Effect Of Fluorofenidone On Cytochrome P450 Enzyme Activity

OBJECTIVESTo investigate the inhibit or induce effects of fluorofenidone on the activities of cytochrome P450.METHODS1.In vitroCaffeine,midazolam,tolbutamide,chlorzoxazone,debrisoquine,and mephenytoin were incubated as probes with or without fluorofenidone respectively to study the effect of fluorofenidone on cytochrome P450 activities including CYP1A2,CYP3A4,CYP2C9,CYP2E1,CYP2D6 and CYP2C 19 in rat and human liver microsomes.2.In vivoRats were administrated by gastrogavage with different doses(250 500,and 1000 mg·kg^-1·day^-1,respectively)of fluorofenidone twice daily for five consecutive days.Liver microsomes were extracted at the sixth day. Probe drugs including caffeine,tolbutamide,mephenytoin,debrisoquine, chlorzoxazone and midazolam were used to estimation CYP1A2,CYP2C9, CYP2C19,CYP2D6,CYP2E1 and CYP3A4 activities,respectively. Concentrations of the probe drugs and their metabolites in the incubated system were determined by HPLC and the cytochrome P450 activities were measured by the production of metabolites.The protein contents of CYP2E1 and CYP3A4 in the liver microsomes were determined by western-blotting method.RESULT 1.In vitroOur data indicated that fluorofenidone has not significant inhibition on the activities of CYP450 in human but has inhibition on CYP2C19、CYP2C9 and CYP2E1.2.In vivoIn 250 mg·kg^-1·day^-1dose group,fluorofenidone pretreatment cause 723%,142%and 129%increase of chlorzoxazone 6-hydroxylation, tolbutamide 4-hydroxylation and midazolam 1-hydroxylation respectively.In 500 mg·kg^-1·day^-1dose group fluorofenidone pretreatment cause 14 fold,52%,and 232%increase of chlorzoxazone 6-hydroxylation, tolbutamide 4-hydroxylation and midazolam 1-hydroxylation,respectively.In 1000 mg·kg^-1·day^-1dose group fluorofenidone pretreatment induce 14 fold,74%and 85%increase of chlorzoxazone 6-hydroxylation, tolbutamide 4-hydroxylation and midazolam 1-hydroxylation,respectively.Significant differences in ennyme activitiy between control group and treatment groups were observed for CYP2E1（P＜0.05）.The activity of CYP2C9 and CYP3A4 increased but not significantly.There are not differences in caffeine 3-demethylation,mephenytoin 4-hydroxylation and debrisoquine 4-hydroxylation in different doses and there is no correlation between the dose and the changes of activities.CONCLUSIONSFluorofenidone has not inhibition effect on CYP450 in human liver microsome but it has inhibition effect on CYP2C19,CYP2C9 and CYP2E1 in rat liver microsome.The value of IC₅₀of CYP2C19 was about 400μmol·L^-1and the values of IC₅₀of CYP2C9 and CYP2E1 were; higher than 788.2μmol·L^-1.Fluorofenidone is a potential CYP2E1,CYP3A4 and CYP2C9 inducer in vivo.The protein expression of CYP2E1 and CYP3A4 are increased after fluorofenidoneadministration.