Influence of diet and other factors on urinary levels of thioethers.

Urinary excretion of thioethers has been used as an indicator of exposure to potentially alkylating agents in several studies. These studies, however, often had the disadvantage of high and varying background values. We have studied methods for sampling and determination of urinary thioethers. Modifications have been made making it possible to increase the sensitivity of the method substantially. The thioethers were extracted with ethyl acetate and hydrolyzed with sodium hydroxide. The thiols were then determined spectrophotometrically with the reagent of Ellman. The extraction procedure and the addition of the reagent were found to be critical steps, whereas the crude urine samples were comparatively stable during storage at -20 degrees C. Diet was found to be the most important factor. Using a standardized diet over 24 h with chicken, potatoes, bread and dairy products as the major components, excluding vegetables of the Cruciferae family, 24 subjects excreted low amounts of thioethers, 3.2 +/- 0.2 mmol/mol creatinine, (mean +/- SEM). Individual values did not exceed 6.5 mmol/mol creatinine. Without food restrictions the mean values and the standard deviations were increased up to five and ten times respectively. Ingestion of certain foodstuffs increased the thioether excretion up to 20 times. Twelve smokers (20 cig/d) excreted 6.7 +/- 0.4 mmol/mol creatinine (mean +/- SEM, afternoon samples and standardized diet). No effects of gender and age of the subject could be observed. It is recommended that diet factors be kept under strict control to increase the sensitivity of the thioether assay and to avoid misleading results due to diet effects.