In vitro alterations in fecal short chain fatty acids and organic anions induced by the destruction of intestinal microflora under hypotonic and aerobic conditions

The pathogenesis of inflammatory bowel disease (IBD) remains unknown. It has been suggested that luminal factors such as the microflora, short chain fatty acids (SCFAs), food antigens and so on play important roles in the disease progression. Many reports have revealed alterations in the SCFA and organic acid concentration of the colon, especially increased lactate and decreased butyrate, in IBD patients. The mechanisms responsible for these alterations, however, remain unclear. Therefore, the effects of aerobic conditions on the alterations in the SCFA and organic anion levels in the feces was evaluated. Fecal specimens were collected from 5 healthy volunteers. Under aerobic condition, a mixture of feces and distilled water was incubated in 37°C for 1 and 3 h. The pH, osmotic pressures, the concentrations of potassium, bicarbonate, SCFA and organic anion, and the activities of α-amylase and lactate dehydrogenase (LDH) in the mixture were then measured. We also examined any changes in the microscopic microflora under the hypotonic and aerobic conditions. The results showed the osmotic pressure, and the concentrations of lactate and SCFAs (formate, acetate, propionate and n-valerate) were progressively increased with longer incubation times, and reached a statistically significant difference. In particular, the ratios of lactate, succinate and n-valerate after 1 and 3 h of incubation increased remarkably. In contrast, the electrolyte levels and both α-amylase and LDH activities were not altered significantly. Microscopically, the microflora in the mixture decreased with prolonged incubation times. These data suggest that under these in vitro conditions, the organic anion and SCFA levels in the feces easily increased. It is probable that the alterations in the SCFA and organic anion levels in IBD patients may be partly due to intracellular components derived from microflora destroyed under hypotonic and aerobic conditions in the colonic lumen, for example caused by mucosal bleeding. These alterations may influence the pathogenesis and progression of IBD.