Harmful interactions of non-essential heavy metals with cells of the innate immune system

In trace amounts, some heavy metals are essential for optimum health, while exposure to others, which are non-essential, presents the potential hazard of acute or chronic organ toxicity. Cadmium, mercury, lead, vanadium, platinum and palladium are commonly encountered, non-essential heavy metals which mediate their toxic activities by various mechanisms. All have the potential to interact with extracellular and intracellular protein sulfhydryls, rendering them not only potentially allergenic, but also predisposing to oxidative stress, while displacement of essential elements from their protein carriers may result in deficiency disorders. In addition, several of these metals, especially cadmium, palladium, platinum, and vanadium interact pro-oxidatively with the phagocytic cells of the innate immune system, potentiating the reactivity and toxicity of phagocyte-derived reactive oxygen species. This review is focused on the pro-oxidative/pro-inflammatory interactions of non-essential heavy metals with the cells of the innate immune system, a somewhat under-appreciated mechanism of metal induced toxicity.This article was originally published in a special issue, Heavy Metal Toxicity handled by Editor(s). Dr. Noreen Khan-Mayberry, National Aeronautics & Space Administration at Lyndon B. Johnson Space Center in Houston, USAhttp://http://www.omicsonline.org/jcthome.phpam201

Pharmacological control of neutrophil-mediated inflammation: Strategies targeting calcium handling by activated polymorphonuclear leukocytes

Unlike most other effector cells of the innate, as well as the adaptive immune systems, the neutrophil is a relatively undiscerning aggressor with scant regard for damage limitation. Although this highly combative, professional phagocyte has become increasingly implicated in the immunopathogenesis of many acute and chronic inflammatory disorders, of both infective and noninfective origin, effective pharmacological strategies to counter neutrophilaggression have remained elusive. Activation of neutrophils results in rapid mobilization of both stored and extracellular Ca2+, resulting in abrupt, usually transient increases in cytosolic Ca2+, which precede, and are a prerequisite for activation of the Ca2+-dependent pro-inflammatory activities of these cells. Mobilization of Ca2+ by, and restoration of Ca2+ homeostasis to activated neutrophils are multistep processes which present a number of potential targets, some well recognized and others noveland unconventional, for the pharmacological control of neutrophil-mediated inflammation. Uncovering these targets represents the primary focus of this review

Cigarette smoke condensate attenuates phorbol ester-mediated neutrophil extracellular trap formation.

Background: Neutrophil extracellular traps (NETs) constitute a network of chromatin fibres containing histone and antimicrobial peptides that are released by activated neutrophils. NETs protect the host against infection by trapping and facilitating phagocytosis of potentially harmful pathogens. Objectives: The aim of the current study was to investigate the effects of cigarette smoke condensate (CSC) on phorbol-ester (PMA)-mediated NETosis in vitro. Methods: Isolated human blood neutrophils were exposed to PMA (6.25 ng/ml) in the presence or absence of CSC (40-80 \ub5g/ ml) for 90 min at 37oC. NET formation was measured using a spectrofluorimetric procedure to detect extracellular DNA and fluorescence microscopy was used to visualize nets. Oxygen consumption by PMA-activated neutrophils was measured using an oxygen sensitive electrode. Results: Activation of neutrophils with PMA was associated with induction of NETosis that was significantly attenuated in the presence of CSC (40 and 80 \ub5g/ml), with mean fluorescence intensities of 65% and 66% of that observed with untreated cells, respectively, and confirmed by fluorescence microscopy. The rate and magnitude of oxygen consumption by activated neutrophils pre-treated with CSC (80 \ub5g/ml) was significantly less than that observed with untreated cells (73% of the control system), indicative of decreased production of reactive oxidants in the presence of CSC. Conclusion: The inhibition of NETosis observed in the presence of CSC correlated with attenuation of oxygen consumption by PMA-activated neutrophils suggesting a mechanistic relationship between these events. If operative in vivo, smoking-related attenuation of NETosis may impair host immune responses and increase the risk of respiratory infections

Montelukast: More than a Cysteinyl Leukotriene Receptor Antagonist?

The prototype cysteinyl leukotriene receptor antagonist, montelukast, is generally considered to have a niche application in the therapy of exercise- and aspirin-induced asthma. It is also used as add-on therapy in patients whose asthma is poorly controlled with inhaled corticosteroid monotherapy, or with the combination of a long-acting β(2)-agonist and an inhaled corticosteroid. Recently, however, montelukast has been reported to possess secondary anti-inflammatory properties, apparently unrelated to conventional antagonism of cysteinyl leukotriene receptors. These novel activities enable montelukast to target eosinophils, monocytes, and, in particular, the corticosteroid-insensitive neutrophil, suggesting that this agent may have a broader spectrum of anti-inflammatory activities than originally thought. If so, montelukast is potentially useful in the chemotherapy of intermittent asthma, chronic obstructive pulmonary disease, cystic fibrosis, and viral bronchiolitis, which, to a large extent, involve airway epithelial cell/neutrophil interactions. The primary objective of this mini-review is to present evidence for the cysteinyl leukotrien–independent mechanisms of action of montelukast and their potential clinical relevance

