TABLE 4.
Effect of nucleophilic trapping agents, glutathione or methoxylamine, on the inhibition of CYP2A6 by t-CA in microsomal and recombinant systems
Data points are the mean ± standard deviation of individual experiments conducted on three separate days (N = 3 and 9) or two separate days (N = 6). The value of N is shown in parentheses.
| Percentage of Remaining Activity |
||
|---|---|---|
| Substrate/Trapping Agent | rCYP2A6 | HLM |
| Coumarin (80 µM t-CA) | ||
| None | 41.1 ± 3.5 (3)a | 31.7 ± 1.9 (6)b |
| Glutathione (5 mM) | 57.4 ± 9.5 (3)** | 67.5 ± 10.9 (6)*** |
| Methoxylamine (1 mM) | 0.8 ± 0.2 (9)*** | 9.5 ± 1.5 (9)*** |
| Letrozole (80 µM t-CA) | ||
| None | 48.9 ± 17.2 (9)c | 70.8 ± 5.0 (9)d |
| Methoxylamine (1 mM) | 8.2 ± 13.9 (9)*** | 45.0 ± 16.0 (9)*** |
HLM, human liver microsomes.
a
Control activity = 5.7 pmol/min/pmol P450.
b
Control activity = 924.0 ± 49.9 pmol/min/mg protein.
c
Control activity = 0.62 ± 0.04 pmol/min/nmol P450.
d
Control activity = 0.30 ± 0.03 pmol/min/mg protein.
**
P < 0.01 in comparison with samples without trapping agent (i.e., with t-CA and NADPH); ***P < 0.001 in comparison with samples without trapping agent (i.e., with t-CA and NADPH).