Chronic arsenic exposure and urinary 8-hydroxy-2'-deoxyguanosine in an arsenic-affected area in Inner Mongolia, China

Association of urinary arsenic with the oxidative DNA damage marker 8-hydroxy-2 deoxyguanosine: A meta-analysis

BACKGROUND

The International Agency for Research on Cancer has classified arsenic as a class I carcinogen. Oxidative DNA damage is a typical early precursor to recognized malignancies. The most sensitive early independent marker of oxidative DNA damage is believed to be 8-hydroxy-2 deoxyguanosine (8-OHdG). To date, research on the link between urinary arsenic and 8-OHdG has not been consistent.

OBJECTIVE

This study was aimed at exploring the effects of urinary arsenic on 8-OHdG in human urine.

METHODS

A literature search until January 2023 was performed on the PubMed, Cochrane Library, Web of Science, Embase, and Scopus databases through a combination of computer and manual retrieval. Stata 12.0 was used to examine the degree of heterogeneity among included studies. The percentage change and 95 % confidence interval (95 % CI) of 8-OHdG were calculated between populations exposed to different doses. We used a random effect model because the degree of heterogeneity exceeded 50 %. Sensitivity analysis and testing for publication bias were performed.

RESULTS

This meta-analysis included nine studies, most of which were performed in China. After exposure to arsenic, urinary arsenic (per 10 μg/g creatinine increase) was associated with the increased 8-OHdG (% change = 41.49 %, 95 % CI: 19.73 %, 63.25 %). Subgroup analysis indicated that the percentage change in 8-OHdG in urine was more pronounced in people exposed to arsenic <50 μg/L (% change = 24.60 %, 95 % CI: 17.35 %, 37.85 %). In studies using total urinary arsenic content as an indicator, the percentage change in 8-OHdG in urine was more significant (% change = 60.38 %, 95 % CI: 15.08 %, 105.68 %).

CONCLUSION

The 8-OHdG levels in human urine significantly increased after exposure to environmental arsenic, thus suggesting that arsenic exposure is correlated with oxidative DNA damage.

Association of low blood arsenic exposure with level of malondialdehyde among Chinese adults aged 65 and older

High environmental arsenic exposure can increase chronic oxidative stress in experimental studies and in occupational epidemiology studies. Many regulatory agencies have put forth arsenic exposure limits, it is still unclear that whether low environmental arsenic exposure was associated with adverse health outcome in general population. This study aimed to explore the association of low blood arsenic with malondialdehyde in community-dwelling older adults. We used a cross-sectional study of 2384 older adult individuals aged ≥65 years (mean age: 85 years) from the Healthy Aging and Biomarkers Cohort Study in 2017. The median blood arsenic level was 1.41 μg/L. High oxidative stress was categorized according to the 95th percentile of MDA levels (7.47 nmol/mL). Restricted cubic spline models showed that blood arsenic levels were positively associated with malondialdehyde levels (P < 0.01); and the risk of high oxidative stress was no longer significantly increased when blood arsenic level up to 8.74 μg/L. After adjusting for potential confounders, the odds ratios of high oxidative stress for the second, third, and fourth quartiles of blood arsenic were 2.35 (1.11-4.96), 3.87 (1.90-7.91), and 4.18 (2.00-8.72) (P_trend < 0.01), compared with the first quartile. We concluded that even low arsenic exposure was associated with higher risk of oxidative stress, in a nonlinear dose-response.

MiADMSA ameliorate arsenic induced urinary bladder carcinogenesis in vivo and in vitro

BACKGROUND AND PURPOSE

Arsenicosis is a major threat to public health and is a major cause of the development of urinary bladder cancer. Oxidative/ nitrosative stress is one of the key factors for these effects but the involvement of other associated factors is less known. There is a lack of data for the efficacy of chelator against urinary bladder carcinogenesis. The present study demonstrates the early signs of arsenic exposed urinary bladder carcinogenesis and its attenuation by Monoisoamyl dimercaptosuccinic acid (MiADMSA).

METHODS

Male rats were exposed to 50 ppm of sodium arsenite and dimethylarsinic acid (DMA) via drinking water for 18 weeks and treated with MiADMSA (50 mg/kg, orally once daily for 5 days) for 3 weeks with a gap one week between the two courses of treatments. We compared in vivo data with in vitro by co-exposing 100 nM of sodium arsenite and DMA to rat (NBT-II) as well as human transitional epithelial carcinoma (T-24) cells with 100 nM of MiADMSA.

RESULTS

The data showed that sodium arsenite and DMA exposure significantly increased the tissue arsenic contents, ROS, TBARS levels, catalase, SOD activities and significantly decreased GSH level which might be responsible for an increased 8-OHdG level. These changes might have increased pro-oncogenic biomarkers like MMP-9 and survivin in serum, bladder tissues, NBT-II, and T-24 cells. High cell migration and clonogenic potential in NBT-II and T-24 cells exposed to arsenic suggest pronounced carcinogenic potential. Significant recovery in these biomarkers was noted on treatment with MiADMSA.

CONCLUSION

Early signs of urinary bladder carcinogenesis were observed in arsenic and DMA exposed rats which were linked to metal accumulation, oxidative/ nitrosative stress, 8-OHdG, MMP-9 and survivin which were reduced by MiADMSA possibly via its efficient chelation abilities in vivo and in vitro.

