Adenosine A1 receptors and mitochondria: targets of remote ischemic preconditioning

Problems and prospects for finding new pharmacological agents among adenosine receptor agonists, antagonists, or their allosteric modulators for the treatment of cardiovascular diseases

A1-adenosine receptors (A1AR) are widely distributed in the human body and mediate many different effects. They are abundantly present in the cardiovascular system, where they control angiogenesis, vascular tone, heart rate, and conduction. This makes the cardiovascular system A1AR an attractive target for the treatment of cardiovascular diseases (CVD). The review summarizes the literature data on the structure and functioning of A1AR, and analyzes their involvement in the formation of myocardial hypertrophy, ischemia-reperfusion damage, various types of heart rhythm disorders, chronic heart failure, and arterial hypertension. Special attention is paid to the role of some allosteric regulators of A1AR as potential agents for the CVD treatment.

Endless Journey of Adenosine Signaling in Cardioprotective Mechanism of Conditioning Techniques: Clinical Evidence

Myocardial ischemic injury is a primary cause of death among various cardiovascular disorders. The condition occurs due to an interrupted supply of blood and vital nutrients (necessary for normal cellular activities and viability) to the myocardium, eventually leading to damage. Restoration of blood supply to ischemic tissue is noted to cause even more lethal reperfusion injury. Various strategies, including some conditioning techniques, like preconditioning and postconditioning, have been developed to check the detrimental effects of reperfusion injury. Many endogenous substances have been proposed to act as initiators, mediators, and end effectors of these conditioning techniques. Substances, like adenosine, bradykinin, acetylcholine, angiotensin, norepinephrine, opioids, etc., have been reported to mediate cardioprotective activity. Among these agents, adenosine has been widely studied and suggested to have the most pronounced cardioprotective effects. The current review article highlights the role of adenosine signaling in the cardioprotective mechanism of conditioning techniques. The article also provides an insight into various clinical studies that substantiate the applicability of adenosine as a cardioprotective agent in myocardial reperfusion injury.

Stimulation of adenosine A1 receptor prevents oxidative injury in H9c2 cardiomyoblasts: Role of Gβγ-mediated Akt and ERK1/2 signaling

Oxidative stress causes cellular injury and damage in the heart primarily through apoptosis resulting in cardiac abnormalities such as heart failure and cardiomyopathy. During oxidative stress, stimulation of adenosine receptor (AR) has been shown to protect against oxidative damage due to their cytoprotective properties. However, the subtype specificity and signal transductions of adenosine A₁ receptor (A₁R) on cardiac protection during oxidative stress have remained elusive. In this study, we found that stimulation of A₁Rs with N⁶-cyclopentyladenosine (CPA), a specific A₁R agonist, attenuated the H₂O₂-induced intracellular and mitochondrial reactive oxygen species (ROS) production and apoptosis. In addition, A₁R stimulation upregulated the synthesis of antioxidant enzymes (catalase and GPx-1), antiapoptotic proteins (Bcl-2 and Bcl-xL), and mitochondria-related markers (UCP2 and UCP3). Blockades of Gβγ subunit of heterotrimeric Gα_i protein antagonized A₁R-mediated antioxidant and antiapoptotic effects, confirming the potential role of Gβγ subunit-mediated A₁R signaling. Additionally, cardioprotective effects of CPA mediated through PI3K/Akt- and ERK1/2-dependent signaling pathways. Thus, we propose that A₁R represents a promising therapeutic target for prevention of oxidative injury in the heart.

