Kinetic parameters quantified using the substrate depletion and metabolite formation approach in pooled HLMs
Data shown are mean ± S.D. of three to four independent experiments with duplicate determinations per experiment. Error propagation was applied to the S.D. of Km,u and CLint using 
where 
± 
and 
± 
represents the mean ± S.D. of fuinc and Km or CLint,u, respectively. The values shown here were used as initial estimates for the P450 and UGT kinetic model (Fig. 3).
| Pathway | Inhibitor | Vmax | Kma | Km,ub | CLint |
|---|---|---|---|---|---|
| pmol/min per milligram | μM | nM | ml/min per milligram | ||
| THC depletion | None | 3150 ± 1310 | 0.18 ± 0.10 | 7 ± 5 | 435.3 ± 217.0 |
| Sulfaphenazole (10 μM) | 1064 ± 580 | 0.57 ± 0.47 | 24 ± 21 | 50.9 ± 21.3 | |
| 11-OH-THC formation | None | 803 ± 162 | 0.18 ± 0.05 | 8 ± 3 | 111.1 ± 48.8 |
| Sulfaphenazole (10 μM) | 515 ± 136 | 1.42 ± 0.13 | 60 ± 21 | 8.7 ± 2.9 | |
| 11-OH-THC depletion (P450s) | None | 2550 ± 107 | 11.0 ± 0.6 | 669 ± 296 | 3.8 ± 1.7 |
| Sulfaphenazole (10 μM) | 1701 ± 96.0 | 10.5 ± 1.1 | 679 ± 242 | 2.5 ± 0.9 | |
| Itraconazole (2 μM) | 194 ± 111 | 1.7 ± 1.1 | 112 ± 78 | 1.8 ± 0.6 | |
| COOH-THC formation | None | 8 ± 1 | 1.5 ± 0.3c | 92 ± 45 | 0.09 ± 0.04 |
| Sulfaphenazole (10 μM) | n.d. | n.d. | n.d. | 0.01 ± 0.00d | |
| Itraconazole (2 μM) | 5 ± 1 | 0.98 ± 0.55 | 63 ± 42 | 0.09 ± 0.07 | |
| 11-OH-THC depletion (UGTs) | None | 910 ± 99 | 1.87 ± 0.24 | 114 ± 52 | 8.1 ± 3.9 |
n.d., not determined.
Inhibition by sulfaphenazole did not lead to saturation of COOH-THC formation, and, as such, Vmax and Km could not be determined.
↵a Not adjusted for incubation binding (fuinc).
↵b Adjusted for incubation binding (fuinc).
↵c COOH-THC formation was fitted using a substrate inhibition model (eq. 8); Ki was 52.1 ± 14.3 μM.
↵d CLint was determined from the linear slope of [11-OH-THC] vs. velocity of COOH-THC formation.