Inhibition of mitochondrial remodeling by cyclosporine A preserves myocardial performance in a neonatal rabbit model of cardioplegic arrest

Cyclosporine A-enhanced cardioplegia preserves mitochondrial basal respiration after ischemic arrest

BACKGROUND

Mitochondrial permeability transition pore (mPTP) opening plays a crucial role in cell death during ischemia-reperfusion injury (IRI). Cyclosporine A (CsA) inhibits mPTP opening. This study aimed to investigate the effects of CsA treatment during cardioplegia on the mitochondrial function and cardiac IRI.

METHODS

Landrace pigs (52.9 ± 3.7 kg) were subjected to midline sternotomy, cardiopulmonary bypass at 34°C and 90 minutes of cardiac arrest. They received either a single shot of standard 4°C cold histidine-tryptophan-α-ketoglutarate (HTK)-Bretschneider solution (n = 11) or HTK-Bretschneider plus 1.2 mg/L CsA (histidine-tryptophan-α-ketoglutarate plus cyclosporine A (HTK/CsA); n = 11). During reperfusion global left-ventricular function was assessed and myocardial biopsies were harvested at baseline, during ischemia and 45 minutes following reperfusion. High-resolution respirometry and hydrogen peroxide production were measured. Immunohistochemical stainings for apoptosis-inducing factor and hypoxia-inducible factor-1α as well as a flow cytometry-based JC-1 mitochondrial membrane potential assay were performed.

RESULTS

Hemodynamic parameters were comparable between both groups. The cytochrome C release (HTK: 930.3 ± 804.4 pg/mg, HTK/CsA: 699.7 ± 394.0 pg/mg, p = 0.457) as well as PGC1α content (HTK: 66.7%, HTK/CsA: 33.3%, p = 0.284) was lower in the HTK/CsA group. Respiratory measurements revealed that the oxygen flux under basal respiration was higher in the HTK/CsA group (8.2 ± 1.3 pmol·O2·s-1·mg-1·ww) than in the HTK group (3.8 ± 1.4 pmol·O2·s-1·mg-1·ww, p = 0.045). There were no significant differences regarding histological surrogates of apoptosis and necrosis.

CONCLUSIONS

Supplementing cardioplegic solutions with CsA enhances the basal mitochondrial respiration thereby exerting a cardioprotective effect and diminishing IRI-induced damage. CsA seems to preserve mitochondrial function via non-ROS related pathways.

Cannabinoid receptor agonist attenuates angiotensin II-induced enlargement and mitochondrial dysfunction in rat atrial cardiomyocytes

Pathological remodeling of atrial tissue renders the atria more prone to arrhythmia upon arrival of electrical triggers. Activation of the renin-angiotensin system is an important factor that contributes to atrial remodeling, which may result in atrial hypertrophy and prolongation of P-wave duration. In addition, atrial cardiomyocytes are electrically coupled via gap junctions, and electrical remodeling of connexins may result in dysfunction of coordinated wave propagation within the atria. Currently, there is a lack of effective therapeutic strategies that target atrial remodeling. We previously proposed that cannabinoid receptors (CBR) may have cardioprotective qualities. CB13 is a dual cannabinoid receptor agonist that activates AMPK signaling in ventricular cardiomyocytes. We reported that CB13 attenuates tachypacing-induced shortening of atrial refractoriness and inhibition of AMPK signaling in the rat atria. Here, we evaluated the effects of CB13 on neonatal atrial rat cardiomyocytes (NRAM) stimulated by angiotensin II (AngII) in terms of atrial myocyte enlargement and mitochondrial function. CB13 inhibited AngII-induced enhancement of atrial myocyte surface area in an AMPK-dependent manner. CB13 also inhibited mitochondrial membrane potential deterioration in the same context. However, AngII and CB13 did not affect mitochondrial permeability transition pore opening. We further demonstrate that CB13 increased Cx43 compared to AngII-treated neonatal rat atrial myocytes. Overall, our results support the notion that CBR activation promotes atrial AMPK activation, and prevents myocyte enlargement (an indicator that suggests pathological hypertrophy), mitochondrial depolarization and Cx43 destabilization. Therefore, peripheral CBR activation should be further tested as a novel treatment strategy in the context of atrial remodeling.

