Absence of mitochondrial activation during levosimendan inotropic action in perfused paced guinea pig hearts as demonstrated by modular control analysis

Integrative Methods for Studying Cardiac Energetics

The more recent studies of human pathologies have essentially revealed the complexity of the interactions involved at the different levels of integration in organ physiology. Integrated organ thus reveals functional properties not predictable by underlying molecular events. It is therefore obvious that current fine molecular analyses of pathologies should be fruitfully combined with integrative approaches of whole organ function. It follows that an important issue in the comprehension of the link between molecular events in pathologies and whole organ function/dysfunction is the development of new experimental strategies aimed at the study of the integrated organ physiology. Cardiovascular diseases are a good example as heart submitted to ischemic conditions has to cope both with a decreased supply of nutrients and oxygen, and the necessary increased activity required to sustain whole body-including the heart itself-oxygenation.By combining the principles of control analysis with noninvasive ³¹P NMR measurement of the energetic intermediates and simultaneous measurement of heart contractile activity, we developed MoCA (for Modular Control and regulation Analysis), an integrative approach designed to study in situ control and regulation of cardiac energetics during contraction in intact beating perfused isolated heart (Diolez et al., Am J Physiol Regul Integr Comp Physiol 293(1):R13-R19, 2007). Because it gives real access to integrated organ function, MoCA brings out a new type of information-the "elasticities," referring to integrated internal responses to metabolic changes-that may be a key to the understanding of the processes involved in pathologies. MoCA can potentially be used not only to detect the origin of the defects associated with the pathology, but also to provide the quantitative description of the routes by which these defects-or also drugs-modulate global heart function, therefore opening therapeutic perspectives. This review presents selected examples of the applications to isolated intact beating heart that evidence different modes of energetic regulation of cardiac contraction. We also discuss the clinical application by using noninvasive ³¹P cardiac energetics examination under clinical conditions for detection of heart pathologies.

An update on levosimendan in acute cardiac care: applications and recommendations for optimal efficacy and safety

Introduction: In the 20 years since its introduction to the palette of intravenous hemodynamic therapies, the inodilator levosimendan has established itself as a valuable asset for the management of acute decompensated heart failure. Its pharmacology is notable for delivering inotropy via calcium sensitization without an increase in myocardial oxygen consumption.Areas covered: Experience with levosimendan has led to its applications expanding into perioperative hemodynamic support and various critical care settings, as well as an array of situations associated with acutely decompensated heart failure, such as right ventricular failure, cardiogenic shock with multi-organ dysfunction, and cardio-renal syndrome. Evidence suggests that levosimendan may be preferable to milrinone for patients in cardiogenic shock after cardiac surgery or for weaning from extracorporeal life support and may be superior to dobutamine in terms of short-term survival, especially in patients on beta-blockers. Positive effects on kidney function have been noted, further differentiating levosimendan from catecholamines and phosphodiesterase inhibitors.Expert opinion:Levosimendan can be a valuable resource in the treatment of acute cardiac dysfunction, especially in the presence of beta-blockers or ischemic cardiomyopathy. When attention is given to avoiding or correcting hypovolemia and hypokalemia, an early use of the drug in the treatment algorithm is preferred.

Potential of the Cardiovascular Drug Levosimendan in the Management of Amyotrophic Lateral Sclerosis: An Overview of a Working Hypothesis

Levosimendan is a calcium sensitizer that promotes myocyte contractility through its calcium-dependent interaction with cardiac troponin C. Administered intravenously, it has been used for nearly 2 decades to treat acute and advanced heart failure and to support the heart function in various therapy settings characterized by low cardiac output. Effects of levosimendan on noncardiac muscle suggest a possible new application in the treatment of people with amyotrophic lateral sclerosis (ALS), a neuromuscular disorder characterized by progressive weakness, and eventual paralysis. Previous attempts to improve the muscle response in ALS patients and thereby maintain respiratory function and delay progression of disability have produced some mixed results. Continuing this line of investigation, levosimendan has been shown to enhance in vitro the contractility of the diaphragm muscle fibers of non-ALS patients and to improve in vivo diaphragm neuromuscular efficiency in healthy subjects. Possible positive effects on respiratory function in people with ALS were seen in an exploratory phase 2 study, and a phase 3 clinical trial is now underway to evaluate the potential benefit of an oral form of levosimendan on both respiratory and overall functions in patients with ALS. Here, we will review the various known pharmacologic effects of levosimendan, considering their relevance to people living with ALS.

