Zinc and myocardial ischemia/reperfusion injury

Genetic insights into the effect of trace elements on cardiovascular diseases: multi-omics Mendelian randomization combined with linkage disequilibrium score regression analysis

Objective

Epidemiological evidence indicates that trace elements are significantly associated with cardiovascular health. However, its causality and underlying mechanisms remain unclear. Therefore, this study aimed to investigate the causal relationship between trace elements and cardiovascular disease, as well as their potential mechanism of action.

Method

Two-sample Mendelian randomization (MR) analyses along with mediated and multivariate MR analyses were employed. These analyses utilized 13 trace elements as exposure variables and 20 cardiovascular diseases as outcome variables, with 4907 circulating plasma proteins, 1400 serum metabolites, 731 immune cell phenotypes, and 473 intestinal flora as potential mediators. The Bayesian weighted MR method was used to validate the MR results, and linkage disequilibrium score regression (LDSC) was applied to explore the genetic correlation between trace elements and cardiovascular disease.

Result

Our findings indicated a positive or negative causal relationship between genetically predicted trace elements and cardiovascular disease. An analysis using the Bayesian weighted MR method demonstrated that our causal inference results were reliable. The results of the mediated MR analyses indicate that potassium may reduce the risk of ischemic heart disease by influencing the expression of the plasma proteins BDH2 and C1R. Vitamin B12 may increase the risk of coronary atherosclerosis and cardiovascular death by reducing the levels of VPS29 and PSME1 proteins, while vitamin C may mitigate the risk of cardiac arrest by inhibiting the expression of the TPST2 protein. In addition, potassium can reduce the risk of ischemic heart disease by lowering 4-methoxyphenyl sulfate levels. None of the instrumental variables exhibited pleiotropy in the MR analysis. A sensitivity analysis using the leave-one-out method further confirmed the robustness of our findings. LDSC results indicated a genetic correlation between multiple trace elements and various cardiovascular diseases.

Conclusion

This study uncovered the true causal relationship between trace elements and cardiovascular disease risk using genetic methods, and revealed the significant mediating role of specific plasma proteins and metabolites in this relationship.

Exploring the correlation between dietary zinc intake and stroke risk in adults based on NHANES database

OBJECTIVE

To explore the relationship between dietary zinc intake and stroke.

METHODS

Subjects from the National Health and Nutrition Examination Survey (NHANES) database (2015 to 2020) were included. Zinc intake was determined using two 24-h dietary recall interviews, and stroke was determined using the Medical Condition Questionnaire (MCQ). Logistic analysis was used to analyze the association between zinc intake and stroke risk. 1:1 nearest neighbor propensity score matching (PSM) was used to reduce selection bias.

RESULTS

4705 subjects were included in the study. Multivariate logistic regression analysis before and after matching showed that increased zinc intake was associated with a reduced risk of stroke. And as zinc intake increases, the risk of stroke shows a gradually decreasing trend. Compared with the Q1 group, the risk of stroke in the Q2, Q3, and Q4 groups was reduced by approximately 0.27 times, 0.29 times, and 0.31 times respectively. And there is no interaction between dietary zinc intake and gender in stroke patients.

CONCLUSION

Dietary zinc intake may be a protective factor against stroke, and increasing its intake may prevent or reduce the symptoms of stroke and related diseases.

Determination of metal ion transport rate of human ZIP4 using stable zinc isotopes

The essential microelement zinc is absorbed in the small intestine mainly by the zinc transporter ZIP4, a representative member of the Zrt/Irt-like protein (ZIP) family. ZIP4 is reportedly upregulated in many cancers, making it a promising oncology drug target. To date, there have been no reports on the turnover number of ZIP4, which is a crucial missing piece of information needed to better understand the transport mechanism. In this work, we used a nonradioactive zinc isotope, 70Zn, and inductively coupled plasma mass spectrometry to study human ZIP4 (hZIP4) expressed in Human embryonic kidney 293 cells. Our data showed that 70Zn can replace the radioactive 65Zn as a tracer in kinetic evaluation of hZIP4 activity. This approach, combined with the quantification of the cell surface expression of hZIP4 using biotinylation or surface-bound antibody, allowed us to estimate the apparent turnover number of hZIP4 to be in the range of 0.08 to 0.2 s-1. The turnover numbers of the truncated hZIP4 variants are significantly smaller than that of the full-length hZIP4, confirming a crucial role for the extracellular domain in zinc transport. Using 64Zn and 70Zn, we measured zinc efflux during the cell-based transport assay and found that it has little effect on the zinc import analysis under these conditions. Finally, we demonstrated that use of laser ablation inductively coupled plasma-TOF-mass spectrometry on samples applied to a solid substrate significantly increased the throughput of the transport assay. We envision that the approach reported here can be applied to the studies of metal transporters beyond the ZIP family.

An Overexpression of SLC30A6 Gene Contributes to Cardiomyocyte Dysfunction via Affecting Mitochondria and Inducing Activations in K-Acetylation and Epigenetic Proteins

Intracellular free Zn2+ ([Zn2+]i) is less than 1-nM in cardiomyocytes and its regulation is performed with Zn2+-transporters. However, the roles of Zn2+-transporters in cardiomyocytes are not defined exactly yet. Here, we aimed to examine the role of an overexpression and subcellular localization of a ZnT6 in insulin-resistance mimic H9c2 cardiomyoblasts (IR-cells; 50-μM palmitic acid for 24-h incubation). We used both IR-cells and ZnT6-overexpressed (ZnT6OE) cells in comparison to those of H9c2 cells (CON-cells). The IR-cells have higher ZnT6-protein levels than CON-cells while this level was similar to those of ZnT6OE-cells. The [Zn2+]i in IR-cells was increased significantly and mitochondrial localization of ZnT6 was demonstrated in these cells by using confocal microscopy visualization. Furthermore, electron microscopy analysis demonstrated abnormal morphological appearance in both IR-cells and ZnT6OE-cells characterized by irregular mitochondrion cristae and condensed and dilated cisterna in the sarcoplasmic reticulum. Mitochondria were similarly depolarized in both IR-cells and ZnT6OE-cells. The protein expression level of a mitofusin protein MFN2 in the IR-cells was decreased, significantly, whereas, it was found significantly upregulated in both ZnT6-OE-cells and IR-incubated ZnT6OE-cells, which demonstrates the role of ZnT6-overexpression but not IR. Additionally, the total protein level of a mitochondrial fission protein, dynamin-related protein 1, DRP1 was found to be increased over 1.5-fold in IR-cells while this increase was found to be higher in the ZnT6OE-cells than those of IR-cells, demonstrating an additional effect on IR-increase. ZnT6-overexpression induced also significant increases in K-acetylation, trimethylation of histone H3 lysine27, and mono-methylation of histone H3 lysine36, in a similar manner to those of IR-cells. Overall, our data point out an important contribution of ZnT6-overexpression to IR-induced cellular changes, such as alteration in mitochondria function and activation of epigenetic modifications.

