| Popis: |
Background and aims: Although induction has long been investigated in patients with cirrhosis, highly discrepant results have been obtained; moreover, the mechanism underlying the possible effect of cirrhosis on induction has not been clarified. This study was designed to compare induction of CYP1A and CYP3A enzymes in healthy rats and rats with experimentally induced liver cirrhosis. Since differences in CYP1A induction in Sprague-Dawley and Wistar rats have been reported, the secondary aim of this study was to quantify the magnitude of CYP1A induction in these two rat strains. Methods: We used 3 groups of male Wistar rats, one of healthy animals and two groups of rats with carbon tetrachloride (CCl4)-induced cirrhosis, stratified according to the degree of liver dysfunction. Each group was divided in 2 subgroups of 8 rats, one treated with vehicle (oil), the other with an inducing agent [benzo[a]pyrene (BaP) or dexamethasone (DEX) for CYP1A and CYP3A, respectively]. To investigate the difference between Sprague-Dawley and Wistar rats, we used 2 groups of 8 healthy animals for each strain: one treated with vehicle, the other treated with BaP. The inducing effect was assessed by measuring the activity of CYP1A and CYP3A enzymes, using O-dealkylation of ethoxyresorufin and methoxyresorufin, and hydroxylation of testosterone and midazolam as markes reactions, respectively. Western blot analysis and qRT-PCR were performed to evaluate protein and gene expression of CYP1A, CYP3A and nuclear receptors responsible for their transcriptional control (Aryl Hydrocarbon receptor and Pregnane X Receptor, respectively). Results and conclusion: 1) BaP treatment increased mRNA and protein expression of both CYP1A enzymes (CYP1A1 and CYP1A2) and AhR to a greater extent in Wistar than Sprague-Dawley rats. By contrast, CYP1A2 enzyme activity was much more markedly increased in Sprague-Dawley than Wistar rats and CYP1A1 activity was induced to similar levels in the two rat strains. A BaP-induced increase in the turnover number of CYP1A enzymes in Sprague-Dawley rats, relative to Wistar rats, may provide a plausible explanation for the differential effect of BaP on gene expression and enzyme activity in these rat strains. 2) The inducibility of CYP1A enzymes is well preserved in non ascitic rats, whereas it is markedly reduced when liver dysfunction becomes severe. Induction appears to be impaired at the transcriptional level, due to the reduced expression of AhR, which controls the transcription of CYP1A genes. 3) Cirrhosis has a differential effect on the induction by DEX of the two CYP3A isoforms CYP3A1 and CYP3A2. The induction of CYP3A1 mRNA and protein is well preserved in both compensated and decompensated cirrhosis, whereas that of CYP3A2 is markedly reduced when liver dysfunction becomes severe. Consistently, CYP3A1 activity is significantly increased in DEX-treated rats irrespective of the degree of liver dysfunction, whareas CYP3A2 activity is not significantly induced in ascitic rats after DEX treatment. At variance with AhR, no significant increase in PXR gene and protein expression is observed in DEX-treated healthy or cirrhotic rats. In conclusion, the effect of cirrhosis on enzyme induction is dependent in the type of nuclear receptor that mediates the inducing effect. Therefore, no generalization can be made and the influence of cirrhosis on inducibility has to be assessed for each class of inducing agents |
