Endoplasmic reticulum stress in diabetic hearts abolishes erythropoietin-induced myocardial protection by impairment of phospho-glycogen synthase kinase-3beta-mediated suppression of mitochondrial permeability transition

Role of AMP deaminase in diabetic cardiomyopathy

Diabetes mellitus is one of the major causes of ischemic and nonischemic heart failure. While hypertension and coronary artery disease are frequent comorbidities in patients with diabetes, cardiac contractile dysfunction and remodeling occur in diabetic patients even without comorbidities, which is referred to as diabetic cardiomyopathy. Investigations in recent decades have demonstrated that the production of reactive oxygen species (ROS), impaired handling of intracellular Ca2+, and alterations in energy metabolism are involved in the development of diabetic cardiomyopathy. AMP deaminase (AMPD) directly regulates adenine nucleotide metabolism and energy transfer by adenylate kinase and indirectly modulates xanthine oxidoreductase-mediated pathways and AMP-activated protein kinase-mediated signaling. Upregulation of AMPD in diabetic hearts was first reported more than 30 years ago, and subsequent studies showed similar upregulation in the liver and skeletal muscle. Evidence for the roles of AMPD in diabetes-induced fatty liver, sarcopenia, and heart failure has been accumulating. A series of our recent studies showed that AMPD localizes in the mitochondria-associated endoplasmic reticulum membrane as well as the sarcoplasmic reticulum and cytosol and participates in the regulation of mitochondrial Ca2+ and suggested that upregulated AMPD contributes to contractile dysfunction in diabetic cardiomyopathy via increased generation of ROS, adenine nucleotide depletion, and impaired mitochondrial respiration. The detrimental effects of AMPD were manifested at times of increased cardiac workload by pressure loading. In this review, we briefly summarize the expression and functions of AMPD in the heart and discuss the roles of AMPD in diabetic cardiomyopathy, mainly focusing on contractile dysfunction caused by this disorder.

Endoplasmic reticulum stress signaling modulates ischemia/reperfusion injury in the aged heart by regulating mitochondrial maintenance

Aging is associated with an increased risk of myocardial ischemia/reperfusion injury (IRI). With an increasing prevalence of cardiovascular diseases such as coronary arteriosclerosis in older people, there has been increasing interest in understanding the mechanisms of myocardial IRI to develop therapeutics that can attenuate its damaging effects. Previous studies identified that abnormal mitochondria, involved in cellar senescence and oxidative stress, are the master subcellular organelle that induces IRI. In addition, endoplasmic reticulum (ER) stress is also associated with IRI. Cellular adaptation to ER stress is achieved by the activation of ER molecular chaperones and folding enzymes, which provide an important link between ER stress and oxidative stress gene programs. In this review, we outline how these ER stress-related molecules affect myocardial IRI via the crosstalk of ER stress and mitochondrial homeostasis and discuss how these may offer promising novel therapeutic targets and strategies against age-related cardiovascular diseases.

Role of Erythropoiesis-Stimulating Agents in Cardiovascular Protection in CKD Patients: Reappraisal of Their Impact and Mechanisms

Erythropoiesis-stimulating agents (ESAs) have markedly reduced the need for blood transfusion for renal anemia and are included in standard therapies for patients with chronic kidney disease (CKD). Various protective effects of ESAs on the cardiovascular system have been discovered through basic research, and the effects have received much attention because the rates of cardiovascular events and mortality are high in CKD patients. However, randomized clinical trials did not provide strong evidence that ESAs exert cardioprotection in humans, including CKD patients. It is difficult to assess the cardioprotective effects of ESAs in CKD patients through the clinical data that has been reported to date because the relationship between hemoglobin level rather than ESA dose and cardiovascular event rates was examined in most studies. Interestingly, recent studies using a rat model of CKD showed that the infarct size-limiting effect of an ESA was lost when its dose was increased to a level that normalized blood hemoglobin levels, suggesting that the optimal dose of an ESA for myocardial protection is less than the dose required to normalize hemoglobin levels. Furthermore, animal models of traditional coronary risk factors or comorbidities were resistant to the cardioprotective effects of ESAs because of interruptions in signal-mediated mechanisms downstream of erythropoietin receptors. In this review, we briefly discuss basic and clinical data on the impact of anemia on coronary and systemic circulation, the effects of CKD on the cardiovascular system, and the multiple pharmacological actions of ESAs to examine whether the ESAs that are prescribed for renal anemia exert any cardioprotection in patients with CKD.

Adenosine monophosphate deaminase in the endoplasmic reticulum-mitochondria interface promotes mitochondrial Ca2+ overload in type 2 diabetes rat hearts

AIMS/INTRODUCTION

We previously showed that upregulation of myocardial adenosine monophosphate deaminase (AMPD) is associated with pressure overload-induced diastolic dysfunction in type 2 diabetes hearts. Here, we examined involvement of AMPD localized in the endoplasmic reticulum-mitochondria interface in mitochondrial Ca²⁺ overload and its pathological significance.

MATERIALS AND METHODS

We used type 2 diabetes Otsuka Long-Evans Tokushima Fatty rats (OLETF) and non-diabetes Long-Evans Tokushima Otsuka Fatty rats (LETO) as well as AMPD3-overexpressing H9c2 cells and human embryonic kidney 293 cells.

RESULTS

OLETF, but not LETO, showed diastolic dysfunction under the condition of phenylephrine-induced pressure overload. The levels of 90-kDa AMPD3 in outer mitochondrial membranes/endoplasmic reticulum and mitochondria-associated endoplasmic reticulum membrane (MAM) fractions were significantly higher in OLETF than in LETO. The area of the MAM quantified by electron microscopic analysis was 57% larger, mitochondrial Ca²⁺ level under the condition of pressure overload was 47% higher and Ca²⁺ retention capacity in MAM-containing crude mitochondria isolated before the pressure overloading was 21% lower in OLETF than in LETO (all P-values <0.05). Transfection of FLAG-AMPD3 in cells resulted in significant enlargement of the MAM area, and impairment in pyruvate/malate-driven adenosine triphosphate-stimulated and uncoupler-stimulated mitochondrial respiration compared with those in control cells.

CONCLUSIONS

The findings suggest that 90-kDa AMPD3 localized in the endoplasmic reticulum-mitochondria interface promotes formation of the MAM, inducing mitochondrial Ca²⁺ overload and dysfunction in type 2 diabetes hearts.

Natural compounds regulate the PI3K/Akt/GSK3β pathway in myocardial ischemia-reperfusion injury

The PI3K/Akt/GSK3β pathway is crucial in regulating cardiomyocyte growth and survival. It has been shown that activation of this pathway alleviates the negative impact of ischemia-reperfusion. Glycogen synthase kinase-3 (GSK3β) induces apoptosis through stimulation of transcription factors, and its phosphorylation has been suggested as a new therapeutic target for myocardial ischemia-reperfusion injury (MIRI). GSK3β regulatory role is mediated by the reperfusion injury salvage kinase (RISK) pathway, and its inhibition by Akt activation blocks mitochondrial permeability transition pore (mPTP) opening and enhances myocardial survival. The present article discusses the involvement of the PI3K/Akt/GSK3β pathway in cardioprotective effects of natural products against MIRI.Abbreviations: Akt: protein kinase B; AMPK: AMP-activated protein kinase; ATP: adenosine triphosphate; Bad: bcl2-associated agonist of cell death; Bax: bcl2-associated x protein; Bcl-2: B-cell lymphoma 2; CK-MB: Creatine kinase-MB; CRP: C-reactive-protein; cTnI: cardiac troponin I; EGCG: Epigallocatechin-3-gallate; Enos: endothelial nitric oxide synthase; ER: endoplasmic reticulum; ERK ½: extracellular signal‑regulated protein kinase ½; GSK3β: glycogen synthase kinase-3; GSRd: Ginsenoside Rd; GSH: glutathione; GSSG: glutathione disulfide; HO-1: heme oxygenase-1; HR: hypoxia/reoxygenation; HSYA: Hydroxysafflor Yellow A; ICAM-1: Intercellular Adhesion Molecule 1; IKK-b: IκB kinase; IL: interleukin; IPoC: Ischemic postconditioning; IRI: ischemia-reperfusion injury; JNK: c-Jun N-terminal kinase; Keap1: kelch-like ECH-associated protein- 1; LDH: lactate dehydrogenase; LVEDP: left ventricular end diastolic pressure; LVP: left ventricle pressure; LVSP: left ventricular systolic pressure; MAPK: mitogen-activated protein kinase; MDA: malondialdehyde; MIRI: myocardial ischemia-reperfusion injury; MnSOD: manganese superoxide dismutase; mPTP: mitochondrial permeability transition pore; mtHKII: mitochondria-bound hexokinase II; Nrf-1: nuclear respiratory factor 1; Nrf2: nuclear factor erythroid 2-related factor; NO: nitric oxide; PGC-1α: peroxisome proliferator‑activated receptor γ coactivator‑1α; PI3K: phosphoinositide 3-kinases; RISK: reperfusion injury salvage kinase; ROS: reactive oxygen species; RSV: Resveratrol; SOD: superoxide dismutase; TFAM: transcription factor A mitochondrial; TNF-α: tumor necrosis factor-alpha; VEGF-B: vascular endothelial growth factor B.

Renin-Angiotensin System Antagonism Protects the Diabetic Heart from Ischemia/Reperfusion Injury in Variable Hyperglycemia Duration Settings by a Glucose Transporter Type 4-Mediated Pathway

BACKGROUND

Diabetes mellitus (DM) is a risk factor for cardiovascular diseases, specifically, the ischemic heart diseases (IHD). The renin-angiotensin system (RAS) affects the heart directly and indirectly. However, its role in the protection of the heart against I/R injury is not completely understood. The aim of the current study was to evaluate the efficacy of the angiotensin-converting enzyme (ACE) inhibitor and Angiotensin II receptor (AT1R) blocker or a combination thereof in protection of the heart from I/R injury.

