Sodium arsenite-induced inhibition of cell proliferation is related to inhibition of IL-2 mRNA expression in mouse activated T cells

Guardians under Siege: Exploring Pollution's Effects on Human Immunity

Chemical pollution poses a significant threat to human health, with detrimental effects on various physiological systems, including the respiratory, cardiovascular, mental, and perinatal domains. While the impact of pollution on these systems has been extensively studied, the intricate relationship between chemical pollution and immunity remains a critical area of investigation. The focus of this study is to elucidate the relationship between chemical pollution and human immunity. To accomplish this task, this study presents a comprehensive review that encompasses in vitro, ex vivo, and in vivo studies, shedding light on the ways in which chemical pollution can modulate human immunity. Our aim is to unveil the complex mechanisms by which environmental contaminants compromise the delicate balance of the body's defense systems going beyond the well-established associations with defense systems and delving into the less-explored link between chemical exposure and various immune disorders, adding urgency to our understanding of the underlying mechanisms and their implications for public health.

Mechanistic understanding of the toxic effects of arsenic and warfare arsenicals on human health and environment

Worldwide, more than 200 million people are estimated to be exposed to unsafe levels of arsenic. Chronic exposure to unsafe levels of groundwater arsenic is responsible for multiple human disorders, including dermal, cardiovascular, neurological, pulmonary, renal, and metabolic conditions. Consumption of rice and seafood (where high levels of arsenic are accumulated) is also responsible for human exposure to arsenic. The toxicity of arsenic compounds varies greatly and may depend on their chemical form, solubility, and concentration. Surprisingly, synthetic organoarsenicals are extremely toxic molecules which created interest in their development as chemical warfare agents (CWAs) during World War I (WWI). Among these CWAs, adamsite, Clark I, Clark II, and lewisite are of critical importance, as stockpiles of these agents still exist worldwide. In addition, unused WWII weaponized arsenicals discarded in water bodies or buried in many parts of the world continue to pose a serious threat to the environment and human health. Metabolic inhibition, oxidative stress, genotoxicity, and epigenetic alterations including micro-RNA-dependent regulation are some of the underlying mechanisms of arsenic toxicity. Mechanistic understanding of the toxicity of organoarsenicals is also critical for the development of effective therapeutic interventions. This review provides comprehensive details and a critical assessment of recently published data on various chemical forms of arsenic, their exposure, and implications on human and environmental health.

Is Arsenic Exposure a Risk Factor for Metabolic Syndrome? A Review of the Potential Mechanisms

Exposure to arsenic in drinking water is a worldwide health problem. This pollutant is associated with increased risk of developing chronic diseases, including metabolic diseases. Metabolic syndrome (MS) is a complex pathology that results from the interaction between environmental and genetic factors. This condition increases the risk of developing type 2 diabetes, cardiovascular diseases, and cancer. The MS includes at least three of the following signs, central obesity, impaired fasting glucose, insulin resistance, dyslipidemias, and hypertension. Here, we summarize the existing evidence of the multiple mechanisms triggered by arsenic to developing the cardinal signs of MS, showing that this pollutant could contribute to the multifactorial origin of this pathology.

Prenatal arsenic exposure interferes in postnatal immunocompetence despite an absence of ongoing arsenic exposure

Arsenic (As) readily crosses the placenta and exposure of the fetus may cause adverse consequences later in life, including immunomodulation. In the current study, the question was asked how the immune repertoire might respond in postnatal life when there is no further As exposure. Here, pregnant mice (Balb/c [H-2^d]) were exposed to arsenic trioxide (As₂O₃) through their drinking water from time of conception until parturition. Their offspring, 4-week-old mice who had not been exposed again to As, were used for functional analyses of innate, humoral and cellular immunity. Compared to cells from non-As-exposed dam offspring, isolated peritoneal macro-phages (Mϕ) displayed no differences in T-cell stimulating ability. Levels of circulating IgG_2a but not IgG₁ were decreased in As-exposed dam offspring as compared to control offspring counterparts. Mixed-leukocyte reactions (MLR) indicated that CD4⁺ T-cells from the prenatal As-exposed mice were significantly less responsive to allogenic stimulation as evidenced by decreases in interferon (IFN)-γ and IL-2 production and in expression of CD44 and CD69 (but not CD25) activation markers. Interestingly, the Mϕ from the prenatal As-exposed mice were capable of stimulating normal allogenic T-cells, indicating that T-cells from these mice were refractory to allogenic signals. There was also a significant decrease in absolute numbers of splenic CD4⁺ and CD8⁺ T-cells due to prenatal As exposure (as compared to control). Lastly, the impaired immune function of the prenatal As-exposed mice was correlated with a very strong susceptibility to Escherichia coli infection. Taken together, the data from this study clearly show that in utero As exposure may continue to perpetuate a dampening effect on the immune repertoire of offspring, even into the early stages of postnatal life.

Urinary arsenic is associated with wasting and underweight status in young children in rural Bangladesh

BACKGROUND

Deficits in child growth are associated with poor cognitive outcomes and an increased risk for infection and mortality globally. One hundred forty million people are chronically exposed to arsenic from contaminated drinking water worldwide. While arsenic exposure has been associated with cognitive developmental delays in children, there is limited research on the association between arsenic exposure and growth deficits in young children.

PURPOSE

The objective of this study was to assess the association between chronic arsenic exposure and deficits in growth among children under 5 years in a rural setting in Bangladesh.

