Cytochrome P450-catalyzed hydroxylation of Δ8-tetrahydrocannabinol and implications for pharmacogenetics

The use of Δ8-tetrahydrocannabinol (Δ8-THC) has become increasingly prevalent in the United States but its metabolic pathways remain poorly characterized. This study aimed to identify the key enzymes responsible for the 11'-hydroxylation of Δ8-THC, its primary metabolic pathway, and assess the effect of metabolizing enzyme genotype on this activity. The intrinsic clearance of recombinant (r) CYP2C9 was >6,200-fold higher than that observed for rCYP2C19, the only other tested CYP450 with detectable activity against Δ8-THC. The $K_{m,u}$ of rCYP2C9 (0.013 ± 0.0032 μM) was comparable to that observed in human intestinal microsomes (0.0076 ± 0.00067 μM) but it was substantially lower than that observed for human liver microsomes (0.73 ± 0.065 μM). Inhibition of 11-OH-Δ8-THC formation in rCYP overexpressing microsomes was observed when using CYP probe inhibitors (sulfaphenazole for CYP2C9 and tranylcypromine for CYP2C19). The intrinsic clearance was markedly reduced in CYP2C9 variant microsomes, with 20- to 60-fold decreases observed for CYP2C9*2 (59 ± 7.9 μL·min^-1·mg^-1 protein), CYP2C9*3 (34 ± 3.6 μL·min^-1·mg^-1 protein), CYP2C9*8 (96 ± 13 μL·min^-1·mg^-1 protein), and CYP2C9*9 (34 ± 11 μL·min^-1·mg^-1 protein) as compared to wild-type CYP2C9*1 (6,028 ± 266 μL·min^-1·mg^-1 protein). Given that the expression of CYP2C9 is much higher that CYP2C19 in both human intestine and liver, these data suggest that CYP2C9 is the primary enzyme responsible for intestinal 11'-hydroxylation of Δ8-THC and that other untested CYPs may be important in hepatic Δ8-THC hydroxylation. In addition, the reduced 11-OH-Δ8-THC formation activity observed with CYP2C9 variants (*2, *3, *8, *9) suggests interindividual variability in Δ8-THC disposition.