Cytochrome P4501A1 polymorphism as a susceptibility factor for breast cancer in postmenopausal Chinese women in Taiwan

Genic-intergenic polymorphisms of CYP1A genes and their clinical impact

The humancytochrome P450 1A (CYP1A) subfamily genes, CYP1A1 and CYP1A2, encoding monooxygenases are critically involved in biotransformation of key endogenous substrates (estradiol, arachidonic acid, cholesterol) and exogenous compounds (smoke constituents, carcinogens, caffeine, therapeutic drugs). This suggests their significant involvement in multiple biological pathways with a primary role of maintaining endogenous homeostasis and xenobiotic detoxification. Large interindividual variability exist in CYP1A gene expression and/or catalytic activity of the enzyme, which is primarily due to the existence of polymorphic alleles which encode them. These polymorphisms (mainly single nucleotide polymorphisms, SNPs) have been extensively studied as susceptibility factors in a spectrum of clinical phenotypes. An in-depth understanding of the effects of polymorphic CYP1A genes on the differential metabolic activity and the resulting biological pathways is needed to explain the clinical implications of CYP1A polymorphisms. The present review is intended to provide an integrated understanding of CYP1A metabolic activity with unique substrate specificity and their involvement in physiological and pathophysiological roles. The article further emphasizes on the impact of widely studied CYP1A1 and CYP1A2 SNPs and their complex interaction with non-genetic factors like smoking and caffeine intake on multiple clinical phenotypes. Finally, we attempted to discuss the alterations in metabolism/physiology concerning the polymorphic CYP1A genes, which may underlie the reported clinical associations. This knowledge may provide insights into the disease pathogenesis, risk stratification, response to therapy and potential drug targets for individuals with certain CYP1A genotypes.

Meta-analysis of genetic polymorphisms in xenobiotic metabolizing enzymes and their association with breast cancer risk

Studies on the association of cytochrome p450 A1 (m1, m2), catechol-O-methyltransferase (COMT) H108L, glutathione S-transferase (GST) T1 and M1 polymorphisms with breast cancer risk were inconclusive. The current study was aimed to clarify the ambiguity in genetic associations of these enzymes with breast cancer risk on a global perspective. A systematic literature search was carried out in PubMed, Google Scholar and Medline, covering all the case-control studies published until September 2017. A meta-analysis was performed based on the random-effect and fixed-effect models to calculate the overall association of each genetic variant with breast cancer risk. Of the five polymorphisms studied, GSTT1 (OR: 1.07, 95% CI: 1.02-1.12 and OR: 1.08, 95% CI: 1.01-1.15 for fixed-effect and random-effect models, respectively) and GSTM1 (OR: 1.22, 95% CI: 1.17-1.26 and OR: 1.25, 95% CI: 1.12-1.35 for fixed-effect and random-effect models, respectively) null polymorphisms exhibited an increased risk for breast cancer in both the models. Cochrane Q-test and I² statistics revealed heterogeneity in association with these polymorphisms (P< 0.0001) with no evidence of publication bias. Thus, GSTT1 and GSTM1 null polymorphisms are risk factors for breast cancer.

Association of Cytochrome CYP1A1 Gene Polymorphisms and Tobacco Smoking With the Risk of Breast Cancer in Women From Iraq

BACKGROUND

CYP1A1 gene polymorphisms and tobacco smoking are among several risk factors for various types of cancers, but their influence on breast cancer remains controversial. We analyzed the possible association of CYP1A1 gene polymorphisms and tobacco smoking-related breast cancer in women from Iraq.

MATERIALS AND METHODS

In this case-control study, gene polymorphism of CYP1A1 gene (CYP1A1m1, T6235C and CYP1A1m2, A4889G) of 199 histologically verified breast cancer patients' and 160 cancer-free control women's specimens were performed by using PCR-based restriction fragment length polymorphism.

RESULTS

Three genotype frequencies (TT, TC, and CC) of CYP1A1m1T/C appeared in 16.1, 29.6, and 54.3% of women with breast cancer, respectively, compared with 41.2, 40, and 18.8% in the control group, respectively. CYP1A1m1 CC genotype and C allele were significantly associated with increased risks for breast cancer in patients (54.3 and 69%, respectively) compared with controls (18.8 and 39%, respectively). While the three genotype frequencies (AA, AG, and GG) of CYP1A1m2A/G were detected in 20.1, 31.2, and 48.7% in patients compared with 46.3, 40.6, and 13.1% in controls, respectively. The frequency of GG genotypes and G allele was significantly higher in patients (48.7 and 64%, respectively) than in the controls (13.1 and 33%, respectively). Smoking women having either CC or GG genotypes showed a highly significant association with increased risk of breast cancer [odds ratio (OR) = 1.607, 95% confidence interval (CI) 0.91-1.64, p = 0.0001, and OR, 1.841, 95% CI, 0.88-1.67, p = 0.0001, respectively]. On the other hand, the T and A alleles of predominantly seen in healthy smoking women (83 and 85%, p = 0.0001, respectively).

CONCLUSION

These findings indicated that both C and G alleles of CYP1A1m1 and m2 were significantly associated with elevated risk of breast cancer in Iraqi women, while the T and A alleles were predominantly seen in healthy controls which may indicate their protective role. The C and G association with breast cancer incidence was more prevalent among tobacco smoking patients. These polymorphisms may be used as biomarkers of breast cancer in women from Iraq.

Distinct role of endothelial nitric oxide synthase gene polymorphisms from menopausal status in the patients with sporadic breast cancer in Taiwan

Breast cancer has a high incidence in Taiwanese women and worldwide. Previous studies have indicated that NO has multiple independent roles in carcinogenesis; genetic polymorphisms in the endothelial nitric oxide synthase (eNOS) gene could modify its transcription and endogenous NO production. Previous studies have reported conflicting results for the relationship between polymorphisms in the eNOS gene and breast cancer risk. Estrogen levels are associated with eNOS expression; accordingly, variation in estrogen levels may contribute to the discordant results. Therefore, in this study, the effects of eNOS polymorphisms on breast cancer susceptibility were examined in terms of menopausal status in Taiwanese women. Three eNOS polymorphisms (-786T > C, VNTR, and 894G > T) were genotyped in 283 patients with breast cancer (139 premenopausal and 144 postmenopausal) and 200 cancer-free controls (100 premenopausal and 100 postmenopausal) by PCR-RFLP. There was a significantly higher breast cancer risk in premenopausal women carrying 894G > T T than in those with the 894G > T GG genotype; however, postmenopausal women carrying 894G > T T had a lower risk of developing breast cancer. In addition, based on a binary logistic regression analysis, interaction effects of these polymorphisms differed according to menopausal status. The relationship between eNOS polymorphisms and breast cancer hazard depended on menopause status, especially for the 894G > T polymorphism, which may provide an explanation for previous conflicting results.

Epidemiology of estrogen and dementia in women with Down syndrome

Several lines of investigation have shown a protective role for estrogen in Alzheimer's disease through a number of biological actions. This review examines studies of the role of estrogen-related factors in age at onset and risk for Alzheimer's disease in women with Down syndrome, a population at high risk for early onset of dementia. The studies are consistent in showing that early age at menopause and that low levels of endogenous bioavailable estradiol in postmenopausal women with Down syndrome are associated with earlier age at onset and overall risk for dementia. Polymorphisms in genes associated with estrogen receptor activity and in genes for estrogen biosynthesis affecting endogenous estrogen are related to age at onset and cumulative incidence of dementia, and may serve as biomarkers of risk. To date, no clinical trials of estrogen or hormone replacement therapy (ERT/HRT) have been published for women with Down syndrome. While findings from clinical trials of ERT or HRT for dementia have generally been negative among women in the neurotypical population, the short interval between menopause and onset of cognitive decline, together with a more positive balance between potential benefits and risks, suggests an opportunity to evaluate the efficacy of ERT/HRT for delaying or preventing dementia in this high risk population, although questions concerning the optimal formulation and timing of the hormone therapy are not yet resolved.