METHODS

Urinary arsenic measurements were collected from 465 children between the ages of 28 days-59 months in rural Matlab, Bangladesh, and analyzed by graphite furnace atomic absorption. Height and weight measurements were collected from children according to World Health Organization child growth standards. A z-score cutoff2 standard deviations below the mean was used to define stunting (height-for-age z-score), underweight (weight-for-age z-score), and wasting (weight-for-height z-score).

RESULTS

Children under 5 years with urinary arsenic concentrations in the third tertile (greater than 31 μg per liter (μg/L)) had a two times higher odds of being underweight after adjustment for age, creatinine, paternal education, breastfeeding, number of individuals using the same sleeping room, and physician-diagnosed pneumonia (Odds Ratio (OR): 2.29 (95% Confidence Interval (CI): 1.16, 4.52)). Children under 2 years of age had a two times higher odds of being wasted after adjustment for age, creatinine, paternal education, breastfeeding, number of individuals using the same sleeping room, and physician-diagnosed pneumonia (OR: 2.85 (95% CI: 1.18, 6.89)).

CONCLUSIONS

These findings suggest that arsenic exposure is associated with an increased odds of being wasted and underweight among young children in rural Bangladesh.

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.

DNMT1-mediated Foxp3 gene promoter hypermethylation involved in immune dysfunction caused by arsenic in human lymphocytes

Growing evidence indicates that arsenic can cause long-lasting and irreversible damage to the function of the human immune system. It is known that forkhead box protein 3(Foxp3), which is specifically expressed in regulatory T cells (Tregs), plays a decisive role in immunoregulation and is regulated by DNA methylation. While evidence suggests that epigenetic regulated Foxp3 is involved in the immune disorders caused by arsenic exposure, the specific mechanism remains unclear. In this study, after primary human lymphocytes were treated with different doses of NaAsO₂, our results showed that arsenic induced the high expression of DNMT1 and Foxp3 gene promoter methylation level, thereby inhibiting the expression levels of Foxp3, followed by decreasing Tregs and reducing related anti-inflammatory cytokines, such as interleukin 10 (IL-10) and interleukin 10 (IL-35), and increasing the ratio of CD4⁺/CD8⁺ T cells in lymphocytes. Treatment with DNA methyltransferase inhibitor 5-Aza-CdR can notably inhibit the expression of DNMT1, effectively restoring the hypermethylation of the Foxp3 promoter region in primary human lymphocytes and upregulating the expression levels of Foxp3, balancing the ratio of CD4⁺/CD8⁺ T cells in lymphocytes. It also activates the secretion of anti-inflammatory cytokines and restores the immune regulatory functions of Tregs. In conclusion, our study provides limited evidence that DNMT1-mediated Foxp3 gene promoter hypermethylation is involved in immune dysfunction caused by arsenic in primary human lymphocytes. The study can provide a scientific basis for further understanding the arsenic-induced immune dysfunction in primary human lymphocytes.

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.

A prospective cohort study of in utero and early childhood arsenic exposure and infectious disease in 4- to 5-year-old Bangladeshi children

Previous research found that infants who were exposed to high levels of arsenic in utero had an increased risk of infectious disease in the first year of life. This prospective study examined the association between arsenic exposures during gestation, and respiratory, diarrheal, and febrile morbidity in children 4–5 years of age.

Old dog, new trick: Trivalent arsenic as an immunomodulatory drug

Trivalent arsenic (As(III)) is recently found to be an immunomodulatory agent. As(III) has therapeutic potential in several autoimmune and inflammatory diseases in vivo. In vitro, it selectively induces apoptosis of immune cells due to different sensitivity. At a non-toxic level, As(III) shows its multifaceted nature by inducing either pro- or anti-inflammatory functions of immune subsets. These effects are exerted by either As(III)-protein interactions or as a consequence of As(III)-induced homeostasis imbalance. The immunomodulatory properties also show synergistic effects of As(III) with cancer immunotherapy. In this review, we summarize the immunomodulatory effects of As(III), focusing on the effects of As(III) on immune subsets in vitro, on mouse models of immune-related diseases, and the role of As(III) in cancer immunotherapy. Updates of the mechanisms of action, the pioneer clinical trials, dosing, and adverse events of therapeutic As(III) are also provided.

ABCA1 Is Coordinated with ABCB1 in the Arsenic-Resistance of Human Cells

Arsenic is one of the most widespread global environmental toxicants associated with endemic poisoning. ATP-binding cassette (ABC) proteins are transmembrane channels that transport and dispose of lipids and metabolic products across the plasma membrane. The majority of ABC family members (including ABCB1 and ABCC1) are reported to play a role in the development of arsenic and drug resistance in mammals. Previously, we established a human arsenic-resistant ECV-304 (AsRE) cell line and identified ABCA1 as a novel arsenic resistance gene. In the current study, we further investigated the potential contribution of ABCA1, ABCB1, and ABCC1 to arsenic resistance through measurement of survival rates and arsenic accumulation in AsRE cells with RNA interference. The arsenic resistance capacity of ABCC1 was the strongest among the three genes, while those of ABCA1 and ABCB1 were similar. Double or triple gene knockdown of ABCA1, ABCB1, and ABCC1 via RNA interference led to a decrease significant in arsenic resistance when ABCA1/ABCB1 or ABCB1/ABCC1 were simultaneously silenced. Interestingly, no differences were evident between cells with ABCA1/ABCC1 and ABCC1 only knockdown. Our findings suggest that ABCA1 and ABCB1 proteins display similar arsenic resistance capabilities and possibly coordinate to promote arsenic resistance in AsRE cells.

