Activation of peroxisome proliferator-activated receptor gamma suppresses inducible cyclooxygenase and nitric oxide synthase during oral mucosal ulcer healing.

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a ligand-dependent transcription factor, belonging to the steroid hormone receptor family, known to play a pivotal role in the resolution of inflammation. In this study, we investigated the effect of a specific PPARgamma ligand, ciglitazone, on the course of buccal mucosal ulcer healing by analyzing mucosal activity of inducible nitric oxide synthase (NOS-2) and the expression cyclooxygenases (COX-1 and COX-2) responsible for prostaglandin (PG) generation.

METHODS

Groups of rats with experimentally induced buccal mucosal ulcers were administered twice daily for up to 10 days with ciglitazone at 5, 10, and 15 mg/kg or the vehicle, and their mucosal tissue subjected to assessment of ulcer healing rate and biochemical measurements.

RESULTS

The ulcer onset, characterized by up-regulation of NOS-2 and COX-2 protein expression, was reflected in a marked increase in the mucosal PGE2 generation and NOS-2 activity, whereas healing was accompanied by a drop in PGE2 and NOS-2 activity, and a decrease in COX-2 and NOS-2 protein expression. The mucosal expression of COX-1 protein, however, remained unchanged. Administration of ciglitazone led to a significant dose-dependent acceleration in the mucosal reduction of PGE2 generation and NOS-2 activity, and produced a marked decline in COX-2 and NOS-2 protein expression, but the rate of ulcer healing and the expression of COX-1 protein remained unaffected.

CONCLUSIONS

Our findings thus suggest that the products of induced NOS-2 and COX-2 enzymes, associated with mucosal inflammatory responses to injury, do not play a significant role in oral mucosal ulcer healing.