Chronic Mercury Exposure and GSTP1 Polymorphism in Munduruku Indigenous from Brazilian Amazon

[Exposure to methylmercury and neurodevelopment in Indigenous children: a theoretical model]

Neurodevelopment spans from conception to adulthood, encompassing the growth and maturation of the nervous system. Indigenous children living in the Amazon face several circumstances that can adversely impact their neurodevelopment, including prenatal care, birth conditions, malnutrition, infectious diseases, and socioeconomic challenges. Prenatal exposure to toxic substances configures another determinant influencing neurodevelopment. Exposure to methylmercury is associated with the maternal consumption of contaminated fish. After birth, children continue to undergo exposure by breastfeeding or feeding. This trial aimed to develop a theoretical model to find the determinants of neurodevelopment in the first 1,000 days of life considering prenatal exposure to methylmercury in Indigenous children. The seven steps of the Checklist for Theoretical Report in Epidemiological Studies were followed to elaborate this theoretical model. We offer theoretical-methodological reflections on the dimensions and explanatory variables that highlight how exposure to adverse conditions since intrauterine life worsens in the presence of methylmercury, which can damage human health. This theoretical model is unprecedented in considering the complex causal network involved and contributes to research and actions on maternal and child health.

Cadmium Exposure and Noncommunicable Diseases in Environmentally Exposed Brazilian Population: Cross-Sectional Study without Association of GSTP1 Polymorphism

Cadmium (Cd) is a toxic metal which is harmful to humans and the environment. Cd levels and adverse effects may be associated with genetic polymorphisms in genes involved in its toxicokinetics. This study investigated Cd levels in 198 residents of a condominium in Rio de Janeiro, Brazil, built on industrial steel slag waste and the influence of glutathione S-transferase pi isoform 1 (GSTP1) rs1695 A>G polymorphism. Polymorphism was genotyped using a validated TaqMan assay; Cd levels were measured in blood (BCd) and urine (UCd) by graphite furnace atomic absorption spectrometry. Associations were evaluated by multiple logistic regression, odds ratios (ORs), and 95% confidence intervals (CIs). The mean Cd levels were 0.70 ± 0.20 µg L-1 (BCd), 0.58 ± 0.57 µg L-1 (UCd), and 0.61 ± 0.65 µg g-1 in urine corrected by creatinine (UcCd), and the Cd results were above tolerable levels (BCd > 0.5 µg L-1) in 87.4% of subjects. Higher blood Cd levels (>0.69 µg L-1) were associated with respiratory disease (OR = 2.4; 95%CI = 1.2-5.0), as almost 30% of people with respiratory diseases had higher Cd levels. The GSTP1 rs1695AA genotype frequency was 38.1%, and there were no significant differences between the SNP and Cd levels. High Cd levels and a high prevalence of diseases highlight the importance of implementing public policies and the continuous monitoring of this at-risk population.

The GSTP1 rs1695 Polymorphism Is Associated with Mercury Levels and Neurodevelopmental Delay in Indigenous Munduruku Children from the Brazilian Amazon

Genetic polymorphisms may influence mercury (Hg) toxicity. The aims of this study were to evaluate individual factors, such as the presence of the GSTP1 rs1695 polymorphism, associated with internal Hg dose and child neurodevelopment in indigenous people from the Brazilian Amazon chronically exposed to Hg. Eighty-two indigenous children were clinically evaluated, hair Hg was measured, and the GSTP1 rs1695 polymorphism was genotyped. The mean age was 4.8 years, the median Hg was 5.5 µg/g, and 93.8% of children exceeded the safe limit (2.0 µg/g). Fish consumption was associated with Hg levels (p = 0.03). The GSTP1 rs1695 A>G polymorphism was in the Hardy-Weinberg equilibrium and the highest prevalence of the GSTP1 AA genotype (80%) was found in Sawré Aboy, which had the highest Hg levels (10 µg/g) among the studied villages. The Hg levels tended to increase over the years in males and in carriers of the GSTP1 AA genotype (0.69 µg/g and 0.86 µg/g, respectively). Nine children failed the neurodevelopmental test, all of whom had Hg > 2.0 µg/g, and 88.9% carried the GSTP1 AA or AG genotypes, previously associated with the highest internal Hg doses and neurocognitive disorders. The genetic counseling of this population is important to identify the individuals at greater risk for neurodevelopmental disorders resulting from chronic Hg exposure.

