Visualization of labile zinc and its role in apoptosis of primary airway epithelial cells and cell lines

Zinc Deficiency and Zinc Supplementation in Allergic Diseases

In recent decades, it has become clear that allergic diseases are on the rise in both Western and developing countries. The exact reason for the increase in prevalence has not been conclusively clarified yet. Multidimensional approaches are suspected in which diet and nutrition seem to play a particularly important role. Allergic diseases are characterized by a hyper-reactive immune system to usually harmless allergens, leading to chronic inflammatory diseases comprising respiratory diseases like asthma and allergic rhinitis (AR), allergic skin diseases like atopic dermatitis (AD), and food allergies. There is evidence that diet can have a positive or negative influence on both the development and severity of allergic diseases. In particular, the intake of the essential trace element zinc plays a very important role in modulating the immune response, which was first demonstrated around 60 years ago. The most prevalent type I allergies are mainly based on altered immunoglobulin (Ig)E and T helper (Th)2 cytokine production, leading to type 2 inflammation. This immune status can also be observed during zinc deficiency and can be positively influenced by zinc supplementation. The underlying immunological mechanisms are very complex and multidimensional. Since zinc supplements vary in dose and bioavailability, and clinical trials often differ in design and structure, different results can be observed. Therefore, different results are not surprising. However, the current literature suggests a link between zinc deficiency and the development of allergies, and shows positive effects of zinc supplementation on modulating the immune system and reducing allergic symptoms, which are discussed in more detail in this review.

Zinc Protects against Swine Barn Dust-Induced Cilia Slowing

Agricultural workers exposed to organic dust from swine concentrated animal feeding operations (CAFOs) have increased chances of contracting chronic lung disease. Mucociliary clearance represents a first line of defense against inhaled dusts, but organic dust extracts (ODEs) from swine barns cause cilia slowing, leading to decreased bacterial clearance and increased lung inflammation. Because nutritional zinc deficiency is associated with chronic lung disease, we examined the role of zinc supplementation in ODE-mediated cilia slowing. Ciliated mouse tracheal epithelial cells were pretreated with 0-10 µg/mL ZinProTM for 1 h, followed by treatment with 5% ODE for 24 h. Cilia beat frequency (CBF) and protein kinase C epsilon (PKCε) activity were assayed. ODE treatment resulted in cilia slowing after 24 h, which was reversed with 0.5 and 1.0 µg/mL ZinPro pre-treatment. No zinc protection was observed at 50 ng/mL, and ciliated cells detached at high concentrations (100 µg/mL). ZinPro alone produced no changes in the baseline CBF and showed no toxicity to the cells at concentrations of up to 10 µg/mL. Pre-treatment with ZinPro inhibited ODE-stimulated PKCε activation in a dose-dependent manner. Based on ZinPro's superior cell permeability compared to zinc salts, it may be therapeutically more effective at reversing ODE-mediated cilia slowing through a PKCε pathway. These data demonstrate that zinc supplementation may support the mucociliary transport apparatus in the protection of CAFO workers against dust-mediated chronic lung disease.

The Role of Zinc in Developed Countries in Pediatric Patients: A 360-Degree View

Zinc is an important trace element for growth and health at pediatric ages. Zinc is fundamental in inflammatory pathways, oxidative balance, and immune function. Zinc exhibits anti-inflammatory properties by modulating Nuclear Factor-kappa (NF-κB) activity and reducing histamine release from basophils, leukocytes, and mast cells. Furthermore, its antioxidant activity protects against oxidative damage and chronic diseases. Finally, zinc improves the ability to trigger effective immune responses against pathogens by contributing to the maturation of lymphocytes, the production of cytokines, and the regulation of apoptosis. Given these properties, zinc can be considered an adjunctive therapy in treating and preventing respiratory, nephrological, and gastrointestinal diseases, both acute and chronic. This review aims to deepen the role and metabolism of zinc, focusing on the role of supplementation in developed countries in pediatric diseases.

Cooperation of quorum sensing and central carbon metabolism in the pathogenesis of Gram-positive bacteria

Quorum sensing (QS), an integral component of bacterial communication, is essential in coordinating the collective response of diverse bacterial pathogens. Central carbon metabolism (CCM), serving as the primary metabolic hub for substances such as sugars, lipids, and amino acids, plays a crucial role in the life cycle of bacteria. Pathogenic bacteria often utilize CCM to regulate population metabolism and enhance the synthesis of specific cellular structures, thereby facilitating in adaptation to the host microecological environment and expediting infection. Research has demonstrated that QS can both directly or indirectly affect the CCM of numerous pathogenic bacteria, thus altering their virulence and pathogenicity. This article reviews the interplay between QS and CCM in Gram-positive pathogenic bacteria, details the molecular mechanisms by which QS modulates CCM, and lays the groundwork for investigating bacterial pathogenicity and developing innovative infection treatment drugs.

Acrolein increases the concentration of intracellular Zn2⁺ by producing mitochondrial reactive oxygen species in A549 cells

Smoking or occupational exposure leads to low concentrations of acrolein on the surface of the airways. Acrolein is involved in the pathophysiological processes of various respiratory diseases. Reports showed that acrolein induced an increase in mitochondrial reactive oxygen species (mROS). Furthermore, exogenous H₂O₂ was found to increase intracellular Zn2⁺ concentration ([Zn2⁺]ᵢ). However, the specific impact of acrolein on changes in intracellular Zn2⁺ levels has not been fully investigated. Therefore, this study aimed to investigate the effects of acrolein on mROS and [Zn2⁺]ᵢ in A549 cells. We used Mito Tracker Red CM-H2Xros (MitoROS) and Fluozin-3 fluorescent probes to observe changes in mROS and intracellular Zn2⁺. The results revealed that acrolein increased [Zn2⁺]ᵢ in a time- and dose-dependent manner. Additionally, the production of mROS was observed in response to acrolein treatment. Subsequent experiments showed that the intracellular Zn2⁺ chelator TPEN could inhibit the acrolein-induced elevation of [Zn2⁺]ᵢ but did not affect the acrolein-induced mROS production. Conversely, the acrolein-induced elevation of mROS and [Zn2⁺]ᵢ were significantly decreased by the inhibitors of ROS formation (NaHSO₃, NAC). Furthermore, external oxygen free radicals increased both [Zn2⁺]ᵢ levels and mROS production. These results demonstrated that acrolein-induced elevation of [Zn2⁺]ᵢ in A549 cells was mediated by mROS generation, rather than through a pathway where [Zn2⁺]ᵢ elevation leads to mROS production.

Aberrance of Zinc Metalloenzymes-Induced Human Diseases and Its Potential Mechanisms

Zinc, an essential micronutrient in the human body, is a component in over 300 enzymes and participates in regulating enzymatic activity. Zinc metalloenzymes play a crucial role in physiological processes including antioxidant, anti-inflammatory, and immune responses, as well as apoptosis. Aberrant enzyme activity can lead to various human diseases. In this review, we summarize zinc homeostasis, the roles of zinc in zinc metalloenzymes, the physiological processes of zinc metalloenzymes, and aberrant zinc metalloenzymes in human diseases. In addition, potential mechanisms of action are also discussed. This comprehensive understanding of the mechanisms of action of the regulatory functions of zinc in enzyme activity could inform novel zinc-micronutrient-supply strategies for the treatment of diseases.

A follow-up study of mucociliary clearance and trace element and mineral status in children with chronic rhinosinusitis before and three months after endoscopic sinus surgery

BACKGROUND

The existing data demonstrate the potential role of trace elements in nasal mucociliary clearance, although the association between trace element and mineral status and ciliary function in children with chronic rhinosinusitis is insufficiently studied. Therefore, the objective of the present study is evaluation of trace element and mineral status and mucociliary function in pediatric CRS patients before and after functional endoscopic sinus surgery.

METHODS

The present study involved 30 children with chronic rhinosinusitis without nasal polyps. During this follow-up the patients were examined preoperatively (point 0), underwent functional endoscopic sinus surgery, and were repeatedly examined at three months postoperatively (point 1). At both points the patients were subjected to quality-of-life assessment using SNOT-20 questionnaire; endoscopic and computer tomography examination of the nasal sinuses; evaluation of ciliary function and mucosal cytology using high-speed videomicroscopy; assessment of blood count and inflammatory markers; as well as analysis of trace element and mineral levels in whole blood, serum, and hair using inductively-coupled plasma mass-spectrometry.

