Effects of OR-1896, an active metabolite of levosimendan, on contractile force and aequorin light transients in intact rabbit ventricular myocardium

Levosimendan inhibits disulfide tau oligomerization and ameliorates tau pathology in TauP301L-BiFC mice

Tau oligomers play critical roles in tau pathology and are responsible for neuronal cell death and transmitting the disease in the brain. Accordingly, preventing tau oligomerization has become an important therapeutic strategy to treat tauopathies, including Alzheimer's disease. However, progress has been slow because detecting tau oligomers in the cellular context is difficult. Working toward tau-targeted drug discovery, our group has developed a tau-BiFC platform to monitor and quantify tau oligomerization. By using the tau-BiFC platform, we screened libraries with FDA-approved and passed phase I drugs and identified levosimendan as a potent anti-tau agent that inhibits tau oligomerization. ¹⁴C-isotope labeling of levosimendan revealed that levosimendan covalently bound to tau cysteines, directly inhibiting disulfide-linked tau oligomerization. In addition, levosimendan disassembles tau oligomers into monomers, rescuing neurons from aggregation states. In comparison, the well-known anti-tau agents methylene blue and LMTM failed to protect neurons from tau-mediated toxicity, generating high-molecular-weight tau oligomers. Levosimendan displayed robust potency against tau oligomerization and rescued cognitive declines induced by tauopathy in the Tau^P301L-BiFC mouse model. Our data present the potential of levosimendan as a disease-modifying drug for tauopathies.

The Adenylate Cyclase Activator Forskolin Potentiates the Positive Inotropic Effect of the Phosphodiesterase Inhibitor Milrinone But Not of the Calcium Sensitizer Levosimendan nor of Its Hemodynamically Active Metabolites: An Apparent Conundrum

ABSTRACT

OR-1855 and OR-1896 are 2 hemodynamically active metabolites of the inodilator levosimendan, with calcium sensitizing activity, but their mechanism of action is still not fully understood. It has been previously reported that the positive inotropic effect of levosimendan is not potentiated by the adenylate cyclase activator forskolin, whereas forskolin does potentiate the effects of the phosphodiesterase (PDE) inhibitor milrinone. To ascertain whether the active metabolites follow the same pattern of levosimendan, the positive inotropic effects of OR- 1855 and OR-1896 were studied in guinea-pig-isolated papillary muscle in the presence and absence of forskolin. OR-1855 and OR-1896 were also tested as inhibitors of PDE-III and PDE-IV. Our results show that 0.1 µM forskolin did not potentiate the positive inotropic effect of OR-1855 or OR-1896, as in the case of the parent compound levosimendan. As in previous studies, the positive inotropic effect of milrinone was markedly potentiated in the presence of forskolin. From these data, we propose an explanation for the divergent behavior of the calcium sensitizing drugs and PDE inhibitors.

Levosimendan Efficacy and Safety: 20 years of SIMDAX in Clinical Use

Levosimendan was first approved for clinic use in 2000, when authorisation was granted by Swedish regulatory authorities for the haemodynamic stabilisation of patients with acutely decompensated chronic heart failure. In the ensuing 20 years, this distinctive inodilator, which enhances cardiac contractility through calcium sensitisation and promotes vasodilatation through the opening of adenosine triphosphate-dependent potassium channels on vascular smooth muscle cells, has been approved in more than 60 jurisdictions, including most of the countries of the European Union and Latin America. Areas of clinical application have expanded considerably and now include cardiogenic shock, takotsubo cardiomyopathy, advanced heart failure, right ventricular failure and pulmonary hypertension, cardiac surgery, critical care and emergency medicine. Levosimendan is currently in active clinical evaluation in the US. Levosimendan in IV formulation is being used as a research tool in the exploration of a wide range of cardiac and non-cardiac disease states. A levosimendan oral form is at present under evaluation in the management of amyotrophic lateral sclerosis. To mark the 20 years since the advent of levosimendan in clinical use, 51 experts from 23 European countries (Austria, Belgium, Croatia, Cyprus, Czech Republic, Estonia, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Russia, Slovenia, Spain, Sweden, Switzerland, UK and Ukraine) contributed to this essay, which evaluates one of the relatively few drugs to have been successfully introduced into the acute heart failure arena in recent times and charts a possible development trajectory for the next 20 years.

Levosimendan Efficacy and Safety: 20 Years of SIMDAX in Clinical Use

Levosimendan was first approved for clinical use in 2000, when authorization was granted by Swedish regulatory authorities for the hemodynamic stabilization of patients with acutely decompensated chronic heart failure (HF). In the ensuing 20 years, this distinctive inodilator, which enhances cardiac contractility through calcium sensitization and promotes vasodilatation through the opening of adenosine triphosphate-dependent potassium channels on vascular smooth muscle cells, has been approved in more than 60 jurisdictions, including most of the countries of the European Union and Latin America. Areas of clinical application have expanded considerably and now include cardiogenic shock, takotsubo cardiomyopathy, advanced HF, right ventricular failure, pulmonary hypertension, cardiac surgery, critical care, and emergency medicine. Levosimendan is currently in active clinical evaluation in the United States. Levosimendan in IV formulation is being used as a research tool in the exploration of a wide range of cardiac and noncardiac disease states. A levosimendan oral form is at present under evaluation in the management of amyotrophic lateral sclerosis. To mark the 20 years since the advent of levosimendan in clinical use, 51 experts from 23 European countries (Austria, Belgium, Croatia, Cyprus, Czech Republic, Estonia, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Russia, Slovenia, Spain, Sweden, Switzerland, the United Kingdom, and Ukraine) contributed to this essay, which evaluates one of the relatively few drugs to have been successfully introduced into the acute HF arena in recent times and charts a possible development trajectory for the next 20 years.

Inhibition of phosphodiesterase-3 by levosimendan is sufficient to account for its inotropic effect in failing human heart

BACKGROUND AND PURPOSE

Levosimendan is known as a calcium sensitizer, although it is also known to inhibit PDE3. We aimed to isolate each component and estimate their contribution to the increased cardiac contractility induced by levosimendan.

EXPERIMENTAL APPROACH

Contractile force was measured in electrically stimulated ventricular strips from explanted failing human hearts and left ventricular strips from normal male Wistar rats. PDE activity was measured in a two-step PDE activity assay on failing human ventricle.

