Involvement of N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) in arsenic biomethylation and its role in arsenic-induced toxicity

Background

In humans, inorganic arsenic (iAs) is metabolized to methylated arsenical species in a multistep process mainly mediated by arsenic (+3 oxidation state) methyltransferase (AS3MT). Among these metabolites is monomethylarsonous acid (MMA^III), the most toxic arsenic species. A recent study in As3mt-knockout mice suggests that unidentified methyltransferases could be involved in alternative iAs methylation pathways. We found that yeast deletion mutants lacking MTQ2 were highly resistant to iAs exposure. The human ortholog of the yeast MTQ2 is N-6 adenine-specific DNA methyltransferase 1 (N6AMT1), encoding a putative methyltransferase.

Objective

We investigated the potential role of N6AMT1 in arsenic-induced toxicity.

Methods

We measured and compared the cytotoxicity induced by arsenicals and their metabolic profiles using inductively coupled plasma–mass spectrometry in UROtsa human urothelial cells with enhanced N6AMT1 expression and UROtsa vector control cells treated with different concentrations of either iAs^III or MMA^III.

Results

N6AMT1 was able to convert MMA^III to the less toxic dimethylarsonic acid (DMA) when overexpressed in UROtsa cells. The enhanced expression of N6AMT1 in UROtsa cells decreased cytotoxicity of both iAs^III and MMA^III. Moreover, N6AMT1 is expressed in many human tissues at variable levels, although at levels lower than those of AS3MT, supporting a potential participation in arsenic metabolism in vivo.

Conclusions

Considering that MMA^III is the most toxic arsenical, our data suggest that N6AMT1 has a significant role in determining susceptibility to arsenic toxicity and carcinogenicity because of its specific activity in methylating MMA^III to DMA and other unknown mechanisms.     

Protective effect of resveratrol on arsenic trioxide-induced nephrotoxicity in rats

BACKGROUD/OBEJECTIVES

Arsenic, which causes human carcinogenicity, is ubiquitous in the environment. This study was designed to evaluate modulation of arsenic induced cancer by resveratrol, a phytoalexin found in vegetal dietary sources that has antioxidant and chemopreventive properties, in arsenic trioxide (As₂O₃)-induced Male Wistar rats.

MATERIALS/METHODS

Adult rats received 3 mg/kg As₂O₃ (intravenous injection, iv.) on alternate days for 4 days. Resveratrol (8 mg/kg) was administered (iv.) 1 h before As₂O₃ treatment. The plasma and homogenization enzymes associated with oxidative stress of rat kidneys were measured, the kidneys were examined histologically and trace element contents were assessed.

RESULTS

Rats treated with As₂O₃ had significantly higher oxidative stress and kidney arsenic accumulation; however, pretreatment with resveratrol reversed these changes. In addition, prior to treatment with resveratrol resulted in lower blood urea nitrogen, creatinine and insignificant renal tubular epithelial cell necrosis. Furthermore, the presence of resveratrol preserved the selenium content (0.805 ± 0.059 µg/g) of kidneys in rats treated with As₂O₃. However, resveratrol had no effect on zinc level in the kidney relative to As₂O₃-treated groups.

CONCLUSIONS

Our data show that supplementation with resveratrol alleviated nephrotoxicity by improving antioxidant capacity and arsenic efflux. These findings suggest that resveratrol has the potential to protect against kidney damage in populations exposed to arsenic.     

Speciation of Arsenic in Exfoliated Urinary Bladder Epithelial Cells from Individuals Exposed to Arsenic in Drinking Water

Background

The concentration of arsenic in urine has been used as a marker of exposure to inorganic As (iAs). Relative proportions of urinary metabolites of iAs have been identified as potential biomarkers of susceptibility to iAs toxicity. However, the adverse effects of iAs exposure are ultimately determined by the concentrations of iAs metabolites in target tissues.

Objective

In this study we examined the feasibility of analyzing As species in cells that originate in the urinary bladder, a target organ for As-induced cancer in humans.

