Impairment of endothelial-myocardial interaction increases the susceptibility of cardiomyocytes to ischemia/reperfusion injury

Optimizing myocardial cell protection with xanthine derivative KMUP-3 potentiates autophagy through the PI3K/Akt/eNOS axis

BACKGROUND

Autophagy can have either beneficial or detrimental effects on various heart diseases. Pharmacological interventions improve cardiac function, which is correlated with enhanced autophagy. To assess whether a xanthine derivative (KMUP-3) treatment coincides with enhanced autophagy while also providing cardio-protection, we investigated the hypothesis that KMUP-3 treatment activation of autophagy through PI3K/Akt/eNOS signalling offered cardioprotective properties.

METHODS

The pro-autophagic effect of KMUP-3 was performed in a neonatal rat model targeting cardiac fibroblasts and cardiomyocytes, and by assessing the impact of KMUP-3 treatment on cardiotoxicity, we used antimycin A-induced cardiomyocytes.

RESULTS

As determined by transmission electron microscopy observation, KMUP-3 enhanced autophagosome formation in cardiac fibroblasts. Furthermore, KMUP-3 significantly increased the expressions of autophagy-related proteins, LC3 and Beclin-1, both in a time- and dose-dependent manner; moreover, the pro-autophagy and nitric oxide enhancement effects of KMUP-3 were abolished by inhibitors targeting eNOS and PI3K in cardiac fibroblasts and cardiomyocytes. Notably, KMUP-3 ameliorated cytotoxic effects induced by antimycin A, demonstrating its protective autophagic response.

CONCLUSION

These findings enable the core pathway of PI3K/Akt/eNOS axis in KMUP-3-enhanced autophagy activation and suggest its principal role in safeguarding against cardiotoxicity.

Heart-on-a-chip systems: disease modeling and drug screening applications

Cardiovascular disease (CVD) is the leading cause of death worldwide, casting a substantial economic footprint and burdening the global healthcare system. Historically, pre-clinical CVD modeling and therapeutic screening have been performed using animal models. Unfortunately, animal models oftentimes fail to adequately mimic human physiology, leading to a poor translation of therapeutics from pre-clinical trials to consumers. Even those that make it to market can be removed due to unforeseen side effects. As such, there exists a clinical, technological, and economical need for systems that faithfully capture human (patho)physiology for modeling CVD, assessing cardiotoxicity, and evaluating drug efficacy. Heart-on-a-chip (HoC) systems are a part of the broader organ-on-a-chip paradigm that leverages microfluidics, tissue engineering, microfabrication, electronics, and gene editing to create human-relevant models for studying disease, drug-induced side effects, and therapeutic efficacy. These compact systems can be capable of real-time measurements and on-demand characterization of tissue behavior and could revolutionize the drug development process. In this review, we highlight the key components that comprise a HoC system followed by a review of contemporary reports of their use in disease modeling, drug toxicity and efficacy assessment, and as part of multi-organ-on-a-chip platforms. We also discuss future perspectives and challenges facing the field, including a discussion on the role that standardization is expected to play in accelerating the widespread adoption of these platforms.

Endothelial cell dysfunction in cardiac disease: driver or consequence?

The vascular endothelium is a multifunctional cellular system which directly influences blood components and cells within the vessel wall in a given tissue. Importantly, this cellular interface undergoes critical phenotypic changes in response to various biochemical and hemodynamic stimuli, driving several developmental and pathophysiological processes. Multiple studies have indicated a central role of the endothelium in the initiation, progression, and clinical outcomes of cardiac disease. In this review we synthesize the current understanding of endothelial function and dysfunction as mediators of the cardiomyocyte phenotype in the setting of distinct cardiac pathologies; outline existing in vivo and in vitro models where key features of endothelial cell dysfunction can be recapitulated; and discuss future directions for development of endothelium-targeted therapeutics for cardiac diseases with limited existing treatment options.

Newly Developed Di-Block Copolymer-Based Cell Membrane Stabilizers Protect Mouse Coronary Artery Endothelial Cells against Hypoxia/Reoxygenation Injury

Reperfusion after ischemia causes additional cellular damage, known as reperfusion injury, for which there is still no effective remedy. Poloxamer (P)188, a tri-block copolymer-based cell membrane stabilizer (CCMS), has been shown to provide protection against hypoxia/reoxygenation (HR) injury in various models by reducing membrane leakage and apoptosis and improving mitochondrial function. Interestingly, substituting one of its hydrophilic poly-ethylene oxide (PEO) blocks with a (t)ert-butyl terminus added to the hydrophobic poly-propylene oxide (PPO) block yields a di-block compound (PEO-PPOt) that interacts better with the cell membrane lipid bi-layer and exhibits greater cellular protection than the gold standard tri-block P188 (PEO75-PPO30-PEO75). For this study, we custom-made three different new di-blocks (PEO113-PPO10t, PEO226-PPO18t and PEO113-PPO20t) to systemically examine the effects of the length of each polymer block on cellular protection in comparison to P188. Cellular protection was assessed by cell viability, lactate dehydrogenase release, and uptake of FM1-43 in mouse artery endothelial cells (ECs) following HR injury. We found that di-block CCMS were able to provide the same or better EC protection than P188. Our study provides the first direct evidence that custom-made di-block CCMS can be superior to P188 in improving EC membrane protection, raising their potential in treating cardiac reperfusion injury.

Exercise training maintains cardiovascular health: signaling pathways involved and potential therapeutics

Exercise training has been widely recognized as a healthy lifestyle as well as an effective non-drug therapeutic strategy for cardiovascular diseases (CVD). Functional and mechanistic studies that employ animal exercise models as well as observational and interventional cohort studies with human participants, have contributed considerably in delineating the essential signaling pathways by which exercise promotes cardiovascular fitness and health. First, this review summarizes the beneficial impact of exercise on multiple aspects of cardiovascular health. We then discuss in detail the signaling pathways mediating exercise's benefits for cardiovascular health. The exercise-regulated signaling cascades have been shown to confer myocardial protection and drive systemic adaptations. The signaling molecules that are necessary for exercise-induced physiological cardiac hypertrophy have the potential to attenuate myocardial injury and reverse cardiac remodeling. Exercise-regulated noncoding RNAs and their associated signaling pathways are also discussed in detail for their roles and mechanisms in exercise-induced cardioprotective effects. Moreover, we address the exercise-mediated signaling pathways and molecules that can serve as potential therapeutic targets ranging from pharmacological approaches to gene therapies in CVD. We also discuss multiple factors that influence exercise's effect and highlight the importance and need for further investigations regarding the exercise-regulated molecules as therapeutic targets and biomarkers for CVD as well as the cross talk between the heart and other tissues or organs during exercise. We conclude that a deep understanding of the signaling pathways involved in exercise's benefits for cardiovascular health will undoubtedly contribute to the identification and development of novel therapeutic targets and strategies for CVD.