Arsenic Exposure and Methylation Efficiency in Relation to Oxidative Stress in Semiconductor Workers

This study examined associations between oxidative stress and arsenic (As) exposure and methylation efficiency in semiconductor workers. An As-exposed group (n = 427) and a control group (n = 91) were included. The As-exposure group (n = 427) included 149 maintenance staff members and 278 production staff members representing high As exposure and low As exposure, respectively. The control group included 91 administrative staff members with no or minimal As exposure. An occupational exposure assessment was conducted to assess personal As exposure by measuring As concentrations in urine, hair, and fingernails of the subjects. Urinary As(III), As(V), monomethylarsonic (MMA), and dimethylarsinic acid (DMA) were quantified to assess an internal dose of inorganic As. Urinary 8-hydroxy-2’-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) were measured to asses oxidative DNA damage and lipid peroxidation, respectively. As concentrations in urine, hair, and fingernails significantly increased (p < 0.05) in the As-exposed group in comparison to the control group. Geometric mean urinary concentrations of As, 8-OHdG, and MDA in the As-exposed group significantly exceeded those in the control group. As exposure to As-exposed workers had increased concentrations of 8-OHdG in contrast to those in control subjects. Moreover, urinary 8-OHdG concentrations in the semiconductor workers were positively correlated with urinary total As metabolite (As(III) + As(V) + MMA + DMA) concentrations. Furthermore, urinary excretion of 8-OHdG concentrations in As-exposed workers were positively associated with urinary excretion of MMA concentrations and primary methylation index values (the ration of MMA/inorganic As). However, fingernail and hair samples did not perform as well as urinary samples to measure oxidative stress induced by As exposure. 8-OHdG could serve as a more reliable biomarker for assessing As methylation than MDA did. Occupational exposure to inorganic As was associated with increased oxidative stress among semiconductor workers.

Arsenic exposure through drinking Water and oxidative stress Status: A cross-sectional study in the Ayeyarwady region, Myanmar

Arsenic is a well-known toxic heavy metal that is naturally dispersed in groundwater. Whereas arsenic is widely accepted to be involved in oxidative stress damage, little is known about arsenic-induced oxidative damage in relationship to contaminated drinking water as a source. The aim of this study was to determine the association between arsenic exposure through drinking water and oxidative stress status by measuring levels of urinary 8-hydroxydeoxyguanosine (8-OHdG) as a biomarker of oxidative stress damage in a Myanmar population. A questionnaire-based survey and drinking water and urine sampling (n = 198) were performed to assess the association between arsenic exposure and urinary 8-OHdG concentration in the Ayeyarwady Region, Myanmar. Urinary arsenic concentrations were significantly correlated with drinking water arsenic concentrations (Spearman's rho = 0.32, p < 0.001). Multivariate linear regression analysis showed that higher urinary arsenic concentrations were significantly associated with higher 8-OHdG concentrations (coefficient = 0.09, 95% confidence interval, 0.03 - 0.15; p =  0.002). The present study identified that exposure to arsenic through drinking water could induce an increase in the urinary 8-OHdG concentration, reflecting increased oxidative DNA damage. These findings provide evidence that may explain the role of arsenic-induced oxidative stress in the pathophysiology of arsenic-induced diseases including cancers.

Effect of Curcumin and N-Acetylcysteine on Brain Histology and Inflammatory Factors (MMP-2, 9 and TNF-α) in Rats Exposed to Arsenic

Background: Arsenic is a toxic element that widely widespread in environment. Inflammation is now considered as one of the major mechanisms implicated in arsenic poisoning. Curcumin (Cur) and N-acetylcysteine (NAC) are potential antioxidants that protect cells against inflammation. This study aimed to compare the protective effect of Cur and NAC on brain histology and inflammatory factors, including matrix metalloproteinases-2, -9 (MMP-2, 9) and tumor necrosis factor-α (TNF-α) in rats exposed to single dose of arsenic. Methods: Rats were exposed to single dose of arsenic (20mg/kg, by gavage) for 30 days and then treated with 300mg/kg NAC (by gavage) and 100mg/kg Cur (by gavage), individually. Serum level of TNF-α was measured using specific ELISA kits. MMP2 and MMP9 contents were measured using Gelatin Zymography method. Brain samples were collected for histopathological and morphological examinations. Results: Arsenic treatment induced white matter lesions and cellular damages at hippocampal CA1 area of the brain. The number of hippocampal CA1 pyramidal cells was significantly declined in arsenic exposed rats (p<0.05). Treatment with NAC and Cur improved these abnormalities. The mean levels of MMP2, MMP9 and TNF-α inflammatory biomarkers were slightly declined after treatment with NAC and Cur (p>0.05). Conclusion: NAC and Cur play an important role in protecting the hippocampal CA1 cells injury induced by arsenic.

The impact of BMI on non-malignant respiratory symptoms and lung function in arsenic exposed adults of Northern Chile

BACKGROUND

Elevated body mass index (BMI) and arsenic are both associated with cancer and with non-malignant lung disease. Using a unique exposure situation in Northern Chile with data on lifetime arsenic exposure, we previously identified the first evidence of an interaction between arsenic and BMI for the development of lung cancer.

OBJECTIVES

We examined whether there was an interaction between arsenic and BMI for the development of non-malignant lung disease.

METHODS

Data on lifetime arsenic exposure, respiratory symptoms, spirometry, BMI, and smoking were collected from 751 participants from cities in Northern Chile with varying levels of arsenic water concentrations. Spirometry values and respiratory symptoms were compared across subjects in different categories of arsenic exposure and BMI.

RESULTS

Adults with both a BMI above the 90th percentile (>33.9kg/m²) and arsenic water concentrations ≥11µg/L exhibited high odds ratios (ORs) for cough (OR = 10.7, 95% confidence interval (CI): 3.03, 50.1), shortness of breath (OR = 14.2, 95% CI: 4.79, 52.4), wheeze (OR = 14.4, 95% CI: 4.80, 53.7), and the combined presence of any respiratory symptom (OR = 9.82, 95% CI: 4.22, 24.5). In subjects with lower BMIs, respiratory symptom ORs for arsenic water concentrations ≥11µg/L were markedly lower. In never-smokers, reductions in forced vital capacity associated with arsenic increased as BMI increased. Analysis of the FEV₁/FVC ratio in never-smokers significantly increased as BMI and arsenic concentrations increased. Similar trends were not observed for FEV₁ alone or in ever-smokers.

