We previously reported that global DNA hypomethylation, measured as Sat2 methylation in white blood cells (WBC), and aflatoxin B1 (AFB1) exposure were associated with increased hepatocellular carcinoma risk. In this study, we assessed the association between AFB1 exposure and global DNA methylation. We measured LINE-1 and Sat2 methylation in WBC DNA samples from 1140 cancer free participants of the Cancer Screening Program (CSP) cohort. Blood and urine samples were used to determine the level of AFB1-albumin (AFB1-Alb) adducts and urinary AFB1 metabolites. In continuous models, we found reverse associations of urinary AFB1 with LINE-1 and Sat2 methylation. The odds ratio (OR) per 1 unit decrease were 1.12 (95%CI = 1.03–1.22) for LINE-1 and 1.48 (95%CI = 1.10–2.00) for Sat2 methylation. When compared with subjects in the highest quartile of LINE-1, we found that individuals in the 2nd and 3rd quartiles were less likely to have detectable AFB1-Alb adducts, with ORs (95%CI) of 0.61 (0.40–0.93), 0.61 (0.40-.94), and 1.09 (0.69–1.72), respectively. The OR for detectable AFB1-Alb was 1.81 (95%CI = 1.15–2.85) for subjects in the lowest quartile of Sat2 methylation. The OR for detection of urinary AFB1 for those with LINE-1 methylation in the lowest quartile compared with those in the highest quartile was 1.87 (95%CI = 1.15–3.04). The corresponding OR was 1.75 (95%CI = 1.08–2.82) for subjects in the lowest quartile of Sat2 methylation. The association between AFB1 exposure and global DNA methylation may have implications for the epigenetic effect of AFB1 on hepatocellular carcinoma development and also suggests that changes in DNA methylation may represent an epigenetic biomarker of dietary AFB1 exposure.
DNA methylation; Hepatitis B virus; LINE-1; Sat2; aflatoxin B1; global DNA methylation; white blood cell
Hepatocellular carcinoma (HCC) incidence has increased in the US and also has one of the fastest growing death rates of any cancer. The purpose of the current study was to discover novel genome-wide aberrant DNA methylation patterns in HCC tumors that are predominantly HCV-related. Infinium HumanMethylation 450K BeadChip arrays were used to examine genome-wide DNA methylation profiles in 66 pairs of HCC tumor and adjacent non-tumor tissues. After Bonferroni adjustment, a total of 130,512 CpG sites significantly differed in methylation level in tumor compared with non-tumor tissues, with 28,017 CpG sites hypermethylated and 102,495 hypomethylated in tumor tissues. Absolute tumor/non-tumor methylation differences ≥ 20% were found in 24.9% of the hypermethylated and 43.1% of the hypomethylated CpG sites; almost 10,000 CpG sites have ≥ 30% DNA methylation differences. Most (60.1%) significantly hypermethylated CpG sites are located in CpG islands, with 21.6% in CpG shores and 3.6% in shelves. In contrast, only a small proportion (8.2%) of significantly hypomethylated CpG sites are situated in islands, while most are found in open sea (60.2%), shore (17.3%) or shelf (14.3%) regions. A total of 2,568 significant CpG sites (2,441 hypermethylated and 127 hypomethylated) covering 589 genes are located within 684 differentially methylated regions defined as regions with at least two significant CpG sites displaying > 20% methylation differences in the same direction within 250-bp. The top 500 significant CpG sites can significantly distinguish HCC tumor from adjacent tissues with one misclassification. Within adjacent non-tumor tissues, we also identified 75 CpG sites significantly associated with gender, 228 with HCV infection, 17,207 with cirrhosis, and 56 with both HCV infection and cirrhosis after multiple comparisons adjustment. Aberrant DNA methylation profiles across the genome were identified in tumor tissues from US HCC cases that are predominantly related to HCV infection. These results demonstrate the significance of aberrant DNA methylation in HCC tumorigenesis.