Methods

Exfoliated bladder epithelial cells (BECs) were collected from urine of 21 residents of Zimapan, Mexico, who were exposed to iAs in drinking water. We determined concentrations of iAs, methyl-As (MAs), and dimethyl-As (DMAs) in urine using conventional hydride generation-cryotrapping-atomic absorption spectrometry (HG-CT-AAS). We used an optimized HG-CT-AAS technique with detection limits of 12–17 pg As for analysis of As species in BECs.

Results

All urine samples and 20 of 21 BEC samples contained detectable concentrations of iAs, MAs, and DMAs. Sums of concentrations of these As species in BECs ranged from 0.18 to 11.4 ng As/mg protein and in urine from 4.8 to 1,947 ng As/mL. We found no correlations between the concentrations or ratios of As species in BECs and in urine.

Conclusion

These results suggest that urinary levels of iAs metabolites do not necessarily reflect levels of these metabolites in the bladder epithelium. Thus, analysis of As species in BECs may provide a more effective tool for risk assessment of bladder cancer and other urothelial diseases associated with exposures to iAs.     

Arsenite Tolerance is Related to Proportional Thiolic Metabolite Synthesis in Rice (Oryza sativa L.)

Thiol metabolism is the primary detoxification strategy by which rice plants tolerate arsenic (As) stress. In light of this, it is important to understand the importance of harmonised thiol metabolism with As accumulation and tolerance in rice plant. For this aim, tolerant (T) and sensitive (S) genotypes were screened from 303 rice (Oryza sativa) genotypes on exposure to 10 and 25 μM arsenite (As^III) in hydroponic culture. On further As accumulation estimation, contrasting (13-fold difference) T (IC-340072) and S (IC-115730) genotypes were selected. This difference was further evaluated using biochemical and molecular approaches to understand involvement of thiolic metabolism vis-a-vis As accumulation in these two genotypes. Various phytochelatin (PC) species (PC₂, PC₃ and PC₄) were detected in both the genotypes with a dominance of PC₃. However, PC concentrations were greater in the S genotype, and it was noticed that the total PC (PC₂ + PC₃ + PC₄)–to–As^III molar ratio (PC-SH:As^III) was greater in T (2.35 and 1.36 in shoots and roots, respectively) than in the S genotype (0.90 and 0.15 in shoots and roots, respectively). Expression analysis of several metal(loid) stress–related genes showed significant upregulation of glutaredoxin, sulphate transporter, and ascorbate peroxidase in the S genotype. Furthermore, enzyme activity of phytochelatin synthase and cysteine synthase was greater on As accumulation in the S compared with the T genotype. It was concluded that the T genotype synthesizes adequate thiols to detoxify metalloid load, whereas the S genotype synthesizes greater but inadequate levels of thiols to tolerate an exceedingly greater load of metalloids, as evidenced by thiol-to-metalloid molar ratios, and therefore shows a phytotoxicity response.     

L-Ascorbic Acid and α-Tocopherol Reduces Hepatotoxicity Associated with Arsenic Trioxide Chemotherapy by Modulating Nrf2 and Bcl2 Transcription Factors in Chang liver Cells

Arsenic trioxide (As₂O₃) is a promising new regimen for the treatment of acute promyelocytic leukemia (APL). The induction of oxidative stress mediated by reactive oxygen species (ROS) and excessive intracellular calcium influx are the main reasons behind As₂O₃ toxicity. Since liver is the major organ for xenobiotic metabolism, it is always under stress. Antioxidant vitamins such as L-Ascorbic acid (L-AA) and α-Tocopherol (α-TOC) have been proposed to have beneficial effects against a variety of pathological conditions and are known by their free radical scavenging properties. The present study evaluates the curative efficacy of L-AA and α-TOC against As₂O₃ toxicity using immortalized human Chang liver cells. Our results suggest that L-AA (100 µM) and α-TOC (50 µM) recovered As₂O₃ (10 µM) cytotoxicity. Furthermore, As₂O₃ treatment showed an increase in lipid peroxidation and depletion in antioxidant status, mitochondrial trans membrane potential and values of total antioxidant capacity. Cotreatment of antioxidant vitamins with As₂O₃ resulted in a significant reversal of oxidative stress markers. Our findings substantiate the effect of antioxidant vitamins in protecting the hepatocytes from oxidative stress which may be attributed through Nrf2 (Nuclear factor erythroid 2-related factor 2) mediated upregulation of Bcl2 (B-cell lymphoma 2) expression.     