CONCLUSIONS

This study provides preliminary evidence that BMI may increase the risk for arsenic-related non-malignant respiratory disease.

Arsenic exposure and risk of preeclampsia in a Mexican mestizo population

BACKGROUND

Exposure to arsenic in drinking water has been associated with various complications of pregnancy including fetal loss, low birth weight, anemia, gestational diabetes and spontaneous abortion. However, to date, there are no studies evaluating its possible association with preeclampsia.

METHODS

This case-control study involved 104 preeclamptic and 202 healthy pregnant women. The concentrations of arsenic in drinking water and urine were measured using a Microwave Plasma-Atomic Emission Spectrometer.

RESULTS

We found relatively low levels of arsenic in household tap water (range of 2.48-76.02 μg/L) and in the urine of the participants (7.1 μg/L vs 6.78 μg/L in cases and controls, respectively).

CONCLUSIONS

The analysis between groups showed for the first time that at these lower levels of exposure there is no association with preeclampsia.

Protective Effect of Folic Acid on Oxidative DNA Damage: A Randomized, Double-Blind, and Placebo Controlled Clinical Trial

Although previous reports have linked DNA damage with both transmissions across generations as well as our own survival, it is unknown how to reverse the lesion. Based on the data from a Randomized, Double-blind, Placebo Controlled Clinical Trial, this study aimed to assess the efficacy of folic acid supplementation (FAS) on DNA oxidative damage reversal.In this randomized clinical trial (RCT), a total of 450 participants were enrolled and randomly assigned to 3 groups to receive folic acid (FA) 0.4 mg/day (low-FA), 0.8 mg/day (high-FA), or placebo (control) for 8 weeks. The urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and creatinine (Cr) concentration at pre- and post-FAS were measured with modified enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC), respectively. A multivariate general linear model was applied to assess the individual effects of FAS and the joint effects between FAS and hypercholesterolemia on oxidative DNA damage improvement. This clinical trial was registered with ClinicalTrials.gov, number NCT02235948.Of the 438 subjects that received FA fortification or placebo, the median (first quartile, third quartile) of urinary 8-OHdG/Cr for placebo, low-FA, and high-FA groups were 58.19 (43.90, 82.26), 53.51 (38.97, 72.74), 54.73 (39.58, 76.63) ng/mg at baseline and 57.77 (44.35, 81.33), 51.73 (38.20, 71.30), and 50.65 (37.64, 76.17) ng/mg at the 56th day, respectively. A significant decrease of urinary 8-OHdG was observed after 56 days FA fortification (P < 0.001). Compared with the placebo, after adjusting for some potential confounding factors, including the baseline urinary 8-OHdG/Cr, the urinary 8-OHdG/Cr concentration significantly decreased after 56 days FAS [β (95% confidence interval) = -0.88 (-1.62, -0.14) and P = 0.020 for low-FA; and β (95% confidence interval) = -2.68 (-3.42, -1.94) and P < 0.001 for high-FA] in a dose-response fashion (Ptrend < 0.001). Test of interaction between hypercholesterolemia and FA supplementation on urinary 8-OHdG reduction was significant (P = 0.001).The present study demonstrates that FA fortification is independently linked to the reduction of urinary 8-OHdG/Cr in a dose-related pattern, which suggests that FA is beneficial to protect against oxidative damage to DNA. This effect is apparently stronger in those with hypercholesterolemia. The authors provide a new insight into the prevention and reversal of oxidative DNA damage.

Use of mode of action data to inform a dose-response assessment for bladder cancer following exposure to inorganic arsenic

In the recent National Research Council report on conducting a dose-response assessment for inorganic arsenic, the committee remarked that mode of action data should be used, to the extent possible, to extrapolate below the observed range for epidemiological studies to inform the shape of the dose-response curve. Recent in vitro mode of action studies focused on understanding the development of bladder cancer following exposure to inorganic arsenic provide data to inform the dose-response curve. These in vitro data, combined with results of bladder cancer epidemiology studies, inform the dose-response curve in the low-dose region, and include values for both pharmacokinetic and pharmacodynamic variability. Integration of these data provides evidence of a range of concentrations of arsenic for which no effect on the bladder would be expected. Specifically, integration of these results suggest that arsenic exposures in the range of 7-43 ppb in drinking water are exceedingly unlikely to elicit changes leading to key events in the development of cancer or noncancer effects in bladder tissue. These findings are consistent with the lack of evidence for bladder cancer following chronic ingestion of arsenic water concentrations <100 ppb in epidemiological studies.

Biomarkers of arsenic exposure and effects in a Canadian rural population exposed through groundwater consumption

Drinking water intake of arsenic (As) from private wells may represent a significant exposure pathway and induce oxidative DNA damage. We measured total As concentrations in hair and nails, and concentrations of the different species of As and its metabolites as well as 8-OHdG in urine of 110 non-smoking adults living in a rural region of the Province of Quebec, Canada. Significant differences in exposure biomarker levels were observed between individuals consuming drinking water with As levels of≤1.0,>1.0 -≤10 and>10 μg/l. Multivariate linear regression analysis also showed a significant relationship between estimated daily drinking water intakes of As and biomarker levels. Conversely, 8-OHdG levels were not significantly related to daily drinking water intakes of As or to hair, nail or urinary exposure biomarker levels, according to multivariate linear regression analysis. Even at the relatively low levels of As found in well water of our participants, water consumption significantly increases their body load of As, as confirmed by multiple matrix measurements, which reflected exposure over different time frames. However, this increased internal As dose was not associated with higher oxidative damage to DNA as reflected by urinary 8-OHdG levels.