genome-wide; DNA methylation; alterations; hepatocellular carcinoma; 450K BeadChips
Mature microRNAs (miRNAs) are a class of small non-coding RNAs involved in posttranslational gene silencing. Previous studies found that downregulation of miRNAs is a common feature observed in solid tumors, including hepatocellular carcinoma (HCC). We employed a genome-wide approach to test the hypothesis that DNA methylation alterations in miRNA host genes may cause deregulated miRNA expression in HCC. We analyzed tumor and adjacent non-tumor tissues from 62 Taiwanese HCC cases using Infinium HumanMethylation27 DNA Analysis BeadChips that include 254 CpG sites covering 110 miRNAs from 64 host genes. Expression levels of three identified miRNAs (miR-10a, miR-10b and miR-196b) were measured in a subset of 37 HCC tumor and non-tumor tissues. After Bonferroni adjustment, a total of 54 CpG sites from 27 host genes significantly differed in DNA methylation levels between tumor and adjacent non-tumor tissues with 53 sites significantly hypermethylated in tumor tissues. Among the 54 significant CpG sites, 15 sites had more than 2-fold tumor/non-tumor changes, 17 sites had differences > 10%, and 10 sites had both features [including 8 significantly hypermethylated CpG sites in the host genes of miR-10a, miR-10b and miR-196b (HOXB4, HOXD4 and HOXA9, respectively)]. Significant downregulation of miR-10a was observed in tumor compared with non-tumor tissues (0.50 vs. 1.73, p = 0.031). The concordance for HOXB4 methylation alteration and dysregulation of miR-10a was 73.5%. No significant change was observed for miR-10b expression. Unexpectedly, miR-196b was significantly upregulated in tumor compared with non-tumor tissues (p = 0.0001). These data suggest that aberrant DNA methylation may lead to dysregulation of miR-10a in HCC tumor tissues.
HCC; genome-wide; host gene; microRNA; DNA methylation
Alterations in DNA methylation frequently occur in hepatocellular cancer (HCC). We have previously demonstrated that hypermethylation in candidate genes can be detected in plasma DNA prior to HCC diagnosis. To identify with a genome-wide approach additional genes hypermethylated in HCC that could be used for more accurate analysis of plasma DNA for early diagnosis, we analyzed tumor and adjacent non-tumor tissues from 62 Taiwanese HCC cases using Illumina methylation arrays that screen 26,486 autosomal CpG sites. After Bonferroni adjustment, a total of 2,324 CpG sites significantly differed in methylation level, with 684 CpG sites significantly hypermethylated and 1,640 hypomethylated in tumor compared to non-tumor tissues. Array data were validated with pyrosequencing in a subset of 5 of these genes; correlation coefficients ranged from 0.92 to 0.97. Analysis of plasma DNA from 38 cases demonstrated that 37% to 63% of cases had detectable hypermethylated DNA (≥5% methylation) for these 5 genes individually. At least one of these genes was hypermethylated in 87% of cases, suggesting that measurement of DNA methylation in plasma samples is feasible. The panel of methylated genes indentified in the current study will be further tested in large cohort of prospectively collected samples to determine their utility as early biomarkers of hepatocellular carcinoma.
Genome-wide; DNA mehtylation; Hepatocellular Carcinoma
The association between promoter methylation status and survival was investigated in a large cohort of women with breast cancer, participants in the Long Island Breast Cancer Study Project. Archived tumor tissues (n=839) were collected from women diagnosed with a first primary invasive or in situ breast cancer in 1996-1997. Vital status was followed through the end of 2005 with a mean follow up time of 8 years. Promoter methylation of 8 breast cancer-related genes was assessed by MethyLight. The frequencies of methylation for HIN1, RASSF1A, DAPK1, GSTP1, CyclinD2, TWIST, CDH1 and RARβ were 62.9%, 85.2%, 14.1%, 27.8%, 19.6%, 15.3%, 5.8% and 27.6%, respectively. Since survival rates of in situ and invasive breast cancers are substantially different, survival analyses were conducted within 670 invasive cases with complete data on all genes. Age-adjusted Cox-proportional hazards models revealed that GSTP1, TWIST and RARβ methylation was significantly associated with higher breast cancer-specific mortality. Methylation of GSTP1 and RARβ were significantly associated with higher all-cause mortality. To investigate the relationship between the number of methylated genes and breast cancer-specific mortality, we included previously published MethyLight data on p16 and APC methylation status. Breast cancer-specific mortality increased in a dose-dependent manner with increasing number of methylated genes (Ptrend = 0.002), although confidence intervals were wide. Our results suggest that promoter methylation, particularly for a panel of genes, has the potential to be used as a biomarker for predicting prognosis in breast cancer.
Promoter methylation; Tumor suppressor gene; Breast cancer; Mortality
Promoter hypermethylation and global hypomethylation in the human genome are hallmarks of most cancers. Detection of aberrant methylation in white blood cells (WBC) has been suggested as a marker for cancer development, but has not been extensively investigated. This study was carried out to determine whether aberrant methylation in WBC DNA can be used as a surrogate biomarker for breast cancer risk.
Patients and Methods
Promoter hypermethylation of 8 tumor suppressor genes (RASSF1A, APC, HIN1, BRCA1, cyclinD1, RARβ, CDH1 and TWIST1) and DNA methylation for three repetitive elements (LINE1, Sat2M1 and AluM2) were analyzed in invasive ductal carcinoma of the breast, paired adjacent normal tissue and WBC from 40 breast cancer patients by the MethyLight assay. Methylation in WBC from 40 controls was also analyzed.