Protective effects of trehalose preconditioning on cardiac and coronary endothelial function through eNOS signaling pathway in a rat model of ischemia-reperfusion injury

Coronary endothelial dysfunction is a major cause of ischemia-reperfusion (I/R) injury. Trehalose, a natural disaccharide, has been reported to ameliorate endothelial dysfunction during aging by activating endothelial nitric oxide synthase (eNOS); however, its role in I/R injury is unknown. This study evaluated the effects of trehalose preconditioning on cardiac and coronary endothelial function after I/R. Langendorff-perfused rat hearts underwent 30 min of global ischemia followed by 80 min of reperfusion with or without trehalose preconditioning. Rate pressure product (RPP) and coronary flow (CF) were measured during reperfusion. Perivascular edema was assessed by hematoxylin and eosin staining. Myocardial oxidative stress and apoptosis were evaluated by immunohistochemistry and TUNEL staining, respectively. eNOS dimerization was determined by western blotting. An eNOS inhibitor was used to examine the role of eNOS. Trehalose preconditioning showed a higher recovery rate after I/R as indicated by high RPP (control vs. trehalose, 28 ± 6% vs. 46 ± 9%; P = 0.017, Cohen's d = 2.3) and CF values (35 ± 10% vs. 55 ± 9%; P = 0.025, d = 1.7). Furthermore, trehalose preconditioning reduced perivascular edema, myocardial oxidative stress, and apoptosis. The eNOS dimerization ratio was increased by trehalose (1.2 ± 0.2 vs. 1.6 ± 0.2; P = 0.023, d = 2.1), which was associated with the recovery of RPP and CF. These effects of trehalose were abolished by the eNOS inhibitor. Trehalose preconditioning showed protective effects on cardiac and coronary endothelial function after I/R through the eNOS signaling pathway.

CU06-1004 enhances vascular integrity and improves cardiac remodeling by suppressing edema and inflammation in myocardial ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury accelerates the cardiomyocytes (CMs) death by oxidative stress, and thereby deteriorates cardiac function. There has been a paradigm shift in the therapeutic perspective more towards the prevention or amelioration of damage caused by reperfusion. Cardiac microvascular endothelial cells (CMECs) are more vulnerable to reperfusion injury and play the crucial roles more than CMs in the pathological process of early I/R injury. In this study, we investigate that CU06-1004, as a vascular leakage blocker, can improve cardiac function by inhibiting CMEC's hyperpermeability and subsequently reducing the neutrophil's plugging and infiltration in infarcted hearts. CU06-1004 was delivered intravenously 5 min before reperfusion and the rats were randomly divided into three groups: (1) vehicle, (2) low-CU06-1004 (1 mg/kg, twice at 24 h intervals), and (3) high-CU06-1004 (5 mg/kg, once before reperfusion). CU06-1004 treatment reduced necrotic size and cardiac edema by enhancing vascular integrity, as demonstrated by the presence of intact junction proteins on CMECs and surrounding pericytes in early I/R injury. It also decreased the expression of vascular cell adhesion molecule 1 (VCAM-1) on CMECs, resulting in reduced infiltration of neutrophils and macrophages. Echocardiography showed that the CU06-1004 treatment significantly improved cardiac function compared with the vehicle group. Interestingly, single high-dose treatment with CU06-1004 provided a greater functional improvement than repetitive low-dose treatment until 8 weeks post I/R. These findings demonstrate that CU06-1004 enhances vascular integrity and improves cardiac function by preventing lethal myocardial I/R injury. It can provide a promising therapeutic option, as potential adjunctive therapy to current reperfusion strategies.

Cancer therapy-related cardiac dysfunction: is endothelial dysfunction at the heart of the matter?

Significant improvements in cancer survival have brought to light unintended long-term adverse cardiovascular effects associated with cancer treatment. Although capable of manifesting a broad range of cardiovascular complications, cancer therapy-related cardiac dysfunction (CTRCD) remains particularly common among the mainstay anthracycline-based and human epidermal growth factor receptor-targeted therapies. Unfortunately, the early asymptomatic stages of CTRCD are difficult to detect by cardiac imaging alone, and the initiating mechanisms remain incompletely understood. More recently, circulating inflammatory markers, cardiac biomarkers, microRNAs, and extracellular vesicles (EVs) have been considered as early markers of cardiovascular injury. Concomitantly, the role of the endothelium in regulating cardiac function in the context of CTRCD is starting to be understood. In this review, we highlight the impact of breast cancer therapies on the cardiovascular system with a focus on the endothelium, and examine the status of circulating biomarkers, including inflammatory markers, cardiac biomarkers, microRNAs, and endothelial cell-derived EVs. Investigation of these emerging biomarkers may uncover mechanisms of injury, detect early stages of cardiovascular damage, and elucidate novel therapeutic approaches.

Hypoxia-induced amniotic fluid stem cell secretome augments cardiomyocyte proliferation and enhances cardioprotective effects under hypoxic-ischemic conditions

Secretome derived from human amniotic fluid stem cells (AFSC-S) is rich in soluble bioactive factors (SBF) and offers untapped therapeutic potential for regenerative medicine while avoiding putative cell-related complications. Characterization and optimal generation of AFSC-S remains challenging. We hypothesized that modulation of oxygen conditions during AFSC-S generation enriches SBF and confers enhanced regenerative and cardioprotective effects on cardiovascular cells. We collected secretome at 6-hourly intervals up to 30 h following incubation of AFSC in normoxic (21%O₂, nAFSC-S) and hypoxic (1%O₂, hAFSC-S) conditions. Proliferation of human adult cardiomyocytes (hCM) and umbilical cord endothelial cells (HUVEC) incubated with nAFSC-S or hAFSC-S were examined following culture in normoxia or hypoxia. Lower AFSC counts and richer protein content in AFSC-S were observed in hypoxia. Characterization of AFSC-S by multiplex immunoassay showed higher concentrations of pro-angiogenic and anti-inflammatory SBF. hCM demonstrated highest proliferation with 30h-hAFSC-S in hypoxic culture. The cardioprotective potential of concentrated 30h-hAFSC-S treatment was demonstrated in a myocardial ischemia–reperfusion injury mouse model by infarct size and cell apoptosis reduction and cell proliferation increase when compared to saline treatment controls. Thus, we project that hypoxic-generated AFSC-S, with higher pro-angiogenic and anti-inflammatory SBF, can be harnessed and refined for tailored regenerative applications in ischemic cardiovascular disease.

