Comparison of the antiarrhythmic potential of doxapram and its metabolite ketodoxaparam

Background

A few years ago, the TASK-1 channel has been established as a potential new target for the therapy of atrial fibrillation (AF). In the heart, TASK-1 is almost exclusively expressed in the atria and is significantly upregulated in AF patients. Therefore, it plays an important role in the shortening of the atrial action potential observed during AF, making TASK-1 a promising target for AF therapy. This could be proven in a porcine model of persistent AF in which an intravenous application of the TASK-1 inhibitor doxapram led to a termination of AF and the restoration of sinus rhythm (SR). Doxapram's metabolite ketodoxapam is described in the literature as being active with limited data available on its usage. Therefore, the effect of ketodoxapram on TASK-1 and its possible use in AF therapy still needs to be investigated.

Purpose

The purpose of the present study was to assess the potential of ketodoxapram in the termination of AF. Furthermore, a comparison between doxapram and ketodoxapram was performed based on electrophysiological and pharmacological data.

Methods

UPLC-MS/MS assays were developed and validated for the measurement of doxapram and ketodoxapram in porcine plasma and brain tissue. Using these assays, the pharmacokinetics of both substances, after intravenous injections of 1 mg/kg, were determined in pigs. Furthermore, brain and plasma concentrations were measured to assess brain-to-plasma ratios. A porcine AF model was used to estimate the antiarrhythmic potential. Electrophysiological properties were evaluated, using two-electrode voltage clamp experiment on Xenopus laevis oocytes which heterologously expressed atrial potassium channels, to calculate the effect of doxapram and ketodoxapram on channel function. Furthermore, whole-cell patch clamp measurements were performed on isolated human cardiomyocytes.

Results

Doxapram and ketodoxapram showed strong inhibitory effects on TASK-1 (IC50 1.0 μM and 0.8 μM) and TASK-3 (5.9 μM and 1.5 μM), but no significant effect on the other measured ion channels. The maximal inhibition on TASK-1 was 96%. The brain-to-plasma ratio for doxapram (0.58) was almost ten-fold higher than for ketodoxapram (0.065), hinting at a reduced crossing of the blood-brain barrier (BBB) for ketodoxapram. The terminal half-life (t1/2) of ketodoxapram (1.71 h) was longer and the maximal concentration (Cmax; 4,604 ng/ml) was higher than for doxapram (1.38 h; 1,780 ng/ml). In a porcine model of AF, ketodoxapram led to a significantly reduced AF burdens comparable to doxapram.

Conclusions

Doxapram and ketodoxapram both show strong inhibitory effects on TASK-1, making them good candidates for a TASK-1 based AF therapy. Ketodoxapram with its longer t1/2, reduced crossing of the BBB and higher Cmax points towards a possible superiority in the treatment of AF compared to doxapram. Studies in a porcine AF model showed promising results for the use of doxapram and ketodoxapram in AF therapy.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): German Research Foundation

Dapagliflozin exhibits class I antiarrhythmic effects which suppress action potential formation in human atrial cardiomyocytes

Background

Recently, inhibitors of sodium-glucose transporter 2 (SGLT2i) were shown to have tremendous cardioprotective effects in patients with type 2 diabetes mellitus (T2DM) as well as heart failure (HF) patients, regardless of their glycemic status. Among other beneficial effects on cardiovascular outcome an antiarrhythmic effect of SGLT2i was indicated. In patients with T2DM therapy with SGLT2i was associated with a significantly reduced risk of atrial arrhythmias and sudden cardiac death. As sodium-glucose transporter 2 (SGLT2) is not expressed within the heart underlying molecular modes of action remain unclear. Therefore, investigating possible antiarrhythmic mechanisms is crucial to determine whether SGLT2i might be beneficial for all patients suffering from arrhythmias, regardless of other comorbidities.

Purpose

To assess antiarrhythmic effects of SGLT2i on a molecular and cellular level. Therefore, direct electrophysiological effects of dapagliflozin – the most advanced SGLT2i in clinical trials – on action potential (AP) formation in atrial cardiomyocytes (CM) was investigated.