Tumor and adjacent tissues showed frequent hypermethylation for all genes tested, while WBC DNA was rarely hypermethylated. For HIN1, RASSF1A, APC and TWIST1 there was agreement between hypermethylation in tumor and adjacent tissues (P=0.04, P=0.02, P=0.005 and P<0.0001, respectively). DNA methylation for the three repetitive elements was lower in tumor compared to adjacent tissue and WBC DNA. Significant correlations in the methylation of Sat2M1 between tumor and adjacent tissues and WBC DNA were found (P<0.0001 and P=0.046, respectively). There was also a significant difference in methylation of Sat2M1 between cases and controls (P=0.01).
These results suggest that further studies of WBC methylation, including prospective studies, may provide biomarkers of breast cancer risk.
Breast cancer; promoter hypermethylation; genomic methylation; tumor suppressor genes; repetitive elements; WBC DNA
To evaluate the role of aflatoxin B1 (AFB1) exposure on risk of hepatocellular carcinoma (HCC), a case-control study nested within a community-based cohort was conducted. Baseline blood and urine samples were used to determine the level of AFB1-albumin adducts and urinary AFB1 metabolites. Conditional logistic regression analysis was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to assess the effect of AFB1 exposure on risk of HCC. The adjusted-ORs (95%CIs) were 1.54 (1.01–2.36) and 1.76 (1.18–2.58), respectively, for those with AFB1-albumin adducts and urinary AFB1 metabolites levels above the mean compared to those with levels below the mean. When compared to subjects in the lowest quartile of urinary AFB1 metabolites, there was an increase in risk of HCC, with adjusted ORs (95% CIs) of 0.57 (0.14–2.43), 1.43 (0.32–6.42) and 4.91 (1.18–20.48; Ptrend=0.02), respectively, among noncarriers of hepatitis B virus (HBV) infection. The adjusted OR (95%CI) was 7.49 (5.13–10.93) for carriers of HBsAg compared to noncarriers, regardless of AFB1 status. The ORs (95%CI) were 10.38 (5.73–18.82) and 15.13 (7.83–29.25), for carriers of HBsAg with levels of AFB1-albumin adducts and urinary AFB1 metabolites above the mean, respectively. The combined effect of aflatoxin exposure and HBV infection did not differ by duration of follow-up. Consistent with our previous study with fewer subjects, these data demonstrate that AFB1 exposure is a risk factor for HCC risk. However, in this larger study, the effect of combined AFB1 exposure and HBV infection is more consistent with an additive than a multiplicative model.
Aflatoxins; AFB1-albumin adducts; Hepatitis B virus; Hepatocellular carcinoma; Urinary aflatoxin metabolites
AIM: To determine global DNA methylation in paired hepatocellular carcinoma (HCC) samples using several different assays and explore the correlations between hypomethylation and clinical parameters and biomarkers, including that of aflatoxin B1 exposure.
METHODS: Using the radio labeled methyl acceptance assay as a measure of global hypomethylation, as well as two repetitive elements, including satellite 2 (Sat2) by MethyLight and long interspersed nucleotide elements (LINE1), by pyrosequencing.
RESULTS: By all three assays, mean methylation levels in tumor tissues were significantly lower than that in adjacent tissues. Methyl acceptance assay log (mean ± SD) disintegrations/min/ng DNA are 70.0 ± 54.8 and 32.4 ± 15.6, respectively, P = 0.040; percent methylation of Sat2 42.2 ± 55.1 and 117.9 ± 88.8, respectively, P < 0.0001 and percent methylation LINE1 48.6 ± 14.8 and 71.7 ± 1.4, respectively, P < 0.0001. Aflatoxin B1-albumin (AFB1-Alb) adducts, a measure of exposure to this dietary carcinogen, were inversely correlated with LINE1 methylation (r = -0.36, P = 0.034).
CONCLUSION: Consistent hypomethylation in tumor compared to adjacent tissue was found by the three different methods. AFB1 exposure is associated with DNA global hypomethylation, suggesting that chemical carcinogens may influence epigenetic changes in humans.
