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 meta bolism of the skeletal muscle relaxant, dantrolene, was studied. Follo wing incubation of dantrolene with hepatic microsomes from 3-methylcho lanthrene-treated rats, two major hydroxylated metabolites were identi fied. Using inhibitory antibodies specific for individual cytochrome P -450 isozymes, cytochromes P-450 1A1, 1A2, and 3A were identified to b e involved in dantrolene hydroxylations. In liver microsomes from 3-me thylcholanthrene-treated rats, antibodies specific for cytochrome P-45 0 1A1 and 1A2 inhibited hydroxylation of dantrolene by 60% and 20%, re spectively. Kinetics studies using these microsomes showed that dantro lene hydroxylation was biphasic with a low K(M) (0.06-0.08 muM) and hi gh 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 respo nsible for the high K(M). In hepatic microsomes from pregnenolone-16al pha-carbonitrile-treated rats, an antibody specific for cytochrome P-4 50 3A completely inhibited the formation of 5-hydroxydantrolene, the m ajor metabolite formed by these microsomes.