Age-Dependent Myocardial Dysfunction in Critically Ill Patients: Role of Mitochondrial Dysfunction

Myocardial dysfunction is common in septic shock and post-cardiac arrest but manifests differently in pediatric and adult patients. By conventional echocardiographic parameters, biventricular systolic dysfunction is more prevalent in children with septic shock, though strain imaging reveals that myocardial injury may be more common in adults than previously thought. In contrast, diastolic dysfunction in general and post-arrest myocardial systolic dysfunction appear to be more widespread in the adult population. A growing body of evidence suggests that mitochondrial dysfunction mediates myocardial depression in critical illness; alterations in mitochondrial electron transport system function, bioenergetic production, oxidative and nitrosative stress, uncoupling, mitochondrial permeability transition, fusion, fission, biogenesis, and autophagy all may play key pathophysiologic roles. In this review we summarize the epidemiologic and clinical phenotypes of myocardial dysfunction in septic shock and post-cardiac arrest and the multifaceted manifestations of mitochondrial injury in these disease processes. Since neonatal and pediatric-specific data for mitochondrial dysfunction remain sparse, conclusive age-dependent differences are not clear; instead, we highlight what evidence exists and identify gaps in knowledge to guide future research. Finally, since focal ischemic injury (with or without reperfusion) leading to myocardial infarction is predominantly an atherosclerotic disease of the elderly, this review focuses specifically on septic shock and global ischemia-reperfusion injury occurring after resuscitation from cardiac arrest.

Evaluation of cyclosporine a as a cardio- and neuroprotective agent after cardiopulmonary resuscitation in a rat model

The immunosuppressant drug cyclosporine A (CsA) is a direct inhibitor of the mitochondrial permeability transition pore, which is the common end point of many pathways of ischemic preconditioning and postconditioning. We studied the neuroprotective and cardioprotective effect of CsA after cardiac arrest (CA) in a rat model of cardiopulmonary resuscitation. After institutional approval by the Governmental Animal Care Committee, 83 rats were subjected to 6 min of CA and were randomly and investigator-blinded allocated either to placebo (n = 15) or interventional group (n = 15; 10-mg/kg body weight CsA intravenously) after restoration of spontaneous circulation (ROSC). Before CA (baseline) as well as 1 h and 3 h after ROSC, continuous measurement of stroke volume, left ventricular ejection fraction, preload adjusted maximum power, and end diastolic volume was performed using a conductance catheter. One day, 3 days, and 7 days after ROSC, neurological outcome was evaluated by a tape removal test. After 7 days of reperfusion, coronal brain sections were analyzed by counting Nissl-positive (i.e., viable) neurons and terminal deoxynucleotidyl transferase dUTP nick end labeling positive (i.e., apoptotic) cells. Animals treated with CsA had a higher stroke volume (96 [93; 107] μL vs. 78 [73; 94] μL; P = 0.02), higher ejection fraction (58% [51%; 63%] vs. 42% [35%; 51%]; P = 0.002), and higher preload adjusted maximum power (4.8 [3.9; 6.1] vs. 2.3 [2.0; 2.6] mW/μL; P < 0.001). End diastolic volume remained stable in the CsA group 3 h after ROSC in comparison to baseline (160 [143; 181] μL vs. 157 [148; 192] μL; P = 0.56), whereas it increased in the placebo group (169 [153; 221] μL vs. 156 [138; 166] μL, P = 0.05). More neurons survived after administration of CsA (2.5 [1.6; 4.9] vs. 0.7 [0.4; 1.4]; P = 0.005). Compared to placebo-treated animals, the time in the tape removal test 7 days after ROSC was reduced by half in the CsA group without reaching statistical significance (26 [22; 51] vs. placebo 53 [38; 56] s; P = 0.13). Cyclosporine A treatment neither affected the number of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells nor the survival rate. Pharmacological postconditioning with CsA after successful cardiopulmonary resuscitation attenuates myocardial dysfunction and reduces neuronal damage.

Coronary flow and reactivity, but not arrhythmia vulnerability, are affected by cardioplegia during cardiopulmonary bypass in piglets

Background

Surgery under cardiopulmonary bypass (CPB) is still associated with significant cardiovascular morbidity in both pediatric and adult patients but the mechanisms are not fully understood. Abnormalities in coronary flow and function have been suggested to play an important role. Prior studies suggest protective effects on coronary and myocardial function by short intravenous (i.v.) infusion of cyclosporine A before CPB.