Association of CYP1A1 A4889G and T6235C polymorphisms with the risk of sporadic breast cancer in Brazilian women

OBJECTIVES

We examined the influence of CYP1A1 A4889G and T6235C polymorphisms on the risk of sporadic breast cancer.

METHODS

DNA from 742 sporadic breast cancer patients and 742 controls was analyzed using the polymerase chain reaction, followed by the restriction fragment length polymorphism technique.

RESULTS

More patients had the CYP1A1 4889AG+GG genotype compared to controls (29.0% versus 23.2%, p=0.004). The G allele carriers had a 1.50-fold increased risk (95% CI: 1.14-1.97) of sporadic breast cancer compared to the other study participants. The frequency of the 4889AG+GG genotype among the Caucasian patients was higher than in the non-Caucasian patients (30.4% versus 20.2%, p=0.03) and controls (30.4% versus 23.2%, p=0.002). Caucasians and G allele carriers had a 1.61-fold increased risk (95% CI: 1.20-2.15) of sporadic breast cancer compared to other subjects. The CYP1A1 4889AG+GG genotype was more common among patients with a younger median age at first full-term pregnancy than among controls (33.8% versus 23.2%, p=0.001) and subjects whose first full-term pregnancies occurred at an older age (33.8% versus 26.1%, p=0.03). Women with the CYP1A1 4889AG+GG genotype and earlier first full-term pregnancies had a 1.87-fold (95% CI: 1.32-2.67) increased risk of sporadic breast cancer compared to the other study participants. Excess CYP1A1 4889AG+GG (39.8% versus27.1%, p=0.01) and 6235TC+CC (48.4% versus 35.9%, p=0.02) genotypes were also observed in patients with grade I and II tumors compared to patients with grade III tumors and controls (39.8% versus 23.2%, p=0.04; 48.4% versus 38.6%, p=0.04). The G and C allele carriers had a 2.44-fold (95% CI: 1.48-4.02) and 1.67-fold (95% CI: 1.03-2.69) increased risk, respectively, of developing grade I and II tumors compared to other subjects.

CONCLUSIONS

The CYP1A1 A4889G and T6235C polymorphisms may alter the risk of sporadic breast cancer in Brazilian women.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

CHRNA9 polymorphisms and smoking exposure synergize to increase the risk of breast cancer in Taiwan

Previous studies indicated that smoking exposure is associated with an increased risk of breast cancer, and α9-nicotine acetylcholine receptors (α9-nAChRs) are involved in breast tumorigenesis. However, no studies have explored the joint effect of α9-nAChRs (CHRNA9) genes and cigarette smoking exposure on breast cancer risk. A case-control study was conducted on 737 breast cancer patients and 719 age-matched healthy controls. Three single-nucleotide polymorphisms (SNPs) of CHRNA9 located in the promoter region were genotyped and compared between cases and controls to identify those SNPs associated with breast cancer susceptibility. A dual-luciferase reporter assay was used to analyze the promoter activities of these SNPs of the CHRNA9 gene. After a Bonferroni correction, the G allele of the CHRNA9 rs7329797 SNP was significantly associated with an increased risk of developing breast cancer compared with A/A genotype carriers (odds ratio, 1.8; 95% confidence interval, 1.2-2.6). A multiplicative interaction between passive smoking exposure and the CHRNA9 rs73229797 SNP on the risk of breast malignancy was observed. A functional assay further showed that rs73229797 was associated with increased promoter activity of the CHRNA9 gene. Our findings support a significant interaction effect existing between the CHRNA9 gene and smoking exposure on the risk of breast cancer development.

Active and passive smoking with breast cancer risk for Chinese females: a systematic review and meta-analysis

Previous studies suggested that smoking and passive smoking could increase the risk of breast cancer, but the results were inconsistent, especially for Chinese females. Thus, we systematically searched cohort and case-control studies investigating the associations of active and passive smoking with breast cancer risk among Chinese females in four English databases (PubMed, Embase, ScienceDirect, and Wiley) and three Chinese databases (CNKI, WanFang, and VIP). Fifty-one articles (3 cohort studies and 48 case-control studies) covering 17 provinces of China were finally included in this systematic review. Among Chinese females, there was significant association between passive smoking and this risk of breast cancer [odds ratio (OR): 1.62; 95% confidence interval (CI): 1.39-1.85; I2 = 75.8%, P < 0.001; n = 26] but no significant association between active smoking and the risk of breast cancer (OR: 1.04; 95% CI: 0.89-1.20; I2 = 13.9%, P = 0.248; n = 31). The OR of exposure to husband's smoking and to smoke in the workplace was 1.27 (95% CI: 1.07-1.50) and 1.66 (95% CI: 1.07-2.59), respectively. The OR of light and heavy passive smoking was 1.11 and 1.41, respectively, for women exposed to their husband's smoke (< 20 and ≥ 20 cigarettes per day), and 1.07 and 1.87, respectively, for those exposed to smoke in the workplace (< 300 and ≥ 300 min of exposure per day). These results imply that passive smoking is associated with an increased risk of breast cancer, and the risk seems to increase as the level of passive exposure to smoke increases among Chinese females. Women with passive exposure to smoke in the workplace have a higher risk of breast cancer than those exposed to their husband's smoking.

Polymorphism of the cytochrome P-450 1A1 (A2455G) in women with breast cancer in Eastern Azerbaijan, Iran

OBJECTIVE(S)

Cytochrome P-450 1A1 is an important enzyme in the first phase of the metabolism of some carcinogens such as polycyclic aromatic hydrocarbons (PAHs), as well as estrogen. The present study evaluates the existence of CYP1A1 polymorphism in a number of breast cancer samples.

MATERIALS AND METHODS

One hundred breast cancer patients and the same number of healthy controls were analyzed for the A2455G polymorphism of cytochrome P-450 1A1 by the polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

Frequency of heterozygote genotype (A/G) indicated significant increase in case group (17%) compared to control group (7%) (OR=2.7; 95% CI=1.07-6.89; P-value=0.03). The related result of (A/A) genotype showed significantly decreased risk of breast cancer (OR=0.34; P-value=0.01). Higher frequency of heterozygotes was mainly observed among premenopausal breast cancer patients.

CONCLUSION

Our results suggest that the CYP1A1 polymorphism may be useful for predicting breast cancer risk in our study population.

Variants in CYP17 and CYP19 cytochrome P450 genes are associated with onset of Alzheimer's disease in women with down syndrome

CYP17 and CYP19 are involved in the peripheral synthesis of estrogens, and polymorphisms in CYP17 and CYP19 have been associated with increased risk of estrogen-related disorders. Women with Down syndrome (DS) have early onset and high risk for Alzheimer's disease (AD). We conducted a prospective community-based cohort study to examine the relationship between SNPs in CYP17 and CYP19 and cumulative incidence of AD, hormone levels and sex hormone binding globulin in women with DS. Two hundred and thirty-five women with DS, 31 to 67 years of age and nondemented at initial examination, were assessed for cognitive and functional abilities, behavioral/psychiatric conditions, and health status at 14-20 month intervals over five assessment cycles. We genotyped these individuals for single-nucleotide polymorphisms (SNPs) in CYP17 and CYP19. Four SNPs in CYP17 were associated with a two and one half-fold increased risk of AD, independent of APOE genotype. Four SNPs in CYP19 were associated with a two-fold increased risk of AD, although three were significant only in those without an APOE ε4 allele. Further, carrying high risk alleles in both CYP17 and CYP19 was associated with an almost four-fold increased risk of AD (OR = 3.8, 95% CI, 1.6-9.5) and elevated sex hormone binding globulin in postmenopausal women. The main effect of the CYP17 and CYP19 variants was to decrease the age at onset. These findings suggest that genes contributing to estrogen bioavailability influence risk of AD in women with DS.