Oral levosimendan in amyotrophic lateral sclerosis: a phase II multicentre, randomised, double-blind, placebo-controlled trial

OBJECTIVE

To evaluate the efficacy and safety of oral levosimendan in patients with amyotrophic lateral sclerosis (ALS). This phase II, randomised, double-blind, placebo-controlled, crossover, three-period study with 6 months open-label follow-up enrolled adults with ALS and sitting slow vital capacity (SVC) 60%-90 % of predicted from 11 sites in four countries.

METHODS

Patients received levosimendan 1 mg daily, 1 mg two times a day or placebo during three 14-day crossover periods and levosimendan 1-2 mg daily during open-label follow-up. Primary endpoint was sitting SVC; secondary endpoints included supine SVC, ALS Functional Rating Scale-Revised (ALSFRS-R), tolerability and safety.

RESULTS

Of 66 patients randomised, 59 contributed to the double-blind results and 50 entered open-label follow-up. Sitting SVC was not significantly different between the treatments. In post hoc analysis using period-wise baselines, supine SVC favoured levosimendan over placebo, estimated mean differences from baseline being -3.62% on placebo, +0.77% on levosimendan 1 mg daily (p=0.018) and +2.38% on 1 mg two times a day (p=0.001). Headache occurred in 16.7% of patients during levosimendan 1 mg daily (p=0.030), 28.6% during 1 mg two times a day (p=0.002) and 3.3% during placebo. The respective frequencies for increased heart rate were 5.1% (p=0.337), 18.5% (p=0.018) and 1.7%. No significant differences between the treatments were seen for other adverse events.

CONCLUSIONS

Levosimendan did not achieve the primary endpoint of improving sitting SVC in ALS. Headache and increased heart rate were increased on levosimendan, although it was otherwise well tolerated. A phase III study to evaluate the longer term effects of oral levosimendan in ALS is ongoing.

Multiorgan Drug Action of Levosimendan in Critical Illnesses

Cardiotonic drugs mainly include digitalis, catecholamines, phosphodiesterase inhibitors, and calcium sensitizers, which have been successively discovered and applied in clinical practice. However, there are only a few new drugs available in this field, and the selection is very limited. Digitalis, catecholamines, and phosphodiesterase inhibitors increase myocardial contractility by increasing intracellular concentrations of cyclic adenosine monophosphate (cAMP) and Ca²⁺, and this increase in intracellular calcium ion concentration enhances myocardial oxygen consumption and causes arrhythmia. For these reasons, the research focus on positive inotropic agents has shifted from calcium mobilization to calcium sensitization. Intracellular calcium sensitizers are more effective and safer drugs because they do not increase the intracellular concentration of calcium ions. However, only three calcium sensitizers have been fully developed and used in the past three decades. One of these drugs, levosimendan, has multiple molecular targets and exerts its pharmacological effects by not only increasing myocardial contractility, but also enhancing respiratory muscle function and liver and kidney protection, and it is useful for patients with severe sepsis and septic shock. Recently, more than 60 randomized controlled clinical trials of levosimendan have been reported; however, these clinical trials have occasionally shown different findings. This article reviews the research progress of levosimendan in critical illnesses in recent years.

Probing the mechanism of cardiovascular drugs using a covalent levosimendan analog

One approach to improve contraction in the failing heart is the administration of calcium (Ca^2 +) sensitizers. Although it is known that levosimendan and other sensitizers bind to troponin C (cTnC), their in vivo mechanism is not fully understood. Based on levosimendan, we designed a covalent Ca^2 + sensitizer (i9) that targets C84 of cTnC and exchanged this complex into cardiac muscle. The NMR structure of the covalent complex showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing troponin I affinity, i9 enhanced the Ca^2 + sensitivity of cardiac muscle. We conclude that i9 enhances Ca^2 + sensitivity by stabilizing the open conformation of cTnC. These findings provide new insights into the in vivo mechanism of Ca^2 + sensitization and demonstrate that directly targeting cTnC has significant potential in cardiovascular therapy.

•

A Ca^2 + sensitizer, i9 was designed that forms a covalent bond with C84 of cTnC.

•

i9 stabilized the open state of the N-domain of cTnC.

•

The structure of the covalent cTnC-cTnI-i9 complex was solved by NMR.

•

The structure showed that i9 binds deep in the hydrophobic pocket of cTnC.

•

Despite slightly reducing cTnI affinity, i9 enhanced the Ca^2 + sensitivity of cardiac muscle.

