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.

Esophageal and gastric cardia cancer risk and folate- and vitamin B(12)-related polymorphisms in Linxian, China.

Linxian, a rural county in North Central China, has among the highest rates of esophageal squamous cell carcinoma (ESCC) and gastric cardia adenocarcinoma (GCA) in the world. Its inhabitants have documented chronic nutritional inadequacies, including folate and vitamin B(12) deficiencies. Using a cohort we have been studying in Linxian since 1985, we examined the relationship between incident ESCC and GCA cancers and three polymorphisms in two genes that code for enzymes that require folate and B(12) as cofactors: methionine synthase reductase (MTRR) A66G and methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C. We conducted a case-cohort study among 4005 individuals in our cohort who were alive and cancer free in 1991 and had blood samples adequate for DNA extraction. Polymorphisms were measured on all 219 incident cancers (129 ESCCs and 90 GCAs) that developed through May 1996 and on 398 controls. Cox proportional hazard models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). Individuals with the MTHFR 677TT genotype had significantly higher combined ESCC/GCA risks (RR, 1.45; 95% CI, 1.02-2.05) than those with CC or CT genotypes. The only subjects to have MTHFR 1298CC were three ESCC cases (P = 0.03). Compared with subjects with the MTRR 66AA genotype, subjects with the AG or GG genotypes had significantly higher risk of ESCC (RR, 1.59; 95% CI, 1.04-2.42). No association was observed for GCA. Our results suggest that the MTHFR C677T and MTRR A66G polymorphisms influence the risk of ESCC and GCA in this population.

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.

Gene-environment interactions between the codon 194 polymorphism of XRCC1 and antioxidants influence lung cancer risk.

X-ray repair cross complementing group 1 (XRCC1) is a DNA repair gene whose polymorphisms appear to influence the risk of lung cancer. We explored the influence of antioxidants on the association between the codon 194 arganine to tryptophan substitution polymorphism of XRCC1 and lung cancer risk. In a case-control study nested within a cohort of tin miners the cases were those diagnosed with lung cancer over 6 years of follow-up (n = 108). Two controls, matched on age and sex, were selected for each case by incidence density sampling. Individuals with the variant Arg194Trp allele seemed to be at lower risk for lung cancer (odds ratio (OR): 0.7, 95% confidence interval (95%CL): 0.4-1.2). Furthermore, high serum alpha-tocopherol (OR: 0.4, 95%CL: 0.2-0.9) and retinol (OR: 0.4, 95%CL: 0.2-0.9) levels were associated with significantly reduced risk of lung cancer among individuals with the Arg194Trp variant allele, but not among individuals with the wild-type genotype. In addition, the Arg194Trp variant reduced the risk of lung cancer associated with increased serum carotenoids compared to those with the homozygous wild-type allele. Our results show that Arg194Trp XRCC1 variant modifies the association between serum antioxidants and lung cancer risk.

Common genetic polymorphisms in the 5'-flanking region of the SULT1A1 gene: haplotypes and their association with platelet enzymatic activity.

SULT1A1 is a phase II detoxification enzyme involved in the biotransformation of a wide variety of endogenous and exogenous phenolic compounds. Human platelet SULT1A1 enzymatic activity shows marked inter-individual variability and a common coding polymorphism, SULT1A1*1/*2, has been described that accounts for a proportion of this variability. We examined the 5'-flanking region of the SULT1A1 gene to determine if genetic variability in this portion of the gene influenced enzymatic activity. Direct sequencing revealed five common genetic polymorphisms (-624G>C, -396G>A, -358A>C, -341C>G and -294T>C) that were present at different allele frequencies in Caucasian, African-American and Chinese groups. Platelet SULT1A1 enzymatic activity was significantly correlated with individual promoter region polymorphisms and the associations were different between African-Americans and Caucasians. Haplotypes were constructed and platelet enzymatic activity according to haplotype was examined. The haplotypes were also significantly correlated with activity; haplotypes GAACT and GGACT (accounting for 13% and 5% of inter-individual variability in platelet activity, respectively) were important in Caucasians while haplotypes GAACC, GAACT and GGACC (accounting for 8%, 5% and 4% of variability) were significantly associated with activity in African-Americans. The coding region polymorphism, SULT1A1*1/*2 was in linkage disequilibrium with the promoter region polymorphisms and showed no effect on activity when examined in the context of the 5'-flanking region polymorphisms. These studies indicate that variation in the promoter region of the SULT1A1 gene exerts a significant influence on enzymatic activity.

Identification of aminobiphenyl derivatives in commercial hair dyes.

A recent epidemiological study suggested that aromatic amines present in hair dyes may contribute to an increased risk of bladder cancer (Gago-Dominguez, et al. (2003) Carcinogenesis 24, 483-489). Moreover, a preliminary study linked frequent hair dye usage with elevated levels of DNA adducts of 4-aminobiphenyl (4-ABP) in human epithelial breast cells (Gorlewska, et al. Proc. Am. Assoc. Cancer Res. 43, 1018-1019). Therefore, we sought to determine if 4-ABP, a recognized human urinary bladder carcinogen, is present in commercial hair dyes. 4-ABP was isolated from dyes by solvent extraction with hexane, followed by silica gel chromatography, either with or without chemical treatment of the extract with Zinc/HCl, and a final purification with a mixed cation exchange reversed-phase resin. The identity of 4-ABP was confirmed by both HPLC with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) and gas chromatography with negative ion chemical ionization mass spectrometry (GC-NICI-MS) following chemical derivatization with pentafluoropropionic anhydride (PFPA). The levels of 4-ABP ranged from not detectable (<0.29 parts per billion (ppb)) up to 12.8 ppb. The noncarcinogenic isomer 2-aminobiphenyl (2-ABP) was also found at quantities up to 310 ppb. 4-ABP was detected in eight of the 11 hair dyes and found in black, red, and blonde hair dyes but not in brown hair dyes. 1,4-Phenylenediamine (PPD) is a key constituent for color development of many permanent hair dyes. Some batches of chemical research grade PPD were contaminated with 4-ABP (up to 500 ppb) and 2-ABP (up to 70 parts per million) and may be a source of ABP contamination in hair dyes. These analytical data demonstrate that 4-ABP is present in some hair dyes. Studies on dermal absorption and bioavailability of 4-ABP from hair dyes are required to determine if this aromatic amine contributes to the increased risk of bladder cancer reported in frequent users of hair dyes.