Hepatocellular carcinoma; Epigenetics; Hypomethylation; [3H]-methyl acceptance assay; Satellite 2; Long interspersed nucleotide element-1; Aflatoxin B1
To evaluate the role of oxidative stress in prostate cancer risk, we analyzed serum levels of protein carbonyl groups in 1808 prostate cancer cases and 1805 controls, nested in the Prostate Cancer Prevention Trial, a randomized, placebo-control trial that found finasteride decreased prostate cancer risk. There were no significant differences in protein carbonyl levels in baseline samples between those later diagnosed with prostate cancer and those without at the end of study biopsy. Adjusted ORs and 95% CIs for the 4th quartile of protein carbonyl level for the combined, placebo and finasteride arms were 1.03 (95% CI 0.85–1.24), 0.88 (95% CI 0.69–1.12) and 1.27 (95% CI 0.94–1.71), respectively. There were no significant associations between carbonyl level and risk when analyzing high- and low-grade disease separately, nor did finasteride impact protein oxidation levels. The results of this large nested case-control study do not support the hypothesis that oxidative stress, at least as measured by protein carbonyl level, plays a role in prostate cancer.
Reactive Oxygen Species (ROS) are important in the pathogenesis of many diseases, including breast cancer. Several population-based case-control studies have demonstrated that various biomarkers of oxidative stress are associated with an increase in breast cancer risk. We selected sisters discordant for breast cancer (n=645) from the New York site of the Breast Cancer Family Registry to explore factors that contribute to variation in plasma protein carbonyls, and to determine whether this biomarker is associated with an increase in breast cancer risk among those with a family history. Late age at menarche, HRT use, and Hispanic race were significantly associated with lower plasma protein carbonyl levels in unaffected sisters. Plasma protein carbonyls were associated with an increase in breast cancer risk (Q2 OR = 1.4, 95% CI=0.8–2.7; Q3 OR= 2.4, 95% CI = 1.1–4.9, Q4 OR= 1.9, 95% CI=0.8–4.2), though not in a dose-dependent manner. These data suggest that oxidative damage is a risk factor for breast cancer in high risk women.
Breast cancer; Oxidative stress; Biomarkers
To investigate oxidative stress biomarkers in a cross-sectional pilot study of 50 participants with sporadic ALS (sALS) compared to 46 control subjects.
We measured urinary 8-oxodeoxyguanosine (8-oxodG), urinary 15-F2t-isoprostane (IsoP), and plasma protein carbonyl by ELISA methods. We also determined if ELISA measurement of 8-oxodG could be validated against measures from high pressure liquid chromatography coupled with electrochemical detection, the current standard method.
8-oxodG and IsoP levels adjusted for creatinine were significantly elevated in sALS participants. These differences persisted after age and gender were controlled in regression analyses. These markers are highly and positively correlated with each other. 8-oxodG measured by the two techniques from the same urine sample were positively correlated (P < .0001). Protein carbonyl was not different between sALS participants and controls.
Using ELISA we confirmed that certain oxidative stress biomarkers were elevated in sALS participants. ELISA may be reliable and thus useful in epidemiology studies requiring large numbers of samples to determine the significance of increased oxidative stress markers in sALS. Further studies are required.
epidemiology; amyotrophic lateral sclerosis (ALS); biomarkers; oxidative stress; neurodegeneration
DNA extraction from blood and genotyping for candidate single nucleotide polymorphisms (SNP) is now an important part of almost all molecular epidemiologic studies. However, in many studies, the amount of blood sample is limited or only serum is available. We conducted several pilot studies to identify methods for DNA extraction and high-throughput SNP genotyping of both white blood cell (WBC) and serum DNA that can be done centrally and reliably for large numbers of samples.
We used biospecimens from The Prostate Cancer Prevention Trial (PCPT), a phase III, double-blind, placebo-controlled trial that tested the efficacy of finasteride for the primary prevention of prostate cancer. DNA was extracted from WBCs, from serum, and also from serum after organic solvent extraction for analysis of hormones. We also conducted blinded high-throughput genotyping in 3 laboratories to assess feasibility and reliability of results with differing methodologies using DNA from WBCs and from serum.
Genotyping of DNA extracted from WBCs resulted in highly reliable, reproducible results across laboratories using different genotyping platforms. However, genotyping with DNA extracted from serum did not provide reliable data using high-throughput multiplex approaches such as Sequenom (hME and iPLEX) and Applied Biosystems SNPlex, but was successful using Taqman.
Based upon the results of these pilot studies, we conclude that DNA obtained from serum must be used judiciously, and that genotyping using multiplex methods is not suitable for serum DNA.