Baicalein Preconditioning Cardioprotection Involves Pro-Oxidant Signaling and Activation of Pyruvate Dehydrogenase

Preconditioning has a powerful protective potential against myocardial ischemia-reperfusion injury (I/R). Our prior work demonstrated that baicalein, a flavonoid derived from the root of Scatellaria baicalensis Georgi (also known as Huangqin), confers this preconditioning protection. This study further explored the mechanisms of baicalein preconditioning (BC-PC) in mouse cardiomyocytes. Cells were treated with baicalein (10 μM) for a brief period of time (10 min) prior to simulated ischemia 90 min/reperfusion for 180 min. Baicalein triggered an induction of a small amount of mitochondrial reactive oxygen species (ROS) prior to the initiation of ischemia, assessed by 6-carboxy-2^', 7^'-dichlorodihydrofluorescein diacetate (6-carboxy-H₂DCFDA). It also significantly increased cell viability measured by propidium iodide (PI) and lactate dehydrogenase and preserved mitochondrial membrane potential assessed by TMRM fluorescence intensity. Myxothiazol, a mitochondrial electron transport chain complex III inhibitor, partially blocked ROS generation induced by BC-PC and reduced cell viability. BC-PC increased phosphorylation of Akt (Thr308 and Ser473) and eNOS Ser1177, and nitric oxide (NO) production measured using 4,5-diaminofluorescein diacetate (DAF-2 DA, 1 μM). Akt inhibitor API-2 abolished Akt phosphorylation and reduced DAF-2 production and cell viability. In addition, BC-PC decreased phosphorylation of pyruvate dehydrogenase (PDH) reflecting upregulated PDH activity, and increased ATP production at 30 min during reperfusion. Taken together, baicalein preconditioning-induced cardioprotection involves pro-oxidant generation, activates survival signaling Akt/eNOS/NO, and improves metabolic recovery after I/R injury. Our work provides new perspectives on the effect of baicalein on cardiac preconditioning against I/R injury.

Blockage of Fibronectin 1 Ameliorates Myocardial Ischemia/Reperfusion Injury in Association with Activation of AMP-LKB1-AMPK Signaling Pathway

Myocardial ischemia/reperfusion injury (I/RI) is closely associated with energy substrate metabolism. Fibronectin 1 (Fn1) was markedly elevated in the heart of I/R pigs and ischemic patients, but its role in myocardial I/RI is controversial and the precise mechanism involved remains elusive. Herein, we tested whether blockage of Fn1 with its inhibitor (fibronectin tetrapeptide, RGDS) would alleviate myocardial I/RI. Wild-type (WT) mice were administered with RGDS once 3 h before I/R operation and once at 24 or 48 h postreperfusion, and sacrificed at 24 or 72 h post-I/R, respectively. Cardiac function was evaluated by echocardiography. Myocardial infarction size, apoptosis, fibrosis, and inflammation were examined via histological staining. Uptake of glucose and fatty acids were detected by positron emission tomography (PET) and computer tomography (CT) with [¹⁸F]-2-fluoro-2-deoxy-D-glucose (FDG) and [¹⁸F]-fluoro-6-thia-heptadecanoic acid (FTHA), respectively. Our results showed that administration of RGDS to mice remarkably limited the I/R-induced myocardial infarct size, myocyte apoptosis, inflammation, oxidative stress, and fibrosis and improved cardiac contractile dysfunction. These protective effects were associated with upregulation of the AMP/ATP ratio and the activation of LKB1-AMPK signaling, which subsequently increased AS160-GLUT4-mediated glucose and fatty acid uptake, improved mitochondrial dynamic imbalance, and inactivated TGF-β and NF-κB signals in the I/R heart. In conclusion, the current study identified that blocking Fn1 protects against myocardial I/RI likely through activating the LKB1-AMPK-dependent signals and highlights that inhibition of Fn1 may be a novel therapeutic option for treating ischemic heart diseases.

Nrg1β Released in Remote Ischemic Preconditioning Improves Myocardial Perfusion and Decreases Ischemia/Reperfusion Injury via ErbB2-Mediated Rescue of Endothelial Nitric Oxide Synthase and Abrogation of Trx2 Autophagy

