A comprehensive evaluation of the vial equilibration method for quantification of the metabolism of volatile organic chemicals. Trichloroethylene.

A study was undertaken, using 1,1,2-trichloroethylene (TCE), to: a) evaluate and improve the efficiency of the vial equilibration method, as first reported by Sato and Nakajima (Toxicol. Appl. Pharmacol. 47, 41-46, 1979); b) select an appropriate vehicle for the volatile substrate; c) examine the rate of metabolism of TCE by different rat hepatic microsomal preparations; d) determine TCE metabolic rate constants; and e) assess the influence of oleic acid and linoleic acid (the two major fatty acids in corn oil) on TCE metabolism. TCE was incorporated into a 1% Alkamuls aqueous emulsion and incubated with cofactors and the 10,000g supernatant or the microsomal fraction of livers of male Sprague-Dawley rats (275-325 g) in sealed headspace vials. Different trials were conducted to elucidate time-, enzyme-, and substrate-activity relationships. The apparent Km and Vmax were 2.0 microM and 1.9 nmol/mg protein/10 min for substrate concentrations ranging from 0.3 to 34 microM in the 10,000g fraction. The apparent Km and Vmax for the microsomal fraction were 4.17 microM and 8.0 nmol/mg protein/10 min, respectively. Linoleic acid concentrations of 10 microM and higher reduced TCE metabolism by the 10,000g fraction, whereas oleic acid concentrations of 50 microM and higher were required to inhibit TCE metabolism. Isooctane and dimethylsulfoxide caused a significant decrease in TCE metabolism. The vial equilibrium technique, as described herein, is relatively simple, rapid, and reliable, and may be applicable as a standard procedure for quantifying volatile organic chemical metabolism by different tissues of different species, including humans.