IDENTIFICATION OF CYTOCHROME-P-450 ISOZYMES INVOLVED IN THE HYDROXYLATION OF DANTROLENE BY RAT-LIVER MICROSOMES

The role of individual rat liver cytochrome P-450 isozymes in the metabolism of the skeletal muscle relaxant, dantrolene, was studied. Following incubation of dantrolene with hepatic microsomes from 3-methylcholanthrene-treated rats, two major hydroxylated metabolites were identified. Using inhibitory antibodies specific for individual cytochrome P-450 isozymes, cytochromes P-450 1A1, 1A2, and 3A were identified to be involved in dantrolene hydroxylations. In liver microsomes from 3-methylcholanthrene-treated rats, antibodies specific for cytochrome P-450 1A1 and 1A2 inhibited hydroxylation of dantrolene by 60% and 20%, respectively. Kinetics studies using these microsomes showed that dantrolene hydroxylation was biphasic with a low K(M) (0.06-0.08 muM) and high K(M) (5-7 muM). Cytochrome P-450 1A1 was responsible for the low K(M) hydroxylation of dantrolene, whereas cytochrome P-450 1A2 was responsible for the high K(M). In hepatic microsomes from pregnenolone-16alpha-carbonitrile-treated rats, an antibody specific for cytochrome P-450 3A completely inhibited the formation of 5-hydroxydantrolene, the major metabolite formed by these microsomes.