NO mobilizes intracellular Zn2+ via cGMP/PKG signaling pathway and prevents mitochondrial oxidant damage in cardiomyocytes

Chemical profiling and investigation of molecular mechanisms underlying anti-hepatocellular carcinoma activity of extracts from Polygonum perfoliatum L

Polygonum perfoliatum L. is an herbal medicine that has been extensively used in traditional Chinese medicine to treat various health conditions ranging from ancient internal to surgical and gynecological diseases. Numerous studies suggest that P. perfoliatum extract elicits significant anti-tumor, anti-inflammatory, anti-bacterial, and anti-viral effects. Nevertheless, the underlying mechanisms of its anti-liver cancer effects remain poorly understood. Our study suggests that P. perfoliatum stem extract (PPLA) has a favorable safety profile and exhibits a significant anti-liver cancer effect both in vitro and in vivo. We identified that PPLA activates the cGMP-PKG signaling pathway, and key regulatory genes including ADRA1B, PLCB2, PRKG2, CALML4, and GLO1 involved in this activation. Moreover, PPLA modulates the expression of genes responsible for the cell cycle. Additionally, we identified four constituents of PPLA, namely taxifolin, myricetin, eriodictyol, and pinocembrin, that plausibly act via the cGMP-PKG signaling pathway. Both in vitro and in vivo experiments confirmed that PPLA, along with its constituting compounds taxifolin, myricetin, and eriodictyol, exhibit potent anti-cancer activities and hold the promise of being developed into therapeutic agents.

Regulatory effects of trimetazidine in cardiac ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is a tissue damage during reperfusion after an ischemic condition. I/R injury is induced by pathological cases including stroke, myocardial infarction, circulatory arrest, sickle cell disease, acute kidney injury, trauma, and sleep apnea. It can lead to increased morbidity and mortality in the context of these processes. Mitochondrial dysfunction is one of the hallmarks of I/R insult, which is induced via reactive oxygen species (ROS) production, apoptosis, and autophagy. MicroRNAs (miRNAs, miRs) are non-coding RNAs that play a main regulatory role in gene expression. Recently, there are evidence, which miRNAs are the major modulators of cardiovascular diseases, especially myocardial I/R injury. Cardiovascular miRNAs, specifically miR-21, and probably miR-24 and miR-126 have protective effects on myocardial I/R injury. Trimetazidine (TMZ) is a new class of metabolic agents with an anti-ischemic activity. It has beneficial effects on chronic stable angina by suppressing mitochondrial permeability transition pore (mPTP) opening. The present review study addressed the different mechanistic effects of TMZ on cardiac I/R injury. Online databases including Scopus, PubMed, Web of Science, and Cochrane library were assessed for published studies between 1986 and 2021. TMZ, an antioxidant and metabolic agent, prevents the cardiac reperfusion injury by regulating AMP-activated protein kinase (AMPK), cystathionine-γ-lyase enzyme (CSE)/hydrogen sulfide (H2S), and miR-21. Therefore, TMZ protects the heart against I/R injury by inducing key regulators such as AMPK, CSE/H2S, and miR-21.

Identification and characterization of circRNAs related to meat quality during embryonic development of the longissimus dorsi muscle in two pig breeds

Meat quality, an important economic trait, is regulated by many factors, especially by genetic factors, including coding genes, miRNAs, and lncRNAs. Recent studies have elucidated that circRNAs also play a key role in muscle development and lipid deposition. However, the functions and regulatory mechanisms of circRNAs in meat quality remain mostly unknown. The circRNA expression profiles between Huainan pigs (Chinese indigenous pigs, fat-type, Huainan HN) and Large White pigs (Western commercial pigs, lean-type, LW) in the longissimus dorsi (LD) muscle at 38, 58, and 78 days post conception (dpc) were compared by sequencing. In total, 39,887 circRNAs were identified in 18 samples, and 60, 78, and 86 differentially expressed circRNAs (DECs) were found at the three stages mentioned above between these two breeds. The parent genes of DECs were enriched in myogenesis, proliferation, adipogenesis and muscle fiber-type transition. The circRNA-miRNA interaction networks included 38 DECs and 47 miRNAs, and these miRNAs were involved in muscle development and lipid metabolism. Two shared DECs (circ_0030593 and circ_0032760) of these three stages were selected, their head-to-tail junction sites were validated by Sanger sequencing, and RT‒qPCR results suggested that these two DECs might be involved in intramuscular fat deposition. These findings provide a basis for understanding the role of circRNAs in meat quality.

Nitric Oxide Mobilizes Intracellular Zn2+ via the GC/cGMP/PKG Signaling Pathway and Stimulates Adipocyte Differentiation

Plasma and tissue zinc ion levels are associated with the development of obesity. Previous studies have suggested that zinc ions may regulate adipocyte metabolism and that nitric oxide (NO) plays a pivotal role in the regulation of adipocyte physiology. Our previous study showed that chronic NO deficiency causes a significant decrease in adipose tissue mass in rats. Studies also suggested that zinc ions play an important modulatory role in regulating NO function. This study aims to explore the role of zinc ions in NO-regulated adipocyte differentiation. We hypothesized that NO could increase intracellular Zn2+ level and then stimulate adipocyte differentiation. ZnCl2 and the NO donor, NONOate, were used to explore the effects of Zn2+ and NO on adipocyte differentiation. Regulatory mechanisms of NO on intracellular Zn2+ mobilization were determined by detection. Then, Zn2+-selective chelator TPEN was used to clarify the role of intracellular Zn2+ on NO-regulated adipocyte differentiation. Furthermore, the relationship between adipocyte size, Zn2+ level, and NOS expression in human subcutaneous fat tissue was elucidated. Results showed that both ZnCl2 and NO stimulated adipocyte differentiation in a dose-dependent manner. NO stimulated intracellular Zn2+ mobilization in adipocytes through the guanylate cyclase (GC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) pathway, and NO-stimulated adipocyte differentiation was Zn2+-dependent. In human subcutaneous adipose tissue, adipocyte size was negatively correlated with expression of eNOS. In conclusion, NO treatment stimulates intracellular Zn2+ mobilization through the GC/cGMP/PKG pathway, subsequently stimulating adipocyte differentiation.

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.

Potential Mechanism of Dingji Fumai Decoction Against Atrial Fibrillation Based on Network Pharmacology, Molecular Docking, and Experimental Verification Integration Strategy

Background: Dingji Fumai Decoction (DFD), a traditional herbal mixture, has been widely used to treat arrhythmia in clinical practice in China. However, the exploration of the active components and underlying mechanism of DFD in treating atrial fibrillation (AF) is still scarce.

Methods: Compounds of DFD were collected from TCMSP, ETCM, and literature. The targets of active compounds were explored using SwissTargetPrediction. Meanwhile, targets of AF were collected from DrugBank, TTD, MalaCards, TCMSP, DisGeNET, and OMIM. Then, the H-C-T-D and PPI networks were constructed using STRING and analyzed using CytoNCA. Meanwhile, VarElect was utilized to detect the correlation between targets and diseases. Next, Metascape was employed for systematic analysis of the mechanism of potential targets and protein complexes in treating AF. AutoDock Vina, Pymol, and Discovery Studio were applied for molecular docking. Finally, the main findings were validated through molecular biology experiments.

