Differential susceptibility of human peripheral blood T cells to suppression by environmental levels of sodium arsenite and monomethylarsonous acid

Co-administration of L-Ascorbic Acid and α-Tocopherol Alleviates Arsenic-Induced Immunotoxicities in the Thymus and Spleen by Dwindling Oxidative Stress-Induced Inflammation

Herein, we investigated whether L-ascorbic acid (L-AA) and α-tocopherol (α-T) co-administration has the potential to alleviate arsenic-induced immunotoxicities in the thymus, spleen, and circulating leukocytes. Forty-eight adult male Wistar rats were randomly divided into four groups before the treatment: group I (control); group II (sodium arsenite, 3 mg/kg/day/rat); group III (sodium arsenite + L-AA (200 mg/kg/day/rat) and α-T (400 mg/kg/day/rat)); group IV (L-AA and α-T). The result showed that sodium arsenite exposure (consecutive 30 days) caused weight reduction, structural alterations in the thymus and spleen, accompanied by a decrease in thymocyte and splenocyte count. Decreased superoxide dismutase and catalase activity, increased malondialdehyde and protein-carbonyl content, reduced Nrf2 and Bcl2 expression, and increased p-ERK, NF-kβ, Bax, and cleaved-caspase-3 expression were also observed in the thymus and spleen of arsenic-exposed rats. Enhanced plasma ACTH and corticosterone, ROS-induced apoptosis of lymphocytes were also observed. L-AA and α-T co-administration has the potential to abrogate the deleterious impact of arsenic on the thymus, spleen, and circulating lymphocytes. Whole transcriptome analysis of leukocytes revealed that arsenic treatment augmented the expression of Itga4, Itgam, and MMP9 genes, which might help in transient migration of the leukocytes through the endothelial cell layer. Co-administration with L-AA and α-T maintained Itga4, Itgam, and MMP9 gene expression within leukocytes at a lower level.

Update of the risk assessment of inorganic arsenic in food

The European Commission asked EFSA to update its 2009 risk assessment on arsenic in food carrying out a hazard assessment of inorganic arsenic (iAs) and using the revised exposure assessment issued by EFSA in 2021. Epidemiological studies show that the chronic intake of iAs via diet and/or drinking water is associated with increased risk of several adverse outcomes including cancers of the skin, bladder and lung. The CONTAM Panel used the benchmark dose lower confidence limit based on a benchmark response (BMR) of 5% (relative increase of the background incidence after adjustment for confounders, BMDL05) of 0.06 μg iAs/kg bw per day obtained from a study on skin cancer as a Reference Point (RP). Inorganic As is a genotoxic carcinogen with additional epigenetic effects and the CONTAM Panel applied a margin of exposure (MOE) approach for the risk characterisation. In adults, the MOEs are low (range between 2 and 0.4 for mean consumers and between 0.9 and 0.2 at the 95th percentile exposure, respectively) and as such raise a health concern despite the uncertainties.

Association between urinary arsenic concentration and genetic polymorphisms in Korean adults

Arsenic (As) is a human carcinogen widely distributed in the environment. This study evaluated the association between the urinary As concentration and single nucleotide polymorphisms (SNPs) in Korean adults to determine the genetic factors related to As concentration. The study included 496 participants for the genome-wide association study (GWAS) and 1483 participants for the candidate gene approach study. Participants were 19 years and older. The concentrations of total As (Tot As) and total As metabolites (Tmet As, the sum of inorganic As and their metabolites; arsenite, arsenate, monomethylarsonic, and dimethylarsinic acid) in the urine were analyzed. The GWAS identified four SNPs (rs1432523, rs3776006, rs11171747, and rs807573) associated with urinary Tot As and four SNPs (rs117605537, rs3776006, rs11171747, and rs148103384) significantly associated with urinary Tmet As concentration (P < 1 × 10-4). The candidate gene study identified two SNPs (PRDX2 rs10427027 and GLRX rs3822751) in genes related to the reduction reaction associated with urinary Tot As and Tmet As. This study suggests that genetic factors may play a role in regulating As metabolism in the human body, affecting both exposure levels and its potential health risks in the general Korean population, even at low exposure levels.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00216-x.

Arsenic: a Culpable Element and a Possible Menace for HIV/AIDS Patients

Arsenic contamination has long been recognized as one of the most harmful environmental pollutants resulting from anthropogenic activity. Apart from being an environmental toxicant or pollutant, this culpable heavy metal also has detrimental effects on human health. People throughout the world are exposed to arsenic (As) mostly through polluted drinking water. Acute inorganic arsenic (iAs) poisoning causes nausea, vomiting, stomach discomfort, and severe diarrhea. As on long-term exposure is a potent carcinogen, characterized by IARC (International Agency for Research on Cancer). As levels are high mainly in Gangetic regions due to which the people living around are suffering the consequences. The carcinogenicity of As is well established but the immunotoxicity caused by it is still unknown. Some animal model supports the toxicity of As in the immune system as well, but in humans, mainly suffering from human immunodeficiency virus (HIV), it is not well established. iAs suppresses the immune system by acting on different targets and exacerbating infections. Although animal studies have demonstrated that arsenic trioxide (As₂O₃) reduces viral rebound and restores CD4 + count in vivo when coupled with antiretroviral medications, elemental AS may have devastating effects on the immune system of HIV patients, making them more prone to opportunistic infections (OIs). It is well known that in later stages of HIV infection, neurological problems also complicate the conditions such as cognitive impairment and AIDS dementia complex (ADC). Along with immunotoxicity, As has the potential to damage HIV patients' brains. This article addresses the immunotoxicity of arsenic and exacerbations caused by it, along with the neurotoxicity, particularly in HIV patients residing near the Gangetic belt.

