Zinc differentially regulates mitogen-activated protein kinases in human T cells

Metal coordination polymer nanoparticles for cancer therapy

Metal ions are essential elements in biological processes and immune homeostasis. They can regulate cancer cell death through multiple distinct molecular pathways and stimulate immune cells implicated in antitumor immune responses, suggesting opportunities to design novel metal ion-based cancer therapies. However, their small size and high charge density result in poor target cell uptake, uncontrolled biodistribution, and rapid clearance from the body, reducing therapeutic efficacy and increasing potential off-target toxicity. Metal coordination polymer nanoparticles (MCP NPs) are nanoscale polymer networks composed of metal ions and organic ligands linked via noncovalent coordination interactions. MCP NPs offer a promising nanoplatform for reshaping metal ions into more drug-like formulations, improving their in vivo pharmacological performance and therapeutic index for cancer therapy applications. This review provides a comprehensive overview of the inherent biological functions of metal ions in cancer therapy, showcasing examples of MCP NP systems designed for preclinical cancer therapy applications where drug delivery principles play a critical role in enhancing therapeutic outcomes. MCP NPs offer versatile metal ion engineering approaches using selected metal ions, various organic ligands, and functional payloads, enabling on-demand nano-drug designs that can significantly improve therapeutic efficacy and reduce side effects for effective cancer therapy.

Ca2+ signals are essential for T-cell proliferation, while Zn2+ signals are necessary for T helper cell 1 differentiation

The regulation of T-cell fate is crucial for the balance between infection control and tolerance. Calcium (Ca2+) and zinc (Zn2+) signals are both induced after T-cell stimulation, but their specific roles in the fate of activation and differentiation remain to be elucidated. Are Zn2+- and Ca2+ signals responsible for different aspects in T-cell activation and differentiation and do they act in concert or in opposition? It is crucial to understand the interplay of the intracellular signals to influence the fate of T cells in diseases with undesirable T-cell activities or in Zn2+-deficient patients. Human peripheral blood mononuclear cells were stimulated with the Zn2+ ionophore pyrithione and thapsigargin, an inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA). Intracellular Zn2+ and Ca2+ signals were monitored by flow cytometry and ELISA, quantitative PCR and western blot were used to evaluate T-cell differentiation and the underlying molecular mechanism. We found that Zn2+ signals upregulated the early T-cell activation marker CD69, interferon regulatory factor 1 (IRF-1), and Krüppel-like factor 10 (KLF-10) expression, which are important for T helper cell (Th) 1 differentiation. Ca2+ signals, on the other hand, increased T-bet and Forkhead box P3 (FoxP3) expression and interleukin (IL)-2 release. Most interestingly, the combination of Zn2+ and Ca2+ signals was indispensable to induce interferon (IFN)-γ expression and increased the surface expression of CD69 by several-fold. These results highlight the importance of the parallel occurrence of Ca2+ and Zn2+ signals. Both signals act in concert and are required for the differentiation into Th1 cells, for the stabilization of regulatory T cells, and induces T-cell activation by several-fold. This provides further insight into the impaired immune functions of patients with zinc deficiency.

A combined biochemical and cellular approach reveals Zn2+-dependent hetero- and homodimeric CD4 and Lck assemblies in T cells

The CD4 or CD8 co-receptors' interaction with the protein-tyrosine kinase Lck initiates the tyrosine phosphorylation cascade leading to T cell activation. A critical question is: to what extent are co-receptors and Lck coupled? Our contribution concerns Zn2+, indispensable for CD4- and CD8-Lck formation. We combined biochemical and cellular approaches to show that dynamic fluctuations of free Zn2+ in physiological ranges influence Zn(CD4)2 and Zn(CD4)(Lck) species formation and their ratio, although the same Zn(Cys)2(Cys)2 cores. Moreover, we demonstrated that the affinity of Zn2+ to CD4 and CD4-Lck species differs significantly. Increased intracellular free Zn2+ concentration in T cells causes higher CD4 partitioning in the plasma membrane. We additionally found that CD4 palmitoylation decreases the specificity of CD4-Lck formation in the reconstituted membrane model. Our findings help elucidate co-receptor-Lck coupling stoichiometry and demonstrate that intracellular free Zn2+ has a major role in the interplay between CD4 dimers and CD4-Lck assembly.

Understanding How Minerals Contribute to Optimal Immune Function

Sufficient mineral supply is vital not only for the innate immune system but also for the components of the adaptive immune defense, which encompass defense mechanisms against pathogens and the delicate balance of pro- and anti-inflammatory regulation in the long term. Generally, a well-balanced diet is capable of providing the necessary minerals to support the immune system. Nevertheless, specific vulnerable populations should be cautious about obtaining adequate amounts of minerals such as magnesium, zinc, copper, iron, and selenium. Inadequate levels of these minerals can temporarily impair immune competence and disrupt the long-term regulation of systemic inflammation. Therefore, comprehending the mechanisms and sources of these minerals is crucial. In exceptional circumstances, mineral deficiencies may necessitate supplementation; however, excessive intake of supplements can have adverse effects on the immune system and should be avoided. Consequently, any supplementation should be approved by medical professionals and administered in recommended doses. This review emphasizes the crucial significance of minerals in promoting optimal functioning of the immune system. It investigates the indispensable minerals required for immune system function and the regulation of inflammation. Moreover, it delves into the significance of maintaining an optimized intake of minerals from a nutritional standpoint.

Zinc depletion induces JNK/p38 phosphorylation and suppresses Akt/mTOR expression in acute promyelocytic NB4 cells

BACKGROUND

Myeloid leukemia is associated with reduced serum zinc and increased intracellular zinc. Our previous studies found that zinc depletion by TPEN induced apoptosis with PML-RARα oncoprotein degradation in acute promyelocytic NB4 cells. The effect of zinc homeostasis on intracellular signaling pathways in myeloid leukemia cells remains unclear.