OBJECTIVE: Remote ischemic preconditioning (RIPC) is an intervention process where the application of multiple cycles of short ischemia/reperfusion (I/R) in a remote vascular bed provides protection against I/R injury. However, the identity of the specific RIPC factor and the mechanism by which RIPC alleviates I/R injury remains unclear. Here, we have investigated the identity and the mechanism by which the RIPC factor provides protection. APPROACH AND RESULTS: Using fluorescent in situ hybridization and immunofluorescence, we found that RIPC induces Nrg1β expression in the endothelial cells, which is secreted into the serum. Whereas, RIPC protected against myocardial apoptosis and infarction, treatment with neutralizing-Nrg1 antibodies abolished the protective effect of RIPC. Further, increased superoxide anion generated in RIPC is required for Nrg1 expression. Improved myocardial perfusion and nitric oxide production were achieved by RIPC as determined by contrast echocardiography and electron spin resonance. However, treatment with neutralizing-Nrg1β antibody abrogated these effects, suggesting Nrg1β is a RIPC factor. ErbB2 (Erb-B2 receptor tyrosine kinase 2) is not expressed in the adult murine cardiomyocytes, but expressed in the endothelial cells of heart which is degraded in I/R. RIPC-induced Nrg1β interacts with endothelial ErbB2 and thereby prevents its degradation. Mitochondrial Trx2 (thioredoxin) is degraded in I/R, but rescue of ErbB2 by Nrg1β prevents Trx-2 degradation that decreased myocardial apoptosis in I/R. CONCLUSIONS: Nrg1β is a RIPC factor that interacts with endothelial ErbB2 and prevents its degradation, which in turn prevents Trx2 degradation due to phosphorylation and inactivation of ATG5 (autophagy-related 5) by ErbB2. Nrg1β also restored loss of eNOS (endothelial nitric oxide synthase) function in I/R via its interaction with Src.

Metabolic Reprogramming: Strategy for Ischemic Stroke Treatment by Ischemic Preconditioning

Stroke is one of the leading causes of death and permanent disability worldwide. Ischemic preconditioning (IPC) is an endogenous protective strategy, which has been reported to exhibit a significant neuroprotective effect in reducing the incidence of ischemic stroke. However, the underlying neuroprotective mechanisms of IPC remain elusive. An increased understanding of the pathogenic mechanisms of stroke and IPC serves to highlight the importance of metabolic reprogramming. In this review, we summarize the metabolic disorder and metabolic plasticity in the incidence and progression of ischemic stroke. We also elaborate how IPC fully mobilizes the metabolic reprogramming to maintain brain metabolic homeostasis, especially for energy and redox homeostasis, and finally protects brain function in the event of an ischemic stroke.

Potential Therapeutic Role of Purinergic Receptors in Cardiovascular Disease Mediated by SARS-CoV-2

Novel coronavirus disease 2019 (COVID-19) causes pulmonary and cardiovascular disorders and has become a worldwide emergency. Myocardial injury can be caused by direct or indirect damage, particularly mediated by a cytokine storm, a disordered immune response that can cause myocarditis, abnormal coagulation, arrhythmia, acute coronary syndrome, and myocardial infarction. The present review focuses on the mechanisms of this viral infection, cardiac biomarkers, consequences, and the possible therapeutic role of purinergic and adenosinergic signalling systems. In particular, we focus on the interaction of the extracellular nucleotide adenosine triphosphate (ATP) with its receptors P2X1, P2X4, P2X7, P2Y1, and P2Y2 and of adenosine (Ado) with A2A and A3 receptors, as well as their roles in host immune responses. We suggest that receptors of purinergic signalling could be ideal candidates for pharmacological targeting to protect against myocardial injury caused by a cytokine storm in COVID-19, in order to reduce systemic inflammatory damage to cells and tissues, preventing the progression of the disease by modulating the immune response and improving patient quality of life.

Remote ischaemic preconditioning influences the levels of acylcarnitines in vascular surgery: a randomised clinical trial

Background

Vascular surgery patients have reduced tissues` blood supply, which may lead to mitochondrial dysfunction and accumulation of acylcarnitines (ACs). It has been suggested that remote ischaemic preconditioning (RIPC) has its organ protective effect via promoting mitochondrial function. The aim of this study was to evaluate the effect of RIPC on the profile of ACs in the vascular surgery patients.

