Arsenic metabolites; selenium; and AS3MT, MTHFR, AQP4, AQP9, SELENOP, INMT, and MT2A polymorphisms in Croatian-Slovenian population from PHIME-CROME study

The relationships between inorganic arsenic (iAs) metabolism, selenium (Se) status, and genetic polymorphisms of various genes, commonly studied in populations exposed to high levels of iAs from drinking water, were studied in a Croatian- Slovenian population from the wider PHIME-CROME project. Population consisted of 136 pregnant women in the 3rd trimester and 176 non-pregnant women with their children (n = 176, 8–9 years old). Their exposure to iAs, defined by As (speciation) analyses of biological samples, was low. The sums of biologically active metabolites (arsenite + arsenate + methylated As forms) for pregnant women, non-pregnant women, and children, respectively were: 3.23 (2.84–3.68), 1.83 (1.54– 2.16) and 2.18 (1.86–2.54) ng/mLSG ; GM (95 CI). Corresponding plasma Se levels were: 54.8 (52.8– 56.9), 82.3 (80.4–84.0) and 65.8 (64.3–67.3) ng/mL ; GM (95 CI). As methylation efficiency indexes confirmed the relationship between pregnancy/childhood and better methylation efficiency. Archived blood and/or saliva samples were used for single nucleotide polymorphism (SNP) genotyping of arsenic(3+) methyltransferase - AS3MT (rs7085104, rs3740400, rs3740393, rs3740390, rs11191439, rs10748835, rs1046778 and the corresponding AS3MT haplotype) ; methylene tetrahydrofolate reductase - MTHFR (rs1801131, rs1801133) ; aquaporin - AQP 4 and 9 (rs9951307 and rs2414539) ; selenoprotein P1 - SELENOP (rs7579, rs3877899) ; indolethylamine N- methyltransferase - INMT (rs6970396) ; and metallothionein 2A - MT2A (rs28366003). Associations of SNPs with As parameters and urine Se were determined through multiple regression analyses adjusted using appropriate confounders (blood As, plasma Se, ever smoking, etc.). SNPs’ influence on As methylation, defined particularly by the secondary methylation index (SMI), confirmed the ‘protective’ role of minor alleles of six AS3MT SNPs and their haplotype only among non-pregnant women. Among the other investigated genes, the carriers of AQP9 (rs2414539) were associated with more efficient As methylation and higher urine concentration of As and Se among non-pregnant women ; poorer methylation was observed for carriers of AQP4 (rs9951307) among pregnant women and SELENOP (rs7579) among non- pregnant women ; MT2A (rs28366003) was associated with higher urine concentration of AsIII regardless of the pregnancy status ; and INMT (rs6970396) was associated with higher As and Se concentration in non-pregnant women. Among confounders, the strongest influence was observed for plasma Se ; it reduced urine AsIII concentration during pregnancy and increased secondary methylation index among non-pregnant women. In the present study of populations with low As exposure, we observed a few new As–gene associations (particularly with AQPs). More reliable interpretations will be possible after their confirmation in larger populations with higher As exposure levels.