associated changes. To test this hypothesis, female 3×Tg-AD mice were treated with either weekend-like binge EtOH or alternating 10% and 20% EtOH in drinking water for four months. Groups of EtOH treated mice also received TB supplementation (2g/kg) twice per week throughout EtOH exposure and non-transgenic mice were used as controls. Analyses were performed on the GM, behavior and memory, biochemical endpoints associated with AD pathogenesis, and the mid-brain region with RNA-seq. Chronic weekend binge EtOH induced persistent memory deficits in female 3×Tg-AD mice along with neurodegeneration, disrupted neuronal homeostasis, and increased tau phosphorylation at Thr217 accompanied by increased activation of the tau phosphorylation enzyme GSK3β. Chronic alternating 10% and 20% EtOH in drinking water induced persistent gut barrier breakdown and peripheral endotoxemia that was reduced with TB supplementation. Additionally, TB supplementation improved grip strength in both 3×Tg-AD and NonTg mice while reducing anxiety measures in only 3×Tg-AD mice. Nevertheless, 16S rRNA gene sequencing of the GM revealed significant changes only with alternating 10% and 20% EtOH treatments, and no additional effects of TB supplementation. Together, these studies highlight the persistent neurodegenerative effects of chronic binge EtOH in genetically prone AD mice, as well as showing potential therapeutic effects of TB supplementation, improving AD-associated neurobehavioral deficits and reducing EtOH-induced peripheral endotoxemia.