Soy isoflavones, CYP1A1, CYP1B1, and COMT polymorphisms, and breast cancer: a case-control study in southwestern China

CYP1A1, CYP1B1, and COMT are key enzymes involved in estrogen metabolism. Soy isoflavones, phytoestrogens found in soy foods, may modify the activity of these enzymes. A case-control study was conducted to assess the associations between soy isoflavone intake and the CYP1A1 Ile462Val, CYP1B1 Val432Leu, and COMT Val158Met polymorphisms and breast cancer, as well as their combined effects on breast cancer. A total of 400 newly diagnosed breast cancer cases and 400 healthy controls were recruited. Participants' daily intake of soy isoflavones (DISI [mg/day]) was calculated and transformed to energy-adjusted DISI by the residual method. Gene sequencing was used to analyze CYP1A1, CYP1B1, and COMT polymorphisms. Adjusted odds ratios (aORs) and 95% confidence intervals (95% CIs) were estimated by conditional logistic regression. A strong protective dose-dependent effect of energy-adjusted DISI on breast cancer was found in both pre- and postmenopausal women (P(trend) < 0.05). Among all women and in the postmenopausal subgroup, COMT Met/Met and CYP1B1 Leu/Leu susceptible genotype carriers had higher risk of breast cancer (aORs > 1, OR 95% CIs exclude 1). In premenopausal women, only carrying CYP1B1 Leu/Leu was associated with breast cancer risk (aOR = 2.05, 95% CI: 1.11-3.79). Carrying CYP1A1 Val/Val was related to breast cancer risk only among all women. A stratified analysis was performed at two levels of energy-adjusted DISI, with wildtype homozygous genotypes and low energy-adjusted DISI as the reference. In the high energy-adjusted DISI subgroup, carrying the CYP1B1 Leu/Leu genotype did not affect breast cancer risk in either all women or in the menopausal subgroups, compared with the reference. Overall, in Han Chinese women, carrying CYP1A1 Val/Val and COMT Met/Met appears to be associated with breast cancer risk, especially in postmenopausal women. CYP1B1 susceptible genotypes (Val/Leu or Leu/Leu) also contribute to increased breast cancer risk, regardless of menopausal status, but high soy isoflavone intake may reduce this risk.

Relation of FGFR2 genetic polymorphisms to the association between oral contraceptive use and the risk of breast cancer in Chinese women

The fibroblast growth factor receptor 2 gene (FGFR2) has been associated with the risk of breast cancer in multiple ethnic populations, and its effect has been suggested to be hormone-dependent. A large, 2-stage, population-based case-control study was conducted in urban Shanghai, China, during the periods of 1996-1998 and 2002-2005. Exposure and genotyping information from 2,073 patients with breast cancer and 2,084 age-matched population controls was available for evaluation of the interactions between FGFR2 polymorphisms and exogenous estrogen exposure in the development of breast cancer. A logistic regression model was used to compute adjusted odds ratios and 95% confidence intervals. Of 20 genotyped and 25 imputed single nucleotide polymorphisms (SNPs), 22 were significantly associated with breast cancer. Three genotyped SNPs in close linkage disequilibrium, rs2303568, rs3135730, and rs1078806, and an imputed SNP of rs755793 in complete linkage disequilibrium with other 8 SNPs were observed to interact significantly with oral contraceptive (OC) use. The SNP-cancer association was evident only among OC users, and the OC use was only associated with the risk of breast cancer among carriers of these minor alleles at these loci. These findings suggest that genetic variants in FGFR2 may modify the role of OC use in causing breast cancer in Chinese women.

Population analysis of xenobiotic metabolizing genes in South Brazilian Euro and Afro-descendants

Individual variability in xenobiotic metabolism has been associated with susceptibility to developing complex diseases. Genes involved in xenobiotic metabolism have been evaluated in association studies; the difficulty of obtaining accurate gene frequencies in mixed populations makes interpretation of the results difficult. We sought to estimate population parameters for the cytochrome P450 and glutathione S-transferase gene families, thus contributing to studies using these genes as markers. We describe the frequencies of six genes (CYP1A1, CYP2D6, CYP2E1, GSTM1, GSTT1, and GSTP1) and estimate population parameters in 115 Euro-descendants and 196 Afro-descendants from Curitiba, South of Brazil. PCR-based methods were used for genotyping, and statistical analysis were performed by AMOVA with ARLEQUIN software. The mutant allele frequencies in the Afro-descendants and Euro-descendants, respectively, were: CYP1A1*2A = 30.1% and 15.2%; CYP2D6*4 = 14.5% and 21.5%; CYP2E1*5B = 7.9% and 5%; GSTP1*B = 37.8% and 28.3%. The null genotype frequencies were: GSTM1*0 = 36.8% and 46.1%; GSTT1*0 = 24.2% and 17.4%.

Association of CYP1A1*2A polymorphism with male infertility in Indian population

BACKGROUND

The CYP1A1 gene is a polymorphic gene and encodes for the CYP1A1 enzyme that catalyzes the bioactivation of polycyclic aromatic hydrocarbons (PAHs). PAHs are ubiquitous pollutants in the natural environment, which are capable of forming DNA adducts once being activated to generate DNA reactive metabolites. DNA adducts in sperm cells could be considered as a sign of severe DNA damage, which played an important role in meiotic division during spermatogenesis and could be associated with infertility. Lipophilic compounds undergo metabolic activation by phase I enzymes, which introduce a reactive center into the molecule, followed by phase II conjugation reaction resulting in a water soluble product.

METHODS

We genotyped CYP1A1*2A, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in a hospital based case-control study including 206 infertile men and 230 healthy fertile (control) subjects.

RESULTS

Analysis showed that CYP1A1*2A CC genotype is associated with increased risk of male infertility (OR=6.08, 95% CI=1.91-25.27), while TC genotype showed a non-significantly increased risk of male infertility (OR=1.35 95% CI=0.89-2.05). Further, when the variant genotypes were combined (CYP1A1*2A TC+CC) assuming a co-dominant allele effect, TC plus CC genotypes were also found to be significant with increased risk of male infertility (OR=1.57 95% CI=1.05-2.35 p=0.02). Allele frequencies are calculated for each genotype of CYP1A1*2A and the differences for allele frequencies between the infertile and fertile men are determined using Fisher's exact test. T and C allele frequencies in infertile men are 71% and 29% as against 80% and 20% in fertile men. The differences for allele frequencies are found to be statistically significant (p=0.002). The results showed a drastic decrease in the sperm count and motility and increase in dead sperms in CC genotype when compared to other genotypes in infertile men.

CONCLUSION

Based on Indian study we conclude that CC genotype of CYP1A1 is associated in the pathogenesis of male infertility.