Methods

Barrier-bred piglets (10–12 kg, n=20) underwent CPB for 45 min, with or without antegrade administration of cardioplegic solution. Prior to CPB, half of the animals in each group received an i.v. infusion of 100 mg/kg cyclosporine A. The left anterior descending coronary flow velocity responses to adenosine, serotonin, and atrial pacing, as well as left ventricular function and postsurgical vulnerability to atrial fibrillation (Afib) were assessed by intracoronary Doppler, epicardial echocardiography, and in vivo electrophysiological study, before and 8 hours after surgery. Plasma C-reactive protein (CRP) and fibrinogen were measured at both time-points.

Results

Cyclosporine infusion did not influence any of the studied variables (p>0.4). Coronary peak flow velocity (cPFV) rose significantly after surgery especially in the cardioplegia group (p<0.01 vs. non-cardioplegia group and pre-surgery). cPFV responses to adenosine, but not to serotonin, tended to decrease (p=0.06) after surgery only in cardioplegia group (p=0.06; p=0.8 in non-cardioplegia group vs pre-surgery). Also, cPFV response to atrial pacing was lower in the cardioplegia than in the non-cardioplegia group (p=0.02). Neither vulnerability nor duration of induced Afib after CPB differed between groups (Chi-square p=0.4). Cyclosporine had no significant effect on coronary indexes or arrhythmia vulnerability (p>0.4). There was no difference in systolic myocardial function between groups at any time point.

Conclusion

In piglets, CPB with cardioplegia was associated with profound abnormalities in coronary vasomotor tone and receptor-related flow regulation, whereas arrhythmia vulnerability appeared to be comparable with that in non-cardioplegia group. In this study, preconditioning with cyclosporine had no detectable protective effect on coronary circulation or arrhythmia vulnerability after CPB.

Cyclosporin A and cardioprotection: from investigative tool to therapeutic agent

Ischaemic heart disease (IHD) is the leading cause of death and disability worldwide. The pathophysiological effects of IHD on the heart most often result from the detrimental effects of acute ischaemia-reperfusion injury (IRI) on the myocardium. Therefore, novel therapeutic targets for protecting the myocardium against acute IRI are required to reduce injury to the heart, preserve cardiac function and improve clinical outcomes in patients with IHD. In this regard, the mitochondrial permeability transition pore (mPTP) has emerged as a critical target for cardioprotection which is readily amenable to intervention at the time of myocardial reperfusion. The formation and opening of the mPTP at the onset of myocardial reperfusion is a major determinant of mitochondrial dysfunction and cardiomyocyte death in the setting of acute IRI. The seminal discovery in the late 1980s that mPTP opening could be pharmacologically inhibited by the immunosuppressive agent, cyclosporin A (CsA), has been fundamental in the elucidation of the critical role of the mPTP as a mediator of acute IRI and, therefore, a viable target for cardioprotection. Its initial role as an investigative tool was used to identify mitochondrial cyclophilin D to be a regulatory component of the mPTP. The mPTP as a viable target for cardioprotection has recently been translated into the clinical setting with CsA reducing myocardial infarct size in patients. In this article, we review the intriguing role of CsA as a tool for investigating the mPTP as a target for cardioprotection and its potential role as a therapeutic agent for patients with IHD.

Pharmacological postconditioning protects isolated rat hearts against ischemia-reperfusion injury: the role of mitochondrial permeability transition pore

