Diets rich in cruciferous vegetables such as broccoli are associated with a reduced risk of cancer. Animal studies have identified sulforaphane, an isothiocyanate, as the ingredient in broccoli responsible for protection against cancer. In humans, sulforaphane is conjugated with glutathione and that conjugate is then modified by a series of further reactions. These metabolites, termed dithiocarbamates, are excreted in the urine. Urinary dithiocarbamates are readily measured by cyclocondensation with benzenedithiol. This assay has very recently been suitably modified to permit quantitative determination of low levels of dithiocarbamates in serum, plasma, and red cells. This is a pilot study to measure dithiocarbamate levels in plasma and red cells in healthy volunteers fed a single dose of 200 micromol broccoli sprout isothiocyanates. Subjects will be admitted for two days, maintained on a diet free of isothiocyanates or glucosinolates (the precursors of isothiocyanates) and dosed on the second morning. Eleven blood samples and 11 timed urine samples will be collected, for 8 hr after dosing. Samples will be assayed for isothiocyanate and dithiocarbamate levels.
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