Selenium prevents diabetes-induced alterations in [Zn2+]iand metallothionein level of rat heart via restoration of cell redox cycle

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.

The role of Zn2+ in shaping intracellular Ca2+ dynamics in the heart

Increasing evidence suggests that Zn2+ acts as a second messenger capable of transducing extracellular stimuli into intracellular signaling events. The importance of Zn2+ as a signaling molecule in cardiovascular functioning is gaining traction. In the heart, Zn2+ plays important roles in excitation-contraction (EC) coupling, excitation-transcription coupling, and cardiac ventricular morphogenesis. Zn2+ homeostasis in cardiac tissue is tightly regulated through the action of a combination of transporters, buffers, and sensors. Zn2+ mishandling is a common feature of various cardiovascular diseases. However, the precise mechanisms controlling the intracellular distribution of Zn2+ and its variations during normal cardiac function and during pathological conditions are not fully understood. In this review, we consider the major pathways by which the concentration of intracellular Zn2+ is regulated in the heart, the role of Zn2+ in EC coupling, and discuss how Zn2+ dyshomeostasis resulting from altered expression levels and efficacy of Zn2+ regulatory proteins are key drivers in the progression of cardiac dysfunction.

Overexpression of Slc30a7/ZnT7 increases the mitochondrial matrix levels of labile Zn2+ and modifies histone modification in hyperinsulinemic cardiomyoblasts

BACKGROUND

Cellular free Zn²⁺ concentrations ([Zn²⁺]) are primarily coordinated by Zn²⁺-transporters, although their roles are not well established in cardiomyocytes. Since we previously showed the important contribution of a Zn²⁺-transporter ZnT7 to [Zn²⁺]_i regulation in hyperglycemic cardiomyocytes, here, we aimed to examine a possible regulatory role of ZnT7 not only on [Zn²⁺]_i but also both the mitochondrial-free Zn²⁺ and/or Ca²⁺ in cardiomyocytes, focusing on the contribution of its overexpression to the mitochondrial function.

METHODS

We mimicked either hyperinsulinemia (by 50-μM palmitic acid, PA-cells, for 24-h) or overexpressed ZnT7 (ZnT7OE-cells) in H9c2 cardiomyoblasts.

RESULTS

Opposite to PA-cells, the [Zn²⁺]_i in ZnT7OE-cells was not different from untreated H9c2-cells. An investigation of immunofluorescence imaging by confocal microscopy demonstrated a ZnT7 localization on the mitochondrial matrix. We demonstrated the ZnT7 localization on the mitochondrial matrix by using immunofluorescence imaging. Later, we determined the mitochondrial levels of [Zn²⁺]_Mit and [Ca²⁺]_Mit by using the Zn²⁺ and Ca²⁺ sensitive FRET probe and a Ca²⁺-sensitive dye Fluo4, respectively. The [Zn²⁺]_Mit was found to increase significantly in ZnT7OE-cells, similar to the PA-cells while no significant changes in the [Ca²⁺]_Mit in these cells. To examine the contribution of ZnT7 overexpression on the mitochondria function, we determined the level of reactive oxygen species (ROS) and the mitochondrial membrane potential (MMP) in these cells in comparison to the PA-cells. There were significantly increased production of ROS and depolarization in MMP and increases in marker proteins of mitochondria-associated apoptosis and autophagy in ZnT7-OE cells, similar to the PA-cells, parallel to increases in K-acetylation. Moreover, we determined significant increases in trimethylation of histone H3 lysine27, H3K27me3, and the mono-methylation of histone H3 lysine36, H3K36 in the ZnT7OE-cells, demonstrating the role of [Zn²⁺]_Mit in epigenetic regulation of cardiomyocytes under hyperinsulinemia through histone modification.

CONCLUSIONS

Overall, our data have shown an important contribution of high expression of ZnT7-OE, through its buffering and muffling capacity in cardiomyocytes, on the regulation of not only [Zn²⁺_]i but also both [Zn²⁺]_Mit and [Ca²⁺]_Mit affecting mitochondria function, in part, via histone modification.

ZIP14 is involved in iron deposition and triggers ferroptosis in diabetic nephropathy

Ferroptosis is caused by lipid peroxidation and iron accumulation and can cause cell death. Abnormally expressed iron transporters are involved in ferroptosis in a variety of diseases. ZRT/IRT-like protein 14 (ZIP14) is a transport protein that can mediate cellular uptake of iron, zinc and manganese. Herein, we have tested the hypothesis that the divalent metal transporter ZIP14 is involved in the initiation of ferroptosis in diabetic nephropathy (DN). DN was induced in eight-week old male rats by streptozotocin (STZ) before analysis of the degree of renal tubular injury. In addition, an in vitro model of DN in HK2 cells was used. We showed that ZIP14 was upregulated and Fe2+ levels increased both in vivo and in vitro. Expression of glutathione peroxidase 4 (GPX4) and the level of glutathione (GSH) were reduced, whereas that of malondialdehyde (MDA) increased. Ferrostatin-1(Fer-1) treatment reduced the expression of ZIP14 and the levels of Fe2+ and MDA, which is consistent with ferroptosis. Fer-1 improved kidney function in DN rats. This was characterized by urine levels of protein-to-creatinine ratio, α 1-microglobulin and N-acetyl-β-D-glucosaminidase. Our study demonstrates a novel role for ZIP14 in diabetic kidney injury mediated by ferroptosis, and suggests a potential new therapeutic approach for the treatment of diabetic nephropathy.

Self-Assembling Nucleic Acid Nanostructures Functionalized with Aptamers

Researchers have worked for many decades to master the rules of biomolecular design that would allow artificial biopolymer complexes to self-assemble and function similarly to the diverse biochemical constructs displayed in natural biological systems. The rules of nucleic acid assembly (dominated by Watson-Crick base-pairing) have been less difficult to understand and manipulate than the more complicated rules of protein folding. Therefore, nucleic acid nanotechnology has advanced more quickly than de novo protein design, and recent years have seen amazing progress in DNA and RNA design. By combining structural motifs with aptamers that act as affinity handles and add powerful molecular recognition capabilities, nucleic acid-based self-assemblies represent a diverse toolbox for use by bioengineers to create molecules with potentially revolutionary biological activities. In this review, we focus on the development of self-assembling nucleic acid nanostructures that are functionalized with nucleic acid aptamers and their great potential in wide ranging application areas.

