Hypothesis: a unifying mechanism for nutrition and chemicals as lifelong modulators of DNA hypomethylation

LINE-1 DNA methylation, smoking and risk of Parkinson's disease

BACKGROUND

Long interspersed nucleotide element-1 (LINE-1) retrotransposons are located throughout the human genome. Those retaining an intact 5' promoter can copy and insert themselves into the DNA of neural progenitor cells that express tyrosine hydroxylase, which may influence differentiation and survival of these cells. LINE-1 promoter methylation is associated with decreased LINE-1 propagation.

OBJECTIVE

To investigate whether LINE-1 promoter methylation is associated with Parkinson's disease (PD).

METHODS

We compared LINE-1 methylation profiles in blood mononuclear cells between 292 newly diagnosed PD cases and 401 unrelated, neurologically normal controls, all non-Hispanic Caucasians in western Washington state.

RESULTS

Overall, PD was not associated with percent methylation of the LINE-1 promoter. However, the predictable inverse association between PD and ever smoking tobacco was strongest for men and women with the lowest LINE-1 promoter methylation, and less apparent as LINE-1 methylation increased. Underlying this possible interaction, ever regularly smoking tobacco was associated with decreased LINE-1 methylation in controls (age- and sex-adjusted linear regression β = -0.24, 95% confidence interval [CI] -0.43, -0.04), but not in cases (β = 0.06, 95% CI -0.17, 0.28, interaction p = 0.06).

CONCLUSION

PD cases may have innate differences in their ability to respond to tobacco smoke.

Environmental stressors and the epigenome

Epigenetic modification and transgenerational transfer of phenotype at the individual or population level, particularly in response to environmental change, is at the forefront of biological investigation. The plasticity of this process allows an organism to respond to changes in environmental conditions, potentially conferring a survival advantage. In this review, we discuss epigenetic transgenerational phenomena in the specific context of environmental stressors including hypoxia and environmental toxicants.:

DNA methylation in the 5' flanking region of cytochrome P450 17 in adult rare minnow Gobiocypris rarus - tissue difference and effects of 17α-ethinylestradiol and 17α-methyltestoterone exposures

Cytochrome P450 17 (CYP17) plays a vital role in hormone production in the body. In our previous study, mRNA expression of cyp17a1 was regulated by endocrine disrupting chemicals in rare minnow Gobiocypris rarus. However, the mechanism underlying the regulation is unclear. In the present study, we aim to explore whether the differential expression of cyp17a1 in distinct tissues and the modulation of its expression upon 17α-ethinylestradiol (EE2) and 17α-methyltestoterone (MT) are related to the DNA methylation status in G. rarus. The 732-bp fragment of 5' flanking region of cyp17a1 gene was isolated in G. rarus. The bisulfite sequencing PCR result showed that DNA methylation levels in 5' flanking of cyp17a1 in the gonads were significantly lower than those in the brains, which is negatively related to its mRNA expression in the 2 tissues in the previous study. The 7-day EE2 exposure of 25 ng/L caused a significant increase of methylation levels of cyp17a1 gene and a significant decrease of its transcript in testis. While 100 ng/L MT exposure for 7 days caused a significant decrease of methylation levels of cyp17a1 gene and a significant increase of its transcript in the ovary. The present findings indicate that the methylation status of cyp17a1 gene is negatively correlated with its mRNA expression in response to EE2 and MT in G. rarus. We hypothesize that the regulation of cyp17a1 expression by EE2 and MT might attribute to the change of its DNA methylation status in G. rarus.

Patterns of DNA methylation in animals: an ecotoxicological perspective

DNA methylation refers to the addition of a methyl group to nucleotides within DNA. As with other epigenetic endpoints, patterns of DNA methylation are susceptible to alterations due to exposure to environmental stressors, including contaminants. These alterations can persist in the absence of the initial stressor as cells divide, and can even be inherited between generations if they occur in the germ line. Although our knowledge concerning patterns of DNA methylation in animals is increasing, there remains a gap in the literature when it comes to species outside of those typically used for biomedical research. Here, I review the literature relating to DNA methylation in an array of taxa (mammals, fish, birds, amphibians, reptiles, and invertebrates) and discuss these data from an ecotoxicological perspective. The pattern and extent of DNA methylation is well conserved across species of vertebrates; methylation appears mainly on cytosine residues within a CpG context, and much of the genome is methylated, with the notable exception of cytosines within CpG islands in the promoters of genes. Highly methylated genes in vertebrates tend to be transcriptionally repressed. However, large differences occur between classes of vertebrates in terms of the timing and nature of reprogramming and genomic imprinting: epigenetic processes that establish patterns of DNA methylation in the early embryo and which are sensitive to environmental stress. In invertebrates, patterns of DNA methylation are extremely variable and differ significantly from the condition observed in vertebrates. Some invertebrate genomes exhibit no DNA methylation while others are methylated to a level that is comparable to vertebrates. Additionally, DNA methylation may have different functions in invertebrates, e.g., alternative splicing. This variability in basic patterns of DNA methylation among species during sensitive periods of development suggests that responses to epigenetically active environmental contaminants may be similarly variable. For example, the timing of exposure to a contaminant may be a critical factor when considered in the light of variable reprogramming schedules among species. With this in mind, I review data relating to the effects of contaminants on DNA methylation in animals, focusing on non-model organisms and on exposures in natural environments, when possible. An ecotoxicological perspective on patterns of DNA methylation in animals may improve our understanding of the range and diversity of epigenetic phenomena in the natural world.

Toxicity of arsenite and thio-DMAV after long-term (21 days) incubation of human urothelial cells: cytotoxicity, genotoxicity and epigenetics

This study aims to further mechanistically understand toxic modes of action after chronic arsenic species exposure.