Arsenic as an immunotoxicant

Arsenic is world-wide contaminant to which millions of people are exposed. The health consequences of arsenic exposure are varied, including cancer, cardiometabolic disease, and respiratory disorders. Arsenic is also toxic to the immune system, which may link many of the pathologies associated with arsenic exposure. The immune system can be classified into two interconnected arms: the innate and the adaptive immune responses. Herein, we discuss the effects of arsenic on key cell types within each of these arms, highlighting both in vitro and in vivo responses. These cells include macrophages, neutrophils, dendritic cells, and both B and T lymphocytes. Furthermore, we will explore data from human populations where altered immune status is implicated in disease and identify several data gaps where research is needed to complete our understanding of the immunotoxic effects of arsenic.

Exposure to arsenic and level of Vitamin D influence the number of Th17 cells and production of IL-17A in human peripheral blood mononuclear cells in adults

There is limited evidence on the effects of environmental exposure to arsenic (As) on the immune system in adults. In a population-based study, we have found that urinary As (UAs), and its metabolites [inorganic As (InAs), monomethylated arsenicals (MMA^+3/+5), and dimethylated arsenicals (DMA^+3/+5)] modulate or influence the number of T-helper 17 (Th17) cells and IL-17A cytokine production. In non-smoking women, we observed that UAs and DMA^+3/+5 were associated with changes in Th17 cell numbers in a nonlinear fashion. In smoking males, we found that UAs was associated with a significant decrease of Th17 cell numbers. Similar association was observed among non-smoking males. Likewise, UAs, DMA^+3/+5 and MMA^+3/+5 were associated with diminished production of IL-17A among non-smoking males. When stratified by Vitamin D levels defined as sufficient (≥20 ng/ml) and insufficient (<20 ng/ml), we found a substancial decrease in Th17 cell numbers among those with insufficient levels. Individuals with sufficient VitD levels demonstrated significant inhibition of IL-17A production in non-smoking males. Collectively, we find that exposure to As via drinking water is associated with alterations in Th17 numbers and IL-17A production, and that these associations may be modified by Vitamin D status. Our findings have significance for health outcomes associated with As exposure.

Potential value and mechanism of Rosa roxburghii tratt juice on pro-inflammatory responses in peripheral blood of patients with arsenic poisoning

Increasing evidence supports the role of arsenic in dysregulated immune and inflammation responses, while, safe and effective treatments have not been fully examined. Rosa roxburghii Tratt (RRT), a traditional Chinese edible fruit with potential immunoregulatory activities, was considered as a dietary supplement to explore its protective effects and possible mechanism in arsenic-induced dysregulated inflammation responses. We enrolled 209 arsenicosis patients and 41 controls to obtain baseline data, including the degree of arsenic poisoning prior to the RRT juice (RRTJ) intervention. Then, based on criteria of inclusion and exclusion and the principle of voluntary participation, 106 arsenicosis patients who volunteered to receive treatment were divided into RRTJ (n = 53) and placebo (n = 53) groups randomly. After three months follow-up, 89 subjects (46 and 43 of the RRTJ and placebo groups, respectively) completed the study and were examined for the effects and possible mechanisms of RRTJ on the Th17 cells-related pro-inflammatory responses in peripheral blood mononuclear cells (PBMCs). The PBMCs had higher levels of Th17 and Th17-related inflammatory cytokines IL-17, IL-6, and RORγt. Furthermore, the gene expressions of STAT3 and SOCS3 in PBMCs increased and decreased, respectively. Conversely, RRTJ decreased the number of Th17 cells, secretion of IL-17, IL-6, RORγt, and relative mRNA levels of STAT3, and increased the transcript levels of SOCS3. This study provides limited evidence that possible immunomodulatory effects of RRTJ on the critical regulators, IL-6 and STAT3, of the Th17 cells in arsenicosis patients, which indicated that IL-6/STAT3 pathway might appear as a potential therapeutic target in arsenicosis.

Differential response of human T-lymphocytes to arsenic and uranium

Elevated levels of arsenic and uranium have been detected in water sources near abandoned uranium mines in the Southwest. Evidence suggests uranium exposure increases the likelihood of immune dysfunction and this study investigates the impact of arsenic and uranium on human immune cell lines. Concentration-dependent cytotoxicity occurred following exposure to arsenite, whereas cells remained viable after 48 -h treatment with up to 100 μM uranyl acetate despite uptake of uranium into cells. Arsenite stimulated an oxidative stress response as detected by Nrf-2 nuclear accumulation and induction of HMOX-1 and NQO1, which was not detected with up to 30 μM uranyl acetate. Cellular oxidative stress can promote DNA damage and arsenite, but not uranium, stimulated DNA damage as measured by pH2AX. Arsenic enhanced the cytotoxic response to etoposide suggesting an inhibition of DNA repair, unlike uranium. Similarly, uranium did not inhibit PARP-1 activity. Because uranium reportedly stimulates oxidative stress, DNA damage and cytotoxicity in adherent epithelial cells, the current study suggests distinct cell type differences in response to uranium that may relate to generation of oxidative stress and associated downstream consequences. Delineating the actions of uranium across different cell targets will be important for understanding the potential health effects of uranium exposures.

Effect of arsenic trioxide on the Tregs ratio and the levels of IFN-γ, IL-4, IL-17 and TGF-β1 in the peripheral blood of severe aplastic anemia patients