Zinc ionophores isolated from Terminalia bellirica fruit rind extract protect against cardiomyocyte hypoxia/reoxygenation injury

The study aimed to isolate and characterize zinc ionophores from Terminalia bellirica fruit using a liposome assay and test its utility in H9c2 rat cardiomyoblasts cells subjected to hypoxia/reoxygenation. Ethyl acetate extract that exhibited zinc ionophore activity was resolved to yield three polyphenols that were characterized as epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG) and epigallocatechin (EGC) by nuclear magnetic resonance and electrospray ionization-mass spectra. The polyphenols enhanced the uptake of zinc into the liposomes and increased FluoZin-3 fluorescence. These polyphenols in the presence of 10 μM ZnCl₂ enhanced the zinc import into H9c2 cells, whose intracellular zinc levels were otherwise lowered upon hypoxia/reoxygenation. EGCG proved to be more potent than ECG, which indeed was more effective than EGC in improving cellular zinc levels and in attenuating the apoptosis of H9c2 cells after hypoxia/reoxygenation injury. The polyphenols required zinc for anti-apoptotic effect. The cardioprotective effect is indeed due to enhanced zinc uptake mediated by these polyphenols.

Melatonin and Selenium Suppress Docetaxel-Induced TRPV1 Activation, Neuropathic Pain and Oxidative Neurotoxicity in Mice

Docetaxel (DT) has been reported to positive therapeutic actions in the treatment of glioblastoma, breast tumors, and prostate cancers. However, it can also induce peripheral neuropathic pain and neurotoxicity as adverse effects. Expression level of TRPV1 cation channel is high in dorsal root ganglion (DRG), and its activation via capsaicin and reactive oxygen species (ROS) mediates peripheral neuropathic pain in mice. As cancer is known to increase the levels of ROS, the protective roles of melatonin (MT) and selenium (Se) were evaluated on the TRPV1-mediated neurotoxicity and pain in the DT-treated mice. Mice and TRPV1 expressing SH-SY5Y cells were equally divided into control, MT, Se, DT, DT+MT, and DT+Se groups. In the results of pain tests in the mice, we observed a decrease in DT-mediated mechanical and heat neuropathic pain by MT and Se. The results of plate reader assay and laser confocal microscopy image analyses indicated a protective role of MT and Se on the DT-induced increase of mitochondrial ROS, cytosolic ROS, apoptosis, lipid peroxidation, intracellular free Zn²⁺, Ca²⁺, and caspase-3 and -9 levels in the DRG and SH-SY5Y cells. MT and Se modulated DT-induced decreases of total antioxidant status, reduced glutathione and glutathione peroxidase in the DRG. However, the effects of DT were not observed in the non-TRPV1 expressing SH-SY5Y cells. Hence, MT and Se mediated protective effects against DT-induced adverse peripheral oxidative neurotoxicity and peripheral pain. These effects may be attributed to potent antioxidant properties of MT and Se.

Taohuajing reduces oxidative stress and inflammation in diabetic cardiomyopathy through the sirtuin 1/nucleotide-binding oligomerization domain-like receptor protein 3 pathway

Background

Oxidative stress and inflammation promote the development of diabetic cardiomyopathy (DCM). Therefore, inhibiting these processes may show beneficial effects in the treatment of patients with DCM. Taohuajing (THJ) is prepared using Persicae semen (Taoren), Polygonatum sibiricum (Huangjing), and Carthami flos (Honghua) and may have applications in the treatment of DCM. However, the protective effects of THJ have not been thoroughly assessed. Accordingly, in this study, we aimed to investigate the protective effects of THJ in a model of DCM and further clarify the potential mechanisms.

Methods

A type 2 diabetes mellitus model was generated using male C57BL/6 mice. Echocardiography and histopathology were used to evaluate cardiac function. The expression levels of cytokines were measured using enzyme-linked immunosorbent assays. Western blotting and small interfering RNA were used to evaluate the targets of THJ.

Results

Compared with the control group, DCM mice showed cardiac dysfunction, metabolic disorder, fibrosis, and disorganized ultrastructure, and THJ treatment significantly inhibited these changes significantly. THJ treatment also inhibited the production of reactive oxygen species (ROS) and malondialdehyde (MDA), induced the production of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), decreased the levels of pro-inflammatory cytokines, and suppressed the activation of the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome. These protective effects were abolished by sirtinol, an inhibitor of sirtuin1 (SIRT1).

Conclusions

Overall, THJ protected the heart from hyperglycemia-induced oxidative stress and inflammation in DCM mice via a mechanism involving SIRT1-mediated antioxidant proteins and suppression of the NLRP3 inflammasome.

The role of labile Zn2+ and Zn2+-transporters in the pathophysiology of mitochondria dysfunction in cardiomyocytes

An important energy supplier of cardiomyocytes is mitochondria, similar to other mammalian cells. Studies have demonstrated that any defect in the normal processes controlled by mitochondria can lead to abnormal ROS production, thereby high oxidative stress as well as lack of ATP. Taken into consideration, the relationship between mitochondrial dysfunction and overproduction of ROS as well as the relation between increased ROS and high-level release of intracellular labile Zn²⁺, those bring into consideration the importance of the events related with those stimuli in cardiomyocytes responsible from cellular Zn²⁺-homeostasis and responsible Zn²⁺-transporters associated with the Zn²⁺-homeostasis and Zn²⁺-signaling. Zn²⁺-signaling, controlled by cellular Zn²⁺-homeostatic mechanisms, is regulated with intracellular labile Zn²⁺ levels, which are controlled, especially, with the two Zn²⁺-transporter families; ZIPs and ZnTs. Our experimental studies in mammalian cardiomyocytes and human heart tissue showed that Zn²⁺-transporters localizes to mitochondria besides sarco(endo)plasmic reticulum and Golgi under physiological condition. The protein levels as well as functions of those transporters can re-distribute under pathological conditions, therefore, they can interplay among organelles in cardiomyocytes to adjust a proper intracellular labile Zn²⁺ level. In the present review, we aimed to summarize the already known Zn²⁺-transporters localize to mitochondria and function to stabilize not only the cellular Zn²⁺ level but also cellular oxidative stress status. In conclusion, one can propose that a detailed understanding of cellular Zn²⁺-homeostasis and Zn²⁺-signaling through mitochondria may emphasize the importance of new mitochondria-targeting agents for prevention and/or therapy of cardiovascular dysfunction in humans.

SGLT2 Inhibitors: A Novel Player in the Treatment and Prevention of Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) characterized by diastolic and systolic dysfunction independently of hypertension and coronary heart disease, eventually develops into heart failure, which is strongly linked to a high prevalence of mortality in people with diabetes mellitus (DM). Sodium-glucose cotransporter type2 inhibitors (SGLT2Is) are a novel type of hypoglycemic agent in increasing urinary glucose and sodium excretion. Excitingly, the EMPA-REG clinical trial proved that empagliflozin significantly reduced the relative risk of cardiovascular (CV) death and hospitalization for heart failure (HHF) in patients with type 2 DM (T2DM) plus CV disease (CVD). The EMPRISE trial showed that empagliflozin decreased the risk of HHF in T2DM patients with and without a CVD history in routine care. These beneficial effects of SGLT2Is could not be entirely attributed to glucose-lowering or natriuretic action. There could be potential direct mechanisms of SGLT2Is in cardioprotection. Recent studies have shown the effects of SGLT2Is on cardiac iron homeostasis, mitochondrial function, anti-inflammation, anti-fibrosis, antioxidative stress, and renin-angiotensin-aldosterone system activity, as well as GlcNAcylation in the heart. This article reviews the current literature on the effects of SGLT2Is on DCM in preclinical studies. Possible molecular mechanisms regarding potential benefits of SGLT2Is for DCM are highlighted, with the purpose of providing a novel strategy for preventing DCM.

