Hepatic fibrosis and cytochrome P450: experimental models of fibrosis compared to AHR knockout mice

Hepatic fibrosis is characterized by abnormal collagen deposition resulting fi om increased collagen synthesis and decreased collagen degradation. Cyt ochrome P450 mediates major drug metabolizing enzyme activity in the liver and this activity is reduced in hepatic fibrosis. In this study we assess c ytochrome P450 and CYP 1A mRNA in livers of animals that have been induced to hepatic fibrosis using the heterologous serum induced model of fibrosis in rats compared to controls. Fibrosis was confirmed by assessing the colla gen in liver sections as quantified by Sirius red/Fast green staining, a qu antitative measure of fibrosis as well as by visualization of the hepatic f ibrosis. Collagen levels in the liver sections of heterologous serum induce d fibrotic rats was increased by 33% compared to controls and a typical fib rotic pattern was seen. Messenger RNA was prepared from heterologous serum induced fibrotic rats and compared to controls. CYP 1A2 was assessed using a specific probe and the CYP 1A2 level was significantly reduced in the het erologous serum induced fibrotic rats compared to controls. These results f urther suggest that cytochrome P450 is reduced in the presence of hepatic f ibrosis. Thus, in three well established experimental models of hepatic fib rosis which had clearly developed hepatic fibrosis (as shown by Sirius red/ Fast green staining), cytochrome P450 mediated enzyme activity, or specific ally. CYP 1A messenger RNA is decreased. We then investigated a transgenic mouse, deficient in the arylhydrocarbon hydroxylase receptor (AHR), which h as undetectable levels of CYP 1A messenger RNA. We quantitated the collagen in liver sections obtained from AHR knockout mice compared to controls, as an indication of the presence of hepatic fibrosis. Collagen concentration was significantly increased by 53% (P < 0.0005) in sections from Ahr- / - ( knockout) mice compared to wild-type controls. Collagen in livers of the Ah r + / - heterozygous mice was nor different from wild-type controls. The in crease in collagen concentration in liver sections is an indication of fibr osis in Ahr - / - mice. Collagen protein deposition was also elevated in li ver sections from bile duct ligated rats (by 44%) compared to sham operated controls, was elevated in liver sections from heterologous serum induced f ibrosis in rats (33%) compared to controls, and was elevated in liver secti ons from yellow phosphorous induced hepatic fibrosis (74%) compared to vehi cle treated controls. In conclusion, these results indicate that cytochrome P450 and specific subtypes of P450, the CYP 1A subgroup, are significantly reduced in three experimental models of hepatic fibrosis when there is evi dence of increased collagen deposition in the livers. These results also in dicate that mice that are deficient in CYP 1A have elevated levels of hepat ic collagen protein, an indication of hepatic fibrosis. (C) 2000 Elsevier S cience Ireland Ltd. All rights reserved.