OBJECTIVE

This study examined how zinc homeostasis affected MAPK and Akt/mTOR pathways in NB4 cells.

METHODS

We used western blotting to detect the activation of p38 MAPK, JNK, ERK1/2, and Akt/mTOR pathways in NB4 cells stimulated with the zinc chelator TPEN. Whether the effects of TPEN on these pathways could be reversed by zinc or the nitric oxide donor sodium nitroprusside (SNP) was further explored by western blotting. We used Zinpyr-1 staining to assess the role of SNP on labile zinc levels in NB4 cells treated with TPEN. In additional, we evaluated expressional correlations between the zinc-binding protein Metallothionein-2A (MT2A) and genes related to MAPKs and Akt/mTOR pathways in acute myeloid leukemia (AML) based on the TCGA database.

RESULTS

Zinc depletion by TPEN activated p38 and JNK phosphorylation in NB4 cells, whereas ERK1/2 phosphorylation was increased first and then decreased. The protein expression levels of Akt and mTOR were downregulated by TPEN. The nitric oxide donor SNP promotes zinc release in NB4 cells under zinc depletion conditions. We further found that the effects of zinc depletion on MAPK and Akt/mTOR pathways in NB4 cells can be reversed by exogenous zinc supplementation or treatment with the nitric oxide donor SNP. By bioinformatics analyses based on the TCGA database, we demonstrated that MT2A expression was negatively correlated with the expression of JNK, and was positively correlated with the expression of ERK1 and Akt in AML.

CONCLUSION

Our findings indicate that zinc plays a critical role in leukemia cells and help understanding how zinc depletion induces apoptosis.

Adjunct Therapy of Zinc Supplementation Increases Immunological Response in HIV-Infected Patients: A Systematic Review and Meta-Analysis

Introduction:

Malnutrition greatly accelerates the impairment of immune function among HIV-infected patients. Zinc deficiency is often found in people living with HIV/AIDS, affecting their immune function. Several studies have evaluated the effect of zinc in HIV-infected patients, including CD4+ T-cells. However, the results have varied. This review aimed to evaluate the effect of zinc supplementation in HIV patients, particularly its effect on CD4+ T-cells count.

Methods:

Relevant publications were obtained from PubMed database, Google Scholar, COCHRANE, and Science Direct. The primary outcome was CD4+ T-cells count, while the secondary outcomes were viral load and zinc levels. Year of publication, type of study, population, doses of zinc given, duration of zinc administration, sample size, age, and baseline CD4+ T-cells counts were also obtained and reported. Quantitative data from the publications were analyzed using a fixed-effect model or a random-effect model.

Results:

We evaluated 13 full-text articles on zinc supplementation in HIV-infected patients, involving 802 subjects for the experiment group and 742 subjects for the control group. Overall, zinc supplementation, whether as zinc supplementation-only or prepared as multiple micronutrient or multivitamin preparation, increases CD4+ T-cells counts by 33.14 cells/mm3 (p =0.02; 95% CI: 6.09 to 60.19), irrespective of age. Subgroup analysis revealed CD4+ T-cells counts also increase in patients who receive zinc supplementation-only preparation by 33.56 cells/mm3 (p = 0.04; 95% CI: 1.5 to 65.63). Zinc supplementation increases serum zinc levels with pooled mean difference of 15.41 µg/dl (p < 0.05; 95% CI: 12.77 to 18.06). However, the viral load did not significantly decrease with zinc supplementation, with a pooled mean difference of -4.02 copies/ml (p =0.7; 95% CI: -24.78 to 16.75), based on the random-effect model.

Conclusion:

Zinc supplementation in HIV-infected patients enhances immunological response, characterized by an increase in CD4+ T-cells counts. In addition, it increases zinc serum levels in HIV-infected patients, indicating the importance of zinc supplementation in this group of patients.

The Role of Zinc in GM-CSF-Induced Signaling in Human Polymorphonuclear Leukocytes

SCOPE

Zinc is suggested to be necessary for functional signaling induced by certain growth factors. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is a key factor for differentiation and activation of myeloid cells. This report analyses the impact of different zinc concentrations on GM-CSF-induced signaling in mature polymorphonuclear leukocytes (PMN).

METHODS AND RESULTS

As measured by flow cytometry, zinc increases surface GM-CSF receptor (GM-CSFR) in PMN, whereas monocytes respond with decreased GM-CSFR surface expression. Since total cellular GM-CSFR expression remains unaffected, the observed zinc-induced GM-CSFR surface dynamics may be explained by receptor redistribution. In PMN, zinc enhanced phosphorylation of mitogen-activated protein kinases (MAPK) in a dose-dependent manner as found in western blot. Zinc-induced MAPK phosphorylation is additionally augmented by moderate GM-CSF stimulation.

CONCLUSION

The present study demonstrates the opposing influence of zinc on GM-CSFR surface expression in monocytes and PMN. Zinc and GM-CSF, use in optimized concentrations, augment MAPK signaling, and increase expression of MAPK-induced myeloid cell leukemia-1 (Mcl-1) in PMN. Thus, this study concludes that zinc strengthens growth factor-induced signaling. Hence, the study provides a basis for further in vivo studies, focusing on the therapeutic value of zinc in patients with a disturbed GM-CSF signaling.

