Immunosuppression by arsenic: a comparison of cathepsin L inhibition and apoptosis

DNA methylation analysis reveals the effect of arsenic on gestational diabetes mellitus

BACKGROUND

Arsenic (As) exposure is one of the risk factors for gestational diabetes mellitus (GDM). This study aimed to explore the effect of As-exposure on DNA methylation in GDM and to establish a risk assessment model of GDM in As exposed pregnant women.

METHOD

We collected elbow vein blood of pregnant women before delivery to measure As concentration and DNA methylation data. Then compared the DNA methylation data and established a nomogram.

RESULT

We identified a total of 10 key differentially methylated CpGs (DMCs) and found 6 corresponding genes. Functions were enriched in Hippo signaling pathway, cell tight junction, prophetic acid metabolism, ketone body metabolic process, and antigen processing and presentation. A nomogram was established that can predict GDM risks (c-index = 0.595, s:p = 0.973).

CONCLUSION

We found 6 genes associated with GDM with high As exposure. The prediction of the nomograms has been proven to be effective.

Arsenic and Diabetes Mellitus: A Putative Role for the Immune System

Diabetes mellitus (DM) is an enormous public health issue worldwide. Recent data suggest that chronic arsenic exposure is linked to the risk of developing type 1 and type 2 DM, albeit the underlying mechanisms are unclear. This review discusses the role of the immune system as a link to possibly explain some of the mechanisms of developing T1DM or T2DM associated with arsenic exposure in humans, animal models, and in vitro studies. The rationale for the hypothesis includes: (1) Arsenic is a well-recognized modulator of the immune system; (2) arsenic exposures are associated with increased risk of DM; and (3) dysregulation of the immune system is one of the hallmarks in the pathogenesis of both T1DM and T2DM. A better understanding of DM in association with immune dysregulation and arsenic exposures may help to understand how environmental exposures modulate the immune system and how these effects may impact the manifestation of disease.

Arsenic exposure and non-carcinogenic health effects

Inorganic arsenic (iAs) exposure is a serious health problem that affects more than 140 million individuals worldwide, mainly, through contaminated drinking water. Acute iAs poisoning produces several symptoms such as nausea, vomiting, abdominal pain, and severe diarrhea, whereas prolonged iAs exposure increased the risk of several malignant disorders such as lung, urinary tract, and skin tumors. Another sensitive endpoint less described of chronic iAs exposure are the non-malignant health effects in hepatic, endocrine, renal, neurological, hematological, immune, and cardiovascular systems. The present review outlines epidemiology evidence and possible molecular mechanisms associated with iAs-toxicity in several non-carcinogenic disorders.

T helper 2-driven immune dysfunction in chronic arsenic-exposed individuals and its link to the features of allergic asthma

Limited information is available regarding the effects of arsenic exposure on immune function. We have recently reported that chronic exposure to As was associated asthma, as determined by spirometry and respiratory symptoms. Because T helper 2 (Th2)-driven immune responses are implicated in the pathogenesis of allergic diseases, including asthma, we studied the associations of serum Th1 and Th2 mediators with the As exposure markers and the features of asthma among individuals exposed to As. A total of 553 blood samples were selected from the same study subjects recruited in our previous asthma study. Serum levels of Th1 and Th2 cytokines were analyzed by immunoassay. Subjects' arsenic exposure levels (drinking water, hair and nail arsenic concentrations) were determined by inductively coupled plasma mass spectroscopy. Arsenic exposure levels of the subjects showed significant positive associations with serum Th2-mediators- interleukin (IL)-4, IL-5, IL-13, and eotaxin without any significant changes in Th1 mediators- interferon-γ and tumor necrosis factor-α. The ratios of Th2 to Th1 mediators were significantly increased with increasing exposure to As. Notably, most of the Th2 mediators were positively associated with serum levels of total immunoglobulin E and eotaxin. The serum levels of Th2 mediators were significantly higher in the subjects with asthma than those without asthma. The results of our study suggest that the exacerbated Th2-driven immune responses are involved in the increased susceptibility to allergic asthma among individuals chronically exposed to As.

