Background/aims: The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor highly expressed in the colon which plays an anti-inflammatory role through the inhibition of nuclear factor-kappaB (NF-kappaB) pathway. Probiotics have been shown to exert beneficial effects on inflammatory bowel diseases. However, the exact mechanism by which probiotics exert protection against intestinal inflammation is not well understood. The aims of this study were to evaluate the attenuation of inflammatory response by probiotics in intestinal epithelial cells and to study the association between probiotics and PPARgamma.
Methods: HT-29 human epithelial cells were stimulated with LPS (20 microg/mL) and probiotics, Lactobacillus casei (L. casei) (10(5)-10(7) cfu/mL), or with LPS (20 microg/mL) alone for 24 hours. Interleukin-8 (IL-8), cyclooxygenase-2 (COX-2), toll-like receptor-4 (TLR-4) and PPARgamma mRNA expressions were assessed by RT-PCR. IL-8 protein secretion was measured by ELISA. HT-29 cells were transfected with tk promoter-luciferase plasmid containing a peroxisome proliferator response element (PPRE). After stimulation with L. casei or PPARgamma agonist (15d-PGJ2 or ciglitazone), luciferase activities were measured.
Results: LPS induced IL-8, COX-2, TLR-4 mRNA expression, and IL-8 protein secretion in HT-29 cells. Treatment with LPS and L. casei in comparison with LPS stimulation alone lowered IL-8, COX-2, TLR-4 mRNA expression, and IL-8 protein secretion. L. casei increased PPARgamma mRNA expression in dose-dependent manner. L. casei activated PPRE in HT-29 cells transfected with PPRE3-tk-luciferase construct.
Conclusions: Probiotics, L. casei, suppresses the expression of inflammatory mediators in intestinal epithelial cells. The anti-inflammatory action of L. casei might be partially related to PPARgamma activation.