Metabolic profile in workers occupationally exposed to arsenic: role of GST polymorphisms

Arsenic inorganic exposure, metabolism, genetic biomarkers and its impact on human health: A mini-review

Inorganic arsenic species exist in the environment as a result of both natural sources, such as volcanic and geothermal activities, and geological formations, as well as anthropogenic activities, including smelting, exploration of fossil fuels, coal burning, mining, and the use of pesticides. These species deposit in water, rocks, soil, sediments, and the atmosphere. Arsenic-contaminated drinking water is a global public health issue because of its natural prevalence and toxicity. Therefore, chronic exposure to arsenic can have deleterious effect on humans, including cancer and other diseases. This work describes the mechanisms of environmental exposure to arsenic, molecular regulatory factors involved in its metabolism, genetic polymorphisms affecting individual susceptibility and the toxic effects of arsenic on human health (oxidative stress, DNA damage and cancer). We conclude that the role of single nucleotide variants affecting urinary excretion of arsenic metabolites are highly relevant and can be used as biomarkers of the intracellular retention rates of arsenic, showing new avenues of research in this field.

Additive and Interactive Associations of Environmental and Sociodemographic Factors with the Genotypes of Three Glutathione S-Transferase Genes in Relation to the Blood Arsenic Concentrations of Children in Jamaica

Arsenic (As) is a metalloid that has been classified as a xenobiotic with toxic effects on human beings, especially on children. Since the soil in Jamaica contains As, dietary intake is considered the main source of As exposure in Jamaicans. In addition, glutathione S-transferase (GST) genes, including GSTT1, GSTP1, and GSTM1, play an important role in the metabolism of xenobiotics including As in humans. Using data from 375 typically developing children (2–8 years) in Jamaica, we investigated the environmental and sociodemographic factors, as well as their possible interactions with the children’s genotype for GST genes in relation to having a detectable level of blood As concentration (i.e., >1.3 μg/L). Using multivariable logistic regression, we have identified environmental factors significantly associated with blood As concentrations that include a child’s age, parental education levels, and the consumption of saltwater fish, cabbage, broad beans, and avocado (all p < 0.01). Based on the multivariable analysis including gene x environment interactions, we found that among children with the Ile/Ile genotype for GSTP1 Ile105Val, children who consumed avocado had higher odds of having a detectable blood As concentration compared to children who did not eat avocado.

GSTM1 and GSTT1 Null Genotype Polymorphisms and Susceptibility to Arsenic Poisoning: a Meta-analysis

The value of the glutathione S-transferase (GST) null genotype in patients with arsenic poisoning has been recognized, but the conclusions of previous studies remain inconsistent. The objective of this study was to evaluate the relationship between GST mu 1 (GSTM1) and GST theta 1 (GSTT1) null genotype polymorphisms and susceptibility to arsenic poisoning. PubMed, Medline, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), WanFang, and WeiPu databases were systematically searched for publications up to March 31, 2020. The quality of the studies was assessed using the Newcastle-Ottawa Quality Assessment Scale. The pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated to estimate the relationship between GSTM1 and GSTT1 null genotype polymorphisms and arsenic poisoning. The meta-analysis was conducted using STATA 14.0 software. Nine articles with 3324 subjects were included in the meta-analysis. A significantly negative correlation was observed between the GSTM1 null genotype and susceptibility to arsenic poisoning (OR = 0.731; 95% CI: 0.536-0.999; P = 0.049; I² = 70.5%). There was no significant correlation between the GSTT1 null genotype (OR = 1.009; 95% CI: 0.856-1.189; P = 0.915, I² = 36.8%) and GSTM1-GSTT1 double null genotype (OR = 1.105; 95% CI: 0.670-1.822; P = 0.695; I² = 64.7%) and the risk of arsenic poisoning. Egger's and Begg's tests indicated no publishing bias. Compared with controls, individuals with the GSTM1 null genotype were less susceptible to arsenic poisoning. The GSTT1 single null genotype and GSTM1-GSTT1 dual-null genotype were not associated with the risk of arsenic poisoning. The GSTM1 single null genotype may have potential as a genotoxic biomarker to identify individuals who are not prone to arsenic poisoning, and as a reference for guiding the prevention of arsenic poisoning.

As3MT and GST Polymorphisms Influencing Arsenic Metabolism in Human Exposure to Drinking Groundwater

The urinary arsenic metabolites may vary among individuals and the genetic factors have been reported to explain part of the variation. We assessed the influence of polymorphic variants of Arsenic-3-methyl-transferase and Glutathione-S-transferase on urinary arsenic metabolites. Twenty-two groundwater wells for human consumption from municipalities of Colombia were analyzed for assessed the exposure by lifetime average daily dose (LADD) (µg/kg bw/day). Surveys on 151 participants aged between 18 and 81 years old were applied to collect demographic information and other factors. In addition, genetic polymorphisms (GSTO2-rs156697, GSTP1-rs1695, As3MT-rs3740400, GSTT1 and GSTM1) were evaluated by real time and/or conventional PCR. Arsenic metabolites: As^III, As^V, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) were measured using HPLC-HG-AFS. The influence of polymorphic variants, LADD and other factors were tested using multivariate analyses. The median of total arsenic concentration in groundwater was of 33.3 μg/L and the median of LADD for the high exposure dose was 0.33 µg/kg bw/day. Univariate analyses among arsenic metabolites and genetic polymorphisms showed MMA concentrations higher in heterozygous and/or homozygous genotypes of As3MT compared to the wild-type genotype. Besides, DMA concentrations were lower in heterozygous and/or homozygous genotypes of GSTP1 compared to the wild-type genotype. Both DMA and MMA concentrations were higher in GSTM1-null genotypes compared to the active genotype. Multivariate analyses showed statistically significant association among interactions gene-gene and gene-covariates to modify the MMA and DMA excretion. Interactions between polymorphic variants As3MT*GSTM1 and GSTO2*GSTP1 could be potential modifiers of urinary excretion of arsenic and covariates as age, LADD, and alcohol consumption contribute to largely vary the arsenic individual metabolic capacity in exposed people.