Genetic polymorphisms in oestrogen metabolic pathway and breast cancer: a positive association with combined CYP/GST genotypes

The cytochrome P450 family (CYPs) and the glutathione S-transferase (GSTs) enzymes play an important role in the metabolism of environmental carcinogens and of oestrogen and can affect breast cancer risk. In this study we examine the role of the genes CYP1A1, CYP17, CYP2D6, GSTM1, GSTP1 and GSTT1 in breast cancer risk in Brazilian women. The study population consisted of 102 incident breast cancer cases and 102 healthy controls. Genotyping analyses were performed by PCR-based methods. A significant finding was observed between GSTP1 Ile-Val polymorphism and breast cancer risk (OR = 1.81; CI 95% = 1.04-3.16). A significant association was observed between women with 0-2 risk genotypes and those with 4 or more risk genotypes (OR = 2.42; CI 95% = 1.13-5.18) when the potential combined effects of the risk genotypes were examined. No significant differences between cases and controls were found correlating the genotypes and the clinical-histopathological parameters. In conclusion, in our population only GSTP1 was associated with breast cancer risk. However, when the genes were tested in combination, a significant association in the breast cancer risk was observed.

The CYP19 TTTA repeat polymorphism is related to the prognosis of premenopausal stage I-II and operable stage III breast cancers

PURPOSE

Given the critical role of the CYP19 gene, encoding aromatase, in estrogen synthesis and the association of the estrogen level with its TTTA repeat polymorphism, the potential influence of this polymorphism on breast cancer survival, and hence management, deserves further study.

METHODS

Genotyping for the CYP19 TTTA repeat polymorphism was performed on 482 stage I-II and operable stage III Taiwanese breast cancer patients. Patients with more than seven TTTA repeats in either allele of CYP19 were defined as having the long allele. We correlated clinical variables and CYP19 genotypic polymorphism with outcome.

RESULTS

In hormone receptor (HR)-positive breast cancers, premenopausal patients with the long allele of the CYP19 polymorphism had a significantly higher overall survival (OS) rate (8-year, 89% versus 68%; p= .003) than those without it. This difference was further demonstrated by a multivariate analysis (OS hazard ratio, 1.53; p= .041). In postmenopausal women or patients with HR-negative breast cancer, there was no significant difference in OS between patients with or without the long allele. In premenopausal women with HR-positive cancers, adequate intensity adjuvant chemotherapy did not achieve a greater OS rate than suboptimal chemotherapy in patients with the long allele, but it resulted in a significantly higher OS rate (p= .011) than suboptimal chemotherapy in women without the long allele.

CONCLUSIONS

The CYP19 TTTA repeat polymorphism is associated with survival in premenopausal women, but not in postmenopausal women, with HR-positive breast cancers. Premenopausal women with the long allele have a greater survival rate and may not gain benefit from adjuvant chemotherapy.

Dietary soya isoflavones and breast carcinogenesis: a perspective from a cell-culture model

Southeast Asian women have a lower incidence of breast cancer than their counterparts in the West. Epidemiological studies have indicated that soya consumption may be a contributing factor. Carcinogenesis is a process involving multiple stages. The present review attempts to fit the cellular mechanisms attributed to soya isoflavones into these different stages. Many cell-culture studies have reported the growth-inhibitory effect of soya isoflavones; however, with the non-physiological concentrations employed in these studies it would be difficult to explain the protection mechanisms observed in epidemiological studies. Our laboratory has previously found that genistein inhibits cytochrome P450 (CYP)1A1 and CYP1B1. The inhibition implies that soya consumption may have the potential to prevent chemical carcinogenesis. The preferential inhibition of CYP1B1 may also block the oestrogen-initiated carcinogenesis. The antagonism of oestrogen receptor (ER) binding can affect the cell-proliferative phase, which is likely to be important in the promotion stage of breast cancer. Since our laboratory and others have indicated that genistein at physiological concentrations has no effect on the downstream activities of ER binding, the antagonism of ER is not likely to be a contributing factor in the disease prevention. Moreover, soya isoflavones cannot inhibit aromatase (CYP19), which is the enzyme responsible for oestrogen synthesis. In the present review various cellular activities altered by soya isoflavones are discussed

Differential effect of over-expressing UGT1A1 and CYP1A1 on xenobiotic assault in MCF-7 cells

Gene mutation has been considered as a major step of carcinogenesis. Some defective genes may induce spontaneous tumorigenesis, while others are required to interact with the environment to induce cancer. CYP1A1 and UGT1A1 are encoded for the respective phase I and II drug-metabolizing enzymes. Their expressions have been associated with breast cancer incidence in women, and some xenobiotics are substrates of these two enzymes. In the current study, cytochrome P450 (CYP) 1A1 and UDP-glucuronosyltransferase (UGT) 1A1 were over-expressed in the breast cancer MCF-7 cells, and potential interactions between these enzymes and estrogen or polycyclic aromatic hydrocarbon were evaluated. Compared with control cells (MCF-7(VEC)), reduced cell proliferation was seen in cells expressing UGT1A1 (MCF-7(UGT1A1)) under estradiol treatment. 7,12-Dimethylbenz[a]anthracene (DMBA) is an established breast cancer initiator in animal model. Over-expressing UGT1A1 reduced the binding of DMBA to DNA, and increased MCF-7(UGT1A1) intact cells under DMBA treatment was verified by comet assay. On the other hand, intensified DMBA binding and damages were observed in MCF-7(CYP1A1) cells. This study supported that UGT1A1 but not CYP1A1 expression could protect against xenobiotic assault.

Polymorphism of cytosolic serine hydroxymethyltransferase, estrogen and breast cancer risk among Chinese women in Taiwan

Cytosolic serine hydroxymethyltransferase (cSHMT) is key to intersection of folate-metabolic pathway, participating in the pyrimidine synthesis for DNA repair. Based on the hypothesis that variants of the cSHMT C1420T together with methionine synthase (MS A2756G) and 5,10-methylenetetrahydrofolate reductase (MTHFR C677T and A1298C) are associated with breast cancer, we performed a multigenic case-control study of the effects to breast cancer risk of four polymorphisms of folate-metabolizing genes against duration of estrogen exposure. Support of our hypothesis came from the following observations: (i) Allelic frequency of cSHMT C1420T was higher in the controls than in the cases, manifesting a 0.56-fold risk reduction in breast cancer (95%CI = 0.39-0.80); and this association was more significant in those women are susceptible to time of estrogen exposure. (ii) A joint effect of the cSHMT and MS polymorphisms significantly reduced susceptibility to breast cancer (aOR = 0.55; 95%CI = 0.34-0.88). (iii) There was a trend toward a reduced risk of breast cancer in women carrying a greater number of putative low-risk genotypes (Ptrend = 0.048). (iv) This synergistic effects on risk reduction was significantly interacted with length of estrogen exposure, exhibiting a longer time of estrogen exposure (> or =30 years), menarche-to-FFTP interval (>11 years), age at the first full-term pregnancy (< or =25 years), and body mass index (< or =24). In conclusion, our study provides support to account for the preferential role of cSHMT polymorphism to lower risk of female breast cancer, and such reduced risk would be more significant in carriers with the polymorphisms of MS and MTHFR genes.

Recalling P446. P4501A1 (CYP1A1) opting for clinical application

This review goes back to spectral studies [see Hildebrandt et al., 1968]. The findings of apparent absolute spectra of two interconvertible forms of microsomal mixed function oxidases are looked back on to recall whether their impact sustained scrutiny or are rather remembered as of sentimental value only. The second part summarizes studies on the clinical relevance of CYP1A1 with special reference to our investigations. The impact of genetic variability of CYP1A1 on cancer susceptibility, differential effects of polyphenols and hyperforin on toxification and detoxification pathways of benzo[a]pyrene, and differential metabolite patterns of 17 beta-estradiol, estrone, and eicosapentaenoic acid are presented.