Contribution of zinc accumulation to ischemic brain injury and its mechanisms about oxidative stress, inflammation, and autophagy: an update

Ischemic stroke is a leading cause of death and disability worldwide, and presently, there is no effective neuroprotective therapy. Zinc is an essential trace element that plays important physiological roles in the central nervous system. Free zinc concentration is tightly regulated by zinc-related proteins in the brain under normal conditions. Disruption of zinc homeostasis, however, has been found to play an important role in the mechanism of brain injury following ischemic stroke. A large of free zinc releases from storage sites after cerebral ischemia, which affects the functions and survival of nerve cells, including neurons, astrocytes, and microglia, resulting in cell death. Ischemia-triggered intracellular zinc accumulation also disrupts the function of blood-brain barrier via increasing its permeability, impairing endothelial cell function, and altering tight junction levels. Oxidative stress and neuroinflammation have been reported to be as major pathological mechanisms in cerebral ischemia/reperfusion injury. Studies have showed that the accumulation of intracellular free zinc could impair mitochondrial function to result in oxidative stress, and form a positive feedback loop between zinc accumulation and reactive oxygen species production, which leads to a series of harmful reactions. Meanwhile, elevated intracellular zinc leads to neuroinflammation. Recent studies also showed that autophagy is one of the important mechanisms of zinc toxicity after ischemic injury. Interrupting the accumulation of zinc will reduce cerebral ischemia injury and improve neurological outcomes. This review summarizes the role of zinc toxicity in cellular and tissue damage following cerebral ischemia, focusing on the mechanisms about oxidative stress, inflammation, and autophagy.

Interactions between zinc and NRF2 in vascular redox signalling

Recent evidence highlights the importance of trace metal micronutrients such as zinc (Zn) in coronary and vascular diseases. Zn2+ plays a signalling role in modulating endothelial nitric oxide synthase and protects the endothelium against oxidative stress by up-regulation of glutathione synthesis. Excessive accumulation of Zn2+ in endothelial cells leads to apoptotic cell death resulting from dysregulation of glutathione and mitochondrial ATP synthesis, whereas zinc deficiency induces an inflammatory phenotype, associated with increased monocyte adhesion. Nuclear factor-E2-related factor 2 (NRF2) is a transcription factor known to target hundreds of different genes. Activation of NRF2 affects redox metabolism, autophagy, cell proliferation, remodelling of the extracellular matrix and wound healing. As a redox-inert metal ion, Zn has emerged as a biomarker in diagnosis and as a therapeutic approach for oxidative-related diseases due to its close link to NRF2 signalling. In non-vascular cell types, Zn has been shown to modify conformations of the NRF2 negative regulators Kelch-like ECH-associated Protein 1 (KEAP1) and glycogen synthase kinase 3β (GSK3β) and to promote degradation of BACH1, a transcriptional suppressor of select NRF2 genes. Zn can affect phosphorylation signalling, including mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinases and protein kinase C, which facilitate NRF2 phosphorylation and nuclear translocation. Notably, several NRF2-targeted proteins have been suggested to modify cellular Zn concentration via Zn exporters (ZnTs) and importers (ZIPs) and the Zn buffering protein metallothionein. This review summarises the cross-talk between reactive oxygen species, Zn and NRF2 in antioxidant responses of vascular cells against oxidative stress and hypoxia/reoxygenation.

Vascular protection afforded by zinc supplementation in human coronary artery smooth muscle cells mediated by NRF2 signaling under hypoxia/reoxygenation

Zinc (Zn) has antioxidant, anti-inflammatory and anti-proliferative actions, with Zn dysregulation associated with coronary ischemia/reperfusion injury and smooth muscle cell dysfunction. As the majority of studies concerning Zn have been conducted under non-physiological hyperoxic conditions, we compare the effects of Zn chelation or supplementation on total intracellular Zn content, antioxidant NRF2 targeted gene transcription and hypoxia/reoxygenation-induced reactive oxygen species generation in human coronary artery smooth muscle cells (HCASMC) pre-adapted to hyperoxia (18 kPa O2) or normoxia (5 kPa O2). Expression of the smooth muscle marker SM22-α was unaffected by lowering pericellular O2, whereas calponin-1 was significantly upregulated in cells under 5 kPa O2, indicating a more physiological contractile phenotype under 5 kPa O2. Inductively coupled plasma mass spectrometry established that Zn supplementation (10 μM ZnCl2 + 0.5 μM pyrithione) significantly increased total Zn content in HCASMC under 18 but not 5 kPa O2. Zn supplementation increased metallothionein mRNA expression and NRF2 nuclear accumulation in cells under 18 or 5 kPa O2. Notably, NRF2 regulated HO-1 and NQO1 mRNA expression in response to Zn supplementation was only upregulated in cells under 18 but not 5 kPa. Furthermore, whilst hypoxia increased intracellular glutathione (GSH) in cells pre-adapted to 18 but not 5 kPa O2, reoxygenation had negligible effects on GSH or total Zn content. Reoxygenation-induced superoxide generation in cells under 18 kPa O2 was abrogated by PEG-superoxide dismutase but not by PEG-catalase, and Zn supplementation, but not Zn chelation, attenuated reoxygenation-induced superoxide generation in cells under 18 but not 5kPaO2, consistent with a lower redox stress under physiological normoxia. Our findings highlight that culture of HCASMC under physiological normoxia recapitulates an in vivo contractile phenotype and that effects of Zn on NRF2 signaling are altered by oxygen tension.