Ogg1 genetic background determines the genotoxic potential of environmentally relevant arsenic exposures

Inorganic arsenic (i-As) is a well-established human carcinogen to which millions of people are exposed worldwide. It is generally accepted that the genotoxic effects of i-As after an acute exposure are partially linked to the i-As-induced production of reactive oxygen species, but it is necessary to better determine whether chronic sub-toxic i-As doses are able to induce biologically significant levels of oxidative DNA damage (ODD). To fill in this gap, we have tested the genotoxic and oxidative effects of environmentally relevant arsenic exposures using mouse embryonic fibroblast MEF mutant Ogg1 cells and their wild-type counterparts. Effects were examined by using the comet assay complemented with the use of FPG enzyme. Our findings indicate that MEF Ogg1-/- cells are more sensitive to arsenite-induced acute toxicity, genotoxicity and ODD. Long-term exposure to sub-toxic doses of arsenite generates a detectable increase in ODD and genotoxic DNA damage only in MEF Ogg1-deficient cells. Altogether, the data presented here point out the relevance of ODD and Ogg1 genetic background on the genotoxic risk of i-As at environmentally plausible doses. The persistent accumulation of DNA 8-OH-dG lesions in Ogg1-/- cells during the complete course of the exposure suggests a relevant role in arsenic-associated carcinogenic risk in turn.

DNA and oxidative damages decrease after ingestion of folic acid in patients with type 2 diabetes

BACKGROUND AND AIMS

Type 2 diabetes mellitus (T2DM) is a chronic degenerative disease that promotes autoxidation of sugars, leading to the production of reactive oxygen species. This damage occurs especially at the level of cellular proteins, carbohydrates, lipids and DNA, thus playing an important role in the pathogenesis of late complications of T2DM. We investigated the effect of folic acid on DNA and oxidative damage in patients with T2DM.

METHODS

We studied 30 individuals diagnosed with T2DM and 30 control individuals without disease. Individuals with T2DM were prescribed 5 mg of folic acid, taken orally three times daily for 1 month. Samples were taken 15 and 30 days after treatment. DNA damage was determined using the micronucleus test in oral mucosa and oxidative stress by quantifying 8-hydroxy-2'-deoxyguanosine (8-OHdG) as well as by quantifying total lipid peroxides.

RESULTS

Individuals with T2DM had a higher number of micronuclei as well as higher levels of 8-OHdG and lipid peroxides than the control group (p = 0.001). Individuals with T2DM showed a significant reduction in the number of micronuclei and the concentration of 8-OHdG and lipid peroxides over time with folic acid intake.

CONCLUSIONS

A positive correlation exists between oxidative stress produced by T2DM and DNA damage, so the use of an antioxidant such as folic acid in DM2 therapy is advisable for delaying complications due to T2DM-induced oxidative stress and DNA damage.

Delineating the degree of association between biomarkers of arsenic exposure and type-2 diabetes mellitus

Non-carcinogenic effects in low-level (< 100 μgL(-1)) arsenic (As)-impacted populations, such as the development and progression of type-2 diabetes mellitus (T2DM), are often neglected given the primary emphasis of public health authorities on As carcinogenicity. We gathered studies reporting urinary biomarkers of As exposure (U-As) and biomarkers associated with T2DM and its complications (U-T2DM), such as renal damage, oxidation stress, low-grade inflammation, and endothelial damage. Studied U-T2DM biomarkers were: 8-hydroxy-2'deoxyguanosine, N-acetyl-β-d-glucosaminidase, β2-microglobulin, and albumin. Data was expressed as: either arithmetic means and standard deviations, or geometric means and geometric standard deviations, or correlation coefficients of U-As and U-T2DM. Urinary As concentrations were consistently associated with the aforementioned biomarkers of T2DM pathologic complications. Despite the limited selectivity of the selected T2DM biomarkers, a per unit change in As exposure level was reflected in the corresponding T2DM biomarker urinary concentrations. Our systematic review provides new evidence on the role of environmental As exposures influencing the T2DM disease process. Additional epidemiologic studies onto the association between As and T2DM should incorporate both urinary As and T2DM biomarkers, as suggested in this study, in order to evaluate subclinical effects of low-level As exposures.

Global gene expression changes in human urothelial cells exposed to low-level monomethylarsonous acid

Bladder cancer has been associated with chronic arsenic exposure. Monomethylarsonous acid [MMA(III)] is a metabolite of inorganic arsenic and has been shown to transform an immortalized urothelial cell line (UROtsa) at concentrations 20-fold less than arsenite. MMA(III) was used as a model arsenical to examine the mechanisms of arsenical-induced transformation of urothelium. A microarray analysis was performed to assess the transcriptional changes in UROtsa during the critical window of chronic 50nM MMA(III) exposure that leads to transformation at 3 months of exposure. The analysis revealed only minor changes in gene expression at 1 and 2 months of exposure, contrasting with substantial changes observed at 3 months of exposure. The gene expression changes at 3 months were analyzed showing distinct alterations in biological processes and pathways such as a response to oxidative stress, enhanced cell proliferation, anti-apoptosis, MAPK signaling, as well as inflammation. Twelve genes selected as markers of these particular biological processes were used to validate the microarray and these genes showed a time-dependent changes at 1 and 2 months of exposure, with the most substantial changes occurring at 3 months of exposure. These results indicate that there is a strong association between the acquired phenotypic changes that occur with chronic MMA(III) exposure and the observed gene expression patterns that are indicative of a malignant transformation. Although the substantial changes that occur at 3 months of exposure may be a consequence of transformation, there are common occurrences of altered biological processes between the first 2 months of exposure and the third, which may be pivotal in driving transformation.