KEY RESULTS

Levosimendan exerted a positive inotropic effect (PIE) reaching maximum at 10(-5)  M in ventricular strips from failing human hearts. In the presence of the selective PDE3 inhibitor cilostamide, the PIE of levosimendan was abolished. During treatment with a PDE4 inhibitor and a supra-threshold concentration of isoprenaline, levosimendan generated an amplified inotropic response. This effect was reversed by β-adrenoceptor blockade and undetectable in strips pretreated with cilostamide. Levosimendan (10(-6)  M) increased the potency of β-adrenoceptor agonists by 0.5 log units in failing human myocardium, but not in the presence of cilostamide. Every inotropic response to levosimendan was associated with a lusitropic response. Levosimendan did not affect the concentration-response curve to calcium in rat ventricular strips, in contrast to the effects of a known calcium sensitizer, EMD57033 [5-(1-(3,4-dimethoxybenzoyl)-1,2,3,4-tetrahydroquinolin-6-yl)-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2-one]. PDE activity assays confirmed that levosimendan inhibited PDE3 as effectively as cilostamide.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that the PDE3-inhibitory property of levosimendan was enough to account for its inotropic effect, leaving a minor, if any, effect to a calcium-sensitizing component.

Peri-operative Levosimendan in Patients Undergoing Cardiac Surgery: An Overview of the Evidence

Levosimendan, a calcium sensitiser, has recently emerged as a valuable agent in the peri-operative management of cardiac surgery patients. Levosimendan is a calcium-sensitising ionodilator. By binding to cardiac troponin C and reducing its calcium-binding co-efficient, it enhances myofilament responsiveness to calcium and thus enhances myocardial contractility without increasing oxygen demand. Current evidence suggests that levosimendan enhances cardiac function after cardiopulmonary bypass in patients with both normal and reduced left ventricular function. In addition to being used as post-operative rescue therapy for low cardiac output syndrome, a pre-operative levosimendan infusion in high risk patients with poor cardiac function may reduce inotropic requirements, the need for mechanical support, the duration of intensive care admissions as well as post-operative mortality. Indeed, it is these higher-risk patients who may experience a greater degree of benefit. Larger, multicentre randomised trials in cardiac surgery will help to elucidate the full potential of this agent.

The inotropic effect of the active metabolite of levosimendan, OR-1896, is mediated through inhibition of PDE3 in rat ventricular myocardium

Aims

We recently published that the positive inotropic response (PIR) to levosimendan can be fully accounted for by phosphodiesterase (PDE) inhibition in both failing human heart and normal rat heart. To determine if the PIR of the active metabolite OR-1896, an important mediator of the long-term clinical effects of levosimendan, also results from PDE3 inhibition, we compared the effects of OR-1896, a representative Ca²⁺ sensitizer EMD57033 (EMD), levosimendan and other PDE inhibitors.

Methods

Contractile force was measured in rat ventricular strips. PDE assay was conducted on rat ventricular homogenate. cAMP was measured using RII_epac FRET-based sensors.

Results

OR-1896 evoked a maximum PIR of 33±10% above basal at 1 μM. This response was amplified in the presence of the PDE4 inhibitor rolipram (89±14%) and absent in the presence of the PDE3 inhibitors cilostamide (0.5±5.3%) or milrinone (3.2±4.4%). The PIR was accompanied by a lusitropic response, and both were reversed by muscarinic receptor stimulation with carbachol and absent in the presence of β-AR blockade with timolol. OR-1896 inhibited PDE activity and increased cAMP levels at concentrations giving PIRs. OR-1896 did not sensitize the concentration-response relationship to extracellular Ca²⁺. Levosimendan, OR-1896 and EMD all increased the sensitivity to β-AR stimulation. The combination of either EMD and levosimendan or EMD and OR-1896 further sensitized the response, indicating at least two different mechanisms responsible for the sensitization. Only EMD sensitized the α₁-AR response.

Conclusion

The observed PIR to OR-1896 in rat ventricular strips is mediated through PDE3 inhibition, enhancing cAMP-mediated effects. These results further reinforce our previous finding that Ca²⁺ sensitization does not play a significant role in the inotropic (and lusitropic) effect of levosimendan, nor of its main metabolite OR-1896.

Levosimendan improves contractility in vivo and in vitro in a rodent model of post-myocardial infarction heart failure

AIM

As few studies have presented a thorough analysis of the effect of levosimendan (LEV) on contractility, our purpose was to investigate in vivo cardiac function as well as in vitro cardiomyocyte function and calcium (Ca(2+) ) handling following LEV treatment.

METHODS

Rats with post-myocardial infarction heart failure (HF) induced by ligation of the left anterior descending coronary artery and sham-operated animals were randomized to the infusion of LEV (2.4 μg kg(-1) min(-1) ) or vehicle for 40 min. Echocardiographic examination was coupled to pressure-volume sampling in the left ventricle before (B) and after (40 min) infusion. Isolated left ventricular cardiomyocytes were studied in an epifluorescence microscope.

RESULTS

HF LEV (n = 6), HF vehicle (n = 7), sham LEV (n = 5) and sham vehicle (n = 6) animals were included. LEV infusion compared to vehicle in HF animals reduced left ventricular end-diastolic pressure and mean arterial pressure (both P < 0.001) and improved the slope of the preload-recruitable stroke work (P < 0.05). Administrating LEV to HF cardiomyocytes in vitro improved fractional shortening and Ca(2+) sensitivity index ratio, and increased the diastolic Ca(2+) (all P < 0.01).

CONCLUSION

In HF animals, LEV improved the contractility by increasing the Ca(2+) sensitivity. Furthermore loading conditions were changed, and LEV could consequently change organ perfusion. An observed increase in diastolic Ca(2+) following LEV treatment and clinical implications of this should be further addressed.

Cardiac Ca2+ signaling and Ca2+ sensitizers

The role of Ca2+ in cardiac excitation-contraction (E-C) coupling has been established by simultaneous measurements of contractility and Ca2+ transients by means of aequorin in intact myocardium and Ca2+ sensitive fluorescent dyes in single myocytes. The E-C coupling process can be classified into 3 processes: upstream (Ca2+ mobilization), central (Ca2+ binding to troponin C) and downstream mechanism (thin filament regulation and crossbridge cycling). These mechanisms are regulated differentially by various inotropic interventions. Positive force-frequency relationship and effects of beta-adrenoceptor stimulation, phosphodiesterase 3 inhibitors and digitalis are essentially exerted via upstream mechanism. Alpha-adrenoceptor stimulation, endothelin-1, angiotensin II, and clinically available Ca2+ sensitizers, such as levosimendan and pimobendan, act by a combination of the upstream and central/downstream mechanism. The Frank-Starling mechanism and effects of Ca2+ sensitizers such as EMD 57033 and Org 30029 are primarily induced via the central/downstream mechanism. Whereas the upstream and central mechanisms are markedly suppressed in failing myocytes and under acidotic conditions, Ca2+ sensitizers such as EMD 57033 and Org 30029 can induce cardiotonic effects under such conditions. Ca2+ sensitizers have high therapeutic potential for the treatment of contractile dysfunction in congestive heart failure and ischemic heart diseases, because they have energetic advantages and less risk of Ca2+ overload and can maintain effectiveness under pathological conditions.

