Determination of sphinganine, sphingosine and Sa/So ratio in urine of humans exposed to dietary fumonisin B1

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Abstract
Fumonisin B1 (FB1) is an inhibitor of sphinganine N-acyltransferase and the increase in the sphinganine/sphingosine (Sa/So) ratio in urine or serum has been proposed as a biomarker to evaluate exposure to fumonisins. The objectives of this study were to (1) develop a liquid chromatographic method sufficiently sensitive to determine the low concentration of free Sa in male human urine, and (2) analyse So and Sa in human urine and monitor the Sa/So ratio in urine of humans exposed to FB1 in corn diets over 1 month. The liquid chromatographic method involved isolation from human urine of exfoliated cells followed by an extraction of free sphingoid bases and their separation and quantification by high performance liquid chromatography. The detection limits for So and Sa were 0.15ng/ml in female urine (2ml used) and 0.005ng/ml in male urine (60ml used). Twenty-eight healthy adult volunteers consumed for 1 month a normal diet containing their homegrown corn potentially contaminated with FB1. Immediately preceding the start of the test, morning urine samples for the determination of So and Sa were collected from each person, and the corn samples used in cooking were obtained from each family for the determination of FB1. At the end of the test period, morning-urine samples were collected from each person and analysed again. The daily FB1 intakes were estimated and used to assess the relationship between them and the urinary Sa/So ratios in humans exposed to dietary FB1 over 1 month. All the home grown corn samples contained FB1 ranging from 0.08 to 41.1mg/kg, and the estimated daily FB1