Many phytochemicals, the bioactive nonnutrient compounds found in plant foods, possess biologic effects associated with reduced risk of various diseases such as cancer. Genetic variation in pathways affecting absorption, metabolism, and distribution of phytochemicals is likely to influence exposure at the tissue level, thus modifying disease risk in individuals. Few studies have examined these genephytochemical interactions in humans. In this review, we discuss the sources of variation in metabolism and disposition of phytochemicals, and focus on two aspects of phytochemical handling that have received some attention: the impact of intestinal bacteria and genetically polymorphic phase II, conjugating enzymes.

ABSTRACT:Acetaminophen (APAP) glucuronidation is thought to occur mainly by UDP-glucuronosyltransferases (UGT) in the UGT1A family. Interindividual variation in APAP glucuronidation is attributed in part to polymorphisms in UGT1As. However, evidence suggests that UGT2B15 may also be important. We evaluated, in a controlled feeding trial, whether APAP conjugation differed by UGT1A6 and UGT2B15 genotypes and whether supplementation of known dietary inducers of UGT (crucifers, soy, and citrus) modulated APAP glucuronidation compared with a diet devoid of fruits and vegetables (F&V). Healthy adults (n ‫؍‬ 66) received 1000 mg of APAP orally on days 7 and 14 of each 2-week feeding period and collected saliva and urine over 12 h. Urinary recovery of the percentage of the APAP dose as free APAP was higher (P ‫؍‬ 0.02), and the percentage as APAP glucuronide (APAPG) was lower (P ‫؍‬ 0.004) in women. The percentage of APAP was higher among UGT1A6*1/*1 genotypes, relative to *1/*2 and *2/*2 genotypes (P ‫؍‬ 0.045). For UGT2B15, the percentage of APAPG decreased (P < 0.0001) and that of APAP sulfate increased (P ‫؍‬ 0.002) in an allelic dosedependent manner across genotypes from *1/*1 to *2/*2. There was a significant diet ؋ UGT2B15 genotype interaction for the APAPG ratio (APAPG/total metabolites ؋ 100) (P ‫؍‬ 0.03), with *1/*1 genotypes having an approximately 2-fold higher F&V to basal diet difference in response compared with *1/*2 and *2/*2 genotypes. Salivary APAP maximum concentration (C max ) was significantly higher in women (P ‫؍‬ 0.0003), with F&V (P ‫؍‬ 0.003), and among UGT1A6*2/*2 and UGT2B15*1/*2 genotypes (P ‫؍‬ 0.02 and 0.002, respectively). APAP half-life was longer in UGT2B15*2/*2 genotypes with F&V (P ‫؍‬ 0.009). APAP glucuronidation was significantly influenced by the UGT2B15*2 polymorphism, supporting a role in vivo for UGT2B15 in APAP glucuronidation, whereas the contribution of UGT1A6*2 was modest. Selected F&V known to affect UGT activity led to greater glucuronidation and less sulfation.

UDP-glucuronosyltransferase (UGT) 1A1 glucuronidates bilirubin, estrogens, and exogenous compounds, including dietary carcinogens. The UGT1A1*28 polymorphism, characterized by variation in the number of thymine-adenine repeats in the promoter region, modulates UGT1A1 transcription. Observational and in vitro studies suggest that certain phytochemicals may increase UGT activity. We investigated, in a randomized, controlled, crossover feeding trial, whether approximately 10 servings/d (doses adjusted for body weight) of crucifers, soy, and citrus for 2 wk compared with a fruit- and vegetable-free basal diet affected UGT1A1 activity as measured by serum bilirubin concentrations and whether effects were modulated by the UGT1A1*28 polymorphism. Healthy men (n = 32) and women (n = 31), aged 20-40 y, enrolled based on UGT1A1 genotype, completed the study. We measured bilirubin in blood collected at d 8 and d 15 of each feeding period. Overall, fruit and vegetables (F&V) did not affect serum bilirubin; however, among 7/7 individuals, d 8 total (P = 0.057) and indirect (unconjugated) (P = 0.051) bilirubin tended to be lower when individuals consumed the F&V diet (28.97 +/- 2.36 micromol/L and 25.97 +/- 2.15 micromol/L) compared with the basal diet (32.46 +/- 2.63 micromol/L and 29.31 +/- 2.43 micromol/L). We no longer detected this difference at d 15, by which time bilirubin had also decreased when participants consumed the basal diet. Additionally, intervention effects on bilirubin were restricted to women with 7/7 genotype (P = 0.002). These results suggest that serum bilirubin glucuronidation is modulated by dietary intervention, but factors such as UGT1A1 genotype and sex may affect the response to diet.