A systematic review of neurodevelopmental effects of prenatal and postnatal organophosphate pesticide exposure

Agricultural and residential use of organophosphate (OP) pesticides has increased in recent decades after banning some persistent pesticides. Although there is evidence of the effects of OPs on neurodevelopment and behaviour in adults, limited information is available about their effects in children, who might be more vulnerable to neurotoxic compounds. This paper was aimed at analysing the scientific evidence published to date on potential neurodevelopmental and behavioural effects of prenatal and postnatal exposure to OPs. A systematic review was undertaken to identify original articles published up to December 2012 evaluating prenatal or postnatal exposure to OPs in children and effects on neurodevelopment and/or behaviour. Articles were critically compared, focusing on the methodology used to assess exposure and adverse effects, as well as potential contributing factors that may modify both exposure and outcomes, such as genetic susceptibility to certain enzymes involved in OPs metabolisation (e.g. paraoxonase-1) and gender differences. Twenty articles met the inclusion criteria, 7 of which evaluated prenatal exposure to OPs, 8 postnatal exposure and 5 both pre- and postnatal exposure. Most of the studies evaluating prenatal exposure observed a negative effect on mental development and an increase in attention problems in preschool and school children. The evidence on postnatal exposure is less consistent, although 2 studies found an increase in reaction time in schoolchildren. Some paraoxonase-1 polymorphisms could enhance the association between OPs exposure and mental and psychomotor development. A large variability in epidemiological designs and methodologies used for assessing exposure and outcome was observed across the different studies, which made comparisons difficult. Prenatal and to a lesser extent postnatal exposure to OPs may contribute to neurodevelopmental and behavioural deficits in preschool and school children. Standardised methodologies are needed to allow results to be better compared and to perform a quantitative meta-analysis before drawing any final conclusions.

Maternal choline modifies fetal liver copper, gene expression, DNA methylation, and neonatal growth in the tx-j mouse model of Wilson disease

Maternal diet can affect fetal gene expression through epigenetic mechanisms. Wilson disease (WD), which is caused by autosomal recessive mutations in ATP7B encoding a biliary copper transporter, is characterized by excessive hepatic copper accumulation, but variability in disease severity. We tested the hypothesis that gestational supply of dietary methyl groups modifies fetal DNA methylation and expression of genes involved in methionine and lipid metabolism that are impaired prior to hepatic steatosis in the toxic milk (tx-j) mouse model of WD. Female C3H control and tx-j mice were fed control (choline 8 mmol/Kg of diet) or choline-supplemented (choline 36 mmol/Kg of diet) diets for 2 weeks throughout mating and pregnancy to gestation day 17. A second group of C3H females, half of which were used to cross foster tx-j pups, received the same diet treatments that extended during lactation to 21 d postpartum. Compared with C3H, fetal tx-j livers had significantly lower copper concentrations and significantly lower transcript levels of Cyclin D1 and genes related to methionine and lipid metabolism. Maternal choline supplementation prevented the transcriptional deficits in fetal tx-j liver for multiple genes related to cell growth and metabolism. Global DNA methylation was increased by 17% in tx-j fetal livers after maternal choline treatment (P<0.05). Maternal dietary choline rescued the lower body weight of 21 d tx-j mice. Our results suggest that WD pathogenesis is modified by maternal in utero factors, including dietary choline.

Folate deficiency triggers an oxidative-nitrosative stress-mediated apoptotic cell death and impedes insulin biosynthesis in RINm5F pancreatic islet β-cells: relevant to the pathogenesis of diabetes

It has been postulated that folic acid (folate) deficiency (FD) may be a risk factor for the pathogenesis of a variety of oxidative stress-triggered chronic degenerative diseases including diabetes, however, the direct evidence to lend support to this hypothesis is scanty. For this reason, we set out to study if FD can trigger the apoptotic events in an insulin-producing pancreatic RINm5F islet β cells. When these cells were cultivated under FD condition, a time-dependent growth impediment was observed and the demise of these cells was demonstrated to be apoptotic in nature proceeding through a mitochondria-dependent pathway. In addition to evoke oxidative stress, FD condition could also trigger nitrosative stress through a NF-κB-dependent iNOS-mediated overproduction of nitric oxide (NO). The latter compound could then trigger depletion of endoplasmic reticulum (ER) calcium (Ca²⁺) store leading to cytosolic Ca²⁺ overload and caused ER stress as evidence by the activation of CHOP expression. Furthermore, FD-induced apoptosis of RINm5F cells was found to be correlated with a time-dependent depletion of intracellular gluthathione (GSH) and a severe down-regulation of Bcl-2 expression. Along the same vein, we also demonstrated that FD could severely impede RINm5F cells to synthesize insulin and their abilities to secret insulin in response to glucose stimulation were appreciably hampered. Even more importantly, we found that folate replenishment could not restore the ability of RINm5F cells to resynthesize insulin. Taken together, our data provide strong evidence to support the hypothesis that FD is a legitimate risk factor for the pathogenesis of diabetes.

Identifying important life stages for monitoring and assessing risks from exposures to environmental contaminants: results of a World Health Organization review

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We propose a harmonized set of age bins for assessing risks from chemical exposure.

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The set of early life age groups will facilitate consistency with recent guidance.

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The age bins allow results from longitudinal birth cohort studies to be combined.

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Region-specific exposure factors and monitoring data are needed to apply the bins.

In this paper, we summarize exposure-related issues to consider in determining the most appropriate age ranges and life stages for risk assessment. We then propose a harmonized set of age bins for monitoring and assessing risks from exposures to chemicals for global use. The focus is on preconception through adolescence, though the approach should be applicable to additional life stages. A two-tiered set of early life age groups is recommended. The first tier involves the adoption of guidance similar to the childhood age groups recommended by the U.S. Environmental Protection Agency, whereas the second tier consolidates some of those age groups to reduce the burden of developing age-specific exposure factors for different regions. While there is no single “correct” means of choosing a common set of age groups to use internationally in assessing early life exposure and risk, use of a set of defined age groups is recommended to facilitate comparisons of potential exposures and risks around the globe, the collection of data and analyses of aggregate exposure and cumulative risk. Application of these age groups for robust assessment of exposure and risk for specific populations will require region-specific exposure factors as well as local environmental monitoring data.

