Doses Of Arsenic Research Articles

Abstract LB-159: A missense variant in FTCD is associated with arsenic metabolism efficiency and arsenic toxicity in Bangladesh

Abstract Exposure to drinking water contaminated with inorganic arsenic (iAs), a known human carcinogen, affects over 100 million people worldwide. Arsenic-induced skin lesions are an early sign of arsenic toxicity and a risk factor for subsequent cancer. Once absorbed into the blood, iAs can be converted to mono-methylated (MMA) and then di-methylated (DMA) forms of arsenic, with methylation facilitating the excretion of arsenic in urine. The relative abundance of these arsenic species in urine (iAs%, MMA%, DMA%) represents the efficiency with which an individual metabolizes arsenic. The AS3MT region is the only locus known to harbor variants that influence arsenic metabolism efficiency in humans. In order to identify additional variants that impact arsenic metabolism, we measured protein-coding variants across the human exome using Illumina’s Exome Chip for 1,660 Bangladeshi individuals participating in the Health Effects of Arsenic Longitudinal Study. Among 20,265 exonic variants with a minor allele frequency greater than 1%, only rs61735836 showed associations of experiment-wide significance for all three arsenic metabolite percentages (P=8x10-22, P=7x10-16, and P=2x10-12 for DMA%, MMA%, and iAs%, respectively). The minor allele (A) has a frequency of ~7% in our study (consistent with 1,000 Genomes data) and is associated with decreased DMA% and increased MMA% and iAs%. In subsequent analyses of 2,401 skin lesions cases and 2,472 controls, the low-efficiency allele (A) was associated with increased skin lesion risk (OR=1.25; P=5x10-4), suggesting this variant impacts arsenic toxicity through its impact on metabolism and internal dose of arsenic. rs61735836 is a missense variant (p.Val101Met) in exon 3 of FTCD, which codes for forminidoyltransferase cyclodeaminase. This enzyme is involved in one-carbon metabolism and is critical for production of methenyltetrahydrofolate, a donor of one-carbon groups to the methionine cycle. Methionine provides methyl groups for arsenic metabolism, and variation in folate status and one-carbon metabolism have long been hypothesized to influence arsenic metabolism, with folate supplementation resulting in increased arsenic metabolism efficiency in a randomized trial. FTCD expression in liver (the primary site of arsenic metabolism) is higher than in any other human tissue, but rs614735826 is not associated with gene expression in any tissue (based on GTEx). Furthermore, rs61735836 is not in LD (r2<0.1) with any nearby variant in South Asian populations, suggesting its effect on arsenic metabolism is likely through an amino acid substitution that alters FTCD function. This work implicates FTCD as a novel locus influencing arsenic metabolism efficiency, with potential implications for arsenic-induced cancer risk, and establishes an additional link between one-carbon metabolism and the methylation/metabolism of inorganic arsenic. Citation Format: Brandon L. Pierce, Lin Tong, Maria Argos, Farzana Jasmine, Mary V. Gamble, Joseph Graziano, Muhammad G. Kibriya, Habibul Ahsan. A missense variant in FTCD is associated with arsenic metabolism efficiency and arsenic toxicity in Bangladesh [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-159. doi:10.1158/1538-7445.AM2017-LB-159

From the Cover: Arsenic Induces Hippocampal Neuronal Apoptosis and Cognitive Impairments via an Up-Regulated BMP2/Smad-Dependent Reduced BDNF/TrkB Signaling in Rats.

Arsenic promotes hippocampal neuronal damage inducing cognitive impairments. However, mechanism arbitrating arsenic-mediated cognitive deficits remains less-known. Here, we identified that chronic exposure to environmentally relevant doses of arsenic increased apoptosis, characterized by caspase-3 activation, poly(ADP-ribose) polymerase cleavage and Terminal deoxynucleotidyl transferase dUTP nick-end labeling of rat hippocampal neurons, marked by NeuN. Investigating apoptotic mechanism through invivo and invitro studies revealed that arsenic promoted bone morphogenetic protein-2 (BMP2) expression, supported by increased BMP-receptor2 (BMPR2) and p-Smad1/5 in hippocampal neurons. BMP2-silencing and treatment with BMP antagonist, noggin, attenuated the arsenic-induced apoptosis and loss in hippocampal neurons. We then investigated whether BMP2/Smad signaling stimulated neuronal apoptosis independently or required other intermediate pathways. We hypothesized participation of brain-derived neurotrophic factor (BDNF) that promotes neuronal survival. We identified an arsenic-mediated attenuation of BDNF-dependent TrkB signaling, and observed that co-treatment with recombinant-BDNF reinstated BDNF/TrkB and reduced neuronal apoptosis. To probe whether BMP2/Smad and BDNF/TrkB pathways could be linked, we co-treated arsenic with noggin or recombinant BDNF. We detected a noggin-mediated restored BDNF/TrkB, while recombinant-BDNF failed to affect BMP2/Smad signaling. In addition, we found that TrkB-inhibitor, K252a, nullified noggin-induced protection, proving the necessity of a downstream reduced BDNF/TrKB signaling for BMP2/Smad-mediated apoptosis in arsenic-treated neurons. We further related our observations with cognitive performances, and detected noggin-mediated restoration of transfer latency time and learning-memory ability for passive avoidance and Y-Maze tests respectively in arsenic-treated rats. Overall, our study proves that arsenic promotes hippocampal neuronal apoptosis through an up-regulated BMP2/Smad-dependent attenuation of BDNF/TrkB pathway, inducing cognitive deficits.

