Mechanism of glutamine-mediated amelioration of lipopolysaccharide-induced IL-8 production in Caco-2 cells.

Abstract

The mechanism of glutamine (Gln)-mediated down-regulation of inflammation in the intestine is poorly understood. We hypothesize that Gln down-regulates lipopolysaccharide (LPS)-stimulated IL-8 production in intestinal epithelial cells via transcription factors that counteract the effect of LPS-mediated increase in IL-8. Caco-2 cells were incubated with different doses of Gln with or without methionine sulfoximine (MS), an inhibitor of glutamine synthetase for 24 h before stimulation by LPS (100 microg/ml for 24 h). Inhibitors of the mitogen activated protein kinase (MAPK) family were added to cells for 1.5 h following stimulation by LPS. The p38 inhibitor SB 203580 resulted in a significant decrease in IL-8 peptide production (p < 0.01). However, p38 MAPK activity increased with Gln (p < 0.05), suggesting that this was not involved with Gln-mediated down-regulation of IL-8. Screening of 54 transcription factors demonstrated that STAT-4 was the only inflammation-related transcription factor that was up-regulated by Gln depletion and down-regulated with Gln supplementation (2-fold increase), paralleling IL-8 production. EMSA analysis confirmed these findings (3.5-fold increase). These results indicate that Gln deprivation enhances IL-8 production by Caco-2 cells after LPS stimulation and that down-regulation of IL-8 production with Gln is associated with alterations in STAT-4 transcription factor binding.