Postconditioning has been verified to provide cardioprotection and is associated with the state of mitochondrial permeability transition pore. However, there are a few limitations with clinical use of classic postconditioning; therefore, the purpose of this investigation was to study whether inhibition of mitochondrial permeability transition pore opening with cyclosporine A also provided cardioprotection. Langendorff-perfused Sprague-Dawley rat hearts were perfused for 20 minutes with Krebs-Henseleit buffer followed by 30 minutes of crystalloid cardioplegia and 60 minutes of reperfusion. Control hearts (Con group) were reperfused with Krebs-Henseleit buffer. Postconditioning hearts (Ipo group) were with six cycles of 10 seconds reocclusion separated by 10 seconds perfusion before reperfusion. Cyclosporine A postconditioning hearts (CsA group) were reperfused with Krebs-Henseleit buffer containing 0.8 μmol/L cyclosporine A at first 5 minutes of reperfusion. Compared with Con group, myocardial performance was better preserved in CsA group. Mitochondrial outer membrane integrity was preserved, with less cytosolic diffusion of cytochrome C (p < 0.05) and less frequency of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labeling-positive myocytes in Ipo and CsA group (p < 0.05). Postconditioning prevented apoptosis-related mitochondrial permeabilization and dysfunction after cardioplegic arrest. Cyclosporine A postconditioning had a better effect than classic postconditioning in myocardial performance.

Mitochondria are sources of metabolic sink and arrhythmias

Mitochondria have long been recognized for their central role in energy transduction and apoptosis. More recently, extensive work in multiple laboratories around the world has significantly extended the role of cardiac mitochondria from relatively static arbitrators of cell death and survival pathways to highly dynamic organelles that form interactive functional networks across cardiomyocytes. These coupled networks were shown to strongly affect cardiomyocyte responses to oxidative stress by modulating cell signaling pathways that strongly impact physiological properties. Of particular importance is the role of mitochondria in modulating key electrophysiological and calcium cycling properties in cardiomyocytes, either directly through activation of a myriad of mitochondrial ion channels or indirectly by affecting cell signaling cascades, ATP levels, and the over-all redox state of the cardiomyocyte. This important recognition has ushered a renewed interest in understanding, at a more fundamental level, the exact role that cardiac metabolism, in general and mitochondria, in particular, play in both health and disease. In this article, we provide an overview of recent advances in our growing understanding of the fundamental role that cardiac mitochondria play in the genesis of lethal arrhythmias.

Postconditioning: From the Bench to Bedside

Infarct size is determined not only by the severity of ischemia but also by pathological processes initiated at reperfusion. Accumulating experimental evidence indicates that lethal reperfusion injury might account for up to half of the final size of the myocardial infarct. Ischemic postconditioning (brief repeated periods of ischemia-reperfusion applied at the onset of coronary reflow) has been recently described as a powerful cardioprotection mechanism that prevents lethal reperfusion injury. This is the first method proven to reduce the final infarct size by about 50% in several in vivo models and to be confirmed in recent preliminary human studies. The molecular pathways are incompletely mapped but they probably converge to a mitochondrial key target: the mitochondrial permeability transition pore (PTP) which opening during early reperfusion is an event that promotes myocardial cell death. In different animal models and experimental settings, pharmacological PTP inhibition at the onset of reperfusion reproduces all the cardioprotective effects of ischemic postconditioning. In a recent proof-of-concept trial, the administration (just before percutaneous coronary intervention) of cyclosporine A, a potent PTP inhibitor, was associated with smaller infarct size. This review will focus on the physiological preclinical data on both ischemic and pharmacological postconditioning that are relevant to their translation to clinical therapeutics.

Cardiac mitochondria and arrhythmias

Despite a high prevalence of sudden cardiac death throughout the world, the mechanisms that lead to ventricular arrhythmias are not fully understood. Over the last 20 years, a growing body of evidence indicates that cardiac mitochondria are involved in the genesis of arrhythmia. In this review, we have attempted to describe the role that mitochondria play in altering the heart's electrical function by introducing heterogeneity into the cardiac action potential. Specifically, we have focused on how the energetic status of the mitochondrial network can alter sarcolemmal potassium fluxes through ATP-sensitive potassium channels, creating a 'metabolic sink' for depolarizing wave-fronts and introducing conditions that favour catastrophic arrhythmia. Mechanisms by which mitochondria depolarize under conditions of oxidative stress are characterized, and the contributions of several mitochondrial ion channels to mitochondrial depolarization are presented. The inner membrane anion channel in particular opens upstream of other inner membrane channels during metabolic stress, and may be an effective target to prevent the metabolic oscillations that create action potential lability. Finally, we discuss therapeutic strategies that prevent arrhythmias by preserving mitochondrial membrane potential in the face of oxidative stress, supporting the notion that treatments aimed at cardiac mitochondria have significant potential in attenuating electrical dysfunction in the heart.