Serum Homocysteine, Arsenic Methylation, and Arsenic-Induced Skin Lesion Incidence in Bangladesh: A One-Carbon Metabolism Candidate Gene Study

Environ Int. 2018 Apr;113:133-142. doi: 10.1016/j.envint.2018.01.015. Epub 2018 Feb 6.

Abstract

Background: Inorganic arsenic (As) is methylated via one carbon metabolism (OCM) to mono- and dimethylated arsenicals (MMA and DMA), facilitating urinary excretion. Hyperhomocysteinemia (HHcys), a marker of impaired OCM, is a risk factor for As-induced skin lesions, but the influences of single nucleotide polymorphisms (SNPs) in OCM genes on Hcys, As metabolism and skin lesion risk is unclear.

Objectives: To (i) explore genetic sources of Hcys and the causal role of HHcys in As-induced skin lesion development using OCM genetic proxies for HHcys and (ii) identify OCM SNPs associated with urinary As metabolite proportions and/or skin lesion incidence.

Methods: We conducted a case-control study nested in the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh which 876 incident skin lesion cases were matched to controls on sex, age, and follow-up time. We measured serum Hcys, urinary As metabolites, and 26 SNPs in 13 OCM genes.

Results: Serum Hcys and urinary %DMA were independently associated with increased and decreased odds of skin lesions, respectively. The T allele of MTHFR 677 C ➔ T (rs1801133) was associated with HHcys, higher %MMA, and lower %DMA, but not with skin lesions. Interactions between SNPs and water As on skin lesion risk were suggestive for three variants: the G allele of MTRR rs1801394 and T allele of FOLR1 rs1540087 were associated with lower odds of skin lesions with lower As (≤50 μg/L), and the T allele of TYMS rs1001761 was associated with higher odds of skin lesions with higher As.

Conclusions: While HHcys and decreased %DMA were associated with increased risk for skin lesions, and MTHFR 677 C ➔ T was a strong predictor of HHcys, MTHFR 677 C ➔ T was not associated with skin lesion risk. Future studies should explore (i) non-OCM and non-genetic determinants of Hcys and (ii) if genetic findings are replicated in other As-exposed populations, mechanisms by which OCM SNPs may influence the dose-dependent effects of As on skin lesion risk.

Keywords: Arsenic; Arsenic metabolism; Gene-environment interaction; Homocysteine; One-carbon metabolism; Skin lesions.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Arsenic* / chemistry
  • Arsenic* / toxicity
  • Arsenicals / urine
  • Bangladesh
  • Case-Control Studies
  • Genetic Predisposition to Disease / epidemiology
  • Genetic Predisposition to Disease / genetics
  • Homocysteine / blood*
  • Humans
  • Methylation
  • Polymorphism, Single Nucleotide
  • Skin Diseases* / chemically induced
  • Skin Diseases* / epidemiology
  • Skin Diseases* / genetics

Substances

  • Arsenicals
  • Homocysteine
  • Arsenic