Prostate cancer prevention; molecular epidemiology; genotyping; serum DNA extraction; multiplex methods
Cigarette smoking is a major source of oxidative stress. Protein carbonyls have been used as a biomarker of oxidative stress because of the relative stability of carbonylated proteins and the high protein concentration in blood. Increased levels of carbonyl groups have been found in serum proteins of smokers compared to nonsmokers. However, neither the dose effect of current cigarette smoke nor other predictors of oxidative stress have been studied. Hence, we used an ELISA (Enzyme-Linked Immunosorbent Assay) to evaluate plasma protein carbonyls in smokers recruited in the Early Lung Cancer Action Project (ELCAP) program. The lung cancer screening program enrolled current and former smokers age 60 years and over without a prior cancer diagnosis. A total of 542 participants (282 men and 260 women) completed a baseline questionnaire and provided blood samples for the biomarker study. Protein oxidation was measured by derivatization of the carbonyl groups with 2,4-dinitrophenylhydrazine (DNPH) and ELISA quantitation of the DNPH group. Current smoking status was confirmed with urinary cotinine. The mean (± SD) protein carbonyl level was 17.9 ± 2.9 nmol carbonyls/ml plasma. Protein carbonyls did not differ significantly by gender. Carbonyl levels were higher among current than former smokers, but these differences did not attain statistical significance, nor did differences by urine cotinine levels, pack-years, pack/day among current smokers, and smoking duration. In a multiple regression analysis, higher protein carbonyl levels were independently associated with increasing age (0.59 nmol/ml increase per 10 years, 95% CI 0.14, 1.05, p = 0.01), African-American vs. white race/ethnicity, (1.30 nmol/ml, 95% CI 0.4, 2.19, p =0.008), and lower educational attainment (0.75 nmol/ml, 95% CI 0.12, 1.38, p = 0.02). Although we found no significant difference between current versus past cigarette smoking and protein carbonyls in this older group of smokers, associations were found for age, ethnicity and educational attainment. Our results indicate that the measurement of plasma carbonyls by this ELISA technique is still an easy and suitable method for studies of diseases related to oxidative stress.
Oxidative stress; Cigarette smoking; Protein carbonyls; Biomarker; ELCAP
In a multicenter study of newly diagnosed ALS patients without a reported family history of ALS, we are prospectively investigating whether markers of oxidative stress (OS) are associated with disease progression.
An extensive structured telephone interview ascertained environmental, lifestyle, dietary and psychological risk factors associated with OS. Detailed assessments were performed at baseline and at 3 to 6 month intervals during the ensuing 30 months. Our biorepository includes DNA, plasma, urine, and skin.
355 patients were recruited. Subjects were enrolled over a 36 month-period at 16 sites. To meet the target number of subjects, the recruitment period was prolonged and additional sites were included. Demographic and disease characteristics were similar between 477 eligible/non-enrolled and enrolled patients, with the only difference being type of health insurance among enrolled patients. Sites were divided into 3 groups by the number of enrolled subjects. Comparing these 3 groups, the Columbia site had fewer “definite ALS” diagnoses.
This is the first prospective, interdisciplinary, in-depth, multicenter epidemiological investigation of OS related to ALS progression and was accomplished by an aggressive recruitment process. The baseline demographic and disease features of the study sample are now fully characterized.
ALS; Oxidative Stress; Disease Progression; Survival; Epidemiology
To determine the association between polycyclic aromatic hydrocarbon (PAH) exposure and risk of hepatocellular carcinoma, a case-control study nested within a community based cohort was conducted in Taiwan. Baseline blood samples, collected from a total of 174 HCC cases and 776 matched controls, were used to determine the level of PAH-albumin adducts by competitive enzyme-linked immunosorbent assay. Conditional logistic regression analysis was used to calculate odds ratios (OR) and 95% confidence intervals (CI) to assess the effect of PAH-albumin adducts on risk of HCC. When compared to subjects in the lowest quantile, there was an increase in risk of HCC, with adjusted ORs of 1.0 (95% CI 0.5-2.0), 1.2 (95% CI 0.6-2.4) and 2.0 (95% CI 1.0-4.2) for subjects in the 2nd, 3rd, and 4th quantile, respectively. In addition, significantly increased risk was observed among cases with high AFB1-albumin adducts with adjusted ORs of 1.9 (95% CI 0.6-6.1), 1.7 (95% CI 0.6-4.9) and 2.1 (95% CI 0.5-8.2) subjects in the 2nd, 3rd, and 4th quantile, respectively, compared with subjects in the 1st quantile. The combination of PAH- and AFB1-albumin adducts above the mean and hepatitis B virus infection resulted in OR of 8.2 (95%CI=3.6-19.0), compared to those with low adducts and virus negative. These results demonstrate that PAH-albumin adducts are associated with an increased risk of HCC, especially among those with high aflatoxin exposure and that environmental PAH exposure may enhance the hepatic carcinogenic potential of hepatitis B virus infection.