Previous studies have suggested that the anticancer agent, arsenic trioxide (ATO), could attenuate T cell mediated immunity by not only inhibiting the proliferative response of T cells but by also increasing the frequency of regulatory T cells (Tregs). Furthermore, ATO represents a reasonable salvage treatment in some patients with refractory severe aplastic anemia (SAA). The current study aimed to evaluate the function of ATO on the Tregs percentage and cytokines changes in the peripheral blood mononuclear cells (PBMCs) of SAA patients.PBMCs were collected from 20 newly diagnosed SAA patients in Henan Cancer Hospital and treated with different concentrations of ATO (0, 1, 2.5, and 5 μmol/L). Then we investigated the efficacy of ATO on Tregs ratio and the levels of interferon (IFN)-γ, interleukin (IL)-4, IL-17 and transforming growth factor (TGF)-β1 in the peripheral blood of SAA patients in vitro.The results showed that ATO significantly increased the proportion of Tregs (P < .001) at 2.5 and 5 μmol/L concentrations, and the proportion of Tregs was increased with increasing ATO concentration (r = 0.524). At 1 (P = .03), 2.5 (P < .001) and 5 μmol/L (P < .001), ATO significantly up-regulated the expression levels of Foxp3 mRNA, which was positively and linearly correlated with the increase of Tregs cell-frequency (r = 0.52, 95%CI, 0.37-0.67). In addition, ATO significantly reduced the levels of IFN-γ (at 1, 2.5 and 5 μmol/L, P < .001), IL-4 (at 2.5 μmol/L, P = .009; at 5 μmol/L, P < .001), and IL-17 (at 2.5, P = .016; at 5 μmol/L, P < .001). ATO significantly reduced the levels of TGF-β1 at 5 μmol/L (P = .03), but showed no significant effects at 1 and 2.5 μmol/L (P > .05).ATO could mediate the immune regulation, which might contribute to improve hematopoietic recovery in SAA patients.

Arsenic exposure associated T cell proliferation, smoking, and vitamin D in Bangladeshi men and women

There are limited data examining the consequences of environmental exposure to arsenic on the immune system in adults, particularly among smokers. Smoking has been shown to exacerbate or contribute to impaired immune function in men chronically exposed to arsenic. In contrast, vitamin D (VitD) is known to have a positive influence on innate and adaptive immune responses. The effect of circulating VitD on arsenic-associated immune dysfunction is not known. Here we examine the relationship of arsenic exposure and T cell proliferation (TCP), a measure of immune responsiveness, and circulating VitD among adult men and women in Bangladesh. Arsenic exposure was assessed using total urinary arsenic as well as urinary arsenic metabolites all adjusted for urinary creatinine. TCP was measured ex vivo in cryopreserved peripheral blood mononuclear cells from 614 adult participants enrolled in the Bangladesh Health Effects of Arsenic Longitudinal Study; serum VitD was also evaluated. The influence of cigarette smoking on arsenic-induced TCP modulation was assessed only in males as there was an inadequate number of female smokers. These studies show that arsenic suppressed TCP in males. The association was significantly strong in male smokers and to a lesser extent in male non-smokers. Interestingly, we found a strong protective effect of high/sufficient serum VitD levels on TCP among non-smoking males. Furthermore, among male smokers with low serum VitD (⊔20 ng/ml), we found a strong suppression of TCP by arsenic. On the other hand, high VitD (>20 ng/ml) was found to attenuate effects of arsenic on TCP among male-smokers. Overall, we found a strong protective effect of VitD, when serum levels were >20 ng/ml, on arsenic-induced inhibition of TCP in men, irrespective of smoking status. To our knowledge this is the first large study of immune function in healthy adult males and females with a history of chronic arsenic exposure.

Effect of low- and high-level groundwater arsenic on peripheral blood and lung function of exposed rural women

The World Health Organization (WHO) recommended maximum contaminant level (MCL) of arsenic (As) in drinking water at 10 μg/L. Many Asian countries still have their MCL for As at 50 μg/L. The current cross sectional study was conducted on asymptomatic females (without As related skin lesions) selected from rural areas of West Bengal, Baruipur and Dhamakhali [low As 11-50 μg/L; N,93]; Kamardanga & Sibhati [high As>50 μg/L; N,70] and Boria [Control; As<10 μg/L N,118] of West Bengal, India. The study was designed to compare the status of peripheral blood and lung function due to prolonged As exposure. The lung function parameters were considered according to Miller's prediction quadrant - FVC less than 80% indicated restrictive lung, FEV1/FVC less than 70% showed obstructive lung and both FVC and FEV1/FVC less than predicted percentage exhibited combined lung function decrement. The study showed that groundwater As concentration [22.5 ± 19.2 (low), 67.8 ± 26.9 (high) and 1.02 ± 2.3 μg/L (control)] was correlated with nail As content of the enrolled women. Linear regression depicted that nail As content influenced reduction of haemoglobin (β: 0.43; 95%CI: 0.02 to -0.006; p = 0.0001) and CD56⁺ NK cells (β: 0.53; 95%CI: 0.07 to -0.03; p = 0.0001) per 1 μg/g increase in As in nails. Multivariate logistic regression exhibited that nail As content was associated with reduction of lung function parameters [FEV1 (Exp B:1.04; 95%CI: 1.022 to 1.055; p = 0.0001) and FVC (Exp B:1.05; 95%CI: 1.03 to 1.07; p = 0.0001) per 1 μg/g increase in As in nails. Hence the study may be indicative of the fact that even in asymptomatic women, increase in chronic As exposure may weaken immune surveillance and provoke respiratory ailments.

Ginkgo biloba extract attenuates the disruption of pro-and anti-inflammatory T-cell balance in peripheral blood of arsenicosis patients

Endemic arsenicosis is a public health problem that affects thousands of people worldwide. However, the biological mechanism involved is not well characterized, and there is no specific treatment. Exposure to arsenic may be associated with immune-related problems. In the present work, we performed an investigation to determine whether the Th17/Treg balance was abnormal in peripheral blood mononuclear cells (PBMCs) of patients with arsenicosis caused by burning coal. Furthermore, we investigated the effect of Ginkgo biloba extract (GBE) on the Th17/Treg imbalance in patients with arsenicosis. In this trial, 81 arsenicosis patients and 37 controls were enrolled. The numbers of Th17 and Treg cells, as well as related transcription factors and serum cytokines, were determined at the beginning and end of the study. Patients with arsenicosis exhibited higher levels of Th17 cells, Th17-related cytokines (IL-17A and IL-6), and the transcription factor RORγt. There were lower levels of Treg cells, a Treg-related cytokine (IL-10), and the transcription factor Foxp3 as compared with controls. There was a positive correlation between the levels of Th17 cells and IL-17A and the levels of arsenic in hair. Arsenicosis patients were randomly assigned to a GBE treatment group or a placebo group. After 3 months of follow-up, 74 patients completed the study (39 cases in the GBE group and 35 in the placebo group). Administration of GBE to patient upregulated the numbers of Treg cells and the level of IL-10 and downregulated the numbers of Th17 cells and the levels of cytokines associated with Th17 cells. The mRNA levels of Foxp3 and RORγt were increased and decreased, respectively. These results indicated that exposure to arsenic is associated with immune-related problems. The present investigation describes a previously unknown mechanism showing that an imbalance of pro- and anti-inflammatory T cells is involved in the pathogenesis of arsenicosis and that a GBE exerts effects on arsenicosis through regulation of the pro- and anti-inflammatory T cell balance.