METHODS

Hearts isolated from adult male Wistar rats (n = 8) were subjected to high glucose levels; acute hyperglycemia or streptozotocin (STZ)-induced diabetes were used in this study. Hearts were subjected to I/R injury, treated with Captopril, an ACE inhibitor; Losartan, an AT1R antagonist; or a combination thereof. Hemodynamics data were measured using a suitable software for that purpose. Additionally, infarct size was evaluated using 2,3,5-Triphenyltetrazolium chloride (TTC) staining. The levels of apoptosis markers (caspase-3 and -8), antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), nitric oxide synthase (eNOS), and glucose transporter type 4 (GLUT-4) protein levels were evaluated by Western blotting. Pro-inflammatory and anti-inflammatory cytokines levels were evaluated by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Captopril and Losartan alone or in combination abolished the effect of I/R injury in hearts subjected to acute hyperglycemia or STZ-induced diabetes. There was a significant (p < 0.05) recovery in hemodynamics, infarct size, and apoptosis markers following the treatment with Captopril, Losartan, or their combination. Treatment with Captopril, Losartan, or their combination significantly (p < 0.05) reduced pro-inflammatory cytokines and increased GLUT-4 protein levels.

CONCLUSIONS

The blockade of the RAS system protected the diabetic heart from I/R injury. This protection followed a pathway that utilizes GLUT-4 to decrease the apoptosis markers, pro-inflammatory cytokines, and to increase the anti-inflammatory cytokines. This protection seems to employ a pathway which is not involving ERK1/2 and eNOS.

Downregulation of extramitochondrial BCKDH and its uncoupling from AMP deaminase in type 2 diabetic OLETF rat hearts

Systemic branched-chain amino acid (BCAA) metabolism is dysregulated in cardiometabolic diseases. We previously demonstrated that upregulated AMP deaminase 3 (AMPD3) impairs cardiac energetics in a rat model of obese type 2 diabetes, Otsuka Long-Evans-Tokushima fatty (OLETF). Here, we hypothesized that the cardiac BCAA levels and the activity of branched-chain α-keto acid dehydrogenase (BCKDH), a rate-limiting enzyme in BCAA metabolism, are altered by type 2 diabetes (T2DM), and that upregulated AMPD3 expression is involved in the alteration. Performing proteomic analysis combined with immunoblotting, we discovered that BCKDH localizes not only to mitochondria but also to the endoplasmic reticulum (ER), where it interacts with AMPD3. Knocking down AMPD3 in neonatal rat cardiomyocytes (NRCMs) increased BCKDH activity, suggesting that AMPD3 negatively regulates BCKDH. Compared with control rats (Long-Evans Tokushima Otsuka [LETO] rats), OLETF rats exhibited 49% higher cardiac BCAA levels and 49% lower BCKDH activity. In the cardiac ER of the OLETF rats, BCKDH-E1α subunit expression was downregulated, while AMPD3 expression was upregulated, resulting in an 80% lower AMPD3-E1α interaction compared to LETO rats. Knocking down E1α expression in NRCMs upregulated AMPD3 expression and recapitulated the imbalanced AMPD3-BCKDH expressions observed in OLETF rat hearts. E1α knockdown in NRCMs inhibited glucose oxidation in response to insulin, palmitate oxidation, and lipid droplet biogenesis under oleate loading. Collectively, these data revealed previously unrecognized extramitochondrial localization of BCKDH in the heart and its reciprocal regulation with AMPD3 and imbalanced AMPD3-BCKDH interactions in OLETF. Downregulation of BCKDH in cardiomyocytes induced profound metabolic changes that are observed in OLETF hearts, providing insight into mechanisms contributing to the development of diabetic cardiomyopathy.

Neurological recovery and antioxidant effect of erythropoietin for spinal cord injury: A systematic review and meta-analysis

Background

To critically evaluate the neurological recovery effects and antioxidant effects of erythropoietin (EPO) in rat models of spinal cord injury (SCI).

Methods

The PubMed, EMBASE, MEDLINE, ScienceDirect, and Web of Science were searched for animal experiments applying EPO to treat SCI to January 2022. We included studies which examined neurological function by the Basso, Beattie, and Bresnahan (BBB) scale, as well as cavity area and spared area, and determining the molecular-biological analysis of antioxidative effects by malondialdehyde (MDA) levels in spinal cord tissues. Meta-analysis were performed with Review Manager 5.4 software.

Results

A total of 33 studies were included in this review. The results of the meta-analysis showed that SCI rats receiving EPO therapy showed a significant locomotor function recovery after 14 days compared with control, then the superiority of EPO therapy maintained to 28 days from BBB scale. Compared with the control group, the cavity area was reduced [4 studies, weighted mean difference (WMD) = −16.65, 95% CI (−30.74 to −2.55), P = 0.02] and spared area was increased [3 studies, WMD =11.53, 95% CI (1.34 to 21.72), P = 0.03] by EPO. Meanwhile, MDA levels [2 studies, WMD = −0.63 (−1.09 to −0.18), P = 0.007] were improved in the EPO treatment group compared with control, which indicated its antioxidant effect. The subgroup analysis recommended 5,000 UI/kg is the most effective dose [WMD = 4.05 (2.23, 5.88), P &lt; 0.0001], although its effect was not statistically different from that of 1,000 UI/kg. Meanwhile, the different rat strains (Sprague-Dawley vs. Wistar), and models of animals, as well as administration method (single or multiple administration) of EPO did not affect the neuroprotective effect of EPO for SCI.

Conclusions

This systematic review indicated that EPO can promote the recovery of the locomotor function of SCI rats. The mechanism exploration of EPO needs to be verified by experiments, and then carefully designed randomized controlled trials are needed to explore its neural recovery effects.

Diabetes modulation of the myocardial infarction- acute kidney injury axis

Since there is crosstalk in functions of the heart and kidney, acute or chronic injury in one of the two organs provokes adaptive and/or maladaptive responses in both organs, leading to cardiorenal syndrome (CRS). Acute kidney injury (AKI) induced by acute heart failure is referred to as type 1 CRS, and a frequent cause of this type of CRS is acute myocardial infarction (AMI). Diabetes mellitus increases the risk of AMI and also the risk of AKI of various causes. However, there have been only a few studies in which animal models of diabetes were used to examine how diabetes modulates AMI-induced AKI. In this review, we summarize findings regarding the mechanisms of type 1 CRS and the impact of diabetes on both AMI and renal susceptibility to AKI and we discuss mechanisms by which diabetes modulates AMI-induced AKI. Hemodynamic alterations induced by AMI could be augmented by diabetes via its detrimental effect on infarct size and contractile function of the non-infarcted region in the heart. Diabetes increases susceptibility of renal cells to hypoxia and oxidative stress by modulation of signaling pathways that regulate cell survival and autophagy. Recent studies have shown that diabetes mellitus even at early stage of cardiomyopathy/nephropathy predisposes the kidney to AMI-induced AKI, in which activation of toll-like receptors and reactive oxygen species derived from NADPH oxidases are involved. Further analysis of crosstalk between diabetic cardiomyopathy and diabetic kidney disease is necessary for obtaining a more comprehensive understanding of modulation of the AMI-AKI axis by diabetes.

Mitochondrial proteins that connected with calcium: do their pathways changes in PAH?

Calcium can be regulated by mitochondria and also plays a significant role in mitochondrial pathways. Recent study showed mitochondrial protein changes in the right ventricle in pulmonary arterial hypertension, which affects calcium network at the same time. The specific objective of this study is to assess the pathway of calcium transport by permeable pore in mitochondria and investigate the regulation of mitochondrial proteins in order to find the connection between mitochondrial proteins and right ventricular dysfunction in PAH (pulmonary arterial hypertension). This literature-based review came out by searching articles in Pubmed and Science Direct. And the related flow chart is expressed by the form of PRISMA. There is a network between mitochondria and calcium through the transport chain called mitochondria permeability transition pore (MPTP) as well as different kinds of proteins that are located in the mitochondria. MPTP is a kind of mitochondria pore and can have conformational changes after protein phosphorylation or reaction between mitochondrial proteins to activate the apoptosis capase cascade process in cell death. In addition, MPTP can be activated by other mitochondrial protein like signal transducer activator of transcription3 (STAT3) to activate cytochrome c in pro-apoptosis to initiate cell death at the same time. The most obvious finding from this study is the role of calcium regulation in therapeutic treatment in PAH patients, which suggest an imaginable role for calcium transporter like mitochondria calcium uniporter (MCU) promoting bio-markers in cardiovascular disease resulting from mitochondrial dysfunction. In addition, right ventricle is a target of PAH in which mitochondria in RV would play an essential role in pathways such as ATP production via mitochondria metabolism.

Ischemic brain injury in diabetes and endoplasmic reticulum stress

Diabetes is a widespread disease characterized by high blood glucose levels due to abnormal insulin activity, production, or both. Chronic diabetes causes many secondary complications including cardiovascular disease: a life-threatening complication. Cerebral ischemia-related mortality, morbidity, and the extent of brain injury are high in diabetes. However, the mechanism of increase in ischemic brain injury during diabetes is not well understood. Multiple mechanisms mediate diabetic hyperglycemia and hypoglycemia-induced increase in ischemic brain injury. Endoplasmic reticulum (ER) stress mediates both brain injury as well as brain protection after ischemia-reperfusion injury. The pathways of ER stress are modulated during diabetes. Free radical generation and mitochondrial dysfunction, two of the prominent mechanisms that mediate diabetic increase in ischemic brain injury, are known to stimulate the pathways of ER stress. Increased ischemic brain injury in diabetes is accompanied by a further increase in the activation of ER stress. As there are many metabolic changes associated with diabetes, differential activation of the pathways of ER stress may mediate pronounced ischemic brain injury in subjects suffering from diabetes. We presently discuss the literature on the significance of ER stress in mediating increased ischemia-reperfusion injury in diabetes.