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.

Low 8-oxo-7,8-dihydro-2'-deoxyguanosine levels and influence of genetic background in an Andean population exposed to high levels of arsenic

BACKGROUND

Arsenic (As) causes oxidative stress through generation of reactive oxygen species. 8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a sensitive marker of oxidative DNA damage, has been associated with As exposure in some studies, but not in others, possibly due to population-specific genetic factors.

OBJECTIVES

To evaluate the association between As and 8-oxodG in urine in a population with a low urinary monomethylated As (%MMA) and high dimethylated As (%DMA), as well as the genetic impact on (a) 8-oxodG concentrations and (b) the association between As and 8-oxodG.

MATERIALS AND METHODS

Women (N=108) in the Argentinean Andes were interviewed and urine was analyzed for arsenic metabolites (ICPMS) and 8-oxodG (LC-MS/MS). Twenty-seven polymorphisms in genes related to oxidative stress and one in As(+III)methyltransferase (AS3MT) were studied.

RESULTS

Median concentration of 8-oxodG was 4.7 nmol/L (adjusted for specific weight; range 1.6-13, corresponding to 1.7 microg/g creatinine, range 0.57-4.8) and of total urinary As metabolites (U-As) 290 microg/L (range 94-720; 380 microg/g creatinine, range 140-1100). Concentrations of 8-oxodG were positively associated with %MMA (strongest association, p=0.013), and weakly associated with U-As (positively) and %DMA (negatively). These associations were strengthened when taking ethnicity into account, possibly reflecting genetic differences in As metabolism and genes regulating oxidative stress and DNA maintenance. A genetic influence on 8-oxodG concentrations was seen for polymorphisms in apurinic/apyrimidinic endonuclease 1 (APEX1), DNA-methyltransferases 1 and 3b (DNMT1, DNMT3B), thioredoxin reductase 1 (TXNRD1) and 2 (TXNRD2) and glutaredoxin (GLRX).

CONCLUSION

Despite high As exposure, the concentrations of 8-oxodG in this population were low compared with other As-exposed populations studied. The strongest association was found for %MMA, stressing that some inconsistencies between As and 8-oxodG partly depend on population variations in As metabolism. We found evidence of genetic impact on 8-oxodG concentrations.

Arsenicosis status and urinary malondialdehyde (MDA) in people exposed to arsenic contaminated-coal in China

The current arsenic exposure condition, arsenicosis prevalence, urinary arsenic and MDA (malondialdehyde) concentrations in people were studied. The study area, a village in Xing Ren County in Guizhou Province, PR China, is a coal-borne arsenicosis endemic area that was identified several decades ago. The residents in Xing Ren have been using coal containing high arsenic levels all their life. Urinary arsenic levels of villagers were 192.2+/-22 microg/g creatinine (n=113) in the coal-borne endemic area (Xing Ren county) and were significantly higher than 63.6+/-5.9 microg/g creatinine (n=30) in a neighbouring control site (a village in Xing Yi county). The urinary MDA concentrations of villagers from the endemic area were also significantly higher compared to those of the control area. There was a strong correlation between age and urinary arsenic and MDA concentrations in the endemic area of Xing Ren; urinary arsenic and MDA levels decreased with age. Fifty out of 113 (44.3%) villagers in the endemic area had arsenicosis symptoms and the prevalence in villagers older than 40 y was 100% in male (92.2% overall). Urinary MDA concentration was significantly higher in people with arsenicosis symptoms in the endemic areas. Oxidative stress (urinary MDA concentration) was strongly related to arsenic exposure but not to the age and smoking habit. Higher urinary arsenic and MDA levels in younger villagers from the endemic area suggest that they are having a higher exposure to coal-borne emitted arsenic because they spend more time indoor. There is an urgent need to develop proper intervention methods in the Guizhou endemic areas in order to reduce the risk to the local communities who are still using arsenic contaminated-coal.

Biomarkers of oxidative stress and damage in human populations exposed to arsenic

Arsenic (As) is an ubiquitous element in the environment for which the main route of human exposure is through consumption of drinking water. Reactive oxygen species generation (ROS) associated with As exposure is known to play a fundamental role in the induction of adverse health effects and disease (cancer, diabetes, hypertension, and cardiovascular and neurological diseases). However, the precise mechanisms of oxidative stress and damage from As exposure are not fully understood and moreover the use of non-invasive methods of measuring ROS generation and oxidative damage footprints in humans is no easy task. Although As induces adverse health effects not all exposed individuals develop degenerative chronic diseases or even manifest adverse effects or symptoms, suggesting that genetic susceptibility is an important factor involved in the human response to As exposure. This mini-review summarizes the literature describing the molecular mechanisms affected by As, as well as the most used biomarkers of oxidative stress and damage in human populations. The most reported biomarkers of oxidative DNA damage are the urinary excretion of 8-OHdG and the comet assay in lymphocytes, and more recently DNA repair mechanism markers from the base and nuclear excision repair pathways (BER and NER). Genetic heterogeneity in the oxidative stress pathways involved in As metabolism are important causative factors of disease. Thus further refinement of human exposure assessment is needed to reinforce study design to evaluate exposure-response relationships and study gene-environment interactions. The use of microarray-based gene expression analysis can provide better insights of the underlying mechanisms involved in As-induced diseases and could help to identify target genes that can be modulated to prevent disease.

