Abstract

Disulfiram (DSF) is a mechanism-based inhibitor of cytochrome P-450 2E1 (CYP2E1), resulting in loss of CYP2E1 protein and activity, which may be useful in preventing CYP2E1-mediated xenobiotic toxicity. The duration of inhibition after a single DSF dose is, however, unknown. The purpose of this investigation was to determine this duration, and CYP2E1 formation and degradation rates, in humans. Oral chlorzoxazone (CLZ) was used as the selective in vivo probe for CYP2E1. Healthy subjects received CLZ to determine baseline CYP2E1 activity (CLZ plasma clearance and 6-hydroxychlorzoxazone fractional metabolic clearance). One week later, DSF (500 mg orally) was administered at bedtime, and CLZ administered the following morning and 3, 6, 8, 10, and 13 days after DSF. A terminal DSF metabolite, 2-thiothiazolidine-4 carboxylic acid, was also measured in each 24-h urine sample. The mean CLZ clearance and 6-hydroxychlorzoxazone fractional metabolic clearance on the first day declined to 10.2 and 5.5% of baseline values, indicating rapid and profound CYP2E1 inhibition. CYP2E1 activity returned to half that of control on day 3, and to baseline values on day 8. Assuming zero-order synthesis and first-order degradation, the in vivo CYP2E1 synthesis rate and degradation half-life was estimated to be 11 ± 5 nmol/h and 50 ± 19 h, respectively. Significant amounts of 2-thiothiazolidine-4 carboxylic acid were present only on day 1, suggesting that the return of in vivo CYP2E1 activity was not caused by inhibitor washout, but by enzyme resynthesis. Results regarding CYP2E1 disposition may be useful for modeling the effects of CYP2E1 inducers and inhibitors. For prevention of CYP2E1-mediated bioactivation, depending on protoxicant disposition, a second DSF dose might be necessary to completely prevent toxicity.