Susan Nowell

Analysis of total meat intake and exposure to individual heterocyclic amines in a case-control study of colorectal cancer : contribution of metabolic variation to risk

A case-control study of colorectal cancer, consisting of 157 cases and 380 controls matched by sex, ethnicity, decade of age and county of residence was performed to explore the associations between environmental exposure, metabolic polymorphisms and cancer risk. Participants were required to provide a blood sample, undergo caffeine phenotyping and complete an in-person interview that evaluated meat consumption, cooking methods and degree of doneness. A color atlas of foods cooked to different degrees of doneness was used to estimate food preparation techniques and food models were used to estimate serving portion sizes. Data was analyzed using a reference database of heterocyclic amine (HCA) exposure based on the food preferences chosen from the atlas. Data regarding individual food items cooked to different levels of doneness, as well as summary variables of foods and of food groups cooked to different degrees of doneness were also evaluated in a univariate analysis for association with colorectal cancer case status. Three measures of metabolic variation, hGSTA1 genotype, SULT1A1 genotype and the phenotype for CYP2A6 were also evaluated for possible association with colon cancer. While higher exposure to HCAs was strongly associated with colorectal cancer risk, increased consumption of five red meats cooked well done or very well done produced comparable odds ratios (OR) for colorectal cancer risk (OR=4.36, 95% CI 2.08-9.60) for the highest quartile of exposure. Similarly, individuals in the most rapid CYP2A6 phenotype quartile showed an odds ratio (OR = 4.18, 95% CI 2.03-8.90). The ORs for the low activity hGSTA1 and low activity SULT1A1 alleles were 2.0, 95% CI 1.0-3.7 and 0.6, 95% CI 0.3-1.1, respectively. Individual measures of specific HCAs provided little improvement in risk assessment over the measure of meat consumption, suggesting that exposure to other environmental or dietary carcinogens such as nitrosamines or undefined HCAs may contribute to colorectal cancer risk.

Associations between Catalase Phenotype and Genotype: Modification by Epidemiologic Factors

Catalase is an endogenous antioxidant enzyme that neutralizes hydrogen peroxide and is induced by oxidative challenge. A −262C → T polymorphism in the promoter region of the gene (CAT) is associated with risk of several conditions related to oxidative stress. We sought to determine the functional effects of the CAT polymorphism on enzyme activity in erythrocytes and the potential modifying effects of demographic and lifestyle factors on genotype/phenotype relationships, using specimens and data from controls from breast and prostate cancer studies in Arkansas (n = 420). There was a dose-response reduction in catalase activity by genotype, with geometric means of 115.4 units/mg hemoglobin for those with CC genotypes, 82.1 units/mg for those with CT genotypes, and 73.5 units/mg for those with TT genotypes. Associations were only observed among Caucasians (P < 0.0001), with no effects among African Americans (P = 0.91), and were stronger among women than men, although numbers in stratified analyses were small. Differences in catalase activity by genotype were most pronounced among those in the highest tertiles of consumption of fruits and vegetables (−35%, P = 0.003), with weaker relationships among those who were lower consumers (−21.8%, P = 0.16). Among those with CC genotypes, there was no change in activity by consumption, but there were notable decreases in activity by tertiles of consumption for those with at least one T allele. These data indicate that the CAT −262C → T polymorphism predicts a portion of catalase phenotype, which may be limited to Caucasians. Associations between genotype and phenotype were modified by dietary factors, illustrating the biochemical complexity of studies of genetic polymorphisms and disease risk. (Cancer Epidemiol Biomarkers Prev 2006;15(6):1217-22)

Effect of Dietary Constituents With Chemopreventive Potential on Adduct Formation of a Low Dose of the Heterocyclic Amines PhIP and IQ and Phase II Hepatic Enzymes