Natural Compound Library Screening Identifies New Molecules for the Treatment of Cardiac Fibrosis and Diastolic Dysfunction

BACKGROUND

Myocardial fibrosis is a hallmark of cardiac remodeling and functionally involved in heart failure development, a leading cause of deaths worldwide. Clinically, no therapeutic strategy is available that specifically attenuates maladaptive responses of cardiac fibroblasts, the effector cells of fibrosis in the heart. Therefore, our aim was to develop novel antifibrotic therapeutics based on naturally derived substance library screens for the treatment of cardiac fibrosis.

METHODS

Antifibrotic drug candidates were identified by functional screening of 480 chemically diverse natural compounds in primary human cardiac fibroblasts, subsequent validation, and mechanistic in vitro and in vivo studies. Hits were analyzed for dose-dependent inhibition of proliferation of human cardiac fibroblasts, modulation of apoptosis, and extracellular matrix expression. In vitro findings were confirmed in vivo with an angiotensin II-mediated murine model of cardiac fibrosis in both preventive and therapeutic settings, as well as in the Dahl salt-sensitive rat model. To investigate the mechanism underlying the antifibrotic potential of the lead compounds, treatment-dependent changes in the noncoding RNAome in primary human cardiac fibroblasts were analyzed by RNA deep sequencing.

RESULTS

High-throughput natural compound library screening identified 15 substances with antiproliferative effects in human cardiac fibroblasts. Using multiple in vitro fibrosis assays and stringent selection algorithms, we identified the steroid bufalin (from Chinese toad venom) and the alkaloid lycorine (from Amaryllidaceae species) to be effective antifibrotic molecules both in vitro and in vivo, leading to improvement in diastolic function in 2 hypertension-dependent rodent models of cardiac fibrosis. Administration at effective doses did not change plasma damage markers or the morphology of kidney and liver, providing the first toxicological safety data. Using next-generation sequencing, we identified the conserved microRNA 671-5p and downstream the antifibrotic selenoprotein P1 as common effectors of the antifibrotic compounds.

CONCLUSIONS

We identified the molecules bufalin and lycorine as drug candidates for therapeutic applications in cardiac fibrosis and diastolic dysfunction.

Depression-like behavior, hyperglycemia, oxidative stress, and neuroinflammation presented in diabetic mice are reversed by the administration of 1-methyl-3-(phenylselanyl)-1H-indole

Oxidative stress and neuroinflammation are found both in diabetes mellitus and major depressive disorder (MDD). In addition to damage in peripheral organs, such as liver and kidney, diabetic patients have a higher risk of developing depression. In this sense, the objective of the present study was to characterize the antidepressant-like effect of a selenium-containing compound, the 1-methyl-3-(phenylselanyl)-1H-indole (MFSeI), in streptozotocin (STZ)-induced diabetic mice. STZ (200 mg/kg, i.p.) was used to induce diabetes mellitus type I, and after seven days, the administration of MFSeI (10 mg/kg, i.g.) was initiated and followed for the next 14 days. Twenty-four hours after the last administration of MFSeI, the behavioral tests were performed, followed by euthanasia. The treatment with MFSeI was able to reverse the hyperglycemia induced by STZ. MFSeI also decreased the plasma levels of biomarkers of liver and kidney damage. Importantly, MFSeI reversed the depression-like behavior induced by STZ in the tail suspension test and forced swimming test without promoting locomotor alterations. Furthermore, MFSeI reversed the increased levels of reactive species and lipid peroxidation in the prefrontal cortex (PFC), hippocampus (HC), liver, and kidney of STZ-treated mice. Treatment with MFSeI also decreased the expression of tumor necrosis factor-alpha, inducible nitric oxide synthase and indoleamine 2,3-dioxygenase, while increasing the expression of interleukin-10, insulin receptor substrate-1 and glucose transport-4 in the PFC and HC of mice. Taken together, the results indicate the effectiveness of MFSeI against depression-like behavior and central and peripheral complications caused by diabetes in mice.

The Beneficiary Role of Selenium in Type II Diabetes: A Longitudinal Study

Introduction

Selenium (Se) is an antioxidotic element that is able to protect the pancreatic islets from oxidative stress, improve their functionality, and suspend atherosclerosis. The current paper is an attempt to demonstrate the beneficiary impact of administrating Se to patients with diabetes type 2 who are being treated with oral hypoglycemic agents, based on their glycemic and lipidemic profile.

Methods

The study involves 94 individuals, 72 male and 22 female patients aged 48 to 64 years old with diabetes mellitus type 2. They did not present any diabetic complications or significant comorbidities. They were following a Mediterranean diet and were monitored in order to maintain a steady body mass index (BMI). They were administered with Se 200 μg, taken once daily on an empty stomach. The laboratory testing included fasting blood glucose, hemoglobin A1c (HbA1c), total cholesterol, triglycerides, high-density lipoprotein (HDL), and low-density lipoprotein (LDL). The tests were performed before, three months after, and six months after the administration of selenium.

Results

The study resulted in a statistically significant reduction in the blood levels of glucose, HbA1c, cholesterol, and LDL in both three months and six months after the beginning of the treatment. HDL did not present any change during the first three months but did present a statistically significant increase in six months. Triglycerides did not present a significant reduction in both three and six months.

Conclusion

It appears that the administration of Se to type-2 diabetic patients can improve their glycemic and lipidemic profile, while larger definite trials are needed to provide further evidence.

Selenium and iodine in diabetes mellitus with a focus on the interplay and speciation of the elements

Diabetes mellitus is a chronic metabolic disease caused by insulin deficiency (type I) or dysfunction (type II). Diabetes is a threatening public health concern. It is considered as one of the priority non-communicable diseases, due to its high and increasing incidence, the associated healthcare costs, and threatening medical complications. Two trace elements selenium (Se) and iodine (I) were intensively discussed in the context of diabetic pathology and, possibly, etiology. It seems there is a multilayer involvement of these essential nutrients in glucose tolerance, energy metabolism, insulin signaling and resistance, which are mainly related to the antioxidant selenoenzymes and the thyroid hormones. Other factors might be related to (auto)immunity, protection against endoplasmic reticulum stress, and leptin signaling. The aim of the current review is to evaluate the current understanding of the role of selenium and iodine in diabetes with a focus on the biochemical interplay between the elements, their possible role as biomarkers, and their chemical speciation. Possible impacts from novel analytical techniques related to trace element speciation and isotopic analysis are outlined.

