Effects of arsenic on porcine dendritic cells in vitro

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.

Multivariate Investigation of Toxic and Essential Metals in the Serum from Various Types and Stages of Colorectal Cancer Patients

Colorectal cancer (CRC) is currently one of the most frequent malignant neoplasms, ranking 3rd in incidence and 2nd in mortality both in the USA and across the world. The pathogenesis of CRC is a complex interaction between genetic susceptibility and environmental factors such as exposure to metals. Therefore, the present study was intended to assess the imbalances in the concentrations of selected essential/toxic elements (Pb, Cr, Fe, Zn, As, Cd, Cu, Se, Ni, and Hg) in the serum of newly diagnosed colorectal carcinoma patients (n = 165) in comparison with counterpart controls (n = 151) by atomic absorption spectrometry after wet-acid digestion method. Serum carcinoembryonic antigen (CEA) of the CRC patients was determined using immunoradiometric method. Body mass index (BMI) which is an established risk factor for CRC was also calculated for patients and healthy controls. Conversely, average Ni (2.721 μg/g), Cd (0.563 μg/g), As (0.539 μg/g), and Pb (1.273 μg/g) levels were significantly elevated in the serum of CRC patients compared to the healthy donors, while the average Se (7.052 μg/g), Fe (15.67 μg/g), Cu (2.033 μg/g), and Zn (8.059 μg/g) concentrations were elevated in controls. The correlation coefficients between the elements in the cancerous patients demonstrated significantly dissimilar communal relationships compared with the healthy subjects. Significant differences in the elemental levels were also showed for CRC types (primary colorectal lymphoma, gastrointestinal stromal tumor, and adenocarcinoma) and CRC stages (stage-I, stage-II, stage-III, and stage-IV) among the patients. Majority of the elements demonstrated perceptible disparities in their levels based on dietary, habitat, gender, and smoking habits of the malignant patients and healthy subjects. Multivariate methods revealed noticeably divergent apportionment among the toxic/essential elements in the cancerous patients than the healthy counterparts. Overall, the study showed significantly divergent distribution and associations of the essential and toxic elemental levels in the serum of the CRC patients in comparison with the healthy donors.

Colostrum fails to prevent bovine/camelid neonatal neutrophil damage from AFB1

Exposure to environmental toxicants that affect the immune system and overall health of many mammals is mostly unavoidable. One of the more common substances is the mycotoxins, especially carcinogenic aflatoxin (AF)B₁ which also causes immune suppression/dysregulation in exposed hosts. The present study analyzed the effects of naturally occurring levels of AFB₁ on apoptosis of healthy bovine and camelid neonatal neutrophils (PMN) that were isolated both before and after host consumption of colostrum. Cells from bovine and camel neonates (n = 12 sets of PMN/mammal/timepoint) were exposed for 24 h to a low level of AFB₁ (i.e. 10 ng AFB₁/ml) and then intracellular ATP content and caspase-3, -7, and -9 activities (determined by bioluminescence) were assessed. The results indicated a significant lessening of intracellular ATP content and equivalents of luminescence intensity in AFB₁-treated PMN in all studied samples, i.e. isolated pre-and post-colostrum consumption. In contrast, caspase-3, -7, and -9 activities in both pre- and post-colostrum consumption bovine and camelid PMN were noticeably increased (∼>2-fold). The damaging effects of AFB₁ were more pronounced in bovine neonate PMN than in camelid ones. These results showed that camelid or bovine neonatal PMN collected pre- and post-colostrum are sensitive (moreso after consumption) to naturally occurring levels of AFB₁. While merits of colostrum are well known, its failure to mitigate toxic effects of AFB₁ in what would translate into a critical period in the development of immune competence (i.e. during the first few days of life in bovine and camelid calves) is surprising. The observed in vitro toxicities can help clarify underlying mechanisms of immune disorders caused by AFs in animals/humans.

Microbes involved in arsenic mobilization and respiration: a review on isolation, identification, isolates and implications

Microorganisms play an important role in arsenic (As) cycling in the environment. Microbes mobilize As directly or indirectly, and natural/geochemical processes such as sulphate and iron reduction, oxidative sulphide mineral dissolution, arsenite (AsO₃^3-) oxidation and arsenate (AsO₄^3-) respiration further aid in As cycle in the environment. Arsenate serves as an electron donor for the microbes during anaerobic conditions in the sediment. The present work reviews the recent development in As contamination, various As-metabolizing microbes and their phylogenetic diversity, to understand the role of microbial communities in As respiration and mobilization. It also summarizes the contemporary understanding of the intricate biochemistry and molecular biology of natural As metabolisms. Some successful examples of engineered microbes by harnessing these natural mechanisms for effective remediation are also discussed. The study indicates that there is an exigent need to have a clear understanding of environmental aspects of As mobilization and subsequent oxidation-reduction by a suitable microbial consortium.

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.

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

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

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.