Herpes zoster during arsenic trioxide therapy for acute promyelocytic leukemia

Historically, arsenic exposure has been associated with herpes zoster (HZ) infection, however the risk is not well characterized in arsenic trioxide (ATO) treated patients with acute promyelocytic leukemia (APL). We aimed to characterize the risk of HZ in 112 ATO treated patients with APL with and without antiviral prophylaxis (AVP). HZ occurred in 13/112 (11.6%) within 6 months of completing ATO, including one case of HZ encephalitis. AVP reduced the incidence of HZ (17.5% vs. 4.1%, RR 0.24 [95% CI 0.05-1.0, p = .025]) with a number needed to treat of 7.7. HZ despite AVP occurred later than HZ in patients without AVP (7.8 vs. 2.3 months from starting ATO, p = .11). Older age and prior HZ increased the risk of HZ in patients not receiving AVP. Routine AVP should be considered in patients with APL receiving ATO, particularly in older patients and those with a history of HZ.

Cellular and Molecular Mechanisms of Environmental Pollutants on Hematopoiesis

Hematopoiesis is a complex and intricate process that aims to replenish blood components in a constant fashion. It is orchestrated mostly by hematopoietic progenitor cells (hematopoietic stem cells (HSCs)) that are capable of self-renewal and differentiation. These cells can originate other cell subtypes that are responsible for maintaining vital functions, mediate innate and adaptive immune responses, provide tissues with oxygen, and control coagulation. Hematopoiesis in adults takes place in the bone marrow, which is endowed with an extensive vasculature conferring an intense flow of cells. A myriad of cell subtypes can be found in the bone marrow at different levels of activation, being also under constant action of an extensive amount of diverse chemical mediators and enzymatic systems. Bone marrow platelets, mature erythrocytes and leukocytes are delivered into the bloodstream readily available to meet body demands. Leukocytes circulate and reach different tissues, returning or not returning to the bloodstream. Senescent leukocytes, specially granulocytes, return to the bone marrow to be phagocytized by macrophages, restarting granulopoiesis. The constant high production and delivery of cells into the bloodstream, alongside the fact that blood cells can also circulate between tissues, makes the hematopoietic system a prime target for toxic agents to act upon, making the understanding of the bone marrow microenvironment vital for both toxicological sciences and risk assessment. Environmental and occupational pollutants, therapeutic molecules, drugs of abuse, and even nutritional status can directly affect progenitor cells at their differentiation and maturation stages, altering behavior and function of blood compounds and resulting in impaired immune responses, anemias, leukemias, and blood coagulation disturbances. This review aims to describe the most recently investigated molecular and cellular toxicity mechanisms of current major environmental pollutants on hematopoiesis in the bone marrow.

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.

Sodium arsenite exposure impairs B cell proliferation and enhances vascular inflammation in Plasmodium berghei mouse model

Arsenic exposure has been linked to an impaired immune response and inflammation. Our study investigated the effects of sodium arsenite on host immune response and vascular inflammation during malarial infection. Mice were divided into three groups: control (C), Plasmodium berghei infection (I) and sodium arsenite exposure with Plasmodium berghei infection (As-I). The results showed that splenocyte proliferation stimulated by lipopolysaccharide (LPS) and pokeweed mitogen (PWM) was suppressed in the I group, and the suppression was more pronounced in the As-I group, suggesting that acquired immunity in infected mice was worsening following arsenic exposure. ICAM-1, an adhesion protein involved in parasite-infected red blood cell (iRBC) binding to endothelium, and HIF-1α, a hypoxia marker protein in the descending aorta, were increased in the As-I group compared to the I group. Collectively, our results suggest that arsenic may increase host susceptibility to malaria through suppression of B cell proliferation and enhancement of adhesion between iRBC and endothelium by increasing ICAM-1.

Microenvironmental Scenario of the Bone Marrow of Inorganic Arsenic-Exposed Experimental Mice

Exposure to arsenic on a regular basis, mainly through drinking water, agricultural pesticide, and sometimes therapeutic dose, results in various diseases of different tissues including the bone marrow hematopoietic system. Hematopoiesis is a dynamic process by which bone marrow (BM) hematopoietic stem/progenitor cells (HSPCs) generate a relatively constant pool of functionally mature blood cells by the support of microenvironmental components. The present study has been aimed to understand stem cell microenvironmental status during arsenic toxicity and the consequent reflection of dysregulation involving the hematopoietic machinery in experimental mice. Swiss albino mice were experimentally exposed to 10 μg arsenic trioxide/g body weight through oral gavage and 5 μg arsenic trioxide/g body weight intraperitoneally for a period of 30 days. Altered hemogram values in peripheral blood reflected the impaired hematopoiesis which was further validated by the reduced BM cellularity along with the deviated BM cell morphology as observed by scanning electron microscopy post arsenic exposure. The stromal cells were unable to establish a healthy matrix and the sustainability of hematopoietic progenitors was drastically affected in arsenic-exposed mouse groups, as observed in in vitro explant culture. The inability of stromal cells to establish supportive matrix was also explained by the decreased adherent colony formation in treated animals. Furthermore, the flow cytometric characterization of CXCR4⁺ and Sca-1⁺ CD44⁺ receptor expressions confirmed the dysregulation in the hematopoietic microenvironment. Thus, considering the importance of microenvironment in the maintenance of HSPC, it can be concluded that arsenic toxicity causes microenvironmental damage, leading to niche derangement and impaired hematopoiesis.