Associations between Arsenic Species in Exfoliated Urothelial Cells and Prevalence of Diabetes among Residents of Chihuahua,Mexico

Background: A growing number of studies link chronic exposure to inorganic arsenic (iAs) with the risk of diabetes. Many of these studies assessed iAs exposure by measuring arsenic (As) species in urine. However, this approach has been criticized because of uncertainties associated with renal function and urine dilution in diabetic individuals.Objectives: Our goal was to examine associations between the prevalence of diabetes and concentrations of As species in exfoliated urothelial cells (EUC) as an alternative to the measures of As in urine.Methods: We measured concentrations of trivalent and pentavalent iAs methyl-As (MAs) and dimethyl-As (DMAs) species in EUC from 374 residents of Chihuahua, Mexico, who were exposed to iAs in drinking water. We used fasting plasma glucose, glucose tolerance tests, and self-reported diabetes diagnoses or medication to identify diabetic participants. Associations between As species in EUC and diabetes were estimated using logistic and linear regression, adjusting for age, sex, and body mass index.Results: Interquartile-range increases in trivalent, but not pentavalent, As species in EUC were positively and significantly associated with diabetes, with ORs of 1.57 (95% CI: 1.19, 2.07) for iAs^III, 1.63 (1.24, 2.15) for MAs^III, and 1.31 (0.96, 1.84) for DMAs^III. DMAs/MAs and DMAs/iAs ratios were negatively associated with diabetes (OR = 0.62; 95% CI: 0.47, 0.83 and OR = 0.72; 95% CI: 0.55, 0.96, respectively).Conclusions: Our data suggest that uncertainties associated with measures of As species in urine may be avoided by using As species in EUC as markers of iAs exposure and metabolism. Our results provide additional support to previous findings suggesting that trivalent As species may be responsible for associations between diabetes and chronic iAs exposure.Citation: Currier JM, Ishida MC, González-Horta C, Sánchez-Ramírez B, Ballinas-Casarrubias L, Gutiérrez-Torres DS, Hernández Cerón R, Viniegra Morales D, Baeza Terrazas FA, Del Razo LM, García-Vargas GG, Saunders RJ, Drobná Z, Fry RC, Matoušek T, Buse JB, Mendez MA, Loomis D, Stýblo M. 2014. Associations between arsenic species in exfoliated urothelial cells and prevalence of diabetes among residents of Chihuahua, Mexico. Environ Health Perspect 122:1088–1094; http://dx.doi.org/10.1289/ehp.1307756     

Toxicokinetics of Waterborne Trivalent Arsenic in the Freshwater Bivalve <Emphasis Type="Italic">Corbicula fluminea</Emphasis>

Arsenite (As^III) uptake and elimination kinetics were studied in a freshwater bivalve, Corbicula fluminea, exposed to several nominal concentrations of As^III (0, 100, 300, 500, and 1000 μg L⁻¹) in a static 28-day assay, followed by a depuration stage of 14 days. At the end of each sampling time (days 0, 7, 28, and 42) whole-body portions were surveyed for total As concentrations and, complimentarily, surveyed for whole-body metallothionein (MT) induction to assess its role as a defense mechanism against exposure to As^III. Histochemical evaluation of the digestive gland was performed to verify As deposition and elimination in the tissue. Results show a significant increase in whole-body total As after 28 days of exposure for all treatments, followed by a decrease at the end of the depuration phase. Biodynamic kinetic models for As uptake and elimination were obtained from bioaccumulation data during the exposure phase, for all As treatments, by estimating uptake and elimination rate constants. Bioconcentration factors (BCFs) were estimated by the ratio of these constants. Results revealed that exposure to higher concentrations of As^III causes a decrease in BCFs, suggesting that C. fluminea triggers effective regulatory mechanisms when exposed to higher concentrations of the metalloid. Significant induction of MT was detected during the exposure phase, followed by a decrease in MT concentration to control levels after depuration for all treatments. No significant differences in MT concentrations were observed between treatments. This finding may confirm the role of MT as part of the As regulation process, but its independence relative to concentrations of As^III in water suggests that MT induction is not dose dependent. The histochemical evaluation provided clear evidence that As was effectively accumulated in the digestive gland during exposure and eliminated during depuration. The present work demonstrated that C. fluminea is capable of regulating As, even at exposures as high as 1000 μg L⁻¹ of waterborne As^III. Pedro M. Costa, Hugo M. Santos and Mário S. Diniz contributed equally to this work.     