GSTP1 rs1138272 Polymorphism Affects Prostate Cancer Risk

Background and Objectives: One of the most frequent genetic alterations reported to date in prostate cancer (PC) is aberrant methylation of glutathione transferase P1 (GSTP1). Taking into consideration the involvement of oxidative stress in PC pathogenesis and recent advances in scientific understanding of the role of GSTP1*Ala114Val rs1138272 polymorphism in carcinogenesis, we hypothesized that this single-nucleotide polymorphism (SNP) influences the risk of PC independently of, or in combination with, other GST polymorphisms, including GSTP1*IIe105Val rs1695 or GSTM1 and GSTT1 deletion polymorphisms. Materials and Methods: Genotyping was performed in 237 PC cases and in 236 age-matched controls by multiplex polymerase chain reaction (PCR) for deletion of GST polymorphisms and by quantitative PCR for SNPs. Results: We found that carriers of either GSTP1*Val (rs1138272) or GSTP1*Val (rs1695) variant alleles had a PC risk compared to individuals with both referent alleles (OR = 4.93, 95%CI: 2.89–8.40, p < 0.001 and OR = 1.8, 95%CI: 1.19–2.73, p = 0.006, respectively). Additionally, in a haplotype analysis we found that individuals with GSTP1*C haplotype, represented by both variant alleles (GSTP1*Val rs1695 + GSTP1*Val rs1138272), had a 5.46 times higher risk of PC development compared to individuals with the most frequent haplotype (95%CI = 2.56–11.65, p < 0.001), suggesting a potential role of those variants in PC susceptibility. A regression analysis on the number of risk-associated alleles per individual (GSTM1*active, GSTT1*null, GSTP1*Val rs1695 and GSTP1*Val rs1138272) showed a significant increase in the risk of developing PC, from 3.65-fold in carriers of two risk alleles (95%CI = 1.55–8.61, p = 0.003) to an approximately 12-fold increase in carriers of all four risk alleles (95%CI = 3.05–44.93, p < 0.001). Conclusion: Prostate cancer may be influenced by multiple glutathione transferase (GST) polymorphic genes, especially GSTP1, highlighting the role of gene–gene interactions in human susceptibility to this cancer.

Metal Biomonitoring and Comparative Assessment in Urine of Workers in Lead-Zinc and Steel-Iron Mining and Smelting

The exposure of heavy metals (lead (Pb), cadmium (Cd), copper (Cu), nickel (Ni), and metalloid arsenicals) and their effects on workers' health from a lead-zinc mine (145 workers) and a steel smelting plant (162 workers) was investigated. Information on subject characteristics was obtained through a questionnaire. We determined the urinary levels of Pb, Cd, Cu, Ni, and arsenicals (including inorganic arsenic (iAs), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA), as were 8-hydroxydeoxyguanosine (8-OHdG) and cystatin C. Lead-zinc mine foundry workers had significantly higher concentrations of urinary Pb, Cd, Cu, Ni, iAs, and MMA than did steel smelting plant workers. Individuals who had consumed seafood in the previous 3 days had higher concentrations of urinary Ni than did individuals who had not consumed seafood. The urinary Cd concentrations in the two groups of factory workers may have been affected by daily smoking. There was no significant difference in urinary 8-OHdG between workers from the lead-zinc mine foundry and the steel smelting plant. Urinary Pb and Cd had significant positive linear dose-dependent effects on 8-OHdG. Urinary cystatin C, a sensitive biological indicator reflecting early renal damage, was found at higher levels in lead-zinc mine workers than in steel smelting plant workers. Binary logistic regression analysis showed that age and urinary Cd were significantly associated with urinary cystatin C. These results indicated that workers from lead-zinc mines may be exposed to higher levels of heavy metals which could lead to greater risk of kidney damage.

Arsenic exposure, profiles of urinary arsenic species, and polymorphism effects of glutathione-s-transferase and metallothioneins

This study assessed the effects of polymorphic variants of gutathione-S-transferase and metallothioneins on profiles of urinary arsenic species. Drinking groundwater from Margarita and San Fernando, Colombia were analyzed and the lifetime average daily dose (LADD) of arsenic was determined. Specific surveys were applied to collect demographic information and other exposure factors. In addition, GSTT1-null, GSTM1-null, GSTP1-rs1695 and MT-2A-rs28366003 genetic polymorphisms were evaluated, either by direct PCR or PCR-RFLP. Urinary speciated arsenic concentrations were determined by HPLC-HG-AFS for species such as As^III, As^V, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and total urinary As (TuAs). Primary methylation index (PMI) and secondary methylation index (SMI) were also calculated as indicators of the metabolic capacity. Polymorphisms effects were tested using multivariate analysis, adjusted by potential confounders. The As concentrations in groundwater were on average 34.6 ± 24.7 μg/L greater than the WHO guideline for As (10 μg/L). There was a correlation between As concentrations in groundwater and TuAs (r = 0.59; p = 0.000). Urinary inorganic arsenic (%InAs) was associated with GSTP1, LADD, GSTP1*Age, GSTP1*alcohol consumption (r² = 0.43; likelihood-ratio test, p = 0.000). PMI was associated with sex (r² = 0.20; likelihood-ratio test, p = 0.007). GSTP1 (AG + GG) homozygotes/heterozygotes could increase urinary %InAs and decrease the PMI ratio in people exposed to low and high As from drinking groundwater. Therefore, the explanatory models showed the participation of some covariates that could influence the effects of the polymorphisms on these exposure biomarkers to As.