Copper and Zinc Particles as Regulators of Cardiovascular System Function-A Review

Copper and zinc are micronutrients that play a crucial role in many cellular pathways, act as cofactors in enzymatic systems, and hence, modulate enzyme activity. The regulation of these elements in homeostasis is precisely controlled by various mechanisms. Superoxide dismutase (SOD) is an enzyme requiring both copper and zinc for proper functioning. Additionally, there is an interaction between the concentrations of copper and zinc. Dietary ingestion of large amounts of zinc augments intestinal absorption of this trace element, resulting in copper deficiency secondary to zinc excess. The presence of an overabundance of copper and zinc has a detrimental impact on the cardiovascular system; however, the impact on vascular contractility varies. Copper plays a role in the modulation of vascular remodeling in the cardiac tissue, and the phenomenon of cuproptosis has been linked to the pathogenesis of coronary artery disease. The presence of copper has an observable effect on the vasorelaxation mediated by nitric oxide. The maintenance of proper levels of zinc within an organism influences SOD and is essential in the pathogenesis of myocardial ischemia/reperfusion injury. Recently, the effects of metal nanoparticles have been investigated due to their unique characteristics. On the other hand, dietary introduction of metal nanoparticles may result in vascular dysfunction, oxidative stress, and cellular DNA damage. Copper and zinc intake affect cardiovascular function, but more research is needed.

Redox and metal profiles in human coronary endothelial and smooth muscle cells under hyperoxia, physiological normoxia and hypoxia: Effects of NRF2 signaling on intracellular zinc

Zinc is an important component of cellular antioxidant defenses and dysregulation of zinc homeostasis is a risk factor for coronary heart disease and ischemia/reperfusion injury. Intracellular homeostasis of metals, such as zinc, iron and calcium are interrelated with cellular responses to oxidative stress. Most cells experience significantly lower oxygen levels in vivo (2-10 kPa O₂) compared to standard in vitro cell culture (18kPa O₂). We report the first evidence that total intracellular zinc content decreases significantly in human coronary artery endothelial cells (HCAEC), but not in human coronary artery smooth muscle cells (HCASMC), after lowering of O₂ levels from hyperoxia (18 kPa O₂) to physiological normoxia (5 kPa O₂) and hypoxia (1 kPa O₂). This was paralleled by O₂-dependent differences in redox phenotype based on measurements of glutathione, ATP and NRF2-targeted protein expression in HCAEC and HCASMC. NRF2-induced NQO1 expression was attenuated in both HCAEC and HCASMC under 5 kPa O₂ compared to 18 kPa O₂. Expression of the zinc efflux transporter ZnT1 increased in HCAEC under 5 kPa O₂, whilst expression of the zinc-binding protein metallothionine (MT) decreased as O₂ levels were lowered from 18 to 1 kPa O₂. Negligible changes in ZnT1 and MT expression were observed in HCASMC. Silencing NRF2 transcription reduced total intracellular zinc under 18 kPa O₂ in HCAEC with negligible changes in HCASMC, whilst NRF2 activation or overexpression increased zinc content in HCAEC, but not HCASMC, under 5 kPa O₂. This study has identified cell type specific changes in the redox phenotype and metal profile in human coronary artery cells under physiological O₂ levels. Our findings provide novel insights into the effect of NRF2 signaling on Zn content and may inform targeted therapies for cardiovascular diseases.

Micronutrient deficiencies in heart failure: Mitochondrial dysfunction as a common pathophysiological mechanism?

Heart failure is a devastating clinical syndrome, but current therapies are unable to abolish the disease burden. New strategies to treat or prevent heart failure are urgently needed. Over the past decades, a clear relationship has been established between poor cardiac performance and metabolic perturbations, including deficits in substrate uptake and utilization, reduction in mitochondrial oxidative phosphorylation and excessive reactive oxygen species production. Together, these perturbations result in progressive depletion of cardiac adenosine triphosphate (ATP) and cardiac energy deprivation. Increasing the delivery of energy substrates (e.g., fatty acids, glucose, ketones) to the mitochondria will be worthless if the mitochondria are unable to turn these energy substrates into fuel. Micronutrients (including coenzyme Q10, zinc, copper, selenium and iron) are required to efficiently convert macronutrients to ATP. However, up to 50% of patients with heart failure are deficient in one or more micronutrients in cross-sectional studies. Micronutrient deficiency has a high impact on mitochondrial energy production and should be considered an additional factor in the heart failure equation, moving our view of the failing myocardium away from an "an engine out of fuel" to "a defective engine on a path to self-destruction." This summary of evidence suggests that supplementation with micronutrients-preferably as a package rather than singly-might be a potential therapeutic strategy in the treatment of heart failure patients.

The Oxidative Balance Orchestrates the Main Keystones of the Functional Activity of Cardiomyocytes

This review is aimed at providing an overview of the key hallmarks of cardiomyocytes in physiological and pathological conditions. The main feature of cardiac tissue is the force generation through contraction. This process requires a conspicuous energy demand and therefore an active metabolism. The cardiac tissue is rich of mitochondria, the powerhouses in cells. These organelles, producing ATP, are also the main sources of ROS whose altered handling can cause their accumulation and therefore triggers detrimental effects on mitochondria themselves and other cell components thus leading to apoptosis and cardiac diseases. This review highlights the metabolic aspects of cardiomyocytes and wanders through the main systems of these cells: (a) the unique structural organization (such as different protein complexes represented by contractile, regulatory, and structural proteins); (b) the homeostasis of intracellular Ca²⁺ that represents a crucial ion for cardiac functions and E-C coupling; and (c) the balance of Zn²⁺, an ion with a crucial impact on the cardiovascular system. Although each system seems to be independent and finely controlled, the contractile proteins, intracellular Ca²⁺ homeostasis, and intracellular Zn²⁺ signals are strongly linked to each other by the intracellular ROS management in a fascinating way to form a "functional tetrad" which ensures the proper functioning of the myocardium. Nevertheless, if ROS balance is not properly handled, one or more of these components could be altered resulting in deleterious effects leading to an unbalance of this "tetrad" and promoting cardiovascular diseases. In conclusion, this "functional tetrad" is proposed as a complex network that communicates continuously in the cardiomyocytes and can drive the switch from physiological to pathological conditions in the heart.