Inhibition of early T cell cytokine production by arsenic trioxide occurs independently of Nrf2

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a stress-activated transcription factor that induces a variety of cytoprotective genes. Nrf2 also mediates immunosuppressive effects in multiple inflammatory models. Upon activation, Nrf2 dissociates from its repressor protein, Keap1, and translocates to the nucleus where it induces Nrf2 target genes. The Nrf2-Keap1 interaction is disrupted by the environmental toxicant and chemotherapeutic agent arsenic trioxide (ATO). The purpose of the present study was to determine the effects of ATO on early events of T cell activation and the role of Nrf2 in those effects. The Nrf2 target genes Hmox-1, Nqo-1, and Gclc were all upregulated by ATO (1–2 μM) in splenocytes derived from wild-type, but not Nrf2-null, mice, suggesting that Nrf2 is activated by ATO in splenocytes. ATO also inhibited IFNγ, IL-2, and GM-CSF mRNA and protein production in wild-type splenocytes activated with the T cell activator, anti-CD3/anti-CD28. However, ATO also decreased production of these cytokines in activated splenocytes from Nrf2-null mice, suggesting the inhibition is independent of Nrf2. Interestingly, ATO inhibited TNFα protein secretion, but not mRNA expression, in activated splenocytes suggesting the inhibition is due to post-transcriptional modification. In addition, c-Fos DNA binding was significantly diminished by ATO in wild-type and Nrf2-null splenocytes activated with anti-CD3/anti-CD28, consistent with the observed inhibition of cytokine production by ATO. Collectively, this study suggests that although ATO activates Nrf2 in splenocytes, inhibition of early T cell cytokine production by ATO occurs independently of Nrf2 and may instead be due to impaired AP-1 DNA binding.

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.

Early life arsenic exposure, infant and child growth, and morbidity: a systematic review

Epidemiological studies have suggested a negative association between early life arsenic exposure and fetal size at birth, and subsequently with child morbidity and growth. However, our understanding of the relationship between arsenic exposure and morbidity and growth is limited. This paper aims to systematically review original human studies with an analytical epidemiological study design that have assessed arsenic exposure in fetal life or early childhood and evaluated the association with one or several of the following outcomes: fetal growth, birth weight or other birth anthropometry, infant and child growth, infectious disease morbidity in infancy and early childhood. A literature search was conducted in PubMed, TOXLINE, Web of Science, SciFinder and Scopus databases filtered for human studies. Based on the predefined eligibility criteria, two authors independently evaluated the studies. A total of 707 studies with morbidity outcomes were identified, of which six studies were eligible and included in this review. For the growth outcomes, a total of 2959 studies were found and nine fulfilled the criteria and were included in the review. A majority of the papers (10/15) emanated from Bangladesh, three from the USA, one from Romania and one from Canada. All included studies on arsenic exposure and morbidity showed an increased risk of respiratory tract infections and diarrhea. The findings in the studies of arsenic exposure and fetal, infant, and child growth were heterogeneous. Arsenic exposure was not associated with fetal growth. There was limited evidence of negative associations between arsenic exposures and birth weight and growth during early childhood. More studies from arsenic-affected low- and middle-income countries are needed to support the generalizability of study findings.

Arsenic exposure is associated with pediatric pneumonia in rural Bangladesh: a case control study

BACKGROUND

Pneumonia is the leading cause of death for children under 5 years of age globally, making research on modifiable risk factors for childhood pneumonia important for reducing this disease burden. Millions of children globally are exposed to elevated levels of arsenic in drinking water. However, there is limited data on the association between arsenic exposure and respiratory infections, particularly among pediatric populations.

METHODS

This case control study of 153 pneumonia cases and 296 controls 28 days to 59 months of age in rural Bangladesh is the first to assess whether arsenic exposure is a risk factor for pneumonia in a pediatric population. Cases had physician diagnosed World Health Organization defined severe or very severe pneumonia. Urine collected during hospitalization (hospital admission time point) and 30 days later (convalescent time point) from cases and a single specimen from community controls was tested for urinary arsenic by graphite furnace atomic absorption.

RESULTS

The odds for pneumonia was nearly double for children with urinary arsenic concentrations higher than the first quartile (≥6 μg/L) at the hospital admission time point (Odd Ratio (OR):1.88 (95% Confidence Interval (CI): 1.01, 3.53)), after adjustment for urinary creatinine, weight for height, breastfeeding, paternal education, age, and number of people in the household. This was consistent with findings at the convalescent time point where the adjusted OR for children with urinary arsenic concentrations greater than the first quartile (≥6 μg/L) was 2.32 (95% CI: 1.33, 4.02).

CONCLUSION

We observed a nearly two times higher odds of pneumonia for children with creatinine adjusted urinary arsenic concentrations greater than the first quartile (≥6 μg/L) at the hospital admission time point. This novel finding suggests that low to moderate arsenic exposure may be a risk factor for pneumonia in children under 5 years of age.