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.

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.

A sodium-glucose cotransporter 2 (SGLT2) inhibitor dapagliflozin comparison with insulin shows important effects on Zn2+-transporters in cardiomyocytes from insulin-resistant metabolic syndrome rats through inhibition of oxidative stress 1

Sodium-glucose cotransporter 2 (SGLT2) inhibitors showed significant effects in patients with diabetes or metabolic syndrome (MetS) with high cardiovascular risk. Although the increased intracellular Zn²⁺ level ([Zn²⁺]_i), oxidative stress, and altered cardiac matrix metalloproteinases (MMPs) in diabetic cardiomyopathy can intersect with different signaling pathways, the exact mechanisms are not known yet. Since either MMPs or SGLT2 have important roles in cardiac-fibrosis under hyperglycemia, we aimed to examine the role of SGLT2 inhibitor dapagliflozin (DAP) on cardiac Zn²⁺-transporters responsible for [Zn²⁺]_i-regulation, comparison to insulin (INS), together with MMP levels and systemic oxidative stress status in MetS-rats. High-carbohydrated diet-induced MetS-rats received DAP or INS for 2 weeks. DAP but not INS in MetS-rats significantly decreased high blood-glucose levels, while both treatments exerted benefits on increased total oxidative status and decreased total antioxidant status in MetS-rat plasma as well as in heart tissue. Protein levels of Zn²⁺-transporters, responsible for Zn²⁺-influx into cytosol, ZIP7 and ZIP14 were increased with significant decrease in ZIP8 of MetS-rat cardiomyoctes, while Zn²⁺-transporters, responsible for cytosolic Zn²⁺-efflux, ZnT7 was decreased with no change in ZnT8. Both treatments induced significant beneficial effects on altered ZIP14, ZIP8, and ZnT7 levels. Furthermore, both treatments exerted benefits on depressed gelatin-zymography and protein expression levels of MMP-2 and MMP-9 in MetS-rat ventricular cardiomyocytes. The direct effect of DAP on heart was also confirmed with measurements of left ventricular developed pressure. Overall, we showed that DAP has important antioxidant-like cardio-protective effects in MetS-rats, similar to INS-effect, affecting Zn²⁺-regulation via Zn²⁺-transporters, MMPs, and oxidative stress. Therefore one can suggest that SGLT2 inhibitors can be new therapeutic agents for cardio-protection not only in hyperglycemia but also in failing heart.

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.

The Effect of Selenium on the Cd-Induced Apoptosis via NO-Mediated Mitochondrial Apoptosis Pathway in Chicken Liver

Cd-induced apoptosis and the protective effects of Se against Cd-induced injury have been reported in previous studies. However, little is known regarding the effects of Cd-induced apoptosis in hepatic cells and the antagonistic effects of Se on Cd in poultry. In the present study, 128 healthy 31-week-old laying hens were randomly divided into four groups, which were fed basic diets, with the addition of Se (Na₂SeO₃, 2 mg/kg), Cd (CdCl₂, 150 mg/kg), or Se + Cd (150 mg/kg of CdCl₂ and 2 mg/kg of Na₂SeO₃) for 90 days. Ultrastructural changes, nitric oxide (NO) concentrations, inducible nitric oxide synthase (iNOS) activities, results of the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay of apoptosis, and the expression of iNOS and apoptosis-related genes in livers were determined. It was observed that Cd treatment significantly increased the concentrations of NO and iNOS activity in chicken livers. The production of excessive NO initiated the mitochondrial apoptotic pathway. Exposure to Cd increased the mRNA and the protein expression levels of iNOS, caspase-3, Bax, p53, and Cyt-c. Furthermore, the ratio of Bax/Bcl-2 increased, while the expression of Bcl-2 decreased. Treatment with Se significantly alleviated Cd-induced apoptosis in chicken livers, as evidenced by a reduction in the production of NO, iNOS activity, the number of apoptotic cells, and mRNA and protein expression levels of iNOS, caspase-3, Bax, and Cyt-c. It indicated that Cd induced NO-mediated apoptosis through the mitochondrial apoptotic pathway and Se exerted antagonizing effects. The present study provides new insights as to how Se affects Cd-induced toxicity in the chicken liver.

Dysregulated Zn2+ homeostasis impairs cardiac type-2 ryanodine receptor and mitsugumin 23 functions, leading to sarcoplasmic reticulum Ca2+ leakage

Aberrant Zn²⁺ homeostasis is associated with dysregulated intracellular Ca²⁺ release, resulting in chronic heart failure. In the failing heart a small population of cardiac ryanodine receptors (RyR2) displays sub-conductance-state gating leading to Ca²⁺ leakage from sarcoplasmic reticulum (SR) stores, which impairs cardiac contractility. Previous evidence suggests contribution of RyR2-independent Ca²⁺ leakage through an uncharacterized mechanism. We sought to examine the role of Zn²⁺ in shaping intracellular Ca²⁺ release in cardiac muscle. Cardiac SR vesicles prepared from sheep or mouse ventricular tissue were incorporated into phospholipid bilayers under voltage-clamp conditions, and the direct action of Zn²⁺ on RyR2 channel function was examined. Under diastolic conditions, the addition of pathophysiological concentrations of Zn²⁺ (≥2 nm) caused dysregulated RyR2-channel openings. Our data also revealed that RyR2 channels are not the only SR Ca²⁺-permeable channels regulated by Zn²⁺. Elevating the cytosolic Zn²⁺ concentration to 1 nm increased the activity of the transmembrane protein mitsugumin 23 (MG23). The current amplitude of the MG23 full-open state was consistent with that previously reported for RyR2 sub-conductance gating, suggesting that in heart failure in which Zn²⁺ levels are elevated, RyR2 channels do not gate in a sub-conductance state, but rather MG23-gating becomes more apparent. We also show that in H9C2 cells exposed to ischemic conditions, intracellular Zn²⁺ levels are elevated, coinciding with increased MG23 expression. In conclusion, these data suggest that dysregulated Zn²⁺ homeostasis alters the function of both RyR2 and MG23 and that both ion channels play a key role in diastolic SR Ca²⁺ leakage.

