Influence of glutamine-supplemented Caco-2 cells on cytokine production of mononuclear cells

Background: Caco-2 cells, cultured with mononuclear cells, were used as an in vitro model of human intestinal cell function. This study shows the effect of glutamine (Gln) supplementation on the production of tumor necrosis factor alpha, interleukin-10 (IL-10), and interleukin-6 (IL-6). Methods: Confluent Caco-2 cells were cultured in media with Gln at 0 mmol/L, 4 mmol/L, or 10 mmol/L +/- 1 mug/mL lipopolysaccharide (LPS), treated with fluorescein isothiocyanate- (FITC-) conjugated intercellular adhesion molecule-1 (ICAM-1) mononuclear antibody, and assessed for ICAM-1 expression levels via flow cytometry. Confluent Caco-2 cells alone in apical inserts, or mononuclear cells (MNCs) alone in basal chambers of transwells, were cultured in media with 0 mmol/L, 4 mmol/L, or 10 mmol/L Gln. Supernatants were taken to assess cytokine and endotoxin levels. Confluent Caco-2 cells in apical inserts of transwells were cultured in media containing Gln at 0 mmol/L, 4 mmol/L, or 10 mmol/L, whereas MNCs were cultured in the basal chamber in media containing Gln at 4 mmol/L +/- LPS. Supernatants were collected to determine cytokine levels in each chamber. Results: With Gln supplementation of the media at 10 mmol/L, enterocytes displayed a decrease in ICAM-1 expression. MNCs showed a decrease in tumor necrosis factor a and IL-6 production and an increase in IL-10 production when incubated with Caco-2 cells in media supplemented with Gln at 10 mmol/L. Conclusions: Although cytokine production by Caco-2 or mononuclear cells incubated alone was not influenced by the Gln concentration of the media, cultured together, Gln levels affected cytokine production by mononuclear cells, which suggests that Caco-2 cells produce mediators in Gln-rich conditions that can influence mononuclear cell cytokine production.