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MUCOSAL BIOLOGY

Glutamine preserves protein synthesis and paracellular permeability in Caco-2 cells submitted to "luminal fasting"

Institut National de la Santé et de la Recherche Médicale U.539, Centre de Recherche en Nutrition Humaine, 44093 Nantes, France

Submitted 25 October 2002 ; accepted in final form 27 February 2003

This study used polarized cell line Caco-2 as a model of human enterocytes to determine: 1) whether deprivation of nutrients on the apical (luminal) side of the epithelium (fasting) alters protein synthesis in enterocytes; 2) if so, whether glutamine can attenuate the effects of fasting; and 3) whether the effects of glutamine depend on its route (i.e., apical vs. basolateral) of supply. Caco-2 cells were submitted to nutrient deprivation on the apical side to mimic the effects of fasting, whereas the basolateral side of the epithelium remained exposed to regular medium. Cells were then incubated with [²H₃]leucine with or without glutamine, and the fractional synthesis rate (FSR) of total cell protein was determined from [²H₃]leucine enrichments in protein-bound and intracellular free leucine measured by gas chromatography/mass spectrometry. A 24-h apical nutrient deprivation (luminal fasting) was associated with a decline in intracellular glutamine, glutamate, and glutathione concentrations (–38, –40, and –40%, respectively), protein FSR (–20%), and a rise in passage of dextran, an index of transepithelial permeability. In fasted cells, basolateral or luminal glutamine supplementation did not alter the glutathione pool, but it restored protein FSR and improved permeability. The effects of glutamine were abolished by 6-diazo-oxo-L-norleucine, an inhibitor of glutaminase, and was mimicked by glutamate. We conclude that in Caco-2 cells, protein synthesis depends on nutrient supply on the apical side, and glutamine regardless of the route of supply corrects some of the deleterious effects of fasting in a model of human enterocytes through its deamidation into glutamate.

stable isotopes; leucine; small intestine; gut trophicity; human enterocyte

This article has been cited by other articles:

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