Changes in human peripheral blood mononuclear cell (HPBMC) populations and T-cell subsets associated with arsenic and polycyclic aromatic hydrocarbon exposures in a Bangladesh cohort

Exposures to environmental arsenic (As) and polycyclic aromatic hydrocarbons (PAH) have been shown to independently cause dysregulation of immune function. Little data exists on the associations between combined exposures to As and PAH with immunotoxicity in humans. In this work we examined associations between As and PAH exposures with lymphoid cell populations in human peripheral blood mononuclear cells (PBMC), as well as alterations in differentiation and activation of B and T cells. Two hundred men, participating in the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh, were selected for the present study based on their exposure to As from drinking water and their cigarette smoking status. Blood and urine samples were collected from study participants. We utilized multiparameter flow cytometry in PBMC to identify immune cells (B, T, monocytes, NK) as well as the T-helper (Th) cell subsets (Th1, Th2, Th17, and Tregs) following ex vivo activation. We did not find evidence of interactions between As and PAH exposures. However, individual exposures (As or PAH) were associated with changes to immune cell populations, including Th cell subsets. Arsenic exposure was associated with an increase in the percentage of Th cells, and dose dependent changes in monocytes, NKT cells and a monocyte subset. Within the Th cell subset we found that Arsenic exposure was also associated with a significant increase in the percentage of circulating proinflammatory Th17 cells. PAH exposure was associated with changes in T cells, monocytes and T memory (Tmem) cells and with changes in Th, Th1, Th2 and Th17 subsets all of which were non-monotonic (dose dependent). Alterations of immune cell populations caused by environmental exposures to As and PAH may result in adverse health outcomes, such as changes in systemic inflammation, immune suppression, or autoimmunity.

Health effects inflicted by chronic low-level arsenic contamination in groundwater: A global public health challenge

Groundwater arsenic (As) contamination is a global public health concern. The high level of As exposure (100-1000 μg/L or even higher) through groundwater has been frequently associated with serious public health hazards, e.g., skin disorders, cardiovascular diseases, respiratory problems, complications of gastrointestinal tract, liver and splenic ailments, kidney and bladder disorders, reproductive failure, neurotoxicity and cancer. However, reviews on low-level As exposure and the imperative health effects are far less documented. The World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) has set the permissible standard of As in drinking water at 10 μg/L. Considering the WHO and USEPA guidelines, most of the developed countries have established standards at or below this guideline. Worldwide many countries including India have millions of aquifers with low-level As contamination (≤50 μg/L). The exposed population of these areas might not show any As-related skin lesions (hallmark of As toxicity particularly in a population consuming As contaminated groundwater >300 μg/L) but might be subclinically affected. This review has attempted to encompass the wide range of health effects associated with chronic low-level As exposure ≤50 μg/L and the probable mechanisms that might provide a better insight regarding the underlying cause of these clinical manifestations. Therefore, there is an urgent need to create mass awareness about the health effects of chronic low-level As exposure and planning of proper mitigation strategies.

Assessment of arsenic and polycyclic aromatic hydrocarbon (PAH) exposures on immune function among males in Bangladesh

Arsenic and polycyclic aromatic hydrocarbons (PAH) are environmental pollutants to which people around the world are exposed through water, food and air. In mouse and in vitro studies of human cells, both of these chemicals have been shown to modulate the immune system. In some experimental studies, a synergistic disruption of immune function was observed by a combined exposure to arsenic and PAH. However, a joint effect of arsenic and PAH on immune function has not been studied in humans. We have conducted an epidemiological investigation to examine effects of chronic arsenic and PAH exposures on immune function. We assessed T-cell proliferation (TCP) and cytokine production of anti-CD3/anti-CD28 stimulated lymphocytes in human peripheral blood mononuclear cells (HPBMC) among 197 healthy men enrolled to the Health Effects of Arsenic Longitudinal (HEALS) cohort in Bangladesh. By design, approximately half were active smokers and the rest were never smokers. Our analyses demonstrated that IL-1b, IL-2, IL-4 and IL-6 were significantly stimulated as a function of urinary arsenic levels in models adjusted for age, body mass index (BMI), smoking status and PAH-DNA adducts. After correcting for false detection rate (FDR), only IL-1b remained statistically significant. We found a U-shaped dose response relationship between urinary arsenic and IL-1b. On the other hand, PAH-DNA adducts were associated with an inhibition of TCP and appeared as an inverted U-shape curve. Dose response curves were non-monotonic for PAH-DNA adduct exposures and suggested that cytokine secretion of IFNg, IL-1b, IL-2, IL-10 and IL17A followed a complex pattern. In the majority of donors, there was a trend towards a decrease in cytokine associated with PAH-DNA adducts. We did not observe any interaction between urinary arsenic and PAH-DNA adducts on immune parameters. Our results indicate that long-term exposures to arsenic and PAH have independent, non-monotonic associations with TCP and cytokine production.

