Effect of alcohol consumption on peripheral blood Alu methylation in Korean men

Global DNA methylation patterns in Alcohol Use Disorder

Alcohol Use Disorder (AUD) is a highly prevalent condition worldwide that produces a wide range of pathophysiological consequences, with a critical impact on health and social issues. Alcohol influences gene expression through epigenetic changes mainly through DNA methylation. In this sense, levels of 5-methylcytosine (5-mC), namely Global DNA methylation (GMe), which can be influenced by environmental and hormonal effects, represent a putative biological mechanism underlying alcohol effects. Our aim was to investigate the influence of AUD diagnosis and alcohol patterns (i.e., years of addiction, use in the last 30 days, and alcohol severity) on GMe levels. The sample consisted of 256 men diagnosed with AUD and 361 men without AUD. DNA samples from peripheral blood were used to assess GMe levels, measured through the levels of 5-mC using high-performance liquid chromatography. Results from multiple linear regression analysis indicated that the presence of AUD was associated with lower GMe levels (beta=-0.155, p=0.011). Other alcohol-related outcomes were not associated with DNA methylation. Our findings are consistent with the hypothesis that the impact of chronic and heavy alcohol use in GMe could be a potential mechanism mediating the multiple organ damages related to AUD.

Post-translational modifications of histone and non-histone proteins in epigenetic regulation and translational applications in alcohol-associated liver disease: Challenges and research opportunities

Epigenetic regulation is a process that takes place through adaptive cellular pathways influenced by environmental factors and metabolic changes to modulate gene activity with heritable phenotypic variations without altering the DNA sequences of many target genes. Epigenetic regulation can be facilitated by diverse mechanisms: many different types of post-translational modifications (PTMs) of histone and non-histone nuclear proteins, DNA methylation, altered levels of noncoding RNAs, incorporation of histone variants, nucleosomal positioning, chromatin remodeling, etc. These factors modulate chromatin structure and stability with or without the involvement of metabolic products, depending on the cellular context of target cells or environmental stimuli, such as intake of alcohol (ethanol) or Western-style high-fat diets. Alterations of epigenetics have been actively studied, since they are frequently associated with multiple disease states. Consequently, explorations of epigenetic regulation have recently shed light on the pathogenesis and progression of alcohol-associated disorders. In this review, we highlight the roles of various types of PTMs, including less-characterized modifications of nuclear histone and non-histone proteins, in the epigenetic regulation of alcohol-associated liver disease (ALD) and other disorders. We also describe challenges in characterizing specific PTMs and suggest future opportunities for basic and translational research to prevent or treat ALD and many other disease states.

LINE-1 methylation mediates the inverse association between body mass index and breast cancer risk: A pilot study in the Lebanese population

INTRODUCTION

Lebanon is among the top countries worldwide in combined incidence and mortality of breast cancer, which raises concern about risk factors peculiar to this country. The underlying molecular mechanisms of breast cancer require elucidation, particularly epigenetics, which is recognized as a molecular sensor to environmental exposures.

PURPOSE

We aim to explore whether DNA methylation levels of AHRR (marker of cigarette smoking), SLC1A5 and TXLNA (markers of alcohol consumption), and LINE-1 (a genome-wide repetitive retrotransposon) can act as molecular mediators underlying putative associations between breast cancer risk and pertinent extrinsic (tobacco smoking and alcohol consumption) and intrinsic factors [age and body mass index (BMI)].

METHODS

This is a cross-sectional pilot study which includes breast cancer cases (N = 65) and controls (N = 54). DNA methylation levels were measured using bisulfite pyrosequencing on available peripheral blood samples (N = 119), and Multivariate Imputation by Chained Equations (MICE) was used to impute missing DNA methylation values in remaining samples. Multiple mediation analysis was performed to assess direct and indirect (via DNA methylation) effects of intrinsic and extrinsic factors on breast cancer risk.

RESULTS

In relation to exposure, AHRR hypo-methylation was associated with cigarette but not waterpipe smoking, suggesting potentially different biomarkers of these two forms of tobacco use; SLC1A5 and TXLNA methylation were not associated with alcohol consumption; LINE-1 methylation was inversely associated with BMI (β-value [95% confidence interval (CI)] = -0.04 [-0.07, -0.02]), which remained significant after adjustment for age, smoking and alcohol consumption. In relation to breast cancer, there was no detectable association between AHRR, SLC1A5 or TXLNA methylation and cancer risk, but LINE-1 methylation was significantly higher in breast cancer cases when compared to controls (mean ± SD: 72.00 ± 0.66 versus 70.89 ± 0.73, P = 4.67 × 10-14). This difference remained significant after adjustment for confounders (odds ratio (OR) [95% CI] = 9.75[3.74, 25.39]). Moreover, LINE-1 hypo-methylation mediated 83% of the inverse effect of BMI on breast cancer risk.

