Influence of the level of arsenic (As) exposure and the presence of T860C polymorphism in human As urinary metabolic profile

The level of exposure affects the arsenic urinary methylation profile of a population of children

Differences in the As methylation capacity of Argentine children, exposed to different levels of As in drinking water were evaluated, considering the gender and the presence of the As3MT T860C gene polymorphism. Inorganic As (%IAs), monomethylated As (%MMA) and dimethylated As (%DMA), primary methylation index (PMI) and secondary methylation index (SMI) were evaluated and represented the As methylation capacity. Urinary As ranged from 18 to 5106 µg/g creatinine. Comparisons were performed between lowest and highest quartiles of urinary As. The level of exposure was positively related to urinary %MMA and negatively to %DMA and to SMI. Considering the presence of the As3MT T860C polymorphism, the level of exposure increased %MMA, and decreased %DMA and the SMI in carriers of the T/T genotype. SMI OR for T/T carriers was 10.61 (95% CI: 2.16-52.16, p: 0.0036). Regarding the gender, the level of exposure increased %MMA, and decreased %DMA and the SMI in girls and boys. SMI OR for girls was 8.71 (95% CI: 1.48-51.08, p: 0.0165) and for boys, OR: 18.15 (95% CI: 2.03-162.35, p: 0.0095). It was possible to identify the level of exposure as a factor that can modify the influence that other factors have on the methylation of As.

Elevated arsenic exposure and efficient arsenic metabolism in indigenous women around Lake Poopó, Bolivia

Elevated concentrations of inorganic arsenic, one of the most potent environmental toxicants and carcinogens, have been detected in well water around Lake Poopó, Bolivia. This study aimed to assess human exposure to arsenic in villages around Lake Poopó, and also to elucidate whether the metabolism and detoxification of arsenic in this population is as efficient as previously indicated in other Andean areas. We recruited 201 women from 10 villages around Lake Poopó. Arsenic exposure was determined as the sum concentration of arsenic metabolites (inorganic arsenic; monomethylarsonic acid, MMA; and dimethylarsinic acid, DMA) in urine (U-As), measured by HPLC-HG-ICP-MS. Efficiency of arsenic metabolism was assessed by the relative fractions of the urinary metabolites. The women had a wide variation in U-As (range 12-407 μg/L, median 65 μg/L) and a markedly efficient metabolism of arsenic with low %MMA (median 7.7%, range: 2.2-18%) and high %DMA (80%, range: 54-91%) in urine. In multivariable-adjusted linear regression models, ethnicity (Aymara-Quechua vs. Uru), body weight, fish consumption and tobacco smoking were associated with urinary arsenic metabolite fractions. On average, the Uru women had 2.5 lower % (percentage unit) iAs, 2.2 lower %MMA and 4.7 higher %DMA compared with the Aymara-Quechua women. Our study identified several factors that may predict these women's arsenic methylation capacity, particularly ethnicity. Further studies should focus on mechanisms underlying these differences in arsenic metabolism efficiency, and its importance for the risk of arsenic-related health effects.