In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment

Arsenic (As) is the most frequently occurring contaminant on the priority list of hazardous substances, which lists substances of greatest public health concern to people living at or near U.S. National Priorities List site. Accurate assessment of human health risks from exposure to As-contaminated soils depends on estimating its bioavailability, defined as the fraction of ingested As absorbed across the gastrointestinal barrier and available for systemic distribution and metabolism. Arsenic bioavailability varies among soils and is influenced by site-specific soil physical and chemical characteristics and internal biological factors. This review describes the state-of-the science that supports our understanding of oral bioavailability of soil As, the methods that are currently being explored for estimating soil As relative bioavailability (RBA), and future research areas that could improve our prediction of the oral RBA of soil As in humans. The following topics are addressed: (1) As soil geochemistry; (2) As toxicology; (3) in vivo models for estimating As RBA; (4) in vitro bioaccessibility methods; and (5) conclusions and research needs.

Strain differences in arsenic-induced oxidative lesion via arsenic biomethylation between C57BL/6J and 129X1/SvJ mice

Arsenic is a common environmental and occupational toxicant with dramatic species differences in its susceptibility and metabolism. Mouse strain variability may provide a better understanding of the arsenic pathological profile but is largely unknown. Here we investigated oxidative lesion induced by acute arsenic exposure in the two frequently used mouse strains C57BL/6J and 129X1/SvJ in classical gene targeting technique. A dose of 5 mg/kg body weight arsenic led to a significant alteration of blood glutathione towards oxidized redox potential and increased hepatic malondialdehyde content in C57BL/6J mice, but not in 129X1/SvJ mice. Hepatic antioxidant enzymes were induced by arsenic in transcription in both strains and many were higher in C57BL/6J than 129X1/SvJ mice. Arsenic profiles in the liver, blood and urine and transcription of genes encoding enzymes involved in arsenic biomethylation all indicate a higher arsenic methylation capacity, which contributes to a faster hepatic arsenic excretion, in 129X1/SvJ mice than C57BL/6J mice. Taken together, C57BL/6J mice are more susceptible to oxidative hepatic injury compared with 129X1/SvJ mice after acute arsenic exposure, which is closely associated with arsenic methylation pattern of the two strains.

Association between polymorphisms in arsenic metabolism genes and urinary arsenic methylation profiles in girls and boys chronically exposed to arsenic

Disease manifestations or susceptibilities often differ among individuals exposed to the same concentrations of arsenic (As). These differences have been associated with several factors including As metabolism, sex, age, genetic variants, nutritional status, smoking, and others. This study evaluated the associations between four As metabolism-related gene polymorphisms/null genotypes with urinary As methylation profiles in girls and boys chronically exposed to As. In a total of 332 children aged 6-12 years, the frequency of AS3MT, GSTO1, GSTT1, and GSTM1 polymorphisms/null genotypes and As urinary metabolites were measured. The results revealed that total As and monomethyl metabolites of As (MMA) levels were higher in boys than in girls. No differences in the frequency of the evaluated polymorphisms were found between girls and boys. In AS3MT-Met287Thr carriers, %MMA levels were higher and second methylation levels (defined as dimethylarsinic acid divided by MMA) were lower. In children with the GSTM1 null genotype, second methylation levels were higher. In boys, a positive association between the AS3MT-Met287Thr polymorphism with %MMA and between the GSTO1-Glu155del and As(v) was found; whereas, a negative relationship was identified between AS3MT-Met287Thr and second methylation profiles. In girls, a positive association was found between the GSTO1-Ala140Asp polymorphism with second methylation levels. In conclusion, our data indicate that gender, high As exposure levels, and polymorphisms in the evaluated genes negatively influenced As metabolism. Environ. Mol. Mutagen. 57:516-525, 2016. © 2016 Wiley Periodicals, Inc.

Influence of MRP1 G1666A and GSTP1 Ile105Val genetic variants on the urinary and blood arsenic levels of Turkish smelter workers

To understand the cellular mechanisms responsible for arsenic metabolism and transport pathways plays a fundamental role in order to prevent the arsenic-induced toxicity. The effect of MRP1 G1666A and GSTP1 Ile105Val polymorphisms on blood and urinary arsenic levels were determined in 95 Turkish smelter workers. Blood and urinary arsenic concentrations were measured by GF-AAS with Zeeman correction and gene polymorphisms were investigated by PCR-RFLP method. The mean blood and urinary arsenic levels were 21.60±12.28μg/L and 5.58±4.37μg/L, respectively. A significant association between MRP1 1666A allele and urinary arsenic levels was found (p=0.001). GSTP1 Ile105Val polymorphism was detected not to be associated with either blood or urinary arsenic levels (p=0.384, p=0.440, respectively). Significant association was also detected between MRP1A(-)/GSTP1Val(-) genotypes and urinary arsenic levels (p=0.001). This study suggested that MRP1 G1666A alone and, also, combined with GSTP1 Ile105Val were associated with inter-individual variations in urinary arsenic levels, but not with blood arsenic levels.

