Question: Heart failure (HF) and lethal ventricular arrhythmias remain one of the leading causes of mortality worldwide. There is evidence that the activation of the protective cGMP-pathway is cardioprotective in HF patients. Phosphodiesterase 2 (PDE2) is a cGMP-activated enzyme degrading cAMP and thereby may mediate beneficial cGMP-signalling. Here, we evaluate the activation of PDE2 by using cGMP-enhancing agents as a novel therapeutic strategy of cardiac arrhythmia during HF.

Methods: To reveal the role of PDE2 within cardiac cGMP-signalling, a pharmacological approach using the specific PDE2 inhibitor BAY 60-7550 (BAY) and the cardiomyocyte-specific PDE2 knockout model were used in this study. The natriuretic peptides, ANP and CNP, as well as the NO-donor SNP were used to elevate cGMP-generation via the soluble guanylate cyclase (GC) or the GC-receptors (GC-A, GC-B) and thereby mediate PDE2 activation. Pro-arrhythmic triggers, such as ryanodine receptor-mediated calcium sparks, the late sodium current (INaL) and the L-type calcium current (ICaL) were quantified by patch clamp. Finally, arrhythmic events were detected after reperfusion injury in ex-vivo perfused hearts or after isoprenaline (ISO)-mediated arrhythmia provocation in-vivo via ECG-measurements or -telemetry.

Results: In isolated cardiomyocytes from WT mice, ISO clearly increased Ca-spark frequency. Interestingly, all cGMP-enhancing agents ANP, CNP as well as SNP significantly reduced ISO-induced increase of Ca²⁺-spark frequency. This effect was completely abolished under treatment with PDE2 inhibitor BAY as well as in cells with cardiomyocyte-specific PDE2 deletion. Notably, the inhibition of the cGMP-activated kinase PKG did not affect the CNP-induced reduction of Ca-spark frequency. Similar results were observed for the ISO-induced increase of I_NaL and I_CaL showing a reduction under CNP that was mediated by PDE2. The PDE2 knockout in cardiomyocytes did not affect action potential morphology. To test the beneficial effects of cGMP-stimulated PDE2 on organ level, reperfusion injury experiments in ex-vivo perfused heart of WT mice were performed inducing a high number of arrhythmia like ventricular extrasystole (VES) or tachycardia. Interestingly, the permanent perfusion with CNP clearly reduced the number of arrhythmic events, which was in part prevented by simultaneous perfusion with the PDE2 inhibitor. Finally, the injection of CNP in-vivo significantly reduced the number of VES after ISO-induced arrhythmia provocation. This effect was abolished after PDE2 inhibition.

Conclusion: cGMP-enhancing agents clearly reduced proarrhythmic triggers in isolated cardiomyocytes as well as arrhythmia development in-vivo or in ex-vivo perfused hearts. We could show that this antiarrhythmic effect was mediated by PDE2. Thus, the cGMP-mediated activation of PDE2 with natriuretic peptides and NO donors might represent a potential new therapeutic approaches against arrhythmia during HF.