Results: A total of 168 active compounds and 1,093 targets of DFD were collected, and there were 89 shared targets between DFD and AF. H-C-T-D network showed the relationships among DFD, active compounds, targets, and AF. Three functional protein complexes of DFD were extracted from the PPI network. Further systematic analysis revealed that the regulation of cardiac oxidative stress, cardiac inflammation, and cardiac ion channels were the potential mechanism of DFD in treating AF. Addtionally, molecular docking verified the interactions between active compounds and targets. Finally, we found that DFD significantly increased the level of SIRT1 and reduced the levels of ACE, VCAM-1, and IL-6.

Conclusions: DFD could be utilized in treating AF through a complicated mechanism, including interactions between related active compounds and targets, promoting the explanation and understanding of the molecular biological mechanism of DFD in the treatment of AF.

Zn2+ influx activates ERK and Akt signaling pathways

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

Transcriptome Analysis of Myzus persicae to UV-B Stress

As an environmental stress factor, ultraviolet-B (UV-B) radiation directly affects the growth and development of Myzus persicae (Sulzer) (Homoptera: Aphididae). How M. persicae responds to UV-B stress and the molecular mechanisms underlying this adaptation remain unknown. Here, we analyzed transcriptome data for M. persicae following exposure to UV-B radiation for 30 min. We identified 758 significant differentially expressed genes (DEGs) following exposure to UV-B stress, including 423 upregulated and 335 downregulated genes. In addition, enrichment analysis using the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases illustrated that these DEGs are associated with antioxidation and detoxification, metabolic and protein turnover, immune response, and stress signal transduction. Simultaneously, these DEGs are closely related to the adaptability to UV-B stress. Our research can raise awareness of the mechanisms of insect responses to UV-B stress.

Non-Cell-Autonomous Regulation of Optic Nerve Regeneration by Amacrine Cells

Visual information is conveyed from the eye to the brain through the axons of retinal ganglion cells (RGCs) that course through the optic nerve and synapse onto neurons in multiple subcortical visual relay areas. RGCs cannot regenerate their axons once they are damaged, similar to most mature neurons in the central nervous system (CNS), and soon undergo cell death. These phenomena of neurodegeneration and regenerative failure are widely viewed as being determined by cell-intrinsic mechanisms within RGCs or to be influenced by the extracellular environment, including glial or inflammatory cells. However, a new concept is emerging that the death or survival of RGCs and their ability to regenerate axons are also influenced by the complex circuitry of the retina and that the activation of a multicellular signaling cascade involving changes in inhibitory interneurons - the amacrine cells (AC) - contributes to the fate of RGCs. Here, we review our current understanding of the role that interneurons play in cell survival and axon regeneration after optic nerve injury.

A novel fluorescence sensor for relay recognition of zinc ions and nitric oxide through fluorescence ‘off–on–off’ functionality

The fluorescent ‘off–on–off’ probe for relay recognition of Zn²⁺ and nitro oxide (NO) was constructed with the detection limit of 10⁻⁸ mol L⁻¹.

Ubiquinol-cytochrome c reductase core protein 1 overexpression protects H9c2 cardiac cells against mimic ischemia/reperfusion injury through PI3K/Akt/GSK-3β pathway

Ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) plays a key role in influencing mitochondrial function. Increasing evidence supports that UQCRC1 overexpression takes part in cardioprotection. However, it remains unclear about the signaling pathway mediating the protective role of UQCRC1 overexpression. Thus, the current study aimed to investigate the signaling pathway. Inhibition of PI3K completely abolished the protective effects of UQCRC1 overexpression on cell viability and mitochondrial membrane potential after OGD or hydrogen peroxide injury in H9c2 cardiac cells, while inhibition of ERK only partially abolished these effects. Moreover, UQCRC1 overexpression dramatically increased the phosphorylation of PI3K downstream signal molecules including Akt and GSK-3β. Finally, UQCRC1 overexpression upregulated the expression of antiapoptotic protein Bcl-2, downregulated the expression of proapoptotic protein Bax, decreased active caspase 3 expression and cell apoptosis, which were completely abolished by inhibition of PI3K. In conclusion, UQCRC1 overexpression protects H9c2 cardiac cells against mimic ischemia/reperfusion injury through mediating PI3K/Akt/GSK-3β pathway to regulate apoptosis-related proteins.

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.

Combinatorial roles of mitochondria and cGMP/PKG pathway in the generation of neuronal free Zn2+ under the presence of nitric oxide

BACKGROUND

Nitric oxide (NO), which possesses both protective and toxic properties, has been observed to have a complicated biphasic character within various types of tissues, including neuronal cells. NO was also found to cause the increase of another important signaling molecular Zn (termed as NZR). The molecular mechanism of NZR has been extensively investigated, but the source of Zn is present of a major candidate that is yet to be answered. The NO-protein kinase G (PKG) pathway, mitochondria, and metallothioneins (MTs), are all proposed to be the individual source of NZR. However, this hypothesis remains inconclusive. In this study, we examined the function of PKG signaling cascades, the mitochondria storage, and MT-1 during NZR of living PC12 cells.

METHODS

We applied live-cell imaging in combination with pharmacological inhibitors and activators as well as in vitro Zn assay to dissect the functions of the above candidates in NZR.

RESULTS

Two mechanisms, namely, mitochondria as the only Zn source and the opening of NO-PKG-dependent mitochondrial ATP-sensitive potassium channels (mKATP) as the key to releasing NO-induced increase in mitochondrial Zn, were proven to be the two critical paths of NZR in neuronal-related cells.

CONCLUSION

This new finding provides a reasonable explanation to previously existing and contradictory conclusions regarding the function of mitochondria/mKATP and PKG signaling on the molecular mechanism of NZR.

PCK1 Deficiency Shortens the Replicative Lifespan of Saccharomyces cerevisiae through Upregulation of PFK1

The cytosolic isozyme of phosphoenolpyruvate carboxykinase (PCK1) was the first rate-limiting enzyme in the gluconeogenesis pathway, which exerted a critical role in maintaining the blood glucose levels. PCK1 has been established to be involved in various physiological and pathological processes, including glucose metabolism, lipid metabolism, diabetes, and tumorigenesis. Nonetheless, the association of PCK1 with aging process and the detailed underlying mechanisms of PCK1 on aging are still far to be elucidated. Hence, we herein constructed the PCK1-deficient (pck1Δ) and PCK1 overexpression (PCK1 OE) Saccharomyces cerevisiae. The results unveiled that PCK1 deficiency significantly shortened the replicative lifespan (RLS) in the S. cerevisiae, while overexpression of PCK1 prolonged the RLS. Additionally, we noted that the ROS level was significantly enhanced in PCK1-deficient strain and decreased in PCK1 OE strain. Then, a high throughput analysis by deep sequencing was performed in the pck1Δ and wild-type strains, in an attempt to shed light on the effect of PCK1 on the lifespan of aging process. The data showed that the most downregulated mRNAs were enriched in the regulatory pathways of glucose metabolism. Fascinatingly, among the differentially expressed mRNAs, PFK1 was one of the most upregulated genes, which was involved in the glycolysis process and ROS generation. Thus, we further constructed the pfk1Δpck1Δ strain by deletion of PFK1 in the PCK1-deficient strain. The results unraveled that pfk1Δpck1Δ strain significantly suppressed the ROS level and restored the RLS of pck1Δ strain. Taken together, our data suggested that PCK1 deficiency enhanced the ROS level and shortened the RLS of S. cerevisiae via PFK1.