Non-monotonic relationships between arsenic and selenium excretion and its implication on arsenic methylation pattern in a Bangladeshi population

The toxicity of arsenic differs markedly between individuals and populations, which might be related to the metabolism (methylation) of inorganic arsenic (As), as well as the selenium (Se) nutritional status. Urinary excretion of As (u-As) and Se (u-Se) was examined in an adult population (n=128) living in an As-contaminated area in Bangladesh. Although there was a significant negative correlation between u-Se and u-As (median 137; range 49-927 μg/g creatinine), closer examination revealed a non-monotonous relationship between them. A quadratic curve with an axis of As at 155 μg/g Cre gave a better fit, and u-As and u-Se were positively or negatively correlated depending on whether the As concentration was lower or higher than 155 μg As/g Cre, respectively. Likewise, the relationships between the As methylation pattern and glutathione-S-transferase (GST) polymorphism, body mass index (BMI), and u-Se differed depending on the u-As range; i.e., higher or lower than 155 μg/g Cre. Although we did not determine the causal mechanism for these observations, the non-monotonic relationship between As exposure and the variables examined suggested the existence of a threshold at which the handling of As by human body is qualitatively changed. The possible importance of Se nutrition for As toxicity is also discussed.

Metals exposure and risk of small-for-gestational age birth in a Canadian birth cohort: The MIREC study

BACKGROUND

Lead, mercury, cadmium and arsenic are some of the most common toxic metals to which Canadians are exposed. The effect of exposure to current low levels of toxic metals on fetal growth restriction is unknown.

OBJECTIVE

The aim of this study was to examine relationships between exposure to lead, mercury, cadmium and arsenic during pregnancy, and risk of small for gestational age (SGA) birth.

METHODS

Lead, mercury, cadmium and arsenic levels were measured in blood samples from the first and third trimesters in 1835 pregnant women from across Canada. Arsenic species in first trimester urine were also assessed. Relative risks and 95% confidence intervals were estimated using log binomial multivariate regression. Important covariates including maternal age, parity, pre-pregnancy BMI, and smoking, were considered in the analysis. An exploratory analysis was performed to examine potential effect modification of these relationships by single nucleotide polymorphisms (SNPs) in GSTP1 and GSTO1 genes.

RESULTS

No association was found between blood lead, cadmium or arsenic and risk for SGA. We observed an increased risk for SGA for the highest compared to the lowest tertile of exposure for mercury (>1.6 µg/L, RR=1.56.; 95% CI=1.04-2.58) and arsenobetaine (>2.25 µg/L, RR=1.65; 95% CI=1.10-2.47) after adjustment for the effects of parity and smoking. A statistically significant interaction was observed in the relationship between dimethylarsinic acid (DMA) levels in urinary arsenic and SGA between strata of GSTO1 A104A (p for interaction=0.02). A marginally significant interaction was observed in the relationship between blood lead and SGA between strata of GSTP1 A114V (p for interaction=0.06).

CONCLUSIONS

These results suggest a small increase in risk for SGA in infants born to women exposed to mercury and arsenic. Given the conflicting evidence in the literature this warrants further investigation in other pregnant populations.

Associations between the polymorphisms of GSTT1, GSTM1 and methylation of arsenic in the residents exposed to low-level arsenic in drinking water in China

We carry out a study to analyze the relation between polymorphisms of GSTT1, GSTM1 and the capacity of arsenic methylation in a human population exposed to arsenic in drinking water. 230 randomly chose subjects were divided into four subgroups based on the arsenic levels, and then the associations between the polymorphisms of GSTT1, GSTM1 and methylation of arsenic were investigated. The levels of inorganic arsenic (iAs), monomethylated arsenic (MMA), dimethylated arsenic (DMA) and total arsenic (TAs) in urine were higher in males than that in females. Moreover, the levels of iAs and TAs in urine in the subjects with genotype of GSTM1(+) were significantly higher than those with GSTM1(-); the level of DMA in the subjects with GSTT1(+) and GSTM1(+) were higher than those with GSTT1(-) and GSTM1(-), although it is not statistically significant. Secondary methylation index (SMI) was significantly higher in the subjects with genotype of GSTT1(+) than those with GSTT1(-). The levels of TAs in urine, together with the genotypes of GSTT1/GSTM1 were associated with the levels of MMA and DMA. Our results suggested that the polymorphisms of GSTT1 and GSTM1 were associated with the methylation of arsenic, especially the levels of DMA and SMI.

Biological monitoring and the influence of genetic polymorphism of As3MT and GSTs on distribution of urinary arsenic species in occupational exposure workers

Purpose

To examine the differences in urinary arsenic metabolism patterns in men affected by occupational exposure, we performed a study on 149 participants—workers of a copper mill and 52 healthy controls without occupational exposure. To elucidate the role of genetic factors in arsenic (As) metabolism, we studied the associations of six polymorphisms: As3MT Met287Thr (T>C) in exon 9; As3MT A>G in 5′UTR; As3MT C>G in intron 6; As3MT T>G in intron 1; GSTP1 Ile105Val and GSTO2 T>C.

Methods

Air samples were collected using individual samplers during work shift. Urine samples were analyzed for total arsenic and arsenic chemical forms (As^III; As^V, MMA, DMA, AsB) using HPLC–ICP-MS. A specific polymerase chain reaction was done for the amplification of exons and flanking regions of As3MT and GSTs.

Results

The geometric mean arsenic concentrations in the air were 27.6 ± 4.9 µg/m³. A significant correlation (p < 0.05) was observed between arsenic in air and sum of iAs +MMA and iAs. As3MT (rs3740400) GG homozygotes showed significantly (p < 0.05) higher %iAs (21.8 ± 2.0) in urine than GC+CC heterozygotes (16.0 ± 2.1). A strong association between the gene variants and As species in urine was observed for GSTO2 (rs156697) polymorphism.

