Cancer Prevention Research Cruciferous Vegetable Feeding Alters UGT1A1 Activity: Diet- and Genotype-Dependent Changes in Serum Bilirubin in a Controlled Feeding Trial

Chemoprevention by isothiocyanates from cruciferous vegetables occurs partly through up-regulation of phase II conjugating enzymes, such as UDP-glucuronosyltransferases (UGT). UGT1A1 glucuronidates bilirubin, estrogens, and several dietary carcinogens. The UGT1A1*28 polymorphism reduces transcription compared with the wild-type, resulting in decreased enzyme activity. Isothiocyanates are metabolized by glutathione S-transferases (GST); variants may alter isothiocyanate clearance such that response to crucifers may vary by genotype. We evaluated, in a randomized, controlled, crossover feeding trial in humans (n = 70), three test diets (singleand double-“dose” cruciferous and cruciferous plus apiaceous) compared with a fruit and vegetable–free basal diet. We measured serum bilirubin concentrations on days 0, 7, 11, and 14 of each 2-week feeding period to monitor UGT1A1 activity and determined effects of UGT1A1*28 and GSTM1/GSTT1-null variants on response. Aggregate bilirubin response to all vegetable-containing diets was statistically significantly lower compared with the basal diet (P < 0.03 for all). Within each UGT1A1 genotype, lower bilirubin concentrations were seen in *1/*1 in both singleand double-dose cruciferous diets compared with basal (P < 0.03 for both); *1/*28 in double-dose cruciferous and cruciferous plus apiaceous compared with basal, and cruciferous plus apiaceous compared with single-dose cruciferous (P < 0.02 for all); and *28/*28 in all vegetable-containing diets compared with basal (P < 0.02 for all). Evaluation of the effects of diet stratified by GST genotype revealed some statistically significant genotypic differences; however, the magnitude was similar and not statistically significant between genotypes. These results may have implications for altering carcinogen metabolism through dietary intervention, particularly among UGT1A1*28/*28 individuals. Consumption of cruciferous vegetables (from the Brassicaceae plant family) is associated with a reduced risk of several cancers, particularly cancers of the stomach and lung (1–4). Cruciferous vegetables contain high amounts of sulfurcontaining compounds called glucosinolates (5), which, on hydrolysis by the enzyme myrosinase, results in the formation of biologically active compounds, such as indoles and isothiocyanates. These compounds are hypothesized to play a role in chemoprevention, in part, through regulation of phase II conjugating enzymes, including UDP-glucuronosyltransferase (UGT; refs. 3, 6–11). UGTs are a superfamily of enzymes that catalyze the transfer of the glucuronyl group from uridine 5′-disphosphoglucuronic acid to endogenous molecules, as well as exogenous compounds, including therapeutic drugs and dietary carcinogens, to produce less toxic, more polar molecules that aremore easily excreted (12). UGT1A1, one of nine enzymes in the UGT1A family, conjugates bilirubin and estrogens (17β-estradiol and estriol), as well as heterocyclic amines and polycyclic aromatic hydrocarbons (13). UGT1A1 is also the only UGT that preferentially conjugates bilirubin (14). Polymorphisms in the upstream promoter region of UGT1A1, characterized by variation in the number of thymine-adenine (TA) repeats, alterUGT1A1 transcriptional activity (14, 15). Compared with six TA repeats (UGT1A1*1) found in the wild-type allele, the presence of seven (UGT1A1*28) TA repeats has been shown to down-regulate transcription and is the genetic basis for mild unconjugated hyperbilirubinemia associated with reduced hepatic UGT conjugation of bilirubin (i.e., Gilbert syndrome; ref. 16). Authors' Affiliations: Bastyr University, Kenmore, Washington; Fred Hutchinson Cancer Research Center, Seattle, Washington; and Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota Received 9/30/08; revised 12/15/08; accepted 1/16/09; published OnlineFirst 3/31/09. Grant support: NIH grants R01CA070913 and R01CA92288 and Fred Hutchinson Cancer Research Center. Requests for reprints: Johanna W. Lampe, Cancer Prevention Program, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, M4-B402, Seattle, WA 98109. Phone: 206-667-6580; Fax: 206-667-7850; E-mail: [email protected]. ©2009 American Association for Cancer Research. doi:10.1158/1940-6207.CAPR-08-0178 345 Cancer Prev Res 2009;2(4) April 2009 www.aacrjournals.org Cancer Research. on June 19, 2017. © 2009 American Association for cancerpreventionresearch.aacrjournals.org Downloaded from Published OnlineFirst March 31, 2009; DOI: 10.1158/1940-6207.CAPR-08-0178