ABSTRACT
Title
CYP1A2 induction in liver cirrhosis
Authors
D. Gabbia
Dept. of Pharmacology and Anesthesiology, University of Padua
Dept. of Pharmacology and Anesthesiology, University of Padua
Abstract
Background and objectives: Cytochrome P 450 (CYP) 1A2 is a CYP isoform constitutively expressed in liver. This enzyme catalyzes the metabolism of many drugs, and also participates in the metabolic activation of several chemical mutagens. It is well known that many CYP isoforms are inducible after exposure to chemical compounds; in particular, CYP1A2 is induced by benzo[α]pyrene, via activation of the Ah receptor (AhR).Most drug-drug interactions arise from either inhibition or induction of CYP enzymes. A number of CYP-inducing agents have been reported to cause serious or even fatal drug-drug interactions associated with decreased drug exposure and consequent therapeutic failure.The effect of liver disease on the magnitude of drug interactions due to CYP1A2 induction has been extensively investigated, but highly discrepant results have been obtained.Because of the ethic problems related to the impossibility to administer repeated doses of a non-therapeutic drug to patients with serious liver dysfunction, human studies had to use hepatopathic patients taking inducers for therapeutic purposes and, consequently, these studies often lack rigorous methodology. Animal studies are thereforenecessary to clarify the influence of liver functional status on CYP induction. This study was designed to compare CYP1A2 induction in rats with normal and impaired liver function,classified according to the degree of liver dysfunction.
Methods: In this study, we used 3 groups of animals: one of normal rats and two groups of rats with experimentally-induced cirrhosis, obtained by treatment with carbon tetrachloride (CCl4) administered by inhalation; one group with compensated (corresponding to human Child grade A or B) liver cirrhosis, the other group with decompensated (corresponding to human Child grade C) liver cirrhosis. The severity of cirrhosis was defined on the basis of histological examination (Ishak score), the presence or absence of ascites and laboratory data (PT, albumin, AST and ALT). Each group was then divided into 2 subgroups, one treated with vehicle (olive oil), the other with the inducing agent benzo[α]pyrene (bap). In order to evaluate the inducing effect of bap, we measured the MROD activity (dealkylation of 7-methoxyresorufin to resorufin), a validated marker reaction for CYP1A2, using liver microsomes obtained from normal and CCl4-treated rats.Determination of CYP1A2 expression by Western blot was also performed.
Results and conclusion: Total CYP content per gram of liver tissue decreased in proportion to the decline of liver function (14.04 ± 3.20 nmol/g in normal rats vs 11.00 ± 1.99 nmol/g and 9.16 ± 1.08 nmol/g in rats with compensated and decompensated cirrhosis, respectively). In vehicle-treated rats, Vmax for MROD decreased from 1904 ± 803 nmol/min/g liver in normal animals to 706 ± 171 nmol/min/g liver and 550 ± 102 nmol/min/g liver in rats with compensated and decompensated cirrhosis, respectively. A decrease of intrinsic metabolic clearance (CLint) was also observed, from 7168 ± 2858 µl/min/g liver in normal animals, to 1820 ± 1142 µl/min/g liver and 1492 ± 554µl/min/g liver in rats with compensated and decompensated cirrhosis, respectively. In bap-treated rats, Vmax of normal animals was 8 times higher (14202 ± 2649 nmol/min/g liver) than in the vehicle-treated group, and a similar inducing effect was observed in cirrhotic rats. The CLint data were in accordance with these findings. CYP1A2 measurement by Western blot analysis consistently showed an increase in CYP1A2 protein expression in all rat groups, after bap treatment.
In conclusion, this study clearly demonstrates that CYP1A2 induction does not decrease with the decline of liver function.
Methods: In this study, we used 3 groups of animals: one of normal rats and two groups of rats with experimentally-induced cirrhosis, obtained by treatment with carbon tetrachloride (CCl4) administered by inhalation; one group with compensated (corresponding to human Child grade A or B) liver cirrhosis, the other group with decompensated (corresponding to human Child grade C) liver cirrhosis. The severity of cirrhosis was defined on the basis of histological examination (Ishak score), the presence or absence of ascites and laboratory data (PT, albumin, AST and ALT). Each group was then divided into 2 subgroups, one treated with vehicle (olive oil), the other with the inducing agent benzo[α]pyrene (bap). In order to evaluate the inducing effect of bap, we measured the MROD activity (dealkylation of 7-methoxyresorufin to resorufin), a validated marker reaction for CYP1A2, using liver microsomes obtained from normal and CCl4-treated rats.Determination of CYP1A2 expression by Western blot was also performed.
Results and conclusion: Total CYP content per gram of liver tissue decreased in proportion to the decline of liver function (14.04 ± 3.20 nmol/g in normal rats vs 11.00 ± 1.99 nmol/g and 9.16 ± 1.08 nmol/g in rats with compensated and decompensated cirrhosis, respectively). In vehicle-treated rats, Vmax for MROD decreased from 1904 ± 803 nmol/min/g liver in normal animals to 706 ± 171 nmol/min/g liver and 550 ± 102 nmol/min/g liver in rats with compensated and decompensated cirrhosis, respectively. A decrease of intrinsic metabolic clearance (CLint) was also observed, from 7168 ± 2858 µl/min/g liver in normal animals, to 1820 ± 1142 µl/min/g liver and 1492 ± 554µl/min/g liver in rats with compensated and decompensated cirrhosis, respectively. In bap-treated rats, Vmax of normal animals was 8 times higher (14202 ± 2649 nmol/min/g liver) than in the vehicle-treated group, and a similar inducing effect was observed in cirrhotic rats. The CLint data were in accordance with these findings. CYP1A2 measurement by Western blot analysis consistently showed an increase in CYP1A2 protein expression in all rat groups, after bap treatment.
In conclusion, this study clearly demonstrates that CYP1A2 induction does not decrease with the decline of liver function.