Polymorphisms in CYP1A1 gene are associated with male infertility in a Chinese population

Cytochrome P4501A1 (CYP1A1) is a key enzyme in phase I bioactivation of polycyclic aromatic hydrocarbons (PAHs), which have potential reproductive toxicity. The aim of this study was to investigate the association of the CYP1A1 polymorphisms with male infertility in a Han-Chinese population. We genotyped two polymorphisms, CYP1A1*2A and CYP1A1*2C, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in a hospital-based case-control study including 192 infertile patients with non-obstructive azoospermia or severe oligozoospermia and 226 fertile controls. We found that the genotype distribution of CYP1A1*2C was significantly different between the patients and the controls (p = 0.019). Analysis showed that CYP1A1*2C AG genotype was associated with a significantly decreased risk of male infertility [odds ratio (OR) = 0.56, 95% confidence interval (95% CI) = 0.36-0.86, p = 0.005] compared with the AA genotype. A statistically significantly decreased risk of male infertility was found to be associated with the CYP1A1*2C AG genotype plus GG genotype compared with CYP1A1*2C AA genotype (OR = 0.60, 95% CI = 0.40-0.91, p = 0.011). No significant association was detected between CYP1A1*2A polymorphism and male infertility. Haplotypic analysis showed a significantly increased risk of male infertility associated with the C-A haplotype compared with the T-A haplotype (OR = 1.98, 95% CI = 1.27-3.09), indicating a synergic effect of the two polymorphisms. Our results suggest that the CYP1A1 polymorphisms may contribute to the pathogenesis of male infertility in the Han-Chinese population.

Interaction between cytochrome P450 gene polymorphisms and serum organochlorine TEQ levels in the risk of endometriosis

Exposure to dioxins and polychlorinated biphenyls (PCBs) has been suggested as a possible etiologic factor for endometriosis, but the association remains highly controversial. To assess whether cytochrome P450 (CYP) gene polymorphisms modulate the effect of dioxins and/or PCBs in endometriosis risk, we conducted a case-control study among infertile Japanese women. A total of 138 eligible women aged 20-45 were diagnosed laparoscopically and classified into three subgroups: control (no endometriosis), early endometriosis (stages I-II) and advanced endometriosis (stages III-IV). Neither CYP1A1 Ile462Val and CYP1B1 Leu432Val polymorphisms (genotypes with versus genotypes without the minor allele) nor serum dioxin and PCB toxic equivalency (TEQ) levels (low versus high) were independently associated with either early or advanced endometriosis risk. However, genotypes with the CYP1A1 462Val allele showed a statistically significant reduced risk of advanced endometriosis in combination with high serum dioxin TEQ levels (adjusted odds ratio = 0.13, 95% confidence interval: 0.02-0.76) (P for interaction = 0.08). Although no association was found between serum PCB TEQ level and advanced endometriosis in any stratum of CYP1B1 Leu432Val polymorphism, a statistically significant interaction was found (P for interaction = 0.05). CYP1A1 and CYP1B1 polymorphisms may modify the relation between environmental exposure to organochlorine and advanced endometriosis risk.

Cytochrome P450 1A1 (CYP1A1) T3801C and A2455G polymorphisms in breast cancer risk: a meta-analysis

The cytochrome P450 1A1 gene (CYP1A1), encoding Phase I metabolic enzymes, appeared to be a candidate gene for breast cancer risk. However, studies on the association between polymorphisms in this gene and breast cancer have yielded conflicting results. We performed a meta-analysis to investigate the association with breast cancer of the CYP1A1 polymorphisms T3801C (9,316 cases and 12,714 controls) and A2455G (9,552 cases and 9,320 controls). In the genotype contrast of A2455G, both additive [GG vs AA, P = 0.04, fixed-effects OR 0.72; 95% CI (0.53-0.99), P = 0.95 for heterogeneity] and recessive [GG vs (GA + AA), P = 0.04, fixed-effects OR 0.73; 95% CI (0.53-0.99), P = 0.97 for heterogeneity] models produced significant results in east-Asians. In pre-menopausal women in a worldwide population, significant association between A2455G and breast cancer was also found using both models [additive model: P = 0.02, fixed-effects OR 0.52; 95% CI (0.29-0.92), P = 0.39 for heterogeneity; recessive model: P = 0.02, fixed-effects OR 0.51; 95% CI (0.29-0.90), P = 0.38 for heterogeneity]. Our meta-analysis suggests that an A2455G G/G genotype is associated with a trend of reduced breast cancer risk, both in east-Asian women and in pre-menopausal women worldwide, while the T3801C C allele might not be a risk factor for breast cancer. Larger scale primary studies are required to further evaluate the interaction of CYP1A1 polymorphisms and breast cancer risk in specific populations.

Pairwise Combinations of Estrogen Metabolism Genotypes in Postmenopausal Breast Cancer Etiology

Estrogen exposures have been associated with breast cancer risk, and genes involved in estrogen metabolism have been reported to mediate that risk. Our goal was to better understand whether combinations of candidate estrogen metabolism genotypes are associated with breast cancer etiology. A population-based case-control study in three counties of the Philadelphia Metropolitan area was undertaken. We evaluated seven main effects and 21 first-order interactions in African Americans and European Americans for genotypes at COMT, CYP1A1, CYP1A2, CYP1B1, CYP3A4, SULT1A1, and SULT1E1 in 878 breast cancer cases and 1,409 matched random digit-dialed controls. In European Americans, we observed main effect associations of genotypes containing any CYP1A1*2C (odds ratio, 1.71; 95% confidence interval, 1.09-2.67) and breast cancer. No significant main effects were observed in African Americans. Three significant first-order interactions were observed. In European Americans, interactions between SULT1A1*2 and CYP1A1*2C genotypes (P(interaction) < 0.001) and between SULT1E1 and CYP1A2*1F genotypes were observed (P(interaction) = 0.006). In African Americans, an interaction between SULT1A1*2 and CYP1B1*4 was observed (P(interaction) = 0.041). We applied the false-positive report probability approach, which suggested that these associations were noteworthy; however, we cannot rule out the possibility that chance led to these associations. Pending future confirmation of these results, our data suggest that breast cancer etiology in both European American and African American postmenopausal women may involve the interaction of a gene responsible for the generation of catecholestrogens with a gene involved in estrogen and catecholestrogen sulfation.

CYP17 and COMT gene polymorphisms can influence bone directly, or indirectly through their effects on endogenous sex steroids, in postmenopausal Japanese women

