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ABSTRACT
Extracellular-cAMP Suppresses Pulmonary Arterial Hypertension-induced Ventricular Arrhythmias
Background: Pulmonary Arterial Hypertension (PAH), a major cause of right ventricular failure, is associated with a high 5-year mortality rate. Arrhythmias account for a significant proportion of morbidity and mortality in PAH patients. Hence, there is a critical need for new therapies to effectively treat PAH-related cardiac arrhythmias.
Objective: The purpose of this study was to evaluate the efficacy of extracellular cyclic adenosine monophosphate (e-cAMP) treatment in reversing pathophysiological electrophysiological (EP) remodeling and arrhythmia propensity caused by PAH.
Methods: After three weeks of subcutaneous injection of Monocrotaline (MCT) or left pneumonectomy within VEGFR inhibition by Sugen-5416 (Su/Pn), rats were randomly assigned to receive miniosmotic pumps containing cAMP or a saline solution. At the 5-week terminal time-point, rats were sacrificed for ex-vivo optical action potential (AP) mapping, real-time reverse transcription–polymerase chain reaction, immunostaining, morphological and histologic analyses.
Results: As expected, PAH diseased rats from both models exhibited a high propensity of inducible ventricular tachycardia. Remarkably, e-cAMP treatment suppressed the incidence of ventricular tachycardia in both models. Examination of the EP substrate revealed action potential duration (APD) prolongation and marked conduction slowing in PAH-diseased animals. These features, however, were significantly reversed by e-cAMP treatment. Moreover, the analysis of alternans showed that e-cAMP treatment prevented the incidence of alternans behavior altogether (P = 0.0291 for e-cAMP-treated MCT vs. MCT group, P = 0.021 for e-cAMP-treated Su/Pn vs. Su/Pn group). PAH-diseased rats displayed right ventricular as well as cardiomyocyte hypertrophy, whereas e-cAMP-treated rats exhibited a significant decrease in hypertrophic remodeling both at the chamber and cellular levels. We also uncovered a marked decrease in myocardial fibrosis by e-cAMP treatment in PAH-diseased rats. Reversal of EP remodeling by e-cAMP was accompanied by decreased pulmonary vascular remodeling and by restored cardiac expression of key ion channel transcripts.
Conclusion: Extracellular cAMP treatment reduces the incidence of ventricular arrhythmias and suppresses pathological EP remodeling. This approach may represent a new therapeutic modality for arrhythmia suppression in PAH patients.