Role of Zinc Supplementation on Ischemia/Reperfusion Injury in Various Organs

Ischemia-reperfusion (I/R) injury is a serious condition which is associated with myocardial infarction, stroke, acute kidney injury, trauma, circulatory arrest, sickle cell disease, and sleep apnea and can lead to high morbidity and mortality. Salts of zinc (Zn) are commonly used by humans and have protective effects against gastric, renal, hepatic, muscle, myocardial, or neuronal ischemic injury. The present review evaluates molecular mechanisms underlying the protective effects of Zn supplement against I/R injury. Data of this review have been collected from the scientific articles published in databases such as Science Direct, Scopus, PubMed, and Scientific Information Database from 1991 to 2019. Zn supplementation increased the decreased parameters including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), metallothionein (MT), protein sulfhydryl (P-SH), and nuclear factor-erythroid 2-related factor-2 (Nrf2) expression and decreased the increased elements such as endoplasmic reticulum (ER) stress, mitochondrial permeability transition pore (mPTP) opening, malondialdehyde (MDA), serum level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and microRNAs-(122 and 34a), apoptotic factors, and histopathological changes. Zn also increases phosphatidylinositol 3-kinase (PI3K)/Akt and glycogen synthase kinase-3β (GSK-3β) phosphorylation and preserves protein kinase C isoforms. It is suggested that Zn can be administered before elective surgeries for prevention of side effects of I/R injury.

Why is it worth testing the ability of zinc to protect against ischaemia reperfusion injury for human application

Ischaemia (interruption in the blood/oxygen supply) and subsequent damage induced by reperfusion (restoration of blood/oxygen supply) ultimately leads to cell death, tissue injury and permanent organ dysfunction. The impact of ischaemia reperfusion injury (IRI) is not limited to heart attack and stroke but can be extended to patients undergoing surgeries such as partial nephrectomy for renal cancer, liver resection for colorectal cancer liver metastasis, cardiopulmonary bypass, and organ transplantation. Unfortunately, there are no drugs that can protect organs against the inevitable peril of IRI. Recent data show that a protocol incorporating specific Zn formulation, dosage, number of dosages, time of injection, and mode of Zn delivery (intravenous) and testing of efficacy in a large preclinical sheep model of IRI strongly supports human trials of Zn preconditioning. No doubt, scepticism still exists among funding bodies and research fraternity on whether Zn, a naturally occurring metal, will work where everything else has failed. Therefore, in this article, we review the conflicting evidence on the promoter and protector role of Zn in the case of IRI and highlight factors that may help explain the contradictory evidence. Finally, we review the literature related to the knowledge of Zn's mechanism of action on ROS generation, apoptosis, HIF activation, inflammation, and signal transduction pathways, which highlight Zn's likelihood of success compared to various other interventions targeting IRI.

A Brief Overview from the Physiological and Detrimental Roles of Zinc Homeostasis via Zinc Transporters in the Heart

Zinc (mostly as free/labile Zn²⁺) is an essential structural constituent of many proteins, including enzymes in cellular signaling pathways via functioning as an important signaling molecule in mammalian cells. In cardiomyocytes at resting condition, intracellular labile Zn²⁺ concentration ([Zn²⁺]_i) is in the nanomolar range, whereas it can increase dramatically under pathological conditions, including hyperglycemia, but the mechanisms that affect its subcellular redistribution is not clear. Therefore, overall, very little is known about the precise mechanisms controlling the intracellular distribution of labile Zn²⁺, particularly via Zn²⁺ transporters during cardiac function under both physiological and pathophysiological conditions. Literature data demonstrated that [Zn²⁺]_i homeostasis in mammalian cells is primarily coordinated by Zn²⁺ transporters classified as ZnTs (SLC30A) and ZIPs (SLC39A). To identify the molecular mechanisms of diverse functions of labile Zn²⁺ in the heart, the recent studies focused on the discovery of subcellular localization of these Zn²⁺ transporters in parallel to the discovery of novel physiological functions of [Zn²⁺]_i in cardiomyocytes. The present review summarizes the current understanding of the role of [Zn²⁺]_i changes in cardiomyocytes under pathological conditions, and under high [Zn²⁺]_i and how Zn²⁺ transporters are important for its subcellular redistribution. The emerging importance and the promise of some Zn²⁺ transporters for targeted cardiac therapy against pathological stimuli are also provided. Taken together, the review clearly outlines cellular control of cytosolic Zn²⁺ signaling by Zn²⁺ transporters, the role of Zn²⁺ transporters in heart function under hyperglycemia, the role of Zn²⁺ under increased oxidative stress and ER stress, and their roles in cancer are discussed.