Synergetic Effect of 4-Phenylbutyric Acid in Combination with Cyclosporine A on Cardiovascular Function in Sepsis Rats via Inhibition of Endoplasmic Reticulum Stress and Mitochondrial Permeability Transition Pore Opening

Background: Sepsis/septic shock is a common complication in the intensive care unit, and the opening of the mitochondrial permeability transition pore (mPTP), as well as the endoplasmic reticulum stress (ERS), play important roles in this situation. Whether the combination of anti-ERS and anti-mPTP by 4-phenylbutyric acid (PBA) and Cyclosporine A (CsA) could benefit sepsis is unclear.

Methods: The cecal ligation and puncture-induced septic shock models were replicated in rats, and lipopolysaccharide (LPS)-challenged primary vascular smooth muscle cells and H9C2 cardiomyocytes in vitro models were also used. The therapeutic effects of CsA, PBA, and combined administration on oxygen delivery, cardiac and vascular function, vital organ injury, and the underlying mechanisms were observed.

Results: Septic shock significantly induced cardiovascular dysfunction, hypoperfusion, and organ injury and resulted in high mortality in rats. Conventional treatment including fluid resuscitation, vasoactive agents, and antibiotics slightly restored tissue perfusion and organ function in septic rats. Supplementation of CsA or PBA improved the tissue perfusion, organ function, and survival of septic shock rats. The combined application of PBA and CsA could significantly enhance the beneficial effects, compared with using PBA or CsA alone. Further study showed that PBA enhanced CsA-induced cardiovascular protection, which contributed to better therapeutic effects.

Conclusion: Anti-ERS and anti-mPTP-opening by the combination of PBA and CsA was beneficial to septic shock. PBA enforced the CsA-associated cardiovascular protection and contributed to the synergetic effect.

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

The Diabetic Cardiomyopathy: The Contributing Pathophysiological Mechanisms

Individuals with diabetes mellitus (DM) disclose a higher incidence and a poorer prognosis of heart failure (HF) than non-diabetic people, even in the absence of other HF risk factors. The adverse impact of diabetes on HF likely reflects an underlying “diabetic cardiomyopathy” (DM–CMP), which may by exacerbated by left ventricular hypertrophy and coronary artery disease (CAD). The pathogenesis of DM-CMP has been a hot topic of research since its first description and is still under active investigation, as a complex interplay among multiple mechanisms may play a role at systemic, myocardial, and cellular/molecular levels. Among these, metabolic abnormalities such as lipotoxicity and glucotoxicity, mitochondrial damage and dysfunction, oxidative stress, abnormal calcium signaling, inflammation, epigenetic factors, and others. These disturbances predispose the diabetic heart to extracellular remodeling and hypertrophy, thus leading to left ventricular diastolic and systolic dysfunction. This Review aims to outline the major pathophysiological changes and the underlying mechanisms leading to myocardial remodeling and cardiac functional derangement in DM-CMP.

Xanthine oxidoreductase-mediated injury is amplified by upregulated AMP deaminase in type 2 diabetic rat hearts under the condition of pressure overload

BACKGROUND

We previously reported that upregulated AMP deaminase (AMPD) contributes to diastolic ventricular dysfunction via depletion of the adenine nucleotide pool in a rat model of type 2 diabetes (T2DM), Otsuka Long-Evans-Tokushima Fatty rats (OLETF). Meanwhile, AMPD promotes the formation of substrates of xanthine oxidoreductase (XOR), which produces ROS as a byproduct. Here, we tested the hypothesis that a functional link between upregulated AMPD and XOR is involved in ventricular dysfunction in T2DM rats.

METHODS AND RESULTS

Pressure-volume loop analysis revealed that pressure overloading by phenylephrine infusion induced severer left ventricular diastolic dysfunction (tau: 14.7 ± 0.8 vs 12.5 ± 0.7 msec, left ventricular end-diastolic pressure: 18.3 ± 1.5 vs 12.2 ± 1.3 mmHg, p < 0.05) and ventricular-arterial uncoupling in OLETF than in LETO, non-diabetic rats, though the baseline parameters were comparable in the two groups. While the pressure overload did not affect AMPD activity, it increased XOR activity both in OLETF and LETO, with OLETF showing significantly higher XOR activity than that in LETO (347.2 ± 17.9 vs 243.2 ± 6.1 μg/min/mg). Under the condition of pressure overload, myocardial ATP level was lower, and levels of xanthine and uric acid were higher in OLETF than in LETO. Addition of exogenous inosine, a product of AMP deamination, to the heart homogenates augmented XOR activity. OLETF showed 68% higher tissue ROS levels and 47% reduction in mitochondrial state 3 respiration compared with those in LETO. Overexpression of AMPD3 in H9c2 cells elevated levels of hypoxanthine and ROS and reduced the level of ATP. Inhibition of XOR suppressed the production of tissue ROS and mitochondrial dysfunction and improved ventricular function under the condition of pressure overload in OLETF.

CONCLUSIONS

The results suggest that increases in the activity of XOR and the formation of XOR substrates by upregulated AMPD contribute to ROS-mediated diastolic ventricular dysfunction at the time of increased cardiac workload in diabetic hearts.

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

Distinct intra-mitochondrial localizations of pro-survival kinases and regulation of their functions by DUSP5 and PHLPP-1

ERK and Akt have been shown to regulate cell sensitivity to death-inducing stress by phosphorylating GSK-3β, a major modulator of the threshold for mitochondrial permeability transition. Here we examined intra-mitochondrial localization of the pro-survival kinases and their regulation by phosphatases. Stepwise trypsin digestion of mitochondria isolated from HEK293 or H9c2 cells was performed, and immunoblotting revealed that GSK-3β and ERK localized dominantly in the outer membrane (OM), while Akt resided at comparable levels in OM, the inner membrane (IM) and the matrix. Treatment with IGF-1 increased the protein level of Akt in the matrix, while ERK and GSK-3β protein levels were increased in OM. Simultaneously, IGF-1 treatment elevated the level of Thr202/Tyr204-phospho-ERK in IM and matrix and levels of Ser473-phospho-Akt and Ser9-phospho-GSK-3β in OM, IM and matrix. Exposing cells to reactive oxygen species (ROS) by using antimycin A increased the levels of DUSP5 and PHLPP-1 mainly in OM and induced dephosphorylation of Akt, ERK and GSK-3β. The mitochondrial localization of DUSP5 was confirmed by experiments with mitochondria purified by Percoll gradient centrifugation and by transfection of cells with GFP-tagged DUSP5. Knockdown of either DUSP5 or PHLPP-1 increased the levels of both Thr202/Tyr204-phospho-ERK and Ser473-phospho-Akt in mitochondria. Cell death induced by antimycin A was suppressed by siRNA-mediated knockdown of DUSP5. The results suggest that Akt and ERK in mitochondria show distinct intra-mitochondrial localization and crosstalk in GSK-3β regulation and that recruitment of DUSP5 as well as PHLPP-1 to mitochondria contributes to ROS-induced termination of the protective signaling.

Taurine with combined aerobic and resistance exercise training alleviates myocardium apoptosis in STZ-induced diabetes rats via Akt signaling pathway

AIM

The aim of this study was considering the effects of taurine supplementation with combined aerobic and resistance training (CARE) on myocardial apoptosis and Protein Kinase B (akt) level changes in diabetic rat.

MAIN METHODS

Forty male Wistar rats were randomly divided in to 5 groups of 8 animals in each: 1) control, 2) Diabetes Mellitus (DM), 3) DM with taurine supplementation (DM/T), 4) DM with CARE (DM/CARE), and 5) DM with combination of taurine and CARE (DM/T/CARE). DM was induced by injection of streptozotocin (STZ) and nicotine amid (NA) for 2, 3, 4 and 5 groups. Supplement groups received taurine in gavage, 100 mg/kg of body weight, 6 day per weeks, 8 weeks. CARE was performed at maximal speed and 1RM (40-60% of maximum for both).

KEY FINDINGS

The results of this study showed that DM significantly increased blood glucose and caspase 3, caspase 9 expressions and apoptosis cells in heart tissue and reduced Akt expression (p < 0.001). However, taurine and CARE interventions significantly decreased apoptosis markers (caspase 3 and caspase 9) and significantly increased Akt in heart of diabetic rats compare to DM groups (p < 0.05). The highest improvement observed in DM/T/CARE group (p < 0.05).

SIGNIFICANCE

Based on these results, it seems that the use of taurine with combined aerobic and exercise training minimize the cardiac damage caused by diabetes (especially apoptosis) trough increasing protein kinase Akt expression. This could improve cardiac remodeling after diabetes. However, more research is needed, especially on the human samples.

Nanotoxicology of Dendrimers in the Mammalian Heart: ex vivo and in vivo Administration of G6 PAMAM Nanoparticles Impairs Recovery of Cardiac Function Following Ischemia-Reperfusion Injury

Aim

The effects of polyamidoamine (PAMAM) dendrimers on the mammalian heart are not completely understood. In this study, we have investigated the effects of a sixth-generation cationic dendrimer (G6 PAMAM) on cardiac function in control and diabetic rat hearts following ischemia-reperfusion (I/R) injury.

Methods

Isolated hearts from healthy non-diabetic (Ctr) male Wistar rats were subjected to ischemia and reperfusion (I/R). LV contractility and hemodynamics data were computed digitally whereas cardiac damage following I/R injury was assessed by measuring cardiac enzymes. For ex vivo acute exposure experiments, G6 PAMAM was administered during the first 10 mins of reperfusion in Ctr animals. In chronic in vivo studies, nondiabetic rats (Ctr) received either vehicle or daily i.p. injections of G6 PAMAM (40 mg/kg) for 4 weeks. Diabetic (D) animals received either vehicle or daily i.p. injections of G6 PAMAM (10, 20 or 40 mg/kg) for 4 weeks. The impact of G6 PAMAM on pacing-postconditioning (PPC) was also studied in Ctr and D rats.