Effects of Arsenite Exposure during Fetal Development on Energy Metabolism and Susceptibility to Diet-Induced Fatty Liver Disease in Male Mice

Background

Chronic exposure to arsenicals at various life stages and across a range of exposures has been implicated in cardiometabolic and liver disease, but disease predisposition from developmental exposures remains unclear.

Objectives

In utero and post-weaning exposure to trivalent arsenic (As^III) was examined on the background of a Western-style diet to determine whether As^III exposure affects metabolic disease.

Methods

Male Swiss Webster mice were exposed to 100 ppb As^III in utero, after weaning, or both. Ad libitum access to a Western-style diet was provided after weaning, and the plasma metabolome, liver histopathology, liver enzyme activity, and gene expression were analyzed.

Results

Hepatic lipid composition and histopathology revealed that developmental As^III exposure exacerbated Western-style diet–induced fatty liver disease. Continuous As^III exposure increased cardiometabolic risk factors including increased body weight, insulin resistance, hyperglycemia, and plasma triglycerides. As^III exposure produced a decrease in the intermediates of glycolysis and the TCA cycle while increasing ketones. Hepatic isocitrate dehydrogenase activity was also decreased, which confirmed disruption of the TCA cycle. Developmental As^III exposure increased the expression of genes involved in fatty acid synthesis, lipogenesis, inflammation, and packaging of triglycerides, suggesting an increased acetyl coenzyme A (acetyl-CoA) load.

Conclusions

In utero and continuous early-life exposure to As^III disrupted normal metabolism and elevated the risk for fatty liver disease in mice maintained on a high-fat diet. Our findings suggest that individuals exposed to As^III during key developmental periods and who remain exposed to As^III on the background of a Western-style diet may be at increased risk for metabolic disease later in life.

Citation

Ditzel EJ, Nguyen T, Parker P, Camenisch TD. 2016. Effects of arsenite exposure during fetal development on energy metabolism and susceptibility to diet-induced fatty liver disease in male mice. Environ Health Perspect 124:201–209; http://dx.doi.org/10.1289/ehp.1409501     

Influence of Cobalamin on Arsenic Metabolism in Bangladesh

Background

Arsenic is a carcinogen to which 35 million people in Bangladesh are chronically exposed. The enzymatic transfer of methyl groups to inorganic As (iAs) generates monomethylarsonic (MMA) and dimethylarsinic acids (DMA) and facilitates urinary As (uAs) elimination. This process is dependent on one-carbon metabolism, a pathway in which folate and cobalamin have essential roles in the recruitment and transfer of methyl groups. Although DMA^V is the least toxic metabolite, increasing evidence suggests that MMA^III may be the most cytotoxic and genotoxic As intermediary metabolite.

Objective

We examined the associations between plasma cobalamin and uAs metabolites.

Methods

We conducted a cross-sectional study of 778 Bangladeshi adults in which we over-sampled cobalamin-deficient participants. Participants provided blood samples for the measurement of plasma cobalamin and urine specimens for As measurements.

Results

Cobalamin was inversely associated with the proportion of total uAs excreted as iAs (%iAs) [unstandardized regression coefficient (b) = –0.10; 95% confidence interval (CI), −0.17 to −0.02; p = 0.01] and positively associated with %MMA (b = 0.12; 95% CI, 0.05 to 0.20; p = 0.001). Both of these associations were stronger among folate-sufficient participants (%iAs: b = −0.17; 95% CI, −0.30 to −0.03; p = 0.02. %MMA: b = 0.20; 95% CI, 0.11 to 0.30; p < 0.0001), and the differences by folate status were statistically significant.

Conclusions

In this group of Bangladeshi adults, cobalamin appeared to facilitate the first As methylation step among folate-sufficient individuals. Given the toxicity of MMA^III, our findings suggest that in contrast to folate, cobalamin may not favorably influence As metabolism.     

