STAT3-dependent VEGF production from keratinocytes abrogates dendritic cell activation and migration by arsenic: a plausible regional mechanism of immunosuppression in arsenical cancers

Arsenic as an immunotoxicant

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

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

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

Arsenic leads to autophagy of keratinocytes by increasing aquaporin 3 expression

Exposure to arsenic, a ubiquitous metalloid on Earth, results in human cancers. Skin cancer is the most common arsenical cancers. Both autophagy and aquaporin pathway are known to promote carcinogenesis. However, the mechanisms by which arsenic regulates aquaporin and autophagy in arsenical skin cancers remain elusive. This study aims to address how arsenic regulates aquaporin-3, the predominant aquaporin in epidermal keratinocytes, and how this process would induce autophagy. Quantitative real-time PCR and immunofluorescence were used to measure the expression of aquaporin 3 in arsenical skin cancers and arsenic-treated keratinocytes. Beclin-1 expression and autophagy were measured. We examined if blocking aquaporin 3 could interfere arsenic-induced autophagy in keratinocytes. Expression of aquaporin 3 is increased in arsenical cancers and in arsenic-treated keratinocytes. Arsenic induced autophagy in primary human keratinocytes. Notably, the arsenic-induced autophagy was inhibited by pretreatment of keratinocytes with aquaporin inhibitors Auphen or AgNO₃, or RNA interference against aquaporin 3. The data indicates that the aquaporin 3 is an important cell membrane channel to mediate arsenic uptake and contributes to the arsenic-induced autophagy.

Tumour angiogenesis normalized by myo-inositol trispyrophosphate alleviates hypoxia in the microenvironment and promotes antitumor immune response

Pathologic angiogenesis directly responds to tumour hypoxia and controls the molecular/cellular composition of the tumour microenvironment, increasing both immune tolerance and stromal cooperation with tumour growth. Myo-inositol-trispyrophosphate (ITPP) provides a means to achieve stable normalization of angiogenesis. ITPP increases intratumour oxygen tension (pO₂ ) and stabilizes vessel normalization through activation of endothelial Phosphatase-and-Tensin-homologue (PTEN). Here, we show that the tumour reduction due to the ITPP-induced modification of the tumour microenvironment by elevating pO₂ affects the phenotype and properties of the immune infiltrate. Our main observations are as follows: a relative change in the M1 and M2 macrophage-type proportions, increased proportions of NK and CD8⁺ T cells, and a reduction in Tregs and Th2 cells. We also found, in vivo and in vitro, that the impaired access of PD1⁺ NK cells to tumour cells is due to their adhesion to PD-L1⁺ /PD-L2⁺ endothelial cells in hypoxia. ITPP treatment strongly reduced PD-L1/PD-L2 expression on CD45+/CD31+ cells, and PD1⁺ cells were more numerous in the tumour mass. CTLA-4⁺ cell numbers were stable, but level of expression decreased. Similarly, CD47⁺ cells and expression were reduced. Consequently, angiogenesis normalization induced by ITPP is the mean to revert immunosuppression into an antitumor immune response. This brings a key adjuvant effect to improve the efficacy of chemo/radio/immunotherapeutic strategies for cancer treatment.

Heme oxygenase-1 (HO-1) assists inorganic arsenic-induced immune tolerance in murine dendritic cells

Inorganic arsenic, a well-known human carcinogen, poses a major threat to global health. Given the immunosuppressive potentials of inorganic arsenic as well as limited understanding of this metalloid on antigen-presenting dendritic cells (DCs), we systematically screened the immune targets in response to arsenic treatment, as well as its possible molecular mechanism in cultured murine DCs. Our results denoted that arsenite (As) significantly induced immune tolerance by down-regulating the expression of phenotypic molecules, pro-inflammatory factors and T-lymphocyte helper (Th)1/Th17-inducible cytokines in lipopolysaccharides (LPS)-stimulated myeloid-derived dendritic cells (BMDCs). Inconsistent with dampened phosphorylation of immune-related proteins (nuclear factor kappa-B) NF-κB, p38 and JNK, the metalloid drastically induced the expression of Heme oxygenase-1 (HO-1) protein, which enlightened us to continuously explore the possible roles of HO-1 pathway in As-induced immune tolerance in BMDCs. In this respect, immunosuppressive properties of HO-1 pathway in BMDCs were firstly confirmed through pharmacological overexpression of HO-1 by both CoPP and CORM-2. By contrast, limited HO-1 expression by HO-1 inhibitor ZnPP specifically alleviated As-mediated down-regulation of CD80, chemokine factor C-C chemokine receptor 7 (CCR7), tumor necrosis factor (TNF) -α, Interleukin (IL)-23 and IL-6, which reminds us the peculiarity of HO-1 in As-induced immune tolerance in murine DCs. Based on these experimental findings, we postulated the immunosuppressive property of inorganic arsenic might be mediated partially by HO-1 in DCs, thus contributing to the interactions of DCs-polarized differentiation of T-lymphocyte subtype as well as the development of infections and malignant diseases.