Ionic mitigation of CD4+ T cell metabolic fitness, Th1 central nervous system autoimmunity and Th2 asthmatic airway inflammation by therapeutic zinc

T helper (Th) cells provide immunity to pathogens but also contribute to detrimental immune responses during allergy and autoimmunity. Th2 cells mediate asthmatic airway inflammation and Th1 cells are involved in the pathogenesis of multiple sclerosis. T cell activation involves complex transcriptional networks and metabolic reprogramming, which enable proliferation and differentiation into Th1 and Th2 cells. The essential trace element zinc has reported immunomodulatory capacity and high zinc concentrations interfere with T cell function. However, how high doses of zinc affect T cell gene networks and metabolism remained so far elusive. Herein, we demonstrate by means of transcriptomic analysis that zinc aspartate (UNIZINK), a registered pharmaceutical infusion solution with high bioavailability, negatively regulates gene networks controlling DNA replication and the energy metabolism of murine CD3/CD28-activated CD4+ T cells. Specifically, in the presence of zinc, CD4+ T cells show impaired expression of cell cycle, glycolytic and tricarboxylic acid cycle genes, which functionally cumulates in reduced glycolysis, oxidative phosphorylation, metabolic fitness and viability. Moreover, high zinc concentrations impaired nuclear expression of the metabolic transcription factor MYC, prevented Th1 and Th2 differentiation in vitro and reduced Th1 autoimmune central nervous system (CNS) inflammation and Th2 asthmatic airway inflammation induced by house dust mites in vivo. Together, we find that higher zinc doses impair the metabolic fitness of CD4+ T cells and prevent Th1 CNS autoimmunity and Th2 allergy.

Zn2+ influx activates ERK and Akt signaling pathways

Zinc (Zn²⁺) is an essential metal in biology, and its bioavailability is highly regulated. Many cell types exhibit fluctuations in Zn²⁺ that appear to play an important role in cellular function. However, the detailed molecular mechanisms by which Zn²⁺ dynamics influence cell physiology remain enigmatic. Here, we use a combination of fluorescent biosensors and cell perturbations to define how changes in intracellular Zn²⁺ impact kinase signaling pathways. By simultaneously monitoring Zn²⁺ dynamics and kinase activity in individual cells, we quantify changes in labile Zn²⁺ and directly correlate changes in Zn²⁺ with ERK and Akt activity. Under our experimental conditions, Zn²⁺ fluctuations are not toxic and do not activate stress-dependent kinase signaling. We demonstrate that while Zn²⁺ can nonspecifically inhibit phosphatases leading to sustained kinase activation, ERK and Akt are predominantly activated via upstream signaling and through a common node via Ras. We provide a framework for quantification of Zn²⁺ fluctuations and correlate these fluctuations with signaling events in single cells to shed light on the role that Zn²⁺ dynamics play in healthy cell signaling.

Immunomodulation in Children: The Role of the Diet

Immune maturation and response to inflammation depend on good nutritional status. Protein and amino acid deficiencies can compromise innate and adaptive immune functions, particularly following injury or during illness. Dietary omega-3 long-chain fatty acids, prebiotics and micronutrients are beneficial to the immune system. A complex interplay exists between diet, microbiome, and epigenetic factors. The effect of single nutrients on immune function may hence be difficult to study. Well-designed intervention studies, investigating the effects of whole dietary pattern on the immune system, are needed.

Zinc regulates reactive oxygen species generation in platelets

Vascular complications resulting from atherosclerosis development are a major cause of death. Reactive oxygen species (ROS) are produced by platelets during activation, and have been demonstrated to positively regulate platelet activatory responses. Zn2+ is also an important hemostatic cofactor in platelets, acting both as a platelet agonist and second messenger. Whilst the effect of Zn2+-dependent signaling mechanisms on ROS production in nucleated cells has been demonstrated, comparable roles in platelets have yet to be investigated. In this study we investigated the relationship between fluctuations in cytosolic Zn2 [Zn2+]i and platelet ROS production. Agonist-evoked ROS production, GSH levels and GPx activity are abrogated in platelets treated with the Zn2+-chelator, TPEN. Conversely, increasing platelet [Zn2+]i using Zn2+ ionophores potentiated ROS generation and decreased GSH levels and GPx activity. Zn2+-dependent ROS production was sensitive to pretreatment with DPI or mitoTEMPO, NADPH oxidase and mitochondria inhibitors respectively. Increasing [Zn2+]i resulted in increases of Erk1/2 and JNK phosphorylation. Our data are consistent with a functional association between [Zn2+]i and ROS production in platelets that could influence thrombus formation in a clinical context.

Effects of Quercetin and Resveratrol on Zinc Chloride- and Sodium Metavanadate-Induced Passive Avoidance Memory Retention Deficits in Male Mice

Quercetin and resveratrol are found in a variety of fruits and vegetables and have several biological and pharmacological properties. In this study, the effects of quercetin [50 mg/kg, intraperitoneal (i.p.)] and resveratrol (50 mg/kg, i.p.) on zinc chloride (ZnCl₂; 75 mg/kg/d, 2 weeks oral gavage) and sodium metavanadate (SMV; 22.5 mg/kg/d, 2 weeks oral gavage) induced passive avoidance memory retention were investigated in step-through passive avoidance tasks. ZnCl₂ was dissolved in saline and SMV was dissolved in drinking water. Mice received ZnCl₂ or SMV orally for two weeks and were administered quercetin or resveratrol by i.p. injection on day 14, days 12 and 14, or days 10, 12, and 14. At the end of treatment, animals were trained for one day in a step-through passive avoidance task, then alterations in avoidance memory retention were evaluated after 24, 48, 96, and 168 h. Oral consumption of ZnCl₂ and SMV decreased latency time compared with control groups. Both quercetin and resveratrol (50 mg/kg, i.p.) prevented ZnCl₂- and SMV-induced avoidance memory retention impairments and did not significantly alter muscle strength, as demonstrated in rotarod tasks. No significant differences were observed between mice who received single, double, or triple doses of quercetin or resveratrol. The results suggest that quercetin and resveratrol may have preventive effects on ZnCl₂- and SMV-induced memory impairment in male mice.

