Urinary Mercapturic Acids as Markers for the Determination of Isothiocyanate Release from Glucosinolates in Rats Fed a Cauliflower Diet

Glucosinolates, found in plants of the genus Brassica, release physiologically active metabolites, such as isothiocyanates and nitriles, in the digestive tract under the action of plant or bacterial myrosinase. Isothiocyanates are excreted in the urine as their mercapturic acid derivatives. To study the influence of diet on isothiocyanate release, two groups of eight rats were offered either a cauliflower-based diet or a standard laboratory rat diet. After 10 days' adaptation to the diets release of allyl isothiocyanate (AITC) from a single oral dose of sinigrin, a glucosinolate commonly occurring in brassicas, was quantified. Each rat was dosed with 50 μmol of either sinigrin or AITC by stomach tube and urine was collected at 0, 2, 6, 24 and 48 h after administration. Three days later, rats which had previously received sinigrin were administered with AITC and vice versa. The concentrations of urinary mercapturic acids of isothiocyanates were determined by HPLC. Recoveries of the mercapturic acid derivative of AITC in each animal were used to estimate AITC production in sinigrin-dosed rats. Estimates of AITC release from sinigrin showed that a greater proportion of administered sinigrin was hydrolysed to AITC in cauliflower-fed rats than in rats fed a control diet (0·412 vs 0·134; P〈0·001). The approach should allow more rigorous investigation of the influence of dietary factors on glucosinolate hydrolysis in vivo.