Feed or Food Responsible for the Presence of Low-Level Thiouracil in Urine of Livestock and Humans?

• Published in: Journal of agricultural and food chemistry Vol. 59; no. 10; pp. 5786 - 5792
• Main Authors: Bussche, Julie Vanden, Kiebooms, Julie A. L, De Clercq, Nathalie, Deceuninck, Yoann, Le Bizec, Bruno, De Brabander, Hubert F, Vanhaecke, Lynn
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 25-05-2011
• Subjects: Animal Feed - analysis; Animals; Biological and medical sciences; Brassicaceae; Brassicaceae - metabolism; broccoli; cabbage; cauliflower; Diet; drugs; enzymatic hydrolysis; erucic acid; Feed and pet food industries; Food; Food industries; foods; Fundamental and applied biological sciences. Psychology; glucose; Glycoside Hydrolases - metabolism; Humans; hydrolysis; livestock; Livestock - urine; rapeseed cake; thiouracil; Thiouracil - analysis; Thiouracil - metabolism; Thiouracil - urine; Toxicology in Agriculture and Food; urine; naturally occurring thiouracil; mass spectrometry; liquid chromatography; myrosinase; Brassicaceae; enzymatic hydrolysis; Human; Urine; Biological fluid; Liquid chromatography; Hydrolysis; Cruciferae; Dicotyledones; Angiospermae; Spermatophyta; Mass spectrometry; Feed; Enzymatic reaction
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf200556x

In recent years, questions have been raised on the possible semi-endogenous status of the alleged xenobiotic thyreostatic drug thiouracil; thiouracil has been detected in the urine of various animals (livestock and domesticated) at concentrations between 1 and 10 μg L–1 and also in human urine. Although several studies suggest Brassicaceae-derived feed as potential origin, no traces of thiouracil have been detected in feed so far. Therefore, the aim of this study was to elucidate the origin of thiouracil in the urine of livestock and humans. To this purpose various Brassicaceae feed and food sources (e.g., rapeseed, rapeseed coarse meal, cabbage, cauliflower, broccoli) were investigated for the presence of thiouracil. In addition, the impact of the Brassicaceae-related β-thioglucosidase enzyme was evaluated. This myrosinase enzyme appeared to be crucial, because without its catalyzed hydrolysis no thiouracil could be detected in the various Brassicaceae-derived samples. Therefore, a sample pretreatment with incorporated enzymatic hydrolysis was developed after ensuring the quality performance of the extracted myrosinase mixture with a single-point glucose assay. Upon enzymatic hydrolysis and LC-MS2 analysis, thiouracil was successfully detected in samples of traditional rapeseed, rapeseed-‘00’ variety coarse meal (values of erucic acid <2% and glucosinolates <25 μmol g–1), and rapeseed cake at 1.5, 1.6, and 0.4 μg kg–1, respectively. As for the food samples, broccoli and cauliflower displayed thiouracil concentrations of 6.0 and <1.0 μg kg–1, respectively. To the best of the authors' knowledge this study is the first to report the presence of naturally occurring thiouracil in feed and food samples. Future research should investigate the pathway of thiouracil formation and identify its possible precursors.