RESULTS

The obtained data demonstrate that endoscopic sinus surgery significantly improved sinonasal pathology in children with chronic rhinosinusitis, as evidenced by significantly reduced Lund-Mackay, Lund-Kennedy, and SNOT-20 scores. At the same time, no significant improvement of ciliary functions or mucosal cytology was observed postoperatively. Trace element status assessment demonstrated that postoperative serum Zn, whole blood Mg and Cu were significantly lower as compared to preoperative values. In contrast, serum Mn and Cr, as well as whole blood Cr and hair Se were characterized by a significant increase at three months postoperatively. Multiple linear regression analysis demonstrated that serum Zn is significantly associated with the number of ciliated cells and cell viability, whereas serum Mn and whole blood Cu concentrations are inversely associated with cell viability and ciliary length, respectively. Hair Se was found to be associated with the number of neutrophils in the mucosa biopsy.

CONCLUSION

Redistribution of trace elements and minerals may at least partially mediate prolonged recovery of mucosal ciliary function in children with chronic rhinosinusitis in three months after functional sinus surgery, although the particular mechanisms of these alterations in trace element levels are to be discovered.

Endogenous zinc nanoparticles in the rat olfactory epithelium are functionally significant

The role of zinc in neurobiology is rapidly expanding. Zinc is especially essential in olfactory neurobiology. Naturally occurring zinc nanoparticles were detected in olfactory and nasal respiratory epithelia and cilia in animals. The addition of these nanoparticles to a mixture of odorants, including ethyl butyrate, eugenol, and carvone, considerably increased the electrical responses of the olfactory sensory receptors. Studies of these nanoparticles by ransmission electron microscopy (TEM) and selected area electron diffraction revealed metal elemental crystalline zinc nanoparticles 2–4 nm in diameter. These particles did not contain oxidized zinc. The enhancement of the odorant responses induced by the endogenous zinc nanoparticles appears to be similar to the amplification produced by engineered zinc nanoparticles. Zinc nanoparticles produce no odor response but increase odor response if mixed with an odorant. These effects are dose-dependent and reversible. Some other metal nanoparticles, such as copper, silver, gold, and platinum, do not have the effects observed in the case of zinc nanoparticles. The olfactory enhancement was observed in young and mature mouse olfactory epithelium cultures, in the dissected olfactory epithelium of rodents, and in live conscious dogs. The physiological significance of the detected endogenous metal nanoparticles in an animal tissue has been demonstrated for the first time. Overall, our results may advance the understanding of the initial events in olfaction.

Imbalanced mitochondrial function provokes heterotaxy via aberrant ciliogenesis

About 1% of all newborns are affected by congenital heart disease (CHD). Recent findings identify aberrantly functioning cilia as a possible source for CHD. Faulty cilia also prevent the development of proper left-right asymmetry and cause heterotaxy, the incorrect placement of visceral organs. Intriguingly, signaling cascades such as mTor that influence mitochondrial biogenesis also affect ciliogenesis, and can cause heterotaxy-like phenotypes in zebrafish. Here, we identify levels of mitochondrial function as a determinant for ciliogenesis and a cause for heterotaxy. We detected reduced mitochondrial DNA content in biopsies of heterotaxy patients. Manipulation of mitochondrial function revealed a reciprocal influence on ciliogenesis and affected cilia-dependent processes in zebrafish, human fibroblasts and Tetrahymena thermophila. Exome analysis of heterotaxy patients revealed an increased burden of rare damaging variants in mitochondria-associated genes as compared to 1000 Genome controls. Knockdown of such candidate genes caused cilia elongation and ciliopathy-like phenotypes in zebrafish, which could not be rescued by RNA encoding damaging rare variants identified in heterotaxy patients. Our findings suggest that ciliogenesis is coupled to the abundance and function of mitochondria. Our data further reveal disturbed mitochondrial function as an underlying cause for heterotaxy-linked CHD and provide a mechanism for unexplained phenotypes of mitochondrial disease.

Role of Zinc Signaling in the Regulation of Mast Cell-, Basophil-, and T Cell-Mediated Allergic Responses

Zinc is essential for maintaining normal structure and physiological function of cells. Its deficiency causes growth retardation, immunodeficiency, and neuronal degeneration. Zinc homeostasis is tightly regulated by zinc transporters and metallothioneins that control zinc concentration and its distribution in individual cells and contributes to zinc signaling. The intracellular zinc signaling regulates immune reactions. Although many molecules involved in these processes have zinc-binding motifs, the molecular mechanisms and the role of zinc in immune responses have not been elucidated. We and others have demonstrated that zinc signaling plays diverse and specific roles in vivo and in vitro in studies using knockout mice lacking zinc transporter function and metallothionein function. In this review, we discuss the impact of zinc signaling focusing particularly on mast cell-, basophil-, and T cell-mediated inflammatory and allergic responses. We also describe zinc signaling dysregulation as a leading health problem in inflammatory disease and allergy.

tert-Butylhydroquinone mobilizes intracellular-bound zinc to stabilize Nrf2 through inhibiting phosphatase activity

The nuclear factor erythroid 2-related factor 2 (Nrf2) is required to combat increases in oxidative stress. The chemical compound tert-butylhydroquinone (tBHQ) can downregulate Kelch-like ECH-associated protein 1 (Keap1), a repressor of Nrf2, thus maintaining the stability of Nrf2. tBHQ can also increase intracellular “free” zinc in human bronchial epithelial (16HBE) cells. We aim to investigate whether the intracellular free zinc change plays a role in Nrf2 activation. tBHQ exposure dose-dependently increases intracellular free zinc concentrations within 30 min in 16HBE cells by mobilizing intracellular zinc pools. Active Nrf2 and the antioxidant enzyme heme oxygenase-1 (HO-1) increase at 3 h after tBHQ treatment. Chelating intracellular free zinc with tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN) during tBHQ exposure partially abrogates the tBHQ-induced activation of Nrf2 and HO-1 expression, while Keap1 is further decreased. These results indicate that tBHQ-induced stability of Nrf2 is associated with the intracellular free zinc level. Because the activated Nrf2 is phosphorylated, the serine/threonine protein phosphatase activity, which is known to be inhibited by zinc, is assayed. The results showed that tBHQ treatment can suppress cellular protein phosphatase-2A (PP2A) and protein phosphatase-2C (PP2C) activity, which can be abrogated by adding TPEN. This finding is verified in a cell-free protein extract experiment by supplying zinc or by chelating zinc with TPEN. These results provide a novel mechanistic insight into Nrf2 activation in antioxidant enzyme induction involving zinc signaling. The increase of intracellular free zinc may be one mechanism for Nrf2 activation. The inhibition of PP2A and PP2C activity may be involved in Nrf2 phosphorylation modulation.

Zinc disrupts central carbon metabolism and capsule biosynthesis in Streptococcus pyogenes

Neutrophils release free zinc to eliminate the phagocytosed bacterial pathogen Streptococcus pyogenes (Group A Streptococcus; GAS). In this study, we investigated the mechanisms underpinning zinc toxicity towards this human pathogen, responsible for diseases ranging from pharyngitis and impetigo, to severe invasive infections. Using the globally-disseminated M1T1 GAS strain, we demonstrate that zinc stress impairs glucose metabolism through the inhibition of the glycolytic enzymes phosphofructokinase and glyceraldehyde-3-phosphate dehydrogenase. In the presence of zinc, a metabolic shift to the tagatose-6-phosphate pathway allows conversion of D-galactose to dihydroxyacetone phosphate and glyceraldehyde phosphate, partially bypassing impaired glycolytic enzymes to generate pyruvate. Additionally, zinc inhibition of phosphoglucomutase results in decreased capsule biosynthesis. These data indicate that zinc exerts it toxicity via mechanisms that inhibit both GAS central carbon metabolism and virulence pathways.

Influence of intracellular zinc on cultures of rat cardiac neural crest cells

BACKGROUND

Developmental zinc (Zn) deficiency increases the incidence of heart anomalies in rat fetuses, in regions and structures derived from the outflow tract. Given that the development of the outflow tract requires the presence of cardiac neural crest cells (cNCC), we speculated that Zn deficiency selectively kills cNCC and could lead to heart malformations.

METHODS

Cardiac NCC were isolated from E10.5 rat embryos and cultured in control media (CTRL), media containing 3 μM of the cell permeable metal chelator N, N, N', N'-tetrakis (2-pyridylmethyl) ethylene diamine (TPEN), or in TPEN-treated media supplemented with 3 μM Zn (TPEN + Zn). Cardiac NCC were collected after 6, 8, and 24 h of treatment to assess cell viability, proliferation, and apoptosis.

RESULTS

The addition of TPEN to the culture media reduced free intracellular Zn pools and cell viability as assessed by low ATP production, compared to cells grown in control or Zn-supplemented media. There was an accumulation of reactive oxygen species, a release of mitochondrial cytochrome c into the cytoplasm, and an increased cellular expression of active caspase-3 in TPEN-treated cNCC compared to cNCC cultured in CTRL or TPEN + Zn media.

