Inhibition of 1,25(OH)2D3 mono-hydroxylation activity of CYP3A4, liver microsomes, intestinal homogenate, and CYP24A1 by TAO and ketoconazole (KTZ)
TAO (20 μM) was preincubated with the source enzyme and NADPH for 15 min before a 20-μl aliquot (containing the appropriate amount of source enzyme) was then transferred to the final incubation tube. Ketoconazole (100 nM) was added directly to the incubation mixture before addition of NADPH.
| Recombinant CYP3A4 | Liver Microsomes | Intestinal Homogenate | Recombinant CYP24A1 | |
|---|---|---|---|---|
| % of control | ||||
| TAO (20 μM) | 12 ± 1 | 15 ± 1 | 16 ± 1 | 102 ± 7 |
| KTZ (100 nM) | 2 ± 1 | 2 ± 1 | 2 ± 1 | 95 ± 1a |
↵ a Ketoconazole at 1 μM also showed no inhibition toward CYP24A1 activity.