Cardiomyocyte-derived small extracellular vesicles can signal eNOS activation in cardiac microvascular endothelial cells to protect against Ischemia/Reperfusion injury

Rationale: The crosstalk between cardiac microvascular endothelial cells (CMECs) and cardiomyocytes (CMs) has emerged as a key component in the development of, and protection against, cardiac diseases. For example, activation of endothelial nitric oxide synthase (eNOS) in CMECs, by therapeutic strategies such as ischemic preconditioning, plays a critical role in the protection against myocardial ischemia/reperfusion (I/R) injury. However, much less is known about the signals produced by CMs that are able to regulate CMEC biology. Here we uncovered one such mechanism using Tongxinluo (TXL), a traditional Chinese medicine, that alleviates myocardial ischemia/reperfusion (I/R) injury by activating CMEC eNOS. The aim of our study is to identify the signals produced by CMs that can regulate CMEC biology during I/R. Methods: Ex vivo, in vivo, and in vitro settings of ischemia-reperfusion were used in our study, with the protective signaling pathways activated in CMECs identified using genetic inhibition (p70s6k1 siRNA, miR-145-5p mimics, etc.), chemical inhibitors (the eNOS inhibitor, L-NNA, and the small extracellular vesicles (sEVs) inhibitor, GW4869) and Western blot analyses. TritonX-100 at a dose of 0.125% was utilized to inactivate the eNOS activity in endothelium to investigate the role of CMEC-derived eNOS in TXL-induced cardioprotection. Results: We found that while CMEC-derived eNOS activity was required for the cardioprotection of TXL, activation of eNOS in CMECs by TXL did not occur directly. Instead, eNOS activation in CMECs required a crosstalk between CMs and CMECs through the uptake of CM-derived sEVs. We further demonstrate that TXL induced CM-sEVs contain increased levels of Long Intergenic Non-Protein Coding RNA, Regulator Of Reprogramming (Linc-ROR). Upon uptake into CMECs, linc-ROR downregulates its target miR-145-5p leading to activation of the eNOS pathway by facilitating the expression of p70s6k1 in these cells. The activation of CMEC-derived eNOS works to increase survival in both the CMECs and the CMs themselves. Conclusions: These data uncover a mechanism by which the crosstalk between CMs and CMECs leads to the increased survival of the heart after I/R injury and point to a new therapeutic target for the blunting of myocardial I/R injury.

Therapeutic potential of miR-21 regulation by human peripheral blood derived-small extracellular vesicles in myocardial infarction

Small extracellular vesicles (sEVs) as natural membranous vesicles are on the frontiers of nanomedical research, due to their ability to deliver therapeutic molecules such as microRNAs (miRNAs). The miRNA-21 (miR-21) is thought to be involved in the initiation and development of myocardial infarction (MI). Here, we examined whether miR-21 regulation using human peripheral blood-derived sEVs (PB-sEVs) could serve as a potential therapeutic strategy for MI. First, we examined miR-21 levels in hypoxic conditions and validated the ability of PB-sEVs to serve as a potential delivery system for miRNAs. Further, bioinformatics analysis and luciferase assay were performed to identify target genes of miR-21 mechanistically. Among numerous target pathways, we focused on nitrogen metabolism, which remains relatively unexplored compared with other possible miR-21-mediated pathways; hence, we aimed to determine novel target genes of miR-21 related to nitrogen metabolism. In hypoxic conditions, the expression of miR-21 was significantly up-regulated and correlated with nitric oxide synthase 3 (NOS3) levels, which in turn influences cardiac function. The down-regulation of miR-21 expression by PB-sEVs loaded with anti-miR-21 significantly improved survival rates, consistent with the augmentation of cardiac function. However, the up-regulation of miR-21 expression by PB-sEVs loaded with miR-21 reversed these effects. Mechanistically, miR-21 targeted and down-regulated the mRNA and protein expression of striatin (STRN), which could regulate NOS3 expression. In conclusion, we identified a novel therapeutic strategy to improve cardiac function by regulating the expression of miR-21 with PB-sEVs as an miR-21 or anti-miR-21 delivery vehicle and confirmed the miR-21-associated nitrogen metabolic disorders in MI.

NOS cofactor tetrahydrobiopterin contributes to anesthetic preconditioning induced myocardial protection in the isolated ex vivo rat heart

Anesthetic preconditioning (APC) may decrease the myocardium injury nearly 50% following ischemia/reperfusion (I/R) by enhancing recovery of cardiac function, reducing myocardial enzyme release and lowering infarct size when utilized as pretreatment or posttreatment agents. I/R increases nitric oxide (NO) production through endothelial NO synthase (NOS3) and heat shock protein 90 (HSP90). The present study aimed to observe the role of BH4 availability and the association of HSP90 with NOS3 in APC‑mediated cardioprotection against I/R injury. Isolated rat hearts were subjected to no‑flow ischemia for 30 min and reperfusion for 120 min. Sevoflurane (3.5%) was administered for 15 min followed by a 15 min washout prior to ischemia. 2,4-Diamino-6-hydroxypyrimidine (DAHP) or sepiapterin (SP) was administered for 40 min until the onset of ischemia. The results revealed that compared with pre‑ischemic basal levels, BH4 levels decreased and BH2 levels increased following I/R. BH4 levels were significantly increased and BH2 levels were significantly decreased in the APC + I/R hearts compared with the I/R group hearts. The BH4:BH2 ratio in the APC‑treated hearts was also increased compared with that in the I/R group hearts. SP increased the recovery of contractile function and the production of NO, and decreased the production of superoxide anion (O2·‑) in I/R heart, but did not elicit these effects in APC‑treated hearts. DAHP treatment inhibited the APC‑mediated recovery of contractile function, increased O2·‑ levels and decreased NO production, but had no effect in I/R hearts. The cardioprotection of APC was demonstrated to be modulated by the BH4 precursor SP, which increased BH4 levels, or DAHP, which inhibited GTP cyclohydrolase I. Both APC and SP treatments increased the combination of HSP90 and NOS3, which improved the NOS3 activity and function. The results suggested that BH4, which servesas a cofactor for NOS, mediated the resistance of APC to I/R injury by promoting the binding of HSP90 and NOS3.

Vascular endothelial growth factor regulation of endothelial nitric oxide synthase phosphorylation is involved in isoflurane cardiac preconditioning

Aims

Previous studies indicate that nitric oxide derived from endothelial nitric oxide synthase (eNOS) serves as both trigger and mediator in anaesthetic cardiac preconditioning. The mechanisms underlying regulation of eNOS by volatile anaesthetics have not been fully understood. Therefore, this study examined the role of vascular endothelial growth factor (VEGF) in isoflurane cardiac preconditioning.

Methods and results

Wistar rats underwent 30 min of coronary artery occlusion followed by 2 h of reperfusion. Isoflurane given prior to ischaemia/reperfusion significantly decreased myocardial infarct size from 60 ± 1% in control to 40 ± 3% (n = 8 rats/group, P < 0.05). The beneficial effects of isoflurane were blocked by neutralizing antibody against VEGF (nVEGF). Coronary arterial endothelial cells (ECs) alone or together with cardiomyocytes (CMs) were subjected to hypoxia/reoxygenation injury. The expression of VEGF and eNOS was analysed by western blot, and nitric oxide was measured by ozone-based chemiluminescence. In co-cultured CMs and ECs, isoflurane administered before hypoxia/reoxygenation attenuated lactate dehydrogenase activity and increased the ratio of phosphorylated eNOS/eNOS and nitric oxide production. The protective effect of isoflurane on CMs was compromised by nVEGF and after VEGF in ECs was inhibited with hypoxia inducible factor-1α short hairpin RNA (shRNA). The negative effect of hypoxia inducible factor-1α shRNA was restored by recombinant VEGF.

Conclusion

Isoflurane cardiac preconditioning is associated with VEGF regulation of phosphorylation of eNOS and nitric oxide production.