Zinc in Pancreatic Islet Biology, Insulin Sensitivity, and Diabetes

About 20 chemical elements are nutritionally essential for humans with defined molecular functions. Several essential and nonessential biometals are either functional nutrients with antidiabetic actions or can be diabetogenic. A key question remains whether changes in the metabolism of biometals and biominerals are a consequence of diabetes or are involved in its etiology. Exploration of the roles of zinc (Zn) in this regard is most revealing because 80 years of scientific discoveries link zinc and diabetes. In pancreatic β- and α-cells, zinc has specific functions in the biochemistry of insulin and glucagon. When zinc ions are secreted during vesicular exocytosis, they have autocrine, paracrine, and endocrine roles. The membrane protein ZnT8 transports zinc ions into the insulin and glucagon granules. ZnT8 has a risk allele that predisposes the majority of humans to developing diabetes. In target tissues, increased availability of zinc enhances the insulin response by inhibiting protein tyrosine phosphatase 1B, which controls the phosphorylation state of the insulin receptor and hence downstream signalling. Inherited diseases of zinc metabolism, environmental exposures that interfere with the control of cellular zinc homeostasis, and nutritional or conditioned zinc deficiency influence the patho-biochemistry of diabetes. Accepting the view that zinc is one of the many factors in multiple gene-environment interactions that cause the functional demise of β-cells generates an immense potential for treating and perhaps preventing diabetes. Personalized nutrition, bioactive food, and pharmaceuticals targeting the control of cellular zinc in precision medicine are among the possible interventions.

Heart selenoproteins status of metabolic syndrome-exposed pups: A potential target for attenuating cardiac damage

SCOPE

Cardiac hypertrophy is the greatest complication in metabolic syndrome (MS), in dams and in offspring. The most effective therapies to avoid the evolution of MS are anti-oxidants, anti-inflammatories, and insulin sensitizers. Among anti-oxidant elements, Selenium (Se) exerts its functions through selenoproteins, which are essential for the correct functioning of the cardiovascular system. The aim of the study is analyze selenoproteins' implication in the transmission of future cardiovascular problems to MS progeny.

METHODS AND RESULTS

Heart Se deposits, antioxidant enzymes' activities, biomolecular oxidation, and the expression of selenoproteins, AMPK, and NF-kB were measured in the offspring of dams exposed to a fructose-rich diet (65%) during gestation and lactation, with a normal Se content (0.1 ppm). Thyroid hormones and MCP-1 serum levels, as well as blood pressure and heart rate were also measured. Fructose-exposed pups have cardiomegaly, oxidation, and depletion in Se heart deposits, a decrease in selenoproteins' expression and in the p-AMPK/AMPKt energy ratio; an increase in NF-kB p65 expression, and a decrease of thyroid hormones and MCP-1. Heart rate and blood pressure were altered.

CONCLUSION

These data indicate that dietary Se supplementation could be an inexpensive therapy for avoiding future cardiovascular complication in the progeny of MS dams.

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.

Intracellular Zinc Modulates Cardiac Ryanodine Receptor-mediated Calcium Release

Aberrant Zn²⁺ homeostasis is a hallmark of certain cardiomyopathies associated with altered contractile force. In this study, we addressed whether Zn²⁺ modulates cardiac ryanodine receptor gating and Ca²⁺ dynamics in isolated cardiomyocytes. We reveal that Zn²⁺ is a high affinity regulator of RyR2 displaying three modes of operation. Picomolar free Zn²⁺ concentrations potentiate RyR2 responses, but channel activation is still dependent on the presence of cytosolic Ca²⁺. At concentrations of free Zn²⁺ >1 nm, Zn²⁺ is the main activating ligand, and the dependence on Ca²⁺ is removed. Zn²⁺ is therefore a higher affinity activator of RyR2 than Ca²⁺. Millimolar levels of free Zn²⁺ were found to inhibit channel openings. In cardiomyocytes, consistent with our single channel results, we show that Zn²⁺ modulates both the frequency and amplitude of Ca²⁺ waves in a concentration-dependent manner and that physiological levels of Zn²⁺ elicit Ca²⁺ release in the absence of activating levels of cytosolic Ca²⁺. This highlights a new role for intracellular Zn²⁺ in shaping Ca²⁺ dynamics in cardiomyocytes through modulation of RyR2 gating.

Vimentin filament organization and stress sensing depend on its single cysteine residue and zinc binding

The vimentin filament network plays a key role in cell architecture and signalling, as well as in epithelial-mesenchymal transition. Vimentin C328 is targeted by various oxidative modifications, but its role in vimentin organization is not known. Here we show that C328 is essential for vimentin network reorganization in response to oxidants and electrophiles, and is required for optimal vimentin performance in network expansion, lysosomal distribution and aggresome formation. C328 may fulfil these roles through interaction with zinc. In vitro, micromolar zinc protects vimentin from iodoacetamide modification and elicits vimentin polymerization into optically detectable structures; in cells, zinc closely associates with vimentin and its depletion causes reversible filament disassembly. Finally, zinc transport-deficient human fibroblasts show increased vimentin solubility and susceptibility to disruption, which are restored by zinc supplementation. These results unveil a critical role of C328 in vimentin organization and open new perspectives for the regulation of intermediate filaments by zinc.

Selenoproteins and cardiovascular stress

Dietary selenium (Se) is an essential micronutrient that exerts its biological effects through its incorporation into selenoproteins. This family of proteins contains several antioxidant enzymes such as the glutathione peroxidases, redox-regulating enzymes such as thioredoxin reductases, a methionine sulfoxide reductase, and others. In this review, we summarise the current understanding of the roles these selenoproteins play in protecting the cardiovascular system from different types of stress including ischaemia-reperfusion, homocysteine dysregulation, myocardial hypertrophy, doxirubicin toxicity, Keshan disease, and others.

Selenium nanoparticles involve HSP-70 and SIRT1 in preventing the progression of type 1 diabetic nephropathy

The present study was undertaken to examine the protective effect of selenium nanoparticles (SeNPs) in the progression of diabetic nephropathy (DN). Diabetes was induced in male Sprague Dawley (SD) rats by injecting streptozotocin (STZ) (55mg/kg, i.p). DN was then assessed by measuring blood urea nitrogen (BUN), creatinine, albumin, fibronectin and collagen. Changes in the expression of cytoprotective and apoptotic proteins in the kidney of rats were also examined. Herein we show that SeNPs effectively lowered the levels of BUN, creatinine, fibronectin and collagen and elevated the levels of albumin in diabetic rats. Histological observation corroborated with the above protective effects of SeNPs. Interestingly, SeNPs elevated the levels of heat shock protein (HSP-70), longevity protein SIRT 1 and also modulated apoptotic proteins Bax and Bcl-2 in diabetic kidney. Our data represents a paradigm shift in our understanding about the therapeutic potential of SeNPs in preventing DN by not only quenching oxidative stress but also by activating cyto-protective protein HSP70 and longevity protein SIRT1.

