PARTICIPATION OF CYTOCHROME P450-2B AND P450-2D ISOZYMES IN THE DEMETHYLENATION OF METHYLENEDIOXYMETHAMPHETAMINE ENANTIOMERS BY RATS

The cytochrome P450 isozymes in rat liver microsomes that catalyze the demethylenation of methylenedioxymethamphetamine enantiomers to the c orresponding dihydroxymethamphetamine were characterized. Dihydroxymet hamphetamine formation in liver microsomes from male Sprague-Dawley ra ts exhibited multienzyme kinetics, with K-m values in the micromolar/ millimolar range. The stereoselectivity [(+)-isomer versus (-)-isomer] varied from 0.78 to 1.94 after pretreatment of the rats with phenobar bital, 3-methylcholanthrene, pregnenolone-16 alpha-carbonitrile, or py razole, suggesting that different isozymes participate in the reaction . The low-K-m demethylenation was not induced by these compounds and w as not inhibited by antibodies raised against CYP2C11. Liver microsome s from female Dark-Agouti rats, a strain genetically deficient in CYP2 D1, exhibited demethylenation activities that were 9% of those in micr osomes from male Sprague-Dawley rats. The low-K-m demethylenation was also inhibited by CYP2D substrates such as sparteine, bufuralol, or de sipramine and was almost completely inhibited by antibodies against P4 50 BTL, which belongs to the CYP2D family. The high-K-m demethylenatio n activity was induced by phenobarbital and pregnenolone-16 alpha-carb onitrile and the activity in both untreated and phenobarbital-induced microsomes was suppressed by anti-CYP2B1 IgG. Experiments with IgG rai sed against cytochrome b(5) suggested that the hemoprotein contributed to the low-K-m activity but not the high-K-m activity. These results indicate that cytochrome P450 isozymes belonging to the CYP2D subfamil y catalyze demethylenation with low K-m values and that the reaction o ccurring with high K-m values is likely to be mediated by members of t he CYP2B family, but with the possible participation of other phenobar bital-inducible isoforms.