Time‐dependent effects of Klebsiella pneumoniae endotoxin on the pharmacokinetics of chlorzoxazone and its main metabolite, 6‐hydroxychlorzoxazone, in rats: restoration of the parameters in 96 hour in KPLPS rats to control levels

Abstract

It has been reported that chlorzoxazone (CZX) was primarily metabolized via hepatic Cyp2e1 to form 6-hydroxychlorzoxazone (OH-CZX) in rats, and the activity of aniline hydroxylase (a Cyp2e1 marker) in the liver was significantly decreased in rats at 24 h after pretreatment with lipopolysaccharide derived from Klebsiella pneumoniae (24 h KPLPS rats), whereas the levels were not changed at 2 h and 96 h in the KPLPS rats. Thus, the time-dependent pharmacokinetic parameters of CZX and OH-CZX were evaluated after the intravenous administration of CZX (20 mg/kg) to control rats, and the 2 h, 24 h and 96 h KPLPS rats along with the time-dependent changes in the protein expression of hepatic Cyp2e1. After the intravenous administration of CZX to 24 h KPLPS rats, the AUC(0-2 h) of OH-CZX and AUC(OH-CZX, 0-2 h)/AUC(CZX) were significantly smaller (by 40.5% and 71.2%, respectively) than those of controls due to the significant decrease (by 75.3%) in the protein expression of hepatic Cyp2e1. However, in 96 h KPLPS rats, the pharmacokinetic parameters of both CZX and OH-CZX were unchanged compared with controls due to the restoration of the protein expression of hepatic Cyp2e1 to control levels. These observations highlighted the existence of the time-dependent effects of KPLPS on the pharmacokinetics of CZX and OH-CZX in rats.

Pharmacokinetics of a Cytochrome P450 2E1 Probe, Chlorzoxazone, and its 6-Hydroxy Metabolite in Poloxamer 407-Induced Hyperlipidemic Rats

“…CZX dose for this study (20 mg/kg) was in the intravenous dose range of 15 to 50 mg/kg, which showed linear disposition of CZX (29). The pharmacokinetic parameters of CZX in control rats (Table 2) were similar to those in previous pharmacokinetic studies on CZX including CL (8.96-12.3 mL/min/kg) and V ss (279-391 mL/kg) values (14,20,23,30).…”

“…The methods used for the measurement of V max , K m , and CL int for the formation of OH-CZX from CZX in hepatic microsomes were similar to those reported previously (14). The following components were mixed: the above hepatic microsomes from each group (equivalent to 0.2 mg protein), 0.1 M Tris-HCl buffer (pH 7.4), and 5 L of methanol containing CZX (final CZX concentrations of 2.5, 5, 10, 20, 50, 100, 200, 500, and 1000 M).…”

“…For analysis of plasma lipid profiles, 400 L of blood (200 L of plasma) were obtained from each rat immediately before the start of the experiment. CZX, dissolved in distilled water (an adjusted pH of 8.5) with a minimal amount (5 L/ 1 mL) of 10 N NaOH at a dose of 20 mg (in 2 mL)/kg (14,20), was manually infused over 1 min via the jugular vein of control (n = 9) and HL rats (n = 10). Blood samples (approximately 0.12 mL) were collected via the carotid artery at 0 (control), 1 (end of infusion), 5, 15, 30, 45, 60, 90, 120, and 180 min after the start of intravenous infusion.…”

“…Concentrations of CZX and OH-CZX were determined by HPLC according to previously described methods (14,23) [v/v] for urine samples) was run at a flow rate of 1.0 mL/min, and the column eluent was monitored at 283 nm using an ultraviolet detector. Unconjugated concentrations of OH-CZX were also measured in urine samples without incubation with β-glucuronidase.…”

“…We also evaluated the pharmacokinetics of chlorzoxazone (CZX, 5chloro-3H-benzooxazol-2-one) and its major metabolite, 6-hydroxy CZX (OH-CZX) as probes for CYP2E1 activity after intravenous administration of CZX to both control and HL rats. OH-CZX formation has been used as a chemical probe to assess the activity of CYP2E1 both in vitro and in vivo because of its good correlation with CYP2E1 activity in both humans and rats (13,14). The in vitro metabolic activity of CYP2E1 in hepatic microsomal fractions from HL rats was also evaluated with CZX.…”