Conclusions

The findings of the study point out that the concentration of iAs or the sum of iAs + MMA in urine can be a reliable biological indicator of occupational exposure to arsenic. This study demonstrates that As3MT and/or GSTs genotype may influence As metabolism. Nevertheless, further studies investigating genetic polymorphism in occupational conditions are required.

The factors influencing urinary arsenic excretion and metabolism of workers in steel and iron smelting foundry

In order to evaluate the degree of arsenic (As) exposure and the factors influencing urinary As excretion and metabolism, 192 workers from a steel and iron smelting plant, with different type of work in production such as roller, steel smelting, iron smelting and metallic charge preparation, were recruited. Information about characteristics of each subject was obtained by questionnaire and inorganic As (iAs), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) in urine were determined. The results showed that steel smelters had significantly higher concentrations of DMA and total As (TAs) than rollers and metallic charge preparation workers, and iron and steel smelters had a higher value of primary methylation index and lower proportion of the iAs (iAs%) than rollers and metallic charge preparation workers. In steel smelters, urinary As level exceeded the biological exposure index (BEI) limit for urinary As of 35 μg/l by 65.52%, and higher than metallic charge preparation workers (35.14%). The individuals consumed seafood in recent 3 days had a higher TAs than the individuals without seafood consumption. Multivariate logistic regression analysis showed that different jobs, taken Chinese medicine of bezoar and seafood consumption in recent 3 days were significantly associated with urinary TAs exceeded BEI limit value 35 μg/l. Our results suggest that workers in steel and iron smelting plant had a lower level of As exposure, and seafood consumption and taking Chinese medicine of bezoar also could increase the risk of urinary TAs exceeded BEI limit value.

Arsenic exposure in Latin America: biomarkers, risk assessments and related health effects

In Latin America, several regions have a long history of widespread arsenic (As) contamination from both natural and anthropological sources. Yet, relatively little is known about the extent of As exposure from drinking water and its related health consequences in these countries. It has been estimated that at least 4.5 million people in Latin America are chronically exposed to high levels of As (>50 μg/L), some to as high as 2000 μg/L--200 times higher than the World Health Organization (WHO) provisional standard for drinking water. We conducted a systematic review of 82 peer reviewed papers and reports to fully explore the current understanding of As exposure and its health effects, as well as the influence of genetic factors that modulate those effects in the populations of Latin America. Despite some methodological limitations, these studies suggested important links between the high levels of chronic As exposure and elevated risks of numerous adverse health outcomes in Latin America--including internal and external cancers, reproductive outcomes, and childhood cognitive function. Several studies demonstrated genetic polymorphisms that influence susceptibility to these and other disease states through their modulation of As metabolism, with As methyltransferase (AS3MT), glutathione S-transferase (GST), and genes of one-carbon metabolism being specifically implicated. While the full extent and nature of the health burden are yet to be known in Latin America, these studies have significantly enriched knowledge of As toxicity and led to subsequent research. Targeted future studies will not only yield a better understanding of the public health impact of As in Latin America populations, but also allow for effective and timely mitigation efforts.

Variants of glutathione s-transferase pi 1 exhibit differential enzymatic activity and inhibition by heavy metals

Nonsynonymous single nucleotide polymorphisms in glutathione s-transferase pi 1 (GSTP1; Ile/Val 105, Ala/Val 114) have been associated with altered toxicant metabolism in epidemiological cohorts. We explored the impact of GSTP1 genotype on enzyme kinetics and heavy metal inhibition in vitro. Four GSTP1 allozymes (105/114: Ile/Ala, Val/Ala, Ile/Val, Val/Val) were expressed in and purified from Escherichia coli. Enzyme activity assays quantifying the rate of glutathione conjugation with 1-chloro-2,4-dinitrobenzene (CDNB) revealed significant differences in kinetic parameters depending on genotype (p<0.01). Allozymes with Ile105 had better catalytic efficiency and greater affinity for CDNB (mean ± SEM: Ile105 Ala114 K(m)=0.33 ± 0.07 mM vs. Val105 Ala114 K(m)=1.15 ± 0.07 mM). Inhibition of GSTP1 activity by heavy metals was assessed following treatment with mercury (inorganic-HgCl(2), methylmercury-MeHg), selenium, cadmium, lead, arsenic, and manganese. All allozymes were inhibited by HgCl(2) (IC(50) range: 24.1-172 μM), MeHg (93.9-480 μM), and selenium (43.7-62.8 μM). Genotype significantly influenced the potency of mercury with GSTP1 Ile105 Val114 the least sensitive and Val105 Ala114 the most sensitive to inhibition by HgCl(2) and MeHg. Overall, genotype of two nonsynonymous polymorphisms in GSTP1 influenced enzyme kinetics pertaining to an electrophilic substrate and inhibition by two mercury species.

Individual variations in arsenic metabolism in Vietnamese: the association with arsenic exposure and GSTP1 genetic polymorphism

We investigated the association of As exposure and genetic polymorphism in glutathione S-transferase π1 (GSTP1) with As metabolism in 190 local residents from the As contaminated groundwater areas in the Red River Delta, Vietnam. Total As concentrations in groundwater ranged from <0.1 to 502 μg l(-1). Concentrations of dimethylarsinic acid (DMA(V)), monomethylarsonic acid (MMA(V)), and arsenite (As(III)) in human urine were positively correlated with total As levels in the groundwater, suggesting that people in these areas may be exposed to As through the groundwater. The concentration ratios of urinary As(III)/arsenate (As(V)) and MMA(V)/inorganic As (IA; As(III) + As(V))(M/I), which are indicators of As metabolism, increased with the urinary As level. Concentration and proportion of As(III) were high in the wild type of GSTP1 Ile105Val compared with the hetero type, and these trends were more pronounced in the higher As exposure group (>56 μg l(-1) creatinine in urine), but not in the lower exposure group. In the high As exposure group, As(III)/As(V) ratios in the urine of wild type of GSTP1 Ile105Val were significantly higher than those of the hetero type, while the opposite trend was observed for M/I. These results suggest that the excretion and metabolism of IA may depend on both the As exposure level and the GSTP1 Ile105Val genotype.