Methods

Effects of dapagliflozin on human NaV1.5, heterologously expressed in Chinese hamster ovary (CHO) cells, was investigated using the patch-clamp method. Further, effects on voltage-gated sodium channels (NaV) were also measured in human atrial CM. Consequences of dapagliflozin treatment on AP formation were studied on isolated human and porcine atrial CM using the patch-clamp technique. APs were elicited in current-clamp mode by injection of brief current pulses.

Results

Dapagliflozin (100 μM) significantly decreased peak sodium currents in human atrial CM as well as CHO cells, expressing human NaV1.5 channel subunits. Additionally, half-activation potential of voltage-gated sodium channels was significantly increased after administration of dapagliflozin. Furthermore, dapagliflozin (100 μM) suppressed AP formation in CM isolated from human and porcine left and right atrial tissue. In human CM action potential amplitude (APA) was significantly reduced by 34.3%, while APA inhibition by dapagliflozin averaged out at 30.7% for porcine CM. In porcine CM action potential duration at 50% (APD50) and 90% repolarization (APD90) were also significantly reduced.

Conclusion

Dapagliflozin suppresses AP formation in human and porcine atrial CM by inhibiting voltage-gated sodium currents. Therefore, we suppose that dapagliflozin exhibits class I antiarrhythmic effects.

Funding Acknowledgement

Type of funding sources: None.

Evaluating the reversibility potential of atrial cardiomyopathy on a clinical and cellular level

Background

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is associated with various remodelling processes of the electrical and structural properties of the atrium, collectively referred to as atrial cardiomyopathy. Because these remodelling processes contribute significantly to the high recurrence rates and chronification of AF, the exact time course of their development and their reversion potential need to be further characterized.

Purpose

To investigate the time course and reversibility of atrial cardiomyopathy on a clinical, cellular and molecular level.

Methods

A clinically relevant porcine large animal model was used to study the structural and functional implications of atrial cardiomyopathy after different periods of burst pacing-induced AF (2, 4 and 8 weeks) and after a recovery period, following electrical cardioversion. The pigs were clinically characterized at each time point by echocardiography, cardiac MRI, and electrophysiological studies. After extraction of the heart, action potentials (APs) and ionic currents were measured on isolated atrial cardiomyocytes (CM) using the patch-clamp technique.

Results

After 4 weeks of AF induction, APD90 of isolated atrial cardiomyocytes was attenuated by 26%. Extending the AF induction period to 8 weeks caused an even stronger APD90 reduction by one-third, compared to SR controls. Accompanying, the TASK-1 current density was strongly upregulated in AF pigs. Those observations were in line with significant changes of the right atrial effective refractory period (AERP). At baseline, AERPS1=400 ms yielded 186 ms, whereas it was reduced to 141 ms after eight weeks of AF. Addressing the reversibility of those changes, following cardioversion of AF and an 8 week long SR recovery period, AERP baseline values were almost restored. Likewise, APD90 shortening was partially reversed. Furthermore, indication of reversibility of AF-associated remodelling was also observed on a structural level. After eight weeks of AF induction, echocardiography revealed severe dilatation of both atria, whereas atrial diameters decreased significantly after restoration of SR.

Conclusion

Remodelling processes underlying atrial cardiomyopathy display a partial reversibility upon restoration and maintenance of SR.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG German Research Foundation

Atrial tattoos lines: a new method to terminate atrial fibrillation

Introduction

Atrial fibrillation (AF) is the most common cardiac arrhythmia affecting more than 4% of the world's population. Furthermore, the vulnerable substrate underlying atrial cardiomyopathy remains far from being understood. Atrial cardiomyopathy is a highly complex and heterogeneous disease that occurs in the context of various clinical backgrounds, which explains the heterogenous success of established atrial ablation strategies such as pulmonary vein isolation. Here we developed a new interventional method for the treatment of AF using a tattooing procedure of silver nanowires in the atria to create circular lines of increased conductivity to prevent irregular electrical propagation.

Purpose

In a translational study, we tested a newly developed interventional method to terminate AF by injecting lines of silver nanowires to increase tissue conductivity.