CONCLUSION

Zn deficiency can result in oxidative stress in cNCC, and subsequent decreases in their population and metabolic activity. These data support the concept that Zn deficiency associated developmental heart defects may arise in part as a consequence of altered cNCC metabolism.

Zinc as a micronutrient and its preventive role of oxidative damage in cells

Zinc deficiency leads to increased ROS production, thereby causing lipid peroxidation. Subsequently, signallingviathe NF-κB pathway is increased, resulting in the expression of pro-inflammatory cytokines which in turn cause chronic inflammatory diseases.

Expression of executioner procaspases and their activation by a procaspase-activating compound in chronic lymphocytic leukemia cells

Intrinsic and extrinsic apoptotic pathways converge to activate common downstream executioner caspases (caspase-3, -6, and -7), resulting in cell death. In chronic lymphocytic leukemia (CLL), neoplastic B cells evade apoptosis owing to the overexpression of survival proteins. We hypothesized that direct activation of procaspases could bypass the apoptosis resistance induced by the upstream prosurvival proteins. The procaspase-activating compounds (PAC-1), including B-PAC-1 (L14R8), convert inactive executioner procaspases to their active cleaved forms by chelation of labile zinc ions. Both at transcript and protein levels, primary CLL cells express high levels of latent procaspases (3, -7, and -9). B-PAC-1 treatment induced CLL lymphocyte death which was higher than that in normal peripheral blood mononuclear cells or B cells, and was independent of prognostic markers and microenvironmental factors. Mechanistically, B-PAC-1 treatment activated executioner procaspases and not other Zn-dependent enzymes. Exogenous zinc completely, and pancaspase inhibitors partially, reversed B-PAC-1-induced apoptosis, elucidating the zinc-mediated mechanism of action. The cell demise relied on the presence of caspase-3/7 but not caspase-8 or Bax/Bak proteins. B-PAC-1 in combination with an inhibitor of apoptosis protein antagonist (Smac066) synergistically induced apoptosis in CLL samples. Our investigations demonstrated that direct activation of executioner procaspases via B-PAC-1 treatment bypasses apoptosis resistance and is a novel approach for CLL therapeutics.

Red Mold Rice against Hepatic Inflammatory Damage in Zn-deficient Rats

The protective effect of red mold rice (RMR) against liver injury in rats fed with a Zn-deficient diet for 12 weeks was investigated in this study. Rats were orally administered RMR (151 mg/kg body weight or 755 mg/kg body weight; 1 × dose or 5 × dose, respectively) with or without Zn once a day for 4 consecutive weeks. The severity of liver damage was evaluated by measuring the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in Zn-deficient rats. RMR significantly inhibited the elevation of serum ALT levels by Zn-deficient induction. Hepatic antioxidase activity was also significantly increased in the RMR + Zn group (RZ), thereby suppressing the productions of reactive oxygen species (ROS) and proinflammatory cytokines in the liver of Zn-deficient rats. These findings suggested that RMR exerted hepatoprotective effects against Zn deficiency-induced liver inflammation.

Alcohol-Mediated Zinc Deficiency Within the Alveolar Space: A Potential Fundamental Mechanism Underlying Oxidative Stress and Cellular Dysfunction in the Alcoholic Lung

Zinc is one of the most abundant trace elements in the human body, and its presence is essential for numerous biological processes including enzymatic activity, immune function, protein synthesis, and wound healing. Given these important roles, zinc has a sophisticated transport system to regulate its homeostasis. Determination of zinc status, however, is difficult to determine as serum levels are closely maintained and are not an accurate reflection of total body zinc or metabolism at the organ level. Fortunately, the discovery of zinc-specific fluorescent dyes has allowed for a much better assessment of zinc status in the respiratory system and has revealed that alcoholism perturbs this highly developed zinc metabolism such that its distribution to the lung and alveolar space is significantly decreased. As a result, this pulmonary zinc deficiency impairs function in the alveolar macrophage, which is the primary host immune cell within the lower airway. Experimental models have demonstrated that correction of this zinc deficiency restores immune function to the alveolar macrophage as best reflected by improved bacterial clearance in response to infection. While the precise mechanisms underlying alcohol-induced zinc deficiency are still under investigation, there is experimental evidence of several important connections with granulocyte–macrophage colony-stimulating factor and oxidative stress, suggesting that alteration of zinc homeostasis may be a fundamental mechanism underlying the cellular pathology seen in the alcohol lung phenotype. This chapter reviews zinc homeostasis and offers insight into our understanding of zinc deficiency in the setting of alcoholism and the potential of zinc as a therapeutic modality in the vulnerable alcoholic host.

Zinc-rich inhibitor of apoptosis proteins (IAPs) as regulatory factors in the epithelium of normal and inflamed airways

Integrity of the airway epithelium (AE) is important in the context of inhaled allergens and noxious substances, particularly during asthma-related airway inflammation where there is increased vulnerability of the AE to cell death. Apoptosis involves a number of signaling pathways which activate procaspases leading to cleavage of critical substrates. Understanding the factors which regulate AE caspases is important for development of strategies to minimize AE damage and airway inflammation, and therefore to better control asthma. One such factor is the essential dietary metal zinc. Zinc deficiency results in enhanced AE apoptosis, and worsened airway inflammation. This has implications for asthma, where abnormalities in zinc homeostasis have been observed. Zinc is thought to suppress the steps involved in caspase-3 activation. One target of zinc is the family of inhibitor of apoptosis proteins (IAPs) which are endogenous regulators of caspases. More studies are needed to identify the roles of IAPs in regulating apoptosis in normal and inflamed airways and to study their interaction with labile zinc ions. This new information will provide a framework for future clinical studies aimed at monitoring and management of airway zinc levels as well as minimising airway damage and inflammation in asthma.

Functional role of intracellular labile zinc in pulmonary endothelium

After iron, zinc is the most abundant essential trace metal. Intracellular zinc ([Zn]_i) is maintained across a wide range of cells and species in a tight quota (100 to 500 μM) by a dynamic process of transport, intracellular vesicular storage, and binding to a large number of proteins (estimated at 3-10% of human proteome). As such, zinc is an integral component of numerous metalloenzymes, structural proteins, and transcription factors. It is generally assumed that a vanishingly small component of [Zn]_i, referred to as free or labile zinc, and operationally defined as the pool sensitive to chelation (by agents such as N, N, N’, N’-tetrakis [2-pyridylmethyl] ethylenediamine [TPEN]) and capable of detection by a variety of chemical and genetic sensors, participates in signal transduction pathways. Zinc deficiencies, per se, can arise from acquired (malnutrition, alcoholism) or genetic (mutations in molecules affecting zinc homeostasis, the informative and first example being acrodermatitis enteropathica) factors or as a component of various diseases (e.g., sickle cell disease, cystic fibrosis, sepsis). Hypozincemia has profound effects on developing humans, and all facets of physiological function (neuronal, endocrine, immunological) are affected, although considerably less is known regarding cardiovascular pathophysiology. In this review, we provide an update on current knowledge of molecular and cellular aspects of zinc homeostasis and then focus on implications of zinc signaling in pulmonary endothelium as it relates to programmed cell death, altered contractility, and septic and aseptic injury to this segment of the lung.

A critical role for increased labile zinc in reducing sensitivity of cultured sheep pulmonary artery endothelial cells to LPS-induced apoptosis

We previously noted an important signaling role for decreased labile intracellular zinc ([ Zn ] (i)) in LPS-induced apoptosis in cultured sheep pulmonary artery endothelial cells (SPAEC) (Tang ZL, Wasserloos KJ, Liu X, Stitt MS, Reynolds IJ, Pitt BR, St Croix CM. Mol Cell Biochem 234-235: 211-217, 2002; Thambiayya K, Wasserloos KJ, Huang Z, Kagan VE, St Croix CM, Pitt BR. Am J Physiol Lung Cell Mol Physiol 300: L624-632, 2011). In the present study, we used small interfering RNA (siRNA) to important contributors of zinc homeostasis [ SLC39A14 or Zrt/Irt-like protein 14 (ZIP14), a zinc importer; metallothionein (MT), a zinc binding protein ] to define molecular pathways by which extracellular zinc or nitric oxide (NO) increase labile [ Zn ] (i) [ e.g., zinc-sensitive fluorophore (FluoZin-3) detectable and/or chelatable by N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine ] and reduce the sensitivity of SPAEC to LPS. Addition of 10 μM zinc to serum-free medium of SPAEC increased [ Zn ] (i) and abolished LPS-induced apoptosis (e.g., increased annexin V binding). The increase in [ Zn ] (i) and the protective effect of extracellular zinc were sensitive to reduction in ZIP14 expression (by siRNA), but not affected by collectively knocking down major isoforms of sheep MT (sMT-Ia, -Ib, -Ic, and -II). Pretreatment of wild-type SPAEC with 250 μM of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) increased labile zinc in a relatively similar fashion to addition of extracellular zinc and reduced sensitivity of SPAEC to LPS-induced apoptosis (e.g., caspase-3/7 activation) in a N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine-sensitive fashion. The antiapoptotic effects of SNAP were insensitive to siRNA knockdown of ZIP14, but were abolished (along with SNAP-induced increase in [ Zn ] (i)) when SPAEC were pretreated with siRNA to sheep MT. Zinc was able to directly inhibit recombinant caspase-3 activity in an in vitro assay. Collectively, these data show that increases in labile [ Zn ] (i) are an important component of ZIP14- or NO-mediated resistance to LPS-induced apoptosis. Cytoprotection via ZIP14 appeared to be secondary to transcellular movement of extracellular zinc, whereas NO-mediated protection was secondary to S-nitrosation of MT and redistribution of [ Zn ] (i).

