Gut bacteria may control development of hepatocellular carcinoma
The gut continually encounters many environmental factors, including pathogens and foods. Therefore, the gut requires specialized mechanisms to protect it from the adverse effects of these factors while maintaining gut homeostasis. It has been estimated that more than 1014 microorganisms live in the gastrointestinal (GI) tract, with the numbers and species of these microbes differing by site within the GI tract (1). Gut bacteria have been shown to digest complex carbohydrates and plant polysaccharides, neither of which may be metabolized by human enzymes, and to produce short-chain fatty acids (SCFAs) that regulate cell differentiation and proliferation and have anti-inflammatory or immunomodulatory effects. These bacteria also produce a variety of essential vitamins, including vitamin B12, vitamin K, folate and biotin, which are not produced by host cells. Moreover, gut microbiota play an important role in the regulation of systemic immunity, by stimulating intestinal epithelial cells to produce transforming growth factor-β which regulates the development of FoxP3+ regulatory T (Treg) cells and type 17 helper (Th17) cells (2). Taken together, these findings indicate that gut microbiota are greatly involved in the maintenance of host health, which in turn implies that dysbiosis of gut flora could cause various diseases. Because blood from the intestines flows into the liver, the liver is directly affected by metabolites, cytokines and bacteria (via bacterial translocation) present in the intestines. Therefore, the liver is the organ most affected by the intestinal environment created by microbiota.