Autism and EMF? Plausibility of a pathophysiological link - Part I

Although autism spectrum conditions (ASCs) are defined behaviorally, they also involve multileveled disturbances of underlying biology that find striking parallels in the physiological impacts of electromagnetic frequency and radiofrequency exposures (EMF/RFR). Part I of this paper will review the critical contributions pathophysiology may make to the etiology, pathogenesis and ongoing generation of core features of ASCs. We will review pathophysiological damage to core cellular processes that are associated both with ASCs and with biological effects of EMF/RFR exposures that contribute to chronically disrupted homeostasis. Many studies of people with ASCs have identified oxidative stress and evidence of free radical damage, cellular stress proteins, and deficiencies of antioxidants such as glutathione. Elevated intracellular calcium in ASCs may be due to genetics or may be downstream of inflammation or environmental exposures. Cell membrane lipids may be peroxidized, mitochondria may be dysfunctional, and various kinds of immune system disturbances are common. Brain oxidative stress and inflammation as well as measures consistent with blood-brain barrier and brain perfusion compromise have been documented. Part II of this paper will review how behaviors in ASCs may emerge from alterations of electrophysiological oscillatory synchronization, how EMF/RFR could contribute to these by de-tuning the organism, and policy implications of these vulnerabilities. Changes in brain and autonomic nervous system electrophysiological function and sensory processing predominate, seizures are common, and sleep disruption is close to universal. All of these phenomena also occur with EMF/RFR exposure that can add to system overload ('allostatic load') in ASCs by increasing risk, and worsening challenging biological problems and symptoms; conversely, reducing exposure might ameliorate symptoms of ASCs by reducing obstruction of physiological repair. Various vital but vulnerable mechanisms such as calcium channels may be disrupted by environmental agents, various genes associated with autism or the interaction of both. With dramatic increases in reported ASCs that are coincident in time with the deployment of wireless technologies, we need aggressive investigation of potential ASC - EMF/RFR links. The evidence is sufficient to warrant new public exposure standards benchmarked to low-intensity (non-thermal) exposure levels now known to be biologically disruptive, and strong, interim precautionary practices are advocated.

Influence of ambient air pollution on global DNA methylation in healthy adults: a seasonal follow-up

BACKGROUND

DNA methylation changes are potential pathways of environmentally induced health effects. We investigated whether exposure to ambient concentrations of NO2, PM10, PM2.5 and O3 and traffic parameters were associated with global DNA methylation in blood of healthy adults.

METHODS

48 non-smoking adults (25 males) with a median age of 39years were sampled in winter and summer. Global DNA methylation in whole blood (% 5-methyl-2'-deoxycytidine, %5mdC) was analyzed with HPLC. Exposure to air pollutants at the home address was assessed using interpolated NO2, PM10, PM2.5 and O3 concentrations for various exposure windows (60- to 1-day moving average exposures and yearly averages) and GIS-based traffic parameters. Associations between pollutants and %5mdC were tested with multiple mixed effects regression models.

RESULTS

Average %5mdC (SD) was 4.30 (0.08) in winter and 4.29 (0.08) in summer. Men had higher %5mdC compared to women both in winter (4.32 vs. 4.26) and summer (4.31 vs. 4.27). When winter and summer data were analyzed together, various NO2, PM10 and PM2.5 moving average exposures were associated with changes in %5mdC (95% CI) ranging from -0.04 (-0.09 to 0.00) to -0.14 (-0.28 to 0.00) per IQR increase in pollutant. NO2, PM10, PM2.5 and O3 moving average exposures were associated with decreased %5mdC (95% CI) varying between -0.01 (-0.03 to 0.00) and -0.17 (-0.27 to -0.06) per IQR increase in pollutant in summer but not in winter.

CONCLUSION

Decreased global DNA methylation in whole blood was associated with exposure to NO2, PM10, PM2.5 and O3 at the home addresses of non- adults. Most effects were observed for the 5- to 30-day moving average exposures.

Environmental and occupational interventions for primary prevention of cancer: a cross-sectorial policy framework

BACKGROUND

Nearly 13 million new cancer cases and 7.6 million cancer deaths occur worldwide each year; 63% of cancer deaths occur in low- and middle-income countries. A substantial proportion of all cancers are attributable to carcinogenic exposures in the environment and the workplace.

OBJECTIVE

We aimed to develop an evidence-based global vision and strategy for the primary prevention of environmental and occupational cancer.

METHODS

We identified relevant studies through PubMed by using combinations of the search terms "environmental," "occupational," "exposure," "cancer," "primary prevention," and "interventions." To supplement the literature review, we convened an international conference titled "Environmental and Occupational Determinants of Cancer: Interventions for Primary Prevention" under the auspices of the World Health Organization, in Asturias, Spain, on 17-18 March 2011.

DISCUSSION

Many cancers of environmental and occupational origin could be prevented. Prevention is most effectively achieved through primary prevention policies that reduce or eliminate involuntary exposures to proven and probable carcinogens. Such strategies can be implemented in a straightforward and cost-effective way based on current knowledge, and they have the added benefit of synergistically reducing risks for other noncommunicable diseases by reducing exposures to shared risk factors.

CONCLUSIONS

Opportunities exist to revitalize comprehensive global cancer control policies by incorporating primary interventions against environmental and occupational carcinogens.

Environmental toxicants, epigenetics, and cancer

Tumorigenesis, a complex and multifactorial progressive process of transformation of normal cells into malignant cells, is characterized by the accumulation of multiple cancer-specific heritable phenotypes triggered by the mutational and/or non-mutational (i.e., epigenetic) events. Accumulating evidence suggests that environmental and occupational exposures to natural substances, as well as man-made chemical and physical agents, play a causative role in human cancer. In a broad sense, carcinogenesis may be induced through either genotoxic or non-genotoxic mechanisms; however, both genotoxic and non-genotoxic carcinogens also cause prominent epigenetic changes. This review presents current evidence of the epigenetic alterations induced by various chemical carcinogens, including arsenic, 1,3-butadine, and pharmaceutical and biological agents, and highlights the potential for epigenetic changes to serve as markers for carcinogen exposure and cancer risk assessment.