Protein kinase C promotes restoration of calcium homeostasis to platelet activating factor-stimulated human neutrophils by inhibition of phospholipase C

<p>Abstract</p> <p>Background</p> <p>The role of protein kinase C (PKC) in regulating the activity of phospholipase C (PLC) in neutrophils activated with the chemoattractant, platelet-activating factor (PAF, 20 and 200 nM), was probed in the current study using the selective PKC inhibitors, GF10903X (0.5 - 1 μM) and staurosporine (400 nM).</p> <p>Methods</p> <p>Alterations in cytosolic Ca²⁺, Ca²⁺influx, inositol triphosphate (IP₃), and leukotriene B₄production were measured using spectrofluorimetric, radiometric and competitive binding radioreceptor and immunoassay procedures, respectively.</p> <p>Results</p> <p>Activation of the cells with PAF was accompanied by an abrupt increase in cytosolic Ca²⁺followed by a gradual decline towards basal levels. Pretreatment of neutrophils with the PKC inhibitors significantly increased IP₃production with associated enhanced Ca²⁺release from storage vesicles, prolongation of the peak cytosolic Ca²⁺transients, delayed clearance and exaggerated reuptake of the cation, and markedly increased synthesis of LTB₄. The alterations in Ca²⁺fluxes observed with the PKC inhibitors were significantly attenuated by U73122, a PLC inhibitor, as well as by cyclic AMP-mediated upregulation of the Ca²⁺-resequestering endomembrane ATPase.</p> <p>Taken together, these observations are compatible with a mechanism whereby PKC negatively modulates the activity of PLC, with consequent suppression of IP₃production and down-regulation of Ca²⁺mediated pro-inflammatory responses of PAF-activated neutrophils.</p> <p>Conclusion</p> <p>Although generally considered to initiate and/or amplify intracellular signalling cascades which activate and sustain the pro-inflammatory activities of neutrophils and other cell types, the findings of the current study have identified a potentially important physiological, anti-inflammatory function for PKC, at least in neutrophils.</p

Adverse effects of biologic anti-inflammatory agents on the respiratory system : a review

The therapy of autoimmune rheumatological conditions has undergone significant changes with the introduction of biologic antiinflammatory agents including cytokine antagonists and agents that interfere with the function of T and B cells or those that inhibit intracellular enzymes such as Janus kinase (JAK). Although useful to control inflammation, these agents may be associated with drug-induced lung disease, which may be difficult to differentiate from pulmonary disorders caused by the underlying autoimmune diseases. This review aims to provide a description of lung disease, both infectious and non-infectious, that may be induced by the administration of biologic anti-inflammatory agents with emphasis on inhibitors of tumour necrosis factor, interleukin-1, interleukin-6 and JAK.https://journals.co.za/journal/m.ajtccmam2022Internal Medicin

Neutrophil extracellular traps and their role in health and disease

The human innate immune system is indispensable for protection against potentially invasive microbial and viral pathogens, either neutralising them or containing their spread until effective mobilisation of the slower, adaptive (specific), immune response. Until fairly recently, it was believed that the human innate immune system possessed minimal discriminatory activity in the setting of a rather limited range of microbicidal or virucidal mechanisms. However, recent discoveries have revealed that the innate immune system possesses an array of novel pathogen recognition mechanisms, as well as a resourceful and effective alternative mechanism of phagocyte (predominantly neutrophil)-mediated, anti-infective activity known as NETosis. The process of NETosis involves an unusual type of programmed, purposeful cell death, resulting in the extracellular release of a web of chromatin heavily impregnated with antimicrobial proteins. These structures, known as neutrophil extracellular traps (NETs), immobilise and contribute to the eradication of microbial pathogens, ensuring that the anti-infective potential of neutrophils is sustained beyond the lifespan of these cells. The current review is focused on the mechanisms of NETosis and the role of this process in host defence. Other topics reviewed include the potential threats to human health posed by poorly controlled, excessive formation of NETs, specifically in relation to development of autoimmune and cardiovascular diseases, as well as exacerbation of acute and chronic inflammatory disorders of the airways.http://www.sajs.co.zaam2016HaematologyImmunologyInternal Medicin

Soluble triggering receptor expressed on myeloid cells in sputum of patients with community-acquired pneumonia or pulmonary tuberculosis : a pilot study