Expression profiling and bioinformatics analysis of circulating microRNAs in patients with acute myocardial infarction

OBJECTIVE

Acute Myocardial Infarction (AMI) is the most severe type of coronary atherosclerotic heart diseases. MiRNA is a class of endogenous noncoding small molecule RNA, which plays an important regulatory role in the development of some diseases.

METHODS

We examined the miRNA expression profiles in 16 patients with AMI compared with 6 non-AMI controls using RNA sequencing.

RESULTS

Compared with the miRNA expression profiles of non-AMI controls, a total of 181 differentially expressed miRNAs were discriminated in AMI patients, of which 96 upregulated miRNAs and 85 downregulated miRNAs. The top ten upregulated miRNAs were as follows: miR-449a-5p, miR-126-5p, miR-93-5p, miR-199a-3p, miR-4454, miR-6880-3p, miR-3135a, miR-548ad-5p, miR-4508, and miR-556-5p; while the top ten downregulated were as follows: miR-6805-5p, miR-1228-5p, miR-939-5p, miR-615-3p, miR-6780a-5p, miR-6857-3p, miR-5088-55p, miR-7155-3p, miR-184, and miR-4525. And the qRT-PCR results of differentially expressed miRNAs showed the same result as high-throughput sequencing data. For these 181 differentially expressed miRNAs, 19 841 target genes were predicted by GO analysis. The enrichment analysis revealed 2061 involved in biological processes, 353 in molecular function and 303 in cellular components. To identify biological pathways in AMI as compared to non-AMI, the target genes of differentially expressed miRNAs were mapped to the classical signal transduction pathway in KEGG, indicating that 214 classes were enriched. ROC analysis showed that the circulating miRNAs had the important value for AMI diagnosis and supported the previous conclusions that circulating miRNAs were effective to diagnose the AMI as a novel biomarker.

CONCLUSIONS

Our findings require further research to confirm. It may provide a meaningful reference for the diagnosis and treatment of AMI.

Mitochondria-Targeting Antioxidant Provides Cardioprotection through Regulation of Cytosolic and Mitochondrial Zn2+ Levels with Re-Distribution of Zn2+-Transporters in Aged Rat Cardiomyocytes

Aging is an important risk factor for cardiac dysfunction. Heart during aging exhibits a depressed mechanical activity, at least, through mitochondria-originated increases in ROS. Previously, we also have shown a close relationship between increased ROS and cellular intracellular free Zn²⁺ ([Zn²⁺]_i) in cardiomyocytes under pathological conditions as well as the contribution of some re-expressed levels of Zn²⁺-transporters for redistribution of [Zn²⁺]_i among suborganelles. Therefore, we first examined the cellular (total) [Zn²⁺] and then determined the protein expression levels of Zn²⁺-transporters in freshly isolated ventricular cardiomyocytes from 24-month rat heart compared to those of 6-month rats. The [Zn²⁺]_i in the aged-cardiomyocytes was increased, at most, due to increased ZIP7 and ZnT8 with decreased levels of ZIP8 and ZnT7. To examine redistribution of the cellular [Zn²⁺]_i among suborganelles, such as Sarco/endoplasmic reticulum, S(E)R, and mitochondria ([Zn²⁺]_SER and [Zn²⁺]_Mit), a cell model (with galactose) to mimic the aged-cell in rat ventricular cell line H9c2 was used and demonstrated that there were significant increases in [Zn²⁺]_Mit with decreases in [Zn²⁺]_SER. In addition, the re-distribution of these Zn²⁺-transporters were markedly changed in mitochondria (increases in ZnT7 and ZnT8 with no changes in ZIP7 and ZIP8) and S(E)R (increase in ZIP7 and decrease in ZnT7 with no changes in both ZIP8 and ZnT8) both of them isolated from freshly isolated ventricular cardiomyocytes from aged-rats. Furthermore, we demonstrated that cellular levels of ROS, both total and mitochondrial lysine acetylation (K-Acetylation), and protein-thiol oxidation were significantly high in aged-cardiomyocytes from 24-month old rats. Using a mitochondrial-targeting antioxidant, MitoTEMPO (1 µM, 5-h incubation), we provided an important data associated with the role of mitochondrial-ROS production in the [Zn²⁺]_i-dyshomeostasis of the ventricular cardiomyocytes from 24-month old rats. Overall, our present data, for the first time, demonstrated that a direct mitochondria-targeting antioxidant treatment can be a new therapeutic strategy during aging in the heart through a well-controlled [Zn²⁺] distribution among cytosol and suborganelles with altered expression levels of the Zn²⁺-transporters.

Intracellular Zn2+ transients modulate global gene expression in dissociated rat hippocampal neurons

Zinc (Zn²⁺) is an integral component of many proteins and has been shown to act in a regulatory capacity in different mammalian systems, including as a neurotransmitter in neurons throughout the brain. While Zn²⁺ plays an important role in modulating neuronal potentiation and synaptic plasticity, little is known about the signaling mechanisms of this regulation. In dissociated rat hippocampal neuron cultures, we used fluorescent Zn²⁺ sensors to rigorously define resting Zn²⁺ levels and stimulation-dependent intracellular Zn²⁺ dynamics, and we performed RNA-Seq to characterize Zn²⁺-dependent transcriptional effects upon stimulation. We found that relatively small changes in cytosolic Zn²⁺ during stimulation altered expression levels of 931 genes, and these Zn²⁺ dynamics induced transcription of many genes implicated in neurite expansion and synaptic growth. Additionally, while we were unable to verify the presence of synaptic Zn²⁺ in these cultures, we did detect the synaptic vesicle Zn²⁺ transporter ZnT3 and found it to be substantially upregulated by cytosolic Zn²⁺ increases. These results provide the first global sequencing-based examination of Zn²⁺-dependent changes in transcription and identify genes that may mediate Zn²⁺-dependent processes and functions.

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.

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.

Surfactants Improve Live Cell Imaging of Human Pancreatic Islets

OBJECTIVES

Newport Green is a zinc-specific fluorescent dye developed to monitor cellular zinc transport. In pancreatic islets with zinc-rich β-cells, Newport Green is expected to be useful as an islet-specific indicator for live imaging. However, the low penetration of Newport Green into islets hinders clear detection. The aim of this study was to develop a practical method of live islet imaging by using surfactants to enhance the penetration efficiency.

METHODS

Surfactants (F127, Tween 20, and Triton X-100) were co-incubated with Newport Green for fluorescent imaging of live isolated human islet and nonislet tissues. Toxicity, enhancement of Newport Green fluorescence, and effects on specificity to islets were examined.

RESULTS

Newport Green fluorescent intensity was increased after co-incubation with all surfactants tested (0.2-3.2 mM); however, surfactants were toxic to islets at high concentrations. Within the nontoxic range, high specificity to islets was observed when co-incubated with Tween 20 at 0.2-0.4 mM, compared with F127 and Triton X-100. This optimized range successfully distinguished islets from nonislet tissues using statistically calculated cutoff value of Newport Green fluorescent intensity.

CONCLUSIONS

Surfactants, particularly Tween 20 in the optimized range, effectively and selectively enhanced Newport Green fluorescence in live islets without increasing islet toxicity.

