Effects of Chronic and Acute Zinc Supplementation on Myocardial Ischemia-Reperfusion Injury in Rats

Interactions between zinc and NRF2 in vascular redox signalling

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

Renoprotective effects of zinc sulfate against transient liver ischemia/reperfusion injury in rats

Objectives

Liver ischemia/reperfusion damage frequently occurs in setting of hepatic resection and liver transplantation. It leads to disturbance in remote organs such as heart, lung and kidneys. This study explored the consequences of hepatic ischemia/reperfusion on the oxidative stress parameters, biochemical factors, and histopathological alterations in the kidney's rats, as well as evaluated the role of zinc sulfate on above-mentioned parameters.

Materials and methods

Twenty-eight male Wistar rats were accidently assigned into four groups (n = 7). They were Sham, ischemia/reperfusion, zinc sulfate pretreatment, and zinc sulfate pretreatment + ischemia/reperfusion groups. Sham group: obtained normal saline (2 ml/day, seven consecutive days), intraperitoneally, zinc sulfate pretreatment group: obtained zinc sulfate (5 mg/kg, seven consecutive days, intraperitoneally). Ischemia/reperfusion group: obtained normal saline as mentioned previous, then rats experienced the partial ischemia (%70) for 45 min followed by 60 min reperfusion. Zinc sulfate pretreatment group: obtained zinc sulfate as mentioned previous, then rats experience the partial ischemia/reperfusion as presented earlier. At the end of investigation, blood was withdrawn, liver and renal tissues were removed. Then, biochemical and oxidative stress parameters, and histological changes were evaluated in the mentioned tissues.

Results

The findings of this experiment indicated that zinc sulfate markedly reduced the serum levels of liver and kidney function tests in relative to ischemia/reperfusion group. Also, antioxidant enzymes activity, ferric reducing antioxidant power, and nitric oxide significantly increased, while malondialdehyde level declined in the renal tissue of zinc sulfate + ischemia/reperfusion group compared to ischemia/reperfusion rats. Furthermore, zinc sulfate alleviated the liver and kidneys histopathological alterations following ischemia/reperfusion.

Conclusion

Zinc sulfate ameliorated liver and kidney function, and improved oxidant-antioxidant balance in favor of antioxidants. It is suggested that zinc sulfate may be beneficial effects on hepato-renal injury after ischemia/reperfusion.

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

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

Cardiovascular Diseases and Zinc

Zinc is structurally and functionally essential for more than 300 enzymes and 2000 transcription factors in human body. Intracellular labile zinc is the metabolically effective zinc and tiny changes in its concentrations significantly affect the intracellular signaling and enzymatic responses. Zinc is crucial for the embrionic and fetal development of heart. Therefore, it is shown to be related with a variety of congenital heart defects. It is involved in epithelial-to-mesenchymal transformation including endocardial cushion development, which is necessary for atrioventricular septation as well as the morphogenesis of heart valves. In atherosclerosis, monocyte endothelial adhesion, and diapedesis, activation and transformation into macrophages and forming foam cells by the ingestion of oxidized LDL are monocyte related steps which need zinc. Intracellular zinc increases intracellular calcium through a variety of pathways and furthermore, zinc itself can work as a second messenger as calcium. These demonstrate the significance of intracellular zinc in heart failure and arterial hypertension. However, extracellular zinc has an opposite effect by blocking calcium channels, explaining decreased serum zinc levels, contrary to the increased cardiomyocyte and erythrocyte zinc levels in hypertensive subjects. These and other data in the literature demonstrate that zinc has important roles in healthy and diseased cardiovascular system but zinc-cardiovascular system relationship is so complex that, it has not been explained in all means. In this article, we try to review some of the available knowledge about this complex relationship.

Zn2+ protect cardiac H9c2 cells from endoplasmic reticulum stress by preventing mPTP opening through MCU

Zn2+ regulates endoplasmic reticulum stress (ERS) and is essential for myocardial protection through gating the mitochondrial permeability transition pore (mPTP). However, the underlining mechanism of the mPTP opening remains uncertain. Cells under sustained ERS induce unfolded protein responses (UPR) and cell apoptosis. Glucose regulatory protein 78 (GRP 78) and glucose regulatory protein 94 (GRP 94) are marker proteins of ERS and regulate the onset of apoptosis through the endoplasmic reticulum signaling pathway. We found tunicamycin (TM) treatment activates ERS and significantly increases intracellular Ca2+ and mitochondrial reactive oxygen species (ROS) levels in H9c2 cardiomyocyte cells. Zn2+ markedly decreased protein level of GRP 78/94 and suppressed intracellular Ca2+ and ROS elevation. Mitochondrial calcium uniporter (MCU) is an important Ca2+ transporter protein, through which Zn2+ enter mitochondria. MCU inhibitor ruthenium red (RR) or siRNA significantly reversed the Zinc effect on GRP 78, mitochondrial Ca2+ and ROS. Additionally, Zn2+ prevented TM-induced mPTP opening and decreased mitochondrial Ca2+ concentration, which were blocked through inhibiting or knockdown MCU with siRNA. In summary, our study suggests that Zn2+ protected cardiac ERS by elevating Ca2+ and closing mPTP through MCU.

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.

