Urinary N-acetyl-S-2-hydroxyethyl-L-cysteine in rats as biological indicator of ethylene oxide exposure.

There is no simple method known for the biological monitoring of ethylene oxide exposure. N-Acetyl-S-2-hydroxyethyl-L-cysteine (2-hydroxyethylmercapturic acid) excretion was evaluated as a potential indicator of exposure to this gas. Groups of Sprague-Dawley rats were given iv doses of 1, 10, or 100 mg/kg of ethylene oxide dissolved in water. Urines were collected after 12 and 24 hr. In another experiment groups of Sprague-Dawley rats were exposed by inhalation to concentrations of 1, 5, 10, 25, 50, and 200 ppm of ethylene oxide during a 6-hr period and 24-hr urines were collected subsequently. 2-Hydroxyethylmercapturic acid was analyzed in rat urine after enzymatic deacetylation into S-2-hydroxyethyl-L-cysteine, formation of a fluorescent derivative, and separation from other amino acid derivatives by high performance liquid chromatography. No S-2-hydroxyethyl-L-cysteine was observed in any sample when analysis proceeded without the deacetylation step. 2-Hydroxyethylmercapturic acid, however, was present in the urine of all exposed groups. Doses of 1 and 10 mg/kg were excreted at a fairly constant percentage of the dose, ca. 30% from 0 to 12 hr and 5% from 12 to 24 hr, while at 100 mg/kg the equivalent percentages were 16 and 5%, indicating a possible saturation of glutathione conjugation in the first 12 hr. In inhalation experiments, the amount of 2-hydroxyethylmercapturic acid excreted in 24 hr varied linearly with exposure concentration, averaging 0.27 mumol/ppm. The consistency of the excretion of this metabolite over a wide dose span points to 2-hydroxyethylmercapturic acid as a potential biological indicator of exposure to ethylene oxide.