Cytosolic increased labile Zn2+ contributes to arrhythmogenic action potentials in left ventricular cardiomyocytes through protein thiol oxidation and cellular ATP depletion

Intracellular labile (free) Zn²⁺-level ([Zn²⁺]_i) is low and increases markedly under pathophysiological conditions in cardiomyocytes. High [Zn²⁺]_i is associated with alterations in excitability and ionic-conductances while exact mechanisms are not clarified yet. Therefore, we examined the elevated-[Zn²⁺]_i on some sarcolemmal ionic-mechanisms, which can mediate cardiomyocyte dysfunction. High-[Zn²⁺]_i induced significant changes in action potential (AP) parameters, including depolarization in resting membrane-potential and prolongations in AP-repolarizing phases. We detected also the time-dependent effects such as induction of spontaneous APs at the time of ≥ 3 min following [Zn²⁺]_i increases, a manner of cellular ATP dependent and reversible with disulfide-reducing agent dithiothreitol, DTT. High-[Zn²⁺]_i induced inhibitions in voltage-dependent K⁺-channel currents, such as transient outward K⁺-currents, I_to, steady-state currents, I_ss and inward-rectifier K⁺-currents, I_K1, reversible with DTT seemed to be responsible from the prolongations in APs. We, for the first time, demonstrated that lowering cellular ATP level induced significant decreaeses in both I_ss and I_K1, while no effect on I_to. However, the increased-[Zn²⁺]_i could induce marked activation in ATP-sensitive K⁺-channel currents, I_KATP, depending on low cellular ATP and thiol-oxidation levels of these channels. The mRNA levels of Kv4.3, Kv1.4 and Kv2.1 were depressed markedly with increased-[Zn²⁺]_i with no change in mRNA level of Kv4.2, while the mRNA level of I_KATP subunit, SUR2A was increased significantly with increased-[Zn²⁺]_i, being reversible with DTT. Overall we demonstrated that high-[Zn²⁺]_i, even if nanomolar levels, alters cardiac function via prolonged APs of cardiomyocytes, at most, due to inhibitions in voltage-dependent K⁺-currents, although activation of I_KATP is playing cardioprotective role, through some biochemical changes in cellular ATP- and thiol-oxidation levels. It seems, a well-controlled [Zn²⁺]_i can be novel therapeutic target for cardiac complications under pathological conditions including oxidative stress.

Network Analysis of Se-and Zn-related Proteins in the Serum Proteomics Expression Profile of the Endemic Dilated Cardiomyopathy Keshan Disease

Keshan disease (KD) is an endemic cardiomyopathy with high mortality. Selenium (Se) and zinc (Zn) deficiencies are closely related to KD. The molecular mechanism of KD pathogenesis is still unclear. There are only few studies on the interaction of trace elements and proteins associated with the pathogenesis of KD. In this study, isobaric tags for relative and absolute quantitation (iTRAQ)-coupled two-dimensional liquid chromatography tandem mass spectrometry (2DLC-MS/MS) technique analysis was used to analyze the differential expression of proteins from serum samples. Comparative Toxicogenomics Database (CTD) was used to screen Se- and Zn-associated proteins. Then, pathway and network analyses of Se- and Zn-associated proteins were constituted by Cytoscape ClueGO and GeneMANIA plugins. One hundred and five differentially expressed proteins were obtained by 2DLC-MS/MS, among them 19 Se- and 3 Zn-associated proteins. Fifty-two pathways were identified from ClueGO and 1 network from GeneMANIA analyses. The results showed that Se-associated proteins STAT3 and MAPK1 and Zn-associated proteins HIF1A and PARP1, the proteins involved in HIF-1 signaling pathway and apoptosis pathway, may play significant roles in the pathogenesis of KD. The approach of this study would be also beneficial for further dissecting molecular mechanism of other trace element-associated disease.

Zinc improves mitochondrial respiratory function and prevents mitochondrial ROS generation at reperfusion by phosphorylating STAT3 at Ser727

Serine 727 (Ser⁷²⁷) phosphorylation of STAT3 plays a role in the regulation of mitochondrial respiration. This study aimed to test if zinc could regulate mitochondrial respiration through phosphorylation of STAT3 at Ser⁷²⁷ in the setting of ischemia/reperfusion in the heart. Under normoxic conditions, treatment of isolated rat hearts with ZnCl₂ increased cytosolic STAT3 phosphorylation at Ser⁷²⁷ followed by phospho-STAT3 translocation to mitochondria. In isolated rat hearts subjected to 30 min regional ischemia followed by 20 min of reperfusion, ZnCl₂ given 5 min before the onset of reperfusion also increased mitochondrial phospho-STAT3. ZnCl₂ enhanced ERK phosphorylation and PD98059 reversed the effect of ZnCl₂ on STAT3 phosphorylation. ZnCl₂ improved the mitochondrial oxidative phosphorylation at reperfusion. This effect was abolished by STAT3S727A, a mutant in which Ser⁷²⁷ is replaced with alanine, in H9c2 cells subjected to hypoxia/reoxygenation. In addition, ZnCl₂ increased the mRNA level of the complex I subunit ND6, which was also reversed by STAT3S727A. Moreover, ZnCl₂ attenuated mitochondrial ROS generation and dissipation of mitochondrial membrane potential (ΔΨm) at reoxygenation through Ser⁷²⁷ phosphorylation. Finally, ZnCl₂ suppression of succinate dehydrogenase (SDH) activity upon the onset of reperfusion was nullified by the Ser⁷²⁷ mutation. In conclusion, zinc improves cardiac oxidative phosphorylation and inhibits mitochondrial ROS generation at reperfusion by increasing mitochondrial STAT3 phosphorylation at Ser⁷²⁷ via ERK. The preservation of ND6 mtDNA and the inhibition of SDH activity may account for the role of STAT3 in the beneficial action of zinc on the mitochondrial oxidative phosphorylation and ROS generation at reperfusion.

Intermittent hypoxia-generated ROS contributes to intracellular zinc regulation that limits ischemia/reperfusion injury in adult rat cardiomyocyte

Intermittent hypoxia (IH) has been shown to exert cardioprotective effects against ischemia/reperfusion (I/R) injury through the preservation of ion homeostasis. I/R dramatically elevated cytosolic Zn²⁺ and caused cardiomyocyte death. However, the role of IH exposure in the relationship between Zn²⁺ regulation and cardioprotection is still unclear. The aim of the present study was to study whether IH exposure could help in intracellular Zn²⁺ regulation, hence contributing to cardioprotection against I/R injury. Adult rat cardiomyocytes were exposed to IH (5% O₂, 5% CO₂ and balanced N₂) for 30 min followed by 30 min of normoxia (21% O₂, 5% CO₂ and balanced N₂). Changes in intracellular Zn²⁺ concentration were determined using a Zn²⁺-specific fluorescent dye, FluoZin-3 or RhodZin-3. Fluorescence was monitored under an inverted fluorescent or confocal microscope. The results demonstrated that I/R or 2,2'-dithiodipyridine (DTDP), a reactive disulphide compound, induced Zn²⁺ release from metallothioneins (MTs), subsequently causing cytosolic Zn²⁺ overload, which in turn increased intracellular Zn²⁺ entry into the mitochondria via a Ca²⁺ uniporter, hence inducing mitochondrial membrane potential loss, and eventually led to cell death. However, the cytosolic Zn²⁺ overload and cell death caused by I/R or DTDP was significantly reduced by treatment of cardiomyocytes with IH. The findings from this study suggest that IH might exert its cardioprotective effect through reducing the I/R-induced cytosolic Zn²⁺ overload and cell death in cardiomyocytes.