Impact of levosimendan and ischaemia-reperfusion injury on myocardial subsarcolemmal mitochondrial respiratory chain, mitochondrial membrane potential, Ca2+ cycling and ATP synthesis

OBJECTIVES

Levosimendan (LS) is increasingly used in case of myocardial failure after cardiac surgery. The impact of LS on myocardial mitochondrial functions, such as respiratory chain function (RCF), mitochondrial membrane potential (ΔΨm), Ca(2+) handling, mitochondrial permeability transition pore (mPTP) opening and ATP during ongoing ischaemia/reperfusion (IR) injury, is not well understood. Depending on LS, I/R injury or the combination of both, we analysed myocardial functions in a retrograde Langendorff-model followed by the analysis of subsarcolemmal mitochondrial (SSM) functions.

METHODS

Rat hearts were divided into four study groups; two were subjected to 30 min of perfusion without (control) or with the application of 1.4 µmol/20 min LS (Levo). Experiments were repeated with hearts being subjected to 40 min of normothermic stop-flow ischaemia and 30 min of reperfusion without (IR) or with LS application (Levo-IR). Systolic left ventricular pressure (LVPsys), left ventricular contractility (LVdp/dtmax) and coronary flow were determined. SSM were analysed regarding RCF, ΔΨm, ATP, and Ca(2+) retention capacity (CRC), Ca(2+)-induced swelling and Ca(2+) fluxes after (re)perfusion.

RESULTS

I/R injury suppressed LVdp/dtmax (1381 ± 927 vs 2464 ± 913 mmHg/s; P = 0.01 at 30 min (re-)perfusion time). IR revealed complex I-V state3 (19.1 ± 7.4 vs 27.6 ± 11.0 nmolO2/min; P < 0.044) and II-V state3 (20.6 ± 6.8 vs 37.3 ± 9.10 molO2/min; P < 0.0001) suppression and Levo limited I-V (14.8 ± 11.1 vs 27.6 ± 11.0 nmolO2/min; P < 0.001) and II-V (24.1 ± 6.4 vs 37.3 ± 9.10 molO2/min; P < 0.0001) function. After energizing, ΔΨm hypopolarization was observed in Levo (0.76 ± 0.04 vs 0.84 ± 0.04; P = 0.02), IR (0.75 ± 0.06 vs 0.84 ± 0.04; P = 0.007) and Levo-IR (0.75 ± 0.06 vs 0.06 ± 0.04; P = 0.01). IR (AUC: 626 vs 292; P = 0.023) and Levo-IR (AUC: 683 vs 292, P = 0.003) increased Ca(2+)-induced mPTP-opening susceptibility. CRC declined in IR (6.4 ± 2.1 vs 10.5 ± 2.6; P = 0.04) or Levo (6.5 ± 2.0 vs 10.5 ± 2.6; P = 0.023). Ca(2+) uptake was delayed in IR and Levo-IR without LS impact (P < 0.0001). Ca(2+) liberation was increased in Levo-IR. ATP synthesis was reduced in Levo (0.49 ± 0.14 vs 0.74 ± 0.14; P = 0.002) and Levo-I/R (0.34 ± 0.18 vs 0.74 ± 0.14; P < 0.002).

CONCLUSION

LS limited RCF at complex IV and V with ΔΨm hypopolarization suggesting a specific [Formula: see text]-dependent pathway. Ca(2+) redistribution from SSM by LS during I/R injury possibly prevents from Ca(2+) overload due to mPTP flickering. LS-induced mPTP flickering did not promote permanent Ca(2+)-induced mPTP opening. LS-dependent inhibition of ATP generation presumably resulted from complex IV and V limitations and lowered ΔΨm. However, a resulting impact of limited ATP synthesis on myocardial recovery remains arguable.

Integrative methods for studying cardiac energetics

The more recent studies of human pathologies have essentially revealed the complexity of the interactions involved at the different levels of integration in organ physiology. Integrated organ thus reveals functional properties not predictable by underlying molecular events. It is therefore obvious that current fine molecular analyses of pathologies should be fruitfully combined with integrative approaches of whole organ function. It follows an important issue in the comprehension of the link between molecular events in pathologies, and whole organ function/dysfunction is the development of new experimental strategies aimed at the study of the integrated organ physiology. Cardiovascular diseases are a good example as heart submitted to ischemic conditions has to cope both with a decreased supply of nutrients and oxygen, and the necessary increased activity required to sustain whole body-including the heart itself-oxygenation.By combining the principles of control analysis with noninvasive (31)P NMR measurement of the energetic intermediates and simultaneous measurement of heart contractile activity, we developed MoCA (for Modular Control and Regulation Analysis), an integrative approach designed to study in situ control and regulation of cardiac energetics during contraction in intact beating perfused isolated heart (Diolez et al., Am J Physiol Regul Integr Comp Physiol 293(1):R13-R19, 2007). Because it gives real access to integrated organ function, MoCA brings out a new type of information-the "elasticities," referring to internal responses to metabolic changes-that may be a key to the understanding of the processes involved in pathologies. MoCA can potentially be used not only to detect the origin of the defects associated with the pathology, but also to provide the quantitative description of the routes by which these defects-or also drugs-modulate global heart function, therefore opening therapeutic perspectives. This review presents selected examples of the applications to isolated intact beating heart and a wider application to cardiac energetics under clinical conditions with the direct study of heart pathologies.