Results

In ex vivo studies, acute administration of G6 PAMAM to isolated Ctr hearts during reperfusion dose-dependently impaired recovery of cardiac hemodynamics and vascular dynamics parameters following I/R injury. Chronic daily i.p. injections of G6 PAMAM significantly (P<0.01) impaired recovery of cardiac function following I/R injury in nondiabetic animals but this was not generally observed in diabetic animals except for CF which was impaired by about 50%. G6 PAMAM treatment completely blocked the protective effects of PPC in the Ctr animals.

Conclusion

Acute ex vivo or chronic in vivo treatment with naked G6 PAMAM dendrimer can significantly compromise recovery of non-diabetic hearts from I/R injury and can further negate the beneficial effects of PPC. Our findings are therefore extremely important in the nanotoxicological evaluation of G6 PAMAM dendrimers for potential clinical applications in physiological and pathological settings.

Crizotinib and PARP inhibitors act synergistically by triggering apoptosis in high-grade serous ovarian cancer

High-grade serous ovarian cancer (HGSOC) is the predominant and most lethal histological type of epithelial ovarian cancer. During the last few years, several new treatment options with PARP inhibitors have emerged. The FDA has approved the PARP inhibitor olaparib (Lynparza™) as maintenance treatment after first-line platinum-containing chemotherapy and olaparib, niraparib (Zejula™) and rucaparib (Rubraca™) are approved as maintenance therapies in the recurrent, platinum-sensitive setting; nevertheless, development of resistance limits their efficacy. In this study, new combinatorial treatment strategies targeting key signaling pathways were explored to enhance the activity of PARP inhibitors in HGSOC. Carboplatin, olaparib, niraparib, the PI3K inhibitor LY294002 and the c-Met inhibitor crizotinib were used for this investigation. PARP inhibitors and carboplatin alone and in combination caused accumulation of DNA double-strand breaks and G2/M cell cycle arrest. In contrast, crizotinib alone or in combination with PARP inhibitors induced accumulation of cells in sub-G1. Crizotinib together with either of the PARP inhibitors was more strongly synergistic than combinations with a PARP inhibitor and carboplatin or the PI3K inhibitor. Sequential combination of crizotinib and a PARP inhibitor resulted in activation of ATM/CHK2 and inhibition of c-Met pathways, contributing to a decrease in RAD51 levels and induction of caspase-3 dependent apoptotic cell death and suggesting that the combination of crizotinib with a PARP inhibitor may be considered and further explored as a new therapeutic strategy in HGSOC.

Chronic type 2 but not type 1 diabetes impairs myocardial ischaemic tolerance and preconditioning in C57Bl/6 mice

NEW FINDINGS

• What is the central question of this study? What is the impact of chronic adult-onset diabetes on cardiac ischaemic outcomes and preconditioning? • What is the main finding and its importance? Chronic adult-onset type 2 but not type 1 diabetes significantly impairs myocardial ischaemic tolerance and ischaemic preconditioning. Preconditioning may be detrimental in type 2 diabetes, exaggerating nitrosative stress and apoptotic protein expression.

ABSTRACT

Effects of diabetes on myocardial responses to ischaemia-reperfusion (I-R) and cardioprotective stimuli remain contentious, potentially reflecting influences of disease duration and time of onset. Chronic adult-onset type 1 diabetes (T1D) and type 2 diabetes (T2D) were modelled non-genetically in male C57Bl/6 mice via 5 × 50 mg kg^-1 daily streptozotocin (STZ) injections + 12 weeks' standard chow or 1 × 75 mg kg^-1 STZ injection + 12 weeks' obesogenic diet (32% calories as fat, 57% carbohydrate, 11% protein), respectively. Systemic outcomes were assessed and myocardial responses to I-R ± ischaemic preconditioning (IPC; 3 × 5 min I-R) determined in Langendorff perfused hearts. Uncontrolled T1D was characterised by pronounced hyperglycaemia (25 mm fasting glucose), glucose intolerance and ∼10% body weight loss, whereas T2D mice exhibited moderate hyperglycaemia (15 mm), hyperinsulinaemia, glucose intolerance and 17% weight gain. Circulating ghrelin, resistin and noradrenaline were unchanged with T1D, while leptin increased and noradrenaline declined in T2D mice. Ischaemic tolerance and IPC were preserved in T1D hearts. In contrast, T2D worsened post-ischaemic function (∼40% greater diastolic and contractile dysfunction) and cell death (100% higher troponin efflux), and abolished IPC protection. Whereas IPC reduced post-ischaemic nitrotyrosine and pro-apoptotic Bak and Bax levels in non-diabetic hearts, these effects were reduced in T1D and IPC augmented Bax and nitrosylation in T2D hearts. The data demonstrate chronic T1D does not inhibit myocardial I-R tolerance or IPC, whereas metabolic and endocrine disruption in T2D is associated with ischaemic intolerance and inhibition of IPC. Indeed, normally protective IPC may exaggerate damage mechanisms in T2D hearts.

Disturbed Fatty Acid Oxidation, Endoplasmic Reticulum Stress, and Apoptosis in Left Ventricle of Patients With Type 2 Diabetes

Chronic heart failure is a common complication in patients with type 2 diabetes mellitus (T2DM). T2DM is associated with disturbed metabolism of fat, which can result in excessive accumulation of lipids in cardiac muscle. In the current study, we assessed mitochondrial oxidation of carbohydrates and fatty acids, lipid accumulation, endoplasmic reticulum (ER) stress, and apoptosis in diabetic left ventricle. Left ventricular myocardium from 37 patients (a group of patients with diabetes and a group of patients without diabetes [ejection fraction >50%]) undergoing coronary artery bypass graft surgery was obtained by subepicardial needle biopsy. The group with diabetes had a significantly decreased rate of mitochondrial respiration fueled by palmitoyl-carnitine that correlated with blood glucose dysregulation, while there was no difference in oxidation of pyruvate. Diabetic myocardium also had significantly decreased activity of hydroxyacyl-CoA dehydrogenase (HADHA) and accumulated more lipid droplets and ceramide. Also, markers of ER stress response (GRP78 and CHOP) and apoptosis (cleaved caspase-3) were elevated in diabetic myocardium. These results show that, even in the absence of contractile failure, diabetic heart exhibits a decreased mitochondrial capacity for β-oxidation, increased accumulation of intracellular lipids, ER stress, and greater degree of apoptosis. Lower efficiency of mitochondrial fatty acid oxidation may represent a potential target in combating negative effects of diabetes on the heart.

Empagliflozin normalizes the size and number of mitochondria and prevents reduction in mitochondrial size after myocardial infarction in diabetic hearts

To explore mechanisms by which SGLT2 inhibitors protect diabetic hearts from heart failure, we examined the effect of empagliflozin (Empa) on the ultrastructure of cardiomyocytes in the noninfarcted region of the diabetic heart after myocardial infarction (MI). OLETF, a rat model of type 2 diabetes, and its nondiabetic control, LETO, received a sham operation or left coronary artery ligation 12 h before tissue sampling. Tissues were sampled from the posterior ventricle (i.e., the remote noninfarcted region in rats with MI). The number of mitochondria was larger and small mitochondria were more prevalent in OLETF than in LETO. Fis1 expression level was higher in OLETF than in LETO, while phospho‐Ser637‐Drp1, total Drp1, Mfn1/2, and OPA1 levels were comparable. MI further reduced the size of mitochondria with increased Drp1‐Ser616 phosphorylation in OLETF. The number of autophagic vacuoles was unchanged after MI in LETO but was decreased in OLETF. Lipid droplets in cardiomyocytes and tissue triglycerides were increased in OLETF. Empa administration (10 mg/kg per day) reduced blood glucose and triglycerides and paradoxically increased lipid droplets in cardiomyocytes in OLETF. Empa suppressed Fis1 upregulation, increased Bnip3 expression, and prevented reduction in both mitochondrial size and autophagic vacuole number after MI in OLETF. Together with the results of our parallel study showing upregulation of SOD2 and catalase by Empa, the results indicate that Empa normalizes the size and number of mitochondria in diabetic hearts and that diabetes‐induced excessive reduction in mitochondrial size after MI was prevented by Empa via suppression of ROS and restoration of autophagy.

Effects of Cardiac Hypertrophy, Diabetes, Aging, and Pregnancy on the Cardioprotective Effects of Postconditioning in Male and Female Rats

Background

Aging, left ventricular hypertrophy (LVH), diabetes mellitus, and pregnancy are well-recognized risk factors that increase the prevalence of cardio-ischemic events and are linked to poor clinical recovery following acute myocardial infarction. The coexistence of these risk factors with ischemic heart disease (IHD) deteriorates disease prognosis and could potentially lead to fatal arrhythmias and heart failure. The objective of this study was to investigate the vulnerability of hearts with aging, LVH, diabetes, and pregnancy to ischemic insult and their response to pacing postconditioning- (PPC-) induced heart protection.

Methods

Hearts isolated from aged, spontaneously hypertensive and diabetic male and female rats and hearts from pregnant female rats (n=8 per group) were subjected to coronary occlusion followed by reperfusion using a modified Langendorff system. Hemodynamics data were computed digitally, and cardiac damage was accessed by measurements of infarct size and cardiac enzyme release.

Results

There were no significant differences in the vulnerability of all hearts to ischemic insult compared to their respective controls. PPC improved cardiac hemodynamics and reduced infarct size and cardiac enzyme release in hearts isolated from aged and spontaneously hypertensive female rats and female rats with hypertrophied hearts subjected to PPC (P < 0.001). Aged or hypertrophied male hearts were not protected by PPC maneuver. Moreover, the protective effects of PPC were lost in diabetic male and female hearts although retained in hearts from pregnant rats.

Conclusions

We demonstrate that aging, LVH, diabetes mellitus, and pregnancy do not affect cardiac vulnerability to ischemic insult. Moreover, PPC mediates cardioprotection in a gender-specific manner in aged and spontaneously hypertensive rats. Diabetes mellitus provokes the protective effects of PPC on both genders equally. Finally, we demonstrate that PPC is a new cardioprotective maneuver in hearts from pregnant female rats.