Arsenic exposure and prevalence of the varicella zoster virus in the United States: NHANES (2003-2004 and 2009-2010)

BACKGROUND

Arsenic is an immunotoxicant. Clinical reports observe the reactivation of varicella zoster virus (VZV) in people who have recovered from arsenic poisoning and in patients with acute promyelocytic leukemia that have been treated with arsenic trioxide.

OBJECTIVE

We evaluated the association between arsenic and the seroprevalence of VZV IgG antibody in a representative sample of the U.S.

METHODS

We analyzed data from 3,348 participants of the National Health and Nutrition Examination Survey (NHANES) 2003-2004 and 2009-2010 pooled survey cycles. Participants were eligible if they were 6-49 years of age with information on both VZV IgG and urinary arsenic concentrations. We used two measures of total urinary arsenic (TUA): TUA1 was defined as the sum of arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid, and TUA2 was defined as total urinary arsenic minus arsenobetaine and arsenocholine.

RESULTS

The overall weighted seronegative prevalence of VZV was 2.2% for the pooled NHANES sample. The geometric means of TUA1 and TUA2 were 6.57 μg/L and 5.64 μg/L, respectively. After adjusting for age, sex, race, income, creatinine, and survey cycle, odds ratios for a negative VZV IgG result in association with 1-unit increases in natural log-transformed (ln)-TUA1 and ln-TUA2 were 1.87 (95% CI: 1.03, 3.44) and 1.40 (95% CI: 1.0, 1.97), respectively.

CONCLUSIONS

In this cross-sectional analysis, urinary arsenic was inversely associated with VZV IgG seroprevalence in the U.S.

POPULATION

This finding is in accordance with clinical observations of zoster virus reactivation from high doses of arsenic. Additional studies are needed to confirm the association and evaluate causal mechanisms.

Effect of prenatal arsenic exposure on DNA methylation and leukocyte subpopulations in cord blood

Prenatal arsenic exposure is associated with increased risk of disease in adulthood. This has led to considerable interest in arsenic's ability to disrupt fetal programming. Many studies report that arsenic exposure alters DNA methylation in whole blood but these studies did not adjust for cell mixture. In this study, we examined the relationship between arsenic in maternal drinking water collected ≤ 16 weeks gestational age and DNA methylation in cord blood (n = 44) adjusting for leukocyte-tagged differentially methylated regions. DNA methylation was quantified using the Infinium HumanMethylation 450 BeadChip array. Recursively partitioned mixture modeling examined the relationship between arsenic and methylation at 473,844 CpG sites. Median arsenic concentration in water was 12 µg/L (range<1- 510 µg/L). Log 10 arsenic was associated with altered DNA methylation across the epigenome (P = 0.002); however, adjusting for leukocyte distributions attenuated this association (P = 0.013). We also observed that arsenic had a strong effect on the distribution of leukocytes in cord blood. In adjusted models, every log 10 increase in maternal drinking water arsenic exposure was estimated to increase CD8+ T cells by 7.4% (P = 0.0004) and decrease in CD4+ T cells by 9.2% (P = 0.0002). These results show that prenatal exposure to arsenic had an exposure-dependent effect on specific T cell subpopulations in cord blood and altered DNA methylation in cord blood. Future research is needed to determine if these small changes in DNA methylation alter gene expression or are associated with adverse health effects.

Arsenic and fluoride co-exposure affects the expression of apoptotic and inflammatory genes and proteins in mononuclear cells from children

Humans may be exposed to arsenic (As) and fluoride (F) through water consumption. However, the interaction between these two elements and gene expression in apoptosis or inflammatory processes in children has not been thoroughly investigated. Herein, the expression of cIAP-1, XIAP, TNF-α, ENA-78, survivin, CD25, and CD40 was evaluated by RT-PCR. Additionally, the surface expression of CD25, CD40, and CD40L on peripheral blood mononuclear cells was analyzed by flow cytometry, and TNF-α was measured by Western blotting. This study examined 72 children aged 6-12 years who were chronically exposed to As (154.2μg/L) and F (5.3mg/L) in drinking water and in food cooked with the same water. The urine concentrations of As (6.9-122.4μg/L) were positively correlated with the urine concentrations of F (1.0-8.8mg/L) (r(2)=0.413, p<0.0001). The CD25 gene expression levels and urine concentrations of As and F were negatively correlated, though the CD40 expression levels were negatively correlated only with the As concentration. Age and height influenced the expression of cIAP-1, whereas XIAP expression was correlated only with age. Additionally, there was a lower percentage of CD25- and CD40-positive cells in the group of 6- to 8-year-old children exposed to the highest concentrations of both As and F when compared to the 9- to 12-year-old group (CD25: 0.7±0.8 vs. 1.1±0.9, p<0.0014; CD40: 16.0±7.0 vs. 21.8±5.8, p<0.0003). PHA-stimulated lymphocytes did not show any changes in the induction of CD25, CD69, or CD95. In summary, high concentrations of As and F alter the expression patterns of CD25 and CD40 at both the genetic and protein levels. These changes could decrease immune responses in children exposed to As and F.

Tanshinone I activates the Nrf2-dependent antioxidant response and protects against As(III)-induced lung inflammation in vitro and in vivo

AIMS

The NF-E2 p45-related factor 2 (Nrf2) signaling pathway regulates the cellular antioxidant response and activation of Nrf2 has recently been shown to limit tissue damage from exposure to environmental toxicants, including As(III). In an attempt to identify improved molecular agents for systemic protection against environmental insults, we have focused on the identification of novel medicinal plant-derived Nrf2 activators.

