Impact of Ca2+-Sensitive Potassium Channels in Levosimendan-Induced Postconditioning

The Coadministration of Levosimendan and Exenatide Offers a Significant Cardioprotective Effect to Isolated Rat Hearts against Ischemia/Reperfusion Injury

(1) Background: The present study aims to investigate the effect of administration of Levosimendan and Exenatide in various concentrations, as well as of the coadministration of those agents in an ischemia–reperfusion injury isolated heart model. (2) Methods: After 30 min of perfusion, the hearts underwent a 30 min period of regional ischemia followed by a 120 min period of reperfusion. All animals were randomly divided into 12 experimental groups of nine animals in each group: (1) Control, (2) Sham, (3) Digox (Negative control, Digoxin 1.67 μg/min), (4) Levo 1 (Levosimendan 0.01 μg/min), (5) Levo 2 (Levosimendan 0.03 μg/mL), (6) Levo 3 (Levosimendan 0.1 μg/min), (7) Levo 4 (Levosimendan 0.3 μg/min), (8) Levo 5 (Levosimendan 1 μg/min), (9) Exen 1 (Exenatide 0.001 μg/min), (10) Exen 2 (Exenatide 0.01 μg/min), (11) Exen 3 (Exenatide 0.1 μg/min) and (12) Combi (Levosimendan 0.1 µg/mL + Exenatide 0.001 μg/min). The hemodynamic parameters were recorded throughout the experiment. Arrhythmias and coronary flow were also evaluated. After every experiment the heart was suitably prepared and infarct size was measured. Markers of myocardial injury were also measured. Finally, oxidative stress was evaluated measuring reactive oxygen species. (3) Results: A dose-dependent improvement of the haemodynamic response was observed after the administration of both Levosimendan and Exenatide. The coadministration of both agents presented an even greater effect, improving the haemodynamic parameters further than the two agents separately. Levosimendan offered an increase of the coronary flow and both agents offered a reduction of arrhythmias. A dose-dependent reduction of the size of myocardial infarction and myocardial injury was observed after administration of Levosimendan and Exenatide. The coadministration of both agents offered a further improving the above parameters. Levosimendan also offered a significant reduction of oxidative stress. (4) Conclusions: The administration of Levosimendan and Exenatide offers a significant benefit by improving the haemodynamic response, increasing the coronary flow and reducing the occurrence of arrhythmias, the size of myocardial injury and myocardial oxidative stress in isolated rat hearts.

Levosimendan Postconditioning Attenuates Cardiomyocyte Apoptosis after Myocardial Infarction

BACKGROUND

Levosimendan preconditioning has been shown to attenuate myocardial apoptosis in animal models. However, protective effects of levosimendan postconditioning against myocardial apoptosis following myocardial infarction (MI) have not been evaluated. Therefore, we investigated the effects of levosimendan postconditioning on myocardial apoptosis in MI rat models.

METHODS

In an anoxia/reoxygenation (A/R) model, H9c2 cells were pretreated with or without levosimendan postconditioning after which their apoptosis rates were assessed by flow cytometry, RT-qPCR, and western blot analyses. Then, postconditioning was performed with or without levosimendan in MI rat models. Myocardiocyte apoptosis was evaluated by echocardiography, TTC staining, TUNEL staining, immunohistochemical staining, RT-qPCR, and western blot analysis.

RESULTS

Levosimendan postconditioning inhibited H9c2 cell apoptosis in A/R models by elevating Bcl-2 while suppressing Caspase-3 and Bax at both mRNA and protein levels. Moreover, it improved cardiac functions and reduced the left ventricle infarction area in MI rat models. Compared to the MI control group, cardiomyocyte apoptosis rates in the levosimendan postconditioning group were low. The reduced cardiomyocyte apoptosis rates were associated with downregulation of Bax and Caspase-3 as well as with upregulation of Bcl-2 at mRNA and protein levels.

CONCLUSIONS

Levosimendan postconditioning of MI rat models protected against cardiomyocyte apoptosis, implying that it is a potential strategy for preventing cardiomyocyte apoptosis in the treatment of cardiac dysfunction following MI.