Evaluation of vascular effect of arsenic using in vivo assays.

Arsenic (As) is an abundant toxicant present in groundwater and soil in various parts of the world including eastern part of India. The epidemiological studies have shown that arsenic exposure is linked to developmental defects and miscarriage. Placenta is known to utilize vasculogenesis to develop its vasculature circulation. The effects of four different doses of sodium meta-arsenite (0, 10, 20, 75, and 150ppm) were assessed on the vascular structure using two different in vivo models, i.e., Matrigel and chorioallantoic membrane (CAM) assay. For the Matrigel assay, mice were exposed to different doses of arsenic through drinking water for 1month. Placenta and Matrigel plug (which was inserted on gestational day (GD 0.5)) were removed on GD 14. Similar arsenic concentration was used in CAM assay to observe the effect of vessel development in hen's eggs. The CAM assay outcome evaluated by Angiosys software showed that arsenic exposure reduced the total and mean tubule length in all the arsenic-treated groups. The percentage tubule inhibition was declined significantly in 20, 75, and 150ppm arsenic-treated groups as evaluated by ImageJ software. Analysis of the CAM outcome by both the image analysis software indicated the adverse effect of arsenic on the tubules. Further, a significant higher blood vessel density in 10ppm and lower vessel density in 20, 75, and 150ppm arsenic-exposed mice were also observed in Matrigel plug assay. The placental hypertrophy and dysplasia especially in the labyrinth zone (vasculature) were noted in placenta of arsenic-treated mice. The study indicated that higher arsenic exposures inhibited the angiogenesis which was dose-dependent in both CAM and Matrigel assay and altered structural morphology of placenta. However, no inhibition of blood vessels was noted at lower, i.e., 10ppm of arsenic-treated group.

Environmentally relevant dose of arsenic interferes in functions of human monocytes derived dendritic cells

Arsenic is a major environmental pollutant and highly hazardous toxin to human health, which well established as carcinogen and immune deregulatory properties. Dendritic cells (DCs) have a pivotal role in cell-mediated immunity for T-cell activation and antigen presentation.In this study, T cell activation, some key functional genes expression, cell stability and phagocytosis capacity of human monocytes derived DCs (MDDCs) were analyzed after in vitro exposure to very low dose of arsenic for 12 and 24h. Arsenic decreased continually phagocytosis capacity of MDDCs. Furthermore, down-regulation of the cell-surface expression of the co-stimulatory molecule CD40 after 24h post treatment with arsenic, confirmed arsenic interferers in the phagocytosis process. Pro inflammatory cytokines, IL1β and TNFα were more expressed in arsenic-treated MDDCs while IL6 transiently was down regulated.In general, our novel findings here strongly suggest that low level of arsenic dysregulates four fundamental immune processes of DCs. Mechanistically; this could explain the observed immunodeficiency activity of Arsenic, and give direction for comprehension the pathogenesis of Arsenic-induced diseases.

Dose-Response Relationship between Inorganic Arsenic Exposure and Lung Cancer among Arseniasis Residents with Low Methylation Capacity.

Background: Exposure to inorganic arsenic (InAs) has been documented as a risk factor for lung cancer. This study examined the association between InAs exposure, its metabolism, and lung cancer occurrence.Methods: We followed 1,300 residents from an arseniasis area in Taiwan, determined urinary InAs metabolites, and identified 39 lung cancer cases. Cox proportional hazards model was performed.Results: The results demonstrated that participants with either the primary methylation index [monomethylarsonic acid (MMA)/InAs] or the secondary methylation index [dimethylarsenic acid (DMA)/MMA] lower than their respective median values were at a higher risk of lung cancer (HRs from 3.41 to 4.66) than those with high methylation capacity. The incidence density of lung cancer increased from 79.9/100,000 (year-1) to 467.4/100,000 (year-1) for residents with low methylation capacity and from 0 to 158.5/100,000 (year-1) for residents with high methylation capacity when the arsenic exposure dose increased from 2 to 10 ppb to ≥200 ppb, respectively. The analyses revealed a dose-response relationship between lung cancer occurrence and increasing arsenic concentrations in drinking water as well as cumulative arsenic exposure (monotonic trend test; P < 0.05 and P < 0.05, respectively) among the residents with low methylation capacity. The relationship between arsenic exposure and lung cancer among high methylators was not statistically significant.Conclusions: Hypomethylation responses to InAs exposure may dose dependently increase lung cancer occurrence.Impact: The high-risk characteristics observed among those exposed should be considered in future preventive medicine and research on arsenic carcinogenesis. Cancer Epidemiol Biomarkers Prev; 26(5); 756-61. ©2016 AACR.

