Butyrate inhibits and Escherichia coli-derived mitogen(s) stimulate DNA synthesis in human hepatocytes in vitro

Bacterial constituents and products of the bacterial metabolism pass from t he gut lumen to the portal vein and may influence the homeostasis of the li ver. Our aim is to examine whether DNA synthesis of human hepatocyte cell l ines is affected by constituents of Escherichia coli species as well as by intracolonic products of bacterial fermentation that reach the liver via th e portal vein. Supernatant solutions and bacterial cell fractions (containing either whole dead bacteria, cell walls, cytosol or non-soluble intracellular components ) off. coli K12 and off. coli species from rat fecal flora were separated b y multi-step centrifugation, French press, and microfiltration. The supernatant solution and the cell fractions were incubated with a human hepatoma cell line (Hep-G2) and with a cell line derived from non-malignan t human liver cells (Chang cells) for 24 h. The cells were labeled with tri tiated thymidine before processing to autoradiography. DNA synthesis was es timated by the labeling index (LI%). DNA synthesis was also estimated follo wing incubation of Hep-G2 cells with short chain fatty acids (acetic, propi onic, butyric and succinic acid), acetaldehyde, and ammonium chloride. Epid ermal growth factor and a water extract of Helicobacter pylori were used as references. The fractions of E. coli from rat fecal flora containing cytosol and non-so luble intracellular components significantly increased the labeling index i n both Hep-G2 and Chang cells (p<0.05). In addition, the supernatant soluti on significantly increased the LI in Chang cells(p<0.05). Epidermal growth factor increased the LI of Hep-GZ cells dose-dependently(p<0.05). Butyric a cid reduced DNA synthesis at 10(-4) M (p<0.05). The highest doses of acetal dehyde were cytotoxic and reduced the LI. Escherichia coil species contain mitogenic factors to human hepatocytes. Th e mitogen(s) are present in the supernatant solution, in the cytosol and in non-soluble intracellular components. Butyrate, which is a product of bact erial fermentation of colonic substrates inhibit DNA synthesis in the hepat ocyte cell lines. Our findings suggest that soluble mitogen(s) that diffuse from the microorganism to the outer environment, intracellular bacterial c onstituents, and products of the bacterial metabolism that reach the liver via the portal vein may influence the cell kinetic steady-state of hepatic cells.