Environmental Arsenic Exposure and Urinary 8-OHdG in Arizona and Sonora

Although at high levels arsenic exposure is associated with increased cancer incidence, information on the health effects of lower exposure levels is limited. The objective of this study was to determine whether arsenic at concentrations below 40 microg/L in drinking water is associated with increased urinary 8-hydroxydeoxyguanosine (8-OHdG), a biomarker of DNA oxidative damage and repair. Urine samples were collected from 73 nonsmoking adults residing in two communities in Arizona (mean tap water arsenic (microg/L) 4.0 +/- 2.3 and 20.3 +/- 3.7), and 51 subjects in four communities in Sonora, Mexico (mean tap water arsenic (microg/L) ranging from 4.8 +/- 0.1 to 33.3 +/- 0.6). Although urinary arsenic concentration increased with higher exposure in tap water, urinary 8-OHdG concentration did not differ by community within Arizona or Sonora, and was not associated with urinary arsenic concentration. At the exposure levels evaluated in this study, drinking water arsenic was not associated with increased DNA oxidation as measured by urinary 8-OHdG.

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.

Association of oxidative stress with arsenic methylation in chronic arsenic-exposed children and adults

Though oxidative stress is recognized as an important pathogenic mechanism of arsenic, and arsenic methylation capacity is suggested to be highly involved in arsenic-related diseases, the association of arsenic methylation capacity with arsenic-induced oxidative stress remains unclear. To explore oxidative stress and its association with arsenic methylation, cross-sectional studies were conducted among 208 high and 59 low arsenic-exposed subjects. Levels of urinary arsenic species [inorganic arsenic (iAs), monomethylated arsenic (MMA) and dimethylated arsenic (DMA)] were determined by hydride generation atomic absorption spectrometry. Proportions of urinary arsenic species, the first methylation ratio (FMR) and the secondary methylation ratio (SMR) were used as indicators for arsenic methylation capacity. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) concentrations were analyzed by enzyme-linked immunosorbent assay kits. Reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity in whole blood were determined to reflect anti-oxidative status. The high arsenic-exposed children and adults were significantly increased in urinary 8-OHdG concentrations but decreased in blood GSH levels compared with the low exposed children and adults. In multiple linear regression models, blood GSH levels and urinary 8-OHdG concentrations of arsenic-exposed children and adults showed strong associations with the levels of urinary arsenic species. Arsenic-exposed subjects in the lower and the upper quartiles of proportions of urinary arsenic species, FMR or SMR were significantly different in urinary 8-OHdG, blood GSH and SOD. The associations of arsenic methylation capacity with 8-OHdG, GSH and SOD were also observed in multivariate regression analyses. These results may provide linkage between arsenic methylation capacity and oxidative stress in humans and suggest that adverse health effects induced by arsenic are related to arsenic methylation through oxidative stress.

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.

Health effects of early life exposure to arsenic

Inorganic arsenic is a potent human carcinogen and general toxicant. More than one hundred million people are exposed to elevated concentrations, mainly via drinking water, but also via industrial emissions. Arsenic is metabolized via methylation and reduction reactions, methylarsonic acid and dimethylarsinic acid being the main metabolites excreted in urine. Both inorganic arsenic and its methylated metabolites easily pass the placenta and both experimental and human studies have shown increased risk of impaired foetal growth and increased foetal loss. Recent studies indicate that prenatal arsenic exposure also increases the risk of adverse effects during early childhood. There is a growing body of evidence that the intrauterine or early childhood exposure to arsenic also induces changes that will become apparent much later in life. One epidemiological study indicated that exposure to arsenic in drinking water during early childhood or in utero was associated with an increased mortality in young adults from both malignant and non-malignant lung disease. Furthermore, a series of experimental animal studies provide strong support for late effects of arsenic, including various forms of cancer, following intrauterine arsenic exposure. The involved modes of action include epigenetic effects, mainly via DNA hypomethylation, endocrine effects (most classes of steroid hormones), immune suppression, neurotoxicity, and interaction with enzymes critical for foetal development and programming.

GSTM1 and APE1 genotypes affect arsenic-induced oxidative stress: a repeated measures study

BACKGROUND

Chronic arsenic exposure is associated with an increased risk of skin, bladder and lung cancers. Generation of oxidative stress may contribute to arsenic carcinogenesis.

METHODS

To investigate the association between arsenic exposure and oxidative stress, urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) was evaluated in a cohort of 97 women recruited from an arsenic-endemic region of Bangladesh in 2003. Arsenic exposure was measured in urine, toenails, and drinking water. Drinking water and urine samples were collected on three consecutive days. Susceptibility to oxidative stress was evaluated by genotyping relevant polymorphisms in glutathione-s transferase mu (GSTM1), human 8-oxoguanine glycosylase (hOGG1) and apurinic/apyrimidinic endonuclease (APE1) genes using the Taqman method. Data were analyzed using random effects Tobit regression to account for repeated measures and 8-OHdG values below the detection limit.

RESULTS

A consistent negative effect for APE1 was observed across water, toenail and urinary arsenic models. APE1 148 glu/glu + asp/glu genotype was associated with a decrease in logged 8-OHdG of 0.40 (95%CI -0.73, -0.07) compared to APE1 148 asp/asp. An association between total urinary arsenic and 8-OHdG was observed among women with the GSTM1 null genotype but not in women with GSTM1 positive. Among women with GSTM1 null, a comparison of the second, third, and fourth quartiles of total urinary arsenic to the first quartile resulted in a 0.84 increase (95% CI 0.27, 1.42), a 0.98 increase (95% CI 033, 1.66) and a 0.85 increase (95% CI 0.27, 1.44) in logged 8-OHdG, respectively. No effects between 8-OHdG and toenail arsenic or drinking water arsenic were observed.

CONCLUSION

These results suggest the APE1 variant genotype decreases repair of 8-OHdG and that arsenic exposure is associated with oxidative stress in women who lack a functional GSTM1 detoxification enzyme.