Arsenic treatment increase Aurora-A overexpression through E2F1 activation in bladder cells

BackgroundArsenic is a widely distributed metalloid compound that has biphasic effects on cultured cells. In large doses, arsenic can be toxic enough to trigger cell death. In smaller amounts, non-toxic doses may promote cell proliferation and induces carcinogenesis. Aberration of chromosome is frequently detected in epithelial cells and lymphocytes of individuals from arsenic contaminated areas. Overexpression of Aurora-A, a mitotic kinase, results in chromosomal instability and cell transformation. We have reported that low concentration (≦1 μM) of arsenic treatment increases Aurora-A expression in immortalized bladder urothelial E7 cells. However, how arsenic induces carcinogenesis through Aurora-A activation remaining unclear.MethodsBromodeoxyuridine (BrdU) staining, MTT assay, and flow cytometry assay were conducted to determine cell proliferation. Messenger RNA and protein expression levels of Aurora-A were detected by reverse transcriptional-PCR and Western blotting, respectively.Centrosome of cells was observed by immunofluorescent staining. The transcription factor of Aurora-A was investigated by promoter activity, chromosome immunoprecipitation (ChIP), and small interfering RNA (shRNA) assays. Mouse model was utilized to confirm the relationship between arsenic and Aurora-A.ResultsWe reveal that low dosage of arsenic treatment increased cell proliferation is associated with accumulated cell population at S phase. We also detected increased Aurora-A expression at mRNA and protein levels in immortalized bladder urothelial E7 cells exposed to low doses of arsenic. Arsenic-treated cells displayed increased multiple centrosome which is resulted from overexpressed Aurora-A. Furthermore, the transcription factor, E2F1, is responsible for Aurora-A overexpression after arsenic treatment. We further disclosed that Aurora-A expression and cell proliferation were increased in bladder and uterus tissues of the BALB/c mice after long-term arsenic (1 mg/L) exposure for 2 months.ConclusionWe reveal that low dose of arsenic induced cell proliferation is through Aurora-A overexpression, which is transcriptionally regulated by E2F1 both in vitro and in vivo. Our findings disclose a new possibility that arsenic at low concentration activates Aurora-A to induce carcinogenesis.

Metabolic alterations in liver of fresh water fish, C. punctata exposed to arsenic: an adverse and adaptive response to the environment

Arsenic is a major toxicant impairing in diverse metabolic alterations of the organisms and the mechanism of adaptive response is yet to be identified. In the present study, effects of different doses of arsenic in liver of Channa punctata on the regulation of metabolic activities were done. C. punctata, a variety of fresh water fish were exposed to 1, 10 and 1000 ?M concentration of Na2HAsO4 for 1 h. The amount of protein, in response to 1, 10 and 1000 ?M concentration of arsenic were augmented by 184.47% (2.84-folds), 202.82% (3.0- folds) and 317.49% (4.17-folds), respectively and was found to be higher for 1000 ?M dose. Cholesterol contents in liver were similarly exaggerated by 517.45% (6.17-folds), 308.13% (4.1-folds) and 286.41% (3.86-folds), respectively. However, the higher response was found for 1 ?M dose of Na2HAsO4. Similar stimulatory effects on triglyceride level were observed in response to arsenic. Na2HAsO4 causes 443.74% (5.43-folds), 533.11% (6.33-folds) and 548.48% (6.48-folds) enhanced triglyceride level in liver respectively and the effects were pronounced for 1000 ?M concentration. Our findings conclude that arsenic is involved in impairment of metabolic activities in liver of the species of fish and gives an impact to the environment for survival.Int. J. Agril. Res. Innov. &amp; Tech. 6 (2): 87-94, December, 2016

PSII photochemistry, oxidative damage and anti-oxidative enzymes in arsenate-stressed Oryza sativa L. seedlings

