Introduction:
Heart failure (HF) remains a leading cause of death worldwide. Chronic HF is strongly associated with arrhythmias that increase patient mortality. Today, the most common arrhythmia in HF is atrial fibrillation (AF). AF and ventricular arrhythmia occur in HF due to pathological conditions, such as remodelling and a dysregulated neurohumoral activation. Thereby, the chronically overstimulated β-adrenergic pathway compensates for reduced cardiac function, but also raises intracellular cAMP levels, leading to disturbed Ca2+-homeostasis and thus to pro-arrhythmogenic triggers. Moreover, the pathological remodelling stimulates the production of reactive oxygen species (ROS), promoting arrhythmogenic signalling. Interestingly, the expression of cAMP-degrading phosphodiesterase 2 (PDE2) is upregulated in patients with HF. Moreover, mice with cardiac PDE2 overexpression develop less arrhythmia. Thus, the direct PDE2 stimulator 5,6-DM-cBIMP (cBIMP) might be an interesting therapeutic option. Here, we aim to assess the potential of cBIMP to reduce arrhythmic events via PDE2 stimulation in isolated, atrial and ventricular cardiomyocytes (CM) from murine HF model with preserved ejection fraction.
Materials and Methods:
In wildtype and cardiac-specific PDE2-KO mice, HF was induced over 5 weeks using a high fat diet and the NO-synthase inhibitor L-NAME (0.5g/l). Intracellular cAMP levels were quantified using competitive ELISA. Proarrhythmic Ca2+-releases, Ca2+-sparks (CaSp), were quantified in isolated CM using Ca2+-imaging. The sarcomere contraction was characterized by video-based analysis. EPR-spectroscopy was used to examine intracellular ROS-production. Arrhythmia generation was quantified in ex-vivo perfused hearts from healthy mice after burst pacing protocols by ECG recordings.
Results:
After treatment, mice developed HF with reduced diastolic and preserved systolic function. In ventricular CM of HF mice, the β-adrenergic stimulation with isoprenaline (ISO) significantly raised cAMP whereas simultaneous cBIMP incubation clearly prevented this ISO effect. Importantly, cBIMP markedly lowered the ISO-induced increase of proarrhythmic CaSp-frequency in atrial and ventricular CM. These effects could be significantly prevented by the PDE2 specific inhibitor BAY-607550 and were not observed in CM from PDE2-KO mice. Thereby, cBIMP did not affect sarcomere contraction characteristics under basal or ISO-stimulated conditions. Initial analyses suggest that cBIMP attenuates intracellular ISO-induced ROS production in isolated cardiomyocytes. Finally, cBIMP perfusion clearly reduced the inducibility of atrial fibrillation in ex-vivo perfused hearts compared to controls.
Conclusion:
Direct stimulation of PDE2 by 5,6-DM-cBIMP significantly reduced proarrhythmic Ca²⁺ release events and atrial arrhythmia susceptibility, supporting PDE2 activation as a promising therapeutic strategy for AF in HF.
