Effect of germfree state on the capacities of isolated rat colonocytes to metabolize n-butyrate, glucose, and glutamine

Abstract

Background & aims: Among substrates available to the colonic mucosa, n-butyrate from bacterial origin represents a major fuel. The present work investigated possible modifications of energy substrate metabolism in colonocytes isolated from germfree rats.

Methods: Colonocytes isolated from germfree vs. conventional rats were incubated (30 minutes at 37 degrees C) in the presence of 14C-labeled n-butyrate (10 mmol/L), glucose (5 mmol/L), or glutamine (5 mmol/L). 14CO2 and metabolites generated were measured. Possible regulatory steps were also investigated.

Results: Glucose use rate was 25% lower in germfree rat colonocytes due to a reduced glycolytic capacity in these cells. Differences in 6-phosphofructo-1-kinase activity could account for this decrease. In contrast, glutamine use rate was 45% higher, and this was correlated with a higher maximum velocity of glutaminase in these cells. Nevertheless, the capacities to oxidize glucose and glutamine remained unchanged. Although the capacity to use n-butyrate was maintained in colonocytes of germfree rats, the ketogenic capacity was lower, whereas the capacity to oxidize n-butyrate was higher. The mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme A synthase protein was identified in the colonic mucosa. Moreover, the messenger RNA and amount of protein were 75% lower in the germfree state.

Conclusions: The absence of an intestinal microflora induces specific changes in the metabolic capacities of colonocytes.