ABSTRACTThe aim of the present study was to quantify the arsenic-induced damage in rice seedlings in terms of certain physiological and biochemical parameters. For this, hydroponically grown Oryza sativa L. seedlings were exposed to certain doses of AsV as Na2HAsO4 (10, 25, 50 and 100 µM). All the tested doses manifested in a significant loss in the pigments content and photosynthesis, which culminated in retarded growth of the seedlings. The AsV-mediated decline in PSII photochemistry could be correlated with the decline in ϕP0, ψ0, ϕE0 and PIABS. In vitro and in vivo detection of and H2O2 and the consequent rise in malondialdehyde equivalents after AsV treatments stimulated the anti-oxidant enzymes, that is, superoxide dismutase (SOD) (except at 50 and 100 µM AsV), peroxidase and catalase, activity which was further confirmed by the native polyacrylamide gel electrophoresis (PAGE) that also revealed the least expression of SOD isoforms against 50 and 100 µM AsV treatment. The present investigation is a categorical demonstration of the inhibitory behaviour of AsV in O. sativa L. seedlings. At lower doses of arsenate, reactive oxygen species and anti-oxidants cooperatively acted in such a way that the impacts of the stress were far lesser on various growth and physiological parameters.

Status of photosynthetic pigments, lipid peroxidation and anti-oxidative enzymes in Vigna mungo in presence of arsenic

ABSTRACTThe response to arsenic was evaluated for photosynthetic pigments, lipid peroxidation and anti-oxidative enzymes in black gram. Black gram (Vigna mungo) subjected to arsenic doses of 100 µM and 200 µM, showed increased amount of lipid peroxidation. Activity of peroxidase (POD) increased tremendously in arsenic treated Vigna leaves over control. Similarly, activities of enzymes like superoxide dismutase (SOD) and ascorbate peroxidase (APX) also increased with increase in arsenic. Analysis of native PAGE superoxide dismutase activity showed one manganese (Mn)-SOD and two copper/zinc (Cu/Zn)-SOD isoenzymes in black gram leaves, whose intensity increased especially at 200 µM arsenic treatment. However, activity of catalase (CAT) decreased with increase in concentrations of arsenic. This clearly indicates that except CAT, all studied antioxidative enzymes like SOD, POD and APX showed increased expression at arsenic treatments, which reflects their protective role against arsenic toxicity in black gram plants. Photosynthetic pigments like chlorophyll and carotenoids showed reduction with increasing concentrations of arsenic in treatment solutions.

Oxygen toxicity and antioxidative responses in arsenic stressed Helianthus annuus L. seedlings against UV-B

In order to know the impact of elevated level of UV-B on arsenic stressed Helianthus annuus L. var. DRSF-113 plants, certain physiological (growth – root and shoot lengths, their fresh masses and leaf area; photosynthetic competence and respiration) and biochemical parameters (pigments – Chl a and b, Car, anthocyanin and flavonoids; reactive oxygen species – superoxide radicals, H2O2; reactive carbonyl group, electrolyte leakage; antioxidants – superoxide dismutase, peroxidise, catalase, glutathione-S-transferase, proline) of their seedlings were analysed under the simultaneous exposures of two arsenic doses (6mgkg−1 soil, As1; and 12mgkg−1 soil, As2) and two UV-B doses (1.2kJm−2d−1, UV-B1; and 3.6kJm−2d−1, UV-B2). As1 and As2 alone declined all the studied growth parameters – along with photosynthetic pigments which were further aggravated after the simultaneous exposures of predefined levels of UV-B. Each As exposure was accompanied by significant accumulation of As in root, shoot and leaves and was substantiated by simultaneous exposures of UV-B doses which manifested into suppressed growth, decreased chlorophyll contents and photosynthesis. In similar conditions, other photo-shielding pigments, viz. carotenoids, anthocyanin and flavonoids along with respiration and oxidative stress markers such as O2•¯, H2O2; and indicators of cell membrane damage like MDA (malondialdehyde), RCG (reactive carbonyl group), electrolyte leakage were enhanced by As, and became more pronounced after the simultaneous exposures of UV-B doses. As doses stimulated the activities of SOD, POD, CAT, GST and Pro which got further accelerated after the simultaneous exposures of UV-B doses.

Low doses of arsenic, via perturbing p53, promotes tumorigenesis

In drinking water and in workplace or living environments, low doses of arsenic can exist and operate as a potent carcinogen. Due to insufficient understanding and information on the pervasiveness of environmental exposures to arsenic, there is an urgent need to elucidate the underlying molecular mechanisms of arsenic regarding its carcinogenic effect on human health. In this study, we demonstrate that low doses of arsenic exposure mitigate or mask p53 function and further perturb intracellular redox state, which triggers persistent endoplasmic reticulum (ER) stress and activates UPR (unfolded protein response), leading to transformation or tumorigenesis. Thus, the results suggest that low doses of arsenic exposure, through attenuating p53-regulated tumor suppressive function, change the state of intracellular redox and create a microenvironment for tumorigenesis. Our study also provides the information for designing more effective strategies to prevent or treat human cancers initiated by arsenic exposure.