Comparative effects of levosimendan, OR-1896, OR-1855, dobutamine, and milrinone on vascular resistance, indexes of cardiac function, and O2consumption in dogs

Levosimendan enhances cardiac contractility via Ca2+sensitization and induces vasodilation through the activation of ATP-dependent K+and large-conductance Ca2+-dependent K+channels. However, the hemodynamic effects of levosimendan, as well as its metabolites, OR-1896 and OR-1855, relative to plasma concentrations achieved, are not well defined. Thus levosimendan, OR-1896, OR-1855, or vehicle was infused at 0.01, 0.03, 0.1, and 0.3 μmol·kg−1·30 min−1, targeting therapeutic to supratherapeutic concentrations of total levosimendan (62.6 ng/ml). Results were compared with those of the β1-agonist dobutamine and the phosphodiesterase 3 inhibitor milrinone. Peak concentrations of levosimendan, OR-1896, and OR-1855 were 455 ± 21, 126 ± 6, and 136 ± 6 ng/ml, respectively. Levosimendan and OR-1896 produced dose-dependent reductions in mean arterial pressure (−31 ± 2 and −42 ± 3 mmHg, respectively) and systemic resistance without affecting pulse pressure, effects paralleled by increases in heart rate; OR-1855 produced no effect at any dose tested. Dobutamine, but not milrinone, increased mean arterial pressure and pulse pressure (17 ± 2 and 23 ± 2 mmHg, respectively). Regarding potency to elicit reductions in time to peak pressure and time to systolic pressure recovery: OR-1896 > levosimendan > milrinone > dobutamine. Levosimendan and OR-1896 elicited dose-dependent increases in change in pressure over time (118 ± 10 and 133 ± 13%, respectively), concomitant with reductions in left ventricular end-diastolic pressure and ejection time. However, neither levosimendan nor OR-1896 produced increases in myocardial oxygen consumption at inotropic and vasodilatory concentrations, whereas dobutamine increased myocardial oxygen consumption (79% above baseline). Effects of the levosimendan and OR-1896 were limited to the systemic circulation; neither compound produced changes in pulmonary pressure, whereas dobutamine produced profound increases (74 ± 13%). Thus levosimendan and OR-1896 are hemodynamically active in the anesthetized dog at concentrations observed clinically and elicit cardiovascular effects consistent with activation of both K+channels and Ca2+sensitization, whereas OR-1855 is inactive on endpoints measured in this study.

Pharmacokinetics and excretion balance of OR-1896, a pharmacologically active metabolite of levosimendan, in healthy men

OBJECTIVE

To investigate the pharmacokinetics and excretion balance of [(14)C]-OR-1896, a pharmacologically active metabolite of levosimendan, in six healthy male subjects. In addition, pharmacokinetic parameters of total radiocarbon and the deacetylated congener, OR-1855, were determined.

METHODS

OR-1896 was administered as a single intravenous infusion of 200 microg of [(14)C]-OR-1896 (specific activity 8.6 MBq/mg) over 10 min. The pharmacokinetic parameters were calculated by three-compartmental methods.

RESULTS

During the 14-day collection of urine and faeces, excretion (+/-S.D.) averaged 94.2+/-1.4% of the [(14)C]-OR-1896 dose. Mean recovery of radiocarbon in urine was 86.8+/-1.9% and in faeces 7.4+/-1.5%. Mean terminal elimination half-life of OR-1896 (t(1/2)) was 70.0+/-44.9 h. Maximum concentrations of OR-1855 were approximately 30% to that of OR-1896. Total clearance and the volume of distribution of OR-1896 were 2.0+/-0.4 l/h and 175.6+/-74.5l, respectively. Renal clearances of OR-1896 and OR-1855 were 0.9+/-0.4 l/h and (5.4+/-2.3)x10(-4) l/h, respectively.

CONCLUSIONS

This study provides data to demonstrate that nearly one half of OR-1896 is eliminated unchanged into urine and that the active metabolites metabolite of levosimendan remain in the body longer than levosimendan. The remaining half of OR-1896 dose is eliminated through other metabolic routes, partially through interconversion back to OR-1855 with further metabolism of OR-1855. Given the fact that the pharmacological activity and potency of OR-1896 is similar to levosimendan, these results emphasize the clinical significance of OR-1896 and its contribution to the long-lasting effects of levosimendan.

Effect of severe renal failure and haemodialysis on the pharmacokinetics of levosimendan and its metabolites

BACKGROUND AND OBJECTIVES

Levosimendan is a calcium sensitiser developed for the treatment of congestive heart failure. It increases myocardial contractility, reduces the filling pressure and dilates both the peripheral and coronary vessels. The circulating metabolites of levosimendan, OR-1855 and OR-1896, are formed and eliminated slowly after intravenous administration of levosimendan. The aim of this study was to investigate the effect of impaired renal function and haemodialysis on the pharmacokinetics of levosimendan, OR-1855 and OR-1896.

STUDY DESIGN

This study was an open-label, nonrandomised, phase I pharmacokinetic study. Levosimendan was administered as a single-dose infusion of 0.1 microg/kg/minute for 24 hours. The follow-up period lasted 3 weeks.

STUDY SETTING

Twenty-fivepatients were included:12 patients with severe chronic renal failure (CRF) with creatinine clearance of < 30 mL/minute/1.73 m(2) and 13 patients with end-stage renal disease (ESRD) undergoing haemodialysis. A group of 12 healthy subjects served as controls.