Chronic arsenic exposure in drinking water interferes with the balances of T lymphocyte subpopulations as well as stimulates the functions of dendritic cells in vivo

The immunomodulatory properties of arsenic are nowadays supposed be associated with pathological injuries of this toxicant and the details have not been clarified. Our objective was to explore inflammation, differentiation of diverse T cell subsets, as well as the phenotypic molecules and functions of dendritic cells (DCs) by chronic arsenic exposure in vivo. We exposed different concentrations of arsenic (0, 0.1, 1 and 10 mg/L) in drinking water for 6 and 12 months in C57BL/6 mice. We first confirmed that low levels of arsenic induced excess inflammation evidenced by accumulation of macrophages and lymphocytes in bronchoalveolar lavage fluid (BALF), secretion of pro-inflammatory cytokine IL-1β in BALF and serum, as well as histological analysis. Flow cytometry analysis revealed that arsenic disturbed CD4/CD8 T-cell ratio in isolated pneumonocytes and splenocytes, as well as enhanced IFN-γ and reduced IL-4 in spleen. The mRNA expressions of transcription factors (T-bet, GATA3, ROR-γt) and cytokines (IFN-γ, IL-4, IL-10, IL-23, IL-22) showed the imbalanced Th1/Th2/Th17 differentiation in arsenic exposed lung and spleen. We further testified that arsenic enhanced the percentages of CD11c⁺ DCs, and promoted the expressions of antigen presentation molecule MHC II and cytokine IL-12, co-stimulatory molecules (CD86, CD80), and chemokine receptors (CCR7, CCR5) in vivo. Moreover, arsenic activated the expressions of immune-related MAPKs and NF-κB. Taken together, our study here demonstrated that chronic arsenic exposure could disrupt the immune homeostasis in vivo possibly by interfering with the differentiation of Th1/Th2/Th17 subsets as well as the function of DCs.

Toxicity of environmentally-relevant concentrations of arsenic on developing T lymphocyte

Arsenic is a ubiquitous environmental contaminant that exists in many inorganic and organic forms. In particular, arsenite is known to induce immunotoxicity in humans and animals. There are still major gaps in our understanding of the mechanism(s) of the immunotoxicity induced by arsenic at environmentally-relevant concentrations. T cells are an essential part of the immune system required for host resistance to infections and protection from cancer. Developing T cells in the thymus have been shown to be particularly prone to arsenite-induced toxicity at low concentrations. Suppression of DNA repair proteins and oxidative stress have been identified as a mechanism of genotoxicity that occurs at low to moderate concentrations. Inhibition of the IL-7 signaling pathway was thought to be responsible for the non-genotoxicity induced by low to moderate doses of arsenic. Interestingly, T cells at different stages of their development had distinct sensitivities to arsenite, which was regulated by arsenite exporters. The current evidence strongly suggests that low to moderate doses of arsenic induces toxic effects in the developing T cells and accumulates to highest levels in the early cells that are least capable to pump out arsenic, which may be the mechanism of the high arsenic sensitivity. Therefore, quantification of the exposure levels should be encouraged in future arsenic toxicity studies.

Isolation, Cryopreservation, and Immunophenotyping of Human Peripheral Blood Mononuclear Cells

This unit describes procedures for the isolation, cryopreservation, and thawing of human peripheral blood mononuclear cells (HPBMC) and analysis of cell surface markers (CSM) for immunophenotyping using polychromatic flow cytometry. This methodology can be used to ensure that cell integrity and phenotype stability are not altered through cryopreservation and extended storage. For this analysis, HPBMC were isolated from 7 healthy individuals, and 11-color flow cytometry was performed on freshly isolated samples as well as samples cryopreserved for short- and long-term periods. There is no significant difference in the percentage of cells expressing the CSM CD3, CD4, CD8, CD45RO, CD16, CD19, or CD56 between freshly isolated and cryopreserved HPBMC. Hence, cryopreservation of HPBMC does not influence the phenotype of distinct cellular subsets in isolated mononuclear cells. This protocol for HPBMC isolation, cryopreservation, and thawing of HPBMC is intended for long-term studies of large cohorts requiring sample shipment and subsequent batch analysis. © 2017 by John Wiley & Sons, Inc.

Arsenic and Immune Response to Infection During Pregnancy and Early Life

PURPOSE OF REVIEW

Arsenic, a known carcinogen and developmental toxicant, is a major threat to global health. While the contribution of arsenic exposure to chronic diseases and adverse pregnancy and birth outcomes is recognized, its ability to impair critical functions of humoral and cell-mediated immunity-including the specific mechanisms in humans-is not well understood. Arsenic has been shown to increase risk of infectious diseases that have significant health implications during pregnancy and early life. Here, we review the latest research on the mechanisms of arsenic-related immune response alterations that could underlie arsenic-associated increased risk of infection during the vulnerable periods of pregnancy and early life.

RECENT FINDINGS

The latest evidence points to alteration of antibody production and transplacental transfer as well as failure of T helper cells to produce IL-2 and proliferate. Critical areas for future research include the effects of arsenic exposure during pregnancy and early life on immune responses to natural infection and the immunogenicity and efficacy of vaccines.

PKC θ-mediated Ca2+/NF-AT signalling pathway may be involved in T-cell immunosuppression in coal-burning arsenic-poisoned population

Arsenic poisoning is a worldwide endemic disease that affects thousands of people. Growing evidence from animal, cell, and human studies indicates that arsenic has deleterious effects on the immune system. The present investigation is a population-based study that observed changes in the proliferation of human T-cells and IL-2 and INF-γ mRNA expression. Our results show that coal-burning arsenic can cause T-cell immunosuppression in the population, and participates in the occurrence and development of arsenic poisoning. In addition, we analyzed the intracellular calcium index, expression of protein kinase C theta (PKC θ) and phosphorylated PKC θ, and the DNA-binding activity of NF-AT in peripheral blood mononuclear cells (PBMCs). Our analysis demonstrates that the PKC θ-mediated Ca²⁺/NF-AT signalling pathway may be involved in the T-cell immunosuppression of coal-burning arsenic-poisoned population. This study provides important data for a mechanistic understanding of endemic arsenic poisoning.