Protective roles of selenium on nitric oxide-mediated apoptosis of immune organs induced by cadmium in chickens

Little is known about the influence of subchronic cadmium exposure on apoptosis in the immune organs of birds and the protective effects on apoptosis by selenium against cadmium. The aim of this study was to investigate the effect of subchronic cadmium exposure on nitric oxide and apoptosis in the immune organs of chicken and the protective roles of selenium against cadmium-induced apoptosis. Two hundred ten 30-day-old chickens were randomly assigned to three groups and were fed a basal diet, cadmium+selenium (as 150 mg of CdCl2 per kg of diet+10 mg of Na2SeO3 per kg of diet ) or cadmium (as 150 mg of CdCl2 per kg of diet) in basic diets for 15, 30, 45, and 60 days. Then, the production of nitric oxide, messenger RNA (mRNA level), and the activity of inducible nitric oxide synthase, ultrastructural changes, TUNEL assay, and flow cytometric analysis of apoptosis and Bcl-2 and p53 mRNA levels in the immune organs were examined. The results showed that cadmium exposure caused ultrastructural damage and increased production of nitric oxide, mRNA level, and activity of inducible nitric oxide synthase, the degree, and the number of apoptotic cells in a time-dependent manner. Cadmium exposure decreased Bcl-2 mRNA level and increased p53 mRNA level in a time-dependent manner. Selenium supplementation during dietary cadmium reduced the production of nitric oxide, the mRNA level, and activity of inducible nitric oxide synthase, ultrastructural damage, and apoptosis in the immune organs of chicken. It indicated that cadmium induced nitric oxide-mediated apoptosis of immune organs, and selenium played protective effects against cadmium-induced apoptosis in the immune organs of chickens.

Enhancement of cellular antioxidant-defence preserves diastolic dysfunction via regulation of both diastolic Zn2+ and Ca2+ and prevention of RyR2-leak in hyperglycemic cardiomyocytes

We examined whether cellular antioxidant-defence enhancement preserves diastolic dysfunction via regulation of both diastolic intracellular free Zn²⁺ and Ca²⁺ levels ([Zn²⁺]_i and [Ca²⁺]_i) levels N-acetyl cysteine (NAC) treatment (4 weeks) of diabetic rats preserved altered cellular redox state and also prevented diabetes-induced tissue damage and diastolic dysfunction with marked normalizations in the resting [Zn²⁺]_i and [Ca²⁺]_i. The kinetic parameters of transient changes in Zn²⁺ and Ca²⁺ under electrical stimulation and the spatiotemporal properties of Zn²⁺ and Ca²⁺ sparks in resting cells are found to be normal in the treated diabetic group. Biochemical analysis demonstrated that the NAC treatment also antagonized hyperphosphorylation of cardiac ryanodine receptors (RyR2) and significantly restored depleted protein levels of both RyR2 and calstabin2. Incubation of cardiomyocytes with 10 µM ZnCl₂ exerted hyperphosphorylation in RyR2 as well as higher phosphorphorylations in both PKA and CaMKII in a concentration-dependent manner, similar to hyperglycemia. Our present data also showed that a subcellular oxidative stress marker, NF-κB, can be activated if the cells are exposed directly to Zn²⁺. We thus for the first time report that an enhancement of antioxidant defence in diabetics via directly targeting heart seems to prevent diastolic dysfunction due to modulation of RyR2 macromolecular-complex thereby leading to normalized [Ca²⁺]_i and [Zn²⁺]_i in cardiomyocytes.

Cardioprotective effect of selenium via modulation of cardiac ryanodine receptor calcium release channels in diabetic rat cardiomyocytes through thioredoxin system

Increased oxidative stress contributes to heart dysfunction via impaired Ca(2+) homeostasis in diabetes. Abnormal RyR2 function related with altered cellular redox state is an important factor in the pathogenesis of diabetic cardiomyopathy, while its underlying mechanisms remain poorly understood. In the present study, we used a streptozotocin-induced rat model of diabetic cardiomyopathy and tested a hypothesis that diabetes-related alteration in RyR2 function is related with ROS-induced posttranslational modifications. For this, we used heart preparations from either a diabetic rat or a sodium selenate (NaSe)-treated (0.3 mg/kg for 4 weeks) diabetic rat as well as either NaSe- (100 nmol/L) or thioredoxin (Trx; 5 μmol/L)-incubated (30 min) diabetic cardiomyocytes. Experimental approaches included imaging of intracellular free-Ca(2+) ([Ca(2+)]i) under both electrically stimulated and resting Fluo-3-loaded cardiomyocytes. RyR2-mediated SR-Ca(2+) leak was significantly enhanced in diabetic cardiomyocytes, resulting in reduced amplitude and prolonged time courses of [Ca(2+)]i transients compared to those of controls. Both SR-Ca(2+) leak and [Ca(2+)]i transients were normalized by treating diabetic rats with NaSe or by incubating diabetic myocytes with NaSe or Trx. Moreover, exposure of diabetic cardiomyocytes to antioxidants significantly improved [Ca(2+)]i handling factors such as phosphorylation/protein levels of RyR2, amount of RyR2-bound FKBP12.6 and activities of both protein kinase A and CaMKII. NaSe treatment also normalized the oxidative stress/antioxidant defense biomarkers in plasma as well as Trx activity and nuclear factor-κB phosphorylation in the diabetic rat heart. Collectively, these findings suggest that redox modification through Trx-system besides the glutathione system contributes to abnormal function of RyR2s in hyperglycemic cardiomyocytes, presenting a potential therapeutic target for treating diabetics to preserve cardiac function.

ß-blocker timolol prevents arrhythmogenic Ca²⁺ release and normalizes Ca²⁺ and Zn²⁺ dyshomeostasis in hyperglycemic rat heart

Defective cardiac mechanical activity in diabetes results from alterations in intracellular Ca(2+) handling, in part, due to increased oxidative stress. Beta-blockers demonstrate marked beneficial effects in heart dysfunction with scavenging free radicals and/or acting as an antioxidant. The aim of this study was to address how β-blocker timolol-treatment of diabetic rats exerts cardioprotection. Timolol-treatment (12-week), one-week following diabetes induction, prevented diabetes-induced depressed left ventricular basal contractile activity, prolonged cellular electrical activity, and attenuated the increase in isolated-cardiomyocyte size without hyperglycemic effect. Both in vivo and in vitro timolol-treatment of diabetic cardiomyocytes prevented the altered kinetic parameters of Ca(2+) transients and reduced Ca(2+) loading of sarcoplasmic reticulum (SR), basal intracellular free Ca(2+) and Zn(2+) ([Ca(2+)]i and [Zn(2+)]i), and spatio-temporal properties of the Ca(2+) sparks, significantly. Timolol also antagonized hyperphosphorylation of cardiac ryanodine receptor (RyR2), and significantly restored depleted protein levels of both RyR2 and calstabin2. Western blot analysis demonstrated that timolol-treatment also significantly normalized depressed levels of some [Ca(2+)]i-handling regulators, such as Na(+)/Ca(2+) exchanger (NCX) and phospho-phospholamban (pPLN) to PLN ratio. Incubation of diabetic cardiomyocytes with 4-mM glutathione exerted similar beneficial effects on RyR2-macromolecular complex and basal levels of both [Ca(2+)]i and [Zn(2+)]i, increased intracellular Zn(2+) hyperphosphorylated RyR2 in a concentration-dependent manner. Timolol also led to a balanced oxidant/antioxidant level in both heart and circulation and prevented altered cellular redox state of the heart. We thus report, for the first time, that the preventing effect of timolol, directly targeting heart, seems to be associated with a normalization of macromolecular complex of RyR2 and some Ca(2+) handling regulators, and prevention of Ca(2+) leak, and thereby normalization of both [Ca(2+)]i and [Zn(2+)]i homeostasis in diabetic rat heart, at least in part by controlling the cellular redox status of hyperglycemic cardiomyocytes.

