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

Abstract

Le Bacquer, Olivier, Christian Laboisse, and Dominique Darmaun. Glutamine preserves protein synthesis and paracellular permeability in Caco-2 cells submitted to "luminal fasting." Am J Physiol Gastrointest Liver Physiol 285: G128-G136, 2003; 10.1152/ajpgi.00459.2002.-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 [ 2 H3]leucine with or without glutamine, and the fractional synthesis rate (FSR) of total cell protein was determined from [ 2 H3]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 (Ϫ38, Ϫ40, and Ϫ40%, respectively), protein FSR (Ϫ20%), 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

Glutamine stimulates translation of uncoupling protein 2mRNA

“…Accordingly, efforts have been made to provide conclusive evidence that glutamine indeed stimulates, in a specific way, the translation of the coding sequence situated downstream the wild-type UCP2 mRNA 5UTR (Figs 6-9) and to rule out the possibility that the effect of glutamine on UCP2 production could be the result of a general effect of glutamine on cellular metabolism (Fig. 5) as observed in other conditions [18].…”

Corticosteroids increase glutamine utilization in human splanchnic bed

“…The ultimate fate of the glutamine extracted in the splanchnic bed remains to be elucidated. Glutamine is known to play a pivotal role in the gut, because glutamine not only serves as a preferred fuel for the enterocytes but also helps maintain rates of intestinal protein synthesis (8,30,31) and cell integrity and stimulates immune function as well (9). During inflammation, increased glutamine consumption by lymphocytes and macrophages in gut-associated lymphoid tissue (GALT) could occur, as these cells are avidly utilizing glutamine (27).…”

“…nutrition; protein metabolism; stable isotopes; stress; gut GLUTAMINE PLAYS AN IMPORTANT role in the maintenance of intestinal function (39,43,46). Glutamine indeed is both a preferred fuel (9, 47) for enterocytes and a precursor for the intestinal synthesis of purines, pyrimidines (9), and glutathione (37), and it may regulate gut protein synthesis (21,30,32). In addition, glutamine is a major donor of carbon for gluconeogenesis (19).…”

In Human Entrocytes, GLN Transport and ASCT2 Surface Expression Induced by Short-Term EGF are MAPK, PI3K, and Rho-Dependent

“…In intestinal cell models, Gln prevents increased permeability after fasting [2] or treatment with acetaldehyde [3] and stimulates amino acid transport after ischemia-reperfusion injury [4].…”