Levels of select PCB and PBDE congeners in human postmortem brain reveal possible environmental involvement in 15q11-q13 duplication autism spectrum disorder

Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs) that bioaccumulate in lipid-rich tissues are of concern as developmental neurotoxicants. Epigenetic mechanisms such as DNA methylation act at the interface of genetic and environmental factors implicated in autism-spectrum disorders. The relationship between POP levels and DNA methylation patterns in individuals with and without neurodevelopmental disorders has not been previously investigated. In this study, a total of 107 human frozen postmortem brain samples were analyzed for eight PCBs and seven PBDEs by GC-micro electron capture detector and GC/MS using negative chemical ionization. Human brain samples were grouped as neurotypical controls (n = 43), neurodevelopmental disorders with known genetic basis (n = 32, including Down, Rett, Prader-Willi, Angelman, and 15q11-q13 duplication syndromes), and autism of unknown etiology (n = 32). Unexpectedly, PCB 95 was significantly higher in the genetic neurodevelopmental group, but not idiopathic autism, as compared to neurotypical controls. Interestingly, samples with detectable PCB 95 levels were almost exclusively those with maternal 15q11-q13 duplication (Dup15q) or deletion in Prader-Willi syndrome. When sorted by birth year, Dup15q samples represented five out of six of genetic neurodevelopmental samples born after the 1976 PCB ban exhibiting detectable PCB 95 levels. Dup15q was the strongest predictor of PCB 95 exposure over age, gender, or year of birth. Dup15q brain showed lower levels of repetitive DNA methylation measured by LINE-1 pyrosequencing, but methylation levels were confounded by year of birth. These results demonstrate a novel paradigm by which specific POPs may predispose to genetic copy number variation of 15q11-q13.

Number of persistent organic pollutants detected at high concentrations in a general population

BACKGROUND

Surveys of human exposure to environmental chemicals do not integrate the number of compounds detected per person and the concentration of each compound. This leaves untested relevant exposure scenarios, such as whether individuals with low concentrations of some compounds have high concentrations of the other compounds.

OBJECTIVE

To analyze the number of persistent organic pollutants (POPs) detected at high concentrations.

METHODS

Serum concentrations of 19 POPs were analyzed by gas chromatography with electron-capture detection in a representative sample of the general population of Catalonia, Spain (N=919).

RESULTS

Over 58% of participants had concentrations in the top quartile of ≥1 of the eight most prevalent POPs, and 34% of ≥3 POPs. 83% of women 60 to 74 years old had concentrations of ≥3 POPs in the top quartile; 56% of women 60 to 74 years had p,p'-DDE, HCB and β-HCH all in their respective top quartiles, and 48% had concentrations of ≥6 POPs in the top quartile. Over 30% of subjects had concentrations in the top decile of 1 to 5 of the eight most prevalent POPs. Half of the population had levels of 1 to 5 POPs >500 ng/g. Less than 4% had all eight POPs in the lowest quartile.

CONCLUSIONS

More than half of the study population had concentrations in the top quartile of ≥1 POPs. Significant subgroups of the population accumulate POP mixtures at high concentrations. POP concentrations appear low in most of the population only when each individual compound is looked at separately.

Alterations in histone H4 lysine 20 methylation: implications for cancer detection and prevention

SIGNIFICANCE

Cancer development and progression are associated with numerous genetic, epigenetic, and metabolic changes.

RECENT ADVANCES

A number of epigenetic aberrations have been characterized in cancer, including DNA methylation and various histone modification changes. One of the most unique and enigmatic epigenetic marks that is noticeably altered in several major human cancers is methylation of histone H4 lysine 20; however, there is insufficient knowledge of the underlying molecular mechanisms associated with this abberation.

CRITICAL ISSUES

This review presents current evidence of the role of histone H4 lysine 20 methylation in normal and cancer cells and during tumorigenesis induced by genotoxic and nongenotoxic carcinogens. Additionally, it describes molecular mechanisms that may cause this alteration and highlights the significance of this epigenetic mark as an early indicator of carcinogenesis.

FUTURE DIRECTIONS

Accumulating evidence suggests that dietary components may be significant regulators of the cellular epigenome, including histone methylation, by providing and maintaining the adequate levels of S-adenosyl-L-methionine, flavin adenine dinucleotide, α-ketoglutarate, and iron. Future research should elucidate the potential for modifying cellular metabolism through dietary intervention for timely regulation of the epigenome as means for the prevention of cancer development.

Genetic and epigenetic influence on the response to environmental particulate matter

Ambient air pollution, including particulate matter (PM) and gaseous pollutants, represents important environmental exposures that adversely affect human health. Because of their heritable and reversible nature, epigenetic modifications provide a plausible link between the environment and alterations in gene expression that might lead to disease. Epidemiologic evidence supports that environmental exposures in childhood affect susceptibility to disease later in life, supporting the belief that epigenetic changes can affect ongoing development and promote disease long after the environmental exposure has ceased. Indeed, allergic disorders often have their roots in early childhood, and early exposure to PM has been strongly associated with the subsequent development of asthma. The purpose of this review is to summarize recent findings on the genetic and epigenetic regulation of responses to ambient air pollutants, specifically respirable PM, and their association with the development of allergic disorders. Understanding these epigenetic biomarkers and how they integrate with genetic influences to translate the biologic effect of particulate exposure is critical to developing novel preventative and therapeutic strategies for allergic disorders.

Folate and vitamin B12 deficiency and hyperhomocysteinemia promote oxidative stress in adult type 2 diabetes

OBJECTIVE

The purpose of this study was to examine the status of folate and vitamin B12 (B12) in relation to serum homocysteine (HCY) and oxidative stress indices in patients with type 2 diabetes (T2DM).

METHODS

This case-control study involved 100 Omani adults (50 patients newly diagnosed with T2DM and 50 age- and gender-matched healthy controls). Several parameters were investigated, including dietary intake and biochemical assessments of folate, B12, HCY, oxidative stress markers (glutathione and total antioxidant status), and antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase).

RESULTS

Low serum levels of folate, B12, and hyperhomocysteinemia were prevalent in patients with T2DM compared with controls. Oxidative stress was evident in patients with T2DM as indicated by low serum levels of glutathione, total antioxidant status, and impaired antioxidant enzymatic activities (superoxide dismutase, glutathione peroxidase, and catalase).

CONCLUSION

The low intake of folate and B12 is associated with low serum levels of these two nutrients and hyperhomocysteinemia in Omani adults with T2DM.