We conducted a study to evaluate dietary chemopreventive strategies to reduce genotoxic effects of the carcinogens 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). PhIP and IQ are heterocyclic amines (HCAs) that are found in cooked meat and may be risk factors for cancer. Typical chemoprevention studies have used carcinogen doses many thousand-fold higher than usual human daily intake. Therefore, we administered a low dose of [14C] PhIPand [3H] IQand utilized accelerator mass spectrometry to quantify PhIP adducts in the liver, colon, prostate, and blood plasma and IQadducts in the liver and blood plasma with high sensitivity. Diets supplemented with phenethylisothiocyanate (PEITC), genistein, chlorophyllin, or lycopene were evaluated for their ability to decrease adduct formation of [14C] PhIPand [3H] IQin rats. We also examined the effect of treatments on the activity of the phase II detoxification enzymes glutathione S-transferase (GST), UDP-glucuronyltransferase (UGT), phenol sulfotransferase (SULT) and quinone reductase (QR). PEITC and chlorophyllin significantly decreased PhIP-DNA adduct levels in all tissues examined, which was reflected by similar changes in PhIP binding to albumin in the blood. In contrast, genistein and lycopene tended to increase PhIP adduct levels. The treatments did not significantly alter the level of IQ-DNA or -protein adducts in the liver.With the exception of lycopene, the treatments had some effect on the activity of one or more hepatic phase II detoxification enzymes. We conclude that PEITC and chlorophyllin are protective of PhIP-induced genotoxicity after a low exposure dose of carcinogen, possibly through modification of HCA metabolism.

Relationship of phenol sulfotransferase activity (SULT1A1) genotype to sulfotransferase phenotype in platelet cytosol.

Sulfation catalysed by human cytosolic sulfotransferases is generally considered to be a detoxification mechanism. Recently, it has been demonstrated that sulfation of heterocyclic aromatic amines by human phenol sulfotransferase (SULT1A1) can result in a DNA binding species. Therefore, sulfation capacity has the potential to influence chemical carcinogenesis in humans. To date, one genetic polymorphism (Arg213His) has been identified that is associated with reduced platelet sulfotransferase activity. In this study, data on age, race, gender, SULT1A1 genotype and platelet SULT1A1 activity were available for 279 individuals. A simple colorimetric phenotyping assay, in conjunction with genotyping, was employed to demonstrate a significant correlation (r = 0.23, P < 0.01) of SULT1A1 genotype and platelet sulfotransferase activity towards 2-naphthol, a marker substrate for this enzyme. There was also a difference in mean sulfotransferase activity based on gender (1.28 nmol/min/mg, females; 0.94 nmol/min/mg, males, P = 0.001). DNA binding studies using recombinant SULT1A1*1 and SULT1A1*2 revealed that SULT1A1*1 catalysed N-hydroxy-aminobiphenyl (N-OH-ABP) DNA adduct formation with substantially greater efficiency (5.4 versus 0.4 pmol bound/mg DNA/20 min) than the SULT1A1*2 variant. A similar pattern was observed with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5b]pyridine (N-OH-PhIP) (4.6 versus 1.8 pmol bound/mg DNA/20 min).

An Allele-Specific Polymerase Chain Reaction Method for the Determination of the D85Y Polymorphism in the Human UDPGlucuronosyltransferase 2B15 Gene in a Case-Control Study of Prostate Cancer

AbstractBackground: UDP-glucuronosyltransferase 2B15 (UGT2B15) catalyzes the inactivation of dihydrotestosterone (DHT) by forming the DHT-glucuronide and is expressed in normal and hyperplastic prostate tissue. Alterations in the activity of this enzyme could be a major contributing factor to the bioavailability of androgens in target tissue such as the prostate. Methods: A polymorphism (D85 to Y85) has been identified in the UGT2B15 gene1 that results in a 50% reduction in enzyme activity. Previously, detection of the polymorphic nucleotide has required direct sequencing. We have developed and validated an allele-specific polymerase chain reaction (PCR) assay to identify the polymorphic base pair in the UGT2B15 gene. This assay was used to examine the distribution of the UGT2B15 polymorphism in a small case-control group (64 cases and 64 controls) from a prostate cancer study. Results: The results of this analysis show that prostate cancer patients were significantly more likely to be homozygous for the lower activity D85 UGT2B15 allele than control individuals (41% versus 19%, respectively, odds ratio 5 3.0 (95% confidence intervals 1.3– 6.5)). Conclusions: These results suggest that individuals who are homozygous for the lower activity allele may be at increased risk for developing prostate cancer.