Endothelial-Cell-Derived Human Secretory Leukocyte Protease Inhibitor (SLPI) Protects Cardiomyocytes against Ischemia/Reperfusion Injury

Vascular endothelial cell (EC)-derived factors play an important role in endothelial-cardiomyocyte crosstalk and could save cardiomyocytes (CMs) from injury. The manipulation of endothelial cells to secrete protective factors could enhance cardioprotection. Secretory leukocyte protease inhibitor (SLPI) has been known to protect the heart. The goal of this study was to evaluate the in vitro paracrine protective effect and mechanisms of EC-derived human SLPI on cardiomyocytes subjected to hypoxia/reoxygenation (H/R) injury. Stable endothelial cells overexpressing human SLPI were generated from an endothelial cell line (EA.hy926). The cytoprotective effect was determined by cell survival assay. The results showed that endothelial-derived recombinant human SLPI (rhSLPI) reduced simulated ischemia/reperfusion (I/R)-(81.75% ± 1.42% vs. 60.27% ± 2.52%, p < 0.05) and hypoxia/reoxygenation (H/R)-induced EC injury (83.57% ± 1.78% vs. 63.07% ± 1.93%, p < 0.05). Moreover, co-culture of ECs overexpressing rhSLPI with CMs at ratios 1:1 and 1:3 or treatment with conditioned medium enhanced cell viability by 10.51-16.7% (co-culture) and 15.25-20.45% (conditioned medium) by reducing intracellular reactive oxygen species (ROS) production, the Bax/Bcl-2 expression ratio, caspase-3, and caspase-8, and in preconditioned CMs by activation of p38 MAPK and Akt survival kinase. In conclusion, this study showed for the first time that EC-derived rhSLPI provided cardio-vasculoprotective effects against I/R injury as a possible alternative therapeutic strategy for cardioprotection.

Xin-Ji-Er-Kang Alleviates Myocardial Infarction-Induced Cardiovascular Remodeling in Rats by Inhibiting Endothelial Dysfunction

The present study was designed to elucidate the beneficial effects of XJEK on myocardial infarction (MI) in rats, especially through the amelioration of endothelial dysfunction (ED). 136 Sprague-Dawley rats were randomized into 13 groups: control group for 0wk (n = 8); sham groups for 2, 4, and 6 weeks (wk); MI groups for 2, 4, and 6 wk; MI+XJEK groups for 2, 4, and 6w k; MI+Fosinopril groups for 2, 4, and 6 wk (n = 8~10). In addition, 8 rats were treated for Evans blue staining and Tetrazolium chloride (TTC) staining to determine the infarct size. Cardiac function, ECG, and cardiac morphological changes were examined. Colorimetric analysis was employed to detect nitric oxide (NO), and enzyme-linked immunosorbent assay (ELISA) was applied to determine N-terminal probrain natriuretic peptide (NT-ProBNP), endothelin-1 (ET-1), angiotensin II (Ang II), asymmetric dimethylarginine (ADMA), tetrahydrobiopterin (BH₄), and endothelial NO synthase (eNOS) content. The total eNOS and eNOS dimer/(dimer+monomer) ratios in cardiac tissues were detected by Western blot. We found that administration of XJEK markedly ameliorated cardiovascular remodeling (CR), which was manifested by decreased HW/BW ratio, CSA, and less collagen deposition after MI. XJEK administration also improved cardiac function by significant inhibition of the increased hemodynamic parameters in the early stage and by suppression of the decreased hemodynamic parameters later on. XJEK also continuously suppressed the increased NT-ProBNP content in the serum of MI rats. XJEK improved ED with stimulated eNOS activities, as well as upregulated NO levels, BH₄ content, and eNOS dimer/(dimer+monomer) ratio in the cardiac tissues. XJEK downregulated ET-1, Ang II, and ADMA content obviously compared to sham group. In conclusion, XJEK may exert the protective effects on MI rats and could continuously ameliorate ED and reverse CR with the progression of MI over time.

Dexmedetomidine preconditioning attenuates ischemia/reperfusion injury in isolated rat hearts with endothelial dysfunction

BACKGROUND AND PURPOSES

Dexmedetomidine preconditioning (DP) can mimic pharmacological preconditioning and induce cardiac protection. There are controversies on the roles of coronary endothelia in cardioprotection of dexmedetomidine. Herein, we tested the hypothesis that protection of dexmedetomidine is not endothelial dependent in heart against myocardial ischemia/reperfusion (I/R) injury.

METHODS

Langendorff-perfused rat hearts were pretreated by 60 mM of potassium to produce endothelial dysfunction (ED), then medicated with dexmedetomidine, and subsequently subjected to 30 min of global ischemia followed by 60 min of reperfusion. To investigate the cardioprotective effect of dexmedetomidine in heart with ED, isolated rat hearts were randomly divided into the following six groups: sham, I/R, DP, ED, ED + I/R, and ED + DP + I/R. Heart rates, left ventricular function, and coronary perfusion pressure were assessed for each heart. Infarct size was evaluated by triphenyltetrazolium chloride staining. High-sensitivity cardiac troponin T (hs-cTNT) of coronary flow perfusion was determined.

RESULTS

After the isolated hearts with pretreatment of 60 mM of potassium chloride, diastolic function of coronary endothelia in performance of response to histamine was significantly decreased (P < 0.05). DP attenuated I/R-induced infarct size of the left ventricle (P < 0.05) and decreased hs-cTNT (P < 0.05). Additionally, left ventricular developed pressure, +dp/dt_max, and -dp/dt_max were elevated in rat hearts pretreated with dexmedetomidine. Furthermore, dexmedetomidine-mediated cardiac protection against I/R injury was still remained in isolated hearts with coronary ED.

CONCLUSION

Continuous perfusion of 60 mM of potassium for 10 min can produce coronary ED in isolated rat hearts. Dexmedetomidine maintains its protective function against I/R injury in heart with coronary ED. Myocardial protection of dexmedetomidine is non-endothelial function dependent in alleviating I/R injury.

Endothelial cell-cardiomyocyte crosstalk in heart development and disease

The crosstalk between endothelial cells and cardiomyocytes has emerged as a requisite for normal cardiac development, but also a key pathogenic player during the onset and progression of cardiac disease. Endothelial cells and cardiomyocytes are in close proximity and communicate through the secretion of paracrine signals, as well as through direct cell-to-cell contact. Here, we provide an overview of the endothelial cell-cardiomyocyte interactions controlling heart development and the main processes affecting the heart in normal and pathological conditions, including ischaemia, remodelling and metabolic dysfunction. We also discuss the possible role of these interactions in cardiac regeneration and encourage the further improvement of in vitro models able to reproduce the complex environment of the cardiac tissue, in order to better define the mechanisms by which endothelial cells and cardiomyocytes interact with a final aim of developing novel therapeutic opportunities.

