Glutamine activates peroxisome proliferator-activated receptor-γ in intestinal epithelial cells via 15-S-HETE and 13-OXO-ODE: a novel mechanism

Glutamine possesses gut-protective effects both clinically and in the laboratory. We have shown in a rodent model of mesenteric ischemia-reperfusion that enteral glutamine increased peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and was associated with a reduction in mucosal injury and inflammation. The mechanism by which glutamine activates PPAR-gamma is unknown, and we hypothesized that it was via a ligand-dependent mechanism. Intestinal epithelial cells, IEC-6, were co-transfected with PPAR-gamma response element-luciferase promoter/reporter construct. Cells were pretreated with increasing concentrations of glutamine +/- GW9662 (a specific antagonist of PPAR-gamma) and analyzed for PPAR-gamma response element luciferase activity as an indicator of PPAR-gamma activation. PPAR-gamma nuclear activity was assessed by electrophoretic mobility shift assay. Cell lysates were subjected to tandem mass spectroscopy for measurement of prostaglandin and lipoxygenase metabolites. A time- and concentration-dependent increase in PPAR-gamma transcriptional activity, but not mRNA or protein, was demonstrated. Activity was abrogated by the PPAR-gamma inhibitor, GW9662, and changes in activity correlated with PPAR-gamma nuclear binding. Glutamine, via degradation to glutamate, activated the metabolic by-products of the lipoxygenase and linoleic acid pathways, 15-S-hydroxyeicosatetraenoic acid and dehydrogenated 13-hydroxyoctaolecadienoic acid, known endogenous PPAR-gamma ligands in the small bowel. This novel mechanism may explain the gut-protective effects of enteral glutamine.