Erythrocyte zinc levels in children with bronchial asthma

Zinc deficiency may be suspected to play a role in the pathogenesis, control, and severity of asthma because of its antioxidant, antiapoptotic, and anti-inflammatory effects. We aimed to investigate whether there was any relationship between erythrocyte zinc levels and childhood asthma. The erythrocyte zinc levels of 67 asthmatic and 45 healthy children were analyzed in this case-control study. The mean concentrations of erythrocyte zinc were 1215.8 ± 145.1 µg/dl in asthma patients and 1206.9 ± 119.5 µg/dl in controls with no significant difference (P = 0.472). The erythrocyte zinc level was below 1,000 µg/dl in 6 asthmatic patients (8.9%) and 2 control group patients (4.4%). There was no relationship between erythrocyte zinc levels and duration of follow-up, severity, and control of the asthma (P > 0.05). On the other hand, patients hospitalized for an asthma attack had significantly lower erythrocyte zinc levels compared with nonhospitalized patients and the control group (P = 0.000 and P = 0.004 respectively). This study's findings indicate that asthmatic children are not a risk group for zinc deficiency. We emphasize that checking zinc levels in children who are hospitalized for an asthma attack may be useful.

Apical localization of zinc transporter ZnT4 in human airway epithelial cells and its loss in a murine model of allergic airway inflammation

The apical cytoplasm of airway epithelium (AE) contains abundant labile zinc (Zn) ions that are involved in the protection of AE from oxidants and inhaled noxious substances. A major question is how dietary Zn traffics to this compartment. In rat airways, in vivo selenite autometallographic (Se-AMG)-electron microscopy revealed labile Zn-selenium nanocrystals in structures resembling secretory vesicles in the apical cytoplasm. This observation was consistent with the starry-sky Zinquin fluorescence staining of labile Zn ions confined to the same region. The vesicular Zn transporter ZnT4 was likewise prominent in both the apical and basal parts of the epithelium both in rodent and human AE, although the apical pools were more obvious. Expression of ZnT4 mRNA was unaffected by changes in the extracellular Zn concentration. However, levels increased 3-fold during growth of cells in air liquid interface cultures and decreased sharply in the presence of retinoic acid. When comparing nasal versus bronchial human AE cells, there were significant positive correlations between levels of ZnT4 from the same subject, suggesting that nasal brushings may allow monitoring of airway Zn transporter expression. Finally, there were marked losses of both basally-located ZnT4 protein and labile Zn in the bronchial epithelium of mice with allergic airway inflammation. This study is the first to describe co-localization of zinc vesicles with the specific zinc transporter ZnT4 in airway epithelium and loss of ZnT4 protein in inflamed airways. Direct evidence that ZnT4 regulates Zn levels in the epithelium still needs to be provided. We speculate that ZnT4 is an important regulator of zinc ion accumulation in secretory apical vesicles and that the loss of labile Zn and ZnT4 in airway inflammation contributes to AE vulnerability in diseases such as asthma.

Alterations of the extracellular matrix of lung during zinc deficiency

Suboptimal intake of Zn is one of the most common nutritional problems worldwide. Previously, we have shown that Zn deficiency (ZD) produces oxidative and nitrosative stress in the lung of rats. We analyse the effect of moderate ZD on the expression of several intermediate filaments of the cytoskeleton, as well as the effect of restoring Zn during the refeeding period. Adult male rats were divided into three groups: Zn-adequate control (CO) group; ZD group; Zn-refeeding group. CerbB-2 and proliferating cell nuclear antigen (PCNA) expression was increased in the ZD group while the other parameters did not change. During the refeeding time, CerbB-2, cytokeratins, vimentin and PCNA immunostaining was higher than that in the CO group. The present findings indicate that the overexpression of some markers could lead to the fibrotic process in the lung. Perhaps ZD implications must be taken into account in health interventions because an inflammation environment is associated with ZD in the lung.

Reactions of the fluorescent sensor, Zinquin, with the zinc-proteome: adduct formation and ligand substitution

Zinquin (ZQ) is a commonly used sensor for cellular Zn(2+) status. It has been assumed that it measures accessible Zn(2+) concentrations in the nanomolar range. Instead, this report shows a consistent pattern across seven mammalian cell and tissue types that ZQ reacts with micromolar concentrations of Zn(2+) bound as Zn-proteins. The predominant class of products were ZQ-Zn-protein adducts that were characterized in vivo and in vitro by a fluorescence emission spectrum centered at about 470 nm, by their migration over Sephadex G-75 as protein not low molecular weight species, by the exclusion of reaction with lipid vesicles, and by their large aggregate concentration. In addition, variable, minor formation of Zn(ZQ)(2) with a fluorescence band at about 490 nm was observed in vivo in each case. Because incubation of isolated Zn-proteome with ZQ also generated similar amounts of Zn(ZQ)(2), it was concluded that this species had formed through direct ligand substitution in which ZQ had successfully competed for protein-bound Zn(2+). Parallel studies with the model Zn-proteins, alcohol dehydrogenase (ADH), and alkaline phosphatase (AP) revealed a similar picture of reactivity: ZQ(ACID) (Zinquin acid, (2-methyl-8-p-toluenesulfonamido-6-quinolyloxy)acetate)) able to bind to one Zn(2+) and extract the other in Zn(2)-ADH, whereas it removed one Zn(2+) from Zn(2)-AP and did not bind to the other. Zinquin ethyl ester (ethyl(2-methyl-8-p-toluenesulfonamido-6-quinolyloxy)acetate); ZQ(EE)) bound to both proteins without sequestering Zn(2+) from either one. In contrast to a closely related sensor, 6-methoxy-8-p-toluenesulfonamido-quinoline (TSQ), neither ZQ(ACID) nor ZQ(EE) associated with Zn-carbonic anhydrase. A survey of reactivity of these sensors with partially fractionated Zn-proteome confirmed that ZQ and TSQ bind to distinct, overlapping subsets of the Zn-proteome.

A zinc chelator TPEN attenuates airway hyperresponsiveness and airway inflammation in mice in vivo

BACKGROUND

Zinc is an essential element required for the cell metabolism, including gene transcription, signal transduction, immunity, and apoptosis. The pathophysiological role of zinc in asthma, however, is not entirely clear. Mast cells have been implicated in atopic asthma, and zinc deprivation has been reported to reduce mast cell activation. Here, we investigate the effects of a zinc chelator, N,N,N',N'-tetrakis (2-pyridyl-methyl) ethylenediamine (TPEN), on asthmatic responses in mouse models of ovalbumin (OVA)-induced airway hyperresponsiveness and allergic airway inflammation.

METHODS

Mice were sensitized with OVA with or without the adjuvant aluminum hydroxide (alum) and subjected to OVA exposure with or without treatment of TPEN. Cell profiles and cytokine levels in bronchoalveolar lavage (BAL) fluids, airway responsiveness to inhaled acetylcholine, and goblet cell hyperplasia after allergen exposure were assessed.

RESULTS

In mice sensitized to OVA without alum, TPEN significantly suppressed airway hyperresponsiveness and eosinophilia in BAL fluids. TPEN also attenuated the upregulation of TNFα, IL-13 and IL-4 in BAL fluids and goblet cell hyperplasia after OVA exposure. By contrast, in mice sensitized to OVA with alum, TPEN suppressed eosinophilia in BAL fluids but not airway hyperresponsiveness and goblet cell hyperplasia.

CONCLUSIONS

In pulmonary allergic inflammation induced in mice immunized with antigen without alum, zinc chelator inhibits airway inflammation and hyperresponsiveness. These findings suggest that zinc may be a therapeutic target of allergic asthma.