Proinflammatory effect of trivalent arsenical species in a co-culture of Caco-2 cells and peripheral blood mononuclear cells

Chronic exposure to inorganic arsenic (As) is associated with type 2 diabetes, cardiovascular diseases and cancer. Ingested inorganic As is transformed within the gastrointestinal tract and can give rise to more toxic species such as monomethylarsonous acid [MMA(III)] and dimethylarsinous acid [DMA(III)]. Thus, the intestinal epithelium comes into contact with toxic arsenical species, and the effects of such exposure upon epithelial function are not clear. The present study has evaluated the effect of 1 µM arsenite [As(III)], 0.1 µM MMA(III) and 1 µM DMA(III) upon the release of cytokines [interleukin-6 (IL6), IL8, tumor necrosis factor alpha (TNFα)], using a compartmentalized co-culture model with differentiated Caco-2 cells in the apical compartment and peripheral blood mononuclear cells in the basolateral compartment. In addition, the combined effect of arsenical species and lipopolysaccharide (LPS), both added into the apical compartment, has been analyzed. The results indicate that exposure to the arsenical forms induces a proinflammatory response. An increase in cytokine secretion into the basolateral compartment was observed, particularly as regards TNFα (up to 1,600 %). The cytokine levels on the apical side also increased, though to a lesser extent. As/LPS co-exposure significantly affected the proinflammatory response as compared to treatment with As alone. Treatment with DMA(III) and As/LPS co-exposure increased the permeability of the intestinal monolayer. In addition, As/LPS treatments enhanced As(III) and MMA(III) transport through the intestinal monolayer.

Combined effects of thermal stress and Cd on lysosomal biomarkers and transcription of genes encoding lysosomal enzymes and HSP70 in mussels, Mytilus galloprovincialis

In estuaries and coastal areas, intertidal organisms may be subject to thermal stress resulting from global warming, together with pollution. In the present study, the combined effects of thermal stress and exposure to Cd were investigated in the endo-lysosomal system of digestive cells in mussels, Mytilus galloprovincialis. Mussels were maintained for 24h at 18°C and 26°C seawater temperature in absence and presence of 50 μg Cd/L seawater. Cadmium accumulation in digestive gland tissue, lysosomal structural changes and membrane stability were determined. Semi-quantitative PCR was applied to reveal the changes elicited by the different experimental conditions in hexosaminidase (hex), β-glucuronidase (gusb), cathepsin L (ctsl) and heat shock protein 70 (hsp70) gene transcription levels. Thermal stress provoked lysosomal enlargement whilst Cd-exposure led to fusion of lysosomes. Both thermal stress and Cd-exposure caused lysosomal membrane destabilisation. hex, gusb and ctsl genes but not hsp70 gene were transcriptionally up-regulated as a result of thermal stress. In contrast, all the studied genes were transcriptionally down-regulated in response to Cd-exposure. Cd bioaccumulation was comparable at 18°C and 26°C seawater temperatures but interactions between thermal stress and Cd-exposure were remarkable both in lysosomal biomarkers and in gene transcription. hex, gusb and ctsl genes, reacted to elevated temperature in absence of Cd but not in Cd-exposed mussels. Therefore, thermal stress resulting from global warming might influence the use and interpretation of lysosomal biomarkers in marine pollution monitoring programmes and, vice versa, the presence of pollutants may condition the capacity of mussels to respond against thermal stress in a climate change scenario.

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.