RESULTS

Tanshinones [tanshinone I (T-I), tanshinone IIA, dihydrotanshinone, cryptotanshinone], phenanthrenequinone-based redox therapeutics derived from the medicinal herb Salvia miltiorrhiza, have been tested as experimental therapeutics for Nrf2-dependent cytoprotection. Using a dual luciferase reporter assay overexpressing wild-type or mutant Kelch-like ECH-associated protein-1 (Keap1), we demonstrate that T-I is a potent Keap1-C151-dependent Nrf2 activator that stabilizes Nrf2 by hindering its ubiquitination. In human bronchial epithelial cells exposed to As(III), T-I displays pronounced cytoprotective activity with upregulation of Nrf2-orchestrated gene expression. In Nrf2 wild-type mice, systemic administration of T-I attenuates As(III) induced inflammatory lung damage, a protective effect not observed in Nrf2 knockout mice.

INNOVATION

Tanshinones have been identified as a novel class of Nrf2-inducers for antioxidant tissue protection in an in vivo As(III) inhalation model, that is relevant to low doses of environmental exposure.

CONCLUSION

T-I represents a prototype Nrf2-activator that displays cytoprotective activity upon systemic administration targeting lung damage originating from environmental insults. T-I based Nrf2-directed systemic intervention may provide therapeutic benefit in protecting other organs against environmental insults.

In utero arsenic exposure and infant infection in a United States cohort: a prospective study

Arsenic (As), a ubiquitous environmental toxicant, has recently been linked to disrupted immune function and enhanced infection susceptibility in highly exposed populations. In drinking water, as levels above the EPA maximum contaminant level occur in our US study area and are a particular health concern for pregnant women and infants. As a part of the New Hampshire Birth Cohort Study, we investigated whether in utero exposure to As affects risk of infant infections. We prospectively obtained information on 4-month-old infants (n=214) using a parental telephone survey on infant infections and symptoms, including respiratory infections, diarrhea and specific illnesses, as well as the duration and severity of infections. Using logistic regression and Poisson models, we evaluated the association between maternal urinary As during pregnancy and infection risks adjusted for potentially confounding factors. Maternal urinary As concentrations were related to total number of infections requiring a physician visit (relative risk (RR) per one-fold increase in As in urine=1.5; 95% confidence interval (CI)=1.0, 2.1) or prescription medication (RR=1.6; 95% CI=1.1, 2.4), as well as lower respiratory infections treated with prescription medication (RR=3.3; 95% CI=1.2, 9.0). Associations were observed with respiratory symptoms (RR=4.0; 95% CI=1.0, 15.8), upper respiratory infections (RR=1.6; 95% CI=1.0, 2.5), and colds treated with prescription medication (RR=2.3; 95% CI=1.0, 5.2). Our results provide initial evidence that in utero As exposure may be related to infant infection and infection severity and provide insight into the early life impacts of fetal As exposure.

Arsenic immunotoxicity: a review

Exposure to arsenic (As) is a global public health problem because of its association with various cancers and numerous other pathological effects, and millions of people worldwide are exposed to As on a regular basis. Increasing lines of evidence indicate that As may adversely affect the immune system, but its specific effects on immune function are poorly understood. Therefore, we conducted a literature search of non-cancer immune-related effects associated with As exposure and summarized the known immunotoxicological effects of As in humans, animals and in vitro models. Overall, the data show that chronic exposure to As has the potential to impair vital immune responses which could lead to increased risk of infections and chronic diseases, including various cancers. Although animal and in vitro models provide some insight into potential mechanisms of the As-related immunotoxicity observed in human populations, further investigation, particularly in humans, is needed to better understand the relationship between As exposure and the development of disease.

Effect of vitamin E supplementation on mRNA expression of superoxide dismutase and interleukin-2 in arsenic exposed goat leukocytes

The aim of this study was to quantify the expression level of genes involved in antioxidant defenses during inorganic arsenic (iAs) exposure in the blood of goats and to evaluate the regulative activity on these genes of antioxidant vitamin E in the diet. Twenty-four crossbred lactating goats (Alpine × Beetal) were distributed randomly into four equal groups (Control, T(1), T(2) and T(3)) of six in each, on the basis of average body weight (36.10 ± 0.11 kg) and milk yield (1.61 ± 0.004 kg/day). The animals in T(1), T(2) and T(3) were given 50 mg/kg dry matter arsenic daily, while in T(2) and T(3), vitamin E @100 IU and 150 IU/kg dry matter, respectively, was also supplemented additionally for the period of 12 months. Blood was sampled at 0 day then at 3 months interval and analyzed for the expression level of superoxide dismutase (Cu/Zn SOD) and interleukin-2 (IL-2) using real-time PCR technique. Initially there was no difference (p > 0.05) in relative expression of the two genes. But, at 3 months, relative expression of Cu/Zn SOD increased (p < 0.05) in T(1) groups then, at 6 and 9 months expression was decreased (p < 0.05) in all the iAs treated groups whereas at 12 months, vitamin E supplementation increased (p < 0.05) the expression which is comparable to control groups. IL-2 mRNA expression was decreased (p < 0.05) at 6 months in all iAs treated groups, at 9 months there was decline trend but not significantly different whereas at 12 months decline trend was less (p < 0.05) in vitamin E supplemented groups. The result suggests that vitamin E may have a controlling effect on oxidative stress through modulation of SOD and IL-2 expression.