RESULTS

Levosimendan, the parent drug, was eliminated rapidly from the plasma after discontinuation of its infusion, with an elimination half-life (t(1/2)) [mean +/- standard error of mean] of 1.5 +/- 0.09 hours in ESRD patients undergoing haemodialysis, 1.0 +/- 0.2 hours in patients with severe CRF and 0.91 +/- 0.03 hours in healthy subjects. The t(1/2) of levosimendan was significantly longer (p < 0.001) in ESRD patients undergoing haemodialysis than in healthy subjects. The t(1/2) of OR-1855 and OR-1896 were 94.0 +/- 20.4 hours and 96.5 +/- 19.5 hours, respectively, in ESRD patients undergoing haemodialysis compared with 60.8 +/- 5.2 and 61.6 +/- 5.2 hours, respectively, in healthy subjects (p = not significant). The t(1/2) of OR-1855 was significantly longer (85.0 +/- 13.6 hours) in patients with severe CRF than in healthy subjects (60.8 +/- 5.2 hours, p < 0.05). The area under the plasma concentration-time curve (AUC) and the peak plasma concentration (C(max)) of the metabolites were approximately 2-fold in patients with ESRD undergoing haemodialysis and patients with severe CRF compared with healthy subjects. The mean unbound fraction (f(u)) of levosimendan in plasma was approximately 2% in each study group, whereas the f(u) of the metabolites was considerably higher (63-70%). In contrast to levosimendan, the metabolites were dialysable, with dialysis clearance of approximately 100 mL/minute. The haemodynamic responses and adverse event profiles were similar in the study groups, with headache, palpitations and dizziness being the most frequently recorded adverse events.

CONCLUSION

The t(1/2) of the levosimendan metabolites was prolonged 1.5-fold and their AUC and C(max) were 2-fold in patients with severe CRF and ESRD patients undergoing haemodialysis as compared with healthy subjects. These results suggest that the dose should be reduced when levosimendan is used for the treatment of congestive heart failure in patients with severe renal insufficiency.

Acute heart failure: inotropic agents and their clinical uses

Inotropic agents are indispensable for the improvement of cardiac contractile dysfunction in acute or decompensated heart failure. Clinically available agents, including sympathomimetic amines (dopamine, dobutamine, noradrenaline) and selective phosphodiesterase-3 inhibitors (amrinone, milrinone, olprinone and enoximone) act via cAMP/protein kinase A (PKA)-mediated facilitation of intracellular Ca2+ mobilisation. Phosphodiesterase-3 inhibitors also have a vasodilatory action, which plays a role in improving haemodynamic parameters in certain patients, and are termed inodilators. The available inotropic agents suffer from risks of Ca2+ overload leading to arrhythmias, myocardial cell injury and ultimately, cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and cellular metabolism. Furthermore, they lose their effectiveness under pathophysiological conditions, such as acidosis, stunned myocardium and heart failure. Pimobendan and levosimendan (that act by a combination of an increase in Ca2+ sensitivity and phosphodiesterase-3 inhibition) appear to be more beneficial among existing agents. Novel Ca2+ sensitisers that are under basic research warrant clinical trials to replace available inotropic agents.

Signal transduction and Ca2+ signaling in intact myocardium

The experimental procedures to simultaneously detect contractile activity and Ca(2+) transients by means of the Ca(2+) sensitive bioluminescent protein aequorin in multicellular preparations, and the fluorescent dye indo-1 in single myocytes, provide powerful tools to differentiate the regulatory mechanisms of intrinsic and external inotropic interventions in intact cardiac muscle. The regulatory process of cardiac excitation-contraction coupling is classified into three categories; upstream (Ca(2+) mobilization), central (Ca(2+) binding to troponin C), and/or downstream (thin filament regulation of troponin C property or crossbridge cycling and crossbridge cycling activity itself) mechanisms. While a marked increase in contractile activity by the Frank-Starling mechanism is associated with only a small alteration in Ca(2+) transients (downstream mechanism), the force-frequency relationship is primarily due to a frequency-dependent increase of Ca(2+) transients (upstream mechanism) in mammalian ventricular myocardium. The characteristics of regulation induced by beta- and alpha-adrenoceptor stimulation are very different between the two mechanisms: the former is associated with a pronounced facilitation of an upstream mechanism, whereas the latter is primarily due to modulation of central and/or downstream mechanisms. alpha-Adrenoceptor-mediated contractile regulation is mimicked by endothelin ET(A)- and angiotensin II AT(1)-receptor stimulation. Acidosis markedly suppresses the regulation induced by Ca(2+) mobilizers, but certain Ca(2+) sensitizers are able to induce the positive inotropic effect with central and/or downstream mechanisms even under pathophysiological conditions.

Pharmacological Mechanisms Contributing to the Clinical Efficacy of Levosimendan

Acute decompensation of chronic heart failure is a direct life-threatening situation with short-term mortality approaching 30%. A number of maladaptive changes are amplified within the cardiovascular system during the progression of chronic heart failure that makes the decompensation phase difficult to handle. Levosimendan is a new Ca2+-sensitizer for the treatment of acutely decompensated heart failure that has proved to be effective during the decompensation of chronic heart failure and acute myocardial infarction. Levosimendan differs from other cardiotonic agents that are used for acute heart failure in that it utilizes a unique dual mechanism of action: Ca2+-sensitization through binding to troponin C in the myocardium, and the opening of ATP-sensitive K+ channels in vascular smooth muscle. In general, these mechanisms evoke positive inotropy and vasodilation. Clinical studies suggested long-term benefits on mortality following short-term administration. It may, therefore, be inferred that levosimendan has additional effects on the cardiovascular system that are responsible for the prolongation of survival. Results of preclinical and clinical investigations suggest that the combination of levosimendan-induced cardiac and vascular changes has favorable effects on the coronary, pulmonary and peripheral circulations. Redistribution of the circulating blood offers an improved hemodynamic context for the development of a positive inotropic effect through Ca2+-sensitization of the contractile filaments, without a proportionate increase in myocardial oxygen consumption or the development of arrhythmias. Activation of ATP-sensitive K+ channels, both on sarcolemma and mitochondria, may protect against myocardial ischemia, and decreased levels of cytokines may prevent the development of further myocardial remodeling. Collectively, these effects of levosimendan shift the disturbed cardiovascular parameters towards normalization, thereby halting the perpetuation of the vicious cycle of heart failure progression. This may contribute to stabilization of the circulation and improved life expectancy of patients with chronic heart failure.