Soluble triggering receptor expressed on myeloid cells is upregulated on the surface of inflammatory cells in the presence of bacterial infections apparently excluding those due to Mycobacterium tuberculosis. Therefore, sputum concentrations of Soluble Triggering Receptor Expressed on Myeloid Cells (s-TREM-1) may be of value in distinguishing bacterial pneumonia from pulmonary tuberculosis (PTB) in patients with respiratory infections. The current pilot study was designed to evaluate whether s-TREM-1 concentrations measured in the sputum of patients with suspected community-acquired pneumonia (CAP) allowed differentiation of those patients with PTB from other causes of pneumonia and to correlate s-TREM-1 with the CURB-65, a marker of disease severity. Methods. Soluble s-TREM-1 concentrations were measured in sputum samples from patients admitted to a tertiary hospital with CAP or PTB by means of an ELISA procedure. Results. Soluble-TREM-1 was readily detectable and quantifiable in sputum samples from patients with both CAP and PTB, with concentrations of 234 ± 47 and 178 ± 36 pg/ml respectively, but did not differ significantly between the 2 groups. However, patients with PTB had significantly lower leukocyte counts, 9 ± 1.3 versus 15 ± 1.4 x 109/l compared to those without PTB. Interestingly, sputum s-TREM-1 concentrations correlated significantly with the CURB-65 pneumonia severity score calculated at the time of admission. Conclusions. Soluble-TREM-1 expression is upregulated in patients with both CAP and PTB, but does not differentiate these two conditions. Sputum concentrations of s-TREM-1 may predict the severity of disease in patients with CAP.http://www.springerlink.com/content/0934-9723

Manganese promotes increased formation of hydrogen peroxide by activated human macrophages and neutrophils in vitro

Although pro-inflammatory mechanisms have been implicated in the pathogenesis of manganese (Mn²⁺)-related neurological and respiratory disorders, relatively little is known about the potential of this metal to interact pro-oxidatively with human phagocytes. The primary objective of the current study was to investigate the effects of Mn²⁺ as MnCl₂ (0.5-100 µM) on the generation of the reactive oxygen species (ROS), superoxide, hydrogen peroxide (H₂O₂), and hypohalous acids by isolated human blood neutrophils and monocyte-derived macrophages following activation of these cells with the chemotactic tripeptide, FMLP (1 µM), or the phorbol ester, PMA (25 ng/mL). Generation of ROS was measured using the combination of oxygen consumption, lucigenin/luminol-enhanced chemiluminescence, spectrofluorimetric detection of oxidation of 2,7-dichlorodihydrofluorescein, radiometric assessment of myeloperoxidase (MPO)-mediated protein iodination, release of MPO by ELISA, and spectrophotometric measurement of nitrite formation. Treatment of activated neutrophils with either FMLP or PMA resulted in significantly decreased reactivity of superoxide in the setting of increased formation of H₂O₂ and MPO-mediated iodination, with no detectable effects on either oxygen consumption or MPO release. Similar effects of the metal with respect to superoxide reactivity and H₂O₂ formation were observed with activated macrophages, while generation of NO was unaffected. Taken together with the findings of experiments using cell-free ROS-generating systems, these observations are compatible with a mechanism whereby Mn²⁺, by acting as a superoxide dismutase mimetic, increases the formation of H₂O₂ by activated phagocytes. If operative in vivo, this mechanism may contribute to the toxicity of Mn²⁺http://www.tandfonline.com/loi/iiht20hb2016Immunolog

The Beta-2-Adrenoreceptor Agonists, Formoterol and Indacaterol, but Not Salbutamol, Effectively Suppress the Reactivity of Human Neutrophils In Vitro

The clinical relevance of the anti-inflammatory properties of beta-2 agonists remains contentious possibly due to differences in their molecular structures and agonist activities. The current study has compared the effects of 3 different categories of β2-agonists, namely, salbutamol (short-acting), formoterol (long-acting) and indacaterol (ultra-long-acting), at concentrations of 1–1000 nM, with human blood neutrophils in vitro. Neutrophils were activated with either N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP, 1 µM) or platelet-activating factor (PAF, 200 nM) in the absence and presence of the β2-agonists followed by measurement of the generation of reactive oxygen species and leukotriene B4, release of elastase, and expression of the β2-integrin, CR3, using a combination of chemiluminescence, ELISA, colorimetric, and flow cytometric procedures respectively. These were correlated with alterations in the concentrations of intracellular cyclic-AMP and cytosolic Ca(2+). At the concentrations tested, formoterol and indacaterol caused equivalent, significant (P < 0.05 at 1–10 nM) dose-related inhibition of all of the pro-inflammatory activities tested, while salbutamol was much less effective (P < 0.05 at 100 nM and higher). Suppression of neutrophil reactivity was accompanied by elevations in intracellular cAMP and accelerated clearance of Ca(2+) from the cytosol of activated neutrophils. These findings demonstrate that β2-agonists vary with respect to their suppressive effects on activated neutrophils