The role of retinoic acid (RA) in liver fibrogenesis was previously studied in cultured hepatic stellate cells (HSCs). RA suppresses the expression of alpha(2)(I) collagen by means of the activities of specific nuclear receptors RARalpha, RXRbeta and their coregulators. In this study, the effects of RA in fibrogenesis were examined in carbon tetrachloride (CCl(4)) induced liver fibrosis in mice. Mice were treated with CCl(4) or RA and CCl(4), along side control groups, for 12weeks. RA reduced the amount of histologically detectable fibrosis produced by CCl(4). This was accompanied by a attenuation of the CCl(4) induced increase in alpha(2)(I) collagen mRNA and a lower (2-fold versus 3-fold) increase in liver hydroxyproline. Furthermore, RA reduced the levels of 3-nitrotyrosine (3-NT) protein adducts and thiobarbituric acid (TBA) reactive substance (TBARS) in the liver, which are formed as results of oxidative stress induced by CCl(4) treatment. These in vivo findings support our previous in vitro studies in cultured HSC of the inhibitory effect of RA on type I collagen expression. The data also provide evidence that RA reduces CCl(4) induced oxidative stress in liver, suggesting that the anti-fibrotic role of RA is not limited to the inhibition of type I collagen expression.
PMID: 17011172