Lycopene restores the effect of ischemic postconditioning on myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Ischemic postconditioning (IPoC) has been demonstrated to prevent myocardial ischemia-reperfusion injury (MIRI), but its cardioprotective effect is abrogated by hypercholesterolemia. The aim of the present study was to determine whether lycopene (LP), a type of carotenoid, can restore the cardioprotective effect of IPoC in hypercholesterolemic rats. Male Wistar rats were fed a cholesterol-enriched diet for 12 weeks to establish a hypercholesterolemic model. The rat hearts were isolated and subjected to 30 min ischemia and 60 min reperfusion using a Langendorff apparatus. LP was administered to the rats intraperitoneally for 5 consecutive days prior to ischemia and reperfusion. Myocardial pathological changes, infarct size and cell apoptosis were measured by hematoxylin and eosin, triphenyltetrazolium chloride and TUNEL staining, respectively. The changes in endoplasmic reticulum (ER) stress markers, the reperfusion injury salvage kinase (RISK) pathway and mitochondrial apoptosis-related proteins were detected by western blotting. Overall, the results demonstrated that low-dose LP in combination with IPoC ameliorated myocardial histopathological changes, reduced the infarct size and release of cardiac enzymes, and decreased cardiomyocyte apoptosis in hypercholesterolemic rats, but no beneficial effects were achieved by the same dose of LP or IPoC treatment were used alone. Furthermore, the combination of LP and IPoC inhibited the expression of glucose-regulated protein 78 and C/EBP homologous protein, increased the phosphorylation levels of AKT, ERK1/2 and glycogen synthase kinase-3β, repressed mitochondrial permeability transition pore opening, and reduced the expression of cytochrome c, cleaved caspase-9 and cleaved caspase-3. Collectively, these findings demonstrated that LP can restore the cardioprotective effects of IPoC on MIRI in hypercholesterolemic rats, and this restoration by LP was mediated by inhibition of ER stress and reactivation of the RISK pathway in hypercholesterolemic rat myocardium.

Cardiomyocyte-GSK-3α promotes mPTP opening and heart failure in mice with chronic pressure overload

Chronic pressure-overload (PO)- induced cardiomyopathy is one of the leading causes of left ventricular (LV) remodeling and heart failure. The role of the α isoform of glycogen synthase kinase-3 (GSK-3α) in PO-induced cardiac remodeling is unclear and its downstream molecular targets are largely unknown. To investigate the potential roles of GSK-3α, cardiomyocyte-specific GSK-3α conditional knockout (cKO) and control mice underwent trans-aortic constriction (TAC) or sham surgeries. Cardiac function in the cKOs and littermate controls declined equally up to 2 weeks of TAC. At 4 week, cKO animals retained concentric LV remodeling and showed significantly less decline in contractile function both at systole and diastole, vs. controls which remained same until the end of the study (6 wk). Histological analysis confirmed preservation of LV chamber and protection against TAC-induced cellular hypertrophy in the cKO. Consistent with attenuated hypertrophy, significantly lower level of cardiomyocyte apoptosis was observed in the cKO. Mechanistically, GSK-3α was found to regulate mitochondrial permeability transition pore (mPTP) opening and GSK-3α-deficient mitochondria showed delayed mPTP opening in response to Ca²⁺ overload. Consistently, overexpression of GSK-3α in cardiomyocytes resulted in elevated Bax expression, increased apoptosis, as well as a reduction of maximum respiration capacity and cell viability. Taken together, we show for the first time that GSK-3α regulates mPTP opening under pathological conditions, likely through Bax overexpression. Genetic ablation of cardiomyocyte GSK-3α protects against chronic PO-induced cardiomyopathy and adverse LV remodeling, and preserves contractile function. Selective inhibition of GSK-3α using isoform-specific inhibitors could be a viable therapeutic strategy to limit PO-induced heart failure.

Sitagliptin attenuates myocardial apoptosis via activating LKB-1/AMPK/Akt pathway and suppressing the activity of GSK-3β and p38α/MAPK in a rat model of diabetic cardiomyopathy

The present study aimed to investigate the protective effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on diabetic cardiomyopathy (DCM)-associated apoptosis and if this effect is mediated via modulating the activity of the survival kinases; AMP-activated protein kinase (AMPK) and Akt & the apoptotic kinases; glycogen synthase kinase-3 β (GSK-3β) and p38 mitogen-activated protein kinase (p38MAPK). Diabetes was induced by a single intraperitoneal injection of streptozotocin (55 mg/kg). Diabetic rats were treated with sitagliptin (10 mg/kg/day, p.o.) and metformin (200 mg/kg/day, p.o. as positive control) for six weeks. Chronic hyperglycemia resulted in elevation of serum cardiac biomarkers reflecting cardiac damage which was supported by H&E stain. The mRNA levels of collagen types I and III were augmented reflecting cardiac fibrosis and hypertrophy which was supported by Masson trichome stain and enhanced phosphorylation of p38MAPK. Cardiac protein levels of cleaved casapse-3, BAX were elevated, whereas, the levels of Bcl-2 and p-BAD were reduced indicating cardiac apoptosis which could be attributed to the diabetes-induced reduced phosphorylation of Akt and AMPK with concomitant augmented activation of GSK-3β and p38MAPK. Protein levels of liver kinase B-1, the upstream kinase of AMPK were also supressed. Sitagliptin administration alleviated the decreased phosphorylation of AMPK and Akt, inactivated the GSK-3β and p38 AMPK, therefore, attenuating the apoptosis and hypertrophy induced by hyperglycemia in the diabetic heart. In conclusion, sitagliptin exhibits valuable therapeutic potential in the management of DCM by attenuating apoptosis. The underlying mechanism may involve the modulating activity of AMPK, Akt, GSK-3β and p38MAPK.

Tauroursodeoxycholic Acid Alleviates H2O2-Induced Oxidative Stress and Apoptosis via Suppressing Endoplasmic Reticulum Stress in Neonatal Rat Cardiomyocytes

Introduction:

We aimed to test the mechanism of protective effects of tauroursodeoxycholic acid (TUDCA) on cardiovascular disease using cultured cardiomyocytes.

Methods:

Neonatal rat cardiomyocytes (NRCMs) were isolated and cultured and then the cells were divided into 4 groups based on the treatments: control group (cells treated with culture medium), H₂O₂/thapsigargin (TG) group (cells treated with oxidative stress and endoplasmic reticulum [ER] stress inducer), TUDCA group, and H₂O₂/TG + TUDCA group. The treated NRCMs were then subjected to serial analyses including flow cytometry, enzyme-linked immunosorbent assay, and Western blotting.

Results:

Tauroursodeoxycholic acid significantly attenuated H₂O₂-induced reactive oxygen species generation and lactate dehydrogenase release and restored H₂O₂-induced reductions of glutathione and superoxide dismutase levels in NRCMs. Tauroursodeoxycholic acid also alleviated H₂O₂-induced cardiomyocytes apoptosis, as well as the Bax/Bcl2 ratio compared with that of H₂O₂ treated alone. In addition, TUDCA suppressed TG-induced ER stress as reflected by inversing cell viability and the expression levels of glucose-regulated protein 78 kDa and C/enhancer-binding protein homologous protein.

Conclusion:

Our data indicated that TUDCA-mediated inhibition on H₂O₂-induced oxidative stress and cardiomyocytes apoptosis was through suppressing ER stress, and TUDCA possesses the potential to be developed as therapeutic tool in clinical use for cardiovascular diseases.

Does p53 Inhibition Suppress Myocardial Ischemia-Reperfusion Injury?

p53 is well known as a regulator of apoptosis and autophagy. In addition, a recent study showed that p53 is a modulator of the opening of the mitochondrial permeability transition pore (mPTP), a trigger event of necrosis, but the role of p53 in necrosis induced by myocardial ischemia-reperfusion (I/R) remains unclear. The aim of this study was to determine the role of p53 in acute myocardial I/R injury in perfused mouse hearts. In male C57BL6 mice between 12 and 15 weeks of age, 2 types of p53 inhibitors were used to suppress p53 function during I/R: pifithrin-α, an inhibitor of transcriptional functions of p53, and pifithrin-μ, an inhibitor of p53 translocation from the cytosol to mitochondria. Neither infusion of these inhibitors before ischemia nor infusion for the first 30-minute period of reperfusion reduced infarct size after 20-minute ischemia/120-minute reperfusion. Infarct sizes were similar in p53 heterozygous knockout mice (p53^+/-) and wild-type mice (WT), but recovery of rate pressure product (RRP) 120 minutes after reperfusion was higher in p53^+/- than in WT. The protein expression of p53 in WT was negligible under baseline conditions, during ischemia, and at 10 minutes after the start of reperfusion, but it became detectable at 120 minutes after reperfusion. In conclusion, upregulation of p53 during the late phase of reperfusion plays a significant role in contractile dysfunction after reperfusion, although p53 is not involved in cardiomyocyte necrosis during ischemia or in the early phase of reperfusion.

Induction of endoplasmic reticulum stress and changes in expression levels of Zn2+-transporters in hypertrophic rat heart

Clinical and experimental studies have shown an association between intracellular free Zn2+ ([Zn2+]i)-dyshomeostasis and cardiac dysfunction besides [Ca2+]i-dyshomeostasis. Since [Zn2+]i-homeostasis is regulated through Zn2+-transporters depending on their subcellular distributions, one can hypothesize that any imbalance in Zn2+-homeostasis via alteration in Zn2+-transporters may be associated with the induction of ER stress and apoptosis in hypertrophic heart. We used a transverse aortic constriction (TAC) model to induce hypertrophy in young male rat heart. We confirmed the development of hypertrophy with a high ratio of heart to body weight and cardiomyocyte capacitance. The expression levels of ER stress markers GRP78, CHOP/Gadd153, and calnexin are significantly high in TAC-group in comparison to those of controls (SHAM-group). Additionally, we detected high expression levels of apoptotic status marker proteins such as the serine kinase GSK-3β, Bax-to-Bcl-2 ratio, and PUMA in TAC-group in comparison to SHAM-group. The ratios of phospho-Akt to Akt and phospho-NFκB to the NFκB are significantly higher in TAC-group than in SHAM-group. Furthermore, we observed markedly increased phospho-PKCα and PKCα levels in TAC-group. We, also for the first time, determined significantly increased ZIP7, ZIP14, and ZnT8 expressions along with decreased ZIP8 and ZnT7 levels in the heart tissue from TAC-group in comparison to SHAM-group. Furthermore, a roughly calculated total expression level of ZIPs responsible for Zn2+-influx into the cytosol (increased about twofold) can be also responsible for the markedly increased [Zn2+]i detected in hypertrophic cardiomyocytes. Taking into consideration the role of increased [Zn2+]i via decreased ER-[Zn2+] in the induction of ER stress in cardiomyocytes, our present data suggest that differential changes in the expression levels of Zn2+-transporters can underlie mechanical dysfunction, in part due to the induction of ER stress and apoptosis in hypertrophic heart via increased [Zn2+]i- besides [Ca2+]i-dyshomeostasis.