Levosimendan-induced venodilation is mediated by opening of potassium channels

Unique vascular responses adhere to the cardiovascular efficacy of the inodilator levosimendan. In particular, selective venodilation appears to explain its clinical benefit during pulmonary hypertension complicated by heart failure with preserved ejection fraction. Vasodilators increase vessel diameter in various parts of the vascular system to different degrees and thereby influence blood pressure, its distribution, and organ perfusion depending on their mechanisms of action. Levosimendan and its long‐lived active metabolite OR‐1896 mobilize a set of vasodilatory mechanisms, that is, the opening of the ATP‐sensitive K⁺ channels and other K⁺ channels on top of a highly selective inhibition of the phosphodiesterase III enzyme. A vessel‐specific combination of the above vasodilator mechanisms—in concert with cardiac effects and cardiovascular reflex regulations—illustrates the pharmacological profile of levosimendan in various cardiovascular disorders. While levosimendan has been known to be an inotrope, its properties as an activator of ATP‐sensitive K⁺ channels have gone largely ignored with respect to clinical applications. Here, we provide a summary of what is known about the ATP‐sensitive K⁺ channel properties in preclinical studies and now for the first time, its ATP‐sensitive K⁺ channel properties in a clinical trial.

Combination of Cyclosporine A and Levosimendan Induces Cardioprotection under Acute Hyperglycemia

Prognosis of patients with myocardial infarction is detrimentally affected by comorbidities like diabetes mellitus. In the experimental setting, not only diabetes mellitus but also acute hyperglycemia is shown to hamper cardioprotective properties by multiple pharmacological agents. For Levosimendan-induced postconditioning, a strong infarct size reducing effect is demonstrated in healthy myocardium. However, acute hyperglycemia is suggested to block this protective effect. In the present study, we investigated whether (1) Levosimendan-induced postconditioning exerts a concentration-dependent effect under hyperglycemic conditions and (2) whether a combination with the mitochondrial permeability transition pore (mPTP) blocker cyclosporine A (CsA) restores the cardioprotective properties of Levosimendan under hyperglycemia. For this experimental investigation, hearts of male Wistar rats were randomized and mounted onto a Langendorff system, perfused with Krebs-Henseleit buffer with a constant pressure of 80 mmHg. All isolated hearts were subjected to 33 min of global ischemia and 60 min of reperfusion under hyperglycemic conditions. (1) Hearts were perfused with various concentrations of Levosimendan (Lev) (0.3–10 μM) for 10 min at the onset of reperfusion, in order to investigate a concentration–response relationship. In the second set of experiments (2), 0.3 μM Levosimendan was administered in combination with the mPTP blocker CsA, to elucidate the underlying mechanism of blocked cardioprotection under hyperglycemia. Infarct size was determined by tetrazolium chloride (TTC) staining. (1) Control (Con) hearts showed an infarct size of 52 ± 12%. None of the administered Levosimendan concentrations reduced the infarct size (Lev0.3: 49 ± 9%; Lev1: 57 ± 9%; Lev3: 47 ± 11%; Lev10: 50 ± 7%; all ns vs. Con). (2) Infarct size of Con and Lev0.3 hearts were 53 ± 4% and 56 ± 2%, respectively. CsA alone had no effect on infarct size (CsA: 50 ± 10%; ns vs. Con). The combination of Lev0.3 and CsA (Lev0.3 ± CsA) induced a significant infarct size reduction compared to Lev0.3 (Lev0.3+CsA: 35 ± 4%; p < 0.05 vs. Lev0.3). We demonstrated that (1) hyperglycemia blocks the infarct size reducing effects of Levosimendan-induced postconditioning and cannot be overcome by an increased concentration. (2) Furthermore, cardioprotection under hyperglycemia can be restored by combining Levosimendan and the mPTP blocker CsA.

Pharmacological Conditioning of the Heart: An Update on Experimental Developments and Clinical Implications

The aim of pharmacological conditioning is to protect the heart against myocardial ischemia-reperfusion (I/R) injury and its consequences. There is extensive literature that reports a multitude of different cardioprotective signaling molecules and mechanisms in diverse experimental protocols. Several pharmacological agents have been evaluated in terms of myocardial I/R injury. While results from experimental studies are immensely encouraging, translation into the clinical setting remains unsatisfactory. This narrative review wants to focus on two aspects: (1) give a comprehensive update on new developments of pharmacological conditioning in the experimental setting concentrating on recent literature of the last two years and (2) briefly summarize clinical evidence of these cardioprotective substances in the perioperative setting highlighting their clinical implications. By directly opposing each pharmacological agent regarding its recent experimental knowledge and most important available clinical data, a clear overview is given demonstrating the remaining gap between basic research and clinical practice. Finally, future perspectives are given on how we might overcome the limited translatability in the field of pharmacological conditioning.

