Comparison of cytokine modulation by natural peroxisome proliferator-activated receptor γ ligands with synthetic ligands in intestinal-like Caco-2 cells and human dendritic cells-potential for dietary modulation of peroxisome proliferator-activated receptor γ in intestinal inflammation

Background: Peroxisome proliferator-activated receptor gamma (PPAR gamma) plays a role in the regulation of intestinal inflammation and is activated by both natural (polyunsaturated fatty acid; PUFAs) and synthetic (troglitazone) ligands. The fatty acid content of defined formula diets may play a role in mediating the anti inflammatory effect, but the mechanism is unclear. Objective: We evaluated to what extent the effect of PUFAs on intestinal inflammation is mediated via PPAR gamma. Design: The human enterocyte-like cell line Caco-2 and human dendritic cells were stimulated by interleukin (IL) 1 beta and lipoprotein polysaccharide, respectively, in the presence of PPAR gamma agonists (troglitazone or PUFAs) or antagonist (GW9662). Five PUFAs were tested: a-linolenic acid (ALA), conjugated linoleic acid (CLA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and,gamma-linolenic acid (GLA). Cytokine production was measured by enzyme-linked immunosorbent assay and PPAR gamma, I-kappa B, and inducible nitric oxide synthase (iNOS) expression by Western blot. Results: In Caco-2 cel Is, IL-6 secretion was significantly decreased by troglitazone, DHA, EPA, and GLA. IL-8 production was significantly decreased by troglitazone, ALA, DHA, EPA, and GLA. PPAR gamma expression was significantly increased by troglitazone, DHA, and EPA. iNOS expression was significantly decreased by troglitazone, DHA, and EPA. Troglitazone and PUFAs at 0.1 mu mol/L tended to increase the expression Of I-kappa B. Addition of GW9662 reversed the effect of troglitazone and PUFAs at 0.1 mu mol/L on IL-8 production and decreased the expression of PPAR gamma. EPA and DHA also modulated the dendritic cell response to lipoprotein polysaccharide. Conclusions: The tested PUFAs exerted an antiinflammatory effect in vitro in both models. This effect of PUFAs in Caco-2 cells is similar to that of troglitazone on intestinal inflammation mediated by PPAR gamma, and the potency of the antiinflammatory effect is linked to the number of double bonds.