Exposure, metabolism, and health effects of arsenic in residents from arsenic-contaminated groundwater areas of Vietnam and Cambodia: a review

In this review, we summarize the current knowledge on exposure, metabolism, and health effects of arsenic (As) in residents from As-contaminated groundwater areas of Vietnam and Cambodia based on our findings from 2000 and other studies. The health effects of As in humans include severe gastrointestinal disorders, hepatic and renal failure, cardiovascular disturbances, skin pigmentation, hyperkeratosis, and cancers in the lung, bladder, liver, kidney, and skin. Arsenic contamination in groundwater is widely present at Vietnam and Cambodia and the highest As levels are frequently found in groundwater from Cambodia. Sand filter system can reduce As concentration in raw groundwater. The results of hair and urine analyses indicate that residents from these As-contaminated areas are exposed to As. In general, sex, age, body mass index, and As exposure level are significantly associated with As metabolism. Genetic polymorphisms in arsenic (+III) methyltransferase and glutathione-S-transferase isoforms may be influenced As metabolism and accumulation in a Vietnamese population. It is suggested oxidative DNA damage is caused by exposure to As in groundwater from residents in Cambodia. An epidemiologic study on an association of As exposure with human health effects is required in these areas.

Association between GSTO2 polymorphism and the urinary arsenic profile in copper industry workers

Two members of the recently identified Omega class glutathione S-transferase enzymes (GSTO1 and GSTO2) have been proposed to play a role in the response to arsenic exposure. Therefore, polymorphisms in these genes could be related with variations in the arsenic excretion profile and, consequently, with the individual response to chronic exposure. Exons and flanking regions of GSTO2 gene have been screened in two different ethnic groups (20 Europeans and 20 Chilean Indians), and the urinary arsenic patterns and the GSTO2 Asn142Asp polymorphism have been investigated in 207 copper mine workers occupationally exposed to arsenic. Three polymorphisms of GSTO2 already described were detected in Europeans and Chilean Indians, although with significant different allele frequencies. The genotyping for the Asn142Asp polymorphism revealed that almost no significant association exists between this change and the arsenic excretion profile. However, 142Asp change seems to be correlated with an increase in DMA excretion after age and total urinary arsenic adjustment (OR=3.61; P=0.05). Altogether, our findings indicate that ethnical differences should be taken into account for correlation studies between GST Omega polymorphisms and arsenic susceptibility, and that the 142Asp allozyme could modulate arsenic biotransformation and thereby arsenic toxicity.

Polymorphism of glutathione S-transferase (GST) variants and its effect on distribution of urinary arsenic species in people exposed to low inorganic arsenic in tap water: an exploratory study

Glutathione S-tranferases (GST) are multigenic enzymes that have been associated with arsenic metabolism. The objective of this study was to evaluate the relationship between polymorphic variants of GST and urinary concentration of arsenic species in people exposed to low levels of arsenic. A cross-sectional study among 66 nonoccupationally exposed subjects, living in the city of Antofagasta, Chile. Polymorphic variants were analyzed by polymerase chain reaction (PCR) and arsenic species was determined by atomic absorption spectrometry. The effect of GST variants on arsenic concentration was evaluated using univariate and covariate-adjusted regressions. For both GSTT1 and GSTM1 there were no significant differences in detected arsenic relative species between carriers of the active and null polymorphic variants. There was nondefinitive evidence that polymorphic variants of GST play a role in arsenic metabolism in sample of the Chilean subjects studied.

Interactions of chemical carcinogens and genetic variation in hepatocellular carcinoma

In the etiology of hepatocellular carcinoma (HCC), in addition to hepatitis B virus and hepatitis C virus infections, chemical carcinogens also play important roles. For example, aflatoxin B(1) (AFB(1)) epoxide reacts with guanine in DNA and can lead to genetic changes. In HCC, the tumor suppressor gene p53 codon 249 mutation is associated with AFB(1) exposure and mutations in the K-ras oncogene are related to vinyl chloride exposure. Numerous genetic alterations accumulate during the process of hepatocarcinogenesis. Chemical carcinogen DNA-adduct formation is the basis for these genetic changes and also a molecular marker which reflects exposure level and biological effects. Metabolism of chemical carcinogens, including their activation and detoxification, also plays a key role in chemical hepatocarcinogenesis. Cytochrome p450 enzymes, N-acetyltransferases and glutathione S-transferases are involved in activating and detoxifying chemical carcinogens. These enzymes are polymorphic and genetic variation influences biological response to chemical carcinogens. This genetic variation has been postulated to influence the variability in risk for HCC observed both within and across populations. Ongoing studies seek to fully understand the mechanisms by which genetic variation in response to chemical carcinogens impacts on HCC risk.