Zinc prevents mitochondrial superoxide generation by inducing mitophagy in the setting of hypoxia/reoxygenation in cardiac cells

Zinc plays a role in autophagy and protects cardiac cells from ischemia/reperfusion injury. This study aimed to test if zinc can induce mitophagy leading to attenuation of mitochondrial superoxide generation in the setting of hypoxia/reoxygenation (H/R) in cardiac cells. H9c2 cells were subjected to 4 h hypoxia followed by 2 h reoxygenation. Under normoxic conditions, treatments of cells with ZnCl₂ increased both the LC3-II/LC3-I ratio and GFP-LC3 puncta, implying that zinc induces autophagy. Further experiments showed that endogenous zinc is required for the autophagy induced by starvation and rapamycin. Zinc down-regulated TOM20, TIM23, and COX4 both in normoxic cells and the cells subjected to H/R, indicating that zinc can trigger mitophagy. Zinc increased ERK activity and Beclin1 expression, and zinc-induced mitophagy was inhibited by PD98059 and Beclin1 siRNA during reoxygenation. Zinc-induced Beclin1 expression was reversed by PD98059, implying that zinc promotes Beclin1 expression via ERK. In addition, zinc failed to induce mitophagy in cells transfected with PINK1 siRNA and stabilized PINK1 in mitochondria. Moreover, zinc-induced PINK1 stabilization was inhibited by PD98059. Finally, zinc prevented mitochondrial superoxide generation and dissipation of mitochondrial membrane potential (ΔΨ_m) at reoxygenation, which was blocked by both the Beclin1 and PINK1 siRNAs, suggesting that zinc prevents mitochondrial oxidative stress through mitophagy. In summary, zinc induces mitophagy through PINK1 and Beclin1 via ERK leading to the prevention of mitochondrial superoxide generation in the setting of H/R. Clearance of damaged mitochondria may account for the cardioprotective effect of zinc on H/R injury.

Roles of Endoplasmic Reticulum Stress in NECA-Induced Cardioprotection against Ischemia/Reperfusion Injury

OBJECTIVE

This study aimed to investigate whether the nonselective A2 adenosine receptor agonist NECA induces cardioprotection against myocardial ischemia/reperfusion (I/R) injury via glycogen synthase kinase 3β (GSK-3β) and the mitochondrial permeability transition pore (mPTP) through inhibition of endoplasmic reticulum stress (ERS).

METHODS AND RESULTS

H9c2 cells were exposed to H2O2 for 20 minutes. NECA significantly prevented H2O2-induced TMRE fluorescence reduction, indicating that NECA inhibited the mPTP opening. NECA blocked H2O2-induced GSK-3β phosphorylation and GRP94 expression. NECA increased GSK-3β phosphorylation and decreased GRP94 expression, which were prevented by both ERS inductor 2-DG and PKG inhibitor KT5823, suggesting that NECA may induce cardioprotection through GSK-3β and cGMP/PKG via ERS. In isolated rat hearts, both NECA and the ERS inhibitor TUDCA decreased myocardial infarction, increased GSK-3β phosphorylation, and reversed GRP94 expression at reperfusion, suggesting that NECA protected the heart by inhibiting GSK-3β and ERS. Transmission electron microscopy showed that NECA and TUDCA reduced mitochondrial swelling and endoplasmic reticulum expansion, further supporting that NECA protected the heart by preventing the mPTP opening and ERS.

CONCLUSION

These data suggest that NECA prevents the mPTP opening through inactivation of GSK-3β via ERS inhibition. The cGMP/PKG signaling pathway is responsible for GSK-3β inactivation by NECA.

Impact of Labile Zinc on Heart Function: From Physiology to Pathophysiology

Zinc plays an important role in biological systems as bound and histochemically reactive labile Zn²⁺. Although Zn²⁺ concentration is in the nM range in cardiomyocytes at rest and increases dramatically under stimulation, very little is known about precise mechanisms controlling the intracellular distribution of Zn²⁺ and its variations during cardiac function. Recent studies are focused on molecular and cellular aspects of labile Zn²⁺ and its homeostasis in mammalian cells and growing evidence clarified the molecular mechanisms underlying Zn²⁺-diverse functions in the heart, leading to the discovery of novel physiological functions of labile Zn²⁺ in parallel to the discovery of subcellular localization of Zn²⁺-transporters in cardiomyocytes. Additionally, important experimental data suggest a central role of intracellular labile Zn²⁺ in excitation-contraction coupling in cardiomyocytes by shaping Ca²⁺ dynamics. Cellular labile Zn²⁺ is tightly regulated against its adverse effects through either Zn²⁺-transporters, Zn²⁺-binding molecules or Zn²⁺-sensors, and, therefore plays a critical role in cellular signaling pathways. The present review summarizes the current understanding of the physiological role of cellular labile Zn²⁺ distribution in cardiomyocytes and how a remodeling of cellular Zn²⁺-homeostasis can be important in proper cell function with Zn²⁺-transporters under hyperglycemia. We also emphasize the recent investigations on Zn²⁺-transporter functions from the standpoint of human heart health to diseases together with their clinical interest as target proteins in the heart under pathological condition, such as diabetes.

Overexpression of Ubiquinol-Cytochrome c Reductase Core Protein 1 May Protect H9c2 Cardiac Cells by Binding with Zinc

In several recent studies, proteomics analyses suggest that increase of ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) is cardio-protective. However, direct evidence for this effect has not yet been obtained. Thus, the current study aimed to determine this effect and the mechanism underlying this effect. The results showed that overexpression of UQCRC1 protected H9c2 cardiac cells against in vitro simulated ischemia-reperfusion by maintaining mitochondrial membrane potential and suppressing the expression of caspase-3. These protective effects were significantly enhanced by exogenous Zn²⁺ but completely abolished by Zn²⁺-selective chelator TPEN. Furthermore, the upregulation of UQCRC1 reduced the concentration of free Zn²⁺ in mitochondria, whereas the downregulation of UQCRC1 increased the concentration of free Zn²⁺ in mitochondria. In conclusion, the overexpression of UQCRC1 can protect H9c2 cardiac cells against simulated ischemia/reperfusion, and this cardio-protective effect is likely mediated by zinc binding.

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.

Determination of Islet Viability Using a Zinc-Specific Fluorescent Dye and a Semiautomated Assessment Method

Islet transplantation is an effective therapy that allows the achievement of insulin independence in patients with type 1 diabetes (T1D). To ensure successful transplantation, islet viability and function are of great importance. Viability assessments most often use fluorescein diacetate (FDA)/propidium iodide (PI) staining. However, results using this method often do not correlate well with graft function. Because FDA nonspecifically penetrates all cells present in the islet preparation, including islets and contaminating acinar cells, its use often complicates viability assessments of the overall cell population. Furthermore, the manual method for determining viability percentages is highly subjective. Shortcomings of the conventional islet viability assay can be potentially improved by staining cells with Newport Green (NG). NG, is a zinc-specific fluorescent dye that specifically reacts with zinc-rich β cells. Two kinds of NG dyes, NG-DCF and NG-PDX, are currently available. We examined the zinc specificity of these NG dyes and compared NG staining with traditional FDA staining to explore the potential of NG dyes to improve islet viability assessment. Of the two NGs tested, NG-DCF showed the higher specificity toward a β-cell line as well as human islets. NG-DCF accurately identified the islet area, even in low-purity islets, while neither FDA nor NG-PDX did. Although NG-DCF staining required a longer incubation time, the addition of poloxamer F127 and incubation at 37°C allowed viability assessment to take place within 30 min. Unlike FDA/PI staining, NG-DCF/PI staining allowed for islet-specific assessment. We also introduced a semiautomated measurement to determine NG-DCF/PI staining results, which enabled us to obtain objective and reproducible results. NG-DCF/PI staining is easy and reliable, and this method permits highly objective islet-specific viability assessments.

