Antifibrotic activity of rofecoxib in vivo is associated with reduced portal hypertension in rats with carbon tetrachloride-induced liver injury

Background and aim: Upregulation of cyclooxygenase-2 (COX-2), an inducible enzyme that is actively involved in inflammation and wound healing, has been found in cirrhotic livers. The aim of this study was to investigate the effects of selective inhibition of COX-2 on the development of liver cirrhosis and portal hypertension in rats. Methods: Liver cirrhosis was induced by carbon tetrachloride (CCl4) in Sprague-Dawley rats. Rofecoxib, a highly selective COX-2 inhibitor, was orally administered to rats at a dose of 10 mg/kg/day. Portal pressure was measured at 8 weeks post CCl4 administration with the catheterization method followed by the harvesting of liver samples. Liver histopathology was analyzed with hematoxylin and eosin and Masson's trichrome staining. The activated, alpha smooth muscle actin (alpha-SMA) positive hepatic stellate cells (HSCs) and the protein levels of collagen types I, III, IV, as well as laminin and two fibrogenic mediators, vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF) in the livers, were detected with immunohistochemical staining and western blot methods, respectively. The level of hepatic thromboxane B-2 (TXB2), a potent vasoconstrictive substance derived from COX, was measured with enzyme immunoassay. Results: Oral administration of rofecoxib decreased portal pressure in rats that were treated with CCl4 for 8 weeks. This was associated with a marked reduction in collagen accumulation and TXB2 level in the rat livers. In addition, rofecoxib administration was found to reduce the number of activated HSCs and to downregulate hepatic protein levels of three detected types of collagen, laminin, VEGF and CTGF in CCl4-treated rats. Conclusions: COX-2 is involved in the fibrogenesis of livers and the formation of portal hypertension in CCl4-treated rats. Selective inhibition of COX-2 by rofecoxib reduces portal hypertension and this is associated with antifibrotic activity as well as a reduction of COX-2-derived vasoactive substance.