CONCLUSION

This pilot study demonstrates that alterations in blood LINE-1 methylation mediate the inverse effect of BMI on breast cancer risk. This warrants large scale studies and stratification based on clinic-pathological types of breast cancer.

The Molecular Basis of Alcohol Use Disorder (AUD). Genetics, Epigenetics, and Nutrition in AUD: An Amazing Triangle

Alcohol use disorder (AUD) is a very common and complex disease, as alcohol is the most widely used addictive drug in the world. This disorder has an enormous impact on public health and social and private life, and it generates a huge number of social costs. Alcohol use stimulates hypothalamic-pituitary-adrenal (HPA) axis responses and is the cause of many physical and social problems (especially liver disease and cancer), accidental injury, and risky sexual behavior. For years, researchers have been trying to identify the genetic basis of alcohol use disorder, the molecular mechanisms responsible for its development, and an effective form of therapy. Genetic and environmental factors are known to contribute to the development of AUD, and the expression of genes is a complicated process that depends on epigenetic modulations. Dietary nutrients, such as vitamins, may serve as one these modulators, as they have a direct impact on epigenomes. In this review, we connect gathered knowledge from three emerging fields-genetics, epigenetics, and nutrition-to form an amazing triangle relating to alcohol use disorder.

Changes in DNA methylation persist over time in males with severe alcohol use disorder-A longitudinal follow-up study

Treatment strategies for alcohol use disorder (AUD) aim for abstinence or harm reduction. While deranged biochemical parameters reverse with alcohol abstinence, whether molecular changes at the epigenetic level reverse is not clearly understood. We investigated whether the reduction from high alcohol use reflects DNA methylation at the gene-specific and global level. In subjects seeking treatment for severe AUD, we assessed gene-specific (aldehyde dehydrogenase [ALDH2]/methylene tetrahydrofolate reductase [MTHFR]) and global (long interspersed elements [LINE-1]) methylation across three-time points (baseline, after detoxification and at an early remission period of 3 months), in peripheral blood leukocytes. We observed that both gene-specific and global DNA methylation did not change over time, irrespective of the drinking status at 3 months (52% abstained from alcohol). Further, we also compared DNA methylation in AUD subjects with healthy controls. At baseline, there was a significantly higher gene-specific DNA methylation (ALDH2: p < .001 and MTHFR: p = .001) and a significant lower global methylation (LINE-1: p = .014) in AUD as compared to controls. Our results suggest that epigenetic changes at the DNA methylation level associated with severe AUD persist for at least 3 months of treatment.

Environmental and socio-cultural impacts on global DNA methylation in the indigenous Huichol population of Nayarit, Mexico

Alterations of global DNA methylation have been evaluated in several studies worldwide; however, Long Interspersed Nuclear Elements-1 (LINE-1) methylation in genetically conserved populations such as indigenous communities have not, to our knowledge, been reported. The aim of this study was to evaluate the relationship between LINE-1 methylation patterns and factors such as pesticide exposure and socio-cultural characteristics in the Indigenous Huichol Population of Nayarit, Mexico. A cross-sectional study was conducted in 140 Huichol indigenous individuals. A structured questionnaire was used to determine general and anthropometric characteristics, diet, harmful habits, and pesticide exposure. DNA methylation was determined by pyrosequencing of bisulfite-treated DNA. A lower level of LINE-1 methylation was found in the indigenous population when compared to a Mestizo population previously studied by our group. This difference might be due to the influence of the genetic admixture and differing dietary and lifestyle habits. The males in the indigenous population exhibited increased LINE-1 methylation in comparison to the females. Sex and alcohol consumption showed positive associations with LINE-1 methylation, while weight, current work in the field, current pesticide usage, and folate intake exhibited negative associations with LINE-1 methylation. The results suggest that ethnicity, as well as other internal and environmental factors, might influence LINE-1 methylation.