Association of SULT1A1 phenotype and genotype with prostate cancer risk in African-Americans and Caucasians

Exposure to heterocyclic amines may increase prostate cancer risk. Human sulfotransferase 1A1 (SULT1A1) is involved in the bioactivation of some dietary procarcinogens, including the N-hydroxy metabolite of the food-borne heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo(4,5-b) pyridine. This study compares a polymorphism in the SULT1A1 gene, SULT1A1 enzyme activity, meat consumption, and the risk of prostate cancer in a population based case-control study. Prostate cancer patients (n = 464) and control individuals (n = 459), frequency matched on age and ethnicity, provided informed consent, answered a survey, and provided a blood sample. Platelets were isolated for phenotype analysis, and DNA was isolated from lymphocytes for genotype determination. Meat consumption was assessed using a dietary questionnaire. Caucasians homozygous for the SULT1A1*1 high activity allele were at increased risk for prostate cancer [odds ratio (OR), 1.68; 95% confidence interval (CI), 1.05–2.68] compared with individuals homozygous for the low-activity allele. The association between SULT1A1 genotype and prostate cancer risk in African-Americans did not reach significance (OR, 1.60; 95% CI, 0.46–5.62). When SULT1A1 activity was considered, there was a strong association between increased SULT1A1 activity and prostate cancer risk in Caucasians (OR, 3.04; 95% CI, 1.8–5.1 and OR, 4.96; 95% CI, 3.0–8.3, for the second and third tertiles of SULT1A1 activity, respectively) compared with individuals in the low enzyme activity tertile. A similar association was also found in African-American patients, with ORs of 6.7 and 9.6 for the second and third tertiles of SULT1A1 activity (95% CI, 2.1–21.3 and 2.9–31.3, respectively). When consumption of well-done meat was considered, there was increased risk of prostate cancer (OR, 1.42; 95% CI, 1.01–1.99 and OR, 1.68; 95% CI, 1.20–2.36 for the second and third tertiles, respectively). When SULT1A1 activity was stratified by tertiles of meat consumption, there was greater risk of prostate cancer in the highest tertile of meat consumption. These results indicate that variations in SULT1A1 activity contributes to prostate cancer risk and the magnitude of the association may differ by ethnicity and be modified by meat consumption.

Novel markers of susceptibility to carcinogens in diet: associations with colorectal cancer.

Red meats cooked at high temperatures generate mutagenic heterocyclic amines, which undergo metabolic activation by hepatic cytochrome P450 1A2 and N-acetyltransferase-2. A primary detoxification pathway involves glutathione S-transferase A1 (GSTA1), which catalyzes the reduction of the carcinogenic N-acetoxy derivative back to the parent amine. Recently, we described a polymorphism in the GSTA1 proximal promoter; the variant (GSTA1*B) allele significantly lowers enzyme expression. In a case-control study, GSTA1*B/*B genotype was associated with an increased risk of colorectal cancer, particularly among consumers of well-done meat. Dietary nitrosamines, which are bioactivated by CYP2A6, represent another potential etiologic factor for colorectal cancer. CYP2A6 converts the caffeine metabolite 1,7-dimethylxanthine (17X) to 1,7-dimethyluric acid (17U); we investigated CYP2A6 activity using the 17U/17X urinary metabolite ratio from case-control subjects who completed a caffeine phenotype assay. The distribution of CYP2A6 activity was significantly different between CRCa cases and controls, with subjects in the medium and high activity groups having an increased risk (P for trend=0.001). GSTA1 genotype and CYP2A6 phenotype should be evaluated as markers of susceptibility to dietary carcinogens in future studies.

