Urinary excretion of N-acetyl-S-allyl-L-cysteine upon garlic consumption by human volunteers

Abstract

N-Acetyl-S-allyl-L-cysteine (allylmercapturic acid, ALMA) was previously detected in urine from humans consuming garlic. Exposure of rats to allyl halides is also known to lead to excretion of ALMA in urine. ALMA is a potential biomarker for exposure assessment of workers exposed to allyl halides. It is not known whether garlic consumption can lead to urinary concentrations of ALMA which may interfere with biological monitoring of exposure to allyl halides by determination of urinary ALMA. Therefore, this study was undertaken to determine the cumulative excretion and the excretion kinetics of ALMA in urine of humans consuming garlic. Six human volunteers were given orally two garlic tablets, each containing 100 mg garlic extract (each representing 300 mg fresh garlic). Three of the volunteers consumed additional garlic after the garlic tablet intake. Urine samples were collected up to 24 h after the intake of the garlic tablets. ALMA was identified in the urine using gas chromatography-mass spectrometry (GC-MS) and determined quantitatively with a limit of detection of 0.10 microgram/ml with gas chromatography with sulphur selective detection. The total amount of ALMA found in urine of volunteers who consumed two garlic tablets was 0.43 +/- 0.14 mg (n = 3). In the urine of the three volunteers who consumed not only two garlic tablets but also additional fresh garlic, a significantly higher amount of ALMA was excreted in the urine, 1.4 +/- 0.2 mg (n = 3). The elimination half-life of ALMA, estimated from urinary excretion rate versus time curves, was 6.0 +/- 1.3 h (n = 5). One volunteer, who ate additional garlic, showed an irregular elimination profile and was excluded from this estimation. The highest urinary concentration of ALMA found in this study was 2.2 micrograms/ml. In a preliminary biological monitoring study of exposure in workers with potential exposure to allyl chloride (AC) up to the occupational exposure limit of 1 ppm (8-h TWA), we recently found urinary ALMA concentrations up to 4 micrograms/ml. Based on the results presented here, we conclude that garlic consumption is a potential confounder when monitoring human exposure to allylhalides and other chemicals leading to ALMA excretion when ALMA is used as a biomarker of exposure.