Arsenic Inhibits Myogenic Differentiation and Muscle Regeneration

Background

The incidence of low birth weights is increased in offspring of women who are exposed to high concentrations of arsenic in drinking water compared with other women. We hypothesized that effects of arsenic on birth weight may be related to effects on myogenic differentiation.

Objective

We investigated the effects of arsenic trioxide (As₂O₃) on the myogenic differentiation of myoblasts in vitro and muscle regeneration in vivo.

Methods

C2C12 myoblasts and primary mouse and human myoblasts were cultured in differentiation media with or without As₂O₃ (0.1–0.5 μM) for 4 days. Myogenic differentiation was assessed by myogenin and myosin heavy chain expression and multinucleated myotube formation in vitro; skeletal muscle regeneration was tested using an in vivo mouse model with experimental glycerol myopathy.

Results

A submicromolar concentration of As₂O₃ dose-dependently inhibited myogenic differentiation without apparent effects on cell viability. As₂O₃ significantly and dose-dependently decreased phosphorylation of Akt and p70s6k proteins during myogenic differentiation. As₂O₃-induced inhibition in myotube formation and muscle-specific protein expression was reversed by transfection with the constitutively active form of Akt. Sections of soleus muscles stained with hematoxylin and eosin showed typical changes of injury and regeneration after local glycerol injection in mice. Regeneration of glycerol-injured soleus muscles, myogenin expression, and Akt phosphorylation were suppressed in muscles isolated from As₂O₃-treated mice compared with untreated mice.

Conclusion

Our results suggest that As₂O₃ inhibits myogenic differentiation by inhibiting Akt-regulated signaling.     

Exposure assessment of arsenic speciation in different rice types depending on the cooking mode

Total (As_t), inorganic arsenic (As_i = As(III) + As(V)) and dimethylarsonic acid (DMA) were determined in 37 commercial rice samples collected in France. As_t was measured by inductively coupled plasma-mass spectrometry (ICP-MS) whereas anion-exchange chromatography – ICP-MS was used for As_i and DMA determination. As_t in raw rice varied from 0.041 to 0.535 mg kg⁻¹ whereas As_i varied from 0.025 mg kg⁻¹ (polished Basmati rice) up to 0.471 mg kg⁻¹ (organic rice duo). The daily intake and associated health risk for different population groups as a function of age and gender was also assessed. The intake varied between 0.002 and 0.184 μg kg⁻¹ body weight for As_t and 0.002 and 0.153 μg kg⁻¹ body weight for As_i, which do not pose a chronic toxicity risk. Organic wholegrain rice may entail a risk for children in the case of sole consumption at the expense of polished rice. The impact of rice cooking/boiling in terms of the overall toxicological risk related to As species was also investigated. Pre-rinsing and boiling the raw rice by using an excess of water is the most efficient mode to obtain a significant As_i removal and further reduction of the toxicological risk for children, particularly for white rice varieties.     

Surveillance on chronic arsenic exposure in the Mekong River basin of Cambodia using different biomarkers

Thousands of Cambodia populations are currently at high risks of both toxic and carcinogenic effects through drinking arsenic-rich groundwater. In order to determine and assess the use of arsenic contents in different biological samples as biomarkers of chronic arsenic exposure from drinking arsenic-rich groundwater in Cambodia, individual scalp hair, fingernail and toenail were collected from three different provinces in the Mekong River basin of Cambodia. After washing and acid-digestion, digestate was analyzed for total arsenic by an inductively coupled plasma mass spectrometry. Chemical analysis of the acid-digested hair revealed that among 270 hair samples cut from Kandal, 78.1% had arsenic content in scalp hair (As_h) greater than the typical As_h (1.00 μg g⁻¹), indicating possible arsenic toxicity. Concurrently, 1.2% and 0.6% were found elevated in Kratie (n = 84) and Kampong Cham (n = 173), respectively. Similarly, the upper end of the ranges for arsenic contents in fingernail (As_fn) and toenail (As_tn) clipped from Kandal (fingernail n = 241; toenail n = 187) were higher than the normal arsenic content in nail (0.43–1.08 μg g⁻¹), however, none was observed elevated in both Kratie (fingernail n = 76, toenail n = 42) and Kampong Cham (fingernail n = 83; toenail n = 52). Significant positive intercorrelations between groundwater arsenic concentration (As_w), average daily dose (ADD) of arsenic, As_h, As_fn and As_tn suggest that As_h, As_fn and As_tn can be used as biomarkers of chronic arsenic exposure from drinking arsenic-rich groundwater, in which As_h is more favorable than As_fn and As_tn due to the ease of sample processing and analytical measurements, respectively.     

