Xinran Xu

Choline metabolism and risk of breast cancer in a population-based study

Choline is an essential nutrient required for methyl group metabolism, but its role in carcino genesis and tumor progression is not well understood. By utilizing a population‐based study of 1508 cases and 1556 controls, we investigated the associations of di etary intake of choline and two related micronutrients, methionine and betaine, and risk of breast cancer. The highest quintile of choline consumption was associated with a lower risk of breast cancer [odds ratio (OR): 0.76;95% confidence interval (CI): 0.58–1.00] com pared with the lowest quintile. Two putatively functional single nucleotide polymorphisms of choline‐ metabolizing genes, PEMT ‐774G>C (rs12325817) and CHDH +432G>T (rs12676), were also found be related to breast cancer risk. Compared with the PEMT GG genotype, the variant CC genotype was associated with an increased risk of breast cancer (OR: 1.30;95% CI: 1.01–1.67). The CHDH minor T allele was also associated with an increased risk (OR: 1.19;95% CI: 1.00‐–1.41) compared with the major G allele. The BHMTrs3733890 polymorphism was also examined but was found not to be associated with breast cancer risk. We observed a significant interaction between dietary betaine intake and the PEMT rs7926 polymorphism (Pinteraction = 0.04).OUR finding suggest that cholin metabolism may play an important role in breast cancer etiology.— Xu, X., Gammon, M. D., Zeisel, S. H., Lee, Y. L., Wetmur, J. G., Teitelbaum, S. L., Bradshaw, P. T., Neugut, A. I., Santella, R. M., Chen, J. Choline metab olism and risk of breast cancer in a population‐based study. FASEB J. 22, 2045–2052 (2008)

High intakes of choline and betaine reduce breast cancer mortality in a population-based study

Choline and betaine provide methyl groups for one‐carbon metabolism. Humans obtain these nutrients from a wide range of foods. Betaine can also be synthesized endogenously from its precursor, choline. Although animal studies have implied a causal relationship between choline deficiency and carcinogenesis, the role of these two nutrients in human carcinogenesis and tumor progression is not well understood. We investigated the associations of dietary intakes of choline and betaine and breast cancer risk and mortality in the population‐based Long Island Breast Cancer Study Project. Among the 1508 case‐group women, 308 (20.2%) deaths occurred, among whom 164 (53.2%) died of breast cancer by December 31, 2005. There was an indication that a higher intake of free choline was associated with reduced risk of breast cancer (Ptrend=0.04). Higher intakes of betaine, phosphocholine, and free choline were associated with reduced all‐cause as well as breast cancer‐specific mortality in a dose‐dependent fashion. We also explored associations of polymorphisms of three key choline‐ and betaine‐metabolizing genes and breast cancer mortality. The betaine‐homocysteine methyltransferase gene (BHMT) rs3733890 polymorphism was associated with reduced breast cancer‐specific mortality (hazard ratio, 0.64;95% confidence interval, 0.42–0.97). Our study supports the important roles of choline and betaine in breast carcinogenesis. It suggests that high intake of these nutrients may be a promising strategy to prevent the development of breast cancer and to reduce its mortality.—Xu, X., Gammon, M. D., Zeisal, S. H., Bradshaw, P. T., Wetmur, J. G., Teitelbaum, S. L., Neugut, A. I., Santella, R. M., Chen, J. High intakes of choline and betaine reduce breast cancer mortality in a population‐based study. FASEB J. 23, 4022–4028 (2009). www.fasebj.org

DNA methylation in peripheral blood measured by LUMA is associated with breast cancer in a population-based study

Our purpose was to identify epigenetic markers of breast cancer risk, which can be reliably measured in peripheral blood and are amenable for large population screening. We used 2 independent assays, luminometric methylation assay (LUMA) and long interspersed elements‐1 (LINE‐1) to measure “global methylation content” in peripheral blood DNA from a well‐characterized population‐based case‐control study. We examined associations between methylation levels and breast cancer risk among 1055 cases and 1101 controls and potential influences of 1‐carbon metabolism on global methylation. Compared with women in the lowest quintile of LUMA methylation, those in the highest quintile had a 2.41‐fold increased risk of breast cancer (95% confidence interval: 1.83‐3.16; P, trend>0.0001). The association did not vary by other key tumor characteristics and lifestyle risk factors. Consistent with LUMA findings, genome‐wide methylation profiling of a subset of samples revealed greater promoter hypermethylation in breast cancer case participants (P=0.04); higher LUMA was associated with higher promoter methylation in the controls (P=0.05). LUMA levels were also associated with functional sodium nitroprusside in key 1‐carbon metabolizing genes, MTHFR C677T (P=0.001) and MTRR A66G (P=0.018). LINE‐1 methylation was associated with neither breast cancer risk nor 1‐carbon metabolism. Our results show that global promoter hypermethylation measured in peripheral blood was associated with breast cancer risk.—Xu, X., Gammon, M. D., Hernandez‐Vargas, H., Herceg, Z., Wetmur, J. G., Teitelbaum, S. L., Bradshaw, P. T., Neugut, A. I., Santella, R. M., Chen, J. DNA methylation in peripheral blood measured by LUMA is associated with breast cancer in a population‐based study. FASEB J. 26, 2657‐2666 (2012). www.fasebj.org

