Rat Cytochrome P450 2C11 in Liver Microsomes Involved in Oxidation of Anesthetic Agent Propofol and Deactivated by Prior Treatment with Propofol

Abstract

ABSTRACT:Propofol (2,6-diisopropylphenol) is a widely-used anesthetic agent attributable to its rapid biotransformation. Liver microsomal cytochrome P450 (P450) isoforms involved in the biotransformation of propofol in rats and the effects of propofol in vivo on P450 levels in rats were investigated. Of six cDNA-expressed rat P450 isoforms tested, CYP2B1 and CYP2C11 had high catalytic activities from 5 M and 20 M propofol concentrations, respectively. Rates of propofol metabolism, at a substrate concentration of 20 M based on the reported human blood concentration, were decreased by intraperitoneal treatment of propofol with male rats, in contrast to a strong induction by phenobarbital. Single intravenously administered propofol (10 mg/kg) caused the decrease of total P450 and CYP2C contents and activities of testosterone 16␣-hydroxylation and propofol metabolism in liver microsomes from male rats. The suppressive effects were caused by administered propofol (10 mg/kg) twice every 4 h on CYP2B activities such as testosterone 16␤-hydroxylation or pentoxyresorufin O-depentylation, in addition to the strong suppression of CYP2C function by the single propofol treatment. These results suggest that CYP2C11, presumably deactivated by propofol, has an important role in propofol metabolism in rat liver microsomes. Repeated administration of propofol could markedly decrease the biotransformation of propofol via P450 deactivation.Propofol (2,6-diisopropylphenol) is administered as a bolus for the induction of anesthesia and as an infusion for maintenance of anesthesia or for sedation (Bryson et al., 1995). One of the major advantages of this drug over other injectable anesthetic agents is the rapid and complete recovery that occurs even after relatively prolonged intravenous infusions (Mandsager et al., 1995). This property is attributable to rapid and extensive biotransformation of the parent compound, primarily by the liver. The relative contribution of individual metabolic pathways has been found to vary among animal species and humans (Simons et al., 1991;Sneyd et al., 1994). Although there are several reports of propofol pharmacokinetics or drug interactions in humans (Guitton et al., 1998;McKillop et al., 1998;Hamaoka et al., 1999;Court et al., 2001;Oda et al., 2001;Tanaka et al., 2004), the precise roles of cytochrome P450 (P450) isoforms in the propofol disposition are still unknown. Moreover, there is no report of the effects of propofol on P450 induction or deactivation as a determinant factor of the pharmacodynamic and/or pharmacokinetics of propofol. There has been reported a significant association between receiving a long-term and high-dose propofol infusion and developing progressive myocardial failure (Bray, 1998).In the present study, the roles of rat P450 isoforms involved in propofol metabolism were investigated with recombinant rat P450 isoforms and rat liver microsomes, mainly at a substrate concentration of 20 M, based on the human plasma concentration (McKillop et al., 1998). The effects of P450 dea...

Human Blood Concentrations of Dichlorodiphenyltrichloroethane (DDT) Extrapolated from Metabolism in Rats and Humans and Physiologically Based Pharmacokinetic Modeling

“…Typical P450 substrates, their reaction products, and other reagents used in this study were obtained from sources described previously or were of the highest quality commercially available. 24,26) Typical P450-dependent marker oxidation activities were measured in liver microsomes in rats to evaluate enzyme inductions on treatment with DDT. Activities for the O-dealkylation of ethoxyresorufin (20 µM, for P450 1A) and pentoxyresorufin (100 µM, P450 2B) and for testosterone 7α-hydroxylation (200 µM, P450 2A), tolbutamide methyl hydroxylation (1000 µM, P450 2C), bufuralol 1 -hydroxylation (20 µM, P450 2D), chlorzoxazone 6-hydroxylation (50 µM, P450 2E), and midazolam 1 -and 4-hydroxylation (100 µM, P450 3A) were assayed according to the described HPLC methods.…”

“…Liver microsomes from male rats (7 weeks old) treated with DDT (10 mg/kg) and from untreated controls were prepared as described previously. 24) Microsomal P450 contents were determined spectrally by the established method. 25) Protein concentrations were estimated by using a bicinchoninic acid (BCA) protein assay kit (Pierce, Rockford, IL, U.S.A.).…”

“…Activities for the O-dealkylation of ethoxyresorufin (20 µM, for P450 1A) and pentoxyresorufin (100 µM, P450 2B) and for testosterone 7α-hydroxylation (200 µM, P450 2A), tolbutamide methyl hydroxylation (1000 µM, P450 2C), bufuralol 1 -hydroxylation (20 µM, P450 2D), chlorzoxazone 6-hydroxylation (50 µM, P450 2E), and midazolam 1 -and 4-hydroxylation (100 µM, P450 3A) were assayed according to the described HPLC methods. 24,27,28) DDT and DDE Determinations in Biological Samples from Rats --DDT and DDE in blood and urine samples from individual rats were extracted with ethanol and hexane. DDT and DDE concentrations in these extracts were measured by an HP6890 gas chromatography/mass spectrometry (GC/MS) system equipped with a DB-5MS column (30 m × 0.25 mm i.d.…”

Effects of Genetic Polymorphism of CYP2B6 and UGT1A9 and Sex Differences on Pharmacokinetics of Propofol

“…An aliquot of the supernatant after filter treatment (Millex-LG, 0.20μm, Millipore, Tokyo, Japan) was injected onto an analytical C 18 reversed-phase column (150 mm × 4.6 mm, Capcell Pak C 18 UG120 S5, Shiseido, Tokyo, Japan) maintained at 30°C. The mobile phase was 55% (v/v) acetonitrile at a flow rate of 0.6 mL/ min 20) . The elution profiles of propofol were monitored fluorometrically at an excitation wavelength of 270nm and an emission wavelength of 310 nm.…”

“…Genetic polymorphisms in CYP2B6 and UGT1A9 have been reported, along with their allele frequency in the Japanese population [8][9][10] . Several studies have shown that the allele frequency of the G516T mutation of CYP2B6 was approximately 20%, and the variation among genetic polymorphisms decreased the enzyme activity of CYP2B6 8) [10][11][12] . In contrast, Saito Y et al and Girard H et al have reported that the allele frequency of the I399C>T mutation of UGT1A9 was approximately 64% and that the variant increased the conjugation activity of propofol 9)13) .…”