Hepatic Encephalopathy and the Gut Microbiota: An in Vitro Model to Study the Microbial and Ammonia Modulation Upon Prebiotic, Antibiotic and Probiotic Treatment

Background and Aim: The gut microbiota and their metabolites represent a core actor in human host physiology as well as in certain pathological states. Indeed gut microbiota alteration represents a key factor in cirrhosis progression and appear to be related to neuropsychiatric complications. In particular, gut ammonia production by microbial activities is one of the main factors implicated in hepatic encephalopathy (HE) develop. Even if widely studied, the gut microbial dynamics during HE treatment with prebiotics, antibiotics and probiotics is only partially understood due to the different experimental approaches and inter-patient variability. Moreover, data on ammonia levels are usually related to circulating levels and not production by the gut microbiota. Here, we investigated how gut microbiota is modulated by prebiotic, antibiotic and probiotic interventions commonly used to treat HE with particular attention to ammonia and short chain fatty acid (SCFA) production and microbiota composition using in vitro batch culture models. Methods: Fecal samples from 10 patients with cirrhosis (age 66 ± 3.3, 9 male, 1 female, Child–Pugh A (n = 10) and B (n = 3)) and three healthy subjects (age 63 ± 2.5, 1 male, 2 female) were used to inoculate independent 24-h batch culture fermentations at controlled pH (6.8). Prebiotic (lactulose), antibiotic (rifaximin) and probiotic (VSL#3) treatments were performed alone and in combination. Microbial populations were characterized using high-throughput sequencing of the V3–V4 region of the 16S rDNA gene, ammonia concentrations and SCFA content were determined at 0, 4, 10 and 24 h. Results: Across the ten cirrhotic patients, microbial modulation by prebiotic, antibiotic and probiotic treatment differently effected the microbial community dynamics and its metabolism, as revealed by the different SCFA profiles and the specific increase in beneficial bacteria. Prebiotic and probiotic treatments modulated the cirrhotic microbiota including a significant increase in Bifidobacterium, seen as beneficial microbiota components, while ammonia levels were reduced by prebiotic and antibiotic treatments with respect to the control. The probiotic mixture VSL#3, when considered alone, seemed to increase ammonia levels during the 24 h. The administration of VSL#3 together with rifaximin and lactulose, decreased ammonia concentrations below the starting level, impact differently on SCFA levels. Conclusions: This study 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. Moreover increase SCFA levels evidences potential microbial cross-feeding process under specific treatment condition. The authors have none to declare.