Distribution of blood concentrations of persistent organic pollutants in a representative sample of the population of Barcelona in 2006, and comparison with levels in 2002

INTRODUCTION

POP biomonitoring programs are useful for exposure assessment, to analyze patterns, and to evaluate policies. However, population-representative surveys are scarce and heterogeneous. Reports on time trends in representative samples using the same methods are rare.

OBJECTIVES

To analyze the distribution of serum concentrations of 19 POPs in the general population of Barcelona city in 2006, and to compare it with the distribution in 2002.

METHODS

231 participants in the Barcelona Health Survey were interviewed face-to-face, gave blood, and underwent a physical exam. Density plots ("POP Geoffrey Rose curves") were used to represent the full population distribution of each compound.

RESULTS

Eight POPs were each detected in >80% of the study subjects: p,p'-DDT, p,p'-DDE, PCB congeners 118, 138, 153 and 180, HCB and β-HCH. The minimum number of POPs detected in one person was 5, and 72% of the population accumulated ≥ 10 compounds. p,p'-DDE and HCB showed the highest concentrations (median=219 and 109 ng/g lipid, respectively). Concentrations decreased by 34-56% from 2002 to 2006. The decrease was similar in women and men, and in all age groups/birth cohorts. It was larger with increasing BMI; for p,p'-DDT, HCB and β-HCH the decrease in obese individuals was 31-44 percentage points larger than in subjects with normal weight. The distribution of POP concentrations was always switched towards higher values in women than men. POP levels also differed significantly by age, body mass index, weight gain, birth place and social class, but not by parity and breastfeeding. The two younger cohorts had a higher DDT/DDE ratio than the oldest cohort.

CONCLUSION

Although human POP contamination remains common in the city of Barcelona, concentrations decreased significantly in 4years. Our approach suggests innovative ways to conceive, analyze and present results for other monitoring programs.

Perfluorooctanoic acid induces gene promoter hypermethylation of glutathione-S-transferase Pi in human liver L02 cells

Perfluorooctanoic acid (PFOA) is one of the most commonly used perfluorinated compounds. Being a persistent environmental pollutant, it can accumulate in human tissues via various exposure routes. PFOA may interfere in a toxic fashion on the immune system, liver, development, and endocrine systems. In utero human exposure had been associated with cord serum global DNA hypomethylation. In light of this, we investigated possible PFOA-induced DNA methylation alterations in L02 cells in order to shed light into its epigenetic-mediated mechanisms of toxicity in human liver. L02 cells were exposed to 5, 10, 25, 50 or 100 mg/L PFOA for 72h. Global DNA methylation levels were determined by LC/ESI-MS, glutathione-S-transferase Pi (GSTP) gene promoter DNA methylation was investigated by methylation-specific polymerase chain reaction (PCR) with bisulfite sequencing, and consequent mRNA expression levels were measured with quantitative real-time reverse transcriptase PCR. A dose-related increase of GSTP promoter methylation at the transcription factor specificity protein 1 (SP1) binding site was observed. However, PFOA did not significantly influence global DNA methylation; nor did it markedly alter the promoter gene methylation of p16 (cyclin-dependent kinase inhibitor 2A), ERα (estrogen receptor α) or PRB (progesterone receptor B). In addition, PFOA significantly elevated mRNA transcript levels of DNMT3A (which mediates de novo DNA methylation), Acox (lipid metabolism) and p16 (cell apoptosis). Considering the role of GSTP in detoxification, aberrant methylation may be pivotal in PFOA-mediated toxicity response via the inhibition of SP1 binding to GSTP promoter.

Systematic evaluation of environmental factors: persistent pollutants and nutrients correlated with serum lipid levels

Background Both genetic and environmental factors contribute to triglyceride, low-density lipoprotein-cholesterol (LDL-C), and high-density lipoprotein-cholesterol (HDL-C) levels. Although genome-wide association studies are currently testing the genetic factors systematically, testing and reporting one or a few factors at a time can lead to fragmented literature for environmental chemical factors. We screened for correlation between environmental factors and lipid levels, utilizing four independent surveys with information on 188 environmental factors from the Centers of Disease Control, National Health and Nutrition Examination Survey, collected between 1999 and 2006.

Methods We used linear regression to correlate each environmental chemical factor to triglycerides, LDL-C and HDL-C adjusting for age, age², sex, ethnicity, socio-economic status and body mass index. Final estimates were adjusted for waist circumference, diabetes status, blood pressure and survey. Multiple comparisons were controlled for by estimating the false discovery rate and significant findings were tentatively validated in an independent survey.

Results We identified and validated 29, 9 and 17 environmental factors correlated with triglycerides, LDL-C and HDL-C levels, respectively. Findings include hydrocarbons and nicotine associated with lower HDL-C and vitamin E (γ-tocopherol) associated with unfavourable lipid levels. Higher triglycerides and lower HDL-C were correlated with higher levels of fat-soluble contaminants (e.g. polychlorinated biphenyls and dibenzofurans). Nutrients and vitamin markers (e.g. vitamins B, D and carotenes), were associated with favourable triglyceride and HDL-C levels.

Conclusions Our systematic association study has enabled us to postulate about broad environmental correlation to lipid levels. Although subject to confounding and reverse causality bias, these findings merit evaluation in additional cohorts.

Long-lived epigenetic interactions between perinatal PBDE exposure and Mecp2308 mutation

The widespread use of persistent organic polybrominated diphenyl ethers (PBDEs) as commercial flame retardants has raised concern about potential long-lived effects on human health. Epigenetic mechanisms, such as DNA methylation, are responsive to environmental influences and have long-lasting consequences. Autism spectrum disorders (ASDs) have complex neurodevelopmental origins whereby both genetic and environmental factors are implicated. Rett syndrome is an X-linked ASD caused by mutations in the epigenetic factor methyl-CpG binding protein 2 (MECP2). In this study, an Mecp2 truncation mutant mouse (Mecp2(308)) with social behavioral defects was used to explore the long-lasting effects of PBDE exposure in a genetically and epigenetically susceptible model. Mecp2(308/+) dams were perinatally exposed daily to 2,2',4,4'-tetrabromodiphenyl ether 47 (BDE-47) and bred to wild-type C57BL/6J males, and the offspring of each sex and genotype were examined for developmental, behavioral and epigenetic outcomes. Perinatal BDE-47 exposure negatively impacted fertility of Mecp2(308/+) dams and preweaning weights of females. Global hypomethylation of adult brain DNA was observed specifically in female offspring perinatally exposed to BDE-47 and it coincided with reduced sociability in a genotype-independent manner. A reversing interaction of Mecp2 genotype on BDE-47 exposure was observed in a short-term memory test of social novelty that corresponded to increased Dnmt3a levels specifically in BDE-47-exposed Mecp2(308/+) offspring. In contrast, learning and long-term memory in the Morris water maze was impaired by BDE-47 exposure in female Mecp2(308/+) offspring. These results demonstrate that a genetic and environmental interaction relevant to social and cognitive behaviors shows sexual dimorphism, epigenetic dysregulation, compensatory molecular mechanisms and specific behavioral deficits.