Sputum zinc concentration and clinical outcome in older asthmatics

BACKGROUND AND OBJECTIVE

Mouse models of asthma show that zinc deficiency is associated with airway inflammation (AI), which is attenuated by zinc supplements. Whether zinc has a similar role in the human airway remains controversial, with studies demonstrating both high and low plasma zinc concentrations [Zn] in asthmatic patients compared with control subjects. This variability may reflect the inability of plasma measurements to accurately assess airway zinc levels. Examination of induced sputum is an established technique for measuring AI and mediators of inflammation. Recent advances allow measurement of the rapidly exchangeable (labile) and total zinc pools in sputum. The aims of this study were to measure labile and total [Zn] in sputum and plasma of subjects with or without asthma, and second to correlate [Zn] with symptoms, asthma severity, lung function (FEV(1)) and airway hyper-responsiveness.

METHODS

A total of 163 subjects (114 with asthma) completed a single visit for sputum induction and a blood test. Labile and total [Zn] were measured by Zinquin fluorescence and atomic absorption spectrophotometry.

RESULTS

The mean (SD) age of subjects with and without asthma was 55 (14) and 57 (14) years, respectively. Baseline FEV(1) was significantly lower in subjects with asthma (94.2 (16)%) than in those without asthma (103 (16.6)%). Sputum total and labile [Zn] were lower in subjects with asthma compared with control subjects, with median (interquartile range) values of 31.8 (117) versus 50 (188.5), P = 0.02 and 0 (48) versus 26 (84.5) µg/L, P = 0.05, respectively. Increased frequency of wheeze, as well as asthma severity and reduced FEV(1), was associated with significantly lower labile sputum [Zn].

CONCLUSIONS

These findings suggest that sputum [Zn] reflect clinical outcomes and underlying AI, suggesting a potential role for zinc as a biomarker in asthma.

Zinc homeostasis and signaling in health and diseases: Zinc signaling

The essential trace element zinc (Zn) is widely required in cellular functions, and abnormal Zn homeostasis causes a variety of health problems that include growth retardation, immunodeficiency, hypogonadism, and neuronal and sensory dysfunctions. Zn homeostasis is regulated through Zn transporters, permeable channels, and metallothioneins. Recent studies highlight Zn's dynamic activity and its role as a signaling mediator. Zn acts as an intracellular signaling molecule, capable of communicating between cells, converting extracellular stimuli to intracellular signals, and controlling intracellular events. We have proposed that intracellular Zn signaling falls into two classes, early and late Zn signaling. This review addresses recent findings regarding Zn signaling and its role in physiological processes and pathogenesis.

Serum zinc in critically ill adult patients with acute respiratory failure

BACKGROUND AND AIMS

Zinc deficiency leads to susceptibility to infections and may affect pulmonary epithelial cell integrity. Low zinc levels have also been associated with a degree of organ failure and decreased survival in critically ill children. Accordingly, the purpose of the study was to assess serum zinc in adult patients with acute respiratory failure, its association with ventilatory support time, intensive care unit (ICU) length of stay (LOS), organ dysfunction and 30-day mortality.

METHODS

We included consecutive patients with acute respiratory failure during an eight-week prospective, observational multicentre study (the FINNALI-study). Acute respiratory failure was defined as a need for either non-invasive or invasive positive pressure ventilation for >6 h regardless of the underlying cause or risk factors. After informed consent, a sample for zinc measurement was drawn at 6 h after the start of treatment and analysed from 551 of these patients.

RESULTS

Low serum zinc was frequent (95.8%) at the onset acute respiratory failure. The median interquartile range [IQR] was 4.7 [3.0-6.9] μmol/l. The median [IQR] serum zinc levels in non-infectious, sepsis and septic shock patients were 5.0 [3.1-7.1], 5.1 [3.5-7.3] and 3.8 [2.6-5.9] μmol/l, respectively, P<0.01. Baseline zinc levels were not associated with ventilatory support time (P=0.98) or ICU LOS (P=0.053). The area under curve in receiver operating characteristics analysis for serum zinc regarding 30-day mortality was 0.55 (95% CI 0.49-0.60).

CONCLUSIONS

Serum zinc on initiation of ventilation had no predictive value for 30-day mortality, ventilatory support time or intensive care unit LOS.

Measuring steady-state and dynamic endoplasmic reticulum and Golgi Zn2+ with genetically encoded sensors

Zn(2+) plays essential roles in biology, and cells have adopted exquisite mechanisms for regulating steady-state Zn(2+) levels. Although much is known about total Zn(2+) in cells, very little is known about its subcellular distribution. Yet defining the location of Zn(2+) and how it changes with signaling events is essential for elucidating how cells regulate this essential ion. Here we create fluorescent sensors genetically targeted to the endoplasmic reticulum (ER) and Golgi to monitor steady-state Zn(2+) levels as well as flux of Zn(2+) into and out of these organelles. These studies reveal that ER and Golgi contain a concentration of free Zn(2+) that is 100 times lower than the cytosol. Both organelles take up Zn(2+) when cytosolic levels are elevated, suggesting that the ER and Golgi can sequester elevated cytosolic Zn(2+) and thus have the potential to play a role in influencing Zn(2+) toxicity. ER Zn(2+) homeostasis is perturbed by small molecule antagonists of Ca(2+) homeostasis and ER Zn(2+) is released upon elevation of cytosolic Ca(2+) pointing to potential exchange of these two ions across the ER. This study provides direct evidence that Ca(2+) signaling can influence Zn(2+) homeostasis and vice versa, that Zn(2+) dynamics may modulate Ca(2+) signaling.

LPS-induced decrease in intracellular labile zinc, [Zn]i, contributes to apoptosis in cultured sheep pulmonary artery endothelial cells

A role in signal transduction for a vanishingly small labile pool of intracellular zinc ([Zn](i)) has been inferred by the sensitivity of various physiological pathways to zinc chelators such as N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and/or associations with changes in nonprotein-bound zinc-sensitive fluorophores. Although we (44) reported that LPS-induced apoptosis in cultured sheep pulmonary artery endothelial cells (SPAEC) was exacerbated by TPEN, 1) we did not detect acute (30 min) changes in [Zn](i), and 2) it is unclear from other reports whether LPS increases or decreases [Zn](i) and whether elevations or decreases in [Zn](i) are associated with cell death and/or apoptosis. In the present study, we used both chemical (FluoZin-3 via live cell epifluorescence microscopy and fluorescence-activated cell sorting) and genetic (luciferase activity of a chimeric reporter encoding zinc-sensitive metal-response element and changes in steady-state mRNA of zinc importer, SLC39A14 or ZIP14) techniques to show that LPS caused a delayed time-dependent (2-4 h) decrease in [Zn](i) in SPAEC. A contributory role of decreases in [Zn](i) in LPS-induced apoptosis (as determined by caspase-3/7 activation, annexin-V binding, and cytochrome c release) in SPAECs was revealed by mimicking the effect of LPS with the zinc chelator, TPEN, and inhibiting LPS- (or TPEN)-induced apoptosis with exogenous zinc. Collectively, these are the first data demonstrating a signaling role for decrease in [Zn](i) in pulmonary endothelial cells and suggest that endogenous levels of labile zinc may affect sensitivity of pulmonary endothelium to the important and complex proapoptotic stimulus of LPS.

Dietary zinc mediates inflammation and protects against wasting and metabolic derangement caused by sustained cigarette smoke exposure in mice

In mouse asthma models, inflammation can be modulated by zinc (Zn). Given that appetite loss, muscle wasting and poor nutrition are features of chronic obstructive pulmonary disease (COPD) and that poor dietary Zn intake is in itself accompanied by growth retardation and appetite loss, we hypothesised that dietary Zn limitation would not only worsen airway inflammation but also exaggerate metabolic effects of cigarette smoke (CS) exposure in mice. Conversely, Zn supplementation would lessen inflammation. Mice were exposed to CS [2× 2RF, 3×/day; 15 min/cigarette] and fed diets containing 2, 20 or 140 mg/kg Zn ad libitum. Airway cells were collected by bronchoalveolar lavage (BAL). Plasma Zn was measured by fluorometric assay. Inflammatory, metabolic and Zn transport markers were measured by real-time RT-PCR. Mice fed low Zn diets had less plasma labile zinc (0-0.18 μM) than mice fed moderate (0.61-0.98 μM) or high (0.77-1.1 μM) Zn diets (SDs 0.1-0.4, n = 8-10). Smoke exposure increased plasma and BAL labile Zn (1.5-2.5 fold, P < 0.001), bronchoalveolar macrophages (2.0 fold, P < 0.0001) and MT-1 (1.5 fold), MIP-2 (2.3 fold) and MMP-12 (3.5 fold) mRNA. Zn supplementation reduced alveolar macrophage numbers by 62 and 52% in sham and smoke-exposed mice, respectively (Zn effect: P = 0.011). Gastrocnemius, soleus and tibialis anterior muscle mass were affected by both smoke and dietary Zn in the order of 3-7%. The 50-60% reduction in alveolar macrophages in Zn-supplemented mice supports our evolving hypothesis that Zn is an important anti-inflammatory mediator of airway inflammation. Restoring airway Zn levels through dietary supplementation may lessen the severity of lung inflammation when Zn intake is low.