Abstract LB-029: Negative transcriptional and epigenetic regulation of DNA repair pathways by the heavy metals nickel and arsenic

Abstract Environmental exposure to certain heavy metals, such as nickel and arsenic, has been implicated in a variety of human cancers, including lung, skin, digestive track, and bladder cancers. Importantly, the mechanism underlying the carcinogenicity of nickel and arsenic remains poorly understood as they do not induce direct DNA mutagenesis. However, they do lead to global changes in chromatin structure and transcription, many similar to the effects of hypoxia. Since hypoxia is known to regulate many different DNA repair pathways, we investigated whether nickel and arsenic may similarly affect cellular DNA repair. We discovered that nickel and arsenic can lead to alterations in DNA repair gene expression, stable gene silencing, and decreased DNA repair capacity. First, we measured protein and mRNA levels of different DNA repair genes after NiCl2 or NaAsO2 treatment. We found that both metals induced down-regulation of BRCA1, FANCD2, and MLH1 over 24 to 48 hours at both the protein and mRNA levels. These results were observed in several different cells lines (HeLa, MCF7, BEAS-2B) with one notable exception that high dose arsenic induced up-regulation of BRCA1, FANCD2, and MLH1 in lung cancer-derived cell lines (A549, HCC827, NCI-H460). Next, to study the impact of long-term heavy metal exposure on DNA repair gene expression, we utilized an MLH1 promoter reporter construct that allows selection of cells harboring a silenced MLH1 promoter with ganciclovir. RKO cells stably expressing this construct were grown in the presence of 100 μM NiCl2, 0.5 μM NaAsO2, 1% oxygen, or control conditions. After 3 weeks, we observed that arsenic treatment, like hypoxia, led to a significant increase in promoter silencing compared to control cells, peaking at about 3.7-fold after 4 weeks. Nickel did not increase silencing, which may indicate a different mechanism of gene regulation. Finally, we used a luciferase assay to measure the effect of nickel and arsenic on the two primary DNA double-strand break (DSB) repair mechanisms, homologous recombination (HR) and non-homologous end joining (NHEJ). BEAS-2B cells pretreated with 250 μM NiCl2 or 5 μM NaAsO2 were transfected with a digested, inactive luciferase plasmid and allowed to conduct DSB repair to reactivate luciferase expression. We found that nickel and arsenic led to a 40-50% reduction in cellular HR capacity with no significant effect on NHEJ. To further pursue these results, we are performing chromatin immunoprecipitation studies to identify transcriptional or epigenetic factors mediating nickel and arsenic-induced down-regulation of DNA repair genes. In addition, we are using chromosomal-based assays to further characterize the impact of nickel and arsenic on DNA repair capacity. In conclusion, we have found that nickel and arsenic negatively regulate cellular DNA repair pathways, identifying a novel way in which heavy metals may contribute to carcinogenesis. Citation Format: Susan E. Scanlon, Christine D. Scanlon, Denise C. Hegan, Parker Sulkowski, Peter M. Glazer. Negative transcriptional and epigenetic regulation of DNA repair pathways by the heavy metals nickel and arsenic. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-029.

Arsenic-induced dose-dependent modulation of the NF-κB/IL-6 axis in thymocytes triggers differential immune responses.

Arsenic contamination of drinking water is a matter of global concern. Arsenic intake impairs immune responses and leads to a variety of pathological conditions including cancer. In order to understand the intricate tuning of immune responses elicited by chronic exposure to arsenic, a mouse model was established by subjecting mice to different environmentally relevant concentrations of arsenic in drinking water for 30days. Detailed study of the thymus, a primary immune organ, revealed arsenic-mediated tissue damage in both histological specimens and scanning electron micrographs. Analysis of molecular markers of apoptosis by Western blot revealed a dose-dependent activation of the apoptotic cascade. Enzymatic assays supported oxidative stress as an instigator of cell death. Interestingly, assessment of inflammatory responses revealed disparity in the NF-κB/IL-6/STAT3 axis, where it was found that in animals consuming higher amounts of arsenic NF-κB activation did not lead to the classical IL-6 upregulation response. This deviation from the canonical pathway was accompanied with a significant rise in numbers of CD4+ CD25+ FoxP3 expressing cells in the thymus. The cytokine profile of the animals exposed to higher doses of arsenic also indicated an immune-suppressed milieu, thus validating that arsenic shapes the immune environment in context to its dose of exposure and that at higher doses it leads to immune-suppression. Our study establishes a novel role of arsenic in regulating immune homeostasis in context to its dose, where, at higher doses, arsenic related upregulation of NF-κB cascade takes on an alternative role that is correlated with increased immune-suppression.