Levosimendan in critical illness: a literature review

Levosimendan, the active enantiomer of simendan, is a calcium sensitizer developed for treatment of decompensated heart failure, exerts its effects independently of the beta adrenergic receptor and seems beneficial in cases of severe, intractable heart failure. Levosimendan is usually administered as 24-h infusion, with or without a loading dose, but dosing needs adjustment in patients with severe liver or renal dysfunction. Despite several promising reports, the role of levosimendan in critical illness has not been thoroughly evaluated. Available evidence suggests that levosimendan is a safe treatment option in critically ill patients and may reduce mortality from cardiac failure. However, data from well-designed randomized controlled trials in critically ill patients are needed to validate or refute these preliminary conclusions. This literature review is an attempt to synthesize available evidence on the role and possible benefits of levosimendan in critically ill patients with severe heart failure.

Non-invasive integrative analysis of contraction energetics in intact beating heart

The comprehensive study of human pathologies has revealed the complexity of the interactions involved in cardiovascular physiology. The recent validation of system's biology approaches - like our Modular Control and Regulation Analysis (MoCA) - motivates the current interest for new integrative and non-invasive analyses that could be used for medical study of human heart contraction energetics. By considering heart energetics as a supply-demand system, MoCA gives access to integrated organ function and brings out a new type of information, the "elasticities", which describe in situ the regulation of both energy demand and supply by cellular energetic status. These regulations determine the internal control of contraction energetics and may therefore be a key to the understanding of the links between molecular events in pathologies and whole organ function/dysfunction. A wider application to the effects of cardiac drugs in conjunction with the direct study of heart pathologies may be considered in the near future. MoCA can potentially be used not only to detect the origin of the defects associated with the pathology (elasticity analyses), but also to provide a quantitative description of how these defects influence global heart function (regulation analysis) and therefore open new therapeutic perspectives. Several key examples of current applications to intact isolated beating heart are presented in this paper. The future application to human pathologies will require the use of non-invasive NMR techniques for the simultaneous measurement of energy status ((31)P NMR) and heart contractile activity (3D MRI). This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Acute and chronic effects of bupivacaine on muscle energetics during contraction in vivo: a modular metabolic control analysis

Bupivacaine is a widely used anaesthetic injected locally in clinical practice for short-term neurotransmission blockade. However, persistent side effects on mitochondrial integrity have been demonstrated in muscle parts surrounding the injection site. We use the precise language of metabolic control analysis in the present study to describe in vivo consequences of bupivacaine injection on muscle energetics during contraction. We define a model system of muscle energy metabolism in rats with a sciatic nerve catheter that consists of two modules of reactions, ATP/PCr (phosphocreatine) supply and ATP/PCr demand, linked by the common intermediate PCr detected in vivo by 31P-MRS (magnetic resonance spectroscopy). Measured system variables were [PCr] (intermediate) and contraction (flux). We first applied regulation analysis to quantify acute effects of bupivacaine. After bupivacaine injection, contraction decreased by 15.7% and, concomitantly, [PCr] increased by 11.2%. The regulation analysis quantified that demand was in fact directly inhibited by bupivacaine (−21.3%), causing an increase in PCr. This increase in PCr indirectly reduced mitochondrial activity (−22.4%). Globally, the decrease in contractions was almost fully explained by inhibition of demand (−17.0%) without significant effect through energy supply. Finally we applied elasticity analysis to quantify chronic effects of bupivacaine iterative injections. The absence of a difference in elasticities obtained in treated rats when compared with healthy control rats clearly shows the absence of dysfunction in energetic control of muscle contraction energetics. The present study constitutes the first and direct evidence that bupivacaine myotoxicity is compromised by other factors during contraction in vivo, and illustrates the interest of modular approaches to appreciate simple rules governing bioenergetic systems when affected by drugs.