Alteration in the expression of inflammatory parameters as a result of oxidative stress produced by moderate zinc deficiency in rat lung

Suboptimal intake of dietary zinc (Zn) is one of the most common nutritional problems worldwide. Previously, the authors have shown that zinc deficiency (ZD) produces oxidative and nitrosative stress in lung of male rats. The goal of this study is to test the effect of moderate ZD on insulin-like growth factor (IGF)-1, IGF-binding protein (IGFBP)-5, NADH oxidase (NOX)-2, tumor necrosis factor alpha (TNFalpha), as well as the effect of restoring zinc during the refeeding period. Adult male rats were divided into 3 groups: Zn-adequate control group, Zn-deficient group, and Zn-refeeding group. eNOS, metallothionein (MT) II, and NOX-2 was increased in ZD group. The authors observed an increased gene transcription of superoxide dismutase (SOD)-2 and gluthathione peroxidase (GPx)-1 in ZD group, as well as in ZD-refeeding group, but catalase (CAT) transcription did not change in the treated groups. Proinflammatory factors, such as TNFalpha and vascular cell adhesion molecular (VCAM)-1 increased in ZD, whereas it decreased in ZD refeeding. However, peroxisome proliferator-activated receptor gamma (PPARgamma) and IGF-1 gene transcription decreased in ZD, whereas IGFBP-5 decreased in the ZD group. These parameters are associated to alterations in the lung histoarchitecture. The zinc supplementation period is brief (only 10 days), but it is enough to inhibit some proinflammatory factors. Perhaps, zinc deficiency implications must be taken into account in health interventions because inflammation and prooxidant environment are associated with ZD in lung.

Cytosolic zinc buffering and muffling: their role in intracellular zinc homeostasis

Our knowledge of the molecular mechanisms of intracellular homeostatic control of zinc ions is now firmly grounded on experimental findings gleaned from the study of zinc proteomes and metallomes, zinc transporters, and insights from the use of computational approaches. A cell's repertoire of zinc homeostatic molecules includes cytosolic zinc-binding proteins, transporters localized to cytoplasmic and organellar membranes, and sensors of cytoplasmic free zinc ions. Under steady state conditions, a primary function of cytosolic zinc-binding proteins is to buffer the relatively large zinc content found in most cells to a cytosolic zinc(ii) ion concentration in the picomolar range. Under non-steady state conditions, zinc-binding proteins and transporters act in concert to modulate transient changes in cytosolic zinc ion concentration in a process that is called zinc muffling. For example, if a cell is challenged by an influx of zinc ions, muffling reactions will dampen the resulting rise in cytosolic zinc ion concentration and eventually restore the cytosolic zinc ion concentration to its original value by shuttling zinc ions into subcellular stores or by removing zinc ions from the cell. In addition, muffling reactions provide a potential means to control changes in cytosolic zinc ion concentrations for purposes of cell signalling in what would otherwise be considered a buffered environment not conducive for signalling. Such intracellular zinc ion signals are known to derive from redox modifications of zinc-thiolate coordination environments, release from subcellular zinc stores, and zinc ion influx via channels. Recently, it has been discovered that metallothionein binds its seven zinc ions with different affinities. This property makes metallothionein particularly well positioned to participate in zinc buffering and muffling reactions. In addition, it is well established that metallothionein is a source of zinc ions under conditions of redox signalling. We suggest that the biological functions of transient changes in cytosolic zinc ion concentrations (presumptive zinc signals) complement those of calcium ions in both spatial and temporal dimensions.

Procaspase-3 activation as an anti-cancer strategy: structure-activity relationship of procaspase-activating compound 1 (PAC-1) and its cellular co-localization with caspase-3

A goal of personalized medicine as applied to oncology is to identify compounds that exploit a defined molecular defect in a cancerous cell. A compound called procaspase-activating compound 1 (PAC-1) was reported that enhances the activity of procaspase-3 in vitro and induces apoptotic death in cancer cells in culture and in mouse xenograft models. Experimental evidence indicates that PAC-1 activates procaspase-3 in vitro through chelation of inhibitory zinc ions. Described herein is the synthesis and biological activity of a family of PAC-1 derivatives where key functional groups have been systematically altered. Analysis of these compounds reveals a strong correlation between the in vitro procaspase-3 activating effect and their ability to induce death in cancer cells in culture. Importantly, we also show that a fluorescently labeled version of PAC-1 co-localizes with sites of caspase-3 activity in cancer cells. The data presented herein further bolster the hypothesis that PAC-1 induces apoptosis in cancer cells through the direct activation of procaspase-3, has implications for the design and discovery of next-generation procaspase-3 activating compounds, and sheds light on the anti-apoptotic role of cellular zinc.

The important role of the apoptotic effects of zinc in the development of cancers

Zinc is a trace element that is essential for the normal function of cells. It is a cofactor for the structure and function of a wide range of cellular proteins including enzymes, transcription factors, and structural proteins. Recent studies have shown that zinc plays a role in the development of various cancers. Unfortunately no established common relationships of zinc with cancer development and progression have been identified. Zinc is known to have systemic effects such as regulation of the immune system as well as direct cellular effects resulting in regulation of gene expression, bioenergetics, metabolic pathways, signal transduction and cell invasion. Zinc is also reported to regulate cell proliferation and growth. In this review presentation we focus on the effects of zinc that are involved in the regulation of apoptosis in malignant cells. We selected the apoptotic effects of zinc because zinc is reported to both induce apoptosis in some cancers and to protect other cancer cells against apoptosis induced by other factors. The effects of zinc in the regulation of apoptosis appear to be cell type specific. More importantly the reported effects of zinc on cancer cells must be viewed from the perspective of the physiological regulation of zinc homeostasis. Thus one must be mindful of the experimental conditions under which zinc effects are investigated relative to the physiological and pathological conditions of cellular zinc distribution and concentrations that can exist in situ.

Effect of resveratrol and zinc on intracellular zinc status in normal human prostate epithelial cells

To evaluate the influence of resveratrol on cellular zinc status, normal human prostate epithelial (NHPrE) cells were treated with resveratrol (0, 0.5, 1, 2.5, 5, and 10 microM) and zinc [0, 4, 16, and 32 microM, representing zinc-deficient (ZD), zinc-normal (ZN), zinc-adequate (ZA), and zinc-supplemented (ZS) conditions, respectively]. A progressive reduction in cell growth was observed in cells treated with increasing amounts of resveratrol (2.5-10 microM). Resveratrol at 5 and 10 microM resulted in a dramatic increase in cellular total zinc concentration, especially in ZS cells. Flow cytometry indicated that 10 microM resveratrol induced arrest of the cell cycle at the G(2)/M phase in association with the observed cell growth inhibition. Data from an in vitro experiment using zinquin as an indicator of intracellular free Zn(II) status demonstrated complex interactions between resveratrol and Zn(II). Fluorescence spectrofluorometry and fluorescence microscopic analyses revealed that intracellular free labile zinc was progressively elevated from nearly twofold in ZS cells with no resveratrol to multifold in ZA and ZS cells with 10 microM resveratrol compared with the corresponding ZN cells. Furthermore, increases in cellular zinc status were associated with elevated levels of reactive oxygen species and senescence, as evidenced by morphological and histochemical changes in cells treated with 2.5 or 10 microM resveratrol, especially in ZA and ZS cells. Taken together, the interaction between resveratrol and zinc in NHPrE cells increases total cellular zinc and intracellular free labile zinc status and, subsequently, reactive oxygen species production and senescence.