Unveiling the molecular crosstalk in a human induced pluripotent stem cell-derived cardiac model

In vitro cell-based models that better mimic the human heart tissue are of utmost importance for drug development and cardiotoxicity testing but also as tools to understand mechanisms related with heart disease at cellular and molecular level. Besides, the implementation of analytical tools that allow the depiction and comprehensive understanding of the molecular mechanisms of the crosstalk between the different cell types is also relevant. In this work, we implemented a human cardiac tissue-like in vitro model, derived from human-induced pluripotent stem cell (hiPSC), and evaluated the relevance of the cell-cell communication between the two of the most representative cell populations of the human heart: cardiomyocytes (hiPSC-CM) and endothelial cells (hiPSC-EC). We observed that heterotypic cell communication promotes: (a) structural maturation of hiPSC-CM and (b) deposition of several extracellular matrix components (such as collagens and fibronectin). Overall, the toolbox of analytical techniques used in our study not only enabled us to validate previous reports from the literature on the importance of the presence of hiPSC-EC on hiPSC-CM maturation, but also bring new insights on the molecular mechanisms involved in the communication between these two cell types when cocultured in vitro.

Human Tissue-Engineered Model of Myocardial Ischemia-Reperfusion Injury

IMPACT STATEMENT

Reducing ischemia-reperfusion injury would significantly improve patient survival. Current preclinical models are inadequate because they rely on animals, which do not emulate human physiology and the clinical setting. We developed a human tissue platform that allowed us to assess the human cardiac response, and demonstrated the platform's utility by measuring injury during ischemia-reperfusion and the effects of cardioprotective strategies. The model provides a foundation for future studies on how patient-specific backgrounds may affect response to therapeutic strategies. These steps will be necessary to help translate therapies into the clinical setting.

Endothelial cells release cardioprotective exosomes that may contribute to ischaemic preconditioning

Extracellular vesicles (EVs) such as exosomes are nano-sized vesicles that carry proteins and miRNAs and can transmit signals between cells. We hypothesized that exosomes from endothelial cells can transmit protective signals to cardiomyocytes. Co-culture of primary adult rat cardiomyocytes with normoxic HUVEC cells separated by a cell-impermeable membrane reduced the percentage of cardiomyocyte death following simulated ischaemia and reperfusion (sIR) from 80 ± 11% to 51 ± 4% (P < 0.05; N = 5). When EVs were removed from the HUVEC-conditioned medium it was no longer protective. Exosomes were purified from HUVEC-conditioned medium using differential centrifugation and characterized by nanoparticle tracking analysis, electron microscopy, and flow cytometry. Pre-incubation of cardiomyocytes with HUVEC exosomes reduced the percentage of cell death after sIR from 88 ± 4% to 55 ± 3% (P < 0.05; N = 3). This protection required ERK1/2 activity as it was prevented by inhibitors PD98059 and U0126. Ischaemic preconditioning caused about ~3-fold higher rate of exosome production from HUVEC and from isolated, perfused rat hearts. This increase resulted in significantly greater protection against sIR in cardiomyocytes. In conclusion, exosomes released from endothelial cells can confer resistance to sIR injury in cardiomyocytes via the activation of the ERK1/2 MAPK signalling pathway, and may contribute to IPC.

Orientin Reduces Myocardial Infarction Size via eNOS/NO Signaling and Thus Mitigates Adverse Cardiac Remodeling

Orientin is a flavonoid extracted from Chinese traditional herb, Polygonum orientale L. Previous study has reported that orientin protected myocardial from ischemia reperfusion injury. However, whether orientin could protect against cardiac remodeling after myocardial injury remains unclear. The aim of our study is to investigate the effects of orientin in the progression of cardiac remodeling after myocardial infarction (MI). Mice cardiac remodeling model was established by left coronary artery ligation surgery. Experimental groups were as follows: vehicle-sham, orientin-sham, vehicle-MI, and orientin-MI. Animals were treated with vehicle or orientin (40 mg/kg) for 25 days starting 3 days after surgery. After 4 weeks of MI, mice with orientin treatment had decreased mortality and improved cardiac function. Significantly, at 4 weeks post-MI, orientin treatment decreased fibrosis, inflammatory response, and cardiomyocyte apoptosis. Furthermore, orientin treatment attenuated the hypoxia-induced neonatal rat cardiomyocyte apoptosis and increased cell viability. Additionally, orientin supplementation mitigated oxidative stress in remodeling heart tissue and cardiomyocytes exposed to hypoxia as measured by 2′,7′-dichlorodihydrofluorescein diacetate fluorescent probe. Mechanistically, orientin promotes cardioprotection by activating the eNOS/NO signaling cascades, which was confirmed by eNOS inhibitor (L-NAME) in vitro and in vivo. Inhibition of oxidative stress by orientin via eNOS/NO signaling cascades in the heart may represent a potential therapy for cardiac remodeling.

Myrtenol protects against myocardial ischemia-reperfusion injury through antioxidant and anti-apoptotic dependent mechanisms

Myrtenol is a monoterpene with multiple pharmacological activities. However, although monoterpenes have been proposed to play beneficial roles in a variety of cardiac disorders, pharmacological actions of myrtenol in the heart are not yet reported. Hence, the aim of this study was to evaluate whether myrtenol promotes cardioprotection against myocardial ischemia-reperfusion (IR) injury, and the mechanisms involved in these effects. Male Wistar rats were orally treated for seven consecutive days with myrtenol (50 mg/kg) or N-acetyl cysteine (1.200 mg/kg, NAC). Afterward, hearts were subjected to myocardial IR injury. Here, we show that the severe impairment of contractile performance induced by IR was significantly prevented by myrtenol or NAC. Moreover, myrtenol abolished aberrant electrocardiographic waveform (ST-segment elevation), as well as reduced life-threatening arrhythmias and infarct size induced by IR injury. Importantly, myrtenol fully prevented the massive increase of cardiac reactive oxygen species generation and oxidative stress damage. Accordingly, myrtenol restored the impairment of endogenous antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase and reductase) activities and balance of pro- and anti-apoptotic pathways (Bax and Bcl-2), associated with decreased apoptotic cells. Taken together, our data show that myrtenol promotes cardioprotection against IR injury through attenuation of oxidative stress and inhibition of pro-apoptotic pathway.

An in vitro endothelial cell protective effect of secretory leukocyte protease inhibitor against simulated ischaemia/reperfusion injury

Endothelial dysfunction is an essential deleterious modulator of ischaemia/reperfusion (I/R) injury. Secretory leukocyte protease inhibitor (SLPI) has demonstrated myocardial protection in cardiac transplantation; however, the effect of SLPI in endothelial I/R injury remains unexplored. In the present study, the effect of recombinant human SLPI (rhSLPI) treatment against endothelial cells (ECs) subjected to simulated I/R injury and the effect of treatment at different time points were determined. Human umbilical vein ECs (HUVECs) were subjected to normoxic or simulated I/R (sI/R) conditions, and rhSLPI at concentrations of 1, 10, 100 and 1,000 ng/ml was added to the cells prior to ischaemia, during ischaemia or at the onset of reperfusion. Endothelial injury and cytoskeleton disruption were assessed, and western blot analysis was conducted. The results revealed that rhSLPI treatment at 1,000 ng/ml significantly increased the HUVEC viability under sI/R injury (P<0.05). In addition, treatment with rhSLPI prior to or during ischaemia markedly attenuated the activity of lactase dehydrogenase compared with that in the sI/R group. In addition, the H₂O₂-induced reactive oxygen species production was reduced by ~17% upon rhSLPI pretreatment. Endothelial cytoskeleton disruption was also preserved by rhSLPI added prior to the reperfusion period. Furthermore, pretreatment with rhSLPI promoted protein kinase B activation, as well as reduced p38 mitogen-activated protein kinase phosphorylation and B-cell lymphoma 2-associated X protein expression in response to I/R injury. These findings indicated that rhSLPI possesses antioxidant and antiapoptotic properties against endothelial responses to I/R injury. Therefore, the cytoprotective effect of rhSLPI may provide a potential pharmaceutical target to limit endothelial-mediated I/R injury.