Protective effect of curcumin against arsenic-induced apoptosis in murine splenocytes in vitro

Arsenic is a potent environmental pollutant and immunotoxic agent. Curcumin is a natural anti-oxidant used to treat a broad variety of diseases. Here, the effects were investigated of curcumin on sodium arsenite-induced apoptosis in murine splenocytes in vitro. Cells were exposed to sodium arsenite (NaAsO₂, 5 µM) with and without curcumin (5 and 10 µg/ml) and incubated at 37°C for 12 h. NaAsO₂ caused a decrease in cell viability and induction of apoptosis. These outcomes were concurrent with increases in the numbers of cells with reactive oxygen species generation, loss of mitochondrial transmembrane potential, an increase in the frequency of cells with sub-G₁ DNA content, and DNA fragmentation. Co-administration of curcumin with the NaAsO₂ caused significant recoveries in cell viability values and mitigation of the induced apoptosis-related molecular changes. A significant protection against apoptosis parameters in murine splenocytes simultaneously treated with NaAsO₂ and curcumin suggested a protective efficacy of curcumin. From the results it is concluded that the immuno-modulation exerted by curcumin might be attributed to its multifaceted effects including its anti-oxidative and anti-apoptotic properties. These findings have implications not only for the under-standing of the toxicity of arsenic to murine splenocytes in vitro but are also potentially important for developing preventive and/or corrective strategies against/during chronic arsenicosis.

Results of a long-term carcinogenicity bioassay on Sprague-Dawley rats exposed to sodium arsenite administered in drinking water

Arsenic (As) is a metal found in nature whose acute and chronic toxic effects have been known for decades. Hundreds of millions of people are at risk of exposure to As and its various chemical forms which can occur in the occupational and general environment in air, water, soil, food, and medicines. Several epidemiological studies have shown that prolonged exposure to As can induce various types of malignant tumors in humans, namely, skin, lung, liver, kidney, and bladder cancers. These effects have been observed particularly in geographic areas where people are exposed to well water with high concentrations of As. While the risks of As at high concentrations are well documented, there is still a great deal of uncertainty regarding the risk of exposure to As at very low levels. This uncertainty is due to the absence of adequate epidemiological data and the insufficiency of experimental data currently available. Given the limited evidence demonstrating the carcinogenic potential of As in animals, a long-term carcinogenicity bioassay on sodium arsenite (NaAsO(2)) was performed at the Cesare Maltoni Cancer Research Center (CMCRC) of the European Ramazzini Foundation (ERF). NaAsO(2) was administrated with drinking water at concentrations of 200, 100, 50, or 0 mg/L, for 104 weeks to Sprague-Dawley rats (50/sex/group), 8 weeks old at the start of the study. The animals were monitored until spontaneous death at which time each animal underwent complete necropsy. Histopathological evaluation of all pathological lesions and of all organs and tissues collected was routinely performed on each animal. The results demonstrate that in our experimental conditions NaAsO(2) induces sparse benign and malignant tumors among treated rats. The types of tumors observed are infrequent in the strain of Sprague-Dawley rats of the colony used in our laboratory, namely, lung adenomas and carcinomas, kidney adenomas/papillomas and carcinomas, and bladder carcinomas. Notably, an elevated incidence of these types of oncological lesions is also observed among people living in geographical areas where As is present at higher concentrations in drinking water.

Invasive aspergillosis in association with criminal arsenic poisoning

A 26-year-old man suffered acute arsenic poisoning after a poisoning attempt. He developed multiple organ failure including encephalopathy, bleeding disorders, pancreatitis, renal and hepatocellular impairment. Generalized erythroderma also developed within one week after admission. The developed acute respiratory distress syndrome and Aspergillus fumigatus was isolated from the endotracheal aspirate. Despite intensive care support, antidote administration and various epuration techniques, the patient died on day 26 from subarachnoid bleeding. An autopsy was obtained and the concentration of arsenic was determined in different tissues. Multiple abscesses due to Aspergillus fumigatus were seen in the lungs, myocardium and kidneys. This uncommon complication in a previously immunocompetent patient could be related to impaired immunity directly caused by arsenic poisoning.

Herpes zoster during treatment with arsenic trioxide

In vitro data suggest that arsenic compounds can suppress cell-mediated immunity by inducing apoptosis of T helper lymphocytes. We describe an occurrence of herpes zoster during treatment with arsenic trioxide (ATO) in two patients who were already in remission from acute promyelocytic leukemia and received ATO as consolidation treatment. During this complication, their leukocyte counts and differentials were within normal limits. Our report suggested the immunosuppressive effect of ATO in vivo. Both patients responded well to an oral antiviral. Clinicians should be aware of this complication during treatment with ATO since early antiviral treatment may help avoid complications including post-herpetic neuralgia.