Newport Green, a fluorescent sensor of weakly bound cellular Zn(2+): competition with proteome for Zn(2)

Newport Green (NPG) is a recognized sensor of cellular Zn(2+) that displays fluorescence enhancement upon binding to Zn(2+). Because of its modest affinity for Zn(2+), the extent of its capacity to bind cellular Zn(2+) is unclear. The present study investigated the range of reactivity of NPG(ESTER) with cells, isolated (Zn)-proteome, and model Zn-proteins. The sensor accumulated in pig kidney LLC-PK1 cells and was slowly (>40 min) hydrolyzed to the fluorescent, acid form, NPG(ACID). The powerful, cell permeant Zn(2+) chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)-ethane-1,2-diamine (TPEN) failed to quench the growing fluorescence emission, indicating that Zn-NPG(ACID) had not formed and NPG-Zn-protein adduct species probably were not present. Furthermore, NPG(ACID) did not bind to Zn-carbonic anhydrase or Zn-alcohol dehydrogenase, two proteins that form adducts with some other sensors. Strikingly, most of the NPG(ACID) that had been converted from NPG(ESTER) was detected in the extracellular medium not the cells. As a result, after cells were incubated with NPG(ESTER) and then Zn-pyrithione to raise the internal concentration of mobile Zn(2+), Zn-NPG(ACID) was only observed in the external medium. Residual cellular NPG(ACID) was unable to bind extra intracellular Zn(2+) delivered by pyrithione. Proteome isolated from the sonicated cell supernatant was also unreactive with NPG(ACID). Titration of proteome or glutathione with Zn(2+) in the presence of NPG(ACID) revealed that NPG(ACID) only weakly competes for mobile Zn(2+) in the presence of these cellular components. In addition, when proteomic Zn(2+) was released by a nitric oxide donor or N-ethyl-maleimide, little Zn(2+) was detected by NPG(ACID). However, exposure to nitric oxide independently enhanced the fluorescence properties of NPG(ACID). Thus, the biochemical properties of NPG related to cellular Zn(2+) chelation deepen the question of how it functions as a Zn(2+) sensor.

Intracellular Zn(2+) Increase in Cardiomyocytes Induces both Electrical and Mechanical Dysfunction in Heart via Endogenous Generation of Reactive Nitrogen Species

Oxidants increase intracellular free Zn(2+) concentration ([Zn(2+)]i) in ventricular myocytes, which contributes to oxidant-induced alterations in excitation-contraction coupling (ECC). However, it is not clear whether increased [Zn(2+)]i in cardiomyocytes via increased reactive nitrogen species (RNS) has a role on heart function under pathological conditions, such as hyperglycemia. In this study, first we aimed to investigate the role of increased [Zn(2+)]i under in vitro condition in the development of both electrical and mechanical dysfunction of isolated papillary muscle strips from rat heart via exposed samples to a Zn(2+)-ionophore (Zn-pyrithione; 1 μM) for 20 min. Under simultaneous measurement of intracellular action potential and contractile activity in these preparations, Zn-pyrithione exposure caused marked prolongation in action potential repolarization phase and slowdown in both contraction and relaxation rates of twitch activity. Second, in order to demonstrate an association between increased [Zn(2+)]i and increased RNS, we monitored intracellular [Zn(2+)]i under an acute exposure of nitric oxide (NO) donor sodium nitroprusside, SNP, in freshly isolated quiescent cardiomyocytes loaded with FluoZin-3. Resting level of free Zn(2+) is significantly higher in cardiomyocytes under hyperglycemic condition compared to those of the controls, which seems to be associated with increased level of RNS production in hyperglycemic cardiomyocytes. Western blot analysis showed that Zn-pyrithione exposure induced a marked decrease in the activity of protein phosphatase 1 and 2A, member of macromolecular protein complex of cardiac ryanodine receptors, RyR2, besides significant increase in the phosphorylation level of extracellular signal-regulated kinase1/2 as a concentration-dependent manner. Overall, the present data demonstrated that there is a cross-relationship between increased RNS production and increased [Zn(2+)]i level in cardiomyocytes under pathological conditions such as hyperglycemia.

Zinc and the prooxidant heart failure phenotype

Neurohormonal activation with attendant aldosteronism contributes to the clinical appearance of congestive heart failure (CHF). Aldosteronism is intrinsically coupled to Zn and Ca dyshomeostasis, in which consequent hypozincemia compromises Zn homeostasis and Zn-based antioxidant defenses that contribute to the CHF prooxidant phenotype. Ionized hypocalcemia leads to secondary hyperparathyroidism with parathyroid hormone-mediated Ca overloading of diverse cells, including cardiomyocytes. When mitochondrial Ca overload exceeds a threshold, myocyte necrosis follows. The reciprocal regulation involving cytosolic free [Zn]i as antioxidant and [Ca]i as prooxidant can be uncoupled in favor of Zn-based antioxidant defenses. Increased [Zn]i acts as a multifaceted antioxidant by: (1) inhibiting Ca entry through L-type channels and hence cardioprotectant from the Ca-driven mitochondriocentric signal-transducer effector pathway to nonischemic necrosis, (2) serving as catalytic regulator of Cu/Zn-superoxide dismutase, and (3) activating its cytosolic sensor, metal-responsive transcription factor that regulates the expression of relevant antioxidant defense genes. Albeit present in subnanomolar range, increased cytosolic free [Zn]i enhances antioxidant capacity that confers cardioprotection. It can be achieved exogenously by ZnSO4 supplementation or endogenously using a β3-receptor agonist (eg, nebivolol) that enhances NO generation to release inactive cytosolic Zn bound to metallothionein. By recognizing the pathophysiologic relevance of Zn dyshomeostasis in the prooxidant CHF phenotype and by exploiting the pharmacophysiologic potential of [Zn]i as antioxidant, vulnerable cardiomyocytes under assault from neurohormonal activation can be protected and the myocardium spared from adverse structural remodeling.

Nitric oxide signaling modulates synaptic inhibition in the superior paraolivary nucleus (SPN) via cGMP-dependent suppression of KCC2

Glycinergic inhibition plays a central role in the auditory brainstem circuitries involved in sound localization and in the encoding of temporal action potential firing patterns. Modulation of this inhibition has the potential to fine-tune information processing in these networks. Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential. Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons. Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing. Regulating inhibitory strength, through cGMP-dependent changes in the efficacy of KCC2 in the target neuron provides a postsynaptic mechanism for rapidly controlling the inhibitory drive, without altering the timing or pattern of the afferent spike train. Therefore, this NO-mediated suppression of KCC2 can modulate inhibition in one target nucleus (SPN), without influencing inhibitory strength of other target nuclei (MSO, LSO) even though they are each receiving collaterals from the same afferent nucleus (a projection from the medial nucleus of the trapezoid body, MNTB).