Interactions between arsenic-induced toxicity and nutrition in early life

Exposure to arsenic through drinking water is a major public health problem affecting most countries, although the situation is particularly severe in low-income nations. The health consequences of chronic arsenic exposure include increased risk for various forms of cancer and numerous noncancer effects, including diabetes, skin diseases, chronic cough, and toxic effects on liver, kidney, cardiovascular system, and peripheral and central nervous systems. In recent years increasing reports of effects on fetal and child development have appeared. There seems to be a wide variation in susceptibility to arsenic toxicity, which is likely to be related to factors such as variation in arsenic metabolism, nutrition, host-related defense mechanisms, and genetic predisposition. The main mechanisms of arsenic-nutrition interactions include arsenic-induced oxidative stress, which requires nutrient-dependent defense systems, and arsenic metabolism (methylation) via 1-carbon metabolism, which requires methyl groups, folic acid, vitamin B-12, and betaine for the remethylation of homocysteine to methionine. An efficient first methylation step in combination with a slow second methylation step seems to be most critical from a toxicological point of view. A third mode of arsenic-nutrition interaction involves epigenetic effects and fetal programming via DNA methylation.

Arsenic exposure and age and sex-specific risk for skin lesions: a population-based case-referent study in Bangladesh

BACKGROUND

The objective of this population-based case-referent study in Matlab, Bangladesh, was to assess the susceptibility to arsenic-induced skin lesions by age and sex, in a population drinking water from As-contaminated tube wells.

METHODS

Identification of As-related skin lesions was carried out in three steps: a) screening of the entire population > 4 years of age (n = 166,934) by trained field teams; b) diagnosis of suspected As-related cases by physicians; and c) confirmation by experts based on physicians' records and photographs. A total of 504 cases with skin lesions were confirmed. We randomly selected 2,201 referents from the Matlab health and demographic surveillance system; 1,955 were eligible, and 1,830 (94%) were available for participation in the study. Individual history of As exposure was based on information obtained during interviews and included all drinking-water sources used since 1970 and concentrations of As (assessed by atomic absorption spectrophotometry) in all the tube wells used.

RESULTS

Cases had been exposed to As more than referents (average exposure since 1970: male cases, 200 microg/L; female cases, 211 microg/L; male referents, 143 microg/L; female referents, 155 microg/L). We found a dose-response relationship for both sexes (p < 0.001) and increased risk with increasing socioeconomic status. Males had a higher risk of obtaining skin lesions than females (odds ratio 10.9 vs. 5.78) in the highest average exposure quintile (p = 0.005). Start of As exposure (cumulative exposure) before 1 year of age was not associated with higher risk of obtaining skin lesions compared to start of As exposure later in life.

CONCLUSIONS

The results demonstrate that males are more susceptible than females to develop skin lesions when exposed to As in water from tube wells.

Gender-specific protective effect of hemoglobin on arsenic-induced skin lesions

Chronic arsenic poisoning remains a public health crisis in Bangladesh. As arsenic has been shown to bind to human hemoglobin (Hb), hematologic mechanisms may play a role in the pathway through which arsenic exerts its toxicity. Two separate studies, a case-control and a cohort, were conducted to investigate the role of Hb in the development of arsenic-induced skin lesions. In the first, conditional logistic regression was used to investigate the effect of Hb on skin lesions among 900 case-control pairs from Pabna, Bangladesh, in which individuals were matched on gender, age, and location. In the second, mixed linear regression models were used to examine the association between toenail arsenic, urinary arsenic, and Hb within a cohort of 184 individuals from 50 families in the same region who did not have arsenic-induced skin lesions. Hb was significantly associated with skin lesions but this association was gender specific. In males, a 40% reduction in the odds of skin lesions occurred for every 1 g/dL increase in Hb (odds ratio, 0.60; 95% confidence interval, 0.49-0.73). No effect was observed for females (odds ratio, 1.16; 95% confidence interval, 0.92-1.46). In the cohort of 184 individuals, no associations between toenail arsenic or urinary arsenic species and Hb levels were observed. Low Hb levels may exacerbate the detrimental health effects of chronic arsenic poisoning. Whereas providing clean water remains the optimal solution to Bangladesh's problem of arsenic poisoning, improving nutrition and reducing iron-deficiency anemia may ameliorate negative health effects, such as skin lesions in individuals who have been exposed.

Chronic arsenic exposure and oxidative stress: OGG1 expression and arsenic exposure, nail selenium, and skin hyperkeratosis in Inner Mongolia

Arsenic, a human carcinogen, is known to induce oxidative damage to DNA. In this study we investigated oxidative stress and As exposure by determining gene expression of OGG1, which codes for an enzyme, 8-oxoguanine DNA glycosylase, involved in removing 8-oxoguanine in As-exposed individuals. Bayingnormen (Ba Men) residents in Inner Mongolia are chronically exposed to As via drinking water. Water, toenail, and blood samples were collected from 299 Ba Men residents exposed to 0.34-826 microg/L As. RNA was isolated from blood, and mRNA levels of OGG1 were determined using real-time polymerase chain reaction. OGG1 expression levels were linked to As concentrations in drinking water and nails, selenium concentrations in nails, and skin hyperkeratosis. OGG1 expression was strongly associated with water As concentrations (p < 0.0001). Addition of the quadratic term significantly improved the fit compared with the linear model (p = 0.05) . The maximal OGG1 response was at the water As concentration of 149 microg/L. OGG1 expression was also significantly associated with toenail As concentrations (p = 0.015) but inversely associated with nail Se concentrations (p = 0.0095) . We found no significant differences in the As-induced OGG1 expression due to sex, smoking, or age even though the oldest group showed the strongest OGG1 response (p = 0.0001) . OGG1 expression showed a dose-dependent increased risk of skin hyperkeratosis in males (trend analysis, p = 0.02) , but the trend was not statistically significant in females. The results from this study provide a linkage between oxidative stress and As exposure in humans. OGG1 expression may be useful as a biomarker for assessing oxidative stress from As exposure.