Acute dietary zinc deficiency in rats exacerbates myocardial ischaemia–reperfusion injury through depletion of glutathione

Zn plays an important role in maintaining the anti-oxidant status within the heart and helps to counter the acute redox stress that occurs during myocardial ischaemia and reperfusion. Individuals with low Zn levels are at greater risk of developing an acute myocardial infarction; however, the impact of this on the extent of myocardial injury is unknown. The present study aimed to compare the effects of dietary Zn depletion with in vitro removal of Zn (N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN)) on the outcome of acute myocardial infarction and vascular function. Male Sprague–Dawley rats were fed either a Zn-adequate (35 mg Zn/kg diet) or Zn-deficient (<1 mg Zn/kg diet) diet for 2 weeks before heart isolation. Perfused hearts were subjected to a 30 min ischaemia/2 h reperfusion (I/R) protocol, during which time ventricular arrhythmias were recorded and after which infarct size was measured, along with markers of anti-oxidant status. In separate experiments, hearts were challenged with the Zn chelator TPEN (10 µm) before ischaemia onset. Both dietary and TPEN-induced Zn depletion significantly extended infarct size; dietary Zn depletion was associated with reduced total cardiac glutathione (GSH) levels, while TPEN decreased cardiac superoxide dismutase 1 levels. TPEN, but not dietary Zn depletion, also suppressed ventricular arrhythmias and depressed vascular responses to nitric oxide. These findings demonstrate that both modes of Zn depletion worsen the outcome from I/R but through different mechanisms. Dietary Zn deficiency, resulting in reduced cardiac GSH, is the most appropriate model for determining the role of endogenous Zn in I/R injury.

Zinc preconditioning protects against renal ischaemia reperfusion injury in a preclinical sheep large animal model

Ischaemia-reperfusion injury (IRI) during various surgical procedures, including partial nephrectomy for kidney cancer or renal transplantation, is a major cause of acute kidney injury and chronic kidney disease. Currently there are no drugs or methods for protecting human organs, including the kidneys, against the peril of IRI. The aim of this study was therefore to investigate the reno-protective effect of Zn²⁺ preconditioning in a clinically relevant large animal sheep model of IRI. Further the reno-protective effectiveness of Zn²⁺ preconditioning was tested on normal human kidney cell lines HK-2 and HEK293. Anaesthetised sheep were subjected to uninephrectomy and 60 min of renal ischaemia followed by reperfusion. Sheep were preconditioned with intravenous injection of zinc chloride prior to occlusion. Serum creatinine and urea were measured before ischaemia and for 7 days after reperfusion. HK-2 and HEK293 cells were subjected to in vitro IRI using the oxygen- and glucose-deprivation model. Zn²⁺ preconditioning reduced ischaemic burden determined by creatinine and urea rise over time by ~ 70% in sheep. Zn²⁺ preconditioning also increased the survival of normal human kidney cells subjected to cellular stress such as hypoxia, hydrogen peroxide injury, and serum starvation. Overall, our protocol incorporating specific Zn²⁺ dosage, number of dosages (two), time of injection (24 and 4 h prior), mode of Zn²⁺ delivery (IV) and testing of efficacy in a rat model, a large preclinical sheep model of IRI and cells of human origin has laid the foundation for assessment of the benefit of Zn²⁺ preconditioning for human applications.

Remifentanil Induces Cardio Protection Against Ischemia/Reperfusion Injury by Inhibiting Endoplasmic Reticulum Stress Through the Maintenance of Zinc Homeostasis

BACKGROUND

Although it is well known that remifentanil (Rem) elicits cardiac protection against ischemia/reperfusion (I/R) injury, the underlying mechanism remains unclear. This study tested if Rem can protect the heart from I/R injury by inhibiting endoplasmic reticulum (ER) stress through the maintenance of zinc (Zn) homeostasis.

METHODS

Isolated rat hearts were subjected to 30 minutes of regional ischemia followed by 2 hours of reperfusion. Rem was given by 3 consecutive 5-minute infusions, and each infusion was followed by a 5-minute drug-free perfusion before ischemia. Total Zn concentrations in cardiac tissue, cardiac function, infarct size, and apoptosis were assessed. H9c2 cells were subjected to 6 hours of hypoxia and 2 hours of reoxygenation (hypoxia/reoxygenation [H/R]), and Rem was given for 30 minutes before hypoxia. Metal-responsive transcription factor 1 (MTF1) overexpression plasmids were transfected into H9c2 cells 48 hours before hypoxia. Intracellular Zn level, cell viability, and mitochondrial injury parameters were evaluated. A Zn chelator N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN) or an ER stress activator thapsigargin was administrated during in vitro and ex vivo studies. The regulatory molecules related to Zn homeostasis and ER stress in cardiac tissue, and cardiomyocytes were analyzed by Western blotting.

RESULTS

Rem caused significant reversion of Zn loss from the heart (Rem + I/R versus I/R, 9.43 ± 0.55 vs 7.53 ± 1.18; P < .05) by suppressing the expression of MTF1 and Zn transporter 1 (ZnT1). The inhibited expression of ER stress markers after Rem preconditioning was abolished by TPEN. Rem preconditioning improved the cardiac function accompanied by the reduction of infarct size (Rem + I/R versus I/R, 21% ± 4% vs 40% ± 6%; P < .05). The protective effects of Rem could be reserved by TPEN and thapsigargin. Similar effects were observed in H9c2 cells exposed to H/R. In addition, MTF1 overexpression blocked the inhibitory effects of Rem on ZnT1 expression and ER stress at reoxygenation. Rem attenuated the collapse of mitochondrial membrane potential (ΔΨm) and the generation of mitochondrial reactive oxygen species by inhibiting ER stress via cardiac Zn restoration (Rem + H/R versus H/R, 79.57% ± 10.62% vs 58.27% ± 4.32%; P < .05).

CONCLUSIONS

Rem maintains Zn homeostasis at reperfusion by inhibiting MTF1 and ZnT1 expression, leading to the attenuation of ER stress and cardiac injury. Our findings provide a promising therapeutic approach for managing acute myocardial I/R injury.