Genomic investigation on genes related to mercury metabolism in Amazonian indigenous populations

Studies have identified elevated levels of mercury in Amazonian Indigenous individuals, highlighting them as one of the most exposed to risks. In the unique context of the Brazilian Indigenous population, it is crucial to identify genetic variants with clinical significance to better understand vulnerability to mercury and its adverse effects. Currently, there is a lack of research on the broader genomic profile of Indigenous people, particularly those from the Amazon region, concerning mercury contamination. Therefore, the aim of this study was to assess the genomic profile related to the processes of mercury absorption, distribution, metabolism, and excretion in 64 Indigenous individuals from the Brazilian Amazon. We aimed to determine whether these individuals exhibit a higher susceptibility to mercury exposure. Our study identified three high-impact variants (GSTA1 rs1051775, GSTM1 rs1183423000, and rs1241704212), with the latter two showing a higher frequency in the study population compared to global populations. Additionally, we discovered seven new variants with modifier impact and a genomic profile different from the worldwide populations. These genetic variants may predispose the study population to more harmful mercury exposure compared to global populations. As the first study to analyze broader genomics of mercury metabolism pathways in Brazilian Amazonian Amerindians, we emphasize that our research aims to contribute to public policies by utilizing genomic investigation as a method to identify populations with a heightened susceptibility to mercury exposure.

Chromosomal Damage, Chromosome Instability, and Polymorphisms in GSTP1 and XRCC1 as Biomarkers of Effect and Susceptibility in Farmers Exposed to Pesticides

In the department of Boyacá, Colombia, agriculture stands as one of the primary economic activities. However, the escalating utilization of pesticides within this sector has sparked concern regarding its potential correlation with elevated risks of genotoxicity, chromosomal alterations, and carcinogenesis. Furthermore, pesticides have been associated with a broad spectrum of genetic polymorphisms that impact pivotal genes involved in pesticide metabolism and DNA repair, among other processes. Nonetheless, our understanding of the genotoxic effects of pesticides on the chromosomes (as biomarkers of effect) in exposed farmers and the impact of genetic polymorphisms (as susceptibility biomarkers) on the increased risk of chromosomal damage is still limited. The aim of our study was to evaluate chromosomal alterations, chromosomal instability, and clonal heterogeneity, as well as the presence of polymorphic variants in the GSTP1 and XRCC1 genes, in peripheral blood samples of farmers occupationally exposed to pesticides in Aquitania, Colombia, and in an unexposed control group. Our results showed statistically significant differences in the frequency of numerical chromosomal alterations, chromosomal instability, and clonal heterogeneity levels between the exposed and unexposed groups. In addition, we also found a higher frequency of chromosomal instability and clonal heterogeneity in exposed individuals carrying the heterozygous GSTP1 AG and XRCC1 (exon 10) GA genotypes. The evaluation of chromosomal alterations and chromosomal instability resulting from pesticide exposure, combined with the identification of polymorphic variants in the GSTP1 and XRCC1 genes, and further research involving a larger group of individuals exposed to pesticides could enable the identification of effect and susceptibility biomarkers. Such markers could prove valuable for monitoring individuals occupationally exposed to pesticides.

NUDT15 and TPMT polymorphisms in three distinct native populations of the Brazilian Amazon

This is the first report of the distribution of TPMT and NUDT15 single nucleotide polymorphisms and metabolic phenotypes associated with cytotoxicity of thiopurine drugs, in indigenous groups of Brazilian Amazon: Munduruku, Paiter-Suruí and Yanomami. The minor allele frequency (MAF) of NUDT15 rs116855232 did not differ significantly across the groups; TPMT rs1800462 was absent, while rs1800460 and rs1142345 were in strong linkage disequilibrium, and 10- and 30-fold more common in Paiter-Suruí. Indeed, the MAFs in Paiter-Surui (0.193 and 0.188) are the largest report globally. The distribution of combined NUDT15/TPMT metabolic phenotypes differed significantly (p < 0.0001) and largely (Cramér´s V = 0.37) across cohorts. This has important pharmacogenetic implications: the Clinical Pharmacogenetics Implementation Consortium recommendations to reduce or consider reduction of thiopurine dose applies to 4.4% Yanomami, 5.6% Munduruku, versus 41% Paiter-Suruí. The proportion of Paiter-Suruí at risk of thiopurine intolerance is 3- to 4-fold higher than any other population worldwide.