Clinical-scale high-throughput analysis of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine by isotope-dilution liquid chromatography-tandem mass spectrometry with on-line solid-phase extraction

BACKGROUND

Quantification of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in urine or blood is used to assess and monitor oxidative stress in patients. We describe the use of on-line solid-phase extraction (SPE) and isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) for automated measurement of urinary 8-oxodGuo.

METHODS

Automated purification of urine was accomplished with a switching valve and an Inertsil ODS-3 column. After the addition of 15N5-labeled 8-oxodGuo as an internal standard, urine samples were analyzed within 10 min without sample purification. This method was applied to measure urinary 8-oxodGuo in a group of healthy persons (32 regular smokers and 35 nonsmokers). Urinary cotinine was also assayed by an isotope-dilution LC-MS/MS method.

RESULTS

The lower limit of detection was 5.7 ng/L on column (2.0 fmol). Inter- and intraday imprecision (CV) was < 5.0%. Mean recovery of 8-oxodGuo in urine was 99%-102%. Mean (SD) urinary concentrations of 8-oxodGuo in smokers [7.26 (3.14) microg/g creatinine] were significantly higher than those in nonsmokers [4.69 (1.70) microg/g creatinine; P < 0.005]. Urinary concentrations of 8-oxodGuo were significantly correlated with concentrations of cotinine in smokers (P < 0.05).

CONCLUSIONS

This on-line SPE LC-MS/MS method is sufficiently sensitive, precise, and rapid to provide high-throughput direct analysis of urinary 8-oxodGuo without compromising quality and validation criteria. This method could be applicable for use in daily clinical practice for assessing oxidative stress in patients.

Effects of arsenic exposure among semiconductor workers: a cautionary note on urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine

Arsenic is a notorious environmental toxicant and was found to cause oxidative stress in cultured cells and animals. However, little work has been done in human studies, especially for the population occupationally exposed to arsenic. In order to investigate the effect of occupational exposure to arsenic in oxidative stress, we measured urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) from 90 semiconductor workers including 50 exposed and 40 nonexposed subjects. A highly sensitive and specific isotope dilution LC-MS/MS method was used for quantification of 8-oxodGuo. The levels of inorganic arsenic (iAs3+, iAs5+), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in urine were determined by high-performance liquid chromatography-flow injection atomic absorption spectrometry (HPLC-FIAAS). Results showed that the mean urinary concentrations of total arsenic and 8-oxodGuo were significantly higher for exposed workers compared with the nonexposed workers. In addition, elevated urinary 8-oxodGuo concentrations of exposed workers were correlated with urinary levels of MMA (r = 0.44, P < 0.005) and the extent of primary methylation (the ratio of MMA to inorganic arsenic) (r = 0.40, P < 0.005). These findings suggested that occupational exposure to arsenic could result in the induction of oxidative stress. The presence and/or formation of MMA could play an important role in arsenic-involved injuries.

Urinary 8-hydroxy-2′-deoxyguanosine in inhabitants chronically exposed to arsenic in groundwater in Cambodia

Arsenic concentrations in hair and urine, and urinary levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, were examined for inhabitants of the Mekong Basin in Kratie Province, Cambodia. Also, the arsenic levels of tube-well water were determined. Total arsenic concentrations in tube-well water ranged from <1 to 886 microg L(-1), and 44.8% of these exceeded the WHO drinking water guideline of 10 microg L(-1). Elevated levels of arsenic were observed in the human hair and urine, and also a significant positive correlation was observed between the concentrations in hair and urine. These results suggest that the inhabitants are chronically exposed to arsenic through drinking the tube-well water. Levels of urinary 8-OHdG were higher for the subjects with higher arsenic levels in hair and urine, suggesting that induction of oxidative DNA damage was caused by chronic exposure to arsenic in tube-well water for the inhabitants in Kratie Province. To our knowledge, this is the first report on the oxidative DNA damage caused by chronic exposure to arsenic in groundwater for the inhabitants in Cambodia.

Co-mutagenic activity of arsenic and benzo[a]pyrene in mouse skin

Exposure to inorganic arsenic in drinking water is linked to skin, lung and bladder cancer in humans. The mechanism of arsenic-induced cancer is not clear, but exposure to arsenic and polycyclic arylhydrocarbons (PAH) is more carcinogenic than exposure to either type of carcinogen alone. Arsenic can also generate reactive oxygen species, suggesting that oxidation of DNA may play a role in carcinogenesis. Oxidization of guanosines in polyG tracts is known to cause frameshift mutations, and such events can be detected in situ using the G11 placental alkaline phosphatase (PLAP) transgenic mouse model, which reports frameshift mutations in a run of 11 G:C basepairs by generating cells containing heat-resistant alkaline phosphatase activity. PAH can also induce frameshift mutations. In the study described here, FVB/N mice carrying the G11 PLAP transgene were crossed to C57Bl/6 mice. Half of the hybrid mice were given drinking water with sodium arsenite (10 mg/L) for 10 weeks. Half of the arsenic treated mice were also exposed to benzo[a]pyrene (BaP) by skin painting (500 nmol/week) for 8 weeks. Another group of mice was exposed to BaP but not arsenic. The effect on frameshift mutation was assessed by staining sections of skin tissue to detect cells with PLAP activity. Arsenic alone had no significant effect. On average, mice given BaP alone had approximately three times more PLAP-positive (PLAP+) cells. By contrast, mice exposed to both arsenic and BaP exhibited 10-fold more PLAP+ cells in the skin, and these cells were often arranged in large clusters, suggesting derivation from stem cells. Whereas combined treatment produced more PLAP+ cells, stable BaP adduct levels and arsenic burdens were not higher in mice exposed to both agents compared to mice exposed to either one agent or the other.