We aimed to assess whether circulating sex steroids would influence bone density and bone loss, whether part of this influence could be explained by genetic variation measured as polymorphisms in candidate genes affecting circulating hormone levels, or whether gene polymorphisms would have direct effects on bone in 229 postmenopausal Japanese women aged 46 years and over who had been followed for eight years (Yokohama Cohort). Bone mineral density (BMD) in the lumbar spine (L), femoral neck (FN), total hip (T) and distal radius (R) was measured every year, and endogenous sex steroid levels were determined at the start of the study. We investigated the polymorphisms of estrogen-metabolizing enzyme gene, CYP17; estrogen biosynthesis (high activity, A2/A2), CYP1A1; hydroxylation (high inducibility, vt/vt) and COMT; inactivation (low activity, L/L) with PCR-based restriction fragment length polymorphism assays. Dehydroepiandrosterone (DHEA) and androstenedione (AND) levels significantly correlated with bone density in both the axial (L) and the appendicular skeleton (FN, T and R) (r=0.194-0.229; P<0.05) whereas estradiol (E2) and AND showed significant correlations with bone change only at the axial skeleton (r=0.205 and r=-0.139, respectively; P<0.05) on the total cohort. These correlations remained significant in thin/normal-weight women [body mass index (BMI) <25 kg/m2)] even after adjustment for years since menopause (YSM) and BMI or age and BMI, suggesting an interaction of BMI and sex steroid/BMD association. On the total cohort, a difference in endogenous DHEA levels between CYP17 homozygote A2 and non-homozygote A2; an increasing trend in AND levels from COMT L/L, L/H, to H/H; and a difference in TS level between COMT homozygote L and non-homozygote L were separately observed. All observations were significant for unadjusted and adjusted analysis, except for COMT and TS. In thin/normal-weight women (BMI <25 kg/m2), the same effects of CYP17 genotypes on DHEA were observed as on the total cohort. CYP17 and COMT genes showed some direct influence on bone density. Mean percent change in T-BMD was negative for CYP17 non-homozygote A2 in contrast to a positive value for homozygote A2. Mean percent change in R-BMD showed the difference between COMT homozygote L and non-homozygote L with a larger decrease for the homozygote L. Together, CYP17 and COMT genotypes might have some effect on bone both directly and indirectly through their effects on endogenous sex steroids in postmenopausal Japanese women.

CYP1A1 and CYP1B1 genetic polymorphisms, smoking and breast cancer risk in a Finnish Caucasian population

We investigated the associations between two CYP1A1 polymorphisms (Ile462Val and Thr461Asn) and one CYP1B1 polymorphism (Leu432Val) and breast cancer risk. The study population consisted of 483 breast cancer patients and 482 healthy population controls, all of homogenous Finnish origin. No statistically significant overall associations were found between the CYP1A1 and CYP1B1 genotypes and breast cancer risk. However, a significant increase in the breast cancer risk was seen for women who had smoked 1-9 cigarettes/day and carried the CYP1B1 432Val allele; the OR was 2.6 (95% CI 1.07-6.46) for women carrying the Leu/Val genotype and 5.1 (95% CI 1.30-19.89, P for trend 0.005) for women with the Val/Val genotype compared to similarly smoking women homozygous for the 432Leu allele. Furthermore, when CYP1B1 genotypes were combined with the previously analyzed N-acetyl transferase (NAT2) genotypes, a significant increase in breast cancer risk was found among women who had at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype (OR 1.52; 95% CI 1.03-2.24) compared to women carrying a combination of CYP1B1 Leu/Leu and NAT2 rapid acetylator genotypes. This risk was seen to be confined to ever smokers; the OR was 2.46 (95% CI 1.11-5.45) for ever smokers carrying at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype compared to ever smokers with the CYP1B1 Leu/Leu and NAT2 rapid acetylator genotype combination. Our results suggest that the CYP1B1 polymorphism may be an important modifier of breast cancer risk in Finnish Caucasian women who have been exposed to tobacco smoke and/or carry the NAT2 slow acetylator genotype.

CYP17, CYP1A1 and COMT polymorphisms and the risk of adenomyosis and endometriosis in Taiwanese women

BACKGROUND

The aim of the study was to test whether the COMT, CYP1A1 and CYP17 genes influence the risk of developing adenomyosis and endometriosis.

METHODS

We conducted two case-control studies, where the cases (n = 198) had either of the two diseases, and controls (n = 312) were disease-free women. For the COMT gene, we selected the G/A nonsynonymous single-nucleotide polymorphism (SNP) that leads to valine-to-methionine (Val/Met) substitution. For the CYP1A1 gene, we used a functional T/C SNP in the 3'-noncoding region, and we genotyped a T/C functional SNP in the 5' region of the CYP17 gene for the present study. Hardy-Weinberg equilibrium was checked in both cases and controls. Logistic regression models were used to evaluate the genetic effect, with adjustment for other covariates.

RESULTS

We found that the homozygous COMT genotype that encodes low enzyme activity had an increased risk for adenomyosis with an age-adjusted odds ratio of 3.2 (95% confidence interval 1.3-7.8; P = 0.006). The COMT gene, however, was not associated with endometriosis. Neither the CYP1A1 nor CYP17 genes had any significant association with either of the two diseases.

CONCLUSION

The COMT gene significantly influences the risk of adenomyosis but not endometriosis. The present study does not provide evidence to support any of the three genes exerting pleiotropic effects on both diseases.

Joint Effects of the CYP1A1 MspI, ERα PvuII, and ERα XbaI Polymorphisms on the Risk of Breast Cancer: Results from a Population-Based Case-Control Study in Shanghai, China

Estrogen-metabolizing gene and estrogen receptor (ER) genes are the possible risk factors implicated in the initiation and development of breast through estrogen tumorigenesis pathway. We examined whether CYP1A1 MspI, ERalpha PvuII, and ERalpha XbaI genetic polymorphisms could increase the risk of breast cancer among Chinese women and gene-gene joint effect on the breast cancer risk in a subset from a population-based case-control study conducted in urban Shanghai from January 1, 1998 and November 31, 2001. PCR-RFLP method based on buccal cells was used to examine the three candidate polymorphisms in 282 breast cancer cases and 298 controls. Compared with CYP1A1 MspI m1/m1, the risk of breast cancer was doubled for genotypes CYP1A1 MspI m1/m2 [odds ratio (OR), 1.83; 95% confidence interval (95% CI), 1.24-2.69] and CYP1A1 MspI m2/m2 (OR, 2.22; 95% CI, 1.26-3.85). The association seemed to be stronger among cases diagnosed older than 45 years and women without a family history of breast cancer. ERalpha PvuII pp and ERalpha XbaI xx polymorphisms, which are in possible linkage disequilibrium, were both associated with a nonsignificantly elevated risk in all subjects; the associations seemed to be stronger among women with a family history of breast cancer. There seems to be a joint effect on the breast cancer risk between CYP1A1 MspI and ERalpha XbaI genotypes (m2/m2 and xx; OR, 5.87; 95% CI, 1.38-24.98), between CYP1A1 MspI and ERalpha PvuII genotypes (m2/m2 and pp; OR, 2.39; 95% CI, 0.81-7.07), and among all three genotypes (m2/m2, pp, and xx; OR, 8.07; 95% CI, 1.45-44.77). Results of this study indicate that estrogen-metabolizing genes and estrogen receptor may jointly play a role in the etiology of breast cancer.

Interactive effects between CYP1A1 genotypes and environmental polychlorinated dibenzo-p-dioxins and dibenzofurans exposures on liver function profile

Previous studies reported that polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) induced hepatic cytochrome P-4501A1 (CYP1A1). The aim of this study was to examine the interactive influence of CYP1A1 genotypes and PCDD/Fs exposure on liver function profile. PCDD/Fs levels and liver function parameters were determined in serum and correlated with genetic polymorphism of CYP1A1/Msp 1 in 225 human volunteers who had no or minimal occupational exposure to PCDD/F. The results showed that the highest glutamate pyruvate transaminase (GPT) activity levels were found in subjects with homozygous variant CYP1A1/Msp 1, followed by heterozygous variant, and finally homozygous wild type for those individuals whose serum PCDD/Fs levels were higher than 17.4 pg WHO-TEQ/g lipid. Data suggest that GPT activity levels may be modified by interaction of CYP1A1/Msp 1 genotype with dioxin after adjustment for age, alcohol consumption, and history of liver illness. Further studies are needed to characterize the variation in other related genes to verify whether a correlation exists between serum PCDD/Fs levels and adverse health effects.

