Do endogenous volatile organic chemicals measured in breath reflect and maintain CYP2E1 levels in vivo?

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1 (CYP2E1), on the composition and quantity of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with hepatic P450 activity and content. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 hr postdosing with DCE (100 mg/kg ip), and total P450 content and the activity of CYP2E1 was determined. Breath was collected from parallel groups of rats predose and at several intervals that encompassed the time points for rats euthanized for microsome preparation. Over 100 breath components were identified by GC/MS and quantitated by GC/FID. The overall change in the profile of breath VOCs resulting from administration of DCE was striking. An increase of approximately 1000% was measured in the mass of non-DCE-derived VOCs exhaled 4-6 hr after dosing, but there was no increase in hepatic lipid peroxidation. In addition to hexane, short-chain methyl ketones were particularly affected, and percentage increases in response to inhibition were inversely related to chain length, with acetone and 2-butanone > 2-pentanone >> 2-hexanone > 2-heptanone. There were no statistically significant decreases in total content of P450, but the activity of CYP2E1 was diminished about 65% at 2 and 5 hr after DCE treatment. However, 24 hr after inhibitor administration the total mass of VOCs expired was only marginally elevated above baseline and CYP2E1 activity was not significantly different from that of untreated rats. The compounds most markedly increased upon inhibition of CYP2E1 are also excellent inducers of that isozyme, and this finding is consistent with the hypothesis that these chemicals are important to the normal homeostasis of CYP2E1. The increase in breath components observed following inhibition of CYP2E1 suggests that VOCs in breath can reflect the activity of that isozyme in vivo.

The influence of cytochrome P450 enzyme activity on the composition and quantity of volatile organics in expired breath.

Abstract We have previously described a method to capture, identify and quantify volatile components in expired breath. The purpose of this research is to provide a non-invasive means to measure biomarkers of metabolism in vivo. In the present studies, the effect of 1-aminobenzotriazole (ABT), an inhibitor of diverse cytochrome P450 (P450) enzymes, on the composition of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with the catalytic activities and total content of hepatic P450. lntraperitoneal administration of ABT (100 mg kg-(1)) to rats resulted in markedly diminished hepatic microsomal P450 content and activities. The extent of inhibition was near maximal at 4 h, at which time approximately 50% of the total P450 content, about 65% of the CYPlA2 activity, 55% of the CYP2E1 activity, and about 80% of CYP2B activity were lost. Inhibition was maintained to 48 h post-dosing, but P450 content and activities had largely been restored by day 7. Concomitant with the inhibition of P450 were corresponding increases (up to several hundred-fold) in the molar amount of volatiles appearing in the breath of ABT-treated animals, and the rebound of P450 levels was attended by corresponding decreases in the appearance of breath volatiles. These studies indicate that P450 plays a major role in the metabolism of VOCs appearing in breath, and that these chemicals can serve as markers on P450 activity in vivo.

Determination of acrylamide in rat serum and sciatic nerve by gas chromatography-electron-capture detection.

A modified method for the derivatization and determination of acrylamide as 2-bromopropenamide by gas chromatography-electron-capture detection was developed and applied to serum and sciatic nerve from rats. The method was accurate and precise over the calibration range 2.24-7.47 micrograms/ml in serum diluted 1:125 and 4-122 micrograms/g in sciatic nerve homogenate (5 mg/ml). limits of detection were estimated to be 1200 ng/ml in undiluted serum and 3 micrograms/g in intact sciatic nerve. The use of less dilute samples to allow for lower limits of detection appears feasible. The time-course of acrylamide in serum and sciatic nerve was studied after acute dosing and indicated elimination half-lives of 1.8 and 2.0 h for serum and sciatic nerve, respectively. A dose-effect relationship was established for each matrix after acute dosing and the measured acrylamide concentrations in serum (microgram/ml) were approximately the same as in sciatic nerve (microgram/g).