Interactions of zinc- and redox-signaling pathways

Zinc and cellular oxidants such as reactive oxygen species (ROS) each participate in a multitude of physiological functions. There is considerable overlap between the affected events, including signal transduction. While there is no obvious direct connection between zinc and ROS, mainly because the bivalent cation zinc does not change its oxidation state in biological systems, these are linked by their interaction with sulfur, forming the remarkable triad of zinc, ROS, and protein thiols. First, zinc binds to reduced thiols and can be released upon oxidation. Thereby, redox signals are translated into changes in the free zinc concentration, which can act as zinc signals. Second, zinc affects oxidation of thiols in several ways, directly as well as indirectly. A protein incorporating many of these interactions is metallothionein (MT), which is rich in cysteine and capable of binding up to seven zinc ions in its fully reduced state. Zinc binding is diminished after (partial) oxidation, while thiols show increased reactivity in the absence of bound metal ions. Adding still more complexity, the MT promoter is controlled by zinc (via metal regulatory transcription factor 1 (MTF-1)) as well as redox (via nuclear factor erythroid 2-related factor 2 (NRF2)). Many signaling cascades that are important for cell proliferation or apoptosis contain protein thiols, acting as centers for crosstalk between zinc- and redox-signaling. A prominent example for shared molecular targets for zinc and ROS are active site cysteine thiols in protein tyrosine phosphatases (PTP), their activity being downregulated by oxidation as well as zinc binding. Because zinc binding also protects PTP thiols form irreversible oxidation, there is a multi-faceted reciprocal interaction, illustrating that zinc- and redox-signaling are intricately linked on multiple levels.

Zinc deficiency impairs interferon-γ production on post-transcriptional level

BACKGROUND

Zinc is a trace element and is thus commonly known to be indispensable for regular cellular function. Until today, zinc deficiency is a widespread health problem, affecting approximately one sixth of the world's population. Especially the immune system has proven to be highly dependent on zinc. Interferon-γ (IFN-γ) is a key element in the defense against intracellular pathogens. A lack of this cytokine results in immunological impairment, whereas an excess can lead to autoimmunity, highlighting the importance of a well-regulated IFN-γ expression. In a state of zinc deficiency, the production of this cytokine has long been shown to be reduced. Providing further insight into the molecular mechanisms responsible for this interaction is the primary objective of this study.

METHODS

Zinc-deficient or -supplemented cell culture, ELISA, quantitative PCR, methylation analysis.

RESULTS

Promoter methylation is a typical mechanism of gene silencing and a strong regulating factor for IFN-γ production. An analysis of the methylation status of IFN-γ and its transcription factor IRF4 in human PBMC in a state of cellular zinc deficiency or excess showed no dependency on the trace metal. Unexpectedly, zinc-deficient PBMC, which secreted significantly less IFN-γ protein, showed significantly higher mRNA levels of the cytokine compared to cells with high total zinc levels.

CONCLUSION

This report is the first about this unconventional ratio of IFN-γ mRNA to protein. Such a mismatch is highly relevant to the study of protein production in general and that of IFN-γ in particular. Based on our results and the latest research, we hypothesize a strong post-transcriptional effect of zinc on IFN-γ.

Zinc deficiency leads to reduced interleukin-2 production by active gene silencing due to enhanced CREMα expression in T cells

BACKGROUND & AIMS

The micronutrient zinc is essential for proper immune function. Consequently, zinc deficiency leads to impaired immune function, as seen in decreased secretion of interleukin (IL)-2 by T cells. Although this association has been known since the late 1980s, the underlying molecular mechanisms are still unknown. Zinc deficiency and reduced IL-2 levels are especially found in the elderly, which in turn are prone to chronic diseases. Here, we describe a new molecular link between zinc deficiency and reduced IL-2 expression in T cells.

METHODS

The effects of zinc deficiency were first investigated in vitro in the human T cell lines Jurkat and Hut-78 and complemented by in vivo data from zinc-supplemented pigs. A short- and long-term model for zinc deficiency was established. Zinc levels were detected by flow cytometry and expression profiles were investigated on the mRNA and protein level.

RESULTS

The expression of the transcription factor cAMP-responsive-element modulator α (CREMα) is increased during zinc deficiency in vitro, due to increased protein phosphatase 2A (PP2A) activity, resulting in decreased IL-2 production. Additionally, zinc supplementation in vivo reduced CREMα levels causing increased IL-2 expression. On epigenetic levels increased CREMα binding to the IL-2 promoter is mediated by histone deacetylase 1 (HDAC1). The HDAC1 activity is inhibited by zinc. Moreover, deacetylation of the activating histone mark H3K9 was increased under zinc deficiency, resulting in reduced IL-2 expression.

CONCLUSIONS

With the transcription factor CREMα a molecular link was uncovered, connecting zinc deficiency with reduced IL-2 production due to enhanced PP2A and HDAC1 activity.

Zn-Incorporated TiO2 Nanotube Surface Improves Osteogenesis Ability Through Influencing Immunomodulatory Function of Macrophages

PURPOSE

Zinc (Zn), an essential trace element in the body, has stable chemical properties, excellent osteogenic ability and moderate immunomodulatory property. In the present study, a Zn-incorporated TiO2 nanotube (TNT) was fabricated on titanium (Ti) implant material. We aimed to evaluate the influence of nano-scale topography and Zn on behaviors of murine RAW 264.7 macrophages. Moreover, the effects of Zn-incorporated TNT surface-regulated macrophages on the behaviors and osteogenic differentiation of murine MC3T3-E1 osteoblasts were also investigated.

METHODS

TNT coatings were firstly fabricated on a pure Ti surface using anodic oxidation, and then nano-scale Zn particles were incorporated onto TNTs by the hydrothermal method. Surface topography, chemical composition, roughness, hydrophilicity, Zn release pattern and protein adsorption ability of the Zn-incorporated TiO2 nanotube surface were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), surface profiler, contact angle test, Zn release test and protein adsorption test. The cell behaviors and both pro-inflammatory (M1) and pro-regenerative (M2) marker gene and protein levels in macrophages cultured on Zn-incorporated TNTs surfaces with different TNT diameters were detected. The supernatants of macrophages were extracted and preserved as conditioned medium (CM). Furthermore, the behaviors and osteogenic properties of osteoblasts cultured in CM on various surfaces were evaluated.