S-adenosylmethionine reduces the progress of the Alzheimer-like features induced by B-vitamin deficiency in mice

Methylation reactions linked to homocysteine in the one-carbon metabolism are increasingly elicited in Alzheimer's disease, although the association of hyperhomocysteinemia and of low B vitamin levels with the disease is still debated. We previously demonstrated that hyperhomocysteinemia and DNA hypomethylation induced by B vitamin deficiency are associated with PSEN1 and BACE1 overexpression and amyloid production. The present study is aimed at assessing S-adenosylmethionine effects in mice kept under a condition of B vitamin deficiency. To this end, TgCRND8 mice and wild-type littermates were assigned to control or B vitamin deficient diet, with or without S-adenosylmethionine supplementation. We found that S-adenosylmethionine reduced amyloid production, increased spatial memory in TgCRND8 mice and inhibited the upregulation of B vitamin deficiency-induced PSEN1 and BACE1 expression and Tau phosphorylation in TgCRND8 and wild-type mice. Furthermore, S-adenosylmethionine treatment reduced plaque spreading independently on B vitamin deficiency. These results strengthen our previous observations on the possible role of one-carbon metabolism in Alzheimer's disease, highlighting hyperhomocysteinemia-related mechanisms in dementia onset/progression and encourage further studies aimed at evaluating the use of S-adenosylmethionine as a potential candidate drug for the treatment of the disease.

Total blood mercury and serum measles antibodies in US children, NHANES 2003-2004

BACKGROUND

Environmental toxins, pathogens and host susceptibility cofactors may interact to contribute to disease. In vitro mercury exposure inhibited antiviral cytokines in human cells; however, little is known about the relationship between mercury and viruses in children. Children are susceptible to mercury toxicity; lower vitamin B-12 and folate levels and higher homocysteine levels may represent susceptibility cofactors. This study aimed to evaluate associations between total blood mercury (Hg) and measles antibodies in children, and the influence of these susceptibility cofactors.

DESIGN

Cross-sectional data on serum measles antibodies, Hg, homocysteine, methylmalonic acid (MMA, indicator of B-12 deficiency), and folate were obtained from the 2003-2004 NHANES for children aged 6-11 years with measles seropositivity (n=692). We used linear regression to evaluate relationships between measles antibodies and Hg, stratified by sex, MMA ≥, folate <, and homocysteine≥sample medians, adjusted for demographic, nutritional and environmental cofactors.

RESULTS

Hg (range: 0.10-19.10μg/L) was inversely associated with measles antibodies (range: 1.00-28.24 units) in non-stratified analysis (n=692), yet positively associated among the subset of boys with higher MMA and lower folate (n=98). Among this subset with higher homocysteine levels (n=61), correlations were positive across all Hg quartiles relative to Q1 (Hg≤0.20μg/L): Q2:β=6.60 (3.02, 10.19); Q3:β=8.49 (6.17, 10.81); Q4 (Hg>0.80μg/L):β=4.90 (2.12, 7.67) (p(trend)=0.077).

CONCLUSION

Stratification by susceptibility cofactors revealed opposing directionality for correlations between Hg and measles antibodies, with positive effect estimates at lowest exposures only among boys with higher MMA, lower folate and higher homocysteine levels.

A genomic point-of-view on environmental factors influencing the human brain methylome

The etiologic paradigm of complex human disorders such as autism is that genetic and environmental risk factors are independent and additive, but the interactive effects at the epigenetic interface are largely ignored. Genomic technologies have radically changed perspective on the human genome and how the epigenetic interface may impact complex human disorders. Here, I review recent genomic, environmental, and epigenetic findings that suggest a new paradigm of "integrative genomics" in which genetic variation in genomic size may be impacted by dietary and environmental factors that influence the genomic saturation of DNA methylation. Human genomes are highly repetitive, but the interface of large-scale genomic differences with environmental factors that alter the DNA methylome such as dietary folate is under-explored. In addition to obvious direct effects of some environmental toxins on the genome by causing chromosomal breaks, non-mutagenic toxin exposures correlate with DNA hypomethylation that can lead to rearrangements between repeats or increased retrotransposition. Since human neurodevelopment appears to be particularly sensitive to alterations in epigenetic pathways, a further focus will be on how developing neurons may be particularly impacted by even subtle alterations to DNA methylation and proposing new directions towards understanding the quixotic etiology of autism by integrative genomic approaches.

Assessing causal relationships in genomics: From Bradford-Hill criteria to complex gene-environment interactions and directed acyclic graphs

Observational studies of human health and disease (basic, clinical and epidemiological) are vulnerable to methodological problems -such as selection bias and confounding- that make causal inferences problematic. Gene-disease associations are no exception, as they are commonly investigated using observational designs. A rich body of knowledge exists in medicine and epidemiology on the assessment of causal relationships involving personal and environmental causes of disease; it includes seminal causal criteria developed by Austin Bradford Hill and more recently applied directed acyclic graphs (DAGs). However, such knowledge has seldom been applied to assess causal relationships in clinical genetics and genomics, even in studies aimed at making inferences relevant for human health. Conversely, incorporating genetic causal knowledge into clinical and epidemiological causal reasoning is still a largely unexplored area.

As the contribution of genetics to the understanding of disease aetiology becomes more important, causal assessment of genetic and genomic evidence becomes fundamental. The method we develop in this paper provides a simple and rigorous first step towards this goal. The present paper is an example of integrative research, i.e., research that integrates knowledge, data, methods, techniques, and reasoning from multiple disciplines, approaches and levels of analysis to generate knowledge that no discipline alone may achieve.

