Gut Microbiota and the Liver: A Tale of 2 Cities: A Narrative View in 2 Acts.

Microbes are mostly important for the digestion of food, the absorption of some micronutrients, and the production of vitamins. The microbiota stimulates lymphoid structures in the gastrointestinal mucosa and decrease pathogens by competing for nutrients and space. Bacterial translocation is defined as the escape of gut bacteria and their products through the intestinal mucosa to the outside of the intestine as portovenous or systemic circulation. This is induced by a leaky gut barrier. There is evidence for a role of intestinal permeability in the pathogenesis of nonalcoholic fatty liver disease. In the liver, bacterial products can bind to their specific pathogen recognition receptors on parenchymal and nonparenchymal cells, producing an inflammatory response and enhancing disease progression. When binding, bacterial products bind to their receptors, initiating intracellular signalling and inducing an inflammatory cascade, thus accelerating liver cell damage and fibrosis. However, the liver can also increase gut permeability, producing proinflammatory cytokines, and reversing them into the blood stream. Modification of the gut microbiota could lead to benefit in patients with liver disease. Nonabsorbable antibiotics (rifaximin) prevent and relieve overt encephalopathy. Probiotics alone are not capable of turning back overt encephalopathy, but could prevent its development. There is some evidence that probiotics could relent the progression of nonalcoholic liver disease, and possibly reverse steatosis. Antibiotics, such as fluoroquinolones, reduce the risk of development of the first episode of spontaneous bacterial peritonitis and mortality in cirrhotic patients.