Milk consumption and health outcomes in Western and Asian populations.

In chronic diseases, including cirrhosis, sarcopenia and fatigue are related to impaired ammonia disposal with consequent hyperammonemic stress (HAS) in cells (). In addition to these well-recognized sequelae, patients with cirrhosis and other chronic diseases have an altered gut microbiome (GMB) (, ). Gut dysbiosis contributes to the progression of liver disease and may exacerbate extrahepatic complications (). Specifically, altered GMB contributes to lower skeletal muscle mass (), sarcopenia (), endothelial dysfunction (), and hepatic encephalopathy (). Ammoniagenesis by the GMB is a significant source of hyperammonemia in cirrhosis (), and HAS causes perturbations in multiple organs in disease (), supporting a link between microbiome composition, nitrogen metabolism, and systemic complications. Current evidence shows that HAS causes sarcopenia or skeletal muscle loss and contractile dysfunction, which contribute to physical frailty, resulting in greater morbidity and mortality in chronic diseases (). There is also compelling evidence that dysbiosis in chronic diseases, especially cirrhosis, contributes to increased GMB-derived ammoniagenesis (, , ). In chronic diseases, exercise increases muscle ammoniagenesis, which can limit beneficial responses and potentially contribute to tissue injury (). Exercise modulates the GMB and promotes taxa associated with gut and systemic health (, ). Unlike forced exercise protocols, voluntary wheel running (VWR) in mice replicates the responses to human endurance exercise (, , ). A systematic review evaluating human and preclinical data concluded that in humans, exercise lowered the Bacilliota/Bacteroidetes ratio, with consistent increases in and genera. Endurance exercise increases alpha-diversity with expansion of beneficial taxa, including , (), and members of the Bacilliota phylum in preclinical models and humans (), while sedentary high-fat-fed mice had decreased (). serves as a key anti-inflammatory butyrate producer and is reduced in inflammatory bowel disease. is linked to leanness, favorable plasma glucose and fatty acid profiles, and bile acid regulation (, ). supports fiber degradation, short-chain fatty acid (SCFA) production, immune tolerance, and metabolic health. promotes gut barrier integrity and is linked to mental health via gut-brain axis signaling (, ). Thus, multiple metabolite-driven pathways contribute to microbiome-mediated beneficial responses to voluntary endurance exercise (). The mode of exercise is also an important determinant of physiological and microbial responses (). Unlike VWR, forced exercise protocols (swim-to-exhaustion, forced treadmill running) induce stress in rodents that do not consistently recapitulate human endurance adaptations (, , ). Despite robust data in healthy rodents, there are few data on the GMB responses to VWR in disease models. Recent data show that VWR partially reverses the consequences of HAS in mice (, ); however, it is not known if the GMB changes contribute to these beneficial effects. Bacterial taxa can either produce (, ) or metabolize ammonia (), and exercise-induced modulation of the microbiome can influence systemic ammonia handling. In cattle, the types of substrates utilized and free ammonia have been reported to determine GMB (), but whether such responses occur in rodent models is not known. Therefore, we evaluated the interaction between VWR and HAS in a validated mouse model with constant infusion of ammonium acetate (AmAc) ().