Cyclooxygenase-2 over-expression is associated with increased mast cells in CCl₄-induced hepatic fibrosis

Cyclooxygenase(COX-2) is an inducible enzyme that catalyzes the synthesis of prostaglandins (PGs) from arachidonic acid. Over-expression of COX-2 has been reported to be associated with progressive hepatic fibrosis in chronic hepatic C infection and rat liver fibrosis induced by carbon tetrachloride($CCl_4$). Recently, it is well known that mast cell products can stimulate the proliferation of hepatic stellate cells and key players in liver fibrosis. But little is known regarding their role in $CCl_4$-induced liver fibrosis in rat. Our aim was to investigate the relation between COX-2 expression and mast cells during liver fibrosis after $CCl_4$ treatment. Thirty Wistar rats were divided into five groups (non-treated 0, 2, 4, 6 and 8-week after $CCl_4$-treatment). Reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry were used to assess the expression of ${\alpha}$-smooth muscle actin (${\alpha}$-SMA), collagen-1 and COX-2 in liver tissue from $CCl_4$-treated rats. The density of collagen and mast cells were determined using a computerized image analysis system in liver sections stained with picrosirius red and toluidine blue, respectively. The expression levels of ${\alpha}$-SMA, collagen-1 and COX-2 mRNA were significantly higher at 2 wk in $CCl_4$-treated groups than non-treated group. The number of mast cells in liver tissues increased gradually from 2 wk to 6 wk depending on the fibrosis severity but decreased abruptly at 8 wk. The significant increase of collagen-1 and ${\alpha}$-SMA mRNA expression in $CCl_4$-treated rats was continued until 6 wk while the COX-2 mRNA was significantly decreased at 8 wk. These results suggest that increased mast cells are closely associated with COX-2 over-expression during hepatic fibrogenesis of $CCl_4$-treated rats.