Coordinated release of calcium (Ca2+) from the sarcoplasmic reticulum (SR) through cardiac ryanodine receptor (RYR2) channels is essential for cardiomyocyte function. In catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited disease characterized by stress-induced ventricular arrhythmias in young patients with structurally normal hearts, autosomal dominant mutations in RYR2 or recessive mutations in calsequestrin lead to aberrant diastolic Ca2+ release from the SR causing arrhythmogenic delayed after depolarizations (DADs). Here, we report the generation of induced pluripotent stem cells (iPSCs) from a CPVT patient carrying a novel RYR2 S406L mutation. In patient iPSC-derived cardiomyocytes, catecholaminergic stress led to elevated diastolic Ca2+ concentrations, a reduced SR Ca2+ content and an increased susceptibility to DADs and arrhythmia as compared to control myocytes. This was due to increased frequency and duration of elementary Ca2+ release events (Ca2+ sparks). Dantrolene, a drug effective on malignant hyperthermia, restored normal Ca2+ spark properties and rescued the arrhythmogenic phenotype. This suggests defective inter-domain interactions within the RYR2 channel as the pathomechanism of the S406L mutation. Our work provides a new in vitro model to study the pathogenesis of human cardiac arrhythmias and develop novel therapies for CPVT.

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Background: Glutaraldehyde fixation does not guarantee complete tissue biocompatibility in current clinical bioprosthetic heart valves (BHVs). Particularly, circulating anti-aGal human antibodies increase significantly from just 10 days after a BHV implantation. The inactivation of such epitope should be mandatory to meet the requirements for a perspectively safe clinical application; nevertheless, its quantitative assessment in commercially available BHVs has never been carried out. Methods: In this investigation, seven different models of BHVs were tested. The number of epitopes was determined with reference to a standard aGal source by an ELISA test. The presence of xenoantigen was subsequently confirmed by immunofluorescence analysis. Porcine tissue, knockout for the aGal epitopes, was used as negative control. Results: Epic TM valve was the only model among those tested, in which the aGal antigen appeared to be completely shielded. Composite Trifecta TM valve exhibited conflicting results: cusps of bovine pericardial tissue were devoid of reactive aGal epitopes, while the stent cover strip of porcine pericardium still maintained 30% of active antigens originally present in native tissue. All other tested BHVs express an aGal amount not significantly different from that exhibited by porcine Mosaic â valve (5.2 AE 0.6 9 10 10 each 10 mg of tissue). Conclusions: For the first time, the quantitative evaluation of the aGal epitope in heart valve bioprostheses, already in clinical practice for about 40 yrs, was finally determined. Such quantification might provide indications of biocompatibility relevant for the selection of bioprosthetic devices and an increase in the confidence of the patient. It might become a major quality control tool in the production and redirection of future investigation in the quest for aGal-free long-lasting substitutes.

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