Vaccine specific immune response to an inactivated oral cholera vaccine and EPI vaccines in a high and low arsenic area in Bangladeshi children

BACKGROUND

Immune responses to the inactivated oral whole cell cholera toxin B (CTB) subunit cholera vaccine, Dukoral(®), as well as three childhood vaccines in the national immunization system were compared in children living in high and low arsenic contaminated areas in Bangladesh. In addition, serum complement factors C3 and C4 levels were evaluated among children in the two areas. VACCINATIONS: Toddlers (2-5 years) were orally immunized with two doses of Dukoral 14 days apart. Study participants had also received diphtheria, tetanus and measles vaccines according to the Expanded Program on Immunization (EPI) in Bangladesh.

RESULTS

The mean level of arsenic in the urine specimens in the children of the high arsenic area (HAA, Shahrasti, Chandpur) was 291.8μg/L while the level was 6.60μg/L in the low arsenic area (LAA, Mirpur, Dhaka). Cholera specific vibriocidal antibody responses were significantly increased in the HAA (87%, P<0.001) and the LAA (75%, P<0.001) children after vaccination with Dukoral, but no differences were found between the two groups. Levels of CTB specific IgA and IgG antibodies were comparable between the two groups, whereas LPS specific IgA and IgG were higher in the LAA group, although response rates were comparable. Diphtheria and tetanus vaccine specific IgG responses were significantly higher in the HAA compared to the LAA group (P<0.001, P=0.048 respectively), whereas there were no differences in the measles specific IgG responses between the groups. Complement C3 and C4 levels in sera were higher in participants from the HAA than the LAA groups (P<0.001, P=0.049 respectively).

CONCLUSIONS

The study demonstrates that the oral cholera vaccine as well as the EPI vaccines studied are immunogenic in children in high and low arsenic areas in Bangladesh. The results are encouraging for the potential use of cholera vaccines as well as the EPI vaccines in arsenic endemic areas.

Effects of arsenite and UVA-1 radiation on calcineurin signaling

Calcineurin is a Ca(2+)-dependent serine/threonine phosphatase and the target of the immunosuppressive drugs cyclosporin and tacrolimus, which are used in transplant recipients to prevent rejection. Unfortunately, the therapeutic use of this drugs is complicated by a high incidence of skin malignancy, which has set off a number of studies into the role of calcineurin signaling in skin, particularly with respect to cell cycle control and DNA repair. Both UVA1 radiation and arsenic species are known to promote skin cancer development via production of reactive oxygen species. In light of the well-documented sensitivity of calcineurin to oxidative stress, we examined and compared the effects of UVA1 and arsenite on calcineurin signaling. In this paper, we show that physiologically relevant doses of UVA1 radiation and low micromolar concentrations of arsenite strongly inhibit calcineurin phosphatase activity in Jurkat and skin cells and decrease NFAT nuclear translocation in Jurkat cells. The effects on calcineurin signaling could be partly prevented by inhibition of NADPH oxidase in Jurkat cells or increased dismutation of superoxide in Jurkat and skin cells. In addition, both UVA1 and arsenite decreased NF-κB activity, although at lower concentrations, arsenite enhanced NF-κB activity. These data indicate that UVA1 and arsenite affect a signal transduction route of growingly acknowledged importance in skin and that calcineurin may serve as a potential link between ROS exposure and impaired tumor suppression.

Age-related effects of sodium arsenite on splenocyte proliferation and Th1/Th2 cytokine production

Aging is associated with immune dysfunction and conditions such as inflamm-aging and immunosuppression. Arsenic, an environmental contaminant distributed worldwide, affects the immune system. This study tested the hypothesis that arsenic has distinct effects on T cell proliferation and the production of cytokines by activated T cells. Murine splenocytes from young (2 months) and aged (24-26 months) C57BL/6 mice were exposed to arsenite (As(3+)), the most toxic form of inorganic arsenic, and stimulated with concanavalin A (Con A) or anti-CD3 antibody. T cell proliferation decreased significantly in response to Con A and anti-CD3 at subtoxic doses of arsenite in splenocytes from both young and aged mice. Arsenite, added concurrently with Con A or anti-CD3, significantly inhibited the production of interleukin-2 (IL-2), interferon-γ (IFN-γ), and interleukin-4 (IL-4) by splenocytes from young mice and significantly reduced the production of IL-10 by splenocytes from aged mice. In contrast, the production of IL-2 and IL-4 by splenocytes from aged mice was only slightly affected by arsenite. The results show that arsenic exposure reduces the immune response in splenocytes. Moreover, this effect may be influenced by aging.

Arsenic exposure in pregnancy increases the risk of lower respiratory tract infection and diarrhea during infancy in Bangladesh

BACKGROUND

Previous studies have reported associations between prenatal arsenic exposure and increased risk of infant mortality. An increase in infectious diseases has been proposed as the underlying cause of these associations, but there is no epidemiologic research to support the hypothesis.

OBJECTIVE

We evaluated the association between arsenic exposure in pregnancy and morbidity during infancy.

METHODS

This prospective population-based cohort study included 1,552 live-born infants of women enrolled during 2002-2004 in Matlab, Bangladesh. Arsenic exposure was assessed by the concentrations of metabolites of inorganic arsenic in maternal urine samples collected at gestational weeks 8 and 30. Information on symptoms of lower respiratory tract infection (LRTI) and diarrhea in infants was collected by 7-day recalls at monthly home visits.