Genetic polymorphism of As3MT and delayed urinary DMA excretion after organic arsenic intake from oyster ingestion

Organic arsenic intake from seafood is one of the major arsenic exposure routes among the general population. However, organic arsenic metabolism in the human body is not yet clear. The goal of this study was to explore the effects of genetic polymorphisms of human PNP, As3MT and GSTO1 on organic arsenic metabolism among study subjects after oyster ingestion. During the one-week dietary controlled study, fifty study subjects were provided all their daily meals without seafood, except for two designated amounts of oyster given on the fourth day. First morning voided urine samples were provided by the study subjects for 7 consecutive days and analyzed with HPLC-ICP-MS for As(3+), As(5+), monomethylarsonic acid, and dimethylarsinic acid (DMA). Blood samples were collected later for genetic polymorphisms analysis of PNP, As3MT and GSTO1. Study subjects were categorized into "fast-" (n = 32), "medium-" (n = 13) and "slow-metabolizing" (n = 5) groups based on the number of days after ingestion needed for each subject's urinary DMA level reaching peak. Allele frequencies of single nucleotide polymorphisms (SNP) in intron 6 (G/C, p = 0.024) and in intron 10 (T/C, p = 0.039) of As3MT were significantly associated with the urinary DMA excretion. General estimating equation model analysis indicated that the variants of SNP (G>C) in intron 6 and SNP (T > C) in intron 10 of As3MT were respectively associated with higher or lower urinary DMA level by approximately 9 microg L(-1). As3MT was suggested to be one of the major factors affecting the metabolism of dietary organic arsenic in terms of urinary DMA level.

Genetic variations associated with interindividual sensitivity in the response to arsenic exposure

People are exposed to arsenic compounds environmentally, occupationally or therapeutically. In some areas, where arsenic is present in high proportions in the drinking water, this exposure represents an important health concern. Chronic exposure to arsenic leads to hyperkeratosis and loss of skin pigmentation, as well as to significant increases of different types of cancer in skin, lung, bladder and liver; in addition, other pathologies, such as vascular diseases, hepatotoxicity and diabetes, have also been related to arsenic exposure. Since high interindividual variability is observed among people exposed to equivalent doses, genetic susceptibility factors have been postulated to be involved. When inorganic arsenic enters into the body it undergoes metabolic conversion, in a process where methylation plays a crucial role. Trivalent forms, both inorganic and organic, are the most toxic and genotoxic and, for this reason, metabolic variations owing to variant alleles in genes involved in such a process have been the aim of several studies. Genes involved in other mechanisms, such as antioxidant defense and DNA-repair lesions, among others, have also been the subject of association studies. A survey of those studies related to individual susceptibility is summarized here. Results with genes involved in folate one-carbon metabolism and in arsenic transport across the cell membrane provide promising data for future studies.

Variations in arsenic methylation capacity and oxidative DNA lesions over a 2-year period in a high arsenic-exposed population

OBJECTIVE

To assess long-term variations in arsenic methylation and oxidative DNA lesions of chronic high arsenic-exposed populations.

METHODS

A follow-up study was conducted in 64 chronic high arsenic-exposed subjects from 2004 to 2006. Urinary arsenic species and 8-hydroxydeoxyguanine were measured.

RESULTS

Percentages of urinary inorganic arsenic, monomethylarsonate and urinary 8-hydroxydeoxyguanine (8-OHdG) level were significantly higher, but the percentage of dimethylarsinate, the primary methylation index (PMI) and secondary methylation index (SMI) was lower in the ninth year of arsenic exposure compared with the seventh year. Substantial differences in relative arsenic methylation capacity were observed between the seventh and ninth year. Percentages of arsenic species, PMI and SMI were significantly correlated between siblings, and between parents and children.

CONCLUSIONS

Arsenic methylation may decrease, but oxidative DNA lesions may increase with the increase of cumulative arsenic exposure level. Both genetic and environmental factors may contribute to variability in arsenic methylation.

Evaluation of micronucleus frequencies in blood lymphocytes from smelting plant workers exposed to arsenic

Arsenic is a world health problem due to the seriousness of its effects, mainly related with the increase of cancer. In Chile, the geological characteristics of the northern region, associated with the development of the copper mining and smelting activities, have contributed to increase the environmental levels of arsenic. This study has been conducted to investigate the relationship between arsenic occupational exposure and genotoxic effects in smelting plant workers. To determine the genotoxic risk related to the increase of cancer among the chronically exposed population, the frequency of micronuclei in blood (BNMN) has been evaluated. The study was carried out in a total of 207 men, divided into three groups: an exposed group of 105 individuals working in a smelting plant, an internal reference group with 52 employees at the same mine but in the administrative area, and an external reference group of 50 workers from another copper mine where no significant levels of arsenic were detected. As expected, differences between arsenic levels in urine have been detected between groups, with the exposed group being the one with a higher level of total arsenic in urine, followed by the internal reference group. Despite that, no significant differences in micronuclei frequencies in lymphocytes were detected among these groups.

Polymorphism of glutathione transferase Omega 1 in a population exposed to a high environmental arsenic burden

OBJECTIVES AND METHODS

The aim of this study was to investigate genetic variation in glutathione transferase omega 1 (GSTO1-1) in Atacameños, an indigenous population from Chile that has been exposed to environmental arsenic for many generations. GSTO1-1 is thought to catalyse the rate-limiting step in the biotransformation of arsenic in humans and may modulate the response of cancer patients to arsenic trioxide therapy. Allele frequencies were determined by PCR-based methods and a polymorphic variant (GSTO1-1 Val236) was expressed in Escherichia coli and functionally characterized. Urinary arsenic profiles were determined by inductive coupled plasma/mass spectrometry.