Antiobesity pharmacotherapy: new drugs and emerging targets

Obesity is a growing pandemic, and related health and economic costs are staggering. Pharmacotherapy, partnered with lifestyle modifications, forms the core of current strategies to reduce the burden of this disease and its sequelae. However, therapies targeting weight loss have a significant history of safety risks, including cardiovascular and psychiatric events. Here, evolving strategies for developing antiobesity therapies, including targets, mechanisms, and developmental status, are highlighted. Progress in this field is underscored by Belviq (lorcaserin) and Qsymia (phentermine/topiramate), the first agents in more than 10 years to achieve regulatory approval for chronic weight management in obese patients. On the horizon, novel insights into metabolism and energy homeostasis reveal guanosine 3',5'-cyclic monophosphate (cGMP) signaling circuits as emerging targets for antiobesity pharmacotherapy. These innovations in molecular discovery may elegantly align with practical off-the-shelf approaches, leveraging existing approved drugs that modulate cGMP levels for the management of obesity.

Dual role of cyclic GMP in cardiac cell survival

It is well known that cyclic guanosine 3',5'-monophosphate plays an important role in cardioprotection against ischemia/reperfusion injury through activation of protein kinase G (PKG). We found that cGMP prevents the mitochondrial permeability transition pore (mPTP) opening by inactivating glycogen synthase kinase 3β (GSK-3β) via protein kinase G (PKG) in cardiac H9c2 cells. While GSK-3β and its major upstream regulator phosphoinositide 3-kinase (PI3K)/Akt are critical for acute cardioprotection, an excessive activation of PI3K/Akt or GSK-3β inactivation can also lead to cardiac hypertrophy. Here, we show that cGMP not only inactivates GSK-3β through PKG (this leads to acute cardioprotection) but also negatively regulates Akt activity (this may lead to prevention of hypertrophy and heart failure, and the regulation of NO synthesis) in cardiac cells. We further found that the negative regulatory effect of cGMP on Akt activity is not mediated by PKG but may be through up-regulation of protein phosphatase PP2A activity. We propose that cGMP is a versatile signal with dual beneficial role in cardiac cell survival.

cGMP-dependent protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes-prkg1 and prkg2-code for cGKs, namely, cGKI and cGKII. In mammals, two isozymes, cGKIα and cGKIβ, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxtaglomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all, signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondral bone growth. This chapter focuses on the involvement of cGKs in cardiovascular and non-cardiovascular processes including cell growth and metabolism.

Sensor specific imaging of proteomic Zn2+ with zinquin and TSQ after cellular exposure to N-ethylmaleimide

The impact of the thiol binding reagent N-ethylmaleimide (NEM) on proteomic Zn(2+) availability was investigated in rat glioma cells. Zinquin (ZQ) or TSQ, two related fluorescent sensors, were used to observe reactive Zn(2+). Control cells contained proteomic Zn(2+) but no detectable low molecular weight (LMW) Zn(2+). With either sensor, basal cellular fluorescence emission centered near 470 nm, indicative of sensor-Zn-proteins. ZQ sequestered 13% of proteomic Zn(2+) as Zn(ZQ)(2); TSQ reacted only with the Zn-proteome. NEM (100 μM) abolished LMW thiols, including glutathione (GSH) and lowered proteomic sulfhydryl content about 30%. In ZQ-treated cells, NEM exposure enhanced fluorescent intensity and the formation of Zn(ZQ)(2) (λ(MAX), 492 nm). Cells incubated with TSQ and NEM also displayed increased fluorescence without a spectral shift in wavelength maximum, consistent with increased formation of TSQ-Zn-protein adducts but not Zn(TSQ)(2). In neither experiment was Zn(2+) lost from cells. NEM altered Zn(2+) accessibility to sensors in membrane-nuclear and cytosolic fractions, but Zn(ZQ)(2) was only generated in the cytosol. Similar results were obtained when cell supernatant replaced cells. In contrast, when isolated proteome was reacted with ZQ and 100 μM NEM in the absence of GSH, 70% of the proteomic thiols underwent reaction. As a consequence, most of the ZQ-Zn-protein adducts were converted to Zn(ZQ)(2). Substituting TSQ for ZQ, only increased TSQ-Zn-proteins were observed. Evidently, the results of imaging cells with Zn(2+) sensors are dependent upon the specific chemical properties of the sensors and can only be understood after detailed chemical analysis.

Inhibition of phosphodiesterases leads to prevention of the mitochondrial permeability transition pore opening and reperfusion injury in cardiac H9c2 cells

PURPOSE

We tested if inhibition of phosphodiesterases (PDEs) with IBMX (1-methyl-3-isobutylxanthine) can modulate the mitochondrial permeability transition pore (mPTP) opening by inactivating glycogen synthase kinase 3β (GSK-3β).

METHODS

H9c2 cells were exposed to 600 μM H(2)O(2) for 20 min to cause the mPTP opening. Mitochondrial membrane potential (ΔΨm) was assessed by imaging cells loaded with tetramethylrhodamine ethyl ester (TMRE). Cell viability was measured with propidium iodide (PI) fluorometry using a fluorescence reader. Ischemia/reperfusion injury was induced by exposing cells to ischemic solution for 90 min followed by 30 min of reperfusion.

RESULTS

IBMX reduced loss of ΔΨm caused by H(2)O(2), indicating that inhibition of PDEs can prevent the mPTP opening. However, IBMX could not inhibit the pore opening in cells transfected with the constitutively active GSK-3β (GSK-3β-S9A) mutant, suggesting a critical role of GSK-3β in the action of IBMX. IBMX also reduced reperfusion injury in a GSK-3β dependent manner. In support, IBMX increased GSK-3β phosphorylation at Ser(9), an effect that was reversed by both the PKA inhibitor H89 and the PKG inhibitor KT5823. In support, IBMX activated both PKA and PKG. IBMX failed to prevent the loss of ΔΨm in the presence of H89 or PKA siRNA. Similarly, both KT5823 and PKG siRNA reversed the protective effect of IBMX.

CONCLUSION

Inhibition of PDEs prevents the mPTP opening by inactivating GSK-3β through PKA and PKG. GSK-3β is a common downstream target of PKA and PKG. Inhibition of PDEs may be a useful approach to prevent reperfusion injury.

Biochemistry of mobile zinc and nitric oxide revealed by fluorescent sensors

Biological mobile zinc and nitric oxide (NO) are two prominent examples of inorganic compounds involved in numerous signaling pathways in living systems. In the past decade, a synergy of regulation, signaling, and translocation of these two species has emerged in several areas of human physiology, providing additional incentive for developing adequate detection systems for Zn(II) ions and NO in biological specimens. Fluorescent probes for both of these bioinorganic analytes provide excellent tools for their detection, with high spatial and temporal resolution. We review the most widely used fluorescent sensors for biological zinc and nitric oxide, together with promising new developments and unmet needs of contemporary Zn(II) and NO biological imaging. The interplay between zinc and nitric oxide in the nervous, cardiovascular, and immune systems is highlighted to illustrate the contributions of selective fluorescent probes to the study of these two important bioinorganic analytes.

Intracellular free zinc during cardiac excitation-contraction cycle: calcium and redox dependencies

AIMS

Zinc exists in biological systems as bound and histochemically reactive free Zn(2+). It is an essential structural constituent of many proteins, including enzymes from cellular signalling pathways, in which it functions as a signalling molecule. In cardiomyocytes at rest, Zn(2+) concentration is in the nanomolar range. Very little is known about precise mechanisms controlling the intracellular distribution of Zn(2+) and its variations during cardiac function.