Arsenic exposure impels CD4 commitment in thymus and suppress T cell cytokine secretion by increasing regulatory T cells

Arsenic is globally infamous for inducing immunosuppression associated with prevalence of opportunistic infection in exposed population, although the mechanism remains elusive. In this study, we investigate the effect of arsenic exposure on thymocyte lineage commitment and the involvement of regulatory T cells (T_reg) in arsenic-induced immunosuppression. Male Balb/c mice were exposed to 0.038, 0.38 and 3.8 ppm sodium arsenite for 7, 15 and 30 days through oral gavage. Arsenic exposure promoted CD4 lineage commitment in a dose dependent manner supported by the expression of ThPOK in thymus. Arsenic also increased splenic CD4⁺ T cells and promoted their differentiation into T_reg cells. In parallel, arsenic exposure induced immunosuppression characterized by low cytokine secretion from splenocytes and increased susceptibility to Mycobacterium fortuitum (M. fortuitum) infection. Therefore, we linked arsenic-induced rise in T_reg cells with suppressed T_h1 and T_h2 related cytokines, which has been reversed by inhibition of T_reg cells in-vivo using wortmannin. Other parameters like body weight, kidney and liver function, histoanatomy of thymus and spleen as well as thymocyte and splenocytes viability were unaltered by arsenic exposure. Taken together our findings indicated that environmentally relevant dose of arsenic enhanced differentiation of T_reg cells which in turn induce immunosuppression in experimental animals.

Efflux Transporters Regulate Arsenite-Induced Genotoxicity in Double Negative and Double Positive T Cells

Arsenite (As+3) exposure is known to cause immunotoxicity in human and animal models. Our previous studies demonstrated that As+3 at 50-500 nM concentrations induced both genotoxicity and nongenotoxicity in mouse thymus cells. Developing T cells at CD4-CD8- double negative (DN) stage, the first stage after early T cells are transported from bone marrow to thymus, were found to be more sensitive to As+3 toxicity than the T cells at CD4 + CD8 + double positive (DP) stage in vitro. Induction of Mdr1 (Abcb1) and Mrp1 (Abcc1), 2 multidrug resistance transporters and exporters of As+3, was associated with the reversal of As+3-induced double strand breaks and DNA damage. In order to confirm that the thymus cell populations have different sensitivity to As+3in vivo, male C57BL/6J mice were exposed to 0, 100, and 500 ppb As+3 in drinking water for 30 d. A significant decrease in DN cell percentage was observed with exposure to 500 ppb As+3. Low to moderate concentrations of As+3 were shown to induce higher genotoxicity in sorted DN than DP cells in vitro. Calcein AM uptake and Mdr1/Mrp1 mRNA quantification results revealed that DN cells not only had limited As+3 exporter activity, but also lacked the ability to activate these exporters with As+3 treatments, resulting in a higher accumulation of intracellular As+3. Knockdown study of As+3 exporters in the DN thymic cell line, D1 using siRNA, demonstrated that Mdr1 and Mrp1 regulate intracellular As+3 accumulation and genotoxicity. Taken together, the results indicate that transporter regulation is an important mechanism for differential genotoxicity induced by As+3 in thymocytes at different developmental stages.

Changes in HPBMC markers of immmune function following controlled short-term inhalation exposures of humans to hardwood smoke

Previous studies have shown that complex mixtures containing particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) produce systemic immunotoxicity in animal models following inhalation exposures. While we and others have shown that emissions associated with hardwood smoke (HWS), cigarette smoke and diesel exhaust can suppress the immune systems of animals in vitro and in vivo, there have been few immune function studies on human peripheral blood mononuclear cells (HPBMC) following exposure of humans to HWS. Our work shows that T cells are an important targets of PM and PAH immunotoxicity. These studies were conducted on HPBMC from 14 human volunteers receiving four 2 h nightly exposures to clean air or HWS at a concentration of 500 ug/m(3). We measured anti-CD3/anti-CD28 stimulated T-cell proliferation and HPBMC cytokine production in cell supernatants, including interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), TH1 cytokines γIFN and IL-2, TH2 cytokine IL-4, Th17 cytokine interleukin 17A (IL-17A) and interleukin 10 (IL-10). We analyzed results using analysis of variance (ANOVA), t-tests and Pearson correlation. Results showed that there was significant variation in the amount of T-cell proliferation observed following polyclonal activation with anti-CD3/anti-CD28 antibodies in both the air and HWS-exposed groups. There was not a significant effect of HWS on T-cell proliferation. However, we did find a strong relationship between the presence of proinflammatory cytokines (IL-1β, TNF-α, IL-6, but not IL-8) and the amount of T-cell proliferation seen in individual donors, demonstrating that brief exposures of humans to HWS can produce changes in systemic immunity that is associated with proinflammatory cytokines.

Chronic Arsenic Exposure and Risk of Post Kala-azar Dermal Leishmaniasis Development in India: A Retrospective Cohort Study

Background

Visceral leishmaniasis (VL), with the squeal of Post-kala-azar dermal leishmaniasis (PKDL), is a global threat for health. Studies have shown sodium stibogluconate (SSG) resistance in VL patients with chronic arsenic exposure. Here, we assessed the association between arsenic exposure and risk of developing PKDL in treated VL patients.

Methods

In this retrospective study, PKDL patients (n = 139), earlier treated with SSG or any other drug during VL, were selected from the study cohort. Trained physicians, unaware of arsenic exposure, interviewed them and collected relevant data in a questionnaire format. All probable water sources were identified around the patient’s house and water was collected for evaluation of arsenic concentration. A GIS-based village-level digital database of PKDL cases and arsenic concentration in groundwater was developed and individual point location of PKDL cases were overlaid on an integrated GIS map. We used multivariate logistic regression analysis to assess odds ratios (ORs) for association between arsenic exposure and PKDL development.

