VITAMIN-A-DEFICIENCY POTENTIATES CARBON-TETRACHLORIDE INDUCED LIVER FIBROSIS IN RATS

Earlier studies have shown that retinoid administration suppresses the generation of hepatic fibrosis and stimulates its regression in normal (i.e., vitamin A-sufficient) carbon tetrachloride-treated rats. This study focuses on the possible role of a marginal or deficient vitamin A status on carbon tetrachloride-induced fibrosis. This experimental study in rats shows that vitamin A status, reflected by hepatic retinoid content (retinol and retinyl esters), modulates the development of hepatic fibrosis induced by carbon tetrachloride. In rats with low hepatic retinoid levels (12 +/- 0.9 mug/gm liver), carbon tetrachloride-induced liver fibrosis was more pronounced than in rats with sufficient hepatic retinoid levels (1,065 +/- 327 mug/gm liver). Enhanced liver fibrogenesis was confirmed both morphologically and by a higher hydroxyproline content of the liver. It was associated with a reduced liver weight and the development of parenchymal regeneration nodules. Furthermore, carbon tetrachloride treatment itself reduced the hepatic retinoid content in rats independently of the liver vitamin A status before treatment and increased serum retinol levels in vitamin A-sufficient rats. The results show that the vitamin A status of the liver plays an important role in hepatic fibrogenesis. Low hepatic vitamin A levels, which can be the result not only of low dietary intake but also of interference with vitamin A metabolism by agents such as ethanol and carbon tetrachloride, may be a risk factor for the development of liver fibrosis. We suggest that retinoids modulate collagen synthesis and deposition irrespective of the degree of hepatocellular necrosis induced by carbon tetrachloride. The reduction of retinoid levels in fat-storing cells and fibroblast-like cells by an enhanced secretion of retinol from the liver into the circulation during carbon tetrachloride treatment may stimulate the transformation of these cells to fibroblasts and, in this way, contribute to fibrogenesis of the liver.