Effect of 1-aminobenzotriazole on thein vitrometabolism and single-dose pharmacokinetics of chlorzoxazone, a selective CYP2E1 substrate in Wistar rats

Abstract

The aim of this study was to study the effect of 1-aminobenzotriazole (ABT) on in vitro metabolism, oral, and intravenous (IV) pharmacokinetics of chlorzoxazone (CZX) in rats. Enzyme kinetics of CZX was performed with rat and human liver microsomes and pure isozyme (CYP2E1) with and without ABT. The enzyme kinetics (V(max) and K(m)) of the formation of 6-hydroxychlorzoxazone (OH-CZX) was found to be similar among rat liver microsomes (3486 pmol mg protein(-1) min(-1) and 345 microM), human liver microsomes (3194 pmol mg protein(-1) min(-1) and 335 microM) and pure isozyme (3423 pmol mg protein(-1) min(-1) and 403 microM), but K(I) and K(inact) values for ABT towards the ability to inhibit the formation of OH-CZX from CZX varied between liver microsomes (rat: 32.09 microM and 0.12 min(-1); human: 27.19 microM and 0.14 min(-1)) and pure isozyme (3.18 microM and 0.29 min(-1)). The novel robust analytical method was capable of quantifying CZX, OH-CZX, and ABT simultaneously in a single run, and the method was used for both in vitro and in vivo studies. Pre-treatment of rats with ABT prior to oral and IV administration of CZX significantly decreased the clearance (threefold) and consequently increased the AUC of CZX (approx. three- to fourfold). When rats were pre-treated with ABT, the formation of OH-CZX was completely blocked after oral and IV administration; however, we were able to measure OH-CZX in rats administered with CZX by oral and IV routes without pre-treatment of ABT. The oral bioavailability of CZX was approximately 71% when dosed alone and reached 100% under pre-treatment with ABT. The t(1/2) values of CZX was significantly prolonged for oral dosing compared with IV dosing under pre-treated conditions with ABT, suggesting an involvement of pre-systemic component in the disposition of CZX. The pharmacokinetic parameters of ABT did not change when it was dosed along with CZX (oral and IV), indicating that either CZX or OH-CZX had no effect on disposition of ABT. The plasma concentrations of ABT were above and beyond the required levels to inhibit CYP2E1 enzyme for at least 36 h post-treatment.

Chlorzoxazone, an SK-Type Potassium Channel Activator Used in Humans, Reduces Excessive Alcohol Intake in Rats

“…Prolonged alcohol exposure can upregulate CYP2E1 activity (19–21), including in the brain (22), which could decrease CZX concentrations in alcohol-drinking rats. However, alcohol can act as a moderate competitive inhibitor of CYP2E1 (23) and increase CZX peak concentrations, although this effect would be more pronounced across time and less evident in the first several hours (24–26). We have not examined CZX metabolism here, in part because repeated blood collection would likely disrupt ongoing alcohol intake.…”

In Vivo and in Vitro Characterization of Chlorzoxazone Metabolism and Hepatic CYP2E1 Levels in African Green Monkeys: Induction by Chronic Nicotine Treatment

“…In humans, the K m ranges from 77 to 149 M (Court et al, 1997;Lejus et al, 2002), and in African green monkeys, the K m was 95.4 M. In humans, the V max ranges from 1.43 to 3.19 pmol/min/g (Court et al, 1997;Lejus et al, 2002;Muzeeb et al, 2005); the V max in African green monkeys was 3.5 pmol/min/ g, and in cynomolgus monkeys it ranges from 0.52 to 3.38 pmol/ min/g (Court et al, 1997;Tanaka et al, 2000). The amount of CYP2E1 protein detected in microsomes from African green monkeys is similar to the levels of CYP2E1 in human microsomes, assuming equal detection of the two proteins by the antibody, consistent with the similar V max values for CZN metabolism between African green monkeys and humans (Court et al, 1997;Lejus et al, 2002;Muzeeb et al, 2005). Monkey CYP2E1 is mainly expressed around the central veins in liver tissue (Fig.…”

Biotransformation and pharmacokinetics of the novel anticancer drug, SYUIQ-5, in the rat

“…Activities of EROD, MROD and PROD were determined using the methods as previously described [23][24][25] with some modifications. Since >90% of the dose of chlorzoxazone is oxidized by CYP/Cyp2E1 to 6-hydroxychlorzoxazone in mice, rats and humans, chlorzoxazone has been widely used as a probe substrate for measuring CYP/Cyp2E1 activity in rodents and humans [26][27][28]. Additionally, nifedipine dehydrogenation activity was used to determine the activity of Cyp3A1/2 [29].…”