Aflatoxin-albumin adducts; PAH-albumin adducts; Hepatocellular carcinoma; Hepatitis B virus
Polycyclic aromatic hydrocarbon (PAH)-DNA adducts have been associated with breast cancer in several small studies. The authors’ pooled analysis included 873 cases and 941 controls from a population-based case-control study. Competitive enzyme-linked immunosorbent assay in peripheral mononuclear cells was conducted in 2 rounds, and results were pooled on the basis of round-specific quantiles. The odds ratio for breast cancer was elevated in relation to detectable PAH-DNA adducts (1.29 as compared with non-detectable adduct levels; 95% confidence interval = 1.05, 1.58), but there was no apparent dose-response relationship with increasing quantiles. No consistent pattern emerged when the results were stratified by PAH sources (e.g., active cigarette smoking or PAH-containing foods), or when the cases were categorized by stage of disease or hormone receptor status. These data provide only modest support for an association between PAH-DNA adducts and breast cancer development.
air pollution; breast cancer; cigarette smoking; cooked meat; DNA adducts; passive smoking; polycyclic aromatic hydrocarbons
Previous studies suggest that polycyclic aromatic hydrocarbons (PAHs) may adversely affect breast cancer risk. Indoor air pollution from use of indoor stoves and/or fireplaces is an important source of ambient PAH exposure. However, the association between indoor stove/fireplace use and breast cancer risk is unknown. We hypothesized that indoor stove/fireplace use in a Long Island, New York study population would be positively associated with breast cancer and differ by material burned, and the duration and timing of exposure. We also hypothesized that the association would vary by breast cancer subtype defined by p53 mutation status, and interact with glutathione S-transferases GSTM1, T1, A1 and P1 polymorphisms.
Population-based, case-control resources (1,508 cases/1,556 controls) were used to conduct unconditional logistic regression to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI).
Breast cancer risk was increased among women reporting ever burning synthetic logs (which may also contain wood) in their homes (OR = 1.42, 95% CI 1.11, 1.84), but not for ever burning wood alone (OR = 0.93, 95% CI 0.77, 1.12). For synthetic log use, longer duration >7 years, older age at exposure (>20 years; OR = 1.65, 95% CI 1.02, 2.67) and 2 or more variants in GSTM1, T1, A1 or P1 (OR = 1.71, 95% CI 1.09, 2.69) were associated with increased risk.
Burning wood or synthetic logs are both indoor PAH exposure sources; however, positive associations were only observed for burning synthetic logs, which was stronger for longer exposures, adult exposures, and those with multiple GST variant genotypes. Therefore, our results should be interpreted with care and require replication.
Electronic supplementary material
The online version of this article (doi:10.1186/1476-069X-13-108) contains supplementary material, which is available to authorized users.
Polycyclic aromatic hydrocarbons; GST; p53; Cancer; Breast
Sporadic amyotrophic lateral sclerosis (sALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/anti-oxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine, are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly support the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis.
sALS; oxidative stress; environmental epidemiology; phenotypic variation; disease prognosis
We previously observed that poor DNA repair phenotype is associated with increased breast cancer (BC) risk within families. Here, we examined whether genetic variation in double strand break repair (DSBR) genes is associated with BC risk and if genotypes are related to phenotype in unaffected women.
Using data from the New York site of the Breast Cancer Family Registry, we investigated 25 SNPs involved in DSBR using biospecimens from 337 BC cases and 410 unaffected sister controls.
Genotypes in XRCC4 were associated with BC risk, with ORs of 1.67 (95% CI = 1.01–2.76) for the combined GA/AA of rs1805377 and 1.69 (95%CI=1.03–2.77) for rs1056503 TG/GG; these associations were no longer statistically significant in multivariable conditional logistic regression models. When examining the association of SNPs with phenotype, we found that genotypes of XRCC5 rs3834 and rs1051685, which were highly correlated with each other, were associated with end joining (EJ) capacity; women with the XRCC5 rs3834 GA genotype had better DNA repair as measured by higher levels of EJ capacity (37.8±14.1% for GA versus 27.9±11.8% for GG carriers (p=0.0006). Women with the AA genotype of BRCA1 rs799917 also had higher EJ capacity (35.1±9.2%) than those with GG (26.4±10.1%, p=0.02).
Overall we found that selected DSBR genotypes were associated with phenotype, although they were not associated with BC risk itself, suggesting that phenotypic measures are influenced by endogenous and exogenous factors across the lifecourse and may be better markers than genotypic measures for ascertaining BC risk.
breast cancer; double-strand break; end-joining capacity; polymorphism
MicroRNAs (miRNAs) are abundant in the circulation and play a central role in diverse biological processes; they may be useful for early diagnosis of hepatocellular carcinoma (HCC).
We conducted a two-phase, case-control study (20 pairs for the discovery set and 49 pairs for the validation set) to test the hypothesis that genome-wide dysregulation of circulating miRNAs differentiate HCC cases from controls. Taqman low density arrays were used to examine genome-wide miRNA expression for the discovery set, and quantitative RT-PCR was used to validate candidate miRNAs for both discovery and validation sets.