Administration of Tetrahydrobiopterin (BH4) Protects the Renal Microcirculation From Ischemia and Reperfusion Injury

BACKGROUND

Abdominal aortic aneurysm surgery with suprarenal cross-clamping is often associated with renal injury. Although the mechanism underlying such injury is unclear, tissue ischemia and reperfusion, which induces endothelial dysfunction and decreases the availability of tetrahydrobiopterin (BH4), may play a role. We evaluated whether BH4 administration prevents renal ischemia/reperfusion injury in an animal model of aortic cross-clamping.

METHODS

Nineteen anesthetized, mechanically ventilated, and invasively monitored adult sheep were randomized into 3 groups: sham animals (n = 5) that underwent surgical preparation but no aortic clamping; an ischemia/reperfusion group (n = 7), where the aorta was clamped above the renal arteries for 1 hour, and a BH4 group (n = 7), in which animals received 20 mg/kg of BH4 followed by aortic cross-clamp for 1 hour. Animals were followed for a maximum of 6 hours after reperfusion. The renal microcirculation was evaluated at baseline (before clamping), and 1, 4, and 6 hours after reperfusion using side-stream dark field videomicroscopy. The renal lactate-to-pyruvate ratio was evaluated using microdialysis. The primary outcome was the change in proportion of small perfused vessels before and after injury. Secondary outcomes were renal tissue redox state and renal function.

RESULTS

Ischemia/reperfusion injury was associated with increases in heart rate and mean arterial pressure, which were blunted by BH4 administration. From the first to the sixth hour after reperfusion, the small vessel density (estimated mean difference [EMD], 1.03; 95% confidence interval [CI], 0.41-1.64; P = .003), perfused small vessel density (EMD, 0.84; 95% CI, 0.29-1.39; P = .005), and proportion of perfused small vessels (EMD, 8.60; 95% CI, 0.85-16.30; P = .031) were altered less in the BH4 than in the ischemia/reperfusion group. The renal lactate-to-pyruvate ratios were lower in the cortex in the BH4 than in the ischemia/reperfusion group from the first to the sixth hour after reperfusion (EMD, -19.16; 95% CI, -11.06 to 33.16; P = .002) and in the medulla from the first to the fourth hour (EMD, -26.62; 95% CI, -18.32 to 38.30; P = .020; and EMD, -8.68; 95% CI, -5.96 to 12.65; P = .019). At the sixth hour, serum creatinine was lower in the BH4 than in the ischemia/reperfusion group (EMD, -3.36; 95% CI, -0.29 to 1.39; P = .026).

CONCLUSIONS

In this sheep model of renal ischemia/reperfusion, BH4 pretreatment reduced renal microvascular injury and improved renal metabolism and function. Further work is needed to clarify the potential role of BH4 in ischemia/reperfusion injury.

Transcriptome profiling of 3D co-cultured cardiomyocytes and endothelial cells under oxidative stress using a photocrosslinkable hydrogel system

Myocardial infarction (MI) is one of the most common among cardiovascular diseases. Endothelial cells (ECs) are considered to have protective effects on cardiomyocytes (CMs) under stress conditions such as MI; however, the paracrine CM-EC crosstalk and the resulting endogenous cellular responses that could contribute to this protective effect are not thoroughly investigated. Here we created biomimetic synthetic tissues containing CMs and human induced pluripotent stem cell (hiPSC)-derived ECs (iECs), which showed improved cell survival compared to single cultures under conditions mimicking the aftermath of MI, and performed high-throughput RNA-sequencing to identify target pathways that could govern CM-iEC crosstalk and the resulting improvement in cell viability. Our results showed that single cultured CMs had different gene expression profiles compared to CMs co-cultured with iECs. More importantly, this gene expression profile was preserved in response to oxidative stress in co-cultured CMs while single cultured CMs showed a significantly different gene expression pattern under stress, suggesting a stabilizing effect of iECs on CMs under oxidative stress conditions. Furthermore, we have validated the in vivo relevance of our engineered model tissues by comparing the changes in the expression levels of several key genes of the encapsulated CMs and iECs with in vivo rat MI model data and clinical data, respectively. We conclude that iECs have protective effects on CMs under oxidative stress through stabilizing mitochondrial complexes, suppressing oxidative phosphorylation pathway and activating pathways such as the drug metabolism-cytochrome P450 pathway, Rap1 signaling pathway, and adrenergic signaling in cardiomyocytes pathway.

STATEMENT OF SIGNIFICANCE

Heart diseases are the leading cause of death worldwide. Oxidative stress is a common unwanted outcome that especially occurs due to the reperfusion following heart attack or heart surgery. Standard methods of in vivo analysis do not allow dissecting various intermingled parameters, while regular 2D cell culture approaches often fail to provide a biomimetic environment for the physiologically relevant cellular phenotypes. In this research, a systematic genome-wide transcriptome profiling was performed on myocardial cells in a biomimetic 3D hydrogel-based synthetic model tissue, for identifying possible target genes and pathways as protecting regulators against oxidative stress. Identification of such pathways would be very valuable for new strategies during heart disease treatment by reducing the cellular damage due to reperfusion injury.

Transgenic overexpression of GTP cyclohydrolase 1 in cardiomyocytes ameliorates post-infarction cardiac remodeling

GTP cyclohydrolase 1 (GCH1) and its product tetrahydrobiopterin play crucial roles in cardiovascular health and disease, yet the exact regulation and role of GCH1 in adverse cardiac remodeling after myocardial infarction are still enigmatic. Here we report that cardiac GCH1 is degraded in remodeled hearts after myocardial infarction, concomitant with increases in the thickness of interventricular septum, interstitial fibrosis, and phosphorylated p38 mitogen-activated protein kinase and decreases in left ventricular anterior wall thickness, cardiac contractility, tetrahydrobiopterin, the dimers of nitric oxide synthase, sarcoplasmic reticulum Ca²⁺ release, and the expression of sarcoplasmic reticulum Ca²⁺ handling proteins. Intriguingly, transgenic overexpression of GCH1 in cardiomyocytes reduces the thickness of interventricular septum and interstitial fibrosis and increases anterior wall thickness and cardiac contractility after infarction. Moreover, we show that GCH1 overexpression decreases phosphorylated p38 mitogen-activated protein kinase and elevates tetrahydrobiopterin levels, the dimerization and phosphorylation of neuronal nitric oxide synthase, sarcoplasmic reticulum Ca²⁺ release, and sarcoplasmic reticulum Ca²⁺ handling proteins in post-infarction remodeled hearts. Our results indicate that the pivotal role of GCH1 overexpression in post-infarction cardiac remodeling is attributable to preservation of neuronal nitric oxide synthase and sarcoplasmic reticulum Ca²⁺ handling proteins, and identify a new therapeutic target for cardiac remodeling after infarction.