Gallium Arsenide Selectively Up-Regulates Inflammatory Cytokine Expression at Exposure Site

Gallium arsenide (GaAs), a technologically and economically important semiconductor, is widely utilized in both military and commercial applications. This chemical is a potential health hazard as a carcinogen and immunotoxicant. We previously reported that macrophages at the exposure site exhibit characteristics of activation. In vitro culture of macrophages with GaAs fails to recapitulate the in vivo phenotype, suggesting that complete GaAs-mediated activation in vivo may require other cells or components found in the body's microenvironment. Our present study examined the role of cytokines upon GaAs-mediated macrophage activation. Intraperitoneal administration of GaAs elicited rapid specific recruitment of blood monocytes to the exposure site. This recruitment occurred concomitant with up-regulation of 17 chemokine and inflammatory cytokine mRNAs, while transcripts of three inhibitory cytokines diminished. Administration of latex beads caused less cytokine induction than GaAs, indicating that changes in mRNA levels could not be attributed to phagocytosis. Four representative chemokines and cytokines were selected for further analysis. Increased cytokine mRNA expression was paralleled by similar increases in cytokine protein levels, and secreted protein products were detected in peritoneal fluid. Cytokine protein expression was constrained to myeloid cells, and to a lesser extent to B cells. Alterations in patterns of cytokine gene expression elucidate mechanisms for increased cellular activation and antigen processing, and modulation of the inflammatory response. Our findings indicate that in vivo GaAs exposure alters cytokine gene expression, which may lead to an inflammatory reaction and contribute to pathological tissue damage.

Sodium arsenite retards proliferation of PHA-activated T cells by delaying the production and secretion of IL-2

Arsenic is a metalloid that commonly contaminates drinking water, and is a known human carcinogen. It has been shown that peripheral blood mononuclear cells (PBMCs) from healthy donors treated in vitro with NaAsO(2) and stimulated with phytohemagglutinin (PHA) show a lower proliferation than nontreated cells. We reported previously a reduction in the secretion of IL-2 in NaAsO(2)-treated PBMCs stimulated with PHA, an observation that might explain, in part, the reduction in proliferation. Since arsenic induces cytoskeleton alterations, which in turn may affect protein transport of the cell, we assumed that NaAsO(2) induced an accumulation of IL-2 inside the cells, and thus a reduction in the secretion of IL-2. In order to demonstrate this hypothesis, we assessed the intracellular IL-2 at the single cell level by flow cytometry, and unexpectedly found a reduction in the percentage of IL-2 producing T cells in the presence of NaAsO(2). We tracked the proliferation of T cells by using the 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) dye and found that NaAsO(2) slows down the entrance to cell division and delays the proliferation of cells that have already entered the cell cycle. Nevertheless, the expression of the activation molecules, CD25 and CD69, was unaltered. Assessment of the intracellular and secreted IL-2 in kinetic experiments showed that in fact, NaAsO(2) delays the production of IL-2, given that a recovery of both intracellular and secreted IL-2 was detected at 72 h. Evaluation of the cell cycle showed a higher proportion of cells in G(0)/G(1) and a lower proportion in G(2)/M in the presence of NaAsO(2). We thus conclude that NaAsO(2) reduces proliferation of T cells by delaying the production and secretion of IL-2, thus blocking T cells in G(1); as a consequence, the entry to cell cycle and the rounds of cell division are retarded, and a lower proliferation of T cells is hence observed.

Gallium arsenide exposure impairs splenic B cell accessory function

Gallium arsenide (GaAs) is utilized in industries for its semiconductor and optical properties. Chemical exposure of animals systemically suppresses several immune functions. The ability of splenic B cells to activate antigen-specific helper CD4(+) T cell hybridomas was assessed, and various aspects of antigen-presenting cell function were examined. GaAs-exposed murine B cells were impaired in processing intact soluble protein antigens, and the defect was antigen dependent. In contrast, B cells after exposure competently presented peptides to the T cells, which do not require processing. Cell surface expression of major histocompatibility complex (MHC) class II molecules and several costimulatory molecules on splenic B cells, which are critical for helper T cell activation, was not affected by chemical exposure. GaAs exposure also did not influence the stability of MHC class II heterodimers, suggesting that the defect may precede peptide exchange. GaAs-exposed B cells contained a normal level of aspartyl cathepsin activity; however, proteolytic activities of thiol cathepsins B and L were approximately half the control levels. Furthermore, two cleavage fragments of invariant chain, a molecular chaperone of MHC class II molecules, were increased in GaAs-exposed B cells, indicative of defective degradation. Thus, diminished thiol proteolytic activity in B cells may be responsible for their impaired antigen processing and invariant chain degradation, which may contribute to systemic immunosuppression caused by GaAs exposure.