Enzyme kinetic parameters for the formation of the primary oxidative metabolites of [14C]muraglitazar by CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 and the predicted relative contributions of each P450 enzyme to the metabolite formation at substrate concentrations of 1, 2.5, 3.8, and 25 μM
Kinetic values were estimated by Michaelis-Menten analysis. Vi refers to the individual velocity for the formation of a metabolite by each P450 enzyme; vi refers to the velocity for each P450 enzyme per mg of microsomal protein; Fi refers to the relative contribution of each P450 enzyme to a particular metabolic pathway. Human hepatic P450 concentrations used for scaling (Ai) were 64, 96, 19, 10, and 108 pmol/mg microsomal proteins for CYP2C8, 2C9, 2C19, 2D6, and 3A4, respectively (Rodrigues, 1999).
Metabolite | Enzyme | Km | Vmax a | CLint (Vmax/Km)b | Vi c | vi d | Estimated Relative Contribution Fi | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2.5 | 3.8 | 25 | 1 | 2.5 | 3.8 | 25 | 1 | 2.5 | 3.8 | 25 | ||||||||||||||
| μM | % | ||||||||||||||||||||||||
| M10 | CYP2C8 | 199 | 1.2 | 0.006 | 0.006 | 0.015 | 0.023 | 0.137 | 0.394 | 0.98 | 1.48 | 8.79 | 9.8 | 9.8 | 9.96 | 10.9 | |||||||||
| CYP2C9 | 56.8 | 1.9 | 0.017 | 0.017 | 0.041 | 0.061 | 0.293 | 1.59 | 3.89 | 5.80 | 28.2 | 39.5 | 39.2 | 39.0 | 35.0 | ||||||||||
| CYP2C19 | 53.8 | 1.9 | 0.036 | 0.035 | 0.086 | 0.128 | 0.613 | 0.669 | 1.63 | 2.43 | 11.6 | 16.6 | 16.5 | 16.3 | 14.5 | ||||||||||
| CYP3A4 | 330 | 4.2 | 0.013 | 0.013 | 0.032 | 0.048 | 0.295 | 1.37 | 3.41 | 5.18 | 31.9 | 34.0 | 34.4 | 34.8 | 39.6 | ||||||||||
| HLM | 39.1 | 0.28 | 0.006 | —e | — | — | — | — | — | — | — | — | — | — | — | ||||||||||
| M11 | CYP2C19 | 23.3 | 4.2 | 0.179 | 0.172 | 0.41 | 0.59 | 2.16 | 3.27 | 7.70 | 11.2 | 41.1 | 100 | 100 | 100 | 100 | |||||||||
| HLM | 33.6 | 0.068 | 0.002 | — | — | — | — | — | — | — | — | — | — | — | — | ||||||||||
| M14 | CYP3A4 | 80.2 | 1.9 | 0.024 | 0.024 | 0.058 | 0.088 | 0.459 | 2.57 | 6.30 | 9.47 | 49.5 | 100 | 100 | 100 | 100 | |||||||||
| HLM | 13.8 | 0.074 | 0.012 | — | — | — | — | — | — | — | — | — | — | — | — | ||||||||||
| M15 | CYP2C7 | 42.3 | 0.6 | 0.015 | 0.015 | 0.035 | 0.052 | 0.234 | 0.932 | 2.25 | 3.34 | 15.0 | 94.0 | 93.8 | 93.6 | 91.2 | |||||||||
| CYP2D6 | 559 | 3.4 | 0.006 | 0.006 | 0.015 | 0.023 | 0.145 | 0.06 | 0.15 | 0.23 | 1.45 | 6.0 | 6.3 | 6.4 | 8.8 | ||||||||||
|
| HLM | 9.3 | 0.095 | 0.010 | — | — | — | — | — | — | — | — | — | — | — | — | |||||||||
↵ a The unit for Vmax was pmol/mg protein/min for HLM and pmol/pmol P450/min for expressed enzymes.
↵ b The unit for clearance was μl/mg protein/min for HLM and μl/pmol P450/min for expressed enzymes.
↵ c The unit for Vi was pmol/pmol P450/min.
↵ d the unit for vi was pmol/mg microsomal protein/min.
↵ e —, not applicable.