The cardioprotective effect of thymoquinone on ischemia-reperfusion injury in isolated rat heart via regulation of apoptosis and autophagy

Thymoquinone (TQ), as the active constituents of black cumin (Nigella sativa) seed oil, has been reported to have potential protective effects on the cardiovascular system. This study aimed to investigate the effects and the underlying mechanisms of TQ on myocardial ischemia-reperfusion (I/R) injury in Langendorff-perfused rat hearts. Wister rat hearts were subjected to I/R and the experimental group were pretreated with TQ prior to I/R. Hemodynamic parameters, myocardial infarct size, cardiac marker enzymes, superoxide dismutase (SOD), malondialdehyde (MDA) content, and cardiomyocyte apoptosis were assayed. Compared with the untreated group, TQ preconditioning significantly improved cardiac function, reduced infarct size, decreased cardiac lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) levels, suppressed enedoxidative stress, and apoptosis. In addition, TQ treatment promoted autophagy, which was partially reversed by chloroquine (CQ), a kind of autophagy blocker. Our study suggests that TQ can protect heart against I/R injury, which is associated with anti-oxidative and anti-apoptotic effects through activation of autophagy.

Applications of Nanomaterials Based on Magnetite and Mesoporous Silica on the Selective Detection of Zinc Ion in Live Cell Imaging

Functionalized magnetite nanoparticles (FMNPs) and functionalized mesoporous silica nanoparticles (FMSNs) were synthesized by the conjugation of magnetite and mesoporous silica with the small and fluorogenic benzothiazole ligand, that is, 2(2-hydroxyphenyl)benzothiazole (hpbtz). The synthesized fluorescent nanoparticles were characterized by FTIR, XRD, XRF, ¹³C CP MAS NMR, BET, and TEM. The photophysical behavior of FMNPs and FMSNs in ethanol was studied using fluorescence spectroscopy. The modification of magnetite and silica scaffolds with the highly fluorescent benzothiazole ligand enabled the nanoparticles to be used as selective and sensitive optical probes for zinc ion detection. Moreover, the presence of hpbtz in FMNPs and FMSNs induced efficient cell viability and zinc ion uptake, with desirable signaling in the normal human kidney epithelial (Hek293) cell line. The significant viability of FMNPs and FMSNs (80% and 92%, respectively) indicates a potential applicability of these nanoparticles as in vitro imaging agents. The calculated limit of detections (LODs) were found to be 2.53 × 10⁻⁶ and 2.55 × 10⁻⁶ M for Fe₃O₄-H@hpbtz and MSN-Et₃N-IPTMS-hpbtz-f1, respectively. FMSNs showed more pronounced zinc signaling relative to FMNPs, as a result of the more efficient penetration into the cells.

Critical Role of Zinc as Either an Antioxidant or a Prooxidant in Cellular Systems

Zinc is recognized as an essential trace metal required for human health; its deficiency is strongly associated with neuronal and immune system defects. Although zinc is a redox-inert metal, it functions as an antioxidant through the catalytic action of copper/zinc-superoxide dismutase, stabilization of membrane structure, protection of the protein sulfhydryl groups, and upregulation of the expression of metallothionein, which possesses a metal-binding capacity and also exhibits antioxidant functions. In addition, zinc suppresses anti-inflammatory responses that would otherwise augment oxidative stress. The actions of zinc are not straightforward owing to its numerous roles in biological systems. It has been shown that zinc deficiency and zinc excess cause cellular oxidative stress. To gain insights into the dual action of zinc, as either an antioxidant or a prooxidant, and the conditions under which each role is performed, the oxidative stresses that occur in zinc deficiency and zinc overload in conjunction with the intracellular regulation of free zinc are summarized. Additionally, the regulatory role of zinc in mitochondrial homeostasis and its impact on oxidative stress are briefly addressed.

The Relationship between Serum Zinc Level and Heart Failure: A Meta-Analysis

Zinc is essential for the maintenance of normal cellular structure and functions. Zinc dyshomeostasis can lead to many diseases, such as cardiovascular disease. However, there are conflicting reports on the relationship between serum zinc levels and heart failure (HF). The purpose of the present study is to explore the relationship between serum zinc levels and HF by using a meta-analysis approach. PubMed, Web of Science, and OVID databases were searched for reports on the association between serum zinc levels and HF until June 2016. 12 reports with 1453 subjects from 27 case-control studies were chosen for the meta-analysis. Overall, the pooled analysis indicated that patients with HF had lower zinc levels than the control subjects. Further subgroup analysis stratified by different geographic locations also showed that HF patients had lower zinc levels than the control subjects. In addition, subgroup analysis stratified by HF subgroups found that patients with idiopathic dilated cardiomyopathy (IDCM) had lower zinc levels than the control subjects, except for patients with ischemic cardiomyopathy (ICM). In conclusion, the results of the meta-analysis indicate that there is a significant association between low serum zinc levels and HF.

Protective effects of crocin and zinc sulfate on hepatic ischemia-reperfusion injury in rats: a comparative experimental model study

OBJECTIVES

The aim of this study was to investigate the comparative protective effects of separate and combined pretreatment with Cr and ZnSO4 on serum levels of miR-122, miR-34a, liver function tests, protein expression of Nrf2 and p53, and histopathological changes following IR-induced hepatic injury.

MATERIALS AND METHODS

Fifty-six male Wistar rats randomly assigned into seven groups (n=8). Sham (S), IR, crocin pretreatment (Cr), and crocin pretreatment+IR (Cr+IR), ZnSO4 pretreatment (ZnSO4), ZnSO4 pretreatment+IR (ZnSO4+IR) and their combination (Cr+ZnSO4+IR) groups. In sham, ZnSO4 and Cr groups, animals received normal saline (N/S, 2ml/day), Cr (200mg/kg) and ZnSO4 (5mg/kg) for 7 consecutive days (intraperitoneally; i.p), then only laparotomy was performed. In IR, Cr+IR, ZnSO4+IR and Cr+ZnSO4+IR groups, rats received N/S, Cr and ZnSO4 with same dose and time, then underwent a partial (70%) ischemia for 45min that followed by reperfusion for 60min. Blood sample was taken for biochemical and microRNAs assay, tissue specimens were obtained for antioxidants, protein expression, histopathological and immunohistochemical evaluations.

RESULTS

The results showed that Cr and ZnSO4 increased antioxidants activity and expression of Nrf2, decreased serum levels of liver enzymes, miR-122, miR-34a, p53 expression and also ameliorated histopathological abnormality. However, their combination caused more improvement on IR-induced liver injury.