Results

Out of the 429 water samples tested, 403 had arsenic content of over 10 μg/L, with highest level of 432 μg/L among the seven study villages. Multivariate adjusted ORs for risk of PKDL development in comparison of arsenic concentrations of 10.1–200 μg/L and 200.1–432.0 μg/L were 1.85 (1.13–3.03) and 2.31 (1.39–3.8) respectively. Interestingly, similar results were found for daily dose of arsenic and total arsenic concentration in urine sample of the individual. The multivariate-adjusted OR for comparison of high baseline arsenic exposure to low baseline arsenic exposure of the individuals in the study cohort was 1.66 (95% CI 1.02–2.7; p = 0.04).

Conclusion

Our findings indicate the need to consider environmental factors, like long time arsenic exposure, as an additional influence on treated VL patients towards risk of PKDL development in Bihar.

Post-kala-azar dermal leishmaniasis (PKDL) is a sequela of visceral leishmaniasis (VL) that appears after patients have apparently been cured of visceral leishmaniasis; even been reported in patients without a history of VL. Previous clinical and epidemiological data ascertains the main risk factor associated with the development of PKDL is previous treatment for VL with antimonials (SSG); however, PKDL also occurs after treatment with other drugs like paromomycin, miltefosine etc. Here, in light of the risk of arsenic-associated dermal manifestations, we hypothesized that the long term exposure to groundwater arsenic acts as an additional risk factor for development of PKDL in patients treated for VL with SSG or other drugs. Using a cohort, we retrospectively assessed the risk of arsenic in development of PKDL in treated VL patients. Our findings support a significant association and prompts parasites might persist successfully in individuals over-exposed to arsenic and may exhibit features of dermatotropism leading to development of PKDL after treatment for VL. Further research is needed to dissect the mechanistic role of arsenic on VL, as well as PKDL development.

Differential sensitivities of bone marrow, spleen and thymus to genotoxicity induced by environmentally relevant concentrations of arsenite

It is known in humans and mouse models, that drinking water exposures to arsenite (As⁺³) leads to immunotoxicity. Previously, our group showed that certain types of immune cells are extremely sensitive to arsenic induced genotoxicity. In order to see if cells from different immune organs have differential sensitivities to As⁺³, and if the sensitivities correlate with the intracellular concentrations of arsenic species, male C57BL/6J mice were dosed with 0, 100 and 500ppb As⁺³via drinking water for 30d. Oxidation State Specific Hydride Generation- Cryotrapping- Inductively Coupled Plasma- Mass Spectrometry (HG- CT- ICP- MS) was applied to analyze the intracellular arsenic species and concentrations in bone marrow, spleen and thymus cells isolated from the exposed mice. A dose-dependent increase in intracellular monomethylarsonous acid (MMA⁺³) was observed in both bone marrow and thymus cells, but not spleen cells. The total arsenic and MMA⁺³ levels were correlated with an increase in DNA damage in bone marrow and thymus cells. An in vitro treatment of 5, 50 and 500nM As⁺³ and MMA⁺³ revealed that bone marrow cells are most sensitive to As⁺³ treatment, and MMA⁺³ is more genotoxic than As⁺³. These results suggest that the differential sensitivities of the three immune organs to As⁺³ exposure are due to the different intracellular arsenic species and concentrations, and that MMA⁺³ may play a critical role in immunotoxicity.

Editor's Highlight: Interactive Genotoxicity Induced by Environmentally Relevant Concentrations of Benzo(a)Pyrene Metabolites and Arsenite in Mouse Thymus Cells

Arsenic and polycyclic aromatic hydrocarbon (PAH) exposures affect many people worldwide leading to cancer and other diseases. Arsenite (As⁺³) and certain PAHs are known to cause genotoxicity. However, there is limited information on the interactions between As⁺³ and PAHs at environmentally relevant concentrations. The thymus is the primary immune organ for T cell development in mammals. Our previous studies showed that environmentally relevant concentrations of As⁺³ induce genotoxicity in mouse thymus cells through Poly(ADP-ribose) polymerase (PARP) inhibition. Certain PAHs, such as the metabolites of benzo(a)pyrene (BaP), are known to cause DNA damage by forming DNA adducts. In the present study, primary mouse thymus cells were examined for DNA damage following 18 hr in vitro treatments with 5 or 50 nM As⁺³ and 100 nM BaP, benzo[a]pyrene-7,8-dihydrodiol (BP-Diol), or benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE). An interactive increase in genotoxicity and apoptosis were observed following treatments with 5 nM As ^{+  3}+100 nM BP-diol and 50 nM As ^{+  3}+100 nM BPDE. We attribute the increase in DNA damage to inhibition of PARP inhibition leading to decreased DNA repair. To further support this hypothesis, we found that a PARP inhibitor, 3,4-dihydro-5[4-(1-piperindinyl) butoxyl]-1(2H)-isoquinoline (DPQ), also interacted with BP-diol to produce an increase in DNA damage. Interestingly, we also found that As⁺³ and BP-diol increased CYP1A1 and CYP1B1 expression, suggesting that increased PAH metabolism may also contribute to genotoxicity. In summary, these results show that the suppression of PARP activity and induction of CYP1A1/CYP1B1 may act together to increase DNA damage produced by As⁺³ and PAHs.

Environmentally relevant concentrations of arsenite and monomethylarsonous acid inhibit IL-7/STAT5 cytokine signaling pathways in mouse CD3+CD4-CD8- double negative thymus cells

Environmental arsenic exposure is a public health issue. Immunotoxicity induced by arsenic has been reported in humans and animal models. The purpose of this study was to evaluate mechanisms of As(+3) and MMA(+3) toxicity in mouse thymus cells. Because we know that MMA(+3) inhibits IL-7 signaling in mouse bone marrow pre-B cells, we studied the influence of As(+3) and MMA(+3) on T cell development in the thymus at the earliest stage of T cell development (CD4-CD8-, double negative, DN) which requires IL-7 dependent signaling. We found in a DN thymus cell line (D1) that a low concentration of MMA(+3) (50 nM) suppressed IL-7 dependent JAK1, 3 and STAT5 signaling. As(+3) suppressed STAT5 and JAK3 at higher concentrations (500 nM). Cell surface expression of the IL-7 receptor (CD127) was also suppressed by 50 nM MMA(+)3, but was increased by 500 NM As(+3), indicating possible differences in the mechanisms of action of these agents. A decrease in cyclin D1 protein expression was observed in D1 cells exposed to As(+3) at 500 nM and MMA(+3) starting at 50 nM, suggesting that arsenic at these environmentally-relevant doses suppresses early T cell development through the inhibition of IL-7 signaling pathway.