PAC-1 activates procaspase-3 in vitro through relief of zinc-mediated inhibition

The direct induction of apoptosis has emerged as a powerful anticancer strategy, and small molecules that either inhibit or activate certain proteins in the apoptotic pathway have great potential as novel chemotherapeutic agents. Central to apoptosis is the activation of the zymogen procaspase-3 to caspase-3. Caspase-3 is the key "executioner" caspase, catalyzing the hydrolysis of a multitude of protein substrates within the cell. Interestingly, procaspase-3 levels are often elevated in cancer cells, suggesting a compound that directly stimulates the activation of procaspase-3 to caspase-3 could selectively induce apoptosis in cancer cells. We recently reported the discovery of a compound, PAC-1, which enhances procaspase-3 activity in vitro and induces apoptotic death in cancer cells in culture and in mouse xenograft models. Described herein is the mechanism by which PAC-1 activates procaspase-3 in vitro. We show that zinc inhibits the enzymatic activity of procaspase-3 and that PAC-1 strongly activates procaspase-3 in buffers that contain zinc. PAC-1 and zinc form a tight complex with one another, with a dissociation constant of approximately 42 nM. The combined data indicate that PAC-1 activates procaspase-3 in vitro by sequestering inhibitory zinc ions, thus allowing procaspase-3 to autoactivate itself to caspase-3. The small-molecule-mediated activation of procaspases has great therapeutic potential and thus this discovery of the in vitro mechanism of action of PAC-1 is critical to the development and optimization of other procaspase-activating compounds.

Zinc deficiency mediates alcohol-induced alveolar epithelial and macrophage dysfunction in rats

Chronic alcohol abuse impairs both alveolar epithelial and macrophage function, and renders individuals susceptible to acute lung injury, pneumonia, and other serious lung diseases. Zinc deficiency, which is known to impact both epithelial and immune cell functions, is also associated with alcohol abuse. In this study, chronic alcohol ingestion (6 wk) in rats altered expression of key zinc transporters and storage proteins in the small intestine and the lung, and decreased zinc levels in the alveolar compartment. Zinc supplementation of alveolar epithelial monolayers derived from alcohol-fed rats in vitro, or of the diets of alcohol-fed rats in vivo, restored alveolar epithelial barrier function, and these improvements were associated with salutary changes in tight junction protein expression and membrane localization. In parallel, dietary zinc supplementation increased intracellular zinc levels, GM-CSF receptor expression, and bacterial phagocytic capacity in the alveolar macrophages of alcohol-fed rats. Together, these studies implicate zinc deficiency as a novel mechanism mediating alcohol-induced alveolar epithelial and macrophage dysfunction. Importantly, these findings argue that dietary supplementation can overcome alcohol-induced zinc deficiency and restore alveolar epithelial and macrophage function, and therefore could be an effective treatment for the susceptible alcoholic lung phenotype.

The human zinc transporter SLC39A8 (Zip8) is critical in zinc-mediated cytoprotection in lung epithelia

Zinc is an essential micronutrient and cytoprotectant involved in the host response to inflammatory stress. We tested whether zinc transporters, the critical regulators that maintain intracellular zinc concentrations, play a role in cell survival, particularly in lung epithelia, during inflammation. Initially, mRNA transcripts were quantitatively measured by RT-PCR for all known human zinc transporters, including 14 importers (SLC39A(1-14)) and 10 exporters (SLC30A(1-10)), in primary human lung epithelia obtained from multiple human donors and BEAS-2B cell cultures under baseline and TNF-alpha-stimulated conditions. While many zinc transporters were constitutively expressed, only SLC39A8 (Zip8) mRNA was strongly induced by TNF-alpha. Endogenous Zip8 protein was not routinely detected under baseline conditions. In sharp contrast, TNF-alpha induced the expression of a glycosylated protein that translocated to the plasma membrane and mitochondria. Increased Zip8 expression resulted in an increase in intracellular zinc content and coincided with cell survival in the presence of TNF-alpha. Inhibition of Zip8 expression using a short interfering RNA probe reduced cellular zinc content and impaired mitochondrial function in response to TNF-alpha, resulting in loss of cell viability. These data are the first to characterize human Zip8 and remarkably demonstrate that upregulation of Zip8 is sufficient to protect lung epithelia against TNF-alpha-induced cytotoxicity. We conclude that Zip8 is unique, relative to other Zip proteins, by functioning as an essential zinc importer at the onset of inflammation, thereby facilitating cytoprotection within the lung.

Pyruvate protects against kainate-induced epileptic brain damage in rats

Although the majority of epileptic seizures can be effectively controlled with antiepileptic drugs and/or surgery, a significant number progress to status epilepticus of sufficient duration to cause permanent brain damage. Combined treatment with antiepileptic drugs and neuroprotective agents, however, may help protect these individuals from permanent brain damage. Since toxicity induced by endogenous zinc contributes to epileptic brain injury, and since pyruvate is effective in reducing zinc-triggered neuronal death in cortical culture as well as ischemic neuronal death in vivo, we examined whether systemic pyruvate administration reduces seizure-induced brain damage. Na pyruvate (500 mg/kg) or osmolarity-matched saline (265 mg/kg NaCl, i.p.) were given to adult SD rats 30 or 150 min after 10 mg/kg kainite injection (i.p.), and there was no significant difference in the time course or severity of seizures between these groups. Zinc accumulation in neuronal cell bodies in the hippocampus, however, was much lower in the pyruvate than in the saline group. There was a close correlation between zinc accumulation and cell death, as assessed by acid-fuchsin and TUNEL staining. Pyruvate treatment markedly reduced neuronal death in the hippocampus, neocortex and thalamus. Pyruvate increased HSP-70 expression in hippocampal neurons. These results suggest that pyruvate, a natural glucose metabolite, may be useful as adjunct treatment in status epilepticus to reduce permanent brain damage.

Cytotoxic effects of intra and extracellular zinc chelation on human breast cancer cells

Zinc is an essential trace element with cofactor functions in a large number of proteins of intermediary metabolism, hormone secretion pathways, immune defence mechanisms, and as a cofactor of transcription factors it is also involved in the control of gene expression. Our study demonstrates that the modulation of intra and extracellular zinc alone is sufficient to induce metabolic changes or even apoptosis in two model human breast cancer cell lines MCF-7 and MDA-MB468. Treatment of breast cancer cells with different concentrations of a cell membrane permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and the membrane impermeable zinc chelator, diethylenetriaminepentacetic acid, (DTPA) resulted in a significant increase of cell death. Features of apoptosis, such as chromatin condensation and nuclear fragmentation accompanied the DTPA and TPEN-induced cell death. A significant increase in the activity of caspase-9 was observed in both cell lines; whereas, caspase-3 activity was only increased in MDA-MB468 cells since caspase-3 is not expressed in MCF-7 cells. Caspase-8 activation was negligible in both cell lines. Addition of Zn(2+) or Cu(2+) prevented DTPA and TPEN-induced cytotoxicity, indicating that both bivalent cations can be replaced functionally to a certain extent in our experimental system. Interestingly, addition of Ca(2+), or Mg(2+) had no effect. The antioxidant N-Acetyl-L-Cysteine inhibited the cytotoxic effect of DTPA and TPEN, indicating that oxidative stress is the likely mediator of Zn-deficiency-related cell death.

Anti-inflammatory effects of zinc and alterations in zinc transporter mRNA in mouse models of allergic inflammation

There is clinical evidence linking asthma with the trace element, zinc (Zn). Using a mouse model of allergic inflammation, we have previously shown that labile Zn decreases in inflamed airway epithelium (Truong-Tran AQ, Ruffin RE, Foster PS, Koskinen AM, Coyle P, Philcox JC, Rofe AM, Zalewski PD. Am J Respir Cell Mol Biol 27: 286-296, 2002). Moreover, mild nutritional Zn deficiency worsens lung function. Recently, a number of proteins belonging to the Solute Carrier Family 39 (ZIP) and Solute Carrier Family 30 (ZnT) have been identified that bind Zn and regulate Zn homeostasis. Mice were sensitized, and subsequently aerochallenged, with ovalbumin to induce acute and chronic airway inflammation. Mice received 0, 54, or 100 microg of Zn intraperitoneally. Tissues were analyzed for Zn content and histopathology. Inflammatory cells were counted in bronchoalveolar lavage fluid. Cytokine and Zn transporter mRNA levels were determined by cDNA gene array and/or real-time PCR. Zn supplementation decreased bronchoalveolar lavage fluid eosinophils by 40 and 80%, and lymphocytes by 55 and 66%, in the acute and chronic models, respectively. Alterations in Zn transporter expression were observed during acute inflammation, including increases in ZIP1 and ZIP14 and decreases in ZIP4 and ZnT4. Zn supplementation normalized ZIP1 and ZIP14, but it did not affect mRNA levels of cytokines or their receptors. Our results indicate that inflammation-induced alterations in Zn transporter gene expression are directed toward increasing Zn uptake. Increases in Zn uptake may be needed to counteract the local loss of Zn in the airway and to meet an increased demand for Zn-dependent proteins. The reduction of inflammatory cells by Zn in the airways provides support for Zn supplementation trials in human asthmatic individuals.