CONCLUSION

This study demonstrated that Cr, ZnSO4 and their combination through increasing antioxidant activity and Nrf2 expression, decreasing the serum levels of liver enzymes, miR-122, 34a, p53 expression, and amelioration of histopathological changes, protected liver against IR-induced injury.

Protective effect of zinc preconditioning against renal ischemia reperfusion injury is dose dependent

Objectives

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury and chronic kidney disease. Two promising preconditioning methods for the kidney, intermittent arterial clamping (IC) and treatment with the hypoxia mimetic cobalt chloride, have never been directly compared. Furthermore, the protective efficacy of the chemically related transition metal Zn²⁺ against renal IRI is unclear. Although Co²⁺ ions have been shown to protect the kidney via hypoxia inducible factor (HIF), the effect of Zn²⁺ ions on the induction of HIF1α, HIF2α and HIF3α has not been investigated previously.

Materials and methods

The efficacy of different preconditioning techniques was assessed using a Sprague-Dawley rat model of renal IRI. Induction of HIF proteins following Zn²⁺ treatment of the human kidney cell lines HK-2 (immortalized normal tubular cells) and ACHN (renal cancer) was measured using Western Blot.

Results

Following 40 minutes of renal ischemia in rats, cobalt preconditioning offered greater protection against renal IRI than IC as evidenced by lower peak serum creatinine and urea concentrations. ZnCl₂ (10 mg/kg) significantly lowered the creatinine and urea concentrations compared to saline-treated control rats following a clinically relevant 60 minutes of ischemia. Zn²⁺ induced expression of HIF1α and HIF2α but not HIF3α in HK-2 and ACHN cells.

Conclusion

ZnCl₂ preconditioning protects against renal IRI in a dose-dependent manner. Further studies are warranted to determine the possible mechanisms involved, and to assess the benefit of ZnCl₂ preconditioning for clinical applications.

The Relationship Between Serum Zinc Levels, Cardiac Markers and the Risk of Acute Myocardial Infarction by Zinc Quartiles

BACKGROUND

Zinc is one of the most important microelements in the body and zinc homeostasis plays a critical role in maintaining cellular structure and function. Zinc dyshomeostasis can lead to many diseases, such as cardiovascular disease. Our aim was to investigate whether there is a relationship between zinc and cardiac markers, and the risk of acute myocardial infarction (AMI) by zinc quartiles.

METHODS

We enrolled a total of 529 patients and measured their serum zinc levels and cardiac markers. We performed further studies after dividing subjects into four groups according to their concentrations of zinc by quartile to clarify the relationship between zinc levels and risk of increased acute myocardial infarction prevalence rate.

RESULTS

We observed that there was a significant inverse linear relationship between zinc and Lg(creatine kinase) (p=0.011), Lg(creatine kinase-MB) (p=0.002) and Lg(cardiac troponin T) (p=0.045). In addition, the acute myocardial infarction prevalence rates were 28.8%, 24.8%, 20.5%, and 18.2% by patients with zinc quartiles, respectively. Multivariate logistic regression analysis showed that the odds ratio between the lowest and highest zinc quartile groups was 1.92 (1.019-3.604) (p<0.05).

CONCLUSIONS

The present study revealed a relationship between serum zinc levels in that zinc levels were significantly inversely correlated with serum creatine kinase (CK), creatine kinase-MB (CKMB) and cardiac troponin T (cTnT) levels. Furthermore, we found that the prevalence rate of acute myocardial infarction decreased with increasing zinc quartiles.

Loss of ErbB2-PI3K/Akt signaling prevents zinc pyrithione-induced cardioprotection during ischemia/reperfusion

OBJECTIVES

The purpose of this study was to determine if zinc homeostasis is affected during ischemia/reperfusion, if so, whether zinc pyrithione limits myocardial cell death and improves hemodynamics when administered as an adjunct to reperfusion and if ErbB receptor tyrosine kinases that are important for the long-term structural integrity of the heart are indispensable for reperfusion salvage.

METHODS

Isolated perfused rat hearts were subjected to 35min of global ischemia and reperfused for 120min to determine the relative intracellular zinc levels by TSQ staining. The hearts were reperfused in the presence of incremental concentrations of zinc pyrithione for the first 10min during reperfusion. Silencing or blockade of ErbB2 using a monoclonal antibody, ErbB2 kinase inhibition and PI3kinase inhibition was used to study their critical role in zinc pyrithione-induced cardioprotection.

RESULTS

We found that there was a profound decrease in intracellular zinc after ischemia/reperfusion resulting in increased apoptosis, caspase-3 activation, and infarct size. A dose-dependent reduction of infarct size with zinc pyrithione in the range of 5-20μmol/l (optimal protection was seen at 10μmol/l with infarct size of 16±2% vs. I/R vehicle, 33±2%, p<0.01). Increased TUNEL staining and caspase-3 activity observed after ischemia/reperfusion were attenuated by zinc pyrithione administration during the reperfusion. Moreover, this protection was sensitive to silencing and blockade of ErbB2, inhibition of ErbB2 kinase activity or PI3-kinase activity. Western blot analysis revealed that zinc pyrithione resulted in decreased caspase-3 activation, rapid stabilization of ErbB2/ErbB1 heterodimers, and increased activation of PI3K/Akt signaling cascade.

CONCLUSIONS

Zinc pyrithione attenuates lethal perfusion-induced injury in a manner that is reliant on ErbB2/PI3K/Akt activity.