Naturally Engineered Maturation of Cardiomyocytes

Ischemic heart disease remains one of the most prominent causes of mortalities worldwide with heart transplantation being the gold-standard treatment option. However, due to the major limitations associated with heart transplants, such as an inadequate supply and heart rejection, there remains a significant clinical need for a viable cardiac regenerative therapy to restore native myocardial function. Over the course of the previous several decades, researchers have made prominent advances in the field of cardiac regeneration with the creation of in vitro human pluripotent stem cell-derived cardiomyocyte tissue engineered constructs. However, these engineered constructs exhibit a functionally immature, disorganized, fetal-like phenotype that is not equivalent physiologically to native adult cardiac tissue. Due to this major limitation, many recent studies have investigated approaches to improve pluripotent stem cell-derived cardiomyocyte maturation to close this large functionality gap between engineered and native cardiac tissue. This review integrates the natural developmental mechanisms of cardiomyocyte structural and functional maturation. The variety of ways researchers have attempted to improve cardiomyocyte maturation in vitro by mimicking natural development, known as natural engineering, is readily discussed. The main focus of this review involves the synergistic role of electrical and mechanical stimulation, extracellular matrix interactions, and non-cardiomyocyte interactions in facilitating cardiomyocyte maturation. Overall, even with these current natural engineering approaches, pluripotent stem cell-derived cardiomyocytes within three-dimensional engineered heart tissue still remain mostly within the early to late fetal stages of cardiomyocyte maturity. Therefore, although the end goal is to achieve adult phenotypic maturity, more emphasis must be placed on elucidating how the in vivo fetal microenvironment drives cardiomyocyte maturation. This information can then be utilized to develop natural engineering approaches that can emulate this fetal microenvironment and thus make prominent progress in pluripotent stem cell-derived maturity toward a more clinically relevant model for cardiac regeneration.

Cardiomyocyte GTP Cyclohydrolase 1 Protects the Heart Against Diabetic Cardiomyopathy

Diabetic cardiomyopathy increases the risk of heart failure and death. At present, there are no effective approaches to preventing its development in the clinic. Here we report that reduction of cardiac GTP cyclohydrolase 1 (GCH1) degradation by genetic and pharmacological approaches protects the heart against diabetic cardiomyopathy. Diabetic cardiomyopathy was induced in C57BL/6 wild-type mice and transgenic mice with cardiomyocyte-specific overexpression of GCH1 with streptozotocin, and control animals were given citrate buffer. We found that diabetes-induced degradation of cardiac GCH1 proteins contributed to adverse cardiac remodeling and dysfunction in C57BL/6 mice, concomitant with decreases in tetrahydrobiopterin, dimeric and phosphorylated neuronal nitric oxide synthase, sarcoplasmic reticulum Ca(2+) handling proteins, intracellular [Ca(2+)]i, and sarcoplasmic reticulum Ca(2+) content and increases in phosphorylated p-38 mitogen-activated protein kinase and superoxide production. Interestingly, GCH-1 overexpression abrogated these detrimental effects of diabetes. Furthermore, we found that MG 132, an inhibitor for 26S proteasome, preserved cardiac GCH1 proteins and ameliorated cardiac remodeling and dysfunction during diabetes. This study deepens our understanding of impaired cardiac function in diabetes, identifies GCH1 as a modulator of cardiac remodeling and function, and reveals a new therapeutic target for diabetic cardiomyopathy.

Cellular and molecular mechanisms of endothelial ischemia/reperfusion injury: perspectives and implications for postischemic myocardial protection

Ischemia/reperfusion (I/R) injury is a major cause of myocardial damage. Despite continuous efforts, minimizing I/R injury still represents a great challenge in standard medical treatments of ischemic heart disease, i.e., thrombolytic therapy, primary percutaneous coronary intervention, and coronary arterial bypass grafting. Development of effective interventions and strategies to prevent or reduce myocardial I/R injury is therefore of great clinical significance. Endothelial dysfunction plays a significant role in myocardial I/R injury, which renders endothelial cells an attractive target for postischemic myocardial protection. The rapidly evolving knowledge of the mechanisms of endothelial I/R injury helps broaden perspective for future development of novel strategies targeting endothelium for alleviating myocardial I/R damage. This review provides a comprehensive summary of the cellular and molecular mechanisms of endothelial I/R injury. Current perspectives and future directions for developing endothelium targeting therapeutics for postischemic myocardial protection are further discussed.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Chronic Co-Administration of Sepiapterin and L-Citrulline Ameliorates Diabetic Cardiomyopathy and Myocardial Ischemia/Reperfusion Injury in Obese Type 2 Diabetic Mice

BACKGROUND

Diabetic heart disease is associated with tetrahydrobiopterin oxidation and high arginase activity, leading to endothelial nitric oxide synthase dysfunction. Sepiapterin (SEP) is a tetrahydrobiopterin precursor, and L-citrulline (L-Cit) is converted to endothelial nitric oxide synthase substrate, L-arginine. Whether SEP and L-Cit are effective at reducing diabetic heart disease is not known. The present study examined the effects of SEP and L-Cit on diabetic cardiomyopathy and ischemia/reperfusion injury in obese type 2 diabetic mice.

METHODS AND RESULTS

Db/db and C57BLKS/J mice at 6 to 8 weeks of age received vehicle, SEP, or L-Cit orally alone or in combination for 8 weeks. Cardiac function was evaluated with echocardiography. Db/db mice displayed hyperglycemia, obesity, and normal blood pressure and cardiac function compared with C57BLKS/J mice at 6 to 8 weeks of age. After vehicle treatment for 8 weeks, db/db mice had reduced ejection fraction, mitral E/A ratio, endothelium-dependent relaxation of coronary arteries, tetrahydrobiopterin concentrations, ratio of endothelial nitric oxide synthase dimers/monomers, and nitric oxide levels compared with vehicle-treated C57BLKS/J mice. These detrimental effects of diabetes mellitus were abrogated by co-administration of SEP and L-Cit. Myocardial infarct size was increased, and coronary flow rate and ± dP/dt were decreased during reperfusion in vehicle-treated db/db mice subjected to ischemia/reperfusion injury compared with control mice. Co-administration of SEP and L-Cit decreased infarct size and improved coronary flow rate and cardiac function in both C57BLKS/J and db/db mice.

CONCLUSIONS

Co-administration of SEP and L-Cit limits diabetic cardiomyopathy and ischemia/reperfusion injury in db/db mice through a tetrahydrobiopterin/endothelial nitric oxide synthase/nitric oxide pathway.