Arsenic induces mTOR-dependent autophagy, whereas it impairs the autophagy-lysosome pathway and the potential role of TFEB in cultured dendritic cells

Arsenic is a toxic metalloid, which also compromises immunity and causes various immunological disorders. Exposure to arsenic exerts the immunosuppressive properties of dendritic cells (DCs). Autophagy is a self-renewal process of cells, which degrades damaged macromolecules and organelles through the lysosomal pathway. Thus, herein, we attempt to clarify the impacts of autophagy and the autophagy-lysosome pathway on arsenic-exposed DCs. Bone marrow-derived dendritic cells (BMDCs) were exposed to different concentrations of arsenic (0.25, 0.5 and 1 μM) with or without LPS stimulation. Initially, we observed that arsenic induced autophagosome accumulation, significantly enhanced the LC3 II and p62 expressions and down-regulated the p-mTOR protein levels. We also determined that arsenic-induced autophagy occurred via an mTOR pathway. The results further revealed that arsenic inhibited autophagic flux in LPS-stimulated BMDCs using the autophagy inhibitor chloroquine (CQ). Meanwhile, arsenic significantly decreased the number of lysosomes, protein expression of lysosomal-specific markers LAMP1 and LAMP2, and the protein levels of lysosomal cysteine cathepsins (CTSD and CTSL). Moreover, the overexpression of transcription factor EB (TFEB), the master transcriptional regulator of autophagy and lysosome biogenesis, partially relieved arsenic-inhibited lysosomal CTSD and CTSL expressions, recovered the disorder of autophagic flux, promoted the production of pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-12, and reduced anti-inflammatory cytokine IL-10 secretion. In summary, our results support the idea that arsenic induces autophagy through an mTOR-dependent pathway in cultured BMDCs. Meanwhile, arsenic weakens the process of autophagic flux, which may be partially due to lysosomal dysfunction. Furthermore, we also suggest that TFEB can positively act on the autophagy-lysosome pathway and influence the expression of immunocytokines in DCs.

Tumor microenvironment-related dendritic cell deficiency: a target to enhance tumor immunotherapy

Dendritic cells (DCs), as specialized antigen-presenting cells, are essential for the initiation of specific T cell responses in innate antitumor immunity and, in certain cases, support humoral responses to inhibit tumor development. Mounting evidence suggests that the DC system displays a broad spectrum of dysfunctional status in the tumor microenvironment (TME), which ultimately affects antitumor immune responses. DC-based therapy can restore the function of DCs in the TME, thus showing a promising potential in tumor therapy. In this review, we provide an overview of the DC deficiency caused by various factors in the TME and discuss proposed strategies to reverse DC deficiency and the applications of novel combinatorial DC-based therapy for immune normalization of the tumor.

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

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

Effects of arsenic on porcine dendritic cells in vitro

Exposure to arsenic (As) is an ongoing, and in some places increasing, health problem. Still, however, the effects of As exposure on the immune system are not well understood. Dendritic cells (DC) are a critical immune cell that bridges the innate and adaptive immune systems. To determine the impact of inorganic (i)As exposure on DC, the effects of (geo)anthropogenically relevant levels of NaAsO₂ on the function of porcine monocyte-derived DC (MoDC) were evaluated in an in vitro model. The results showed a low dose of iAs reduced the phagocytic capacity of MoDC. Furthermore, although surface expression of DC activation markers, such as major histocompatibility complex (MHC)-II, CD80/86, CD40 and CD25, were only slightly changed, MoDC T-cell proliferation-inducing capacity was remarkably diminished by iAs treatment. Additionally, iAs induced significant interleukin (IL)-6 secretion by MoDC after 12- or 24-h incubation, whereas IL-1β secretion was only significantly up-regulated after 12 h. The secretion patterns of IL-8, tumor necrosis factor α (TNFα and IL-10 by iAs-treated MoDC were almost similar to that by mock-treated MoDC. Considering the broad roles of DC in immunobiology, this finding deepens the understanding of molecular mechanisms/functional consequences underpinning the immunopathology, inflammation, and increases in infection arising from As exposure.