Methods

The developed tattoo method was tested in vivo using an established large animal AF model of the domestic pig. Pigs (n=10) with atrial fibrillation were either treated with right atrial tattoo lines using a transmural injection procedure of silver nanowires as closed lines in the atrium or got a sham treatment with saline injections. Over 21 days, AF was induced and monitored (AF burden) by an intracardiac dual-chamber device with a biofeedback induction algorithm. Initially and before final termination, conventional electrophysiological investigation and atrial 3D mapping, echocardiography and epicardial multi electrode array (MEA) measurements were performed. Following the 21 days observation period, the heart was extracted and freshly isolated atrial cardiomyocytes were subjected to cellular electrophysiological, molecular and histochemical characterization. Electrophysiological data was used for in silico modelling of arrhythmia termination and wave propagation. The study protocol was approved by the animal ethics committee.

Results

The AF burden was significantly reduced (AF burden <10%) in the group treated with the new atrial tattoo line method compared to sham treated pigs. The bi-atrial diameters, quantified by echocardiography, were significantly smaller in the treatment group. Atrial refractory period was significantly shorter in the sham treated pigs. A significant increase of connexin 43 was observed in the injection area of silver nanowires in the myocardium. Measurements with MEA demonstrated increased conduction velocity by a factor of 1.5–2.0 in the areas of silver nanowire injections. Additionally, in silico modelling showed the termination of AF via the created conduction lines.

Conclusion

The newly developed interventional method of the creation of atrial lines with increased tissue conductivity using silver nanowires could successfully terminate AF in pigs. Perspectively, this new myocardial tattooing technique may be a promising treatment strategy for patients with complex atrial cardiomyopathies to terminate atrial arrhythmias.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Else Kröner Fresenius Foundation

The COVID-19 viral 3a protein forms a potassium channel that can be inhibited by antiarrhythmic drugs

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): Deutsche Gesellschaft für Kardiologie /German Cardiac Society Joachim Herz Stiftung /Joachim Herz Foundation

Background/Introduction

Supraventricular and ventricular arrhythmias can often be observed in patients with COVID-19 infection. Both, the clinically observed increase in cardiac biomarkers as well as histological studies indicate virus replication within cardiomyocytes. The 3a open reading frame of the viral genome encodes for a transmembrane protein that is transported to the cell membrane where it can serve as a potassium channel.

Purpose

The aim of this study was to investigate whether COVID-19 infected induced pluripotent stem cell (iPSC)-derived cardiomyocytes also express the 3a protein and whether the potassium currents that are conducted through the 3a protein can be inhibited by clinically used antiarrhythmic drugs.

Methods and Results

iPSC-derived cardiomyocytes were infected with COVID-19 and subsequently subjected to immunoblotting, where expression of the 3a protein could be observed. Plasmid DNA, encoding the COVID-19 3a protein, was generated by gene synthesis and used for in vitro transcription of cRNA. 3–5 days after intracytoplasmic injection of the 3a protein cRNA into Xenopus laevis oocytes, potassium currents could be measured by two-electrode voltage clamp recordings. While class I and class IV antiarrhythmic drugs showed only minor effects on the potassium currents of the 3a protein, a robust inhibition by several beta-blockers and by class III antiarrhythmic drugs could be observed. The strongest effects were found with dofetilide (58.1 % inhibition at 100 µM) and amiodarone (50.1 % inhibition at 100 µM, IC50 level 4.7 µM). An in silico docking analysis, based on the recently revealed crystal structure of the 3a protein, identified the amino acid residues K61 and D142 as part of the binding site of amiodarone. After deactivation of these amino acid residues by site-directed mutagenesis, the inhibition by amiodarone was significantly attenuated.

Conclusion

The COVID-19 viral 3a protein is expressed in COVID-19-infected iPS-derived cardiomyocytes and forms a potassium channel that can be inhibited by antiarrhythmic drugs.

Fixed posterior cranial vault expansion technique

BACKGROUND

Different techniques to reshape the posterior skull vault have been developed in the last decades, all sharing the same goals of increasing the skull volume, decreasing the intracranial pressure (ICP), correcting the cranial dysmorphy, and contributing to a better growth of the skull. Though over the last years most refinements in these techniques have focused on the use of hardware as distractors or springs, the fixed posterior vault expansion remains a valuable procedure for cranial remodeling.

METHODS

We describe in details the technique used for fixed posterior vault expansion in children that is applied at the French Referral center for Craniosynostosis of Lyon, France.

DISCUSSION

The fixed posterior vault expansion increases the risk of perioperative complications due to the elevation of the posterior bone flap from the dura but allows an immediate decompression and correction of the shape, simplifying the postoperative course.