Cytochrome P4501A1 genetic polymorphisms and breast cancer risk in Nigerian women

In this case-control study based on 250 women with breast cancer and 250 age-matched controls, we sought to evaluate the role of four polymorphic variants in the CYP1A1 gene in breast cancer susceptibility in Nigerian women. Heterozygosity for the CYP1A1 M1 genotype (CYP1A1 M1 [T/C]) was associated with a 21% reduced risk of breast cancer (OR = 0.79, 95% CI 0.46-1.40) while homozygosity for the genotype (CYP1A1 M1 [C/C]) conferred a non-significant 9% reduced risk of breast cancer. These risk profiles were not significantly altered in subgroup analysis by menopausal status. While heterozygosity for the CYP1A1 M3 genotype (T/C) conferred a non-significant 24% reduced risk of breast cancer (OR = 0.76, 95% CI 0.47-1.22), homozygosity for the variant was associated a non-significant 1.95-fold increased risk of breast cancer (OR = 1.95, 95% CI 0.24-6.01). Subgroup analysis showed a non-significant 11% reduced risk in premenopausal heterozygous carriers (OR = 0.89, 95% CI 0.45-1.44) and a non-significant 6% increased risk of postmenopausal breast cancer for carriers of the CYP1A1 M3 (T/C) genotype. The CYP1A1 M2 (isoleucine to valine) polymorphism in exon 7 and CYP1A1 M4 (threonine to asparagine) variant in codon 461 of the CYP1A1 gene were found to be very rare in our study subjects. This study has shown that while the CYP1A1 M1 polymorphism conferred reduced risk of breast cancer, homozygosity for the CYP1A1 M3 (C/C) was associated with increased risk of breast cancer although these risks did not attain statistical significance.

Cytochrome P-450 1A1 gene polymorphisms and risk of breast cancer: a HuGE review

Cytochrome P-450 (CYP) 1A1 plays a key role in phase I metabolism of polycyclic aromatic hydrocarbons and in estrogen metabolism. It is expressed predominantly in extrahepatic tissues, including the breast. Four CYP1A1 gene polymorphisms (3801T --> C, Ile462Val, 3205T --> C, and Thr461Asp) have been studied in relation to breast cancer. The 3801C variant is more common than the Val variant. Both variants occur more frequently in Asians than in White populations. The 3205T --> C polymorphism has been observed in African Americans only. Little data are available on the geographic/ethnic distribution of the Thr461Asp polymorphism. The functional significance of the polymorphisms is unclear. In 17 studies, no consistent association between breast cancer and CYP1A1 genotype was found. Meta-analysis found no significant risk for the genotypes 1) 3801C/C (relative risk (RR) = 0.97, 95% confidence interval (CI): 0.52, 1.80) or 3801T/C (RR = 0.91, 95% CI: 0.70, 1.19) versus 3801T/T, 2) Val/Val (RR = 1.04, 95% CI: 0.63, 1.74) or Ile/Val (RR = 0.92, 95% CI: 0.76, 1.10) versus Ile/Ile, or 3) Asp/Asp (RR = 0.95, 95% CI: 0.20, 4.49) or Thr/Asp (RR = 1.12, 95% CI: 0.87, 1.43) versus Thr/Thr. Future studies should explore possible interactions between CYP1A1 and sources of polycyclic aromatic hydrocarbons, markers of estrogen exposure, other lifestyle factors influencing hormonal levels, and other genes involved in polycyclic aromatic hydrocarbon metabolism or hormonal biosynthesis.

Association of CYP1A1 Polymorphisms with Differential Metabolic Activation of 17β-Estradiol and Estrone

Several epidemiologic studies associate certain CYP1A1 genotypes, alone or in combination, with an increased risk of estrogen-related cancers. To answer the question of whether genotype-dependent activation of estrogens by CYP1A1 could be the underlying mechanism, we studied the hydroxylation activity of the most common allelic variants of human CYP1A1 towards both endogenously occurring estrogens, 17beta-estradiol (E2) and estrone (E1). We expressed and purified CYP1A1.1 (wild-type), CYP1A1.2 (Ile(462)Val), and CYP1A1.4 (Thr(461)Asn) and did enzymatic assays of NADPH-dependent estrogen hydroxylation in reconstituted CYP1A1 systems. All CYP1A1 variants catalyzed the formation of 2-, 4-, 6alpha-, and 15alpha-hydroxylated estrogen metabolites from E2 and E1, yet with varying catalytic efficiency and distinct regiospecificity. Whereas the variant CYP1A1.2 (Ile(462)Val) had a significant higher catalytic activity for all hydroxylation sites and both substrates, it was most pronounced for 2-hydroxylation. Catalytic efficiencies for the formation of the major metabolites, 2-OH-E2 and 2-OH-E1, by CYP1A1.2 were 5.7- and 12-fold higher, respectively, compared with the wild-type enzyme. The catalytic efficiencies for hydroxylations catalyzed by CYP1A1.4 were roughly comparable with those of the wild-type enzyme. Enzyme kinetics showed that the superior activity of CYP1A1.2 (Ile(462)Val) is mainly caused by a higher V(max), whereas K(m) values of all variants were similar. The data suggest that risk of estrogen-induced cancers and cardiovascular diseases might be-at least partially-determined by the CYP1A1 genotype.

Polymorphisms inCYP1A1 and breast carcinoma risk in a population-based case-control study of Chinese women

BACKGROUND

Cytochrome P450 1A1 (CYP1A1) is involved in the 2-hydroxylation of estrogen, the hormone that plays a critical role in the etiology of breast carcinoma.

METHODS

The authors evaluated common polymorphisms in the CYP1A1 gene in relation to breast carcinoma risk in a large population-based case-control study among Chinese women, the Shanghai Breast Cancer Study. Because the CYP1A1*3 and CYP1A1*4 alleles were not detected in the study population, analyses were performed for CYP1A1*2A (T-->C transition in the 3' noncoding region) and CYP1A1*2C (A-->G transition in exon 7, resulting in a substitution of Val for Ile) in 1134 patients with breast carcinoma and 1227 controls.

RESULTS

The frequencies of the variant allele were 38.3% and 38.8% among cases and controls (P = 0.91), respectively, for the CYP1A1*2A polymorphism, and 23.1% and 24.8% (P = 0.26) for the CYP1A1*2C polymorphism. Homozygosity for both variant alleles in these 2 polymorphic sites (CYP1A1*2B) was associated with a borderline significant odds ratio (OR) of 0.71 (95% confidence interval [CI], 0.47-1.06). The reduced risk was more pronounced among postmenopausal women with long duration (> 30 yrs) of menstruation (OR = 0.43; 95% CI, 0.19-0.99) or among women with a low waist-to-hip ratio (OR = 0.52; 95% CI, 0.28-0.94).

CONCLUSIONS

Results from the current study suggest that homozygosity for the CYP1A1*2A and CYP1A1*2C alleles in the CYP1A1 gene may be associated with a reduced risk for breast carcinoma, particularly among lean women with long-term endogenous estrogen exposure.

Pharmacogenomics and breast cancer

Germline variants can be used to study breast cancer susceptibility as well as the variable response to both drug and radiation therapy used in the treatment of breast cancer. In addition to germline high-penetrance mutations important in familial and hereditary breast cancer, a substantial component of breast cancer risk can be attributed to the combined effect of many low-risk germline polymorphisms involved in relevant pathways like those of DNA repair, adhesion, carcinogen and estrogen metabolism. Additionally, the identification of sequence variants in genes involved in response to chemotherapy and radiation treatment, has created the opportunity to apply genomics to individualized treatment. The continued insight into the molecular pathways involved in drug and radiation response has enabled progress in tailoring therapies in such a way as to both maximize efficacy and minimize toxicity. Polymorphisms in genes encoding drug-metabolizing enzymes, drug transporters and drug targets can be used to predict toxicity and response to pharmacologic agents used in breast cancer treatment. Similarly, germline variants in genes involved in DNA repair, radiation-induced fibrosis and reactive oxygen species may be used to predict response to radiation therapy. As a result, pharmacogenomics is rapidly evolving to affect the entire spectrum of breast cancer management, influencing both prevention and treatment choices.