Epigenetics and its implications for ecotoxicology

Epigenetics is the study of mitotically or meiotically heritable changes in gene function that occur without a change in the DNA sequence. Interestingly, epigenetic changes can be triggered by environmental factors. Environmental exposure to e.g. metals, persistent organic pollutants or endocrine disrupting chemicals has been shown to modulate epigenetic marks, not only in mammalian cells or rodents, but also in environmentally relevant species such as fish or water fleas. The associated changes in gene expression often lead to modifications in the affected organism's phenotype. Epigenetic changes can in some cases be transferred to subsequent generations, even when these generations are no longer exposed to the external factor which induced the epigenetic change, as observed in a study with fungicide exposed rats. The possibility of this phenomenon in other species was demonstrated in water fleas exposed to the epigenetic drug 5-azacytidine. This way, populations can experience the effects of their ancestors' exposure to chemicals, which has implications for environmental risk assessment. More basic research is needed to assess the potential phenotypic and population-level effects of epigenetic modifications in different species and to evaluate the persistence of chemical exposure-induced epigenetic effects in multiple subsequent generations.

Total blood mercury, plasma homocysteine, methylmalonic acid and folate in US children aged 3-5 years, NHANES 1999-2004

BACKGROUND

Mercury is a known neurotoxicant; however, the relationship between childhood exposures and neurodevelopmental outcomes is uncertain, and may be modified by nutrition-related susceptibilities. In vitro studies found that mercury inhibited methionine synthase, an enzyme that interacts with vitamin B-12 and folate to regenerate the amino acid methionine from homocysteine, and inhibition of methionine synthase diverted homocysteine to cysteine and glutathione synthesis. The relationships between mercury, homocysteine, B-12, and folate have not been examined in children.

OBJECTIVE

This study aimed to evaluate associations between Hg and homocysteine in male and female children differentiated by higher and lower methylmalonic acid (MMA, an indicator of vitamin B-12 deficiency) and folate status.

DESIGN

Cross-sectional data on total blood mercury (Hg), plasma homocysteine, MMA, and serum folate were obtained from the 1999-2004 National Health and Nutrition Examination Surveys for children aged 3-5 years (n=1005). We used multiple linear regression to evaluate relationships between homocysteine and Hg quartiles, stratified by sex, MMA ≥ and folate < sample medians, adjusted for demographic, anthropometric, and environmental factors.

RESULTS

In boys with higher MMA and lower folate (n=135), but not in other children, we observed inverse associations between homocysteine and Hg. Children with Hg >3.49 μmol/L showed 1.14 μmol/L lower homocysteine (p<0.001) relative to the lowest quartile (≤ 0.70 μmol/L) {p-value for trend<0.001}. Compared to other subsamples, this subsample had significantly higher homocysteine levels.

CONCLUSION

Hg was inversely correlated with plasma homocysteine in young boys, but not girls, with higher MMA and lower folate. Additional studies are merited to evaluate Hg and amino acid metabolism in susceptible children.

Prenatal organochlorine compound exposure, rapid weight gain, and overweight in infancy

BACKGROUND

Although it has been hypothesized that fetal exposure to endocrine-disrupting chemicals may increase obesity risk, empirical data are limited, and it is uncertain how early in life any effects may begin.

OBJECTIVES

We explored whether prenatal exposure to several organochlorine compounds (OCs) is associated with rapid growth in the first 6 months of life and body mass index (BMI) later in infancy.

METHODS

Data come from the INMA (Infancia y Medio-Ambiente) Child and Environment birth cohort in Spain, which recruited 657 women in early pregnancy. Rapid growth during the first 6 months was defined as a change in weight-for-age z-scores > 0.67, and elevated BMI at 14 months, as a z-score ≥ the 85th percentile. Generalized linear models were used to estimate the risk of rapid growth or elevated BMI associated with 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE), hexachlorobenzene, β-hexachlorohexane, and polychlorinated biphenyls in first-trimester maternal serum.

RESULTS

After multivariable adjustment including other OCs, DDE exposure above the first quartile was associated with doubling of the risk of rapid growth among children of normal-weight (BMI < 25 kg/m2), but not overweight, mothers. DDE was also associated with elevated BMI at 14 months (relative risk per unit increase in log DDE = 1.50; 95% confidence interval, 1.11-2.03). Other OCs were not associated with rapid growth or elevated BMI after adjustment.

CONCLUSIONS

In this study we found prenatal DDE exposure to be associated with rapid weight gain in the first 6 months and elevated BMI later in infancy, among infants of normal-weight mothers. More research exploring the potential role of chemical exposures in early-onset obesity is needed.

Coupling global methylation and gene expression profiles reveal key pathophysiological events in liver injury induced by a methyl-deficient diet

SCOPE

A methyl-deficient diet induces liver injury similar to human nonalcoholic steatohepatitis, one of the main risk factors for the development of hepatocellular carcinoma. Previous studies have demonstrated that this diet perturbs DNA methylation by causing a profound loss of global cytosine methylation, predominantly at heavily methylated repetitive sequences. However, whether methyl deficiency affects the methylation status of gene promoters has not been explored.

METHODS AND RESULTS

Mouse gene expression and CpG island microarrays were used to characterize the gene expression and CpG island methylation profiles in the livers of C57BL/6J mice fed a methyl-deficient diet. We detected 164 genes that were differentially expressed and exhibited an inverse relationship between the gene expression and the extent of CpG island methylation. Furthermore, these genes were associated with altered lipid and glucose metabolism, DNA damage and repair, apoptosis, the development of fibrosis, and liver tissue remodeling. Although there were both increased and decreased levels of CpG island methylation, the number of hypomethylated genes was substantially greater than the number of hypermethylated genes.

CONCLUSION

The results this study demonstrate that pairing methylation profiles with gene expression profiles is a powerful approach to identify dysregulated high-priority fundamental pathophysiological pathways associated with disease development.

Distribution of blood concentrations of persistent organic pollutants in a representative sample of the population of Catalonia

BACKGROUND

Although virtually all populations worldwide are commonly exposed to numerous persistent organic pollutants (POPs) and human concentrations vary widely, only a few countries conduct nationwide surveillance programs of POP concentrations in representative samples of the general population.