The inhibition of apoptosis through myocardial postconditioning by affecting Fas/FasIg signaling through miR139-3p and miR181a-1

BACKGROUND AND AIM OF THE STUDY

Ischemic postconditioning (PostC) is considered to be one of the strongest mechanisms limiting the extent of myocardial infarction, and reducing ischemia-reperfusion (I/R) injury. I/R-induced myocardial injury results in apoptosis, autophagy, and necrosis. The aim of the present study was to investigate the roles of the necrotic gene cytochrome b-245 beta chain (Cybb); Cybb-related microRNA miR139-3p; the autophagy gene Beclin-1 (Becn1); proapoptotic genes Fas, Faslg and growth arrest and DNA-damage-inducible 45 alpha (Gadd45a); and apoptosis-related microRNA miR181a-1 levels on I/R injury, as well as, the potential protective effects of PostC through this gene and microRNAs.

METHODS

The left main coronary artery was subjected to ischemia for 30 minutes, followed by reperfusion for 120 minutes. PostC involved three cycles of I/R, each lasting 10 seconds. Gene and microRNA levels were analyzed using a quantitative reverse transcription-polymerase chain reaction.

RESULTS

Although an increase was observed in the expression levels of the Cybb, Fas, Faslg and Gadd45a genes, the miR139-3p, miR181a-1, and Becn1 expression levels were found to decrease with I/R injury. PostC was determined to restore the expression of all the genes to the normal levels.

CONCLUSIONS

The abovementioned genes can be used as important prognostic markers in the diagnosis of reperfusion injury and in the evaluation of treatment efficacy. It was further noted that increased expression of CYBB, which is one of the target genes for miR139-3p, and a decreased expression of miR181a-1 may cause apoptosis by affecting Fas and Faslg signaling. PostC can inhibit apoptosis by increasing miR139-3p and miR181a-1 levels.

Zinc-induced protective effect for testicular ischemia-reperfusion injury by promoting antioxidation via microRNA-101-3p/Nrf2 pathway

The present study was performed to determine the protective effect of Zinc on the rat testicular ischemia-reperfusion (I/R) injury and its mechanism. In vivo, the pathological changes and the apoptosis index were significantly relieved in the rats with Low-dose Zinc pretreatment, compared to the I/R group. After Low-dose Zinc treatment, the levels of tissue Malondialdehyde (MDA) were significantly decreased, while tissue antioxidant indices were significantly increased. Meanwhile, the level of NF-κB was significantly lower compared to I/R group, while the levels of Nrf2-dependent antioxidant enzymes were significantly higher in Low-dose Zinc+I/R group. In vitro, Low-dose Zinc markedly increased Leydig cell (TM3) cell viability, and relieved testicular oxidative damage via down-regulating ROS. A total of 22 differently expressed microRNAs were screened out using microRNA microarray in rat testicular tissue caused by I/R injury, especially showing that miR-101-3p was selected as the target miRNA. Furthermore, the levels of Nrf2 and NF-κB were apparently increased/decreased in TM3 cells treated with Hypoxic/Reoxygenation (H/R) after miR-101-3p mimics/inhibitor. In addition, H/R-induced testicular oxidative damage was recovered in TM3 administrated with miR-101-3p inhibitor and si-Nrf2. Therefore, this study provided a novel insight for investigating protective effect of Zinc on testicular I/R injury by promoting antioxidation via miR-101-3p/Nrf2.

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.

Cross talk between neurometals and amyloidogenic proteins at the synapse and the pathogenesis of neurodegenerative diseases

Increasing evidence suggests that disruption of metal homeostasis contributes to the pathogenesis of various neurodegenerative diseases, including Alzheimer's disease, prion diseases, Lewy body diseases, and vascular dementia. Conformational changes of disease-related proteins (amyloidogenic proteins), such as β-amyloid protein, prion proteins, and α-synuclein, are well-established contributors to neurotoxicity and to the pathogenesis of these diseases. Recent studies have demonstrated that these amyloidogenic proteins are metalloproteins that bind trace elements, including zinc, iron, copper, and manganese, and play significant roles in the maintenance of metal homeostasis. We present a current review of the role of trace elements in the functions and toxicity of amyloidogenic proteins, and propose a hypothesis integrating metal homeostasis and the pathogenesis of neurodegenerative diseases that is focused on the interactions among metals and between metals and amyloidogenic proteins at the synapse, considering that these amyloidogenic proteins and metals are co-localized at the synapse.

The effect of zinc and melatonin supplementation on immunity parameters in breast cancer induced by DMBA in rats

OBJECTIVE

The aim of the study was to determine the effects of zinc and melatonin supplements on the immunity parameters of female rats with breast cancer induced by DMBA.

METHODS

Group 1; Control, Group 2; 7,12-dimethylbenz[a]anthracene (DMBA), Group 3; DMBA + zinc, Group 4; DMBA + melatonin, Group 5; DMBA + zinc + melatonin. The rats' breast cancer was induced by DMBA 80 mg/kg. Groups 3-5 received daily 5 mg/kg doses of zinc, melatonin, and zinc + melatonin, respectively. Lymphocyte rates, T-lymphocyte subgroups, B-lymphocyte and natural killer cells (NK), and natural killer T (NKT) were evaluated.

RESULTS

The most significant increase in lymphocyte, T-lymphocyte, and CD4 lymphocyte rates was found in Group 5. The highest NKT cell rates were found in Group 3.

CONCLUSIONS

Findings show that zinc and melatonin supplements have led to an increase in the immunity parameters of rats with breast cancer.