Cyclooxygenase-2-mediated angiogenesis in carrageenin-induced granulation tissue in rats

The possible participation of cyclooxygenase (COX)-2 in angiogenesis in granulation tissue was analyzed using an air pouch-type carrageenin-induced inflammation model in rats. Injection of carrageenin solution into an air pouch induced gradual increases in the pouch fluid volume and granulation tissue weight as well as angiogenesis in granulation tissue. NS-398 (10-100 μg) inhibited all of these parameters in a dose-dependent manner. NS-398 (100 μg), indomethacin (100 μg), and dexamethasone (10 μg) markedly reduced prostaglandin (PG) E₂ levels in the pouch fluid at day 6. NS-398 and indomethacin did not affect protein levels of COX-1 and COX-2 but dexamethasone significantly reduced the level of COX-2 in granulation tissue at day 6. Protein levels of vascular endothelial growth factor (VEGF) in granulation tissue and in the pouch fluid were higher at day 6 than at day 3, and the levels were decreased by treatment with NS-398 (10-100 μg) in a dose-dependent manner. The inhibitory effects of NS-398 (100 μg) were almost the same as those of indomethacin (100 μg). Dexamethasone (10 μg) also reduced VEGF protein levels in granulation tissue at day 6. To clarify the role of PGE₂ in VEGF production, minced granulation tissue obtained 3 days after carrageenin injection from the indomethacin-treated rats was incubated in the presence of various concentrations of PGE₂. It was shown that VEGF mRNA and protein levels in the minced granulation tissue were increased by PGE₂ in a concentration-dependent manner. These findings suggest that COX-2-derived PGE₂ plays a significant role in angiogenesis in the carrageenin-induced granulation tissue through VEGF formation.