Arsenic and the immune system

Heavy metals, oxidative stress, and the role of AhR signaling

The Aryl Hydrocarbon Receptor (AhR) is a ligand-activated transcriptional factor pivotal in responding to environmental stress and maintaining cellular homeostasis. Exposure to specific xenobiotics or industrial compounds in the environment activates AhR and its subsequent signaling, inducing oxidative stress and related toxicity. Past research has also identified and characterized several classes of endogenous ligands, particularly some tryptophan (Trp) metabolic/catabolic products, that act as AhR agonists, influencing a variety of physiological and pathological states, including the modulation of immune responses and cell death. Heavy metals, being non-essential elements in the human body, are generally perceived as toxic and hazardous, originating either naturally or from industrial activities. Emerging evidence indicates that heavy metals significantly influence AhR activation and its downstream signaling. This review consolidates current knowledge on the modulation of the AhR signaling pathway by heavy metals, explores the consequences of co-exposure to AhR ligands and heavy metals, and investigates the interplay between oxidative stress and AhR activation, focusing on the regulation of immune responses and ferroptosis.

Ginger mitigated the health risks associated with arsenic-contamination of rats feed via inflammatory and apoptosis regulation

Millions of people around the world are inadvertently exposed to arsenic through drinking water and food. However, food spices possess antioxidants and anti-inflammatory potentials. Therefore, this study evaluated the protective potentials of Zingiber officinale (ginger) against the toxic effects of arsenic in male Wistar rats. Thirty-six Wistar rats were assigned into 6 groups (n = 6); group A1 and A2 (control), group B1 and B2 were fed with arsenic-contaminated feed (3.45x10-3 mg/kg), group C1 and C2 were feed with arsenic-contaminated feed (3.45x10-3 mg) supplemented with ginger respectively for 12 and 24 weeks. The blood, bone marrow, and liver of rats were harvested and prepared for various analyses. Micronucleus and Comet analysis were performed for the genotoxicity assessment every 4 weeks. Activities of AST, ALT, GGT, and SOD, and the concentration of GSH, MDA, protein carbonyl, protein thiol, and total protein, were measured by spectrophotometric methods. Quantification of IL-10, 1 L-1β, TNF-α, TGF-β NF-Ƙβ, and 8-oxodeoxyguanosine was done by ELISA method while Bax, Bcl2, and Erk 1/2 were quantified by immuno-histochemical staining. mRNA expression of cyclin D1 was quantified using qRT-PCR. Statistical analysis was performed with SPSS and statistical significance was accepted when p<0.05. Result showed significant (p<0.05) decrease in the haemoglobin concentration, red blood cell, lymphocyte counts, tail DNA and MnPCE of rats fed arsenic-contaminated feed compared with control. The supplementation with ginger significantly reduced serum activities of AST and GGT (p<0.05). Ginger supplementation also lowered the arsenic indued increases in liver MDA, protein carbonyl and 8-OXdG levels. Ginger restores to near normal the histological changes due to arsenic exposure. In the arsenic-exposed group, liver IL-10, IL-1β and TNF-α decreased significantly (p<0.05) at week 24 whereas, NF-Ƙβ and TGF-β increased significantly (p 0.05) at weeks 12 and 24 and TNF-α, Bcl2 at week 24. mRNA expression of cyclin D1 was significantly (p<0.05) downregulated in the arsenic and ginger-supplemented groups. This study showed that long-term consumption of arsenic resulted in immunosuppression, anaemia and activated anti-apoptotic process that was mitigated due to ginger supplementation.

Health risk assessment of arsenic, lead and cadmium from milk consumption in Punjab, India

Milk is an integral part of the human diet and its contamination with heavy metals may alter the health of its consumers. The study was conducted to assess the health risk associated with the heavy metals in milk samples collected from urban and rural households of Ludhiana and Bathinda districts of Punjab, India. One hundred and fifty milk samples were analyzed for heavy metals i.e. arsenic, cadmium, lead and mercury using Inductively Coupled Plasma Mass Spectrometry ICP-MS. The health risks, such as non-carcinogenic and carcinogenic risks from heavy metals in milk samples, were calculated for selected males and females of adults, children and elderly subjects. The results indicated that the arsenic, cadmium and lead content in milk samples were within permissible limit whereas mercury was not detected in any sample. The mean values showed that the selected urban and rural population of both districts was safe from non-carcinogenic risk associated with heavy metal content of milk. However, urban (50% males and 86% females) and rural (25% males) children of Bathinda district were at risk of cancer from arsenic and cadmium present in milk samples, respectively. It was also observed that the selected population of both districts were safe from carcinogenic risk due to the combined effects of heavy metals. It was concluded that even with a small amount of heavy metal in milk samples, the rural adults, rural male children and urban female children of Bathinda district had carcinogenic risk due to milk consumption. Hence, regular monitoring and testing of milk samples must be done as a public health measure to prevent heavy metal contamination in milk to safeguard the health of consumers.