RESULTS

The release profile of Zn on Zn-incorporated TNT surfaces revealed a controlled release pattern. Macrophages cultured on Zn-incorporated TNT surfaces displayed enhanced gene and protein expression of M2 markers, and M1 markers were moderately inhibited, compared with the LPS group (the inflammation model). When cultured in CM, osteoblasts cultured on Zn-incorporated TNTs showed strengthened cell proliferation, adhesion, osteogenesis-related gene expression, alkaline phosphatase activity and extracellular mineralization, compared with their TNT counterparts and the Ti group.

CONCLUSION

This study suggests that the application of Zn-incorporated TNT surfaces may establish an osteogenic microenvironment and accelerate bone formation. It provided a promising strategy of Ti surface modification for a better applicable prospect.

The Interaction of Sodium and Zinc in the Priming of T Cell Subpopulations Regarding Th17 and Treg Cells

SCOPE

Nutrition is a critical determinant of a functional immune system. The aim of this study is to investigate the molecular mechanisms by which immune cells are influenced by zinc and sodium.

METHODS AND RESULTS

Mixed lymphocyte cultures and Jurkat cells are generated and incubated with zinc, sodium, or a combination of both for further tests. Zinc induces the number of regulatory T cells (Treg) and decreases T helper 17 cells (Th17), and sodium has the opposite effect. The transforming growth factor beta receptor signaling pathway is also enhanced by zinc and reduced by sodium as indicated by contrary phosphoSmad 2/3 induction. Antagonistic effects can also be seen on zinc transporter and metallothionein-1 (MT-1) mRNA expression: zinc declines Zip10 mRNA expression while sodium induces it, whereas MT-1 mRNA expression is induced by zinc while it is reduced by sodium.

CONCLUSION

This data indicate that zinc and sodium display opposite effects regarding Treg and Th17 induction in MLC, respectively, resulting in a contrary effect on the immune system. Additionally, it reveals a direct interaction of zinc and sodium in the priming of T cell subpopulations and shows that Zip10 and MT-1 play a significant role in those differentiation pathways.

The Intracellular Free Zinc Level Is Vital for Treg Function and a Feasible Tool to Discriminate between Treg and Activated Th Cells

The intracellular free zinc level and zinc distribution are important for cellular function. Both are highly variable and are altered due to intrinsic zinc pool fluctuation via buffering and muffling reactions. Multiple autoimmune diseases are associated with pathologically changed zinc levels, which provoke altered signal transduction leading to changed immune responses, cell differentiation, and function. For instance, immunological tolerance can be impaired, causing autoimmune diseases because of a malfunction of regulatory T cells (Tregs). We investigated the intracellular free zinc concentration of resting and activated T helper (Th) cells and Tregs in an allogeneic graft versus host disease model using fluorescence-activated cell sorting (FACS) analysis and enlightened cell function under nontoxic zinc concentrations and zinc deficiency by detecting cytokine secretion via enzyme-linked immunosorbent assay (ELISA). We exhibited for the first time that Tregs could be explicitly discriminated from other Th cell subsets using significantly increased intracellular free zinc levels. Moreover, the intracellular free zinc level was essential in maintaining the Treg phenotype and function, since zinc deficiency favored the pro-inflammatory immune response. Therefore, we hypothesize that the intracellular free zinc level in Th cells is essential in guaranteeing proper cellular function and can be used to discriminate Tregs from other Th cell subsets.

Zinc as a Gatekeeper of Immune Function

After the discovery of zinc deficiency in the 1960s, it soon became clear that zinc is essential for the function of the immune system. Zinc ions are involved in regulating intracellular signaling pathways in innate and adaptive immune cells. Zinc homeostasis is largely controlled via the expression and action of zinc "importers" (ZIP 1-14), zinc "exporters" (ZnT 1-10), and zinc-binding proteins. Anti-inflammatory and anti-oxidant properties of zinc have long been documented, however, underlying mechanisms are still not entirely clear. Here, we report molecular mechanisms underlying the development of a pro-inflammatory phenotype during zinc deficiency. Furthermore, we describe links between altered zinc homeostasis and disease development. Consequently, the benefits of zinc supplementation for a malfunctioning immune system become clear. This article will focus on underlying mechanisms responsible for the regulation of cellular signaling by alterations in zinc homeostasis. Effects of fast zinc flux, intermediate "zinc waves", and late homeostatic zinc signals will be discriminated. Description of zinc homeostasis-related effects on the activation of key signaling molecules, as well as on epigenetic modifications, are included to emphasize the role of zinc as a gatekeeper of immune function.

Impact of Childhood Malnutrition on Host Defense and Infection

The global impact of childhood malnutrition is staggering. The synergism between malnutrition and infection contributes substantially to childhood morbidity and mortality. Anthropometric indicators of malnutrition are associated with the increased risk and severity of infections caused by many pathogens, including viruses, bacteria, protozoa, and helminths. Since childhood malnutrition commonly involves the inadequate intake of protein and calories, with superimposed micronutrient deficiencies, the causal factors involved in impaired host defense are usually not defined. This review focuses on literature related to impaired host defense and the risk of infection in primary childhood malnutrition. Particular attention is given to longitudinal and prospective cohort human studies and studies of experimental animal models that address causal, mechanistic relationships between malnutrition and host defense. Protein and micronutrient deficiencies impact the hematopoietic and lymphoid organs and compromise both innate and adaptive immune functions. Malnutrition-related changes in intestinal microbiota contribute to growth faltering and dysregulated inflammation and immune function. Although substantial progress has been made in understanding the malnutrition-infection synergism, critical gaps in our understanding remain. We highlight the need for mechanistic studies that can lead to targeted interventions to improve host defense and reduce the morbidity and mortality of infectious diseases in this vulnerable population.

