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Excerpt
Aim. We wanted to examine the role of apical (luminal) glutamine on bacterial translocation in monolayers of differentiated Caco-2 cells and further investigate its effects in a weanling rabbit ileal loop model for necrotizing enterocolitis (NEC).
Methods. Caco-2 cells were grown on polycarbonate membranes for 12 days. The differentiation of cells was estimated by measuring the brush border membrane enzyme activities. Part of the monolayers was kept on an isonitrogenous glutamine-free medium for 4-48 hours. Bacterial translocation was measured after 4, 18, 24 and 48 hours of glutamine deprivation using an E. coli strain isolated from an infant with NEC. Similar studies were conducted after glutamine replenishment. Apical and basolateral enzyme activities and intracellular ATP concentration were measured concurrently. In vivo studies were carried out by co-inoculation of rabbit ileal loops with different concentrations of glutamine (1, 4, 8 mM) and E. coli.
Results. Absence of apical glutamine for 48 hours resulted in a 4-10-fold increase in bacterial translocation through the fully differentiated Caco-2 cells. Reduction in translocation was noted only after 18 hours of glutamine replenishment and reached normal levels after 48 hours. There were no significant changes in the transepithelial resistance or tight junction structure in the absence of glutamine. Glutamine deprivation resulted in a significant decrease in lactase, maltase and glucoamylase activities at 48 hours and in Na/K-ATPase enzyme activity at 18 hours (n=6, P<0.05). Addition of glutamine prevented E. coli induced damage to the mucosa and deeper intestinal layers in the ileal loops.
Conclusions. Our results demonstrate that presence of apical glutamine is important for the prevention of bacterial translocation across the enterocyte monolayer and in the protection against E. coli induced NEC-like intestinal damage. These data indicate that luminal glutamine exerts its effects primarily on enterocytes. The possible clinical implications of these phenomena warrant further investigations.