One-carbon metabolism and breast cancer: an epidemiological perspective

One-carbon metabolism is a network of biological reactions that plays critical role in DNA methylation and DNA synthesis, and in turn, facilitates the cross-talk between genetic and epigenetic processes. Genetic polymorphisms and supplies of cofactors (e.g. folate, vitamins B) involved in this pathway have been shown to influence cancer risk and even survival. In this review, we summarized the epidemiological evidence for one-carbon metabolism, from both genetics and lifestyle aspects, in relation to breast cancer risk. We also discussed this pathway in relation to breast cancer survival and the modulation of one-carbon polymorphism in chemotherapy. Emerging evidence on modulation of DNA methylation by one-carbon metabolism suggests that disruption of epigenome might have been the underlying mechanism. More results are expected and will be translated to guidance to the general population for disease prevention as well as to clinicians for treatment and management of the disease.

B-Vitamin Intake, One-Carbon Metabolism, and Survival in a Population-Based Study of Women with Breast Cancer

Breast cancer is the second leading cause of cancer mortality among women. Given its important role in DNA methylation and synthesis, one-carbon metabolism may affect breast cancer mortality. We used a population-based cohort of 1,508 women with breast cancer to investigate possible associations of dietary intake of B vitamins before diagnosis as well as nine polymorphisms of one-carbon metabolizing genes and subsequent survival. Women newly diagnosed with a first primary breast cancer in 1996 to 1997 were followed for vital status for an average of 5.6 years. Kaplan-Meier survival and Cox proportional hazard regression analyses were used to evaluate the association between dietary intakes of B vitamins (1,479 cases), genotypes (∼1,065 cases), and all-cause as well as breast cancer–specific mortality. We found that higher dietary intake of vitamin B1 and B3 was associated with improved survival during the follow-up period (Ptrend = 0.01 and 0.04, respectively). Compared with the major genotype, the MTHFR 677 T allele carriers have reduced all-cause mortality and breast cancer–specific mortality in a dominant model [hazard ratio (95% confidence interval): 0.69 (0.49-0.98) and 0.58 (0.38-0.89), respectively]. The BHMT 742 A allele was also associated with reduced all-cause mortality [hazard ratio, 0.70 (0.50-1.00)]. Estrogen receptor/progesterone receptor status modified the association between the MTHFR C677T polymorphism and survival (P = 0.05). The survival associations with one-carbon polymorphisms did not differ with the use of chemotherapy, although study power was limited for examining such effect modification. Our results indicate that one-carbon metabolism may be an important pathway that could be targeted to improve breast cancer survival. (Cancer Epidemiol Biomarkers Prev 2008;17(8):2109–16)

Sources of polycyclic aromatic hydrocarbons are associated with gene-specific promoter methylation in women with breast cancer

BACKGROUND Tobacco smoke, diet and indoor/outdoor air pollution, all major sources of polycyclic aromatic hydrocarbons (PAHs), have been associated with breast cancer. Aberrant methylation may be an early event in carcinogenesis, but whether PAHs influence the epigenome is unclear, particularly in breast tissue where methylation may be most relevant. We aimed to evaluate the role of methylation in the association between PAHs and breast cancer. METHODS In a population-based case-control study, we measured promoter methylation of 13 breast cancer-related genes in breast tumor tissue (n=765-851 cases) and global methylation in peripheral blood (1055 cases/1101 controls). PAH sources (current active smoking, residential environmental tobacco smoke (ETS), vehicular traffic, synthetic log burning, and grilled/smoked meat intake) were evaluated separately. Logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS When comparing methylated versus unmethylated genes, synthetic log use was associated with increased ORs for CDH1 (OR=2.26, 95%CI=1.06-4.79), HIN1 (OR=2.14, 95%CI=1.34-3.42) and RARβ (OR=1.80, 95%CI=1.16-2.78) and decreased ORs for BRCA1 (OR=0.44, 95%CI=0.30-0.66). Residential ETS was associated with decreased ORs for ESR1 (OR=0.74, 95%CI=0.56-0.99) and CCND2 methylation (OR=0.65, 95%CI=0.44-0.96). Current smoking and vehicular traffic were associated with decreased ORs for DAPK (OR=0.53, 95%CI=0.28-0.99) and increased ORs for TWIST1 methylation (OR=2.79, 95%CI=1.24-6.30), respectively. In controls, synthetic log use was inversely associated with LINE-1 (OR=0.59, 95%CI=0.41-0.86). DISCUSSION PAH sources were associated with hypo- and hypermethylation at multiple promoter regions in breast tumors and LINE-1 hypomethylation in blood of controls. Methylation may be a potential biologic mechanism for the associations between PAHs and breast cancer incidence.