Toxicity of heavy metals and salts to eurasian watermilfoil (Myriophyllum spicatum L.)

The toxicity of various heavy metals and salts to Eurasian watermilfoil (Myriophyllum spicatum L.) was determined under controlled growth conditions. Toxicants were added to water or to soil in systems with and without woods earth in the substrate.Fifty precent inhibition of root weight occurred with concentrations of 0.25 ppm Cu⁺², 1.9 ppm Cr₂O₇ ^–2, 3.4 ppm Hg⁺², 2.9 ppm AsO₂ ^–1, 7.4 ppm Cd⁺², 2.5 ppm Al⁺³, 9.9 ppm Cr⁺³, 41.2 ppm Ba⁺², 21.6 ppm Zn⁺², 13.3 ppm NH₄ ⁺¹, 22.4 ppm CN^–1, 143 ppm B₄O₇ ^–2, 363 ppm Pb⁺², 10,228 ppm Na₂SO₄, and 8,183 ppm NaCl. Soil increased toxicity of Cr⁺² and Ba⁺² but decreased toxicity of Cr₂O₇ ^–2, Cu⁺², Cd⁺², Al⁺³, and Hg⁺². In distilled water, CaCl₂ increased toxicity of Cr⁺³ but not Cr₂O₇ ^–2.For most toxicants there was a consistent relationship between inhibition of length and inhibition of weight and between inhibition of roots and inhibition of shoots. However, Cr₂O₇ ^–2 disproportionately decreased dry weight, and Hg⁺² and Na₂SO₄ disproportionately decreased stem length growth. With Cd⁺² and Cu⁺² stem length was greater relative to other measures of growth. Toxicity of Na₂SO₄ and NaCl was the same when concentrations were calculated as osmotic pressure but not when calculated as Na atoms or as total molecules/L.     

Determination of inorganic arsenic in Argentinean rice by selective HGAAS: Analytical performance for paddy,brown and polished rice

Inorganic As (iAs) species require strict monitoring in foodstuff due to their toxicity. Rice is of particular concern, with recent legislations establishing limits for these species. In this work we develop a method based on selective hydride generation atomic absorption spectrometry (HGAAS) for the determination of iAs in different types of rice (polish, parboiled, brown and paddy rice). The multivariate design of experiments used for optimization showed interactions between different factors involved in hydride generation. Matrix effects were systematically studied, where the flow rate of the carrier gas proved to be a critical parameter for the minimization of matrix interferences. Nevertheless, matrix-matching was found to be necessary for accurate quantification of paddy rice samples. Comparison of the iAs concentrations obtained by HGAAS and HPLC-ICP-MS showed non-significant differences between the methods. Analysis of 86 rice samples from the province of Entre Ríos showed relatively low concentrations of iAs (<282 μg kg⁻¹ for paddy rice and <120 μg kg⁻¹ for polished rice), regardless of total As concentrations (which ranged from 63 μg kg⁻¹ to 932 μg kg⁻¹), suggesting that the rice analyzed tends to accumulate As in its organic forms.     

Arsenic-associated oxidative stress, inflammation, and immune disruption in human placenta and cord blood

Background

Arsenic (As) exposure during pregnancy induces oxidative stress and increases the risk of fetal loss and low birth weight.

Objectives

In this study we aimed to elucidate the effects of As exposure on immune markers in the placenta and cord blood, and the involvement of oxidative stress.

Methods

Pregnant women were enrolled around gestational week (GW) 8 in our longitudinal, population-based, mother–child cohort in Matlab, an area in rural Bangladesh with large variations in As concentrations in well water. Women (n = 130) delivering at local clinics were included in the present study. We collected maternal urine twice during pregnancy (GW8 and GW30) for measurements of As, and placenta and cord blood at delivery for assessment of immune and inflammatory markers. Placental markers were measured by immunohistochemistry, and cord blood cytokines by multiplex cytokine assay.