Human glutathione S-transferase A2 polymorphisms: variant expression, distribution in prostate cancer cases/controls and a novel form

Variability of expression of the major glutathione S-transferases (GSTs) of liver, GSTA1 and GSTA2, is thought to affect the efficiency of detoxification of xenobiotics, including chemical carcinogens. Polymorphism of the GSTA1 regulatory sequence determines some of the variation of hepatic GSTA1 expression, but the polymorphisms in GSTA2 (exons 5 and 7) were not thought to affect GSTA2 activity. By examining GST protein expression for a set of human liver and pancreas samples (coupled with a cloning/polymerase chain reaction-restriction fragment length polymorphism strategy), we identified a novel substitution Pro110Ser (328C>T) and the corresponding novel variant GSTA2*E (Ser110Ser112Lys196Glu210), and confirmed the presence of variants GSTA2*A (Pro110Ser112Lys196Glu210), GSTA2*B (Pro110Ser112Lys196Ala210) and GSTA2*C (Pro110Thr112Lys196Glu210). GSTA2*C occurred at 30-60% (i.e. approximately 100-fold more frequent than previously reported) and GSTA2*E occurred (heterozygous) at approximately 11%. Hepatic expression of the Ser112 variants (GSTA2*A, GSTA2*B or GSTA2*E) was approximately four-fold higher than that of the Thr112 variant (GSTA2*C). Compared to any other variant, GSTA2E had lower rates of catalysis towards 1-chloro-2,4-dinitrobenzene (CDNB), 4-vinylpyridine, and cumene-, t-butyl- and arachidonic acid hydroperoxides, although kcat/Km for CDNB were similar for all four variants. Using a prostate cancer case-control population, it was found that GSTA1*A/GSTA2 C335 and GSTA1*B/GSTA2 G335 were in linkage disequilibrium in Caucasians but not in African-Americans. However, there were no significant differences in the distribution of these polymorphisms or resultant haplotypes by case status. Nevertheless, the rare genotypes, GSTA2*E/*E and GSTA1*B/*B + GSTA2*C/*C (potential low GSTA2 activity and low hepatic GSTA1 and GSTA2 expression, respectively) could increase the risk of adverse effects of xenobiotics via compromised efficiency of detoxification.

The role of genetic variability in drug metabolism pathways in breast cancer prognosis

Among patients receiving adjuvant therapy for breast cancer, there is variability in treatment outcomes, and it is unclear which patients will receive the most benefit from treatment and which will have better disease-free survival. To date, most studies of breast cancer prognosis have focused on tumor characteristics, but it is likely that pharmacogenetics, genetic variability in the metabolism of therapeutic agents, also plays a role in the prediction of survival. In this paper, we briefly discuss the metabolic pathways of drugs commonly used for the treatment of breast cancer (cyclophosphamide, doxorubicin, taxanes, tamoxifen and aromatase inhibitors) and describe the known genetic variants that may impact those pathways. Studies that have evaluated potential effects of these genetic variants on treatment outcomes are also discussed. It is likely that the application of pharmacogenetics, particularly in the setting of randomized clinical trials, will contribute to findings that may result in individualized therapeutic dosing.

Associations Between Black Tea and Coffee Consumption and Risk of Lung Cancer Among Current and Former Smokers

Although cigarette smoking is a clear risk factor for lung cancer, the other determinants of lung cancer risk among smokers are less clear. Tea and coffee contain catechins and flavonoids, which have been shown to exhibit anticarcinogenic properties. Conversely, caffeine may elevate cancer risk through a variety of mechanisms. The current study investigated the effects of regular consumption of black tea and coffee on lung cancer risk among 993 current and former smokers with primary incident lung cancer and 986 age-, sex-, and smoking-matched hospital controls with non-neoplastic conditions. Results indicated that lung cancer risk was not different for those with the highest black tea consumption (≥2 cups/day) compared with nondrinkers of tea [adjusted odds ratio (aOR) = 0.90; 95% confidence interval (CI) = 0.66–1.24]. However, elevated lung cancer risk was observed for participants who consumed 2-3 cups of regular coffee daily (aOR = 1.34; 95% CI = 0.99–1.82) or ≥4 cups of regular coffee daily (aOR = 1.51, 95% CI = 1.11–2.05). In contrast, decaffeinated coffee drinking was associated with decreased lung cancer risk for both participants who consumed ≤1 cup/day (aOR = 0.67; 95% CI = 0.54–0.84) and those who consumed ≥2 cups/day (aOR = 0.64; 95% CI = 0.51–0.80). These results suggest that any chemoprotective effects of phytochemicals in coffee and tea may be overshadowed by the elevated risk associated with caffeine in these beverages.