Oxidant balance in brain of rats receiving different compounds of selenium

The influence of two organic selenocompounds and sodium selenite on oxidant processes in rat brain tissue was investigated. The study was performed on male Wistar rats. The animals were divided into four groups: I—control; II—administered with sodium selenite; III—provided with selenoorganic compound A of chain structure 4-(o-tolyl-)-selenosemicarbazide of 2-chlorobenzoic acid and IV—provided with selenoorganic compound B of ring structure 3-(2-chlorobenzoylamino-)-2-(o-tolylimino-)-4-methyl-4-selenazoline. Rats were treated by stomach tube at a dose of 5 × 10⁻⁴ mg of selenium/g of b.w. once a day for a period of 10 days. In brain homogenates total antioxidant status (TAS), activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), concentrations of ascorbic acid (AA) and reduced glutathione (GSH) as well as concentration of malonyl dialdehyde (MDA) were determined. TAS was insignificantly diminished in all selenium-supplemented groups versus control. SOD was not significantly influenced by administration of selenium. GPx was markedly decreased in group III versus control, whereas increased in group IV versus control and group III. Selenosemicarbazide depleted AA in well-marked way versus group II. GSH was significantly depressed in group III versus both control and group II and diminished in group IV versus group II. MDA was significantly decreased in group III versus both control and group II, whereas in group IV increased versus group III. As selenazoline A did not decrease elements of antioxidant barrier and increased GPx activity, it seems to be a promising agent for future studies concerning its possible application as a selenium supplement.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

Zinc biochemistry: from a single zinc enzyme to a key element of life

The nutritional essentiality of zinc for the growth of living organisms had been recognized long before zinc biochemistry began with the discovery of zinc in carbonic anhydrase in 1939. Painstaking analytical work then demonstrated the presence of zinc as a catalytic and structural cofactor in a few hundred enzymes. In the 1980s, the field again gained momentum with the new principle of "zinc finger" proteins, in which zinc has structural functions in domains that interact with other biomolecules. Advances in structural biology and a rapid increase in the availability of gene/protein databases now made it possible to predict zinc-binding sites from metal-binding motifs detected in sequences. This procedure resulted in the definition of zinc proteomes and the remarkable estimate that the human genome encodes ∼3000 zinc proteins. More recent developments focus on the regulatory functions of zinc(II) ions in intra- and intercellular information transfer and have tantalizing implications for yet additional functions of zinc in signal transduction and cellular control. At least three dozen proteins homeostatically control the vesicular storage and subcellular distribution of zinc and the concentrations of zinc(II) ions. Novel principles emerge from quantitative investigations on how strongly zinc interacts with proteins and how it is buffered to control the remarkably low cellular and subcellular concentrations of free zinc(II) ions. It is fair to conclude that the impact of zinc for health and disease will be at least as far-reaching as that of iron.

Quantitative imaging of mitochondrial and cytosolic free zinc levels in an in vitro model of ischemia/reperfusion

The role of zinc ion in cytotoxicity following ischemic stroke, prolonged status epilepticus, and traumatic brain injury remains controversial, but likely is the result of mitochondrial dysfunction. We describe an excitation ratiometric fluorescence biosensor based on human carbonic anhydrase II variants expressed in the mitochondrial matrix, permitting free zinc levels to be quantitatively imaged therein. We observed an average mitochondrial matrix free zinc concentration of 0.2 pM in the PC12 rat pheochromacytoma cell culture line. Cytoplasmic and mitochondrial free zinc levels were imaged in a cellular oxygen glucose deprivation (OGD) model of ischemia/reperfusion. We observed a significant increase in mitochondrial zinc 1 h following 3 h OGD, at a time point when cytosolic zinc levels were depressed. Following the increase, mitochondrial zinc levels returned to physiological levels, while cytosolic zinc increased gradually over a 24 h time period in viable cells. The increase in intramitochondrial zinc observed during reoxygenation after OGD may contribute to bioenergetic dysfunction and cell death that occurs with both in vitro and in vivo models of reperfusion.

Zn(II) complexes of glutathione disulfide: structural basis of elevated stabilities

Glutathione disulfide (GSSG), a long disregarded redox partner of glutathione (GSH), is thought to participate in intracellular zinc homeostasis. We performed a concerted potentiometric and NMR spectroscopic study of protonation and Zn(II) binding properties of GSSG ((γECG)(2)) and a series of its nine analogs with C-terminal modifications, tripeptide disulfides: (γECS)(2), (γECE)(2), (γECG-NH(2))(2), (γECG-OEt)(2), and (γEcG)(2); dipeptide disulfides, (γEC)(2) and (γEC-OEt)(2); and mixed disulfides, γECG-γEC and γECG-γEC-OEt. The acid-base and Zn(II) complexation properties in this group of compounds are strictly correlated to average C-terminal electrostatic charges. In particular, it was demonstrated that GSSG assumes a bent (head-to-tail) conformation in solution at neutral pH, which is controlled by electrostatic attraction between the protonated γ-amino groups of the Glu residue and the deprotonated C-terminal Gly carboxylates. This interaction modulates the ability of GSSG to coordinate Zn(II), both indirectly, by affecting the basicities of the amino groups, and directly, through the participation of the Gly carboxylates in the outer coordination sphere of the Zn(II) ion. A specific coiled structure of the major [Zn-GSSG](2-) complex is additionally stabilized by the formation of hydrogen bonds between glycinyl carboxylates and two Zn(II)-coordinated water molecules. The elevated stability of Zn(II)-GSSG complexes was demonstrated by competition with FluoZin-3, a fluorescent sensor with high Zn(II) affinity, commonly used in in vitro and in vivo studies. The potential biological functions and reactivity of GSSG complexes of Zn(II) ions are discussed.

Antioxidant treatment protects diabetic rats from cardiac dysfunction by preserving contractile protein targets of oxidative stress

BACKGROUND

Animal studies suggest that reactive oxygen species (ROS) play an important role in the development of diabetic cardiomyopathy.

HYPOTHESIS

Matrix metalloproteinase-2 (MMP-2) is activated by ROS and contributes to the acute loss of myocardial contractile function by targeting and cleaving susceptible proteins including troponin I (TnI) and alpha-actinin.

