Table 1.
Recent studies examining the relationship between DNA methylation and arsenic exposure
| Type of study (in vitro, in vivo, human subjects) | Arsenical exposure | Cell type analyzed | Type of DNA methylation analysis and method used | Major findings | Reference |
|---|---|---|---|---|---|
| Women (n = 16) from Zimapán, Mexico | 7.46-90.75 μg arsenic/g creatinine in urine | PBLs | Genome-wide analysis of >14,000 promoter regions using the methylated CpG island recovery (MIRA)-microarray assay. | Identified 183 genes with differentially methylated promoters in individuals with arsenic-associated skin lesions vs. those with unlesioned skin. Several of these genes had known relationships with various iAs-associated diseases. | Smeester et al., 2011 [46•] |
| Women from Argentinian Andes (n = 202) | U-tAs: median=188 μg/L; 5-95 % = 20.8-545 μg/L | PBLs | Analyzed methylation status of regions of p16 and MLH1 genes and repetitive LINE-1 elements using bisulfite conversion of DNA followed by PCR amplification and pyrosequencing. | U-tAs positively associated with p16 and MLH1 methylation; %iAs in urine positively associated with p16 methylation; %DMAs in urine negatively associated with p16 methylation. No associations with LINE-1 methylation. | Hossain et al., 2012 [50•] |
| Newborns from Thailand (n = 71); in vitro exposure to arsenite (lymphoblasts) | Arsenic in cord blood = 0.51-10.37 μg/g; toenail = ND-8.23; hair = ND-0.38 μg/g; in vitro short term: 0, 10, 20, 50 μM NaAsO2 for 0, 2, 4, 8 h; in vitro long term: 0, 0.5, 1 μM NaAsO2 for 0, 2, 4, 6, 8 weeks | Cord blood lymphocytes; Lymphoblast cell line RPMI1788 | Global DNA methylation was calculated by determination of total 5-methyldeoxycytidine content via HPLC-MS/MS and the DNA methylation status of LINE-1 using combined bisulfite restriction analysis (COBRA). DNA methylation status of p53 determined by DNA methylation-specific restriction enzyme nuclease digestion. | Positive association between p53 promoter methylation and toenail arsenic in newborn cord blood. Short-term in vitro studies revealed p53 promoter hypermethylation and global DNA hypomethylation. Long-term in vitro studies revealed transient p53 hypermethylation and slight global DNA hypomethylation. | Intarasunanont et al., 2012 [52] |
| Mother-newborn pairs from Bangladesh (n = 114) | Maternal U-tAs = 0.04-21.87 μg/g creatinine | Peripheral blood leukocytes (mothers); cord blood leukocytes (newborns) | Analyzed methylation status of regions of p16 and p53 genes and LINE-1 and Alu 1 repetitive elements using bisulfite conversion of DNA followed by PCR amplification and pyrosequencing. | In both mothers and newborns, positive association between maternal U-tAs and LINE-1 methylation and some CpG sites within p16 promoter. Results suggest moderate levels of iAs exposure can impact DNA methylome. | Kile et al., 2012 [53] |
| Newborns from New Hampshire (n = 134) | Maternal U-tAs = 1.8-6.6 μg/L | Cord blood | Genome-wide DNA methylation analysis of >485,000 CpG sites at single-nucleotide resolution using bisulfite conversion of DNA followed by hybridization to the Illumina Infinium HumanMethylation450 BeadChip. | Associations between maternal U-tAs and methylation status of several CpG sites identified, several of which had linear relationships. Results suggest low levels of iAs exposure can impact DNA methylome. | Koestler et al., 2013 [54] |
| Mother-newborn pairs from Bangladesh (n = 101) | Maternal U-tAs mean = 271.7 μg/g creatinine | Cord blood | Analysis of global DNA methylation analysis using several methods: 3H-methyl incorporation assay; the luminometric methylation assay (LUMA), and the DNA methylation status of LINE-1 and Alu 1 repetitive elements using bisulfite conversion of DNA followed by PCR amplification and pyrosequencing. | Positive association between maternal U-tAs and global DNA methylation across all newborns (3H-methyl incorporation assay); some analyses revealed this relationship may be sex-dependent, i.e. positive for newborn males and negative for newborn females (Alu, LINE-1 and LUMA). | Pilsner et al., 2012 [55] |
| Women | |||||
| Women (n = 16) from Zimapán, Mexico) | 7.46-90.75 μg arsenic/g creatinine in urine | PBLs | Genome-wide analysis of >14,000 promoter regions using the methylated CpG island recovery (MIRA)-microarray assay. | Distinct promoter DNA methylation patterns associated with urinary levels of iAs, MMAs and DMAs were identified, which included genes with known links to diabetes mellitus. | Bailey et al., 2013 [47] |
| Women from Argentinian Andes (n = 103); newborns from Bangladesh (n = 127) | U-tAs (Argentina): median = 188 μg/L; 5-95 % = 16-620 μg/L; maternal U-tAs (Bangladesh): median = 68 μg/L; 5-95 % = 20-460 μg/L | PBLs (Argentina); cord blood lymphocytes (Bangladesh) | Analysis of DNA methylation status of 10q24 region at a single nucleotide resolution using bisulfite conversion of DNA followed by hybridization to the Illumina Infinium HumanMethylation450 BeadChip. | In Argentinian women, efficient metabolizing phenotype of AS3MT associated methylation status of AS3MT and several other surrounding genes on 10q24. Similar but weaker trends observed in Bangladeshi newborns. | Engstrom et al., 2013 [49] |
| Native American men and women from Arizona (n = 16), Oklahoma (n = 16), North Dakota (n = 16), South Dakota (n = 16); in vitro exposure to arsenite (human PBMCs) | Low exposure group: U-tAs < 7.2 μg/L (mean = 5.2 μg/L; n = 8 from each region); moderate exposure group: U-tAs >14.0 μg/L; (mean = 29.2 μg/L; n = 8 from each region); human PBMCs exposed to 5.0 μM arsenite (NaAsO2) for 48 h | Whole blood (Native Americans); human PBMCs (in vitro) | In samples from Native Americans, analysis of the DNA methylation status of 48 CpG loci within ASM3T promoter region performed by bisulfite conversion of DNA, PCR amplification, and DNA sequencing of cloned PCR products. The DNA methylation status of ASM3T from PBMCs was performed using the MethyLight assay and global DNA methylation levels were determined using a 5′-mC enzyme-linked immunosorbent assay (ELISA). | A region of 30 CpG loci identified within ASM3T promoter that are hypomethylated in moderate exposure group vs. low exposure group. In vitro analyses revealed that exposure to arsenite was associated with increased ASM3T expression and reduced ASM3T promoter DNA methylation levels. Knockdown of ASM3T in vitro resulted in inhibition of arsenite-induced global DNA hypomethylation. | Gribble et al., 2013 [51] |
HPLC-MS/MS: high-performance liquid chromatography tandem mass spectrometry
PBLs: peripheral blood lymphocytes
PBMCs: peripheral blood mononuclear cells
PCR: polymerase chain reaction
ND: non-detectable
U-tAs: total urinary arsenic (sum of iAs, MMAs, DMAs)