The levosimendan metabolite OR-1896 elicits vasodilation by activating the K(ATP) and BK(Ca) channels in rat isolated arterioles

1. We characterized the vasoactive effects of OR-1896, the long-lived metabolite of the inodilator levosimendan, in coronary and skeletal muscle microvessels. 2. The effect of OR-1896 on isolated, pressurized (80 mmHg) rat coronary and gracilis muscle arteriole (approximately 150 microm) diameters was investigated by videomicroscopy. 3. OR-1896 elicited concentration-dependent (1 nM-10 microM) dilations in coronary (maximal dilation: 66+/-6%, relative to that in Ca2+-free solutions; pD2: 7.16+/-0.42) and gracilis muscle arterioles (maximal dilation: 73+/-4%; pD2: 6.71+/-0.42), these dilations proving comparable to those induced by levosimendan (1 nM-10 microM) in coronary (maximal dilation: 83+/-6%; pD2: 7.06+/-0.14) and gracilis muscle arterioles (maximal dilation: 73+/-12%; pD2: 7.05+/-0.1). 4. The maximal dilations in response to OR-1896 were significantly (P<0.05) attenuated by the nonselective K+ channel inhibitor tetraethylammonium (1 mM) in coronary (to 34+/-9%) and gracilis muscle arterioles (to 28+/-6%). 5. Glibenclamide (5 or 10 microM), a selective ATP-sensitive K+ channel (KATP) blocker, elicited a greater reduction of OR-1896-induced dilations in skeletal muscle arterioles than in coronary microvessels. 6. Conversely, the selective inhibition of the large conductance Ca2+-activated K+ channels (BK(Ca)) with iberiotoxin (100 nM) significantly reduced the OR-1896-induced maximal dilation in coronary arterioles (to 21+/-6%), but was ineffective in skeletal muscle arterioles (72+/-8%). 7. Accordingly, OR-1896 elicits a substantial vasodilation in coronary and skeletal muscle arterioles, by activating primarily BK(Ca) and K(ATP) channels, respectively, and it is suggested that OR-1896 contributes to the long-term hemodynamic effects of levosimendan.

Levosimendan in cardiac surgery: current best available evidence

Recent upsurge in referral of patients with high perioperative risk or compromised left ventricular function for cardiac surgery has lead to an increasing use of pharmacologic support in the form of vasodilator and inotropic therapy to achieve improvement of tissue perfusion in the perioperative period or to support weaning from cardiopulmonary bypass. Traditionally, perioperatively used inotropic agents, epinephrine, dobutamine, and milrinone, are limited by significant increases in myocardial oxygen consumption, proarrhythmia, or neurohormonal activation. Levosimendan, a new inodilator for the treatment of decompensated heart failure, has also shown promise in elective therapy of cardiac surgical patients with high perioperative risk or compromised left ventricular function, as well as in rescue therapy of patients with difficult weaning from cardiopulmonary bypass. This review article briefly discusses the pharmacology of levosimendan and evaluates current best available evidence to assess the safety and efficacy of levosimendan usage in cardiac surgery.

Dual regulation of myofilament Ca2+ sensitivity by levosimendan in normal and acidotic conditions in aequorin-loaded canine ventricular myocardium

Experiments were carried out in canine ventricular trabeculae loaded with aequorin to investigate the effects of levosimendan {(R)-([4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]-hydrazono)-propanedinitrile} on contractile force and Ca(2+) transients in normal and acidotic conditions. The concentration-response curve for the positive inotropic effect (PIE) of levosimendan was bell-shaped, that is, it declined markedly at 10(-4) M after achieving the maximum at 10(-5) M in normal (pH(o)=7.4) and acidotic conditions (pH(o)=6.6). The positive inotropic effect (PIE) of levosimendan up to 10(-5) M was associated with an increase in Ca(2+) transients and a shift of the relationship of Ca(2+) transients and force to the left of that of elevation of [Ca(2+)](o). Levosimendan at 10(-4) M elicited a negative inotropic effect (NIE) in association with a further increase in Ca(2+) transients, and during washout Ca(2+) transients increased further, while the force was abolished before both signals recovered to the control. In acidotic conditions, the relationship of Ca(2+) transients and force during the application of levosimendan in normal conditions was essentially unaltered, whereas the PIE was suppressed due to attenuation of the increase in Ca(2+) transients. In summary, in intact canine ventricular myocardium, levosimendan elicits a dual inotropic effect: at lower concentrations, it induces a PIE by a combination of increases in Ca(2+) transients and Ca(2+) sensitivity, while at higher concentrations it elicits an NIE due to a decrease in Ca(2+) sensitivity. Acidosis inhibits the PIE of levosimendan due to suppression of the increase in Ca(2+) transients in response to the compound.

Levosimendan for the treatment of acute heart failure syndromes

Levosimendan is a novel calcium-sensitising agent that has been shown to have beneficial inotropic, metabolic and vasodilatory effects in the treatment of acute and advanced chronic heart failure. Levosimendan binds to troponin-C in cardiomyocytes and, thereby, improves cardiac contractility without disturbing the metabolic status of the heart and increasing myocardial oxygen demand or provoking fatal cardiac arrhythmias. Levosimendan also opens ATP-sensitive potassium channels, causing peripheral arterial and venous dilatation, and increasing coronary flow reserve. When it is given as a short-term therapy, levosimendan enhances cardiac output, reduces systemic vascular resistance and lowers pulmonary capillary wedge pressure. Clinical outcomes were significantly reduced in decompensated or postmyocardial infarction heart failure patients who received levosimendan, compared with those on dobutamine or placebo. Recent investigations focusing on the anti-inflammatory and antiapoptotic actions of levosimendan in the failing heart indicate that improvement of cardiac contractile performance is closely related with the drug-induced reduction of circulating pro-inflammatory cytokines and apoptosis inducers. The most common adverse effects of levosimendan treatment are hypotension and headache. Overall, levosimendan represents an effective and safe option for the treatment of decompensated heart failure patients.

Efficacy and safety of intermittent, long-term, concomitant dobutamine and levosimendan infusions in severe heart failure refractory to dobutamine alone

Thirty-six consecutive patients in New York Heart Association functional class IV, who were resistant to 24-hour continuous dobutamine infusion, were treated with continuous infusions of dobutamine 10 microg/kg/min for > or =48 hours (group I, n = 18), followed by weekly intermittent 8-hour infusions or more often if needed. In group II (n = 18), after the initial 24-hour infusion of dobutamine, a 24-hour levosimendan infusion was added followed by biweekly 24-hour infusions. The addition of intermittent levosimendan infusions prolonged the survival of patients with advanced heart failure refractory to intermittent dobutamine infusions (45-day survival rates were 6% and 61% in groups I and II, respectively; p = 0.0002, log-rank test).

Pharmacokinetics of levosimendan and its active metabolite OR-1896 in rapid and slow acetylators

OBJECTIVE

The purpose of this study was to investigate the pharmacokinetics of levosimendan and to determine the primary pharmacokinetic parameters of the pharmacologically active metabolite OR-1896 in rapid and slow acetylators.

METHODS

Levosimendan was administered as a constant rate (0.1 microg/(kg min)) i.v. infusion for 24h in six rapid and six slow acetylators based on N-acetyltransferase 2 genotyping. At the end of the infusion, a small amount (2.5 microg/kg) of (13)C-labeled OR-1896 was administered by i.v. infusion for 10 min. Blood samples were taken at predefined sampling points 14 days post-infusion and levosimendan and its metabolite concentrations were determined by LC-MS/MS.