Zinc Signals and Immunity

Zinc homeostasis is crucial for an adequate function of the immune system. Zinc deficiency as well as zinc excess result in severe disturbances in immune cell numbers and activities, which can result in increased susceptibility to infections and development of especially inflammatory diseases. This review focuses on the role of zinc in regulating intracellular signaling pathways in innate as well as adaptive immune cells. Main underlying molecular mechanisms and targets affected by altered zinc homeostasis, including kinases, caspases, phosphatases, and phosphodiesterases, will be highlighted in this article. In addition, the interplay of zinc homeostasis and the redox metabolism in affecting intracellular signaling will be emphasized. Key signaling pathways will be described in detail for the different cell types of the immune system. In this, effects of fast zinc flux, taking place within a few seconds to minutes will be distinguish from slower types of zinc signals, also designated as “zinc waves”, and late homeostatic zinc signals regarding prolonged changes in intracellular zinc.

Air pollution-related metals induce differential cytokine responses in bronchial epithelial cells

Different transition metals have been shown to induce inflammatory responses in lung. We have compared eight different metal ions with regard to cytokine responses, cytotoxicity and signalling mechanisms in a human lung epithelial cell model (BEAS-2B). Among the metal ions tested, there were large differences with respect to pro-inflammatory potential. Exposure to Cd(2+), Zn(2+) and As(3+) induced CXCL8 and IL-6 release at concentrations below 100μM, and Mn(2+) and Ni(2+) at concentrations above 200μM. In contrast, VO4(3-), Cu(2+) and Fe(2+) did not induce any significant increase of these cytokines. An expression array of 20 inflammatory relevant genes also showed a marked up-regulation of CXCL10, IL-10, IL-13 and CSF2 by one or more of the metal ions. The most potent metals, Cd(2+), Zn(2+) and As(3+) induced highest levels of oxidative activity, and ROS appeared to be central in their CXCL8 and IL-6 responses. Activation of the MAPK p38 seemed to be a critical mediator. However, the NF-κB pathway appeared predominately to be involved only in Zn(2+)- and As(3+)-induced CXCL8 and IL-6 responses. Thus, the most potent metals Cd(2+), Zn(2+) and As(3+) seemed to induce a similar pattern for the cytokine responses, and with some exceptions, via similar signalling mechanisms.

Metallothionein regulates intracellular zinc signaling during CD4(+) T cell activation

BACKGROUND

The ultra-low redox potential and zinc binding properties of the intracellular pool of mammalian metallothioneins (MT) suggest a role for MT in the transduction of redox signals into intracellular zinc signals. Increased expression of MT after exposure to heavy metals, oxidative stress, or inflammatory cytokines leads to an increased intracellular redox-mobilizable zinc pool that can affect downstream zinc-sensitive signaling pathways. CD4(+) T helper cells are poised to be influenced by MT transduced zinc signaling because they produce intracellular reactive oxygen species following activation through the T cell receptor and are sensitive to small changes in intracellular [Zn(2+)].

RESULTS

MT expression and intracellular [Zn(2+)] are both increased during primary activation and expansion of naïve CD4(+) T cells into the Tr1 phenotype in vitro. When Tr1 cells from wildtype mice are compared with congenic mice lacking functional Mt1 and Mt2 genes, the expression of intracellular MT is associated with a greater increase in intracellular [Zn(2+)] immediately following exposure to reactive oxygen species or upon restimulation through the T cell receptor. The release of Zn(2+) from MT is associated with a greater increase in p38 MAPK activation following restimulation and decreased p38 MAPK activation in MT knockout Tr1 cells can be rescued by increasing intracellular [Zn(2+)]. Additionally, IL-10 secretion is increased in MT knockout Tr1 cells compared with wildtype controls and this increase is prevented when the intracellular [Zn(2+)] is increased experimentally.

CONCLUSIONS

Differences in zinc signaling associated with MT expression appear to be a result of preferential oxidation of MT and concomitant release of Zn(2+). Although zinc is released from many proteins following oxidation, release is greater when the cell contains an intracellular pool of MT. By expressing MT in response to certain environmental conditions, CD4(+) T cells are able to more efficiently release intracellular zinc and regulate signaling pathways following stimulation. The link between MT expression and increased zinc signaling following activation represents an important immunomodulatory mechanism of MT and illuminates the complex role MT plays in shaping immune responses.

Zinc Chelation Mediates the Lysosomal Disruption without Intracellular ROS Generation

We report the molecular mechanism for zinc depletion caused by TPEN (N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine) in neuroblastoma cells. The activation of p38 MAP kinase and subsequently caspase 3 is not due to or followed by redox imbalance or ROS generation, though these are commonly observed in literature. We found that TPEN is not responsible for ROS generation and the mechanism involves essentially lysosomal disruption caused by intracellular zinc depletion. We also observed a modest activation of Bax and no changes in the Bcl-2 proteins. As a result, we suggest that TPEN causes intracellular zinc depletion which can influence the breakdown of lysosomes and cell death without ROS generation.