Twin Research in the Post-Genomic Era: Dissecting the Pathophysiological Effects of Adversity and the Social Environment

The role of twins in research is evolving as we move further into the post-genomic era. With the re-definition of what a gene is, it is becoming clear that biological family members who share a specific genetic variant may well not have a similar risk for future disease. This has somewhat invalidated the prior rationale for twin studies. Case co-twin study designs, however, are slowly emerging as the ideal tool to identify both environmentally induced epigenetic marks and epigenetic disease-associated processes. Here, we propose that twin lives are not as identical as commonly assumed and that the case co-twin study design can be used to investigate the effects of the adult social environment. We present the elements in the (social) environment that are likely to affect the epigenome and measures in which twins may diverge. Using data from the German TwinLife registry, we confirm divergence in both the events that occur and the salience for the individual start as early as age 11. Case co-twin studies allow for the exploitation of these divergences, permitting the investigation of the role of not only the adult social environment, but also the salience of an event or environment for the individual, in determining lifelong health trajectories. In cases like social adversity where it is clearly not possible to perform a randomised-controlled trial, we propose that the case co-twin study design is the most rigorous manner with which to investigate epigenetic mechanisms encoding environmental exposure. The role of the case co-twin design will continue to evolve, as we argue that it will permit causal inference from observational data.

Short-term changes in global methylation and hydroxymethylation during alcohol detoxification

Alcohol dependence is a common public health problem and epigenetics may offer new aspects in understanding the biological and genetic underpinnings and improve treatment of this complex disease. Supposedly, methylation and hydroxymethylation are altered in brain tissues and in synapse-related genes due to chronic alcohol intake and during withdrawal. To assess potential epigenetic changes after cessation of chronic alcohol intake, we compared 23 alcohol-dependent individuals during inpatient alcohol detoxification with 13 carefully matched controls. Blood samples were taken on the day of admission, after one and after two weeks at the end of inpatient treatment. Genome-wide global methylation and global DNA hydroxymethylation were compared across groups. There were significant differences in global methylation across time from admission to one and two weeks of inpatient withdrawal (p < 0.001). These findings were paralleled to changes in global DNA hydroxymethylation across time when age was employed as a cofactor (p < 0.001). Several potentially influencing variables like severity of withdrawal, dose of withdrawal medication and alcohol intake before admission did not yield significant influence on epigenetic changes. The results confirm previous findings of significant alterations of epigenetic patterns during alcohol intoxication and present for the first time hydroxymethylation changes in these individuals.

Alcohol and DNA Methylation: An Epigenome-Wide Association Study in Blood and Normal Breast Tissue

The biological mechanisms driving associations between alcohol consumption and chronic diseases might include epigenetic modification of DNA methylation. We explored the hypothesis that alcohol consumption is associated with methylation in an epigenome-wide association study of blood and normal breast tissue DNA. Infinium HumanMethylation450 BeadChip (Illumina Inc., San Diego, California) array data on blood DNA methylation was examined in a discovery set of 2,878 non-Hispanic white women from the Sister Study (United States, 2004-2015) who provided detailed questionnaire information on lifetime alcohol use. Robust linear regression modeling was used to identify significant associations (false discovery rate of Q < 0.05) between the number of alcoholic drinks per week and DNA methylation at 5,458 cytosine-phosphate-guanine (CpG) sites. Associations were replicated (P < 0.05) for 677 CpGs in an independent set of 187 blood DNA samples from the Sister Study and for 628 CpGs in an independent set of 171 normal breast DNA samples; 1,207 CpGs were replicated in either blood or normal breast, with 98 CpGs replicated in both tissues. Individual gene effects were notable for phosphoglycerate dehydrogenase (PGHDH), peptidyl-prolyl cis-trans isomerase (PPIF), solute carrier 15 (SLC15), solute carrier family 43 member 1 (SLC43A1), and solute carrier family 7 member 11 (SLC7A11). We also found that high alcohol consumption was associated with significantly lower global methylation as measured by the average of CpGs on the entire array.