Disease-associated metabolic pathways affected by heavy metals and metalloid

Increased exposure to environmental heavy metals and metalloids and their associated toxicities has become a major threat to human health. Hence, the association of these metals and metalloids with chronic, age-related metabolic disorders has gained much interest. The underlying molecular mechanisms that mediate these effects are often complex and incompletely understood. In this review, we summarize the currently known disease-associated metabolic and signaling pathways that are altered following different heavy metals and metalloids exposure, alongside a brief summary of the mechanisms of their impacts. The main focus of this study is to explore how these affected pathways are associated with chronic multifactorial diseases including diabetes, cardiovascular diseases, cancer, neurodegeneration, inflammation, and allergic responses upon exposure to arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), mercury (Hg), nickel (Ni), and vanadium (V). Although there is considerable overlap among the different heavy metals and metalloids-affected cellular pathways, these affect distinct metabolic pathways as well. The common pathways may be explored further to find common targets for treatment of the associated pathologic conditions.

Metal mixture exposures and multiplexed autoantibody screening in Navajo communities exposed to uranium mine wastes

Background

Environmental exposures to metals in uranium mining wastes and drinking water were documented in more than half of the 1304 Navajo community members of the Diné Network for Environmental Health (DiNEH) Project, the first comprehensive assessment of exposures to these metals and community health on the Navajo Nation.

Objective

Evaluate environmental exposures among participants who provided blood and urine samples using multiplexed autoantibody positivity as an early effect biomarker.

Methods

Survey and geospatial location data, well water quality, and metals biomonitoring were used to assess exposures to mixed-metal wastes from 100 abandoned uranium waste sites.

Results

We observed that the prevalence of multiplexed autoantibody positivity in 239 participants was more than double that reported for the U.S. population (27.2% v. 13.8%) even though the national prevalence was generated using a different assay, the HEp-2 cell-based antinuclear antibody test. Increased risk of multiplexed autoantibody screening positivity (OR = 3.07,95%CI 1.15-8.22) was found among DiNEH study people who lived close to uranium mine and milling wastes and consumed metals in drinking water. Associations for females were even stronger when they lived closed to contaminated uranium mining and milling sites. Anti-U1-RNP antibodies were associated with water consumption of nickel.

Conclusion

Proximity to waste sites and consumption of metals in water even below current drinking water standards were associated with perturbations of immune tolerance. These findings are consistent with previous studies of autoimmunity in the local population and demonstrate that multiplexed autoantibody screening method has a potential as sentinel indicator of exposures to environmental metals.

Impact statement

This is the first, community-engaged environmental health study in exposed Navajo communities that applied clinical multiplexed testing in risk assessment of environmental metals associated with abandoned, unremediated uranium mining and milling waste sites. Routine clinical autoimmunity measures could be used as early effect biomarkers of environmental metal exposures.

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.

Lysinibacillus sphaericus mediates stress responses and attenuates arsenic toxicity in Caenorhabditis elegans

Exposure to toxic metals alters host response and that leads to disease development. Studies have revealed the effects of metals on microbial physiology, however, the role of metal resistant bacteria on host response to metals is unclear. The hypothesis that xenobiotic interactions between gut microbes and arsenic influence the host physiology and toxicity was assessed in a Caenorhabditis elegans model. The arsenic-resistant Lysinibacillus sphaericus B1CDA was fed to C. elegans to determine the host responses to arsenic in comparison to Escherichia coli OP50 food. L. sphaericus diet extended C. elegans lifespan compared to E. coli diet, with an increased expression of genes involved in lifespan, stress response and immunity (hif-1, hsp-16.2, mtl-2, abf-2, clec-60), as well as reduced fat accumulation. Arsenic-exposed worms fed L. sphaericus also had a longer lifespan than those fed E. coli and had an increased expression of genes involved in cytoprotection, stress resistance (mtl-1, mtl-2) and oxidative stress response (cyp-35A2, isp-1, ctl-2, sod-1), together with a decreased accumulation of reactive oxygen species (ROS). In comparison with E. coli, L. sphaericus B1CDA diet increased C. elegans fitness while detoxifying arsenic induced ROS and extending lifespan.

