Glucobrassicin in Brassica vegetables gives rise to indole-3- carbinol (I3C), a compound with potent anticancer effects in preclinical models. We previously showed that the urinary metabolite 3,3'-diindolylmethane (DIM) could discriminate between volunteers fed high and low doses of Brassica vegetables. However, the quantitative relationship between glucobrassicin exposure and urinary DIM level is unclear. We conducted a clinical trial to examine the hypotheses that a range of glucobrassicin exposure from Brassica vegetables is reflected in urinary DIM and that this effect plateaus. Forty-five subjects consumed vegetables, a mixture of brussels sprouts and/or cabbage, at one of seven discrete dose levels of glucobrassicin ranging from 25 to 500 μmol, once daily for 2 consecutive days. All urine was collected for 24 hours after each vegetable-eating session. Urinary DIMwas measured using our published liquid chromatography-electrospray ionizationtandem mass spectrometry-selected reaction monitoring (LC/ ESI-MS/MS-SRM) method. Urinary DIM excretion increased predictably with increasing glucobrassicin dose and plateaued between 200 and 300 μmol of glucobrassicin. The association between glucobrassicin dose and urinary DIM was strong and positive (R2 = 0.68). The majority of DIM was excreted in the first 12 hours after vegetable consumption. We conclude that urinary DIM is a reliable biomarker of glucobrassicin exposure and I3C uptake and that feeding glucobrassicin beyond 200 mmol did not consistently lead to more urinary DIM, suggesting a plateau in potential chemopreventive benefit.
Bibliographical noteFunding Information:
N. Fujioka was supported in part by NHLBI training grant 5T32HL007062-34 (Gregory Vercellotti, PI). This work was supported in part by NIH P30 CA77598 (Douglas Yee, PI) utilizing the Masonic Cancer Center Analytical Biochemistry shared resource and Minnesota Masonic Charities.
© 2016 American Association for Cancer Research.
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