Zinc Chloride and Lead Acetate-Induced Passive Avoidance Memory Retention Deficits Reversed by Nicotine and Bucladesine in Mice

It is very important to investigate the neurotoxic effects of metals on learning and memory processes. In this study, we tried to investigate the effects and time course properties of oral administration of zinc chloride (25, 50, and 75 mg/kg, for 2 weeks), lead acetate (250, 750, 1,500, and 2,500 ppm for 4, 6 and 8 weeks), and their possible mechanisms on a model of memory function. For this matter, we examined the intra-peritoneal injections of nicotine (0.25, 0.5, 1, and 1.5 mg/kg) and bucladesine (50, 100, 300, and 600 nM/mouse) for 4 days alone and in combination with mentioned metals in the step-through passive avoidance task. Control animals received saline, drinking water, saline, and DMSO (dimethyl sulfoxide)/deionized water (1:9), respectively. At the end of each part of studies, animals were trained for 1 day in step-through task. The avoidance memory retention alterations were evaluated 24 and 48 h later in singular and combinational studies. Zinc chloride (75 mg/kg) oral gavage for 2 weeks decreased latency times compared to control animals. Also, lead acetate (750 ppm oral administrations for 8 weeks) caused significant lead blood levels and induced avoidance memory retention impairments. Four-days intra-peritoneal injection of nicotine (1 mg/kg) increased latency time compared to control animals. Finally, findings of this research showed that treatment with intra-peritoneal injections of nicotine (1 mg/kg) and/or bucladesine (600 nM/mouse) reversed zinc chloride- and lead acetate-induced avoidance memory retention impairments. Taken together, these results showed the probable role of cholinergic system and protein kinase A pathways in zinc chloride- and lead acetate-induced avoidance memory alterations.

Zinc enhances the number of regulatory T cells in allergen-stimulated cells from atopic subjects

PURPOSE

The trace element zinc is essential for immune function and its regulation. Since zinc deficiency and allergic hyperresponsive reactions are often accompanied, the influence of zinc on allergen-induced cell growth, CD4+ regulatory T (Treg) cell numbers and cytokine expression during allergic immune reactions was investigated.

METHODS

Peripheral blood mononuclear cells (PBMCs) from non-atopic and atopic subjects were treated with timothy grass allergen pre-incubated with or without zinc. Proliferation was determined by analyzing the incorporation of ³H-thymidine. Intracellular zinc and Foxp3 levels and cell surface antigens were measured by FACS, cytokine expression by ELISA and real-time PCR.

RESULTS

Incubation with 50 μM zinc sulfate (Zn50) enhances cytosolic zinc concentrations in CD3+ T cells. The data also reveal that the combination of Zn50 plus allergen significantly reduces PBMC proliferation of atopic subjects. Additionally, Zn50 plus allergen enhances Th1 cytokine responses shown by increased interferon (IFN)-γ/interleukin (IL)-10 ratios as well as enhanced tumor necrosis factor-α release. In response to allergen, zinc increases Treg cells and upregulates the mRNA expression of cytotoxic T-lymphocyte antigen-4 in atopic subjects. Interestingly, Zn50 alone leads to an increase of CD4+CD25high(hi)+ cells in atopic and non-atopic subjects.

CONCLUSIONS

Zinc may regulate unwanted hyperresponsive immune reactions by suppressing proliferation through a significant shift from IL-10 to the Th1 cytokine IFN-γ, and enhanced regulatory T cell numbers. Therefore, zinc supplementation may be a promising tool for the therapy of allergies, without negatively affecting the immune system.

Cellular sensing and transport of metal ions: implications in micronutrient homeostasis

Micronutrients include the transition metal ions zinc, copper and iron. These metals are essential for life as they serve as cofactors for many different proteins. On the other hand, they can also be toxic to cell growth when in excess. As a consequence, all organisms require mechanisms to tightly regulate the levels of these metal ions. In eukaryotes, one of the primary ways in which metal levels are regulated is through changes in expression of genes required for metal uptake, compartmentalization, storage and export. By tightly regulating the expression of these genes, each organism is able to balance metal levels despite fluctuations in the diet or extracellular environment. The goal of this review is to provide an overview of how gene expression can be controlled at a transcriptional, posttranscriptional and posttranslational level in response to metal ions in lower and higher eukaryotes. Specifically, I review what is known about how these metalloregulatory factors sense fluctuations in metal ion levels and how changes in gene expression maintain nutrient homeostasis.

Zinc and its role in immunity and inflammation

Zinc (Zn) nutritional importance has been known for a long time, but in the last decades its importance in immune modulation has arisen. This review aims at describing the mechanisms involved in the regulation of Zn homeostasis and their effects on the immune response focusing on those which are implicated in the physiopathology of rheumatoid arthritis. Zn functions as a modulator of the immune response through its availability, which is tightly regulated by several transporters and regulators. When this mechanism is disturbed, Zn availability is reduced, altering survival, proliferation and differentiation of the cells of different organs and systems and, in particular, cells of the immune system. Zn deficiency affects cells involved in both innate and adaptive immunity at the survival, proliferation and maturation levels. These cells include monocytes, polymorphonuclear-, natural killer-, T-, and B-cells. T cell functions and the balance between the different T helper cell subsets are particularly susceptible to changes in Zn status. While acute Zn deficiency causes a decrease in innate and adaptive immunity, chronic deficiency increases inflammation. During chronic deficiency, the production of pro-inflammatory cytokines increases, influencing the outcome of a large number of inflammatory diseases, including rheumatoid arthritis.

Zinc signals and immune function

For more than 50 years, it has been known that zinc deficiency compromises immune function. During this time, knowledge about the biochemistry of zinc has continued to grow, but only recent years have provided in-depth molecular insights into the multiple aspects of zinc as a regulator of immunity. A network based on ZnT and ZIP proteins for transport and metallothionein for storage tightly regulates zinc availability, and virtually all aspects of innate and adaptive immunity are affected by zinc. In vivo, zinc deficiency alters the number and function of neutrophil granulocytes, monocytes, natural killer (NK)-, T-, and B-cells. T cell functions and balance between the different subsets are particularly susceptible to changes in zinc status. This article focuses in particular on the main mechanisms by which zinc ions exert essential functions in the immune system. On the one hand, this includes tightly protein bound zinc ions serving catalytic or structural functions in a multitude of different proteins, in particular enzymes and transcription factors. On the other hand, increasing evidence arises for a regulatory role of free zinc ions in signal transduction, especially in cells of the immune system. Identification of several molecular targets, including phosphatases, phosphodiesterases, caspases, and kinases suggest that zinc ions are a second messenger regulating signal transduction in various kinds of immune cells.

