Sensitive gas chromatographic methods for the determination of vinyl epoxide synthetase activity using trichloroethylene as a model substrate

Dose-dependent induction and suppression of liver mixed-function oxidase system in chlorinated hydrocarbon solvent metabolism

The effect of continuous exposure to trichloroethylene (TRI), tetrachloroethylene (TETRA) or methylchloroform (MC) on the hepatic mixed-function oxidase system (MFOS) was studied in rats by using 10 000 x g supernatant fraction. Exposure to TETRA for 240 h at 200, 100 and 50 ppm enhanced oxidative conversion from TETRA to trichloroacetic acid. When the animals were exposed for 240 h to 200, 400 and 800 ppm, oxidative conversion from MC to trichloroethanol was elevated. However, elevation was less remarkable with the increase of exposure intensities from 400 to 800 ppm. With TRI, MFOS activities were more critically assessed as a function of duration and dose because the variable response in MFOS activity was observed in preliminary studies when rats were exposed to 400 ppm for 240 h. The MFOS activities in rats exposed to TRI at 50, 400 or 800 ppm for 48 h, 72 h, 168 h and 240 h were measured. The MFOS activities were all suppressed after 48-h exposure irrespective of the exposure concentration. After 72--240 h, suppression was superseded by activation at 50 ppm, while continuity of suppressive state was observed at 800 ppm and transitional state was the case of the exposure at 400 ppm. The possibility that epoxide hydratase would be involved in the metabolism of TRI, but not in those of other two chemicals, was also presented. Based on these findings, mathematical models for TRI and TETRA metabolism were established, which can explain hepatotoxicity appearing only after exposure to TRI at 800 ppm for 168 h or more.

Two rapid methods for the simultaneous gas-liquid chromatographic determination of carbon tetrachloride and chloroform in biological material and expired air

Two simple gas-liquid chromatographic techniques were developed for the simultaneous determination of CCl4 and CHCl3 in biological material and expired air and principally for use in the well-known CCl4-induced hepatotoxicity model: a non-extractive head-space analysis by flame ionization detection (FID) and a single-step toluene extraction using electron-capture detection (ECD). For head-space analysis, blood or liver homogenate is incubated with buffer in sealed reaction vials and the head-space vapour sampled for FID determination. Absolute signal response to CCl4 and CHCl3 was used for calibration in the range 5-500 microgram per gram of biological material. The method is reasonably accurate, e.g. CCl4 in liver homogenate 98 +/- 21.8 (S.D.) %, in blood 94 +/- 13.3%, but the precision is poor (rel. S.D. 10-20%). Air samples in volumes of up to 2 ml may be determined by direct FID injection. The ECD sensitivity of to CCl4 and CHCl3 permits determination of microsamples (50-500 microliters) of blood and liver homogenate by extraction with buffer into toluene containing an internal standard (propyl iodide). The linear range of the detector allowed calibration by peak area ratio in the concentration range (10-1500 ng of CCl4 or CHCl3 per millilitre of toluene. The accuracy of the method is high, e.g. in blood CHCl3 101 +/- 9.5 (S.D.)%, CCl4 100 +/- 15.2%, as is the precision: rel. S.D. ca 5% for both CCl4 and CHCl3. For elimination studies, CCl4 and CHCl3 in air may be trapped in toluene and determined by ECD. Recovery of known amounts of CCl4 and CHCl3 from air chamber was high: 100 +/- 4.7 (S.D.)% and 111 +/- 10.9%, respectively, and reduction of CCl4 to CHCl3 by the trapping system negligible (less than 0.01%). Cross-checking of the methods and application to the commonly used CCl4 hepatotoxicity model is demonstrated.

Microsomal vinyl oxide synthetase: modification of its kinetic parameters by chemical carcinogens

The kinetic parameters of liver microsomal vinyl oxide synthetase as well as their modifications under the influence of various pretreatments have been evaluated, using 1,1,2-trichlorethylene (TCE) as a substrate. The results were correlated with those obtained using aldrin oxide synthetase and benzpyrene hydroxylase as typical cytochrome P-450 dependent enzymatic activity. The treatments of animals with chemical carcinogens selectively increase the affinity of those enzymes for their substrates.