Sixty-six miRNAs were found to be significantly over-expressed in plasma of HCC cases compared to controls after adjusting for false discovery rate (p<0.05). A volcano plot indicated that 7 miRNAs had greater than 2-fold case-control differences with p<0.01. Four significant miRNAs (miR-150, miR-30c, miR-483-5p and miR-520b) detectable in all samples with varied expression levels were further validated in a validation set. MiR-483-5p was statistically significantly over-expressed in HCC cases compared with controls (3.20 vs. 0.82, p<0.0001). HCC risk factors and clinic-pathological characteristics did not influence miR-483-5p expression. The combination of plasma miR-483-5p level and HCV status can significantly differentiate HCC cases from controls with an AUC of 0.908 (p<0.0001). The sensitivity and specificity were, respectively, 75.5% and 89.8%.
These preliminary results suggest the importance of dysregulated circulating miR-483-5p as a potential HCC biomarker.
Confirmation of aberrant expression of miR-483-5p in a large prospective HCC study will provide support for its application to HCC detection.
Genome-wide; circulating miRNAs; miR-483-5p; dysregulation; hepatocellular carcinoma
MicroRNAs (miRs) control cell growth, apoptosis and differentiation, and thus play a key role in carcinogenesis. Identification of a set of miRs that demonstrate differential expression in oral squamous cell carcinoma (OSCC) patients with poor prognosis has potential for utility as a prognostic marker. A retrospective study of miR expression was conducted in 20 tissue samples from early stage (Stages I & II) OSCC patients with known clinical outcome (10 from those who had 5-year disease free survival and 10 who died of disease within 5 years) using genome-wide deep sequencing analysis. The promising miR candidates were then validated in 80 tissue samples using quantitative real-time PCR (qRT-PCR). The deep sequencing and qRT-PCR analysis identified two promising miRs, miR-375 and miR-214-3p. Combining the two miRs as a panel with age and gender had a predictive value for the area under the curve (AUC) of 0.932, with a sensitivity of 87.5% and a specificity of 87.2% (p<0.0001) to identify patients with poor prognosis. A miR-based prognostic risk score model was constructed, which included the miR-214-3p, miR-375, age and gender, each weighed by relative contribution. The risk score model was able to identify high-risk individuals who had significantly shorter time to relapse (p<0.001) and time to death (p<0.001). The model consisting of a two-miR panel with age and gender may be useful in prognostication of early stage OSCC patients, which can aid in identifying patients with poor prognosis who will benefit from a subsequent aggressive treatment regimen.
microRNA; deep sequencing; qRT-PCR; prognosis; risk score; oral squamous cell carcinoma
Lower levels of genomic DNA methylation in blood DNA has been associated with risk of different cancers and several cancer risk factors. To understand the use of genomic methylation measures as biomarkers of cancer risk, data are needed on within-individual changes over time.
Using information from 77 subjects with blood collected at 2 visits on average 8 years apart, we examined whether levels of DNA methylation change with time and if so, whether selected cancer risk factors predict these changes. We measured DNA methylation levels in peripheral blood mononuclear cells (PBMC) using three assays that have been used in epidemiologic studies: (i) luminometric methylation assay (LUMA)(ii) LINE-1 by pyrosequencing, and (iii) Sat2 by MethyLight.
Close to a third of all individuals had large changes over time (≥10%) in LUMA with 19.5% increasing and 13.0% decreasing. For Sat2, two-thirds of individuals had large changes with 40% increasing and 26% decreasing over time. In contrast, only 3.9% of individuals had large changes in LINE-1 over time. The degree of change in PBMC DNA methylation was statistically significantly inversely associated with methylation levels at baseline; greater decreases were observed in individuals with higher baseline values for each assay.
These data, if replicated, suggest that changes in DNA methylation over time are highly associated with baseline values of the assay and vary by assay type.
These findings suggest that assays that change more over time may warrant consideration for studies that measure later life exposures.