Inhibitors of soluble epoxide hydrolase minimize ischemia-reperfusion-induced cardiac damage in normal, hypertensive, and diabetic rats

AIM

We designed a study to evaluate the cardioprotective effect of two soluble epoxide hydrolase (sEH) inhibitors, 1-(1-propanoylpiperidin-4-yl)-3-(4-trifluoromethoxy)phenyl)urea (TPPU) and trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]cyclohexyloxy}benzoic acid (t-TUCB), in ischemia-reperfusion (IR) model.

METHODS

Cardioprotective effects of the sEH inhibitors were evaluated against IR-induced myocardial damage in hearts from normal, hypertensive, and diabetic rats using Langendorff's apparatus. In addition, the effect of sEH inhibitors on endothelial function was evaluated in vitro and ex vivo using isolated rat thoracic aorta.

RESULTS

Ischemia-reperfusion (IR) increased the myocardial damage in hearts from normal rats. IR-induced myocardial damage was augmented in hearts isolated from hypertensive and diabetic rats. Myocardial damage as evident from increase in the activities of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) in heart perfusate was associated with significant decrease in the heart rate and developed tension, and increase in the resting tension in isolated heart. Both sEH inhibitors protected the heart in normal, hypertensive, and diabetic rats subjected to IR injury. The sEH inhibitor t-TUCB relaxed phenylephrine precontracted aorta from normal rats. Relaxant effect of acetylcholine (ACh) was reduced in aortas from diabetic and hypertensive rats compared to normal rats. Pretreatment of sEH inhibitors to diabetic and hypertensive rats increased relaxant effect of ACh on aortas isolated from these rats.

CONCLUSIONS

Prophylactic treatment with sEH inhibitors decreased myocardial damage due to IR, hypertension and diabetes, and decreased endothelial dysfunction created by diabetes and hypertension. Therefore, inhibitors of sEH are useful probes to study cardiovascular pathology, and inhibition of the sEH is a potential approach in the management of IR-induced cardiac damage and endothelial dysfunction-related cardiovascular disorders.

Influence of diabetes mellitus duration on the efficacy of ischemic preconditioning in a Zucker diabetic fatty rat model

Augmented mortality and morbidity following an acute myocardial infarction in patients with diabetes mellitus Type 2 (T2DM) may be caused by increased sensitivity to ischemia reperfusion (IR) injury or altered activation of endogenous cardioprotective pathways modified by T2DM per se or ischemic preconditioning (IPC). We aimed to investigate, whether the duration of T2DM influences sensitivity against IR injury and the efficacy of IPC, and how myocardial glucose oxidation rate was involved. Male Zucker diabetic fatty rats (homozygote (fa/fa)) at ages 6-(prediabetic), 12- (onset diabetes) and 24-weeks of age (late diabetes) and their age-matched non-diabetic controls (heterozygote (fa/+) were subjected to IR injury in the Langendorff model and randomised to IPC stimulus or control. T2DM rats were endogenously protected at onset of diabetes, as infarct size was lower in 12-weeks T2DM animals than in 6- (35±2% vs 53±4%; P = 0.006) and 24-weeks animals (35±2% vs 72±4%; P<0.0001). IPC reduced infarct size in all groups irrespective of the presence of T2DM and its duration (32±3%; 20±2%; 36±4% respectively; (ANOVA P<0.0001). Compared to prediabetic rats, myocardial glucose oxidation rates were reduced during stabilisation and early reperfusion at onset of T2DM, but these animals retained the ability to increase oxidation rate in late reperfusion. Late diabetic rats had low glucose oxidation rates throughout stabilisation and reperfusion. Despite inherent differences in sensitivity to IR injury, the cardioprotective effect of IPC was preserved in our animal model of pre-, early and late stage T2DM and associated with adaptations to myocardial glucose oxidation capacity.

Monoamine oxidase-dependent endoplasmic reticulum-mitochondria dysfunction and mast cell degranulation lead to adverse cardiac remodeling in diabetes

Monoamine oxidase (MAO) inhibitors ameliorate contractile function in diabetic animals, but the mechanisms remain unknown. Equally elusive is the interplay between the cardiomyocyte alterations induced by hyperglycemia and the accompanying inflammation. Here we show that exposure of primary cardiomyocytes to high glucose and pro-inflammatory stimuli leads to MAO-dependent increase in reactive oxygen species that causes permeability transition pore opening and mitochondrial dysfunction. These events occur upstream of endoplasmic reticulum (ER) stress and are abolished by the MAO inhibitor pargyline, highlighting the role of these flavoenzymes in the ER/mitochondria cross-talk. In vivo, streptozotocin administration to mice induced oxidative changes and ER stress in the heart, events that were abolished by pargyline. Moreover, MAO inhibition prevented both mast cell degranulation and altered collagen deposition, thereby normalizing diastolic function. Taken together, these results elucidate the mechanisms underlying MAO-induced damage in diabetic cardiomyopathy and provide novel evidence for the role of MAOs in inflammation and inter-organelle communication. MAO inhibitors may be considered as a therapeutic option for diabetic complications as well as for other disorders in which mast cell degranulation is a dominant phenomenon.

Hydrogen sulfide attenuates myocardial fibrosis in diabetic rats through the JAK/STAT signaling pathway

The aim of the present study was to determine the role of hydrogen sulfide (H₂S) in improving myocardial fibrosis and its effects on oxidative stress, endoplasmic reticulum (ER) stress and cell apoptosis in diabetic rats, by regulating the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway. A total of 40 male Sprague-Dawley rats were randomly divided into four groups (n=10) as follows: Normal (control group), diabetes mellitus [streptozotocin (STZ) group], diabetes mellitus treated with H₂S (STZ + H₂S group), and normal rats treated with H₂S (H₂S group). Diabetes in rats was induced by intra-peritoneal (i.p.) injection of STZ at a dose of 40 mg/kg. NaHS (100 µmol/kg, i.p.), which was used as an exogenous donor of H₂S, was administered to rats in the STZ + H₂S and H₂S groups. After 8 weeks, the pathological morphological changes in myocardial fibers were observed following hematoxylin and eosin and Masson's trichrome staining. Apoptosis of myocardial tissue was analyzed by the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Oxidative stress was evaluated through detecting the content of malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), glutathione (GSH) and superoxide dismutase (SOD) in the myocardial cells by ELISA. The expression of collagen III, matrix metalloproteinase (MMP)8, MMP14, tissue inhibitor of metalloproteinase (TIMP)2, transforming growth factor (TGF)-β, cystathionine-γ-lyase (CSE), eukaryotic initiation factor 2α (eIF2α), GRP94, Bcl-2, caspase-3, tumor necrosis factor (TNF)-α, nuclear factor-κB (NF-κB) and proteins related to the JAK/STAT pathway, was detected by western blot analysis. The results indicated that the array of myocardial cells was markedly disordered in STZ group rats; compared with the control group, both myocardial interstitial fibrosis and the deposition of collagen III were increased. Furthermore, the expression ratio of MMPs/TIMPs was dysregulated, while the expression levels of TGF-β, eIF2α, GRP94, caspase-3, TNF-α, NF-κB, MDA and 4-HNE were significantly increased. Furthermore, the expressions of JAK-1/2 and STAT1/3/5/6 were also markedly upregulated, while those of CSE, SOD, GSH and Bcl-2 were downregulated. Compared with the STZ group, these changes were reversed in the STZ + H₂S group. The results of the present study demonstrated that H₂S can improve myocardial fibrosis in diabetic rats, and the underlying mechanism may be associated with the downregulation of the JAK/STAT signaling pathway, thereby suppressing oxidative stress and ER stress, inflammatory reaction and cell apoptosis.

Chronic O-GlcNAcylation and Diabetic Cardiomyopathy: The Bitterness of Glucose

Type 2 diabetes (T2D) is a major risk factor for heart failure. Diabetic cardiomyopathy (DC) is characterized by diastolic dysfunction and left ventricular hypertrophy. Epidemiological data suggest that hyperglycaemia contributes to the development of DC. Several cellular pathways have been implicated in the deleterious effects of high glucose concentrations in the heart: oxidative stress, accumulation of advanced glycation end products (AGE), and chronic hexosamine biosynthetic pathway (HBP) activation. In the present review, we focus on the effect of chronic activation of the HBP on diabetic heart function. The HBP supplies N-acetylglucosamine moiety (O-GlcNAc) that is O-linked by O-GlcNAc transferase (OGT) to proteins on serine or threonine residues. This post-translational protein modification modulates the activity of the targeted proteins. In the heart, acute activation of the HBP in response to ischaemia-reperfusion injury appears to be protective. Conversely, chronic activation of the HBP in the diabetic heart affects Ca²⁺ handling, contractile properties, and mitochondrial function and promotes stress signaling, such as left ventricular hypertrophy and endoplasmic reticulum stress. Many studies have shown that O-GlcNAc impairs the function of key protein targets involved in these pathways, such as phospholamban, calmodulin kinase II, troponin I, and FOXO1. The data show that excessive O-GlcNAcylation is a major trigger of the glucotoxic events that affect heart function under chronic hyperglycaemia. Supporting this finding, pharmacological or genetic inhibition of the HBP in the diabetic heart improves heart function. In addition, the SGLT2 inhibitor dapagliflozin, a glucose lowering agent, has recently been shown to lower cardiac HBP in a lipodystophic T2D mice model and to concomitantly improve the diastolic dysfunction of these mice. Therefore, targeting cardiac-excessive O-GlcNAcylation or specific target proteins represents a potential therapeutic option to treat glucotoxicity in the diabetic heart.