Infant infections, respiratory symptoms, and allergy in relation to timing of rice cereal introduction in a United States cohort

Rice products marketed in the USA, including baby rice cereal, contain inorganic arsenic, a putative immunotoxin. We sought to determine whether the timing of introduction of rice cereal in the first year of life influences occurrence of infections, respiratory symptoms, and allergy. Among 572 infants from the New Hampshire Birth Cohort Study, we used generalized estimating equation, adjusted for maternal smoking during pregnancy, marital status, education attainment, pre-pregnancy body mass index, maternal age at enrollment, infant birth weight, and breastfeeding history. Among 572 infants, each month earlier of introduction to rice cereal was associated with increased risks of subsequent upper respiratory tract infections (relative risk, RR = 1.04; 95% CI: 1.00-1.09); lower respiratory tract infections (RR = 1.19; 95% CI: 1.02-1.39); acute respiratory symptoms including wheeze, difficulty breathing, and cough (RR = 1.10; 95% CI: 1.00-1.22); fever requiring a prescription medicine (RR = 1.22; 95% CI: 1.02-1.45) and allergy diagnosed by a physician (RR = 1.20; 95% CI: 1.06-1.36). No clear associations were observed with gastrointestinal symptoms. Our findings suggest that introduction of rice cereal earlier may influence infants' susceptibility to respiratory infections and allergy.

Down-regulation of RdRp complex and activated immune response due to increased arsenic level leads to decreased corona virus replication

Corona virus is pandemic and responsible for more than 5.6 million deaths. It was observed that its severity was reported in varied ways in different countries and even in different states of India. This variation was critically evaluated in the area with high contamination of Arsenic (As) to understand the arsenic toxicity and Covid epidemiology and associated health effects in the human population. It was reported that the area with low arsenic contamination has a very high incidence rate of Corona infection in the world. Even in the Indian scenario, high As-contaminated states like West Bengal, Jharkhand and Bihar, the incidence rate is 1.994%, 1.114% and 0.661%, respectively. In contrast, states with the least arsenic contamination have a very high corona incidence rate like 6.308, 17.289 and 4.351, respectively. It was evident that Arsenic inhibits the RdRp complex, which leads to the inhibition of viral genome replication. The PAMP associated pathway was activated by Arsenic and effectively bound with viral spike proteins leading to effective clearance of virus through activation of TNF alpha and IL-1. It finally leads to increased production of IgE, IgG and IGA. Arsenic also enhances inflammatory response against the virus through increased production of cytokine. The high arsenic level also induces apoptosis in viral infected cells through Bax/Bak pathway. It activates cytochrome-c and caspase-3 activity, inducing apoptosis in viral infected cells through PARP activation in the nucleus. These combined findings suggest that high arsenic contamination causes replication inhibition, activates an inflammatory response, increases antibody production, and finally leads to apoptosis through the mitochondrial pathway. People residing in arsenic hit areas are at a very low threat of corona infection.

Co-exposure of sodium arsenite and uranyl acetate differentially alters gene expression in CD3/CD28 activated CD4+ T-cells

Communities in the western region of the United States experience environmental exposure to metal mixtures from living in proximity to numerous unremediated abandoned uranium mines. Metals including arsenic and uranium co-occur in and around these sites at levels higher than the United States Environmental Protection Agency maximum contaminant levels. To address the potential effect of these metals on the activation of CD4+ T-cells, we used RNA sequencing methods to determine the effect of exposure to sodium arsenite (1 μM and 10 μM), uranyl acetate (3 μM and 30 μM) or a mixture of sodium arsenite and uranyl acetate (1 μM sodium arsenite + 3 μM uranyl acetate). Sodium arsenite induced a dose dependent effect on activation associated gene expression; targeting immune response genes at the lower dose. Increases in oxidative stress gene expression were observed with both sodium arsenite doses. While uranyl acetate alone did not significantly alter activation associated gene expression, the mixture of uranyl acetate with sodium arsenite demonstrated a combined effect relative to sodium arsenite alone. The results demonstrate the need to investigate metal and metalloid mixtures at environmentally relevant concentrations to better understand the toxicological impact of these mixtures on T-cell activation, function and immune dysregulation.

The Role of Micronutrients and Toxic Metals in the Management of Epidemics in Cambodia

The illegal trade of wildlife in SE Asia has been identified as the likely cause of the COVID-19 pandemic. We reviewed 198 papers on the current COVID pandemic in Cambodia, diseases such as avian influenza and Nipah virus, most likely to develop into a new pandemic in Cambodia, and common features of disease that require mitigation. Artisanal goldmining uses pure mercury in the areas where wildlife is smuggled to China. Moreover, 30-40% of Cambodians are zinc deficient. High levels of arsenic in irrigation water (>1000 µg/L) are associated with very low levels of zinc in rice (5 µg/g) and rice is the primary staple food for the region. Brown rice from nine of 15 paddy fields in the arsenic zone of Cambodia had double the new guidelines of 100 µg/kg inorganic arsenic for children's food in the EU and USA. The combination of deficiencies of essential micronutrients like zinc and pervasive presence of arsenic and mercury has the potential to compromise the immunity of many Cambodians. Innovative solutions are suggested to improve micronutrient nutrition. Toxins that suppress the immune system must be better managed to reduce the virulence of pathogens. Cambodia was not likely the source of the COVID-19 but does have problems that could result in a new pandemic.