METHODS

Using the streptozotocin-induced diabetic rat model, we evaluated the effect of daily in vivo administration of sodium selenate (0.3 mg/kg; DMS group), or a pure omega-3 fish oil with antioxidant vitamin E (omega-3E; 50 mg/kg; DMFA group), which has antioxidant-like effects, for 4 weeks on heart function and on several biochemical parameters related to oxidant stress and MMP-2.

RESULTS

Although both treatments prevented the diabetes-induced depression in left ventricular developed pressure (LVDP) as well as the rates of changes in developed pressure (+/-dP/dt) (P<.001), the improvement in LVDP of the DMS group was greater compared to that of the DMFA group (P<.001). Moreover, these treatments reduced the diabetes-induced increase in myocardial oxidized protein sulfhydryl and nitrite concentrations (P<.001). Gelatin zymography and Western blot data indicated that the diabetes-induced changes in myocardial levels of MMP-2 and tissue inhibitor of matrix metalloproteinase-4 (TIMP-4) and the reduction in TnI and alpha-actinin protein levels were improved in both the DMS and DMFA groups (P<.001).

CONCLUSIONS

These results suggest that diabetes-induced alterations in MMP-2 and TIMP-4 contribute to myocardial contractile dysfunction by targeting TnI and alpha-actinin and that sodium selenate or omega-3E could have therapeutic benefits in diabetic cardiomyopathy.

Myosin binding protein C positioned to play a key role in regulation of muscle contraction: structure and interactions of domain C1

Myosin binding protein C (MyBP-C) is a thick filament protein involved in the regulation of muscle contraction. Mutations in the gene for MyBP-C are the second most frequent cause of hypertrophic cardiomyopathy. MyBP-C binds to myosin with two binding sites, one at its C-terminus and another at its N-terminus. The N-terminal binding site, consisting of immunoglobulin domains C1 and C2 connected by a flexible linker, interacts with the S2 segment of myosin in a phosphorylation-regulated manner. It is assumed that the function of MyBP-C is to act as a tether that fixes the S1 heads in a resting position and that phosphorylation releases the S1 heads into an active state. Here, we report the structure and binding properties of domain C1. Using a combination of site-directed mutagenesis and NMR interaction experiments, we identified the binding site of domain C1 in the immediate vicinity of the S1–S2 hinge, very close to the light chains. In addition, we identified a zinc binding site on domain C1 in close proximity to the S2 binding site. Its zinc binding affinity (K_d of approximately 10–20 μM) might not be sufficient for a physiological effect. However, the familial hypertrophic cardiomyopathy-related mutation of one of the zinc ligands, glutamine 210 to histidine, will significantly increase the binding affinity, suggesting that this mutation may affect S2 binding. The close proximity of the C1 binding site to the hinge, the light chains and the S1 heads also provides an explanation for recent observations that (a) shorter fragments of MyBP-C unable to act as a tether still have an effect on the actomyosin ATPase and (b) as to why the myosin head positions in phosphorylated wild-type mice and MyBP-C knockout mice are so different: Domain C1 bound to the S1–S2 hinge is able to manipulate S1 head positions, thus influencing force generation without tether. The potentially extensive extra interactions of C1 are expected to keep it in place, while phosphorylation dislodges the C1–C2 linker and domain C2. As a result, the myosin heads would always be attached to a tether that has phosphorylation-dependent length regulation.

Protective action of doxycycline against diabetic cardiomyopathy in rats

BACKGROUND AND PURPOSE

Reactive oxygen and nitrogen species play an important role in the development of diabetic cardiomyopathy. They can activate matrix metalloproteinases (MMPs), and MMP-2 in particular is known to mediate early consequences of oxidative stress injury in the heart. Therefore, we investigated the role of MMP-2 and the effect of the MMP inhibitor doxycycline on the changes of heart function caused by diabetes.

EXPERIMENTAL APPROACH

Using streptozotocin-induced diabetic rats, we evaluated the effect of doxycycline on both mechanical and electrical function of isolated hearts, papillary muscle and cardiomyocytes.

KEY RESULTS

Doxycycline abolished the diabetes-induced depression in left ventricular developed pressure and the rates of changes in developed pressure in isolated hearts and normalized the prolongation of the action potential in papillary muscles. In cardiomyocytes isolated from doxycycline-treated diabetic rats, the altered kinetic parameters of Ca(2+) transients, depressed Ca(2+) loading of sarcoplasmic reticulum and basal intracellular Ca(2+) level, and the spatio-temporal properties of Ca(2+) sparks were significantly restored. Gelatin zymography and western blot data indicated that the diabetes-induced alterations in MMP-2 activity and protein level, level of tissue inhibitor of matrix metalloproteinase-4 and loss of troponin I were restored to control levels with doxycycline.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that these beneficial effects of doxycycline on the mechanical, electrical and biochemical properties of the diabetic rat heart appear, at least in part, to be related to inhibition of MMP activity, implying a role for MMPs in the development of diabetic cardiomyopathy.

Zinc signalling and subcellular distribution: emerging targets in type 2 diabetes

A finely tuned subcellular distribution of zinc (Zn), through the coordinated action of Zn transporters (ZnTs) and metallothioneins (MTs), is crucial for optimal cell function. Dysfunctions of these proteins might act as key causative or promoting factors in several chronic pathologies. Evidence of their involvement in the pathogenesis of type 2 diabetes (DM2) is emerging. The association of single nucleotide polymorphisms in genes encoding ZnT-8 and MT with DM2 has drawn attention to the relevance of Zn homeostasis for insulin secretory capacity and responsiveness. Here, we propose that potential mechanisms leading to altered subcellular Zn distribution rather than deficiency might be important in DM2. Increasing knowledge of the mechanisms of Zn homeostasis and signalling should promote the development of targeted interventions with the potential to reduce the burden of disease.

Cellular zinc and redox buffering capacity of metallothionein/thionein in health and disease

Zinc is involved in virtually all aspects of cellular and molecular biology as a catalytic, structural, and regulatory cofactor in over 1000 proteins. Zinc binding to proteins requires an adequate supply of zinc and intact molecular mechanisms for redistributing zinc ions to make them available at the right time and location. Several dozen gene products participate in this process, in which interactions between zinc and sulfur donors determine the mobility of zinc and establish coupling between cellular redox state and zinc availability. Specifically, the redox properties of metallothionein and its apoprotein thionein are critical for buffering zinc ions and for controlling fluctuations in the range of picomolar concentrations of "free" zinc ions in cellular signaling. Metallothionein and other proteins with sulfur coordination environments are sensitive to redox perturbations and can render cells susceptible to injury when oxidative stress compromises the cellular redox and zinc buffering capacity in chronic diseases. The implications of these fundamental principles for zinc metabolism in type 2 diabetes are briefly discussed.