TABLE 2.

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 K_m,u and CL_int using where ± and ± represents the mean ± S.D. of fu_inc and K_m or CL_int,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, V_max and K_m could not be determined.

^aNot adjusted for incubation binding (fu_inc).

^bAdjusted for incubation binding (fu_inc).

^cCOOH-THC formation was fitted using a substrate inhibition model (eq. 8); K_i was 52.1 ± 14.3 μM.

^dCL_int was determined from the linear slope of [11-OH-THC] vs. velocity of COOH-THC formation.