Cardiosphere-derived cell exosomes delivered IM decrease scarring, halt adverse remodelling and improve LVEF in porcine AMI and CMI. While conceptually attractive as cell-free therapeutic agents for myocardial infarction, exosomes have the disadvantage that IM delivery is necessary.

Background Cardiosphere-derived cells (CDCs) confer cardioprotection in acute myocardial infarction (MI) via distinctive macrophage (Mϕ) polarization. Here we demonstrate that CDC-secreted exosomes (CDCexo) recapitulate the cardioprotective effects of CDC therapy known as cellular postconditioning. Methods Rats and pigs underwent MI induced by ischemia-reperfusion prior to intracoronary infusion of CDCexo, inert fibroblast exosomes (Fbexo; control), or vehicle. Two days later, infarct size was quantified. Macrophages were isolated from cardiac tissue or bone marrow for downstream analyses. RNA-sequencing was used to determine exosome content and alterations in gene expression profiles in Mϕ. Results Administration of CDCexo, but not Fbexo, after reperfusion reduces infarct size in rat and pig models of MI. Furthermore, CDCexo reduce the number of CD68+ Mϕ within infarcted tissue and modify the polarization state of Mϕ so as to mimic that induced by CDCs. CDCexo are enriched in several miRNAs (including miR-146a, miR-181b, and miR-126) relative to Fbexo. Reverse pathway analysis of whole-transcriptome data from CDCexo-primed Mϕ implicated miR-181b as a significant (p=1.3×10−21) candidate mediator of CDC-induced Mϕ polarization and protein kinase C δ (PKCδ) as a downstream target. Otherwise-inert Fbexo loaded selectively with miR-181b alter Mϕ phenotype and confer cardioprotective efficacy in a rat model of MI. Adoptive transfer of PKCδ-suppressed Mϕ recapitulates cardioprotection. Conclusions Our data support the hypothesis that exosomal transfer of miR-181b from CDCs into Mϕ reduces PKCδ transcript levels and underlies the cardioprotective effects of CDCs administered after reperfusion.

Background The pathogenesis of HFpEF is unclear, but fibrosis, inflammation and hypertrophy have been put forth as likely contributors. CDCs are heart-derived cell products with anti-fibrotic and anti-inflammatory properties. Objectives We questioned whether allogeneic rat CDCs might be able to decrease manifestations of HFpEF in hypertensive rats. Methods Starting at 7 weeks of age, Dahl salt-sensitive rats were fed a high-salt diet for 6–7 weeks and randomized to receive intracoronary CDCs or placebo. Dahl rats fed normal chow served as controls. Results High-salt rats developed hypertension, left ventricular (LV) hypertrophy and diastolic dysfunction, without impairment of ejection fraction. Four weeks after treatment, diastolic dysfunction resolved in CDC-treated rats but not in placebo. The improved LV relaxation was associated with lower LV end-diastolic pressure, decreased lung congestion and enhanced survival in CDC-treated rats. Histology and echocardiography revealed no decrease in cardiac hypertrophy after CDC treatment, consistent with the finding of sustained, equally-elevated blood pressure in CDC- and placebo-treated rats. Nevertheless, CDC treatment decreased LV fibrosis and inflammatory infiltrates. Serum inflammatory cytokines were likewise decreased after CDC treatment. Whole-transcriptome analysis revealed major HFpEF-related, CDC-reversed changes in numerous transcripts, including many involved in inflammation and/or fibrosis. Conclusion CDCs normalized LV relaxation and LV diastolic pressure while improving survival in a rat model of HFpEF. The benefits of CDCs occurred despite persistent hypertension and cardiac hypertrophy. By selectively reversing inflammation and fibrosis, CDCs may be beneficial in the treatment of HFpEF.

Background Heart failure with preserved ejection fraction (HFpEF) represents approximately half of heart failure, and its incidence continues to increase. The leading cause of mortality in HFpEF is sudden death, but little is known about the underlying mechanisms. Methods Dahl salt-sensitive rats were fed a high-salt diet (8% NaCl) from 7 weeks of age to induce HFpEF (n=38). Rats fed a normal-salt diet (0.3% NaCl) served as controls (n=13). Echocardiograms were performed to assess systolic and diastolic function from 14 weeks of age. HFpEF-verified and control rats underwent programmed electrical stimulation (PES). QTc interval was measured by surface electrocardiography (ECG). The mechanisms of ventricular arrhythmias (VA) were probed by optical mapping, whole-cell patch clamp to measure action potential duration and ionic currents, and quantitative polymerase chain reaction and western blotting to investigate changes in ion channel expression. Results After 7 weeks of high-salt diet, 31 of 38 rats showed diastolic dysfunction and preserved ejection fraction along with signs of heart failure, hence diagnosed with HFpEF. PES demonstrated increased susceptibility to VA in HFpEF rats (p < 0.001 vs. controls). The arrhythmogenicity index was increased (p < 0.001), and the QTc interval on ECG was prolonged (p < 0.001) in HFpEF rats. Optical mapping of HFpEF hearts demonstrated prolonged action potentials (p < 0.05) and multiple re-entry circuits during induced VA. Single-cell recordings of cardiomyocytes isolated from HFpEF rats confirmed a delay of repolarization (p=0.001) and revealed down-regulation of transient outward potassium current (Ito) (p < 0.05). The rapid component of the delayed rectifier potassium current (IKr), and the inward rectifier potassium current (IK1), were also down-regulated (p < 0.05), but the current densities were much lower than for Ito. In accordance with the reduction of Ito, both Kcnd3 transcript and Kv4.3 protein levels were decreased in HFpEF rat hearts. Conclusions Susceptibility to VA was markedly increased in rats with HFpEF. Underlying abnormalities include QTc prolongation, delayed repolarization from down-regulation of potassium currents, and multiple re-entry circuits during VA. Our findings are consistent with the hypothesis that potassium current down-regulation leads to abnormal repolarization in HFpEF, which in turn predisposes to VA and sudden cardiac death.