Crosstalk of Genetic Variants, Allele-Specific DNA Methylation, and Environmental Factors for Complex Disease Risk

Over the past decades, genome-wide association studies (GWAS) have identified thousands of phenotype-associated DNA sequence variants for potential explanations of inter-individual phenotypic differences and disease susceptibility. However, it remains a challenge for translating the associations into causative mechanisms for complex diseases, partially due to the involved variants in the noncoding regions and the inconvenience of functional studies in human population samples. So far, accumulating evidence has suggested a complex crosstalk among genetic variants, allele-specific binding of transcription factors (ABTF), and allele-specific DNA methylation patterns (ASM), as well as environmental factors for disease risk. This review aims to summarize the current studies regarding the interactions of the aforementioned factors with a focus on epigenetic insights. We present two scenarios of single nucleotide polymorphisms (SNPs) in coding regions and non-coding regions for disease risk, via potentially impacting epigenetic patterns. While a SNP in a coding region may confer disease risk via altering protein functions, a SNP in non-coding region may cause diseases, via SNP-altering ABTF, ASM, and allele-specific gene expression (ASE). The allelic increases or decreases of gene expression are key for disease risk during development. Such ASE can be achieved via either a "SNP-introduced ABTF to ASM" or a "SNP-introduced ASM to ABTF." Together with our additional in-depth review on insulator CTCF, we are convinced to propose a working model that the small effect of a SNP acts through altered ABTF and/or ASM, for ASE and eventual disease outcome (named as a "SNP intensifier" model). In summary, the significance of complex crosstalk among genetic factors, epigenetic patterns, and environmental factors requires further investigations for disease susceptibility.

Correlation between global methylation level of peripheral blood leukocytes and serum C reactive protein level modified by MTHFR polymorphism: a cross-sectional study

BACKGROUND

Chronic inflammatory conditions are associated with higher tumor incidence through epigenetic and genetic alterations. Here, we focused on an association between an inflammation marker, C-reactive-protein (CRP), and global DNA methylation levels of peripheral blood leukocytes.

METHODS

The subjects were 384 healthy Japanese women enrolled as the control group of a case-control study for breast cancer conducted from 2001 to 2005. Global DNA methylation was quantified by Luminometric Methylation Assay (LUMA).

RESULTS

With adjustment for lifestyle-related factors, including folate intake, the global DNA methylation level of peripheral blood leukocytes was significantly but weakly increased by 0.43% per quartile category for CRP (P for trend = 0.010). Estimated methylation levels stratified by CRP quartile were 70.0%, 70.8%, 71.4%, and 71.3%, respectively. In addition, interaction between polymorphism of MTHFR (rs1801133, known as C677T) and CRP was significant (P for interaction = 0.046); the global methylation level was significantly increased by 0.61% per quartile category for CRP in the CT/TT group (those with the minor allele T, P for trend = 0.001), whereas no association was observed in the CC group (wild type).

CONCLUSIONS

Our study suggests that CRP concentration is weakly associated with global DNA methylation level. However, this association was observed more clearly in individuals with the minor allele of the MTHFR missense SNP rs1801133. By elucidating the complex mechanism of the regulation of DNA methylation by both acquired and genetic factors, our results may be important for cancer prevention.

Review: DNA methylation and alcohol use disorders: Progress and challenges

BACKGROUND AND OBJECTIVES

Risk for alcohol use disorders (AUDs) is influenced by gene-environment interactions. Environmental factors can affect gene expression through epigenetic mechanisms such as DNA methylation. This review outlines the findings regarding the association of DNA methylation and AUDs.

METHODS

We searched PubMed (by April 2016) and identified 29 studies that examined the association of DNA methylation and AUDs. We also evaluated the methods used in these studies.

RESULTS

Two studies demonstrated elevated global (repetitive element) DNA methylation levels in AUD subjects. Fifteen candidate gene studies showed hypermethylation of promoter regions of six genes (AVP, DNMT3B, HERP, HTR3A, OPRM1, and SNCA) or hypomethylation of the GDAP1 promoter region in AUD subjects. Five genome-wide DNA methylation studies demonstrated widespread DNA methylation changes across the genome in AUD subjects. Six studies showed significant correlations of DNA methylation with gene expression in AUD subjects. Three studies revealed interactive effects of genetic variation and DNA methylation on susceptibility to AUDs. Most studies analyzed AUD-associated DNA methylation changes in the peripheral blood; a few studies examined DNA methylation changes in postmortem brains of AUD subjects.

DISCUSSION AND CONCLUSIONS

Chronic alcohol consumption may result in DNA methylation changes, leading to neuroadaptations that may underlie some of the mechanisms of AUD risk and persistence. Future studies are needed to confirm the few existing results, and then to elucidate whether DNA methylation changes are the cause or consequence of AUDs.

SCIENTIFIC SIGNIFICANCE

DNA methylation profiles may be used to assess AUD status or monitor AUD treatment response. (Am J Addict 2017;26:502-515).