Glutathione S-transferases (GST) detoxify a wide range of carcinogens. Isothiocyanates (ITC), from cruciferous vegetables, are substrates for and inducers of GST. GST variants may alter ITC clearance such that response to crucifers varies by genotype. In a randomized cross-over trial, we tested the hypothesis that changes in serum GSTA1/2 concentration in response to cruciferous vegetable feeding depends on GSTM1/GSTT1 genotype. Thirty-three men and 34 women (age 20-40 years) ate four 14-day controlled diets-basal (vegetable-free), basal supplemented with two different doses of crucifers ("single dose" and "double dose"), and single-dose cruciferousplus-apiaceous vegetables-fed per kilogram of body weight. Fasting bloods from days 0, 7, 11, and 14 of each diet period were analyzed for serum GSTA1/2 by ELISA. GSTA1/2 increased with single-and double-dose cruciferous compared with basal diet (10% and 13%, respectively; P = 0.02 and 0.004), but cruciferous-plus-apiaceous did not differ from basal (P = 0.59). Overall, GSTA1/2 was higher in GSTM1-null/GSTT1-null than GSTM1+/GSTT1+ individuals (4,198 ± 338 and 3,372 ± 183 pg/mL; P = 0.03). The formal interaction of genotype-by-diet was not statistically significant, but the GSTA1/2 increase during the single-dose cruciferous diet was among GSTM1-null/GSTT1-null individuals (by 28%; P = 0.008), largely explained by GSTM1-null/GSTT1-null men (by 41%; P = 0.01). GSTA1/2 increased during the double-dose cruciferous diet in both GSTM1-null/ GSTT1-null men (by 35%; P = 0.04) and GSTM1+/ GSTT1+ men (by 26%; P = 0.01) but not in women. In summary, cruciferous vegetable supplementation increased GSTA1/2, but the effect was most marked in GSTM1-null/GSTT1-null men. (Cancer Epidemiol

UDP-glucuronosyltransferase (UGT) 1A1 glucuronidates bilirubin, estrogens, and xenobiotic compounds. The UGT1A1*28 polymorphism results in lower promoter activity due to 7 thymine-adenine (TA) repeats, rather than the more common 6 TA repeats. Previously, we showed that serum bilirubin, a marker of UGT1A1 activity, was lower among individuals homozygous for the UGT1A1*28 polymorphism (7/7) when randomized to a high fruit and vegetable (F&V) diet, whereas no effect was seen in individuals with the wild-type (6/6) and heterozygous (6/7) genotypes. Our objective here was to determine if we could detect genotype-diet interactions on bilirubin concentrations in an observational study. Healthy non-smoking men (n=146) and women (n=147), recruited from the Seattle area, provided blood samples for genotyping and bilirubin measurements. We used multiple linear regression to assess the relationships between UGT1A1 genotype, bilirubin concentrations and consumption of specific F&V [cruciferous vegetables, citrus fruits, and soy foods (n=268)] based on FFQ, and F&V from 6 botanical families [Cruciferae, Rosaceae, Rutaceae, Umbelliferae, Solanaceae and Leguminosae (n=261)] based on 3 d food records. We observed a significant interaction of UGT1A1 genotype and citrus consumption among women. Women with the 7/7 genotype who consumed 0.5 or more daily servings of citrus fruit or foods from the Rutaceae botanical family had ~30% lower serum bilirubin than those with the same genotype who consumed less, while 6/6 and 6/7 genotypes did not differ by consumption (P for interaction = 0.006 and 0.03 respectively). These results suggest that citrus consumption may increase UGT1A1 activity among women with the 7/7 genotype.

Single-cell gel electrophoresis (the Comet assay) can be used to measure DNA damage and DNA repair capacity (DRC). However, to test DRC of cryopreserved lymphocytes, published methods include steps for cell culturing and phytohemagglutinin stimulation, which may limit use of this assay in intervention studies. We developed a modified Comet assay protocol that allows us to measure DRC from cryopreserved lymphocytes without these in vitro manipulations. Assay reproducibility was evaluated by performing the assay six times on different dates using six aliquots from one blood draw of one individual. The interindividual variation was assessed by performing the assay using one aliquot from six individuals. When gamma-irradiation was used as the mutagen, intra-assay coefficients of variation (CVs.) for baseline DNA damage, damage after gamma-irradiation exposure, and DRC--measured as tail moment--were 8, 31, and 10%, respectively. Interindividual CVs. were higher. When H(2)O(2) was used as the mutagen, intra-assay CVs. for damage measurements were lower for a protocol modification that included damage and repair at 37 degrees C (CVs. ranging from 8 to 35%) than for the more standard 4 degrees C protocol. Analyzing moment arm--the average distance of DNA migration within the tail--yielded similar results. DNA repair was successfully detected in each experiment. Comparing freshly isolated lymphocytes to cryopreserved lymphocytes from the same individuals' blood draw indicated that DRC was highly correlated when determined using moment arm values. This modified protocol extends the use of the Comet assay to measuring DRC in intervention studies (e.g., dietary interventions) in that it assesses cellular response after cryopreservation without cell culture or other extensive manipulation.

Epidemiologic studies have examined the association between fruit and vegetable (F&V) consumption and the risk of cancer. Several cancer-preventive mechanisms have been proposed, such as antioxidant properties and modulation of biotransformation enzyme activities; both may be associated with reducing DNA damage and hence the mutation rate. We investigated, in a randomized, controlled, crossover feeding trial, the effect of 10 servings/day of botanically defined F&V for 2 wk on endogenous DNA damage; resistance to γ-irradiation damage; and DNA repair capacity in lymphocytes, measured by the Comet assay. We also explored the association between the UGT1A1*28 polymorphism and serum bilirubin concentrations and DNA damage and repair measures. Healthy men (n = 11) and women (n = 17), age 20 to 40 yr, provided blood samples at the end of each feeding period. Overall, F&V did not affect DNA damage and repair measures in lymphocytes. The number of UGT1A1*28 alleles was inversely associated with sensitivity to γ-irradiation exposure and DNA repair capacity, but a biological mechanism to explain this association is unclear. A larger sample size is needed to investigate the association between bilirubin concentrations and endogenous DNA damage. With inconsistent findings in the literature, additional dietary intervention studies on the effect of F&V on DNA damage and repair are needed.

Background-β-glucuronidase, an acid hydrolase that deconjugates glucuronides, may increase cancer risk; however, little is known about factors associated with human β-glucuronidase.