An evolutionary perspective on single-nucleotide polymorphism screening in molecular cancer epidemiology

Given that there are millions of single-nucleotide polymorphisms (SNPs) in the entire human genome, a major difficulty faced by scientists in planning costly population-based genotyping is to choose target SNPs that are most likely to affect phenotypic functions and ultimately contribute to disease development. Although it is widely accepted that sequences with important functionality tend to be less variable across species because of selective pressure, to what extent evolutionary conservation is mirrored by epidemiological outcome has never been demonstrated. In this study, we surveyed odds ratios detected for 46 SNPs in 39 different cancer-related genes from 166 molecular epidemiological studies. The conservation levels of amino acid that these SNPs affected were calculated as a tolerance index by comparing sequences from different species. Our results provide evidence of a significant relationship between the detected odds ratios associated with cancer risk and the conservation levels of the SNP-affected amino acids (P = 0.002; R(2) = 0.06). Tolerance indices were further calculated for 355 nonsynonymous SNPs identified in 90 human DNA repair genes, of which 103 caused amino acid changes in very conserved positions. Our findings support the concept that SNPs altering the conserved amino acids are more likely to be associated with cancer susceptibility. Using such a molecular evolutionary approach may hold great promise for prioritizing SNPs to be genotyped in future molecular epidemiological studies.

Potential exposure to PCBs, DDT, and PBDEs from sport-caught fish consumption in relation to breast cancer risk in Wisconsin

In Wisconsin, consumption of Great Lakes fish is an important source of exposure to polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), polybrominated diphenyl ethers (PBDEs), and other halogenated hydrocarbons, all of which may act as potential risk factors for breast cancer. We examined the association between sport-caught fish consumption and breast cancer incidence as part of an ongoing population-based case-control study. We identified breast cancer cases 20-69 years of age who were diagnosed in 1998-2000 (n = 1,481) from the Wisconsin Cancer Reporting System. Female controls of similar age were randomly selected from population lists (n = 1,301). Information about all sport-caught (Great Lakes and other lakes) fish consumption and breast cancer risk factors was obtained through telephone interviews. After adjustment for known and suspected risk factors, the relative risk of breast cancer for women who had recently consumed sport-caught fish was similar to women who had never eaten sport-caught fish [relative risk (RR) = 1.00; 95% confidence interval (CI), 0.86-1.17]. Frequency of consumption and location of sport-caught fish were not associated with an increased risk of breast cancer. Recent consumption of Great Lakes fish was not associated with postmenopausal breast cancer (RR = 0.78; 95% CI, 0.57-1.07), whereas risk associated with premenopausal breast cancer was elevated (RR = 1.70; 95% CI, 1.16-2.50). In this study we found no overall association between recent consumption of sport-caught fish and breast cancer, although there may be an increased breast cancer risk for subgroups of women who are young and/or premenopausal.

Polymorphisms of estrogen synthesizing and metabolizing genes and breast cancer risk in Japanese women

Recent success of chemoprevention with tamoxifen has opened a new era wherein prevention of breast cancer is much more emphasized than treatment of established breast cancer. Since tamoxifen has been shown to reduce the risk of estrogen receptor (ER)-positive, but not ER-negative, breast cancer in the chemoprevention trial (P-1), it seems to be important to develop risk factors for ER-positive breast cancer in order to select the candidates for chemoprevention more appropriately. Estrogens, the major risk factors for breast cancer, are speculated to affect breast cancer risk through ER, thus, genetic polymorphisms of the genes involved in the estrogens biosynthesis and metabolism are expected as risk factors for ER-positive breast cancer. Significance of polymorphisms of the genes involved in estrogens biosynthesis (CYP17, CYP19) and metabolism (CYP1A1, CYP1B1, COMT) in modulating the susceptibility to breast cancer is reviewed. The ethnic difference of the variant allele frequencies between Caucasian women and Asian women is also discussed.

CYP1A1 polymorphism and risk of gynecological malignancy in Japan

The incidence of endometrial cancer and ovarian cancer in Japan has been increasing in recent years. Results of epidemiologic studies suggest that the onset and multiplication of these cancers are associated with estrogen. Estrogens are metabolized by cytochrome P450 1A1 (CYP1A1) and converted into catecholestrogens, which are carcinogens. CYP1A1 has several polymorphisms, the major one being T6235C transition in the non-coding 3'-flanking region (MspI polymorphism), and another being A4889G transition in exon 7 (Ile/Val polymorphism). These polymorphisms can affect the metabolites of estrogens and contribute to the susceptibility to gynecological malignancy. In this study, to determine whether CYP1A1 polymorphism plays a role in the development of gynecological malignancy in the Japanese population, we assessed the association of CYP1A1 polymorphism in Japanese patients with gynecological malignancy in comparison to that in controls. The odds ratios (ORs) of Ile/Val polymorphism were 1.16 in ovarian cancer patients and 1.70 in endometrial cancer patients. The ORs of MspI polymorphism were 1.33 in ovarian cancer patients and 0.88 in endometrial cancer patients. No significant association was found between these CYP1A1 polymorphisms and gynecological malignancy. Although the frequency of CYP1A1 polymorphism in the Japanese population is higher than that in the Caucasian population, CYP1A1 polymorphism is not related to gynecological malignancies in Japanese population.

Association of genetic polymorphisms in CYP19 and CYP1A1 with the oestrogen receptor-positive breast cancer risk

Since tamoxifen has been shown to reduce the risk of oestrogen receptor (ER)-positive, but not ER-negative, breast cancers in a chemoprevention trial (P-1), it is important to develop assays to assess risk factors for ER-positive breast cancer in order to appropriately select candidates for chemoprevention with tamoxifen. Thus, the significance of genetic polymorphisms of genes involved in oestrogen biosynthesis (CYP19) and metabolism (CYP1A1) as a risk factor for ER-positive breast cancers was evaluated. A case-control study was conducted with 257 breast cancer patients and 191 healthy female controls. Two polymorphisms, CYP19 (TTTA repeats) in intron 4 and CYP1A1 6235C/T in the 3' non-coding region, and their association with the breast cancer risk after adjustment for the other epidemiological risk factors were examined. CYP19 (TTTA)7(-3bp) allele carriers showed a significantly (P<0.05) increased risk of ER-positive breast cancers (Odds Ratio (OR)=1.72, 95% Confidence Interval (CI) 1.10-2.69), but not ER-negative breast cancers. CYP1A1 6235C allele carriers showed a non-significant (P=0.06) trend towards a decreased risk of ER-positive breast cancers (OR=0.65, 95% CI 0.42-1.02), but not ER-negative breast cancers. The combination of these two polymorphisms was found to be more useful in the assessment of the ER-positive breast cancer risk (OR=3.00, 95% CI=1.56-5.74) than the CYP19 (TTTA)7(-3bp) polymorphism alone. The combination of CYP19 (TTTA)7(-3bp) and CYP1A1 6235C/T polymorphisms is associated with an ER-positive, but not ER-negative, breast cancer risk, and, thus, would be useful in the selection of candidates for chemoprevention with tamoxifen.