Zinc modulates cytokine-induced lung epithelial cell barrier permeability

Apoptosis plays a causative role in acute lung injury in part due to epithelial cell loss. We recently reported that zinc protects the lung epithelium during inflammatory stress whereas depletion of intracellular zinc enhances extrinsic apoptosis. In this investigation, we evaluated the relationship between zinc, caspase-3, and cell-to-cell contact via proteins that form the adherens junction complex. Cell adhesion proteins are directly responsible for formation of the mechanical barrier of the lung epithelium. We hypothesized that exposure to inflammatory cytokines, in conjunction with zinc deprivation, would induce caspase-3, leading to degradation of junction proteins, loss of cell-to-cell contact, and compromised barrier function. Primary human upper airway and type I/II alveolar epithelial cultures were obtained from multiple donors and exposed to inflammatory stimuli that provoke extrinsic apoptosis in addition to depletion of intracellular zinc. We observed that zinc deprivation combined with tumor necrosis factor-alpha, interferon-gamma, and Fas receptor ligation accelerates caspase-3 activation, proteolysis of E-cadherin and beta-catenin, and cellular apoptosis, leading to increased paracellular leak across monolayers of both upper airway and alveolar lung epithelial cultures. Zinc supplementation inhibited apoptosis and paracellular leak, whereas caspase inhibition was less effective. We conclude that zinc is a vital factor in the lung epithelium that protects against death receptor-mediated apoptosis and barrier dysfunction. Furthermore, our findings suggest that although caspase-3 inhibition reduces lung epithelial apoptosis it does not prevent mechanical dysfunction. These findings facilitate future studies aimed at developing therapeutic strategies to prevent acute lung injury.

Apoptosis may underlie the pathology of zinc-deficient skin

The trace element zinc is essential for the survival and function of all cells. Zinc deficiency, whether nutritional or genetic, is fatal if left untreated. The effects of zinc deficiency are particularly obvious in the skin, seen as an erythematous rash, scaly plaques, and ulcers. Electron microscopy reveals degenerative changes within keratinocytes. Despite the well-documented association between zinc deficiency and skin pathology, it is not clear which cellular processes are most sensitive to zinc deficiency and could account for the typical pathological features. We used the cultured HaCaT keratinocyte line to obtain insight into the cellular effects of zinc deficiency, as these cells show many characteristics of normal skin keratinocytes. Zinc deficiency was induced by growing cells in the presence of the zinc chelator, TPEN, or by growth in zinc-deficient medium. Growth of cells in zinc-deficient medium resulted in a 44% reduction of intracellular zinc levels and a 75% reduction in the activity of the zinc-dependent enzyme, 5'-nucleotidase, relative to the control cells. Over a period of 7 days of exposure to zinc-deficient conditions, no changes in cell viability and growth, or in the cytoskeletal and cell adhesion systems, were found in HaCaT cells. At 7 days, however, induction of apoptosis was indicated by the presence of DNA fragmentation and expression of active caspase-3 in cells. These results demonstrate that apoptosis is the earliest detectable cellular change induced by zinc deficiency in HaCaT keratinocytes. Our observations account for many of the features of zinc deficiency, including the presence of degenerate nuclei, chromatin aggregates and abnormal organization of keratin, that may represent the later stages of apoptosis. In summary, a major causal role for apoptosis in the pathology of zinc deficiency in the skin is proposed. This role is consistent with the previously unexplained diverse range of degenerative cellular changes seen at the ultrastructural level in zinc-deficient keratinocytes.

65Zn2+ Transport by lobster hepatopancreatic lysosomal membrane vesicles

In crustaceans, the hepatopancreas is the major organ system responsible for heavy metal detoxification, and within this structure the lysosomes and the endoplasmic reticulum are two organelles that regulate cytoplasmic metal concentrations by selective sequestration processes. This study characterized the transport processes responsible for zinc uptake into hepatopancreatic lysosomal membrane vesicles (LMV) and the interactions between the transport of this metal and those of calcium, copper, and cadmium in the same preparation. Standard centrifugation methods were used to prepare purified hepatopancreatic LMV and a rapid filtration procedure, to quantify 65Zn2+ transfer across this organellar membrane. LMV were osmotically reactive and exhibited a time course of uptake that was linear for 15-30 sec and approached equilibrium by 300 sec. 65Zn2+ influx was a hyperbolic function of external zinc concentration and followed Michaelis-Menten kinetics for carrier transport (Km = 32.3 +/- 10.8 microM; Jmax = 20.7 +/- 2.6 pmol/mg protein x sec). This carrier transport was stimulated by the addition of 1 mM ATP (Km = 35.89 +/- 10.58 microM; Jmax = 31.94+/-3.72 pmol/mg protein/sec) and replaced by an apparent slow diffusional process by the simultaneous presence of 1 mM ATP+250 microM vanadate. Thapsigargin (10 microM) was also a significant inhibitor of zinc influx (Km = 72.87 +/- 42.75 microM; Jmax =22.86 +/- 4.03 pmol/mg protein/sec), but not as effective in this regard as was vanadate. Using Dixon analysis, cadmium and copper were shown to be competitive inhibitors of lysosomal membrane vesicle 65Zn2+ influx by the ATP-dependent transport process (cadmium Ki = 68.1 +/- 3.2 microM; copper Ki = 32.7 +/- 1.9 microM). In the absence of ATP, an outwardly directed H+ gradient stimulated 65Zn2+ uptake, while a proton gradient in the opposite direction inhibited metal influx. The present investigation showed that 65Zn2+ was transported by hepatopancreatic lysosomal vesicles by ATP-dependent, vanadate-, thapsigargin-, and divalent cation-inhibited, carrier processes that illustrated Michaelis-Menten influx kinetics and was stimulated by an outwardly directed proton gradient. These transport properties as a whole suggest that this transporter may be a lysosomal isoform of the ER Sarco-Endoplasmic Reticulum Calcium ATPase.

Nitric oxide-induced nuclear translocation of the metal responsive transcription factor, MTF-1 is mediated by zinc release from metallothionein

We previously showed that the major Zn-binding protein, metallothionein (MT) is a critical target for nitric oxide (NO) with resultant increases in labile Zn. We now show that NO donors also affected the activity of the metal responsive transcription factor MTF-1 that translocates from the cytosol to the nucleus in response to physiologically relevant increases in intracellular Zn and transactivates MT gene expression. Exposing mouse lung endothelial cells (MLEC) to ZnCl(2) or the NO donor, S-Nitroso-N-acetylpenicillamine (SNAP, 200 microM), caused nuclear translocation of a reporter molecule consisting of enhanced green fluorescent protein (EGFP) fused to MTF-1 (pEGFP-MTF-1). In separate experiments, NO donors induced increases in MT protein levels (Western blot). In contrast, NO did not cause nuclear translocation of EGFP-MTF-1 in MLEC from MT knockouts, demonstrating a central role for MT in mediating this response. These data suggest that S-nitrosation of Zn-thiolate clusters in MT and subsequent alterations in Zn homeostasis are participants in intracellular NO signaling pathways affecting gene expression.

Nitric oxide and zinc homeostasis in acute lung injury

Among putative small molecules that affect sensitivity to acute lung injury, zinc and nitric oxide are potentially unique by virtue of their interdependence and dual capacities to be cytoprotective or injurious. Nitric oxide and zinc appear to be linked via an intracellular signaling pathway involving S-nitrosation of metallothoinein--itself a small protein known to be an important inducible gene product that may modify lung injury. In the present article, we summarize recent efforts using genetic and fluorescence optical imaging techniques to: (1) demonstrate that S-nitrosation of metallothionein affects intracellular zinc homeostasis in intact pulmonary endothelial cells; and (2) reveal a protective role for this pathway in hyperoxic and LPS-induced injury.

Extracellular zinc and ATP-gated P2X receptor calcium entry channels: New zinc receptors as physiological sensors and therapeutic targets

In this review, we focus on two attributes of P2X receptor channel function, one essential and one novel. First, we propose that P2X receptors are extracellular sensors as well as receptors and ion channels. In particular, the large extracellular domain (that comprises 70% of the molecular mass of the receptor channel protein) lends itself to be a cellular sensor. Moreover, its exquisite sensitivity to extracellular pH, ionic strength, and multiple ligands evokes the function of a sensor. Second, we propose that P2X receptors are extracellular zinc receptors as well as receptors for nucleotides. We provide novel data in multiple publications and illustrative data in this invited review to suggest that zinc triggers ATP-independent activation of P2X receptor channel function. In this light, P2X receptors are the cellular site of integration between autocrine and paracrine zinc signaling and autocrine and paracrine purinergic signaling. P2X receptors may sense changes in these ligands as well as in extracellular pH and ionic strength and transduce these sensations via calcium and/or sodium entry and changes in membrane potential.