Probiotics and gut health: a special focus on liver diseases

Abstract

Probiotic bacteria have well-established beneficial effects in the management of diarrhoeal diseases. Newer evidence suggests that probiotics have the potential to reduce the risk of developing inflammatory bowel diseases and intestinal bacterial overgrowth after gut surgery. In liver health, the main benefits of probiotics might occur through preventing the production and/or uptake of lipopolysaccharides in the gut, and therefore reducing levels of low-grade inflammation. Specific immune stimulation by probiotics through processes involving dendritic cells might also be beneficial to the host immunological status and help prevent pathogen translocation. Hepatic fat metabolism also seems to be influenced by the presence of commensal bacteria, and potentially by probiotics; although the mechanisms by which probiotic might act on the liver are still unclear. However, this might be of major importance in the future because low-grade inflammation, hepatic fat infiltration, and hepatitis might become more prevalent as a result of high fat intake and the increased prevalence of obesity.

Figure 1

Potential mechanisms of action by which probiotics can promote GI health and the consequences for the liver. Probiotics and surface-layer proteins competitively exclude microbial pathogens from mucosal surfaces. Tight junction proteins, such as zona occludins-1 and claudin1, remain intact and thereby prevent both uptake of intact macromolecules and translocation of viable organisms (BT) to mesenteric lymph nodes, and ultimately to the liver. Through a cascade of signalling events, probiotics enhance production and secretion of anti-inflammatory cytokines, including interleukin-10 and transforming growth factor-β, by a subset of immune cells, referred to as T regulatory cells. Innate immune responses to probiotics include increased mucin and trefoil factor production by goblet cells and enhanced production of antibacterial defensins by Paneth cells and intestinal epithelia. Probiotics might alter the intestinal microbiota and hence limit intestinal bacteria overgrowth (IBO) and the production of lipopolysaccharides (LPS).