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Urinary 3,3′-Diindolylmethane: A Biomarker of Glucobrassicin Exposure and Indole-3-Carbinol Uptake in Humans

Background: Brassica vegetable consumption may confer a protective effect against cancer, possibly attributable to their glucosinolates. Glucobrassicin is a predominant glucosinolate and is the precursor of indole-3-carbinol (I3C), a compound with anticancer effects. However, objective assessments of I3C uptake from Brassica vegetables have not been successful. Methods: We conducted a randomized, crossover trial to test whether 3,3′-diindolylmethane (DIM, a metabolite of I3C) excreted in the urine after consumption of raw Brassica vegetables with divergent glucobrassicin concentrations is a marker of I3C uptake from such foods. Twenty-five subjects were fed 50 g of either raw “Jade Cross” Brussels sprouts (high glucobrassicin concentration) or “Blue Dynasty” cabbage (low glucobrassicin concentration) once daily for 3 days. All urine was collected for 24 hours after vegetable consumption each day. After a washout period, subjects crossed over to the alternate vegetable. Urinary DIM was measured using a novel liquid chromatography-electrospray ionization-tandem mass spectrometry–selected reaction monitoring (LC-ESI-MS/MS-SRM) method with [2H2]DIM as internal standard. Results: Urinary DIM was consistently and significantly higher after Brussels sprouts feeding than after cabbage feeding, as evidenced by an average difference of 8.73 pmol/mg creatinine (95% confidence interval, 5.36–12.10; P = 0.00002). Conclusion: We have successfully quantified urinary DIM after uptake of I3C from food, and demonstrated that differences in glucobrassicin exposure are reflected in urinary DIM levels. Impact: Our LC-ESI-MS/MS-SRM method and the results of our study indicate urinary DIM is a measure of I3C uptake from Brassica vegetables, a finding that can be utilized in prospective epidemiologic and chemoprevention studies. Cancer Epidemiol Biomarkers Prev; 23(2); 282–7. ©2013 AACR.