RESULTS

In total, 115,850 person-days of observation were contributed by the infants during a 12-month follow-up period. The estimated risk of LRTI and severe LRTI increased by 69% [adjusted relative risk (RR) = 1.69; 95% confidence interval (CI), 1.36-2.09)] and 54% (RR = 1.54; 95% CI, 1.21-1.97), respectively, for infants of mothers with urinary arsenic concentrations in the highest quintile (average of arsenic concentrations measured in early and late gestation, 262-977 µg/L) relative to those with exposure in the lowest quintile (< 39 µg/L). The corresponding figure for diarrhea was 20% (RR = 1.20; 95% CI, 1.01-1.43).

CONCLUSIONS

Arsenic exposure during pregnancy was associated with increased morbidity in infectious diseases during infancy. Taken together with the previous evidence of adverse effects on health, the findings strongly emphasize the need to reduce arsenic exposure via drinking water.

Inorganic arsenic alters expression of immune and stress response genes in activated primary human T lymphocytes

Inorganic arsenic, a carcinogenic environmental contaminant, exerts immunosuppressive effects on human T lymphocytes. In particular, interleukin-2 (IL2) secretion and T cell proliferation are reduced when peripheral blood mononuclear cells (PBMC) from individuals chronically exposed to arsenic are stimulated ex vivo with lectins such as phytohemaglutinin (PHA). However, it is not clear whether the metalloid directly acts on T cells or blocks monocyte-dependent accessory signals activated by PHA. We report that in vitro pre-treatment of PBMC with sodium arsenite (NaAs) reduces IL2 secretion and T cell proliferation induced by PHA, but does not prevent expression of monocyte-derived cytokines (IL1, IL6, TNFα) functioning as lymphocyte-activating factors. In addition, we found that NaAs delays induction of IL2 and IL2 receptor α chain (IL2RA) mRNA levels in human primary isolated T cells activated by PHA. Kinetic analysis showed that NaAs pre-treatment first inhibits, but thereafter markedly increases, induction of IL2 and IL2RA mRNA when T cells are stimulated with PHA for 8 h and 72 h, respectively. We conducted whole genome microarray-based analysis of gene expression in primary T cell cultures derived from independent donors. NaAs systematically and significantly up-regulated a set of 35 genes, including several immune and stress genes, such as IL13, granulocyte-macrophage colony stimulating factor, lymphotoxin α and heme oxygenase-1 (HO-1). Up-regulation of HO-1, a stress and immunosuppressive protein, was rapidly detectable, both in T cells and in PBMC treated with NaAs. Inhibition of the immunosuppressive activity of HO-1 in PBMC however failed to prevent NaAs-dependent inhibition of T cell proliferation induced by PHA. Our findings demonstrate that, at least in vitro, inorganic arsenic acts directly on human T cells and impairs their activity, probably independently of HO-1 expression and monocyte-related accessory signals.

Arsenic alters monocyte superoxide anion and nitric oxide production in environmentally exposed children

Arsenic (As) exposure has been associated with alterations in the immune system, studies in experimental models and adults have shown that these effects involve macrophage function; however, limited information is available on what type of effects could be induced in children. The aim of this study was to evaluate effects of As exposure, through the association of inorganic As (iAs) and its metabolites [monomethylated arsenic (MMA) and dimethylated arsenic (DMA)] with basal levels of nitric oxide (NO(-)) and superoxide anion (O(2)(-)), in peripheral blood mononuclear cells (PBMC) and monocytes, and NO(-) and O(2)(-) produced by activated monocytes. Hence, a cross-sectional study was conducted in 87 children (6-10 years old) who had been environmentally exposed to As through drinking water. Levels of urinary As species (iAs, MMA and DMA) were determined by hydride generation atomic absorption spectrometry, total As (tAs) represents the sum of iAs and its species; tAs urine levels ranged from 12.3 to 1411 microg/g creatinine. Using multiple linear regression models, iAs presented a positive and statistical association with basal NO(-) in PBMC (beta=0.0048, p=0.049) and monocytes (beta=0.0044, p=0.044), while basal O(2)(-) had a significant positive association with DMA (beta=0.0025, p=0.046). In activated monocytes, O(2)(-) showed a statistical and positive association with iAs (beta=0.0108, p=0.023), MMA (beta=0.0066, p=0.022), DMA (beta=0.0018, p=0.015), and tAs (beta=0.0013, p=0.015). We conclude that As exposure in the studied children was positively associated with basal levels of NO(-) and O(2)(-) in PBMC and monocytes, suggesting that As induces oxidative stress in circulating blood cells. Additionally, this study showed a positive association of O(2)(-) production with iAs and its metabolites in stimulated monocytes, supporting previous data that suggests that these cells, and particularly the O(2)(-) activation pathway, are relevant targets for As toxicity.

Pattern of expression of apoptosis and inflammatory genes in humans exposed to arsenic and/or fluoride

We have assessed whether the combined exposure to arsenic (As) and fluoride (F) exerts a different effect than the exposure to As alone on the pattern of expression of apoptosis and inflammatory genes by immune cells. RNA was extracted from peripheral blood mononuclear cells from twenty individuals exposed or not to As or F or both. Then, cDNA was isolated, and the expression of 180 genes related to apoptosis and inflammation was tested by a cDNA array test. We found significant differences in the expression of 9 apoptosis and 15 inflammation genes in the three exposed groups compared to non-exposed individuals. In addition, subjects exposed to As or F or both showed different patterns of expression of at least 19 genes. Our data indicate that the combined exposure to As and F has a different effect on gene expression than the exposure to As or F alone.

