EFFECT OF CARBON TETRACHLORIDE-INDUCED HEPATIC-INJURY ON STEREOSELECTIVE N-DEMETHYLATION OF CHLORPHENIRAMINE BY RAT HEPATIC CYTOCHROME-P4502C11 ISOZYME

We examined the effect of a carbon tetrachloride (CCl4)-induced hepati c injury on the stereoselective N-demethylation of RS-(+/-)-chlorpheni ramine (Chp) by cytochrome P450 (CYP) 2C11 isozyme. In the non-treated rat liver microsomes, the stereoselective N-demethylation of racemic Chp was observed. However, in the CCl4-treated (0.5 ml/kg, i.p.) rat l iver microsomes, the N-demethylation activities of S-(+)- and R-(-)-Ch p decreased continuously up to the third day after the treatment with CCl4, and reached about 9 and 13% of control values, respectively, and the stereoselective N-demethylation of Chp was not observed. Moreover , in the li ver microsomes at the 7th day after the treatment with CCl 4, the N-demethylation activities of both enantiomers recovered to an original level, and the stereoselective N-demethylation of Chp was aga in observed. The addition of 30 mu l of the anti-rat CYP2C11 serum to the reaction mixture containing 1 mg of microsomal protein inhibited t he formation of monodesmethylchlorpheniramine (:DMChp) from both enant iomers to 74 and 57% of the control values for S-(+)- and R-(-)-Chp, r espectively. In the liver microsomes of a male rat at the 1st day afte r the treatment of CCl4, the addition of the anti-rat CYP 2C11 serum ( 30 mu l) also caused 25% inhibition of the formation of DMChp from S-( +)-Chp, but anti-rat CYP2C11 had no inhibitory effect on the rates of microsomal N-demethylation of R-(-)-enantiomer. On the other hand, in the liver microsomes of a male rat at the 7th day after the treatment with CCl4, the anti-rat CYP2C11 serum had an inhibitory effect on the rates of microsomal N-demethylation of either S-(+)- or R-(-)-enantiom ers again. Moreover, it was confirmed by Western blotting analysis tha t the density of the stained bands of CYP2C11 in the liver microsomes from male rats at the 1st, 2nd and 3rd days after the treatment with C Cl4, was thinner than that from non-treatment male rats. These results indicated that the changes of N-demethylation activities of Chp in th e CCl4-induced hepatic injury were due to the variation of microsomal CYP2C11.