RESULTS

Steady-state concentrations of levosimendan were achieved within 4-8h and no differences were found in the pharmacokinetics of the parent compound between the rapid and slow acetylators. The maximum concentrations of amino phenylpyridazinone metabolite OR-1855 and N-acetylated conjugate OR-1896 were observed approximately 24h after terminating the infusion. AUC of OR-1896 was approximately 3.5 times higher in the rapid acetylators compared to the slow acetylators (P = 0.002, 95% confidence interval for group ratio from 2.0 to 8.2). The mean +/- S.D. fraction of levosimendan metabolized to OR-1896 was 6.8 +/- 2.8% in the rapid and 4.3 +/- 2.4% in the slow acetylators (P = 0.12). (13)C-OR-1855 concentrations were detected in plasma after administration of (13)C-OR-1896 indicating deacetylation from OR-1896 to OR-1855.

CONCLUSIONS

Plasma OR-1896 levels during and after levosimendan treatment are dependent on the acetylation status of the subject-rapid acetylators having 3.5 times higher concentrations than slow acetylators.

Levosimendan, a new calcium-sensitizing inotrope for heart failure

Calcium sensitizers are a new class of inotropes that share the in vitro properties of calcium sensitization and phosphodiesterase inhibition. Levosimendan is a distinct calcium sensitizer, as it stabilizes the interaction between calcium and troponin C by binding to troponin C in a calcium-dependent manner, improving inotropy without adversely affecting lusitropy. It does not exhibit clinically relevant phosphodiesterase inhibition at therapeutic concentrations. It also exerts vasodilatory effects, possibly through activation of several potassium channels and other less well characterized mechanisms. The pharmacokinetics of levosimendan are similar in healthy subjects and patients with heart failure and remain relatively unaltered by age, sex, and organ dysfunction. In preclinical and clinical studies, levosimendan exerted potent dose-dependent positive inotropic and vasodilatory activity. Unlike conventional inotropes, levosimendan is not associated with significant increases in myocardial oxygen consumption, proarrhythmia, or neurohormonal activation. The most common adverse effects are attributable to the vasodilation. Two large, double-blind, randomized trials demonstrated favorable hemodynamic effects, improved tolerability, and a possible mortality benefit over dobutamine and placebo in patients who had acute symptoms of failure and required inotropic therapy. The long-term effect on patient outcomes is being confirmed in ongoing placebo- and inotrope-controlled trials. Levosimendan appears to be an effective inodilator devoid of the detrimental effects of conventional inotropes. In the future, levosimendan may provide a promising alternative to conventional inotropes for patients with acutely decompensated heart failure.

Pharmacokinetics of levosimendan in pediatric patients evaluated for cardiac surgery

OBJECTIVE

The objective of the study was to evaluate the pharmacokinetics, hemodynamic effects, and safety of levosimendan in children with congenital heart disease.

DESIGN

Open, one group, single-dose study.

SETTING

Cardiac catheter laboratory in a pediatric cardiology department of a university hospital. PATIENTS AND TREATMENTS: Thirteen children between the ages of 3 months and 7 yrs coming for preoperative cardiac catheterization were enrolled into this study. All children received 12 microg/kg levosimendan as an intravenous infusion given over 10 mins during the catheterization.

MEASUREMENTS

Concentrations of levosimendan and its metabolites were determined at specified time points before and after infusion (0-4 hrs). Invasive hemodynamics was evaluated up to 25 mins after the start of the infusion and echocardiography up to 2 hrs after the start of the infusion.

MAIN RESULTS

The mean maximum concentration of levosimendan was 59 +/- 23 ng/mL in children older than 6 months of age. Levosimendan was rapidly distributed, with a mean half-life of 0.24 +/- 0.07 hrs. Mean terminal elimination half-life was 1.6 +/- 0.80 hrs. Total plasma clearance for the 10-min infusion was 3.6 +/- 1.3 mL/min/kg. Terminal elimination half-life in children aged 3-6 months was slower than in older children, i.e., 2.3 hrs vs. 1.6 hrs. Values of other pharmacokinetic variables were on the same level between the two age groups. The changes in hemodynamic variables were not statistically significant. There were no serious adverse events or unexpected adverse drug reactions during the study.

CONCLUSIONS

The pharmacokinetic profile of levosimendan in children with congenital heart disease is similar to that in adult patients with congestive heart failure. The minimal hemodynamic efficacy after the 12 microg/kg levosimendan bolus was probably due to a small dose relative to body surface area.

Pharmacokinetics of levosimendan and its circulating metabolites in patients with heart failure after an extended continuous infusion of levosimendan

AIMS

The purpose of the study was to characterize the pharmacokinetics of levosimendan and its metabolites OR-1855 and OR-1896 in patients with congestive heart failure.

METHODS

Levosimendan was administered as a continuous intravenous infusion for 7 days. Twelve subjects received the drug at an infusion rate of 0.05 micro g kg(-1) min(-1) and 12 at a rate 0.1 micro g kg(-1) min(-1).

RESULTS

Steady state concentrations of levosimendan were achieved within 4 h. Peak concentrations of the metabolites occurred after termination of the infusion. The mean (+/- SD) half-life of the active metabolite OR-1896 was 81 +/- 37 h after the lower dose and 81 +/- 28 h after the higher dose (P = 0.992, 95% confidence interval on the difference -27.5, 27.7).

CONCLUSIONS

The metabolites of levosimendan, OR-1855 and OR-1896, were formed and eliminated slowly, their peak concentrations occurring after termination of the 7-day infusion of the drug.

Levosimendan: a review of its use in the management of acute decompensated heart failure

Levosimendan (Simdax) is a calcium-sensitising drug that stabilises the troponin molecule in cardiac muscle, thus prolonging its effects on contractile proteins, with concomitant vasodilating properties. Intravenous levosimendan (12-24 microg/kg loading dose followed by 0.1-0.2 microg/kg/min for 24 hours, adjusted for response and tolerability) is approved for the short-term treatment of acute severe decompensated heart failure. Cardiac output increased by about 30% and pulmonary capillary wedge pressure and systemic vascular resistance decreased by about 17-29% in patients with decompensated heart failure receiving intravenous levosimendan. In large, well controlled trials in patients with decompensated heart failure, intravenous levosimendan was significantly more effective than placebo or dobutamine for overall haemodynamic response rate (primary endpoint). Significant benefits were also seen for mortality (versus placebo or dobutamine) and for the combined risk of worsening heart failure or death (versus dobutamine). Improvements in key symptoms (dyspnoea and fatigue) have not been consistently demonstrated. Hospitalisation costs were similar for levosimendan and dobutamine; the total incremental (hospitalisation plus drug) cost per life-year saved (extrapolated to 3 years) for levosimendan relative to dobutamine was estimated at Euro 3205 (year of costing 2000). Levosimendan is generally well tolerated, with an adverse event profile at recommended dosages similar to that in patients receiving placebo. Cardiac rate/rhythm disorders and headache were the most common events. At higher dosages, patients receiving levosimendan had higher rates of sinus tachycardia than those in placebo recipients. More patients receiving dobutamine than those receiving levosimendan experienced angina pectoris/chest pain/myocardial ischaemia or rate/rhythm disorders.