[Perioperative cardioprotection - From bench to bedside : Current experimental evidence and possible reasons for the limited translation into the clinical setting]

Hintergrund

Ziel der perioperativen Kardioprotektion ist es, die Auswirkungen eines Ischämie- und Reperfusionsschadens zu minimieren. Aus anästhesiologischer Sicht spielt dieser Aspekt insbesondere in der Herzchirurgie bei Patienten mit Einsatz der Herz-Lungen-Maschine, aber auch allgemein bei längerfristigen hypotensiven Phasen oder perioperativen ischämischen Ereignissen im nichtkardiochirurgischen Setting eine wichtige Rolle. Im Laufe der letzten Jahre konnten diverse pharmakologische sowie nichtpharmakologische Strategien der Kardioprotektion identifiziert werden. Die Ergebnisse von Studien an isoliertem Gewebe sowie von tierexperimentellen In-vivo-Studien sind vielversprechend. Eine Translation dieser kardioprotektiven Strategien in die klinische Praxis ist bislang jedoch nicht gelungen. Große klinische Studien konnten keine signifikante Verbesserung des Outcome der Patienten zeigen.

Ziel der Arbeit

Dieser Übersichtsartikel gibt einen Überblick über die aktuelle experimentelle Evidenz pharmakologischer und nichtpharmakologischer Kardioprotektion. Außerdem sollen mögliche Gründe für die limitierte Translation diskutiert werden. Schließlich werden Möglichkeiten aufgezeigt, wie der Schritt „from bench to bedside“ in Zukunft doch noch gelingen könnte.

Material und Methoden

Narrative Übersichtsarbeit.

Ergebnisse und Diskussion

Trotz der vielversprechenden präklinischen experimentellen Ansätze zum Thema Kardioprotektion besteht nach wie vor eine große Diskrepanz zu den Ergebnissen aus großen klinischen Studien in der perioperativen Phase. Mögliche Gründe für die limitierte Translation könnten insbesondere Komorbiditäten und Komedikationen, die Wahl des Anästhesieverfahrens, aber auch die Wahl des Studiendesigns sein. Eine sorgfältige Studienplanung mit Berücksichtigung der genannten Probleme sowie ein simultaner Einsatz mehrerer kardioprotektiver Strategien mit dem Ziel eines additiven bzw. synergistischen Effekts stellen mögliche Ansätze für die Zukunft dar.

Perioperative Cardioprotection: General Mechanisms and Pharmacological Approaches

Cardioprotection encompasses a variety of strategies protecting the heart against myocardial injury that occurs during and after inadequate blood supply to the heart during myocardial infarction. While restoring reperfusion is crucial for salvaging myocardium from further damage, paradoxically, it itself accounts for additional cell death-a phenomenon named ischemia/reperfusion injury. Therefore, therapeutic strategies are necessary to render the heart protected against myocardial infarction. Ischemic pre- and postconditioning, by short periods of sublethal cardiac ischemia and reperfusion, are still the strongest mechanisms to achieve cardioprotection. However, it is highly impractical and far too invasive for clinical use. Fortunately, it can be mimicked pharmacologically, for example, by volatile anesthetics, noble gases, opioids, propofol, dexmedetomidine, and phosphodiesterase inhibitors. These substances are all routinely used in the clinical setting and seem promising candidates for successful translation of cardioprotection from experimental protocols to clinical trials. This review presents the fundamental mechanisms of conditioning strategies and provides an overview of the most recent and relevant findings on different concepts achieving cardioprotection in the experimental setting, specifically emphasizing pharmacological approaches in the perioperative context.

Renal and Neurologic Benefit of Levosimendan vs Dobutamine in Patients With Low Cardiac Output Syndrome After Cardiac Surgery: Clinical Trial FIM-BGC-2014-01

Background

Low-cardiac output syndrome (LCOS) after cardiac surgery secondary to systemic hypoperfusion is associated with a higher incidence of renal and neurological damage. A range of effective therapies are available for LCOS. The beneficial systemic effects of levosimendan persist even after cardiac output is restored, which suggests an independent cardioprotective effect.

Methods

A double-blind clinical trial was conducted in patients with a confirmed diagnosis of LCOS randomized into two treatment groups (levosimendan vs. dobutamine). Monitoring of hemodynamic (cardiac index, systolic volume index, heart rate, mean arterial pressure, central venous pressure, central venous saturation); biochemical (e.g. creatinine, S100B protein, NT-proBNP, troponin I); and renal parameters was performed using acute kidney injury scale (AKI scale) and renal and brain ultrasound measurements [vascular resistance index (VRI)] at diagnosis and during the first 48 h.

Results

Significant differences were observed between groups in terms of cardiac index, systolic volume index, NT-proBNP, and kidney injury stage at diagnosis. In the levosimendan group, there were significant variations in AKI stage after 24 and 48 h. No significant differences were observed in the other parameters studied.

Conclusion

Levosimendan showed a beneficial effect on renal function in LCOS patients after cardiac surgery that was independent from cardiac output and vascular tone. This effect is probably achieved by pharmacological postconditioning.

Clinical Trial Registration

EUDRA CT, identifier 2014-001461-27. https://www.clinicaltrialsregister.eu/ctr-search/search?query=2014-001461-27.