Bhas 42 cell transformation activity of cigarette smoke condensate is modulated by selenium and arsenic.

Cigarette smoking remains a major health risk worldwide. Development of newer tobacco products requires the use of quantitative toxicological assays. Recently, v-Ha-ras transfected BALB/c3T3 (Bhas 42) cell transformation assay was established that simulates the two-stage animal tumorigenesis model and measures tumor initiating and promoting activities of chemicals. The present study was performed to assess the feasibility of using this Bhas 42 cell transformation assay to determine the initiation and promotion activities of cigarette smoke condensate (CSC) and its water soluble fraction. Further, the modulating effects of selenium and arsenic on cigarette smoke-induced cell transformation were investigated. Dimethyl sulfoxide (DMSO) and water extracts of CSC (CSC-D and CSC-W, respectively) were tested at concentrations of 2.5-40 µg mL(-1) in the initiation or promotion assay formats. Initiation protocol of the Bhas 42 assay showed a 3.5-fold increase in transformed foci at 40 µg mL(-1) of CSC-D but not CSC-W. The promotion phase of the assay yielded a robust dose response with CSC-D (2.5-40 µg mL(-1)) and CSC-W (20-40 µg mL(-1)). Preincubation of cells with selenium (100 nM) significantly reduced CSC-induced increase in cell transformation in initiation assay. Co-treatment of cells with a sub-toxic dose of arsenic significantly enhanced cell transformation activity of CSC-D in promotion assay. The results suggest a presence of both water soluble and insoluble tumor promoters in CSC, a role of oxidative stress in CSC-induced cell transformation, and usefulness of Bhas 42 cell transformation assay in comparing tobacco product toxicities and in studying the mechanisms of tobacco carcinogenesis.

Cancer Risk from Exposure to Low to Moderate Level of Arsenic Using Meta-Analysis of Flexible Regression Models

These meta-analysis studies on arsenic exposure and disease risk assume linear exposure-response models. The linearity assumption for the logarithm of relative risks and levels of exposure to arsenic is overly simplified and is not adequate to capture the local structure accurately. This article applies fractional polynomial and cubic spline regression models in order to capture the shapes of the exposure-response relationships between both bladder and lung cancer risk and exposure to low to moderate dose arsenic. We consider low to moderate dose levels with concentrations from near 0 to 300µg/l. We also consider more recent studies on low to moderate dose exposure to arsenic and the risk of bladder and lung cancer. These flexible models are used to identify a combined general exposure-response relationship for the logarithm of relative risk and the levels of exposure to arsenic. The primary objective of this study is to predict overall risks of bladder and lung cancers by combining findings from systematically selected studies on these cancers under both linear and non-linear modeling assumptions. We predict overall risks of bladder and lung cancers for a series of exposure levels from the best fitting models.

Effects of inorganic arsenic exposure on glucose transporters and insulin receptor in the hippocampus of C57BL/6 male mice

Children and adolescent populations chronically exposed to high doses of inorganic arsenic (iAs) in drinking water in some regions around the world have shown behavioral and memory deficits. Recent studies have also associated iAs exposure with dysregulation of glucose metabolism. The hippocampus is a cerebral region well known for its role in learning and memory. Studies in vitro and in vivo have shown that the hippocampus is vulnerable to iAs exposure, and to changes in glucose metabolism. The glucose transporters (GLUTs) and insulin receptor (IR) regulate glucose metabolism in brain; they are expressed by hippocampal cells, and alterations in these proteins have been associated with memory deficits. The aims of this study were to evaluate the effects of iAs exposure via drinking water (DW) on GLUT1, GLUT3 and insulin receptor (INSR) mRNA expression in the hippocampus, on performance in a spatial memory task, and on peripheral glucose regulation. C57Bl/6 male mice were exposed to 50mg iAs/L via DW for one, two, or three months. The qRT-PCR analyses indicated that, compared to a control group, GLUT1 and GLUT3 mRNA levels were decreased, while INSR mRNA levels were increased in the hippocampus of iAs exposed animals. The levels of iAs and its methylated species in the hippocampus of the iAs-exposed group were significantly higher than in controls. Mice exposed to iAs learned the spatial task but showed increased latency to find the submerged platform 48h after the last training session; these animals also showed dysregulation of peripheral glucose. These results suggest that the effects of iAs exposure on a spatial memory task performance could be mediated by disruptions of glucose regulation in the CNS.

Divergent Effects of Arsenic on NF-κB Signaling in Different Cells or Tissues: A Systematic Review and Meta-Analysis.

