Gut:liver:brain axis and Hepatic Encephalopathy: in vitro assessment of microbial and ammonia modulation in cirrhosis

Gut microbiota alteration represents a key factor in cirrhosis progression and onset of its neuropsychiatric complications. Particularly, gut ammonia production by microbial activity is one of the main factors implicated in Hepatic Encephalopathy (HE) develop, a debilitating cognitive disorder associated with liver disease. Due to the different experimental approaches and inter-patient variability, the gut microbial dynamics during HE treatment with prebiotic, antibiotic and probiotic is only partially understood, Moreover, data on ammonia levels are usually related to circulating levels. In this work, using feces from patients with cirrhosis, we investigated, how gut microbiota modulation by prebiotic, antibiotic and probiotic treatments affects microbial ammonia production using in vitro batch culture models. Fecal samples from six patients with cirrhosis were used to inoculate independent 24-hour batch culture fermentations at controlled pH. Prebiotic (lactulose), antibiotic (rifaximin) and probiotic (VSL#3) treatments were performed alone and in combination. Microbial populations were enumerated using culture independent Fluorescent In Situ Hybridization (FISH), and ammonia concentrations were determined at 0, 4, 10 and 24 hours. Obtained results showed as prebiotic and probiotic treatments modulate the cirrhotic microbiota including a significant increase in Bifidobacteria, seen as beneficial microbiota components. Ammonia levels were reduced by prebiotic and antibiotic treatments with respect to control, while the probiotic mixture VSL#3, when considered alone, seems to increase ammonia levels during the 24 hours. The administration of VSL#3 together with rifaximin and lactulose, decreased ammonia concentrations below the starting level. In this study we emphasizes the potential of gut microbiota modulation as a target for relieving the symptoms of HE by regulating colonic ammonia production. Differences in ammonia production between antibiotic, prebiotic and probiotic treatments suggest a modulation in ammonia production rather than increased size of the “colonic ammonia sink” via microbial biomass alone, as a possible mode of action.