Inhibition of microsomal N-nitrosodimethylamine demethylase by diethyl ether and other anesthetics

Development, validation, and interlaboratory comparison of an HMG-CoA reductase inhibition assay for quantitation of atorvastatin in plasma matrices

An HMG-CoA reductase inhibition assay was developed and validated for quantitation of atorvastatin in human, dog, rat, and mouse plasma. Atorvastatin was isolated from plasma by protein precipitation. Rat-liver microsomes were used to provide the reductase enzyme. The method was validated by assaying calibration standards and quality controls in triplicate on each of the 3 days. A customized computer program was used for data calculation. Quantitation of the assay ranged from 0.36 to 16 ng/ml of atorvastatin in different plasma matrices. Assay precision and accuracy, based on the coefficient of variation and percent relative error, respectively, of quality controls were 10.4% to 14.5% and within +/- 6.25% in human; 4.89% to 10.6% (+/- 8.13%) in dog; 2.68% to 8.62% (+/- 5.00%) in rat; and 3.68% to 8.96% (+/- 5.38%) in mouse plasma. The method has been applied to pharmacokinetic studies of atorvastatin in human and toxicokinetic studies in dog, rat, and mouse after atorvastatin administration. Atorvastatin equivalent concentrations in a set of plasma samples from subjects receiving single and multiple doses of atorvastatin were determined by validated HMG-CoA reductase inhibition assays at four different laboratories. Results were compared using linear regression and concordance correlation statistical procedures. Good agreements among these data indicated that results from different laboratories with the same validated method can be used interchangeably.

Relationship between cytochrome P450 2E1 and acetone catabolism in rats as studied with diallyl sulfide as an inhibitor

Previous studies have demonstrated that cytochrome P450 2E1 (P450 2E1) catalyzes the oxidation of acetone in vitro. The present study was designed to determine the importance of P450 2E1 in the catabolism of acetone in rats using diallyl sulfide (DAS) as an inhibitor of this enzyme. After a single intragastric dose of DAS, blood samples were collected from rats at different time points, and blood acetone concentrations were measured by gas chromatography. In a low DAS dose (50 mg/kg body weight) group, the maximum acetone level of 6-fold higher than the normal level was reached at 6 hr; the acetone level returned to normal at 48 hr. In a high dose (200 mg/kg) group, the maximum acetone level of 9-fold higher than the normal level was reached at 12 hr; the acetone level returned to normal at 60 hr. The turnover time and fractional turnover rate of elevated acetone were 15.8 +/- 0.5 hr and 0.054 +/- 0.001 hr-1, respectively, for the low dose, and 19.2 +/- 0.6 hr and 0.046 +/- 0.005 hr-1, respectively, for the high dose. In a chronic experiment, DAS (50 and 200 mg/kg, i.g.) was given to rats daily for 29 days, and elevated blood acetone levels were observed during the entire experimental period: 2.0 to 2.8 micrograms/mL for the low dose and 3.4 to 3.9 micrograms/mL for the high dose at 24 hr after the 1st, 7th, 14th and 28th doses versus 0.8 to 0.9 micrograms/mL for the control. The increase of blood acetone level was closely related to the decreases of N-nitrosodimethylamine (NDMA) demethylase activity and P450 2E1 content in liver microsomes. Consistent with the lack of cumulative effect from the multiple doses of DAS on acetone level, rather stable levels of the DAS metabolites, diallyl sulfoxide (45.0 micrograms/mL, range: 33.8 to 58.6 micrograms/mL) and diallyl sulfone (11.7 micrograms/mL, range: 6.9 to 15.6 micrograms/mL), were observed at 24 hr after the 1st, 7th, 21st and 28th doses with DAS (200 mg/kg) in the chronic experiment. It is likely that the inactivation and inhibition of P450 2E1 by DAS and its metabolites block the oxidation of acetone and cause its elevation in blood. The results strongly suggest an important role of P450 2E1 in acetone catabolism under physiological conditions.

Autoxidative injury with loss of cytochrome P-450 following acute exposure of rats to fasting and ether anaesthesia

1. Exposure of fasted rats (20 h) to ether anaesthesia for 4 min resulted in increased exhalation of alkanes, an indication of lipid peroxidation in vivo. 2. Liver and kidney of the fasted rats anaesthetized with ether showed immediate 4-fold increases in luminol-amplified chemiluminescence, reaching maxima 30 min later, indicating the production of reactive oxygen species. 3. Liver and kidney cytosols of the fasted anaesthetized rats similarly showed immediate 4-fold increases of thiobarbituric acid-reactive material (malondialdehyde and other lipid peroxidation breakdown products) which attained maxima 60 min later. 4. Total cytochromes P-450 of liver and kidney of rats were decreased to 25-30% of control values after 20 h fasting and 4 min of ether anaesthesia, but were restored to normal levels 2 h later. Cytochrome P450 I (EROD activity) was decreased to 35-44% of control values by the ether anaesthesia and was restored to 80% of normal levels 2 h later. 5. Diether ether is known to be metabolized by cytochrome P450 IIE1 which is induced by fasting and by diethyl ether, and is possibly involved in the observed radical production, lipid peroxidation, and loss of cytochromes P-450.