title: Effects of arsenic exposure on DNA methylation in cord blood samples from newborn babies and in a human lymphoblast cell line.
abstract: BACKGROUND
  Accumulating evidence indicates that in utero exposure to arsenic is associated with congenital defects and long-term disease consequences including cancers. Recent studies suggest that arsenic carcinogenesis results from epigenetic changes, particularly in DNA methylation. This study aimed to investigate DNA methylation changes as a result of arsenic exposure in utero and in vitro.
  
  
  METHODS
  For the exposure in utero study, a total of seventy-one newborns (fifty-five arsenic-exposed and sixteen unexposed newborns) were recruited. Arsenic concentrations in the drinking water were measured, and exposure in newborns was assessed by measurement of arsenic concentrations in cord blood, nails and hair by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). In the in vitro study, human lymphoblasts were treated with arsenite at 0-100 μM for two, four and eight hours (short-term) and at 0, 0.5 and 1.0 μM for eight-weeks period (long-term). DNA methylation was analyzed in cord blood lymphocytes and lymphoblasts treated with arsenite in vitro. Global DNA methylation was determined as LINE-1 methylation using combined bisulfite restriction analysis (COBRA) and total 5-methyldeoxycytidine (5MedC) content which was determined by HPLC-MS/MS. Methylation of p53 was determined at the promoter region using methylation-specific restriction endonuclease digestion with MspI and HpaII.
  
  
  RESULTS
  Results showed that arsenic-exposed newborns had significantly higher levels of arsenic in cord blood, fingernails, toenails and hair than those of the unexposed subjects and a slight increase in promoter methylation of p53 in cord blood lymphocytes which significantly correlated with arsenic accumulation in nails (p < 0.05) was observed, while LINE-1 methylation was unchanged. Short-term in vitro arsenite treatment in lymphoblastoid cells clearly demonstrated a significant global hypomethylation, determined as reduction in LINE-1 methylation and total 5-MedC content, and p53 hypermethylation (p < 0.05). However, a slight LINE-1 hypomethylation and transient p53 promoter hypermethylation were observed following long-term in vitro treatment.
  
  
  CONCLUSIONS
  This study provides an important finding that in utero arsenic exposure affects DNA methylation, particularly at the p53 promoter region, which may be linked to the mechanism of arsenic carcinogenesis and the observed increased incidence of cancer later in life.
authors.affiliation: Laboratory of Environmental Toxicology, Chulabhorn Research Institute, Bangkok, 10210, Thailand.
authors.forename: Ponpat
authors.initials: P
authors.lastname: Intarasunanont
authors.forename: Panida
authors.initials: P
authors.lastname: Navasumrit
authors.forename: Somchamai
authors.initials: S
authors.lastname: Waraprasit
authors.forename: Krittinee
authors.initials: K
authors.lastname: Chaisatra
authors.forename: William A
authors.initials: WA
authors.lastname: Suk
authors.forename: Chulabhorn
authors.initials: C
authors.lastname: Mahidol
authors.forename: Mathuros
authors.initials: M
authors.lastname: Ruchirawat
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000633:toxicity; D002460:Cell Line; D019175:DNA Methylation; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis* / Q000633:toxicity; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D006197:Hair / Q000737:chemistry; D006801:Humans; D007231:Infant, Newborn; D008214:Lymphocytes / Q000166:cytology; D008431:Maternal-Fetal Exchange; D009262:Nails / Q000737:chemistry; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D014881:Water Supply / Q000032:analysis
chemical_list: D004785:Environmental Pollutants; D016159:Tumor Suppressor Protein p53; D001151:Arsenic