Short chain fatty acid and glucose metabolism in isolated pig colonocytes: modulation by NH4+

Short chain fatty acids (SCFA) from bacterial origin, as well as glucose from vascular origin, are among fuel substrates available to the colonic mucosa. The present work investigated the possible modulation by another bacterial metabolite, i.e. ammonia, of the capacities of colonic epithelial cells to metabolize these substrates. Viable colonocytes were isolated from the proximal colon of 40-50 kg pigs fed a standard diet and were incubated (30 min, 37 degrees C) in the presence of a concentration range of 14C-labeled n-butyrate or acetate, or 14C-labeled glucose (5 mM), with or without NH4Cl (10 mM) addition. 14CO2 and metabolites generated were measured. Butyrate utilization resulted in a high generation of ketone bodies (acetoacetate and beta-OH-butyrate), in addition to 14CO2 production. However, the net ketone body generation was significantly decreased for butyrate concentrations higher than 10 mM. In contrast to n-butyrate, acetate when given as the sole substrate got preferentially metabolized in the oxidation pathway. Acetate metabolism was not affected by NH4Cl, thus indicating that the tricarboxylic acid cycle was unchanged. Conversely, 14CO2 and ketone body production from butyrate were decreased by 30% in the presence of NH4Cl, suggesting that butyrate activation or beta-oxidation was diminished. Glucose utilization rate was increased by 20%, due to an increased glycolytic capacity in the presence of NH4Cl. A dose-dependent stimulation of phosphofructokinase activity by NH4+ could account for this effect. It is concluded that ammonia, whose physiological concentration is high in the colonic lumen, can modulate the metabolism of two major substrates, n-butyrate and glucose, in colonic epithelial cells.