Dexmedetomidine protects the heart against ischemia-reperfusion injury by an endothelial eNOS/NO dependent mechanism

The alpha2-adrenergic receptor agonist Dexmedetomidine (Dex) is a sedative medication used by anesthesiologists. Dex protects the heart against ischemia-reperfusion (IR) and can also act as a preconditioning mimetic. The mechanisms involved in Dex-dependent cardiac preconditioning, and whether this action occurs directly or indirectly on cardiomyocytes, still remain unclear. The endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway and endothelial cells are known to play key roles in cardioprotection against IR injury. Therefore, the aims of this work were to evaluate whether the eNOS/NO pathway mediates the pharmacological cardiac effect of Dex, and whether endothelial cells are required in this cardioprotective action. Isolated adult rat hearts were treated with Dex (10nM) for 25min and the dimerization of eNOS and production of NO were measured. Hearts were then subjected to global IR (30/120min) and the role of the eNOS/NO pathway was evaluated. Dex promoted the activation of eNOS and production of NO. Dex reduced the infarct size and improved the left ventricle function recovery, but this effect was reversed when Dex was co-administered with inhibitors of the eNOS/NO/PKG pathway. In addition, Dex was unable to reduce cell death in isolated adult rat cardiomyocytes subjected to simulated IR. Cardiomyocyte death was attenuated by co-culturing them with endothelial cells pre-treated with Dex. In summary, our results show that Dex triggers cardiac protection by activating the eNOS/NO signaling pathway. This pharmacological effect of Dex requires its interaction with the endothelium.

Isoflurane favorably modulates guanosine triphosphate cyclohydrolase-1 and endothelial nitric oxide synthase during myocardial ischemia and reperfusion injury in rats

BACKGROUND

The authors investigated the hypothesis that isoflurane modulates nitric oxide (NO) synthesis and protection against myocardial infarction through time-dependent changes in expression of key NO regulatory proteins, guanosine triphosphate cyclohydrolase (GTPCH)-1, the rate-limiting enzyme involved in the biosynthesis of tetrahydrobiopterin and endothelial nitric oxide synthase (eNOS).

METHODS

Myocardial infarct size, NO production (ozone-mediated chemiluminescence), GTPCH-1, and eNOS expression (real-time reverse transcriptase polymerase chain reaction and western blotting) were measured in male Wistar rats with or without anesthetic preconditioning (APC; 1.0 minimum alveolar concentration isoflurane for 30 min) and in the presence or absence of an inhibitor of GTPCH-1, 2,4-diamino-6-hydroxypyrimidine.

RESULTS

NO2 production (158 ± 16 and 150 ± 13 pmol/mg protein at baseline in control and APC groups, respectively) was significantly (P < 0.05) increased 1.5 ± 0.1 and 1.4 ± 0.1 fold by APC (n = 4) at 60 and 90 min of reperfusion, respectively, concomitantly, with increased expression of GTPCH-1 (1.3 ± 0.3 fold; n = 5) and eNOS (1.3 ± 0.2 fold; n = 5). In contrast, total NO (NO2 and NO3) was decreased after reperfusion in control experiments. Myocardial infarct size was decreased (43 ± 2% of the area at risk for infarction; n = 6) by APC compared with control experiments (57 ± 1%; n = 6). 2, 4-Diamino-6-hydroxypyrimidine decreased total NO production at baseline (221 ± 25 and 175 ± 31 pmol/mg protein at baseline in control and APC groups, respectively), abolished isoflurane-induced increases in NO at reperfusion, and prevented reductions of myocardial infarct size by APC (60 ± 2%; n = 6).

CONCLUSION

APC favorably modulated a NO biosynthetic pathway by up-regulating GTPCH-1 and eNOS, and this action contributed to protection of myocardium against ischemia and reperfusion injury.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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Cytosolic calreticulin inhibits microwave radiation-induced microvascular endothelial cell injury through the integrin-focal adhesion kinase pathway

OBJECTIVE

To determine the effects of cytosolic CRT on MR-induced MMEC injury, and the underlying mechanism.

METHODS

MMECs were randomized into eight groups: control, AdCRT (infected with pAdCMV/V5-DEST-CRT adenovirus), stCRT (transfected with rCRT-siRNAs), Mock (transfected with scrambled siRNAs), MR (exposed to MR for six minutes), AdCRT + MR, stCRT + MR, and Mock + MR. The magnitude of cell injury were assessed by Annexin V-PI staining, LDH activity in culture medium, MMEC migration ability, ultrastructure and cytoskeletal stability. Subcellular colocalization of CRT and ConA or integrin were evaluated by immunocytochemistry. The mRNA and protein expression levels of target genes were examined by qRT-PCR and western blotting, respectively.

RESULTS

MR-induced cytotoxicity was dose-dependent. Overexpression of cytosolic CRT suppressed MR injury, shown as decreased cell apoptosis, reduced LDH activity, enhanced cell migration capability, and maintenance of ultrastructure and cytoskeleton integrity. Conversely, CRT deficiency aggravated MR-induced injury. Exposure of AdCRT MMECs to MR promoted membrane translocation of CRT and the interaction of CRT-integrin-α. Correlation analysis revealed that integrin-α expression or FAK phosphorylation was positively associated with cytosolic CRT expression.

CONCLUSIONS

Cytosolic CRT inhibits MR-induced MMEC injury through activation of the integrin-FAK pathway.

Ischemia and reperfusion related myocardial inflammation: A network of cells and mediators targeting the cardiomyocyte

Occlusion of a coronary artery if maintained for longer period of time results in damage of the cardiac tissue. However, restoration of blood flow to previously ischemic tissue can itself induce further cardiac damage, a phenomenon known as myocardial reperfusion injury. Cardiac homoeostasis is supported by a network of direct and indirect interactions between cardiomyocytes and resident cell types such as fibroblasts, adipocytes, and endothelial cells or invading blood cells. This review will discuss the role of the cellular interplay in ischemia-reperfusion injury from a cardiomyocyte-centered view, although we are aware that other cellular interactions are equally important. We will try to work out currently unresolved questions and potential future directions in the field.

Exercise protects against chronic β-adrenergic remodeling of the heart by activation of endothelial nitric oxide synthase

Extensive data have shown that exercise training can provide cardio-protection against pathological cardiac hypertrophy. However, how long the heart can retain cardio-protective phenotype after the cessation of exercise is currently unknown. In this study, we investigated the time course of the loss of cardio-protection after cessation of exercise and the signaling molecules that are responsible for the possible sustained protection. Mice were made to run on a treadmill six times a week for 4 weeks and then rested for a period of 0, 1, 2 and 4 weeks followed by isoproterenol injection for 8 days. Morphological, echocardiographic and hemodynamic changes were measured, gene reactivation was determined by real-time PCR, and the expression and phosphorylation status of several cardio-protective signaling molecules were analyzed by Western-blot. HW/BW, HW/TL and LW/BW decreased significantly in exercise training (ER) mice. The less necrosis and lower fetal gene reactivation induced by isoproterenol injection were also found in ER mice. The echocardiographic and hemodynamic changes induced by β-adrenergic overload were also attenuated in ER mice. The protective effects can be sustained for at least 2 weeks after the cessation of the training. Western-blot analysis showed that the alterations in the phosphorylation status of endothelial nitric oxide synthase (eNOS) (increase in serine 1177 and decrease in threonine 495) continued for 2 weeks after the cessation of the training whereas increases of the phosphorylation of Akt and mTOR disappeared. Further study showed that L-NG-Nitroarginine methyl ester (L-NAME) treatment abolished the cardio-protective effects of ER. Our findings demonstrate that stimulation of eNOS in mice through exercise training provides acute and sustained cardioprotection against cardiac hypertrophy.