Arsenic is ubiquitously present in human lives, including in the environment and organisms, and has divergent effects between different cells and tissues and between different exposure times and doses. These observed effects have been attributed to the nuclear transcription factor kappa B(NF-κB) signaling pathway. Herein, a meta-analysis was performed by independently searching databases including the Cochrane Library, PubMed, Springer, Embase, and China National Knowledge Infrastructure, to analyze effects of arsenic exposure on NF-κB signaling. Compared to controls, in the exposed group, p-IκB levels were found to be 8.13-fold higher (95% CI, 2.40–13.85; Z = 2.78; p = 0.005), IκB levels were 16.19-fold lower (95% CI, −27.44–−4.94; Z = 2.78; p = 0.005), and NF-κBp65 levels were 0.77-fold higher (95% CI, 0.13–1.42; Z = 2.34; p = 0.02) for normal cells and tissue, while NF-κBp65 levels were 4.90-fold lower (95% CI, −8.49–1.31; Z = 2.62; p = 0.009), NF-κB activity was 2.45-fold lower (95% CI, −3.66–1.25; Z = 4.00; p < 0.0001), and DNA-binding activity of NF-κB was 9.75-fold lower (95% CI, −18.66–4.54; Z = 2.15; p = 0.03) for abnormal cells and tissue. Short exposure to high arsenic doses activated the NF-κB signaling pathway, while long exposure to low arsenic doses suppressed NF-κB signaling pathway activation. These findings may provide a theoretical basis for injurious and therapeutic mechanisms of divergent effects of arsenic.

Polychlorinated Biphenyls and Cancer: Are Telomeres to Blame?

The accumulating epidemiological evidence of elevated cancer risk and mortality in individuals exposed to polychlorinated biphenyls (PCBs) led to their recent classification as human carcinogen by the International Agency for Research on Cancer (IARC) (International Agency for Research on Cancer (IARC), 2015). However, the mechanisms by which PCBs are linked to cancer are still unclear. In this issue, Scinicariello and Buser (Scinicariello, 2015) conducted a study of the association between leukocyte telomere length (LTL) and PCB blood levels in a nationally representative sample of the civilian US adult population using data from the National Health and Nutrition Examination Survey (NHANES). The authors showed that higher PCB blood levels were associated with longer LTL, and hypothesized that there could be a link to PCB-related carcinogenesis. A separate study reported similar relationships between LTL and PCB blood levels in a subset of NHANES participants (Mitro et al., 2015). However, a small study of healthy Koreans (Shin et al., 2010) showed that this relationship was only present at low PCB levels. In contrast, short LTL has been associated with a number of environmental or occupational exposures including particulate matter, black carbon, benzene, toluene, polycyclic aromatic hydrocarbons, N-nitrosamines, pesticides, and lead (reviewed in Zhang et al., 2013), all of which may contribute to PCB blood levels. Telomere shortening in response to chemical exposures may be explained, at least in part, by the induction of an oxidative stress DNA damage response (Zhang et al., 2013). Telomeres, the long (TTAGGG)n nucleotide repeats and an associated protein complex at chromosome ends, are essential for maintaining chromosomal stability. They shorten with each cell division and therefore are markers for cellular replicative capacity, cellular senescence, and aging. Telomere shortening and chromosomal instability has been described at early stages of carcinogenesis, suggesting a role of telomere dysfunction in cancer initiation (Ferguson et al., 2015). Cancer epidemiology studies have shown relationships with short LTL, but differences by cancer site and study design were noted. In a meta-analysis of 27 reports (Wentzensen et al., 2011), short LTL was associated with cancer risk, primarily in case–control studies (OR = 2.9 in case–control studies vs. 1.2 in prospective studies). This suggests that short LTL is a disease marker rather than a risk factor. Recently, a large study linked long LTL to melanoma risk (Iles et al., 2014). The spectrum of cancers associated with long LTL is not clear yet, but suggested to include lung and Non-Hodgkin's lymphoma (NHL). It is of interest that cutaneous melanoma and possibly NHL are the main cancers associated with excess risk in PCBs exposed individuals (International Agency for Research on Cancer (IARC), 2015), suggesting a possible contribution of LTL in PCB-related carcinogenesis. The large sample size, the national representation, and the wealth of collected information NHANES offers are among the strengths of this study. On the other hand, the cross-sectional design restricted its ability to establish a causal inference between LTL, PCB exposure, and cancer risk. The one-time measurement of PCB blood level and LTL may not reflect the full spectrum of the association. Information on the duration and dose of exposure to PCBs would have been useful (reviewed in Zhang et al., 2013) Short-term exposure to ambient particulate matter was associated with long LTL, while longer exposures were associated with short LTL. Exposure dose in relation to LTL was noted in other environmental exposures. For example, exposure to low dose of arsenic resulted in telomerase overexpression and telomere elongation in cord blood cells, while exposure at large doses suppressed telomerase, shortened telomeres, and induced apoptosis. A recent study (Andreotti et al., 2015) evaluating the association between LTL and pesticide exposure suggested a differential effect on LTL in long-term versus recent exposures for certain pesticides. While LTL may present a good surrogate for telomere length in other tissues, it is not clear how good of a surrogate it is for tissues affected by chemical exposures. Measuring telomere length in organs directly affected by PCB exposure, and comparing this to LTL may explain the role telomeres may play in PCB-related carcinogenesis. Also, LTL measurement obtained by quantitative polymerase chain reaction (qPCR) assay may be affected by the cell composition of the sample since telomere length differs by peripheral blood cell subtype. Using a leukocyte cell-type specific TL measurement assay such as flow FISH may provide better insights into such association. Important considerations in epidemiological studies of telomere length are discussed in details elsewhere (Bodelon et al., 2014). In conclusion, the mechanism behind PCB-related carcinogenesis is still unknown. The similarity between cancer sites associated with long LTL, and cancers linked with PCBs provides an interesting hypothesis to test. A large prospective study with serial LTL and PCBs level measurements is required to better understand this relationship.