Environmentally Relevant Concentrations of Arsenite Induce Dose-Dependent Differential Genotoxicity Through Poly(ADP-Ribose) Polymerase Inhibition and Oxidative Stress in Mouse Thymus Cells

Inhibition of DNA repair and oxidative stress are 2 common mechanisms associated with arsenic-induced genotoxicity. The purpose of this study was to examine mechanisms of genotoxicity induced by environmentally relevant doses of arsenite (As(+3)) in mouse thymus cells. An increase in DNA damage and a decrease in poly(ADP-ribose) polymerase (PARP) activity were seen in vitro following exposure to 50 nM As(+3) in primary mouse thymus cells and a murine thymus pre-T cell line, D1. 3,4-Dihydro-5[4-(1-piperindinyl) butoxyl]-1(2H)-isoquinoline, a well-characterized PARP inhibitor, also produced DNA damage in D1 cells, confirming the correlation between PARP inhibition and DNA damage increase. As(+3) at 500 nM induced double strand breaks (DSBs) in DNA and oxidative stress at 4 h in D1 cells, which was reversed at 18 h. No apoptosis or decrease of viability was observed in these exposures. 4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, a widely-used antioxidant, was utilized to confirm that oxidative stress is partially responsible for the increase of strand breaks in 500 nM As(+3) exposure at 4 h. Expression of As(+3) exporters, Mdr1 and Mrp1, were found to be induced by 500 nM As(+3) in D1 cells, suggesting a possible mechanism for reversal of oxidative stress and DSBs at the 18-h timepoint. Finally, we showed that DNA damage and PARP inhibition by As(+3) were reversed by zinc (Zn(+2)) at approximate equimolar doses. Collectively, these results demonstrate that As(+3) at doses within the nanomolar range induce genotoxicity by inhibiting PARP, and produces oxidative stress at higher concentrations, which can be reversed by a Zn(+2) treatment.

Linkage Analysis of Urine Arsenic Species Patterns in the Strong Heart Family Study

Arsenic toxicokinetics are important for disease risks in exposed populations, but genetic determinants are not fully understood. We examined urine arsenic species patterns measured by HPLC-ICPMS among 2189 Strong Heart Study participants 18 years of age and older with data on ~400 genome-wide microsatellite markers spaced ~10 cM and arsenic speciation (683 participants from Arizona, 684 from Oklahoma, and 822 from North and South Dakota). We logit-transformed % arsenic species (% inorganic arsenic, %MMA, and %DMA) and also conducted principal component analyses of the logit % arsenic species. We used inverse-normalized residuals from multivariable-adjusted polygenic heritability analysis for multipoint variance components linkage analysis. We also examined the contribution of polymorphisms in the arsenic metabolism gene AS3MT via conditional linkage analysis. We localized a quantitative trait locus (QTL) on chromosome 10 (LOD 4.12 for %MMA, 4.65 for %DMA, and 4.84 for the first principal component of logit % arsenic species). This peak was partially but not fully explained by measured AS3MT variants. We also localized a QTL for the second principal component of logit % arsenic species on chromosome 5 (LOD 4.21) that was not evident from considering % arsenic species individually. Some other loci were suggestive or significant for 1 geographical area but not overall across all areas, indicating possible locus heterogeneity. This genome-wide linkage scan suggests genetic determinants of arsenic toxicokinetics to be identified by future fine-mapping, and illustrates the utility of principal component analysis as a novel approach that considers % arsenic species jointly.

Arsenite Interacts with Dibenzo[def,p]chrysene (DBC) at Low Levels to Suppress Bone Marrow Lymphoid Progenitors in Mice

Arsenite (As(+3)) and dibenzo[def,p]chrysene (DBC), a polycyclic aromatic hyrdrocarbon (PAH), are found in nature as environmental contaminants. Both are known to individually suppress the immune system of humans and mice. In order to determine their potential interactive and combined immunosuppressive effects, we examined murine bone marrow (BM) immune progenitor cells' responses following combined oral exposures at very low levels of exposure to As(+3) and DBC. Oral 5-day exposure to DBC at 1 mg/kg (cumulative dose) was found to suppress mouse BM lymphoid progenitor cells, but not the myeloid progenitors. Previously established no-effect doses of As(+3) in drinking water (19 and 75 ppb for 30 days) produced more lymphoid suppression in the bone marrow when mice were concomitantly fed a low dose of DBC during the last 5 days. The lower dose (19 ppb) As(+3) had a stronger suppressive effect with DBC than the higher dose (75 ppb). Thus, the interactive toxicity of As(+3) and DBC in vivo could be As(+3) dose dependent. In vitro, the suppressive interaction of As(+3) and DBC was also evident at low concentrations (0.5 nM), but not at higher concentrations (5 nM) of As(+3). These studies show potentially important interactions between As(+3) and DBC on mouse BM at extremely low levels of exposure in vivo and in vitro.

STAT3 in arsenic lung carcinogenicity

We recently found that the chronic sterile inflammation contributes to arsenic lung tumorigenesis which is inhibited by autophagy. STAT3 regulates the interaction between inflammation and autophagy. STAT3 may also play a critical role in mediating the crosstalk between lung epithelial cells and their microenvironment, including immune cells, during arsenic lung carcinogenesis.