Pharmacokinetic parameters of chlorzoxazone and its main metabolite, 6-hydroxychlorzoxazone, after intravenous and oral administration of chlorzoxazone to liver cirrhotic rats with diabetes mellitus.

Protein expression of the hepatic CYP2E1 has been reported to be increased in diabetic rats. This enzyme is the primary metabolizer of chlorzoxazone (CZX) to 6-hydroxychlorzoxazone (OH-CZX). Although patients with liver cirrhosis have a higher prevalence of diabetes mellitus, there have been no reported studies on the protein expression of CYP2E1 in rats induced to have liver cirrhosis and diabetes mellitus by injection of N-dimethylnitrosamine followed by streptozotocin [liver cirrhosis with diabetes mellitus (LCD) rats]. Thus, in the present study, the pharmacokinetics of CZX and OH-CZX were evaluated in LCD rats. Compared with control rats, LCD rats had significantly decreased (by 62%) total liver protein and significantly increased (by 124%) protein expression of CYP2E1, but the intrinsic clearance (Cl(int); formation of OH-CZX per milligram protein) was comparable in both groups of rats. As a result, the relative Cl(int) was also comparable for the two groups. Thus, OH-CZX formation in LCD and control rats was expected to be similar. As expected, after i.v. (20 mg/kg) and p.o. (50 mg/kg) administration of CZX, the area under the curve (AUC) of OH-CZX was comparable in control and LCD rats (i.v., 571 +/- 85.8 and 578 +/- 413 microg x min/ml, respectively; p.o., 1540 +/- 338 and 2170 +/- 1070 microg x min/ml, respectively). In LCD rats, the AUC(OH-CZX)/AUC(CZX) ratio was similar to the value in control rats after i.v. and p.o. administration. These results indicate that OH-CZX can be used as a chemical probe to assess the activity of CYP2E1 in LCD rats.

Effects of glucose on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate.

The effects of glucose on CYP2E1 expression in rats with acute renal failure induced by uranyl nitrate (U-ARF) have been reported. CYP2E1 was significantly induced (2.3-fold) in rats with U-ARF compared with that in control rats. In contrast, CYP2E1 expression was significantly decreased in rats with U-ARF supplied with glucose (dissolved in tap water to make 10%, w/v) in their drinking water for 5 days (U-ARFG) compared with that in rats with U-ARF. However, CYP2E1 in rats with U-ARFG was significantly greater than that in control rats. Chlorzoxazone (CZX) primarily undergoes hydroxylation, catalyzed mainly by CYP2E1, to form 6-hydroxychlorzoxazone (OH-CZX) rats. Hence, it could be expected that in rats with U-ARFG, formation of OH-CZX could significantly decrease and increase compared with those in rats with U-ARF and control rats, respectively. This expectation is proven by the following results of a study of intravenous administration of CZX at a dose 20 mg/kg to control rats and rats with U-ARF and U-ARFG. First, the total area under the plasma concentration-time curve from time zero to 8 h (AUC(0-8 h)) of OH-CZX in rats with U-ARFG (8730 microg x min/mL) was significantly greater than that in control rats (414 microg x min/mL) and significantly smaller than that in rats with U-ARF (11500 microg x min/mL). Second, the AUC(0-8 h, OH-CZX)/AUC(CZX) ratio in rats with U-ARFG (10.0) was significantly greater than that in control rats (0.252) and significantly smaller than that in rats with U-ARF (17.5). Finally, the in vitro intrinsic OH-CZX formation clearance (CL(int)) in rats with U-ARFG (27.9 mL/min/mg protein) was significantly slower than that in rats with U-ARF (36.7 mL/min/mg protein) and significantly faster than that in control rats (17.7 mL/min/mg protein).

Effects of cysteine on the pharmacokinetics of intravenous clarithromycin in rats with protein-calorie malnutrition.

Effects of cysteine on the pharmacokinetics of clarithromycin were investigated after intravenous administration of the drug at a dose of 20 mg/kg to control rats (4-week fed on 23% casein diet) and rats with PCM (protein-calorie malnutrition, 4-week fed on 5% casein diet) and PCMC (PCM treated with 250 mg/kg for oral cysteine twice daily during the fourth week). Clarithromycin has been reported to be metabolized via hepatic microsomal cytochrome P450 (CYP) 3A4 to 14-hydroxyclarithromycin (primary metabolite of clarithromycin) in human subjects. It has also been reported that in rats with PCM, CYP3A23 level decreased to 40-50% of control level, but decreased CYP3A23 level in rats with PCM completely returned to control level by oral cysteine supplementation (rats with PCMC). Human CYP3A4 and rat CYP3A23 proteins have 73% homology. In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity, AUC (567, 853 and 558 microg min/ml for control rats and rats with PCM and PCMC, respectively) and percentage of clarithromycin remaining after incubation with liver homogenate (69.6, 83.9 and 71.7%) were significantly greater than those in control rats and rats with PCMC. Moreover, in rats with PCM, the total body clearance, CL (35.3, 23.4 and 35.8 ml/min/kg), nonrenal clearance, CL(NR) (21.3, 15.2 and 24.1 ml/min/kg) and maximum velocity for the disappearance of clarithromycin after incubation with hepatic microsomal fraction, V(max) (351, 211 and 372 pmol/min/mg protein) were significantly slower than those in control rats and rats with PCMC. However, above mentioned each parameter was not significantly different between control rats and rats with PCMC. The above data suggested that metabolism of clarithromycin decreased significantly in rats with PCM as compared to control due to significantly decreased level of CYP3A23 in the rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters of clarithromycin (AUC, CL, CL(NR) and V(max)) were restored fully to control levels because CYP3A23 level was completely returned to control level in rats with PCMC.

Effects of cysteine on the pharmacokinetics of itraconazole in rats with protein-calorie malnutrition.

The effects of cysteine on the pharmacokinetics of itraconazole were investigated after intravenous, 20 mg/kg, and oral, 50 mg/kg, administration of the drug to control rats (fed for 4 weeks on 23% casein diet) and rats with PCM (protein-calorie malnutrition, fed for 4 weeks on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily during the fourth week). After intravenous administration of itraconazole to rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of itraconazole was significantly greater (3580 compared with 2670 and 2980 microg min/ml) than those in control rats and rats with PCMC (the values between control rats and rats with PCMC were not significantly different). The above data suggested that metabolism of itraconazole decreased significantly in rats with PCM due to suppression of hepatic microsomal cytochrome p450 (CYP) 3A23 in the rats. The results could be expected since in rats with PCM, the level of CYP3A23 decreased significantly as compared to control. Itraconazole was reported to be metabolized via CYP3A4 to several metabolites, including hydroxyitraconazole, in human subjects. Human CYP3A4 and rat CYP3A1 (CYP3A23) proteins have 73% homology. By cysteine supplementation (rats with PCMC), the AUC of itraconazole was restored fully to control levels.