CONCLUSION

Intravenous levosimendan is an effective calcium-sensitising drug with vasodilatory and inotropic effects, and superior efficacy/tolerability to those of intravenous dobutamine in patients with acute decompensated heart failure. It may be associated with reduced mortality compared with both placebo and dobutamine. Levosimendan is generally well tolerated and may have less potential for cardiac rate/rhythm disorders than dobutamine. While evidence from well designed trials confirming the improved mortality over dobutamine and investigating haemodynamic efficacy and mortality versus other positive inotropes is required, intravenous levosimendan appears to be a useful addition to the treatment options for acute decompensated heart failure in patients with low cardiac output.

Signal transduction and Ca2+ signaling in contractile regulation induced by crosstalk between endothelin-1 and norepinephrine in dog ventricular myocardium

In certain cardiovascular disorders, such as congestive heart failure and ischemic heart disease, several endogenous regulators, including norepinephrine (NE) and endothelin-1 (ET-1), are released from various types of cell. Because plasma levels of these regulators are elevated, it seems likely that cardiac contraction might be regulated by crosstalk among these endogenous regulators. We studied the regulation of cardiac contractile function by crosstalk between ET-1 and NE and its relationship to Ca2+ signaling in canine ventricular myocardium. ET-1 alone did not affect the contractile function. However, in the presence of NE at subthreshold concentrations (0.1 to 1 nmol/L), ET-1 had a positive inotropic effect (PIE). In the presence of NE at higher concentrations (100 to 1000 nmol/L), ET-1 had a negative inotropic effect. ET-1 had a biphasic inotropic effect in the presence of NE at an intermediate concentration (10 nmol/L). The PIE of ET-1 was associated with an increase in myofilament sensitivity to Ca2+ ions and a small increase in Ca2+ transients, which required the simultaneous activation of protein kinase A (PKA) and PKC. ET-1 elicited translocation of PKCepsilon from cytosolic to membranous fraction, which was inhibited by the PKC inhibitor GF 109203X. Whereas the Na+-H+ exchange inhibitor Hoe 642 suppressed partially the PIE of ET-1, detectable alteration of pHi did not occur during application of ET-1 and NE. The negative inotropic effect of ET-1 was associated with a pronounced decrease in Ca2+ transients, which was mediated by pertussis toxin-sensitive G proteins, activation of protein kinase G, and phosphatases. When the inhibitory pathway was suppressed, ET-1 had a PIE even in the absence of NE. Our results indicate that the myocardial contractility is regulated either positively or negatively by crosstalk between ET-1 and NE through different signaling pathways whose activation depends on the concentration of NE in the dog.

The therapeutic potential of novel cardiotonic agents

During the course of treatment of heart failure patients, cardiotonic agents are inevitable for improvement of myocardial dysfunction. Clinically available agents, such as beta-adrenoceptor agonists and selective phosphodiesterase 3 inhibitors, act mainly via cyclic AMP/protein kinase A-mediated facilitation of Ca(2+) mobilisation (upstream mechanism). These agents are associated with the risk of Ca(2+) overload leading to arrhythmias, myocardial cell injury and premature cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and metabolic effects. Cardiac glycosides act also via an upstream mechanism and readily elicit Ca(2+) overload with a narrow safety margin. No currently available agents act primarily via an increase in the myofilament sensitivity to Ca(2+) ions (central and/or downstream mechanisms). Novel Ca(2+) sensitisers under basic research may deserve clinical trials to examine the therapeutic potential to replace currently employed agents in acute and chronic heart failure patients. Molecular mechanisms of action of Ca(2+) sensitisers are divergent. In addition, they show a wide range of discrete pharmacological profiles due to additional actions associated with individual compounds. Therefore, the outcome of clinical trials has to be explained carefully based on these mechanisms of actions.

Sustained hemodynamic effects of intravenous levosimendan

BACKGROUND

The short-term infusion of levosimendan (Levo) improves hemodynamic function in patients with decompensated heart failure. The metabolites of Levo have a prolonged half-life, and one is hemodynamically active. The goal of this study was to determine whether the hemodynamic effects of Levo are sustained during a long-term infusion and beyond the discontinuation of drug infusion.

METHODS AND RESULTS

Patients with decompensated heart failure received escalating infusion rates of intravenous Levo (n=98) or placebo (n=48) for 6 hours. At the end of 6 hours, 85 of the Levo-treated patients were continued on open-label drug for a total of 24 hours, at which time they were randomized 1:1 to an additional 24 hours of Levo (n=43) or placebo (n=42). The hemodynamic effects observed at 24 hours were maintained at 48 hours in both the continuation and withdrawal groups and did not differ between groups. Although the plasma concentration of Levo decreased rapidly in the withdrawal group, concentrations of the active metabolite OR-1896 were similar in the continuation and withdrawal groups at 24 hours and increased further (3.5-fold to 4-fold) and to a similar extent in both groups at 48 hours.

CONCLUSIONS

The hemodynamic effects of Levo were maintained during a 48-hour continuous infusion and for at least 24 hours after discontinuation of a 24-hour infusion. The active metabolite OR-1896 increased for at least 24 hours after cessation of drug infusion and may account for the prolonged hemodynamic effects of Levo.