Tolerance, arsenic uptake, and oxidative stress in Acacia farnesiana under arsenate-stress

ABSTRACTAcacia farnesiana is a shrub widely distributed in soils heavily polluted with arsenic in Mexico. However, the mechanisms by which this species tolerates the phytotoxic effects of arsenic are unknown. This study aimed to investigate the tolerance and bioaccumulation of As by A. farnesiana seedlings exposed to high doses of arsenate (AsV) and the role of peroxidases (POX) and glutathione S-transferases (GST) in alleviating As-stress. For that, long-period tests were performed in vitro under different AsV treatments. A. farnesiana showed a remarkable tolerance to AsV, achieving a half-inhibitory concentration (IC50) of about 2.8 mM. Bioaccumulation reached about 940 and 4380 mg As·kg−1 of dry weight in shoots and roots, respectively, exposed for 60 days to 0.58 mM AsV. Seedlings exposed to such conditions registered a growth delay during the first 15 days, when the fastest As uptake rate (117 mg kg−1 day−1) occurred, coinciding with both the highest rate of lipid peroxidation and the strongest up-regulation of enzyme activities. GST activity showed a strong correlation with the As bioaccumulated, suggesting its role in imparting AsV tolerance. This study demonstrated that besides tolerance to AsV, A. farnesiana bioaccumulates considerable amounts of As, suggesting that it may be useful for phytostabilization purposes.

Influence of arsenic stress on growth, physiological activities and artemisinin production in two varieties of Artemisia (Artemisia annua) differing in artemisinin yield

Artemisinin, extracted from the leaves of Artemisia annua L., has been recognized as an effective and safe remedy against malaria. A pot experiment was conducted according to randomized block design using five replicates to screen the A. annua L. varieties, namely 'CIM-Arogya' and 'Jeevan Raksha' under arsenic stress. Four concentrations of arsenic [0 (control), 15, 30 and 45 mg kg-1 soil] were applied to the soil. Measurements for growth characteristics, physiological attributes, biochemical parameters, yield and quality attributes were carried out at pre-flowering [90 days after planting (DAP)] and flowering (120 DAP) stages. The variety 'Jeevan Raksha' was more adversely affected by arsenic stress than the 'CIM-Arogya', suggesting that the 'CIM-Arogya' was more arsenic tolerant than the 'Jeevan Raksha'. The highest arsenic concentration (45 mg kg-1 soil) proved most toxic dose as compared to other arsenic doses applied. It reduced the rate of photosynthesis and leaf-chlorophyll content significantly both at 90 and 120 DAP. The activities of CAT, POX and APX were also rapidly stimulated due to the highest concentration of arsenic at both the growth stages. Noticeably, all applied doses of arsenic significantly increased the production of artemisinin in the leaves. As compared to control, 'CIM-Arogya' contained the maximum artemisinin content under the highest arsenic stress, increasing the artemisinin content by 38.0 and 42.6% at 90 and 120 DAP, respectively; while, 'Jeevan Raksha' showed an increase in artemisinin content by 32.6 and 35.7% at the respective dates of sampling. At the highest arsenic stress, the yield of artemisinin was increased by 42.9 and 45.7% in 'CIM-Arogya' and by 37.5 and 40.5% in 'Jeevan Raksha'. Generation rate of H2O2 increased consistently when arsenic was applied irrespective of the varieties used, indicating the role of H2O2 in artemisinin biosynthesis in A. annua L.