RESULTS

A novel allele resulting in an Ala236Val substitution that has not been functionally characterized was detected in Atacameños and Chilean participants at a frequency of 0.033 and 0.009, respectively. The Val236 isoenzyme has diminished specific activity (10-20%) with a range of substrates. This loss of activity appears to result from a decrease in the kcat. The Val236 variant is also unstable and rapidly loses activity during purification or when heated at 45 degrees C. The percent of inorganic arsenic in the urine of 205 Chilean participants showed a bimodal distribution that was not associated with the Ala140Asp, Glu155del or Ala236Val polymorphisms in GSTO1-1.

CONCLUSION

It is likely that heterozygotes inheriting the Val236 variant subunit would have a partial deficiency of GSTO1-1 activity. Despite their effects on enzyme function the known variants of GSTO1-1 do not appear to explain the observed variability in the excretion of inorganic arsenic.

Role of the Met(287)Thr polymorphism in the AS3MT gene on the metabolic arsenic profile

Chronic exposure to arsenic involves a biotransformation process leading to the excretion of methylated metabolites, such as monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), as well as the parental inorganic species (As(III) and As(V)). Inter-individual variations in arsenic biotransformation have been reported and polymorphisms affecting the genes involved in arsenic biotransformation have been considered as one of the plausible explanations for this variation. Coding and flanking regions of the human arsenic methyltransferase (AS3MT) gene have been analysed in 50 Chilean men exposed to arsenic. Nine polymorphisms were found, including one non-synonymous SNP at exon 9 (Met(287)Thr) with an allele frequency of 0.14. Other four changes occurred at potentially regulatory regions: a variable number of tandem repeats (VNTR) at the 5'-untranslated region (UTR5'), a G/C substitution at the promoter region, a GC/AT substitution inside the VNTR, and a G/A substitution at the 3'-untranslated region (UTR3'). The rest of polymorphisms were located in non-coding regions: a T/G substitution in intron 1, a CTC deletion in intron 2 and a TTT and ATT insertions in intron 5. In addition, the individual urinary arsenic profiles were analysed. Our results indicate that genetic polymorphisms in AS3MT contribute to inter-individual variation in arsenic biotransformation and, therefore, may contribute to inter-individual variations in risk of arsenic toxicity and arsenic carcinogenesis. Individuals with the Met(287)Thr polymorphism displayed increased arsenic methylation and might be at increased risk for toxic and genotoxic effects of arsenic exposure if, as the classical arsenic metabolic pathway indicates, methylation enhances toxicity.

Consumption of folate-related nutrients and metabolism of arsenic in Bangladesh

BACKGROUND

Inorganic arsenic (InAs) is metabolized to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and this methylation facilitates urinary arsenic excretion. Previous studies suggest that persons with more complete methylation, characterized as greater proportions of DMA and lesser proportions of MMA and InAs in urine, have a lower risk of adverse arsenic-related health outcomes.

OBJECTIVE

The purpose of this study was to examine whether the capacity to methylate arsenic differs by nutrient intake.

DESIGN

Participants were 1016 Bangladeshi adults exposed to arsenic in drinking water. Nutrient intake was assessed with a validated food-frequency questionnaire. Multivariate regression analyses were used to examine associations of nutrients with urinary arsenic metabolite profiles.

RESULTS

In multivariate analyses, higher intakes of cysteine, methionine, calcium, protein, and vitamin B-12 were associated with lower percentages of InAs and higher ratios of MMA to InAs in urine. Higher intakes of niacin (beta=0.22, P=0.02) and choline (beta=0.10, P=0.02) were associated with higher DMA-to-MMA ratios, after adjustment for age, sex, smoking, total urinary arsenic, and total energy intake.

CONCLUSIONS

Findings from the current study show the influence of multiple nutrients on arsenic methylation. In particular, this study highlights the potential importance of dietary intakes of cysteine, methionine, niacin, vitamin B-12, and choline on health effects of arsenic by modulating its metabolism.

Genetic polymorphisms influencing arsenic metabolism: evidence from Argentina

The susceptibility to arsenic-induced diseases differs greatly between individuals, possibly due to interindividual variations in As metabolism that affect retention and distribution of toxic metabolites. To elucidate the role of genetic factors in As metabolism, we studied how polymorphisms in six genes affected the urinary metabolite pattern in a group of indigenous women (n = 147) in northern Argentina who were exposed to approximately 200 microg/L As in drinking water. These women had low urinary percentages of monomethylated As (MMA) and high percentages of dimethylated As (DMA). MMA has been associated with adverse health effects, and DMA has the lowest body retention of the metabolites. The genes studied were arsenic(+III)methyltransferase (AS3MT), glutathione S-transferase omega 1 (GSTO1), 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR), methylenetetrahydrofolate reductase (MTHFR), and glutathione S-transferases mu 1 (GSTM1) and theta 1 (GSTT1). We found three intronic polymorphisms in AS3MT (G12390C, C14215T, and G35991A) associated with a lower percentage of MMA (%MMA) and a higher percentage of DMA (%DMA) in urine. The variant homozygotes showed approximately half the %MMA compared with wild-type homozygotes. These polymorphisms were in strong linkage, with high allelic frequencies (72-76%) compared with other populations. We also saw minor effects of other polymorphisms in the multivariate regression analysis with effect modification for the deletion genotypes for GSTM1 (affecting %MMA) and GSTT1 (affecting %MMA and %DMA). For pregnant women, effect modification was seen for the folate-metabolizing genes MTR and MTHFR. In conclusion, these findings indicate that polymorphisms in AS3MT-and possibly GSTM1, GSTT1, MTR, and MTHFR-are responsible for a large part of the interindividual variation in As metabolism and susceptibility.