Zinc ions as effectors of environmental oxidative lung injury

The redox-inert transition metal Zn is a micronutrient that plays essential roles in protein structure, catalysis, and regulation of function. Inhalational exposure to ZnO or to soluble Zn salts in occupational and environmental settings leads to adverse health effects, the severity of which appears dependent on the flux of Zn(2+) presented to the airway and alveolar cells. The cellular toxicity of exogenous Zn(2+) exposure is characterized by cellular responses that include mitochondrial dysfunction, elevated production of reactive oxygen species, and loss of signaling quiescence leading to cell death and increased expression of adaptive and inflammatory genes. Central to the molecular effects of Zn(2+) are its interactions with cysteinyl thiols, which alters their functionality by modulating their reactivity and participation in redox reactions. Ongoing studies aimed at elucidating the molecular toxicology of Zn(2+) in the lung are contributing valuable information about its role in redox biology and cellular homeostasis in normal and pathophysiology.

Zinc and the modulation of redox homeostasis

Zinc, a redox-inactive metal, has been long viewed as a component of the antioxidant network, and growing evidence points to its involvement in redox-regulated signaling. These actions are exerted through several mechanisms based on the unique chemical and functional properties of zinc. Overall, zinc contributes to maintaining the cell redox balance through various mechanisms including: (i) the regulation of oxidant production and metal-induced oxidative damage; (ii) the dynamic association of zinc with sulfur in protein cysteine clusters, from which the metal can be released by nitric oxide, peroxides, oxidized glutathione, and other thiol oxidant species; (iii) zinc-mediated induction of the zinc-binding protein metallothionein, which releases the metal under oxidative conditions and acts per se as a scavenging oxidant; (iv) the involvement of zinc in the regulation of glutathione metabolism and of the overall protein thiol redox status; and (v) a direct or indirect regulation of redox signaling. Findings of oxidative stress, altered redox signaling, and associated cell/tissue dysfunction in cell and animal models of zinc deficiency highlight the relevant role of zinc in the preservation of cell redox homeostasis. However, although the participation of zinc in antioxidant protection, redox sensing, and redox-regulated signaling is accepted, the molecules, targets, and mechanisms involved are still partially known and the subject of active research.

Repletion of zinc in zinc-deficient cells strongly up-regulates IL-1β-induced IL-2 production in T-cells

Mild zinc deficiency in humans negatively affects IL-2 production resulting in declined percentages of cytolytic T cells and decreased NK cell lytic activity, which enhances the susceptibility to infections and malignancies. T-cell activation is critically regulated by zinc and the normal physiological zinc level in T-cells slightly lies below the optimal concentration for T-cell functions. A further reduction in zinc level leads to T-cell dysfunction and autoreactivity, whereas high zinc concentrations (100 μM) were shown to inhibit interleukin-1 (IL-1)-induced IL-1 receptor kinase (IRAK) activation. In this study, we investigated the molecular mechanism by which zinc regulates the IL-1β-induced IL-2 expression in T-cells. Zinc supplementation to zinc-deficient T-cells increased intracellular zinc levels by altering the expression of zinc transporters, particularly Zip10 and Zip12. A zinc signal was observed in the murine T-cell line EL-4 6.1 after 1 h of stimulation with IL-1β, measured by specific zinc sensors FluoZin-3 and ZinPyr-1. This signal is required for the phosphorylation of MAPK p38 and NF-κB subunit p65, which triggers the transcription of IL-2 and strongly increases its production. These results indicate that short-term zinc supplementation to zinc-deficient T-cells leads to a fast rise in zinc levels which subsequently enhance cytokine production. In conclusion, low and excessive zinc levels might be equally problematic for zinc-deficient subjects, and stabilized zinc levels seem to be essential to avoid negative concentration-dependent zinc effects on T-cell activation.

Mechanism of HIV reverse transcriptase inhibition by zinc: formation of a highly stable enzyme-(primer-template) complex with profoundly diminished catalytic activity

Several physiologically relevant cations including Ca(2+), Mn(2+), and Zn(2+) have been shown to inhibit HIV reverse transcriptase (RT), presumably by competitively displacing one or more Mg(2+) ions bound to RT. We analyzed the effects of Zn(2+) on reverse transcription and compared them to Ca(2+) and Mn(2+). Using nucleotide extension efficiency as a readout, Zn(2+) showed significant inhibition of reactions with 2 mM Mg(2+), even when present at only ∼5 μM. Mn(2+) and Ca(2+) were also inhibitory but at higher concentrations. Both Mn(2+) and Zn(2+) (but not Ca(2+)) supported RT incorporation in the absence of Mg(2+) with Mn(2+) being much more efficient. The maximum extension rates with Zn(2+), Mn(2+), and Mg(2+) were ∼0.1, 1, and 3.5 nucleotides per second, respectively. Zinc supported optimal RNase H activity at ∼25 μM, similar to the optimal for nucleotide addition in the presence of low dNTP concentrations. Surprisingly, processivity (average number of nucleotides incorporated in a single binding event with enzyme) during reverse transcription was comparable with Zn(2+) and Mg(2+), and single RT molecules were able to continue extension in the presence of Zn(2+) for several hours on the same template. Consistent with this result, the half-life for RT-Zn(2+)-(primer-template) complexes was 220 ± 60 min and only 1.7 ± 1 min with Mg(2+), indicating ∼130-fold more stable binding with Zn(2+). Essentially, the presence of Zn(2+) promotes the formation of a highly stable slowly progressing RT-(primer-template) complex.