Effects of an enteral glucose supply on protein synthesis, proteolytic pathways, and proteome in human duodenal mucosa

Background: Previous studies have shown that the glucose supply reduces postoperative insulin resistance and improves patient outcomes. However, the effects of luminal glucose on intestinal mucosal proteins remain unknown. Objective: We aimed to assess the effects of an enteral glucose supply on protein synthesis, proteolytic pathways, and proteome in human duodenal mucosa. Design: Twenty healthy volunteers received a 5-h enteral infusion of either saline or glucose (0.12 g . kg(-1) . h(-1)). Simultaneously, a continuous intravenous infusion of L-[1-(13)C]leucine (12 mu mol . kg(-1) . h(-1)) was maintained until endoscopy. The duodenal mucosal protein fractional synthesis rate (FSR) was calculated from leucine enrichments assessed in protein and free amino acid pools by gas chromatography-mass spectrometry. Cathepsin D, calpains, and chymotrypsin-like proteasome mucosal activities were evaluated by using specific fluorogenic substrates. A 2-dimensional PAGE-based comparative proteomics analysis was also performed on additional duodenal mucosal biopsy samples to identify differentially expressed proteins. Results: Duodenal mucosal protein FSR and protease activities were not affected by glucose infusion relative to saline. Nevertheless, the comparative proteomics analysis indicated that 10 protein spots were significantly differentially expressed (ie, at least +/- 1.5-fold modulated; Student's t test, P < 0.05) in response to the glucose infusion relative to saline. Of the 8 proteins identified by mass spectrometry, alpha-enolase, cytoplasmic aconitate hydratase, and glutathione S-transferase omega-1 were upregulated, whereas epoxide hydrolase 2 was downregulated. Conclusion: Enteral glucose supply affected neither duodenal mucosal protein FSR nor activities of mucosal proteases but altered the duodenal mucosal proteome by modulating the expression of several enzymes involved mainly in carbohydrate and xenobiotic metabolism. This trial is registered at clinicaltrials.gov as NCT00213551. Am J Clin Nutr 2011;94:784-94.