Promoter Hypermethylation in White Blood Cell DNA and Breast Cancer Risk

The role of gene-specific methylation in white blood cells (WBC) as a marker of breast cancer risk is currently unclear. We determined whether promoter hypermethylation in blood DNA of candidate tumor suppressor genes frequently methylated in breast tumors can be used as a surrogate biomarker for breast cancer risk. Promoter methylation of BRCA1, CDH1 and RARβ was analyzed in WBC DNA from a population-based sample of 1,021 breast cancer patients and 1,036 controls by the MethyLight assay. Gene-specific promoter methylation in the DNA of 569 tumor tissue samples was also analyzed to determine the correlation of methylation levels with blood from the same individual. Hypermethylation of BRCA1 (OR: 1.31; 95% CI: 0.98-1.75) in WBC was associated with an increased risk of breast cancer when positive methylation was defined as ≥0.1% methylated. There was lack of concordance between tumor tissue and paired WBC DNA methylation. These results provide limited support that hypermethylation of BRCA1 in WBC DNA may be useful for determination of breast cancer risk. Additional studies with larger numbers of genes are needed to fully understand the relationship between WBC methylation and breast cancer risk.

The influence of one-carbon metabolism on gene promoter methylation in a population-based breast cancer study

Abnormal methylation in gene promoters is a hallmark of the cancer genome; however, factors that may influence promoter methylation have not been well elucidated. As the one-carbon metabolism pathway provides the universal methyl donor for methylation reactions, perturbation of this pathway might influence DNA methylation and, ultimately, affect gene functions. Utilizing approximately 800 breast cancer tumor tissues from a large population-based study, we investigated the relationships between dietary and genetic factors involved in the one-carbon metabolism pathway and promoter methylation of a panel of 13 breast cancer-related genes. We found that CCND2, HIN1 and CHD1 were the most “dietary sensitive” genes, as methylation of their promoters was associated with intakes of at least two out of the eight dietary methyl factors examined. On the other hand, some micronutrients (i.e., B2 and B6) were more “epigenetically active” as their intake levels correlated with promoter methylation status in 3 out of the 13 breast cancer genes evaluated. Both positive (hypermethylation) and inverse (hypomethylation) associations with high micronutrient intake were observed. Unlike what we saw for dietary factors, we did not observe any clear patterns between one-carbon genetic polymorphisms and the promoter methylation status of the genes examined. Our results provide preliminary evidence that one-carbon metabolism may have the capacity to influence the breast cancer epigenome. Given that epigenetic alterations are thought to occur early in cancer development and are potentially reversible, dietary modifications may offer promising venues for cancer intervention and prevention.

Gene-Specific Promoter Methylation Status in Hormone-Receptor-Positive Breast Cancer Associates with Postmenopausal Body Size and Recreational Physical Activity

INTRODUCTION Breast cancer, the leading cancer diagnosis among American women, is positively associated with postmenopausal obesity and little or no recreational physical activity (RPA). However, the underlying mechanisms of these associations remain unresolved. Aberrant changes in DNA methylation may represent an early event in carcinogenesis, but few studies have investigated associations between obesity/RPA and gene methylation, particularly in postmenopausal breast tumors where these lifestyle factors are most relevant. METHODS We used case-case unconditional logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CI) for the associations between body mass index (BMI=weight [kg]/height [m2]) in the year prior to diagnosis, or RPA (average hours/week), and methylation status (methylated vs. unmethylated) of 13 breast cancer-related genes in 532 postmenopausal breast tumor samples from the Long Island Breast Cancer Study Project. We also explored whether the association between BMI/RPA and estrogen/progesterone-receptor status (ER+PR+ vs. all others) was differential with respect to gene methylation status. Methylation-specific PCR and the MethyLight assay were used to assess gene methylation. RESULTS BMI 25-29.9kg/m2, and perhaps BMI≥30kg/m2, was associated with methylated HIN1 in breast tumor tissue. Cases with BMI≥30kg/m2 were more likely to have ER+PR+ breast tumors in the presence of unmethylated ESR1 (OR=2.63, 95% CI 1.32-5.25) and women with high RPA were more likely to have ER+PR+ breast tumors with methylated GSTP1 (OR=2.33, 95% CI 0.79-6.84). DISCUSSION While biologically plausible, our findings that BMI is associated with methylated HIN1 and BMI/RPA are associated with ER+PR+ breast tumors in the presence of unmethylated ESR1 and methylated GSTP1, respectively, warrant further investigation. Future studies would benefit from enrolling greater numbers of postmenopausal women and examining a larger panel of breast cancer-related genes.

Gene expression profiles of the one-carbon metabolism pathway

One-carbon metabolism plays a critical role in both DNA methylation and DNA synthesis. Accumulating evidence has shown that interruptions of this pathway are associated with many disease outcomes including cardiovascular diseases and cancers. Mechanistic studies have been performed on genetic polymorphisms involved in one-carbon metabolism. However, expression profiles of these inter-related genes are not well-known. In this study, we examined the gene expression profiles of 11 one-carbon metabolizing genes by quantifying the mRNA level of the lymphocyte among 54 healthy individuals and explored the correlations of these genes. We found these genes were expressed in lymphocytes at moderate levels and showed significant inter-person variations. We also applied principle component analysis to explore potential patterns of expression. The components identified by the program agreed with existing knowledge about one-carbon metabolism. This study helps us better understand the biological functions of one-carbon metabolism.