OBJECTIVE

To evaluate the distribution of serum concentrations of nineteen POPs and their main predictors in a representative sample of the general population of Catalonia.

METHODS

Participants in the Catalan Health Interview Survey aged 18-74 years were interviewed face-to-face, gave blood, and underwent a physical exam. Graphs (including "POP Geoffrey Rose curves") were used to represent the full population distribution of each POP in the 919 participants. Through multivariate statistical models we analyzed the influence on POP concentrations of sex, age, body mass index (BMI), socioeconomic status and, in women, parity.

RESULTS

We detected dichlorodiphenyltrichloroethane (p,p'-DDT), dichlorodiphenyldichloroethane (p,p'-DDE), polychlorinated biphenyls (PCBs) congeners 118, 138, 153 and 180, hexachlorobenzene (HCB) and beta-hexachlorocyclohexane (beta-HCH) in more than 85% of the subjects. p,p'-DDE, HCB and beta-HCH showed the highest concentrations (median=399, 159 and 92 ng/g lipid, respectively). Distributions were highly skewed and interindividual differences were up to 7700-fold. POP levels differed significantly by gender, age, BMI, educational level, and parity.

CONCLUSIONS

In Catalonia, an advanced European society, exposure to POPs remains common, a vast majority of the population has much lower blood concentrations than a relative minority, and the population distributions of POP are hence highly skewed to the right. Shifting distributions towards lower concentrations requires more energetic policies and population strategies.

Global DNA hypomethylation is associated with in utero exposure to cotinine and perfluorinated alkyl compounds

Environmental exposures in-utero may alter the epigenome, thus impacting chromosomal stability and gene expression. We hypothesized that in utero exposures to maternal smoking and perfluoroalkyl compounds (PFCs) are associated with global DNA hypomethylation in umbilical cord serum. Our objective was to determine if global DNA methylation could be used as a biomarker of in utero exposures to maternal smoking and PFCs. Using an ELISA-based method, global DNA methylation was quantified in umbilical cord serum from 30 newborns with high (> 10 ng/ml, mean 123.8 ng/ml), low (range 1-10 ng/ml, mean 1.6 ng/ml) and very low (< 1 ng/ml, mean 0.06 ng/ml) cord serum cotinine levels. Y chromosome analysis was performed to rule out maternal DNA cross-contamination. Cord serum global DNA methylation showed an inverse dose response to serum cotinine levels (p< 0.001). Global DNA methylation levels in cord blood were the lowest among newborns with smoking mothers (mean=15.04%; 95% CI, 8.4, 21.7) when compared to babies of mothers who were second-hand smokers (21.1%; 95% CI, 16.6, 25.5) and non-smokers (mean=29.2%; 95% CI, 20.1, 38.1). Global DNA methylation was inversely correlated with serum PFOA (r= -0.72, p < 0.01) but not PFOS levels. Serum Y chromosome analyses did not detect maternal DNA cross-contamination. This study supports the use of global DNA methylation status as a biomarker of in utero exposure to cigarette smoke and PFCs.

Nature or nurture: let food be your epigenetic medicine in chronic inflammatory disorders

Numerous clinical, physiopathological and epidemiological studies have underlined the detrimental or beneficial role of nutritional factors in complex inflammation related disorders such as allergy, asthma, obesity, type 2 diabetes, cardiovascular disease, rheumatoid arthritis and cancer. Today, nutritional research has shifted from alleviating nutrient deficiencies to chronic disease prevention. It is known that lifestyle, environmental conditions and nutritional compounds influence gene expression. Gene expression states are set by transcriptional activators and repressors and are often locked in by cell-heritable chromatin states. Only recently, it has been observed that the environmental conditions and daily diet can affect transgenerational gene expression via "reversible" heritable epigenetic mechanisms. Epigenetic changes in DNA methylation patterns at CpG sites (epimutations) or corrupt chromatin states of key inflammatory genes and noncoding RNAs, recently emerged as major governing factors in cancer, chronic inflammatory and metabolic disorders. Reciprocally, inflammation, metabolic stress and diet composition can also change activities of the epigenetic machinery and indirectly or directly change chromatin marks. This has recently launched re-exploration of anti-inflammatory bioactive food components for characterization of their effects on epigenome modifying enzymatic activities (acetylation, methylation, phosphorylation, ribosylation, oxidation, ubiquitination, sumoylation). This may allow to improve healthy aging by reversing disease prone epimutations involved in chronic inflammatory and metabolic disorders.

The relative influence of diet and serum concentrations of organochlorine compounds on K-ras mutations in exocrine pancreatic cancer

BACKGROUND

In exocrine pancreatic cancer (EPC) mechanistic relationships may exist among some organochlorine compounds (OCs) and mutations in the K-ras oncogene, as well as among the latter and dietary factors.

OBJECTIVE

To analyze (1) the relationship between food intake and serum concentrations of OCs in EPC patients and (2) the relative influence of food and OCs on the frequency of K-ras mutations in EPC.

PATIENTS AND METHODS

Incident cases of EPC were prospectively identified, and interviewed face-to-face during hospital admission (N=135 patients with data on OCs and diet, and N=97 with additional information on K-ras status). OCs were measured by high-resolution gas chromatography with electron-capture detection.

RESULTS

Consumption of milk and other dairy products was positively associated with concentrations of p,p'-DDT, PCB 138 and PCB 153 (log-transformed betas=0.652, 0.588 and 0.317, respectively; all p<0.05). When adjusted by OCs, dairy products were no longer associated with K-ras. By contrast, after adjusting by consumption of dairy products, patients with the highest concentrations of p,p'-DDT and some PCBs remained more likely to have a K-ras-mutated EPC than patients with lower concentrations (OR for upper tertile of PCB 138=5.5, 95% CI: 1.3-23.4).

CONCLUSIONS

Dairy products were a source of OCs. The association between dairy products and K-ras mutations was not independent of OCs. By contrast, the association between OCs and K-ras was not confounded by dairy products. OCs may be more likely to contribute to the occurrence of K-ras mutations than nutrients contained in dairy products.