Biophysical Properties and Motility of Human Mature Dendritic Cells Deteriorated by Vascular Endothelial Growth Factor through Cytoskeleton Remodeling

Dendritic cells (DCs), the most potent antigen-presenting cells, play a central role in the initiation, regulation, and maintenance of the immune responses. Vascular endothelial growth factor (VEGF) is one of the important cytokines in the tumor microenvironment (TME) and can inhibit the differentiation and functional maturation of DCs. To elucidate the potential mechanisms of DC dysfunction induced by VEGF, the effects of VEGF on the biophysical characteristics and motility of human mature DCs (mDCs) were investigated. The results showed that VEGF had a negative influence on the biophysical properties, including electrophoretic mobility, osmotic fragility, viscoelasticity, and transmigration. Further cytoskeleton structure analysis by confocal microscope and gene expression profile analyses by gene microarray and real-time PCR indicated that the abnormal remodeling of F-actin cytoskeleton may be the main reason for the deterioration of biophysical properties, motility, and stimulatory capability of VEGF-treated mDCs. This is significant for understanding the biological behavior of DCs and the immune escape mechanism of tumors. Simultaneously, the therapeutic efficacies may be improved by blocking the signaling pathway of VEGF in an appropriate manner before the deployment of DC-based vaccinations against tumors.

Presence of the Merkel cell polyomavirus in Merkel cell carcinoma combined with squamous cell carcinoma in a patient with chronic arsenism

We present a case of Merkel cell carcinoma (MCC) coincident with squamous cell carcinoma (SCC) on the breast of a woman with chronic arsenism. This case demonstrates the distinct association of chronic arsenism with two different primary cutaneous carcinomas. Merkel cell polyomavirus (MCPyV) was identified in the lesional skin of the MCC but not in that of the SCC, suggesting there are different interactions of MCPyV in the pathogenesis of SCC and MCC related to arsenic. Physicians need to be vigilant in the occurrence of both SCC and MCC in patients with chronic arsenism. To our knowledge, this is the first study to show the presence of MCPyV in the MCC but not the SCC portion of an arsenic-induced tumour.

Arsenic exposure, inflammation, and renal function in Bangladeshi adults: effect modification by plasma glutathione redox potential

Exposure to arsenic (As) in drinking water is a widespread public health problem leading to increased risk for multiple outcomes such as cancer, cardiovascular disease, and possibly renal disease; potential mechanisms include inflammation and oxidative stress. We tested the hypothesis that As exposure is associated with increased inflammation and decreased estimated glomerular filtration rate (eGFR) and examined whether the effects of As were modified by plasma glutathione (GSH), glutathione disulfide (GSSG), or the reduction potential of the GSSG/2GSH pair (EhGSH). In a cross-sectional study of N = 374 Bangladeshi adults having a wide range of As exposure, we measured markers of inflammation (plasma C-reactive protein (CRP), α-1 acid glycoprotein (AGP)), renal function (eGFR), GSH, and GSSG. In covariate-adjusted models, a 10% increase in water As, urinary As adjusted for specific gravity (uAs), or blood As (bAs) was associated with a 0.74% (p = 0.01), 0.90% (p = 0.16), and 1.39% (p = 0.07) increase in CRP, respectively; there was no association with AGP. A 10% increase in uAs or bAs was associated with an average reduction in eGFR of 0.16 (p = 0.12) and 0.21 ml/min/1.73 m(2) (p = 0.08), respectively. In stratified analyses, the effect of As exposure on CRP was observed only in participants having EhGSH > median (uAs p(Wald) = 0.03; bAs p(Wald) = 0.05). This was primarily driven by stronger effects of As exposure on CRP in participants with lower plasma GSH. The effects of As exposure on eGFR were not modified significantly by EhGSH, GSH, or GSSG. These data suggest that participants having lower plasma GSH and a more oxidized plasma EhGSH are at increased risk for As-induced inflammation. Future studies should evaluate whether antioxidant treatment lowers plasma EhGSH and reduces risk for As-induced diseases.