METHODS AND RESULTS

Live-cell detection of intracellular Zn(2+) has become feasible through the recent development of Zn(2+)-sensitive and -selective fluorophores able to distinguish Zn(2+) from Ca(2+). Here, in freshly isolated rat cardiomyocytes, we investigated the rapid changes in Zn(2+) homeostasis using the Zn(2+)-specific fluorescent dye, FluoZin-3, in comparison to Ca(2+)-dependent fluo-3 fluorescence. Zn(2+) sparks and Zn(2+) transients, in quiescent and electrically stimulated cardiomyocytes, respectively, were visualized in a similar manner to known rapid Ca(2+) changes. Both Zn(2+) sparks and Zn(2+) transients required Ca(2+) entry. Inhibiting the sarcoplasmic reticulum Ca(2+) release or increasing the Ca(2+) load in a low-Na(+) solution suppressed or increased Zn(2+) movements, respectively. Mitochondrial inhibitors slightly reduced both Zn(2+) sparks and Zn(2+) transients. Oxidation by H₂O₂ facilitated and acidic pH inhibited the Ca(2+)-dependent Zn(2+) release.

CONCLUSION

It is proposed that Zn(2+) release during the cardiac cycle results mostly from intracellular free Ca(2+) increase, triggering production of reactive oxygen species that induce changes in metal-binding properties of metallothioneins and other redox-active proteins, aside from ionic exchange on these proteins.

The protective effects of Polygonum multiflorum stilbeneglycoside preconditioning in an ischemia/reperfusion model of HUVECs

AIM

To investigate the protective effects of preconditioning human umbilical vein endothelial cells (HUVECs) with Polygonum multiflorum stilbeneglycoside (PMS) under anoxia/reoxygenation (A/R), and the mechanism of protection.

METHODS

Prior to A/R, HUVECs were incubated with PMS (0.6 x 10(-11), 1.2 x 10(-11), or 2.4 x 10(-11) mol/L) for 3 h. Cell injury was subsequently evaluated by measuring cell viability with an MTT assay and lactate dehydrogenase (LDH) release, whereas lipid peroxidation was assayed by measuring malondialdehyde (MDA) content. Antioxidant capacity was quantified by superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity. Nitric oxide (NO) production was determined by nitrite accumulation. Endothelial NO synthase (eNOS) and inducible NOS (iNOS) protein expression was detected by Western blotting. Guanylate cyclase activity and cyclic GMP (cGMP) activity were assessed by an enzyme immunoassay kit.

RESULTS

PMS incubation attenuated A/R-induced injury in a concentration-dependent manner, as evidenced by a decrease in LDH activity and an increase in cell viability. PMS exerted its protective effect by inhibiting the A/R-mediated elevation of MDA content, as well as by promoting the recovery of SOD and GSH-Px activities. Additionally, PMS incubation enhanced NO and cGMP formation by increasing iNOS expression and guanylate cyclase activity. The protective effects of PMS were markedly attenuated by NOS inhibitor L-NAME, soluble guanylate cyclase inhibitor ODQ or PKG inhibitor KT5823.

CONCLUSION

PMS preincubation resulted in the enhancement of antioxidant activity and anti-lipid peroxidation. The NO/cGMP/cGMP-dependent protein kinase (PKG) signaling pathway was involved in the effect of PMS on HUVECs.

Stimulation of neuronal KATP channels by cGMP-dependent protein kinase: involvement of ROS and 5-hydroxydecanoate-sensitive factors in signal transduction

The ATP-sensitive potassium (K(ATP)) channel couples intracellular metabolic state to membrane excitability. Recently, we demonstrated that neuronal K(ATP) channels are functionally enhanced by activation of a nitric oxide (NO)/cGMP/cGMP-dependent protein kinase (PKG) signaling cascade. In this study, we further investigated the intracellular mechanism underlying PKG stimulation of neuronal K(ATP) channels. By performing single-channel recordings in transfected HEK293 and neuroblastoma SH-SY5Y cells, we found that the increase of Kir6.2/SUR1 (i.e., the neuronal-type K(ATP)) channel currents by PKG activation in cell-attached patches was diminished by 5-hydroxydecanoate (5-HD), an inhibitor of the putative mitochondrial K(ATP) channel; N-(2-mercaptopropionyl)glycine, a reactive oxygen species (ROS) scavenger, and catalase, a hydrogen peroxide (H(2)O(2))-decomposing enzyme. These reagents also ablated NO-induced K(ATP) channel stimulation and prevented the shifts in the single-channel open- and closed-time distributions resulting from PKG activation and NO induction. Bath application of H(2)O(2) reproduced PKG stimulation of Kir6.2/SUR1 but did not activate tetrameric Kir6.2LRKR368/369/370/371AAAA channels. Moreover, neither the PKG activator nor exogenous H(2)O(2) was able to enhance the function of K(ATP) channels in the presence of Ca(2+) chelators and calmodulin antagonists, whereas the stimulatory effect of H(2)O(2) was unaffected by 5-HD. Altogether, in this report we provide novel evidence that activation of PKG stimulates neuronal K(ATP) channels by modulating intrinsic channel gating via a 5-HD-sensitive factor(s)/ROS/Ca(2+)/calmodulin signaling pathway that requires the presence of the SUR1 subunit. This signaling pathway may contribute to neuroprotection against ischemic injury and regulation of neuronal excitability and neurotransmitter release by modulating the function of neuronal K(ATP) channels.

The critical role of intracellular zinc in adenosine A(2) receptor activation induced cardioprotection against reperfusion injury

Exogenous zinc can protect cardiac cells from reperfusion injury, but the exact roles of endogenous zinc in the pathogenesis of reperfusion injury and in adenosine A(2) receptor activation-induced cardioprotection against reperfusion injury remain unknown. Adenosine A(1)/A(2) receptor agonist 5'-(N-ethylcarboxamido) adenosine (NECA) given at reperfusion reduced infarct size in isolated rat hearts subjected to 30min ischemia followed by 2h of reperfusion. This effect of NECA was partially but significantly blocked by the zinc chelator N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN), and ZnCl(2) given at reperfusion mimicked the effect of NECA by reducing infarct size. Total tissue zinc concentrations measured with inductively coupled plasma optical emission spectroscopy (ICPOES) were decreased upon reperfusion in rat hearts and this was reversed by NECA. NECA increased intracellular free zinc during reperfusion in the heart. Confocal imaging study showed a rapid increase in intracellular free zinc in isolated rat cardiomyocytes treated with NECA. Further experiments revealed that NECA increased total zinc levels upon reperfusion in mitochondria isolated from isolated hearts. NECA attenuated mitochondrial swelling upon reperfusion in isolated hearts and this was inhibited by TPEN. Similarly, NECA prevented the loss of mitochondrial membrane potential (DeltaPsim) caused by oxidant stress in cardiomyocytes. Finally, both NECA and ZnCl(2) inhibited the mitochondrial metabolic activity. NECA-induced cardioprotection against reperfusion injury is mediated by intracellular zinc. NECA prevents reperfusion-induced zinc loss and relocates zinc to mitochondria. The inhibitory effects of zinc on both the mPTP opening and the mitochondrial metabolic activity may account for the cardioprotective effect of NECA.