Methods

This is a randomised, sham-controlled, double-blinded, single-centre study. Patients undergoing open surgical repair of abdominal aortic aneurysm, surgical lower limb revascularisation surgery or carotid endarterectomy were recruited non-consecutively. The RIPC protocol consisting of 4 cycles of 5 min of ischaemia, followed by 5 min of reperfusion, was applied. A blood pressure cuff was used for RIPC or a sham procedure. Blood was collected preoperatively and approximately 24 h postoperatively. The profile of ACs was analysed using the AbsoluteIDQp180 kit (Biocrates Life Sciences AG, Innsbruck, Austria).

Results

Ninety-eight patients were recruited and randomised into the study groups and 45 patients from the RIPC group and 47 patients from the sham group were included in final analysis. There was a statistically significant difference between the groups regarding the changes in C3-OH (p = 0.023)—there was a decrease (− 0.007 µmol/L, ± 0.020 µmol/L, p = 0.0233) in the RIPC group and increase (0.002 µmol/L, ± 0.015 µmol/L, p = 0.481) in the sham group. Additionally, a decrease from baseline to 24 h after surgery (p < 0.05) was detected both in the sham and the RIPC group in the levels of following ACs: C2, C8, C10, C10:1, C12, C12:1, C14:1, C14:2, C16, C16:1, C18, C18:1, C18:2. In the sham group, there was an increase (p < 0.05) in the levels of C0 (carnitine) and a decrease in the level of C18:1-OH. In the RIPC group, a decrease (p < 0.05) was noted in the levels of C3-OH, C3-DC (C4-OH), C6:1, C9, C10:2.

Conclusions

It can be concluded that RIPC may have an effect on the levels of ACs and might therefore have protective effects on mitochondria in the vascular surgery patients. Further larger studies conducted on homogenous populations are needed to make more definite conclusions about the effect of RIPC on the metabolism of ACs.

Trial registration

ClinicalTrials.gov database, NCT02689414. Registered 24 February 2016—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT02689414.

Electronic supplementary material

The online version of this article (10.1186/s12986-020-00495-3) contains supplementary material, which is available to authorized users.

Remote ischemic preconditioning-induced neuroprotection in cerebral ischemia-reperfusion injury: Preclinical evidence and mechanisms

Remote ischemic preconditioning (RIPC) is an intrinsic protective phenomenon in which 3 to 4 interspersed cycles of non-fatal regional ischemia followed by reperfusion to the remote tissues protect the vital organs including brain, heart and kidney against sustained ischemia-reperfusion-induced injury. There is growing preclinical evidence supporting the usefulness of RIPC in eliciting neuroprotection against focal and global cerebral ischemia-reperfusion injury. Scientists have explored the involvement of HIF-1α, oxidative stress, apoptotic pathway, Lcn-2, platelets-derived microparticles, splenic response, adenosine A₁ receptors, adenosine monophosphate activated protein kinase and neurogenic pathway in mediating RIPC-induced neuroprotection. The present review discusses the early and late phases of neuroprotection induced by RIPC against cerebral ischemic injury in animals along with the various possible mechanisms.

Ischemia/Reperfusion Injury Revisited: An Overview of the Latest Pharmacological Strategies

Ischemia/reperfusion injury (IRI) permeates a variety of diseases and is a ubiquitous concern in every transplantation proceeding, from whole organs to modest grafts. Given its significance, efforts to evade the damaging effects of both ischemia and reperfusion are abundant in the literature and they consist of several strategies, such as applying pre-ischemic conditioning protocols, improving protection from preservation solutions, thus providing extended cold ischemia time and so on. In this review, we describe many of the latest pharmacological approaches that have been proven effective against IRI, while also revisiting well-established concepts and presenting recent pathophysiological findings in this ever-expanding field. A plethora of promising protocols has emerged in the last few years. They have been showing exciting results regarding protection against IRI by employing drugs that engage several strategies, such as modulating cell-surviving pathways, evading oxidative damage, physically protecting cell membrane integrity, and enhancing cell energetics.