Results

In multivariable adjusted models, maternal urinary As (U-As) exposure both at GW8 and at GW30 was significantly positively associated with placental markers of 8-oxoguanine (8-oxoG) and interleukin-1β (IL-1β); U-As at GW8, with tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ); and U-As at GW30, with leptin; U-As at GW8 was inversely associated with CD3⁺ T cells in the placenta. Cord blood cytokines (IL-1β, IL-8, IFNγ, TNFα) showed a U-shaped association with U-As at GW30. Placental 8-oxoG was significantly positively associated with placental proinflammatory cytokines. Multivariable adjusted analyses suggested that enhanced placental cytokine expression (TNFα and IFNγ) was primarily influenced by oxidative stress, whereas leptin expression appeared to be mostly mediated by As, and IL-1β appeared to be influenced by both oxidative stress and As.

Conclusion

As exposure during pregnancy appeared to enhance placental inflammatory responses (in part by increasing oxidative stress), reduce placental T cells, and alter cord blood cytokines. These findings suggest that effects of As on immune function may contribute to impaired fetal and infant health.     

Oxidative stress in fish cells:In vitro studies

Bluegill sunfish BF-2 fibroblasts were used in the neutral red (NR) cytotoxicity assay to discern the toxicities of hydrogen peroxide (H₂O₂) and paraquat as indicated by their abilities to induce oxidative stress. The toxicity of H₂O₂ was markedly enhanced in BF-2 cells treated with the glutathione depleting agents, buthionine sulfoximine (BSO), maleic acid, and chlorodinitrobenzene; similar treatments did not sensitize the BF-2 cells to paraquat, a redox cycling xenobiotic. BSO treated BF-2 cells, however, were sensitized to nitrofurantoin, also a redox cycling chemical. Diethyldithiocarbamate, an ihibitor of superoxide dismutase, only weakly enhanced the sensitivity of the BF-2 cells to H₂O₂ and paraquat. 1,10-Phenanthroline, a chelator of Fe²⁺, reduced the cytotoxicity of H₂O₂ and paraquat, presumably by preventing hydroxyl radical formation in the Fenton reaction. Quin 2 AM, an intracellular chelator of Ca²⁺, markedly lessened the toxicity of H₂O₂, but not of paraquat; EGTA, an extracellular chelator of Ca²⁺, had no effect on the toxicity of H₂O₂ or paraquat. Apparently, perturbation of intracellular Ca²⁺ homeostasis is involved in H₂O₂ toxicity. For comparative purposes, some studies were performed with fathead minnow FHM epithelioid cells, BALB/c mouse 3T3 fibroblasts, and human HepG2 hepatoma cells. The BF-2 fibroblast/NR cytotoxicity red assay was shown to be a suitable model to study oxidative stress in fish.     

Relationship Between Proline and Hg<Superscript>2+</Superscript>-Induced Oxidative Stress in a Tolerant Rice Mutant

There has been little agreement regarding the mechanism by which proline reduces heavy metal stress. The present work examines the relationship between Hg²⁺-induced oxidative stress and proline accumulation in rice and explores the possible mechanisms through which proline protects against Hg²⁺ stress. The effect of proline on alleviation of Hg²⁺ toxicity was studied by spectrophotography and enzymatic methods. Hg²⁺ induced oxidative stress in rice by increasing lipid peroxidation. Pretreatment of the rice with 2 mM proline for 12 h profoundly alleviated Hg²⁺-induced lipid peroxidation and minimized H₂O₂ accumulation. Proline pretreatment significantly reduced (p < 0.01) the Hg²⁺ content in rice leaves. A comparison of the effects of proline pretreatment on H₂O₂ accumulation by Hg²⁺ and aminotrazole suggested that proline protected cells from Hg²⁺-induced oxidative stress by scavenging reactive oxygen species. The present work demonstrates a protective effect of proline on Hg²⁺ toxicity through detoxifying reactive oxygen species, rather than chelating metal ions or maintaining the water balance under Hg²⁺ stress.