Essential role for EGFR tyrosine kinase and ER stress in myocardial infarction in type 2 diabetes

We previously reported that EGFR tyrosine kinase (EGFRtk) activity and endoplasmic reticulum (ER) stress are enhanced in type 2 diabetic (T2D) mice and cause vascular dysfunction. In the present study, we determined the in vivo contribution of EGFRtk and ER stress in acute myocardial infarction induced by acute ischemia (40 min)-reperfusion (24 h) (I/R) injury in T2D (db^-/db^-) mice. We treated db^-/db^- mice with EGFRtk inhibitor (AG1478, 10 mg/kg/day) for 2 weeks. Mice were then subjected to myocardial I/R injury. The db^-/db^- mice developed a significant infarct after I/R injury. The inhibition of EGFRtk significantly reduced the infarct size and ER stress induction. We also determined that the inhibition of ER stress (tauroursodeoxycholic acid, TUDCA, 150 mg/kg per day) in db^-/db^- significantly decrease the infarct size indicating that ER stress is a downstream mechanism to EGFRtk. Moreover, AG1478 and TUDCA reduced myocardium p38 and ERK1/2 MAP-kinases activity, and increased the activity of the pro-survival signaling cascade Akt. Additionally, the inhibition of EGFRtk and ER stress reduced cell apoptosis and the inflammation as indicated by the reduction in macrophages and neutrophil infiltration. We determined for the first time that the inhibition of EGFRtk protects T2D heart against I/R injury through ER stress-dependent mechanism. The cardioprotective effect of EGFRtk and ER stress inhibition involves the activation of survival pathway, and inhibition of apoptosis, and inflammation. Thus, targeting EGFRtk and ER stress has the potential for therapy to overcome myocardial infarction in T2D.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

Myocardial injury in diabetic patients with multivessel coronary artery disease after revascularization interventions

BACKGROUND

Diabetic patients may be more susceptible to myocardial injury after coronary interventions. Thus, the aim of this study was to assess the release of cardiac biomarkers, CK-MB and troponin, and the findings of new late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) in patients with type 2 diabetes mellitus after elective revascularization procedures for multivessel coronary artery disease (CAD).

METHODS

Patients with multivessel CAD and preserved systolic ventricular function underwent either elective percutaneous coronary intervention (PCI), off-pump or on-pump bypass surgery (CABG). Troponin and CK-MB were systematically collected at baseline, 6, 12, 24, 36, 48 and 72 h after the procedures. CMR with LGE was performed before and after the interventions. Patients were stratified according to diabetes status at study entry. Biomarkers and CMR results were compared between diabetic and nondiabetics patients. Analyses of correlation were also performed among glycemic and glycated hemoglobin (A1c) levels and troponin and CK-MB peak levels. Patients were also stratified into tertiles of fasting glycemia and A1c levels and were compared in terms of periprocedural myocardial infarction (PMI) on CMR.

RESULTS

Ninety (44.5%) of the 202 patients had diabetes mellitus at study entry. After interventions, median peak troponin was 2.18 (0.47, 5.14) and 2.24 (0.69, 5.42) ng/mL (P = 0.81), and median peak CK-MB was 14.1 (6.8, 31.7) and 14.0 (4.2, 29.8) ng/mL (P = 0.43), in diabetic and nondiabetic patients, respectively. The release of troponin and CK-MB over time was statistically similar in both groups and in the three treatments, besides PCI. New LGE on CMR indicated that new myocardial fibrosis was present in 18.9 and 17.3% (P = 0.91), and myocardial edema in 15.5 and 22.9% (P = 0.39) in diabetic and nondiabetic patients, respectively. The incidence of PMI in the glycemia tertiles was 17.9% versus 19.3% versus 18.7% (P = 0.98), and in the A1c tertiles was 19.1% versus 13.3% versus 22.2% (P = 0.88).

CONCLUSIONS

In this study, diabetes mellitus did not add risk of myocardial injury after revascularization interventions in patients with multivessel coronary artery disease. Trial Registration Name of Registry: Evaluation of cardiac biomarker elevation after percutaneous coronary intervention or coronary artery bypass graft; URL: http://www.controlled-trials.com.ISRCTN09454308.

4-Phenylbutyrate Benefits Traumatic Hemorrhagic Shock in Rats by Attenuating Oxidative Stress, Not by Attenuating Endoplasmic Reticulum Stress

OBJECTIVE

Vascular dysfunction such as vascular hyporeactivity following severe trauma and shock is a major cause of death in injured patients. Oxidative stress and endoplasmic reticulum stress play an important role in vascular dysfunction. The objective of the present study was to determine whether or not 4-phenylbutyrate can improve vascular dysfunction and elicit antishock effects by inhibiting oxidative and endoplasmic reticulum stress.

DESIGN

Prospective, randomized, controlled laboratory experiment.

SETTING

State key laboratory of trauma, burns, and combined injury.

SUBJECTS

Five hundred and fifty-two Sprague-Dawley rats.

INTERVENTIONS

Rats were anesthetized, and a model of traumatic hemorrhagic shock was established by left femur fracture and hemorrhage. The effects of 4-phenylbutyrate (5, 20, 50, 100, 200, and 300 mg/kg) on vascular reactivity, animal survival, hemodynamics, and vital organ function in traumatic hemorrhagic shock rats and cultured vascular smooth muscle cells, and the relationship to oxidative stress and endoplasmic reticulum stress was observed.

MEASUREMENTS AND MAIN RESULTS

Lower doses of 4-phenylbutyrate significantly improved the vascular function, stabilized the hemodynamics, and increased the tissue blood flow and vital organ function in traumatic hemorrhagic shock rats, and markedly improved the survival outcomes. Among all dosages observed in the present study, 20 mg/kg of 4-phenylbutyrate had the best effect. Further results indicated that 4-phenylbutyrate significantly inhibited the oxidative stress, decreased shock-induced oxidative stress index such as the production of reactive oxygen species, increased the antioxidant enzyme levels such as superoxide dismutase, catalase, and glutathione, and improved the mitochondrial function by inhibiting the opening of the mitochondrial permeability transition pore in rat artery and vascular smooth muscle cells. In contrast, 4-phenylbutyrate did not affect the changes of endoplasmic reticulum stress markers following traumatic hemorrhagic shock. Furthermore, 4-phenylbutyrate increased the nuclear levels of nuclear factor-E2-related factor 2, and decreased the nuclear levels of nuclear factor κB in hypoxic vascular smooth muscle cells.

CONCLUSIONS

4-phenylbutyrate has beneficial effects for traumatic hemorrhagic shock including improving animal survival and protecting organ function. These beneficial effects of 4-phenylbutyrate in traumatic hemorrhagic shock result from its vascular function protection via attenuation of the oxidative stress and mitochondrial permeability transition pore opening. Nuclear factor-E2-related factor 2 and nuclear factor-κB may be involved in 4-phenylbutyrate-mediated inhibition of oxidative stress.

Pharmacological postconditioning with atorvastatin calcium attenuates myocardial ischemia/reperfusion injury in diabetic rats by phosphorylating GSK3β

Diabetes is an independent risk factor for myocardial ischemia, and many epidemiological data and laboratory studies have revealed that diabetes significantly exacerbated myocardial ischemia/reperfusion injury and ameliorated protective effects. The present study aimed to determine whether pharmacological postconditioning with atorvastatin calcium lessened diabetic myocardial ischemia/reperfusion injury, and investigated the role of glycogen synthase kinase (GSK3β) in this. A total of 72 streptozotocin-induced diabetic rats were randomly divided into six groups, and 24 age-matched male non-diabetic Sprague-Dawley rats were randomly divided into two groups. Rats all received 40 min myocardial ischemia followed by 180 min reperfusion, except sham-operated groups. Compared with the non-diabetic ischemia/reperfusion model group, the diabetic ischemia/reperfusion group had a comparable myocardial infarct size, but a higher level of serum cardiac troponin I (cTnI) and morphological alterations to their myocardial cells. Compared with the diabetic ischemia/reperfusion group, the group that received pharmacological postconditioning with atorvastatin calcium had smaller myocardial infarct sizes, lower levels of cTnI, reduced morphological alterations to myocardial cells, higher levels of p-GSK3β, heat shock factor (HSF)-1 and heat shock protein (HSP)70. The cardioprotective effect conferred by atorvastatin calcium did not attenuate myocardial ischemia/reperfusion injury following application of TDZD-8, which phosphorylates and inactivates GSK3β. Pharmacological postconditioning with atorvastatin calcium may attenuate diabetic heart ischemia/reperfusion injury in the current context. The phosphorylation of GSK3β serves a critical role during the cardioprotection in diabetic rats, and p-GSK3β may accelerate HSP70 production partially by activating HSF-1 during myocardial ischemic/reperfusion injury.