Effect of arsenic on regulatory T cells

INTRODUCTION

Arsenic (As) affects the function and survival of lymphocytes, and some arsenic compounds exert a relevant antineoplastic effect. We have explored the effect of As on T regulatory cells.

RESULTS AND DISCUSSION

In vitro experiments with peripheral blood mononuclear cells from healthy subjects showed that low concentrations of As tended to increase the number of natural T regulatory (nTreg) lymphocytes, whereas concentrations >5.0 muM had an opposite effect. Furthermore, rats exposed to As showed redistribution of nTreg cells, and As administration to rats with experimental allergic encephalomyelitis increased the levels of nTreg cells in spleen and diminished the severity of this condition. On the other hand, in 47 apparently healthy subjects chronically exposed to As, we found significant inverse correlation between urinary As levels and the number and function of nTreg lymphocytes. Although most of these individuals showed enhanced levels of apoptotic lymphocytes in peripheral blood, with a diminution of mitochondrial membrane potential, no significant correlation between these parameters and urinary As was detected.

CONCLUSION

Our data indicate that As seems to have a relevant and complex effect on nTreg cells.

Effects of in utero arsenic exposure on child immunity and morbidity in rural Bangladesh

Chronic exposure to arsenic, a potent carcinogen and toxicant, via drinking water is a worldwide public health problem. Because little is known about early-life effects of arsenic on immunity, we evaluated the impact of in utero exposure on infant immune parameters and morbidity in a pilot study. Pregnant women were enrolled at 6-10 weeks of gestation in Matlab, a rural area of Bangladesh, extensively affected by arsenic contamination of tubewell water. Women (n=140) delivering at local clinics were included in the study. Anthropometry and morbidity data of the pregnant women and their children, as well as infant thymic size by sonography were collected. Maternal urine and breast milk were collected for immune marker and arsenic assessment. Maternal urinary arsenic during pregnancy showed significant negative correlation with interleukin-7 (IL-7) and lactoferrin (Ltf) in breast milk and child thymic index (TI). Urinary arsenic was also positively associated with fever and diarrhea during pregnancy and acute respiratory infections (ARI) in the infants. The effect of arsenic exposure on ARI was only evident in male children. The findings suggest that in utero arsenic exposure impaired child thymic development and enhanced morbidity, probably via immunosuppression. The effect seemed to be partially gender dependent. Arsenic exposure also affected breast milk content of trophic factors and maternal morbidity.

Arsenic-induced suicidal erythrocyte death

Environmental exposure to arsenic has been associated with anemia, which could result from suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. Eryptosis is triggered by increase in cytosolic Ca2+ concentration, ceramide and energy depletion. The present experiments explored, whether arsenic stimulates eryptosis. According to annexin V-binding, arsenic trioxide (7 microM) within 48 h significantly increased phosphatidylserine exposure of human erythrocytes without inducing hemolysis. According to forward scatter, arsenic trioxide (7 microM) significantly decreased cell volume. Moreover, Fluo3-fluorescence showed that arsenic (10 microM) significantly increased cytosolic Ca2+ concentration. According to binding of respective fluorescent antibodies, arsenic trioxide (10 microM) significantly increased ceramide formation. Arsenic (10 microM) further lowered the intracellular ATP concentration. Removal of extracellular Ca2+ or inhibition of the Ca2+-permeable cation channels with amiloride blunted the effects of arsenic on annexin V-binding and cell shrinkage. In conclusion, arsenic triggers suicidal erythrocyte death by increasing cytosolic Ca2+ concentration, by stimulating the formation of ceramide and by decreasing ATP availability.

Drinking-water arsenic exposure modulates gene expression in human lymphocytes from a U.S. population

BACKGROUND

Arsenic exposure impairs development and can lead to cancer, cardiovascular disease, and diabetes. The mechanism underlying these effects remains unknown. Primarily because of geologic sources of contamination, drinking-water arsenic levels are above the current recommended maximum contaminant level of 10 microg/L in the northeastern, western, and north central regions of the United States.

OBJECTIVES

We investigated the effects of arsenic exposure, defined by internal biomarkers at levels relevant to the United States and similarly exposed populations, on gene expression.

METHODS

We conducted separate Affymetrix microarray-based genomewide analyses of expression patterns. Peripheral blood lymphocyte samples from 21 controls interviewed (1999-2002) as part of a case-control study in New Hampshire were selected based on high- versus low-level arsenic exposure levels.

RESULTS

The biologic functions of the transcripts that showed statistically significant abundance differences between high- and low-arsenic exposure groups included an overrepresentation of genes involved in defense response, immune function, cell growth, apoptosis, regulation of cell cycle, T-cell receptor signaling pathway, and diabetes. Notably, the high-arsenic exposure group exhibited higher levels of several killer cell immunoglobulin-like receptors that inhibit natural killer cell activity.

CONCLUSIONS

These findings define biologic changes that occur with chronic arsenic exposure in humans and provide leads and potential targets for understanding and monitoring the pathogenesis of arsenic-induced diseases.