Few studies had investigated genome-wide methylation in glioblastoma multiforme (GBM). Our goals were to study differential methylation across the genome in gene promoters using an array-based method, as well as repetitive elements using surrogate global methylation markers. The discovery sample set for this study consisted of 54 GBM from Columbia University and Case Western Reserve University, and 24 brain controls from the New York Brain Bank. We assembled a validation dataset using methylation data of 162 TCGA GBM and 140 brain controls from dbGAP. HumanMethylation27 Analysis Bead-Chips (Illumina) were used to interrogate 26,486 informative CpG sites in both the discovery and validation datasets. Global methylation levels were assessed by analysis of L1 retrotransposon (LINE1), 5 methyl-deoxycytidine (5m-dC) and 5 hydroxylmethyl-deoxycytidine (5hm-dC) in the discovery dataset. We validated a total of 1548 CpG sites (1307 genes) that were differentially methylated in GBM compared to controls. There were more than twice as many hypomethylated genes as hypermethylated ones. Both the discovery and validation datasets found 5 tumor methylation classes. Pathway analyses showed that the top ten pathways in hypomethylated genes were all related to functions of innate and acquired immunities. Among hypermethylated pathways, transcriptional regulatory network in embryonic stem cells was the most significant. In the study of global methylation markers, 5m-dC level was the best discriminant among methylation classes, whereas in survival analyses, high level of LINE1 methylation was an independent, favorable prognostic factor in the discovery dataset. Based on a pathway approach, hypermethylation in genes that control stem cell differentiation were significant, poor prognostic factors of overall survival in both the discovery and validation datasets. Approaches that targeted these methylated genes may be a future therapeutic goal.
Both hepatitis B virus (HBV) and aflatoxin B1 (AFB1) exposure can cause liver damage as well as increase the probability of hepatocellular carcinoma (HCC). To investigate the underlying genetic changes that may influence development of HCC associated with HBV infection and AFB1 exposure, HCC patients were subdivided into 4 groups depending upon HBV and AFB1 exposure status: (HBV(+)/AFB1(+), HBV(+)/AFB1(-), HBV(-)/AFB1(+), HBV(-)/AFB1(-)). Genetic abnormalities and protein expression profiles were analyzed by array-based comparative genomic hybridization and isobaric tagging for quantitation. A total of 573 chromosomal aberrations (CNAs) including 184 increased and 389 decreased were detected in our study population. Twenty-five recurrently altered regions (RARs; chromosomal alterations observed in ≥10 patients) in chromosomes were identified. Loss of 4q13.3-q35.2, 13q12.1-q21.2 and gain of 7q11.2-q35 were observed with a higher frequency in the HBV(+)/AFB1(+), HBV(+)/AFB1(-) and HBV(-)/AFB1(+) groups compared to the HBV(-)/AFB(-) group. Loss of 8p12-p23.2 was associated with high TNM stage tumors (P = 0.038) and was an unfavorable prognostic factor for tumor-free survival (P =0.045). A total of 133 differentially expressed proteins were identified in iTRAQ proteomics analysis, 69 (51.8%) of which mapped within identified RARs. The most common biological processes affected by HBV and AFB1 status in HCC tumorigenesis were detoxification and drug metabolism pathways, antigen processing and anti-apoptosis pathways. Expression of AKR1B10 was increased significantly in the HBV(+)/AFB1(+) and HBV(-)/AFB1(+) groups. A significant correlation between the expression of AKR1B10 mRNA and protein levels as well as AKR1B10 copy number was observered, which suggest that AKR1B10 may play a role in AFB1-related hepatocarcinogenesis. In summary, a number of genetic and gene expression alterations were found to be associated with HBV and AFB1- related HCC. The possible synergistic effects of HBV and AFB1 in hepatocarcinogenesis warrant further investigations.
The mechanisms driving the physical activity–breast cancer association are unclear. Exercise both increases reactive oxygen species production, which may transform normal epithelium to a malignant phenotype, and enhances antioxidant capacity, which could protect against subsequent oxidative insult. Given the paradoxical effects of physical activity, the oxidative stress pathway is of interest. Genetic variation in CAT or antioxidant-related polymorphisms may mediate the physical activity–breast cancer association.
We investigated the main and joint effects of three previously unreported polymorphisms in CAT on breast cancer risk. We also estimated interactions between recreational physical activity (RPA) and 13 polymorphisms in oxidative stress-related genes. Data were from the Long Island Breast Cancer Study Project, with interview and biomarker data available on 1,053 cases and 1,102 controls.
Women with ≥1 variant allele in CAT rs4756146 had a 23 % reduced risk of postmenopausal breast cancer compared with women with the common TT genotype (OR = 0.77; 95 % CI = 0.59–0.99). We observed two statistical interactions between RPA and genes in the anti-oxidant pathway (p = 0.043 and 0.006 for CAT and GSTP1, respectively). Highly active women harboring variant alleles in CAT rs1001179 were at increased risk of breast cancer compared with women with the common CC genotype (OR = 1.61; 95 % CI, 1.06–2.45). Risk reductions were observed among moderately active women carrying variant alleles in GSTP1 compared with women homozygous for the major allele (OR = 0.56; 95 % CI, 0.38–0.84).
Breast cancer risk may be jointly influenced by RPA and genes involved in the antioxidant pathway, but our findings require confirmation.
Breast cancer; Epidemiology; Catalase; Physical activity; Oxidative stress