Insufficient activation of Akt upon reperfusion because of its novel modification by reduced PP2A-B55α contributes to enlargement of infarct size by chronic kidney disease

Chronic kidney disease (CKD) increases myocardial infarct size by an unknown mechanism. Here we examined the hypothesis that impairment of protective PI3K-PDK1-Akt and/or mTORC-Akt signaling upon reperfusion contributes to CKD-induced enlargement of infarct size. CKD was induced in rats by 5/6 nephrectomy (SNx group) 4 weeks before myocardial infarction experiments, and sham-operated rats served as controls (Sham group). Infarct size as a percentage of area at risk after ischemia/reperfusion was significantly larger in the SNx group than in the Sham group (56.3 ± 4.6 vs. 41.4 ± 2.0%). In SNx group, myocardial p-Akt-Thr308 level at baseline was elevated, and reperfusion-induced phosphorylation of p-Akt-Ser473, p-p70s6K and p-GSK-3β was significantly suppressed. Inhibition of Akt-Ser473 phosphorylation upon reperfusion by Ku-0063794 significantly increased infarct size in the Sham group but not in the SNx group. There was no difference between the two groups in activities of mTORC2 and PDK1 and protein level of PTEN. However, the PP2A regulatory subunit B55α, which specifically targets Akt-Thr308, was reduced by 24% in the SNx group. Knockdown of B55α by siRNA increased baseline p-Akt-Thr308 and blunted Akt-Ser473 phosphorylation in response to insulin-like growth factor-1 (IGF-1) in H9c2 cells. A blunted response of Akt-Ser473 to IGF-1 was also observed in HEK293 cells transfected with a p-Thr308-mimetic Akt mutant (T308D). These results indicate that increased Akt-Thr308 phosphorylation by down-regulation of B55α inhibits Akt-Ser473 phosphorylation upon reperfusion in CKD and that the impaired Akt activation by insufficient Ser473 phosphorylation upon reperfusion contributes to infarct size enlargement by CKD.

Insights for Oxidative Stress and mTOR Signaling in Myocardial Ischemia/Reperfusion Injury under Diabetes

Diabetes mellitus (DM) displays a high morbidity. The diabetic heart is susceptible to myocardial ischemia/reperfusion (MI/R) injury. Impaired activation of prosurvival pathways, endoplasmic reticulum (ER) stress, increased basal oxidative state, and decreased antioxidant defense and autophagy may render diabetic hearts more vulnerable to MI/R injury. Oxidative stress and mTOR signaling crucially regulate cardiometabolism, affecting MI/R injury under diabetes. Producing reactive oxygen species (ROS) and reactive nitrogen species (RNS), uncoupling nitric oxide synthase (NOS), and disturbing the mitochondrial quality control may be three major mechanisms of oxidative stress. mTOR signaling presents both cardioprotective and cardiotoxic effects on the diabetic heart, which interplays with oxidative stress directly or indirectly. Antihyperglycemic agent metformin and newly found free radicals scavengers, Sirt1 and CTRP9, may serve as promising pharmacological therapeutic targets. In this review, we will focus on the role of oxidative stress and mTOR signaling in the pathophysiology of MI/R injury in diabetes and discuss potential mechanisms and their interactions in an effort to provide some evidence for cardiometabolic targeted therapies for ischemic heart disease (IHD).

Upregulation of endoplasmic reticulum stress is associated with diaphragm contractile dysfunction in a rat model of sepsis

Sepsis often causes diaphragm contractile dysfunction. Endoplasmic reticulum (ER) stress has been implicated in muscle contractile dysfunction. However, it remains unknown if ER stress occurs in the diaphragm during sepsis. In the present study, rats were divided into 4 groups and received placebo or one of three durations of endotoxin treatment (24, 48 h and 7 days). Isometric contractile force of the diaphragm was measured and lung wet-to-dry ratio (W/D) was calculated. Hematoxylin and eosin (H&E) staining of lung tissue was performed and electron microscopy assessed ER damage in the diaphragm during sepsis. The mRNA and protein expression of glucose‑regulated protein 78 kDa (GRP78), glucose-regulated protein 94 kDa (GRP94), C/EBP homologous protein (CHOP), endoplasmic reticulum protein 44 (ERP44), protein disulfide-isomerase like protein (ERP57) and protein disulfide isomerase family A member 4 (ERP72) in diaphragm muscles were measured using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. The level of cleaved caspase-12 was analyzed by western blot analysis. The results demonstrated that sepsis increased lung W/D. H&E staining revealed that sepsis caused alveolar congestion, hemorrhage and rupture. Swollen and distended ER was observed using electron microscopy during sepsis and decreased diaphragm contractile function was also observed. The expression levels of ER stress markers (GRP78, GRP94, CHOP, ERP44, ERP57 and ERP72) and the level of cleaved caspase‑12 were significantly elevated in septic rats compared with control rats, particularly in the 48 h group. In conclusion, the present study indicated that weakened diaphragm contraction and damaged ER in septic rats was associated with increased expression of ER stress markers.

Tauroursodeoxycholic acid inhibits endoplasmic reticulum stress, blocks mitochondrial permeability transition pore opening, and suppresses reperfusion injury through GSK-3ß in cardiac H9c2 cells

This study investigates whether inhibition of endoplasmic reticulum (ER) stress prevents opening of the mitochondrial permeability transition pore (mPTP) and evaluates the corresponding signaling pathways involved in this process. Exposure of cardiac H9c2 cells to 800 µM H₂O₂ for 20 min opened mPTP in response to oxidative stress, as demonstrated by quenching of tetramethylrhodamine ethyl ester (TMRE) fluorescence. Oxidative stress-induced mPTP opening was rescued by the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) in a dose-dependent manner at low concentrations. The PI3K and PKG inhibitors LY294002 and KT5823 inhibited the effect of TUDCA on mPTP opening, suggesting the involvement of PI3K/Akt and PKG signaling pathways. TUDCA significantly increased glycogen synthase kinase 3 (GSK-3β) phosphorylation at Ser-9, with peak effect at 30 µM TUDCA. The level of GRP78 (ER chaperone) expression was significantly upregulated by 30 µM TUDCA. TUDCA-induced increases in Akt and GSK-3β phosphorylation were inhibited by LY294002, whereas KT5823 suppressed TUDCA-induced increases in VASP and GSK-3β phosphorylation. Oxidative stress severely affected cell morphology and ultrastructure. TUDCA prevented H₂O₂-induced ER swelling and mitochondrial damage. TUDCA boosted the viability of cells disrupted by ischemia/reperfusion (I/R), indicating that TUDCA eased reperfusion injury. However, TUDCA did not improve the viability of cells expressing the constitutively active GSK-3β mutant (GSK-3β-S9A-HA) that were subjected to I/R, suggesting an essential role of GSK-3β inactivation in TUDCA-mediated cardioprotection against reperfusion damage. These data indicate that ER stress inhibition prevents mPTP opening and attenuates reperfusion injury through GSK-3β inactivation. The PI3K/Akt and PKG pathways may mediate GSK-3β inactivation.

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.

Deciphering the role of ferulic acid against streptozotocin-induced cellular stress in the cardiac tissue of diabetic rats

The cardiomyocytes are one of the major sources of hyperglycemia induced ROS generation. The present study focuses on the ameliorative role of ferulic acid in combating cardiac complications in diabetic rats. Induction of diabetes by STZ in male Wistar rats (at a dose of 50 mg kg-1 body wt, i.p.) reduced body weight and plasma insulin level, enhanced blood glucose, disturbed the intra-cellular antioxidant machineries and disintegrated the normal radiation pattern of cardiac muscle fibers. Induction of ER stress (up-regulation in the levels of CHOP, GRP78, eIF2α signaling, increased calpain-1 expression), caspase-3 activation, PARP cleavage and DNA fragmentation were evidenced from immunoblot analyses and DNA fragmentation assay. However, ferulic acid administration, (at a dose of 50 mg kg-1 body wt, orally for eight weeks) in post-hyperglycemia could reverse such adverse effects. Also, the molecule increased GLUT-4 translocation to the cardiac membrane by enhanced phosphorylation of PI3Kinase, AKT and inactivation of GSK-3β thereby altering the hyperglycemic condition in the cardiac tissue of diabetic rats. Therefore, as a potential therapeutic, ferulic acid, exhibiting antioxidant and hypoglycemic effects, may hold promise in circumventing stress mediated diabetic cardiomyopathy in rats.

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.

Ischaemic conditioning and targeting reperfusion injury: a 30 year voyage of discovery

To commemorate the auspicious occasion of the 30th anniversary of IPC, leading pioneers in the field of cardioprotection gathered in Barcelona in May 2016 to review and discuss the history of IPC, its evolution to IPost and RIC, myocardial reperfusion injury as a therapeutic target, and future targets and strategies for cardioprotection. This article provides an overview of the major topics discussed at this special meeting and underscores the huge importance and impact, the discovery of IPC has made in the field of cardiovascular research.

JNK/PI3K/Akt signaling pathway is involved in myocardial ischemia/reperfusion injury in diabetic rats: effects of salvianolic acid A intervention

Recent studies have demonstrated that diabetes impairs the phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathway, while insulin resistance syndrome has been associated with alterations of this pathway in diabetic rats after ischemia/reperfusion (I/R), and activation of C-jun N-terminal kinase (JNK) is involved. The present study was designed to investigate whether inhibiting JNK activity would partially restore the PI3K/Akt signaling pathway and protect against myocardial I/R injury in diabetic rats, and to explore the effect of intervention with salvianolic acid A (Sal A). The inhibitor of JNK (SP600125) and Sal A were used in type 2 diabetic (T2D) rats, outcome measures included heart hemodynamic data, myocardial infarct size, the release of lactate dehydrogenase (LDH), SERCA2a activity, cardiomyocyte apotosis, expression levels of Bcl-2, Bax and cleaved caspase-3, and the phosphorylation status of Akt and JNK. The p-Akt levels were increased after myocardial I/R in non-diabetic rats, while there was no change in diabetic rats. Pretreatment with the SP600125 and Sal A decreased the p-JNK levels and increased the p-Akt levels in diabetic rats with I/R, and heart hemodynamic data improved, infarct size and LDH release decreased, SERCA2a activity increased, Bax and cleaved caspase-3 expression levels decreased, and the expression of Bcl-2 and the Bcl-2/Bax ratio increased. Our results suggest that the JNK/PI3K/Akt signaling pathway is involved in myocardial I/R injury in diabetic rats and Sal A exerts an anti-apoptotic effect and improves cardiac function following I/R injury through the JNK/PI3K/Akt signaling pathway in this model.