Toxic metal exposure as a possible risk factor for COVID-19 and other respiratory infectious diseases

Multiple medical, lifestyle, and environmental conditions, including smoking and particulate pollution, have been considered as risk factors for COronaVIrus Disease 2019 (COVID-19) susceptibility and severity. Taking into account the high level of toxic metals in both particulate matter (PM2.5) and tobacco smoke, the objective of this review is to discuss recent data on the role of heavy metal exposure in development of respiratory dysfunction, immunotoxicity, and severity of viral diseases in epidemiological and experimental studies, as to demonstrate the potential crossroads between heavy metal exposure and COVID-19 severity risk. The existing data demonstrate that As, Cd, Hg, and Pb exposure is associated with respiratory dysfunction and respiratory diseases (COPD, bronchitis). These observations corroborate laboratory findings on the role of heavy metal exposure in impaired mucociliary clearance, reduced barrier function, airway inflammation, oxidative stress, and apoptosis. The association between heavy metal exposure and severity of viral diseases, including influenza and respiratory syncytial virus has been also demonstrated. The latter may be considered a consequence of adverse effects of metal exposure on adaptive immunity. Therefore, reduction of toxic metal exposure may be considered as a potential tool for reducing susceptibility and severity of viral diseases affecting the respiratory system, including COVID-19.

Arsenite induces dysfunction of regulatory T cells through acetylation control of the Foxp3 promoter

Arsenic is known to cause damage to the body's immune system by inducing epigenetic changes. However, the molecular mechanism of this damage remains elusive. Here, we report that arsenic disrupts the morphology of lymphocytes, decreases cell viability, and results in abnormal proportions of T lymphocyte subsets. Moreover, our results revealed that arsenic can reduce global acetylation of histone H4 at K16 (H4K16 ac) in lymphocytes via decreasing the level of males absent on the first but upregulates mRNA and protein levels of the forkhead/winged-helix box P3 (Foxp3) gene by increasing the acetylation of histone H4 at K16 (H4K16) at the promoter of Foxp3. Finally, arsenic-induced dysfunction of regulatory T cells (Tregs) could be ameliorated by trichostatin A. Our research indicates that arsenic-induced immunosuppressive effect in human lymphocytes may be related to the acetylation of H4K16 at the promoter of Foxp3 and that histone deacetylase inhibitors may play a role in the prevention and treatment of immune injury caused by arsenic.

Exploring the use of current immunological assays for the developmental immunotoxicity assessment of food contact materials

The mammalian immune system is a highly complex, interactive network of cells that facilitates innate and adaptive immune responses. The neonatal immune system may be more susceptible to chemical perturbations than that of the adult. The effects of immunotoxicants during development may not be fully detected in toxicity studies performed on adult animals. Studies characterizing the ontogeny of the immune system in developing animals have shown that there are different critical windows of susceptibility to immunotoxicants. Developmental differences are evident among species compared to humans. Functional immune assays, such as the T-cell antibody dependent response assay, in rat models have been validated for use in the assessment of immunotoxicity with other assays. Recently, published studies have explored the feasibility of using additional techniques, such as in vitro studies using human whole blood cells or cell lines, mostly lacking either sensitivity or proper validation for regulatory purposes. However, some techniques may be developed further to enable translation of animal toxicity findings to human risk assessment of potential immunotoxicants. This paper summarizes the information on the developing immune system in humans versus rats and how the currently available assays might be used to contribute to the safety assessment of food contact substances.

Selective Separation of Arsenic from Lead Smelter Flue Dust by Alkaline Pressure Oxidative Leaching

This study investigated the feasibility of using an alkaline pressure oxidative leaching process to treat lead smelter flue dust containing extremely high levels of arsenic with the aim of achieving the selective separation of arsenic. The effects of different parameters including NaOH concentration, oxygen partial pressure, liquid-to-solid ratio, temperature, and time for the extraction of arsenic were investigated based on thermodynamic calculation. The results indicated that the leaching efficiency of arsenic reached 95.6% under the optimized leaching conditions: 80 g/L of NaOH concentration, 1.0 MPa of oxygen partial pressure, 8 mL/g of liquid-to-solid ratio, 120 °C of temperature, 2.0 h of time. Meanwhile, the leaching efficiencies of antimony, cadmium, indium and lead were less than 4.0%, basically achieving the selective separation of arsenic from lead smelter flue dust. More than 99.0% of arsenic was converted into calcium arsenate product and thus separated from the leach solution by a causticization process with CaO after other metal impurities were removed from the solution with the addition of Na2S. The optimized causticization conditions were established as: 4.0 of the mole ratio of calcium to arsenic, temperature of 80 °C, reaction time of 2.0 h. The resulting product of calcium arsenate may be used for producing metallic arsenic.