Mechanisms of action of novel cardiotonic agents

Regulation of myocardial contractility by cardiotonic agents is achieved by an increase in intracellular Ca2+ mobilization (upstream mechanism), an increase in Ca2+ binding affinity to troponin C (central mechanism), or facilitation of the process subsequent to Ca2+ binding to troponin C (downstream mechanism). cAMP mediates the regulation induced by Ca2+ mobilizers such as beta-adrenoceptor agonists and selective phosphodiesterase III inhibitors acting through the upstream mechanism. These agents act likewise on the central mechanism to decrease Ca2+ sensitivity of troponin C in association with the cAMP-mediated phosphorylation of troponin I. In addition to such a well-known action of cAMP, recent experimental findings have revealed that Ca2+ sensitizers, such as levosimendan, OR-1896, and UD-CG 212 Cl, require the cAMP-mediated signaling for induction of Ca2+ sensitizing effect. These agents shift the [Ca2+] -force relationship to the left, but their positive inotropic effect (PIE) is inhibited by carbachol, which suppresses selectively the cAMP-mediated PIE. These findings imply that cAMP may play a crucial role in increasing the myofilament Ca2+ sensitivity by cross-talk with the action of individual cardiotonic agents. No clinically available cardiotonic agents act primarily via Ca2+ sensitization, but the PIE of pimobendan and levosimendan is partly mediated by an increase in myofilament Ca2+ sensitivity. Evidence is accumulating that cardiotonic agents with Ca2+ sensitizing action are more effective than agents that act purely via the upstream mechanism in clinical settings. Further clinical trials are required to establish the effectiveness of Ca2+ sensitizers in long-term therapy for congestive heart failure patients.

Pharmacodynamics and safety of a new calcium sensitizer, levosimendan, and its metabolites during an extended infusion in patients with severe heart failure

Levosimendan is a new calcium sensitizer developed for the short-term intravenous treatment of congestive heart failure. The aims of the present open-label, nonrandomized study were to determine the tolerability, hemodynamic effects, and the basic pharmacokinetics of levosimendan and its metabolites during an extended continuous infusion of levosimendan. Twenty-four patients with New York Heart Association (NYHA) III-IV heart failure in two groups of 12 patients were exposed to either 0.05 microg/kg/min or 0.1 microg/kg/min of levosimendan for 7 days. Heart rate and blood pressure were measured, and blood samples for the determination of plasma concentrations of the parent drug and its metabolites were drawn daily during the infusion and the 10 to 15 days' follow-up. The 7-day infusion was well tolerated and no premature discontinuations occurred. Both systolic and diastolic blood pressure decreased maximally by 6 mmHg in the lower and by 11 mmHg in the higher levosimendan dose groups during the infusion period (p < 0.05 for both groups). The mean heart rate values increased maximally by 18 and 26 beats/min in the lower and higher levosimendan dose groups, respectively (p < 0.001 for both groups). The hemodynamic effects peaked at the end of the infusion period and thereafter slowly declined during the follow-up. After the recommended infusion period of 24 hours, the mean heart rate increase was only 2 and 6 beats/min in the lower and higher levosimendan dose groups, respectively. The elimination half-life of levosimendan was approximately 1 hour and of the metabolites 70 to 80 hours. It can be concluded that levosimendan, even administered considerably longer than the recommended 24 hours, was well tolerated. The 7-day infusion induced a prolonged increase in heart rate and a minor decrease in blood pressure. The long-lasting effects are probably explained by the active metabolite.

Levosimendan

Levosimendan, a pyridazinone-dinitrile derivative, is a calcium sensitiser with additional action on adenosine triphosphate (ATP)-sensitive potassium channels. It is used intravenously (IV) for the treatment of decompensated cardiac failure. At therapeutic doses, levosimendan exhibits enhanced contractility with no increase in oxygen demands. It also produces antistunning effects without increasing myocardial intracellular calcium concentrations or prolonging myocardial relaxation. Levosimendan also causes coronary and systemic vasodilation. In patients with decompensated congestive heart failure (CHF), IV levosimendan significantly reduced the incidence of worsening CHF or death. IV levosimendan significantly increased cardiac output or cardiac index and decreased filling pressure in the acute treatment of stable or decompensated CHF in large, double-blind, randomised trials and after cardiac surgery in smaller trials. Levosimendan is well tolerated, with the most common adverse events (headache, hypotension, nausea) being secondary to vasodilation. It has not been shown to be arrhythmogenic. Levosimendan has shown no clinically important pharmacokinetic interactions with captopril, felodipine, beta-blockers, digoxin, warfarin, isosorbide-5-mononitrate, carvedilol, alcohol (ethanol) or itraconazole.

Levosimendan: a parenteral calcium-sensitising drug with additional vasodilatory properties

Levosimendan (Simdax) is a new inodilator developed specifically for the treatment of decompensated heart failure. Its inotropic mechanism is based on calcium sensitisation of myofilaments and its vasodilator actions are related to the opening of ATP-dependent K-channels in the vasculature. Since the inotropic action of levosimendan does not require an increase in cytosolic free calcium, it is less arrhythmogenic than the conventional parenteral beta-agonist inotropes or PDE III inhibiting drugs. Due to the calcium-dependent binding of the drug to troponin C, levosimendan, unlike some other calcium-sensitising drugs, does not prolong diastolic relaxation of the myocytes but acts in synergy with the intramyocellular calcium levels. Furthermore, due to the anti-ischaemic effects of the K-channel opening in myocytes, levosimendan can be used during myocardial ischaemia. In clinical trials, levosimendan has dose-dependently increased cardiac output and decreased pulmonary capillary wedge pressure in patients with heart failure. On the other hand, it also increases heart rate and decreases blood pressure in these patients. In major clinical trials, where patients with decompensated heart failure have been treated with levosimendan, a reduction of overall mortality in comparison to placebo or dobutamine has been seen. This interesting finding should be verified in prospective outcome trials. In any case, the safety of levosimendan during myocardial ischaemia makes this drug valuable in the short-term treatment of decompensated heart failure.

Increase in myofibrillar Ca2+ sensitivity induced by UD-CG 212 Cl, an active metabolite of pimobendan, in canine ventricular myocardium

We performed experiments in canine ventricular trabeculae loaded with aequorin to elucidate the mechanism of positive inotropic effect of UD-CG 212 Cl (4,5-dihydro-6-[2-(4-hydroxyphenyl)-1H-benzimidazole-5-yl]-5-methyl-3(2H)-pyridazinone), an active metabolite of pimobendan. The maximum response to UD-CG 212 Cl achieved at 10(-5) M was 18% of ISOmax and it was associated with an increase in Ca2+ transients of 7% of ISOmax. For a given increase in force, the increase in Ca2+ transients induced by UD-CG 212 Cl was less than that induced by elevation of [Ca2+]o. The positive inotropic effect of UD-CG 212 Cl was not associated with an impairment of relaxation and it was abolished by carbachol. In conclusion, UD-CG 212 Cl has a positive inotropic effect partly due to an increase in myofibrillar Ca2+ sensitivity that is exerted via cross talk with a signal transduction pathway that involves cAMP.