Abstract 4651: Analysis of 3,3′-diindolylmethane in urine after consumption of cruciferous vegetables in the Singapore Cohort Study

Abstract

Abstract Background: Indole-3-carbinol (I3C) may be a chemopreventive agent against cancer. Until recently, there has not been a method to quantitatively assess human dietary I3C exposure or dietary exposure to its specific metabolites in biologic samples collected in a non-invasive manner. We have developed a LC-ESI-MS/MS-SRM analysis to quantify 3,3′-diindolylmethane (DIM), a specific metabolite of I3C in urine. This assay has not been validated as a biomarker of I3C intake in free-living people. Methods: We conducted a small feeding study involving 3 subjects. Subjects consumed approximately 300∼500 g of broccoli and collected 24 h urine samples. The developed LC-ESI-MS/MS-SRM analysis on urinary DIM assay showed the expected m/z 247 → 130 in all 24 h urine samples collected after consumption of broccoli; d2-DIM was used as an internal standard. The assay was then used to quantify urinary DIM in 246 subjects of the Singapore Chinese Health Study, a prospective, population-based cohort of middle aged Chinese men and women residing in Singapore. Random, non-fasting, non-timed urine samples were collected from the cohort between 1994 and 1999. Detailed dietary information and urinary levels of isothiocyanates (ITC) were available for these 246 subjects. The dietary information included intake of 8 cruciferous vegetables that had been previously assayed for glucobrassicins, the precursor of I3C.Estimated dietary intake of glucobrassicins was calculated for each individual based on reported intake of each cruciferous vegetable. Spearman correlation coefficients were calculated to determine the correlation between urinary DIM and reported intake of cruciferous vegetables. Results: Among the 246 subjects, urinary DIM levels ranged from undetectable to 167.8 pmol/mg Cr with a mean (sd) of 14.5 (9.59) pmol/mg Cr. The average intake of total cruciferous vegetables was 40.6 g/day and mean estimated intake of glucobrassicins was 6.5 µmol/day. The Spearman correlation coefficients (p-values) for urinary DIM and dietary intake of total cruciferous vegetables and estimated glucobrassicins were 0.09 (0.18) and 0.10 (0.10) respectively. The coefficients for urinary DIM and intake of each cruciferous vegetable were as follows: kaichoi, 0.01 (0.87); watercress, 0.09 (0.15); choisum, 0.04 (0.52); pakchoi, 0.01 (0.84); kailan, 0.02 (0.74), cabbage/wong nga pak, 0.14 (0.03); broccoli, 0.04 (0.58) and cauliflower, 0.14 (0.03). Urinary DIM also was statistically significantly, albeit weakly, associated with urinary total ITC (coefficient = 0.17, P=0.008), a validated biomarker for consumption of dietary ITC. Conclusion: Although lacking of a significant relationship with intake of total cruciferous vegetables, urinary DIM was statistically significantly associated with intake of cabbage/wong nga pak and cauliflower, two cruciferous vegetables with relatively high contents of I3C precursor. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4651. doi:10.1158/1538-7445.AM2011-4651