Abstract
Higher consumption of cruciferous vegetables is associated with lower risk of several cancers. Isothiocyanates (ITC), the bioactive compounds derived from glucosinolates in cruciferous vegetables, are thought to exert chemoprotective effects through modulation of several pathways critical to carcinogenesis. Urinary ITC excretion is used in epidemiologic studies as a measure of cruciferous vegetable intake; however, considerable inter-individual variation in ITC excretion is observed. Several factors may influence glucosinolate metabolism and excretion, including gut microbial hydrolysis and genetic variation in human enzymes. Thus, intake is not necessarily equivalent to ITC exposure. In a randomized cross-over trial, we evaluated total urinary ITC excretion in healthy participants (n=12 men; n=13 women) in response to 100 μmol glucosinolate intake from three acute feedings of cooked cruciferous vegetables– watercress (67 g), broccoli (125 g), and cabbage (250 g). The vegetables were fed alongside a standardized frozen pasta meal (227 g). GSTM1 genotyping (present or null) was conducted on buccal cell DNA. Total urinary ITC excretion (dithiocarbamates plus glutathione-derived conjugates) was assayed by HPLC from 24 h urine collections adjusted for completeness by creatinine. Linear mixed models were used to assess the effects of dietary exposure and urinary ITC excretion. Mean urinary ITC excretion was 7.21 (95% CI: 5.81, 8.94); 8.35 (95% CI: 6.73, 10.35); and 10.08 (95% CI: 8.20, 12.41) μmol/24 h for watercress, cabbage and broccoli, respectively. As a group, participants excreted significantly more ITC after consumption of broccoli compared to watercress (P=0.01). Intra- and inter-individual variances across all 3 vegetables were 0.29 and 0.07, respectively, and the intra-class correlation (ICC) was 0.20 when evaluating the three dietary measures as replicates of 100 μmol glucosinolate intakes. There were no main effects of GSTM1 genotype (n=9 positive; n=16 null) or ethnicity (n=14 Caucasians; n=9 Asians). Urinary ITC excretion profiles significantly differed between broccoli and watercress, as well as within and between individuals (ICCs below 0.45 indicate poor correlation between repeated measures). This suggests that ITC bioavailability within individuals differs by type of crucifer consumed. ITC are involved in the modulation of several pathways involved in carcinogenesis, therefore an individual's actual exposure to ITC may affect their ultimate risk of cancer.
Citation Format: Sandi L. Navarro, Hannah Frenkel, Wendy K. Thomas, Karen Makar, C.Y. Wang, Johanna W. Lampe. Urinary isothiocyanate excretion profiles in response to acute feeding of various cruciferous vegetables in humans. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A101.
