Kinetics of TPA023 t-butyl hydroxylation and N-deethylation in the presence of human liver microsomes and recombinant CYP3A4 and CYP3A5
Pooled CYP3A5-Rich Human Liver Microsomes (n = 3) | Pooled CYP3A5-Deficient Human Liver Microsomes (n = 3) | CYP3A4 + OR | CYP3A5 + OR + b5 | |
|---|---|---|---|---|
| t-Butyl hydroxylation (M1) | ||||
| Best model fit | Multienzymea | Inhibition | Inhibition | Biphasic |
| Vmaxb (or Vmax1) | 239 ± 11 | 249 ± 11 | 75 ± 4 | |
| Km (or Km1) | 3.4 ± 1.1 | 5.7 ± 0.7 | 3.0 ± 0.4 | 1.3 ± 0.1 |
| Vmax2 | 235 ± 15 | |||
| Km2 | 12.7 ± 0.6 | 18.9 ± 3.6 | ||
| Ksi | 185 ± 25 | 167 ± 22 | ||
| CLintc | 0.042 | 0.083 | 0.058 | |
| N-Deethylation (M2) | ||||
| Best model fit | Multienzyme | Hyperbolic | Hyperbolic | Biphasic |
| Vmax (or Vmax1) | 366 ± 3 | 220 ± 3 | 22 ± 3 | |
| Km (or Km1) | 4.5 ± 2.0 | 7.5 ± 0.4 | 3.7 ± 0.3 | 0.6 ± 0.2 |
| Vmax2 | 404 ± 40 | |||
| Km2 | 40.0 ± 1.8 | 82.3 ± 12.6 | ||
| Ksi | ||||
| CLin |
| 0.049 | 0.059 | 0.037 |
↵ a The values of Vmax, Ksi, and/or CLint in a multienzyme system were not estimated.
↵ b The unit for the Vmax value was pmol/min/mg protein for human liver microsomes and pmol/min/nmol P450 for recombinant P450 enzymes. The unit for the Km value was μM. Values are the mean ± S.E.
↵ c Calculation of the in vitro intrinsic clearance (CLint): hyperbolic model, CLint = Vmax/Km; and substrate inhibition model, CLint = Vmax/Km; biphasic model, CLint = Vmax1/Km1 (high affinity, low capacity). The unit for the CLint value determined in human liver microsomes and in recombinant P450 was ml/min/mg protein and ml/min/nmol, respectively.