Interplay Between Cytosolic Free Zn2+ and Mitochondrion Morphological Changes in Rat Ventricular Cardiomyocytes

The Zn²⁺ in cardiomyocytes is buffered by structures near T-tubulus and/or sarcoplasmic/endoplasmic reticulum (S(E)R) while playing roles as either an antioxidant or a toxic agent, depending on the concentration. Therefore, we aimed first to examine a direct effect of ZnPO₄ (extracellular exposure) or Zn²⁺ pyrithione (ZnPT) (intracellular exposure) application on the structure of the mitochondrion in ventricular cardiomyocytes by using histological investigations. The light microscopy data demonstrated that Zn²⁺ exposure induced marked increases on cellular surface area, an indication of hypertrophy, in a concentration-dependent manner. Furthermore, a whole-cell patch-clamp measurement of cell capacitance also supported the hypertrophy in the cells. We observed marked increases in mitochondrial matrix/cristae area and matrix volume together with increased lysosome numbers in ZnPO₄- or ZnPT-incubated cells by using transmission electron microscopy, again in a concentration-dependent manner. Furthermore, we observed notable clustering and vacuolated mitochondrion, markedly disrupted and damaged myofibrils, and electron-dense small granules in Zn²⁺-exposed cells together with some implications of fission-fusion defects in the mitochondria. Moreover, we observed marked depolarization in mitochondrial membrane potential during 1-μM ZnPT minute applications by using confocal microscopy. We also showed that 1-μM ZnPT incubation induced significant increases in the phosphorylation levels of GSK3β (Ser21 and Ser9), Akt (Ser473), and NFκB (Ser276 and Thr254) together with increased expression levels in ER stress proteins such as GRP78 and calregulin. Furthermore, a new key player at ER-mitochondria sites, promyelocytic leukemia protein (PML) level, was markedly increased in ZnPT-incubated cells. As a summary, our present data suggest that increased cytosolic free Zn²⁺ can induce marked alterations in mitochondrion morphology as well as depolarization in mitochondrion membrane potential and changes in some cytosolic signaling proteins as well as a defect in ER-mitochondria cross talk.

Zn2+ and mPTP Mediate Endoplasmic Reticulum Stress Inhibition-Induced Cardioprotection Against Myocardial Ischemia/Reperfusion Injury

The purpose of this study was to determine whether Zn²⁺ is involved in endoplasmic reticulum (ER) stress inhibition-induced cardioprotection against ischemia/reperfusion (I/R) injury by modulation of the mitochondrial permeability transition pore (mPTP) opening. Isolated rat hearts were subjected to 30-min regional ischemia followed by 2 h of reperfusion. Expression of glucose regulated protein 78 (GRP 78 or BIP), an ER homeostasis marker, was not increased during ischemia but was increased upon reperfusion, indicating that ER stress was initiated upon reperfusion but not during ischemia. The ER stress inhibitor tauroursodeoxycholic acid (TUDCA) given at reperfusion resulted in a significant reduction of GRP78 expression 30 and 60 min after the onset of reperfusion, an effect that was reversed by the zinc chelator N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN). The immunofluorescence study also showed that the effect of TUDCA on GRP78 expression was reversed by TPEN. TUDCA reduced infarct size and this was reversed by the mPTP opener atractyloside, indicating that ER stress inhibition may induce cardioprotection by modulating the mPTP opening. Experiments with transmission electron microscopy and hematoxylin-eosin staining also revealed that TUDCA prevented endoplasmic reticulum and mitochondrial damages at reperfusion, which was blocked by TPEN. Exposure of cardiac H9c2 cells to H₂O₂ increased GRP 78 and GRP 94 expressions, suggesting that oxidative stress can induce ER stress. Cells treated with H₂O₂ showed a significant decrease in tetramethylrhodamine ethyl ester (TMRE) fluorescence, indicating that H₂O₂ triggers the mPTP opening. In contrast, TUDCA prevented the loss of TMRE fluorescence, the effect that was blocked by TPEN, indicating a role of Zn in the preventive effect of ER stress inhibition on the mPTP opening. In support, TUDCA significantly increased intracellular free zinc. These data suggest that reperfusion but not ischemia initiates ER stress and inhibition of ER stress protects the heart from reperfusion injury through prevention of the mPTP opening. Increased intracellular free Zn accounts for the cardioprotective effect of ER stress inhibition.

The Critical Roles of Zinc: Beyond Impact on Myocardial Signaling

Zinc has been considered as a vital constituent of proteins, including enzymes. Mobile reactive zinc (Zn(2+)) is the key form of zinc involved in signal transductions, which are mainly driven by its binding to proteins or the release of zinc from proteins, possibly via a redox switch. There has been growing evidence of zinc's critical role in cell signaling, due to its flexible coordination geometry and rapid shifts in protein conformation to perform biological reactions. The importance and complexity of Zn(2+) activity has been presumed to parallel the degree of calcium's participation in cellular processes. Whole body and cellular Zn(2+) levels are largely regulated by metallothioneins (MTs), Zn(2+) importers (ZIPs), and Zn(2+) transporters (ZnTs). Numerous proteins involved in signaling pathways, mitochondrial metabolism, and ion channels that play a pivotal role in controlling cardiac contractility are common targets of Zn(2+). However, these regulatory actions of Zn(2+) are not limited to the function of the heart, but also extend to numerous other organ systems, such as the central nervous system, immune system, cardiovascular tissue, and secretory glands, such as the pancreas, prostate, and mammary glands. In this review, the regulation of cellular Zn(2+) levels, Zn(2+)-mediated signal transduction, impacts of Zn(2+) on ion channels and mitochondrial metabolism, and finally, the implications of Zn(2+) in health and disease development were outlined to help widen the current understanding of the versatile and complex roles of Zn(2+).

The direct modulatory activity of zinc toward ion channels

The divalent zinc ion is a cation that plays an indispensable role as a structural constituent of numerous proteins, including enzymes and transcription factors. Recently, it has been suggested that zinc also plays a dynamic role in extracellular and intracellular signaling as well. Ion channels are pore-forming proteins that control the flow of specific ions across the membrane, which is important to maintain ion gradients. In this review, we outline the modulatory effect of zinc on the activities of several ion channels through direct binding of zinc into histidine, cysteine, aspartate, and glutamate moieties of channel proteins. The binding of zinc to ion channels results in the activation or inhibition of the channel due to conformational changes. These novel aspects of ion-channel activity modulation by zinc provide new insights into the physiological regulation of ion channels.