Abstract 343: Embryonic Extracellular Matrix and Cardiomyocyte Maturation

Background: The progression of cell maturation is governed by intrinsic factors, but also by interaction with the milieu in which they reside. The extracellular matrix (ECM) from rapidly developing tissue should form a rich signaling environment for cellular development. Hypothesis: Murine embryonic ECM can be prepared by detergent decellularization that is morphologically preserved, biocompatible for cell culture, and at E13.5, substantial enough to permit vascular catheterization and recellularization by perfusion. When used as a scaffold for cell culture, it can be shown to have a salutatory effect on the morphologic and physiologic maturation of post-natal cardiomyocytes (CM). Methods and Results: To test the contribution of embryonic ECM to the performance of cardiomyocytes in culture, we undertook the isolation of ECM from developing murine embryos. Using a detergent decellularization protocol, we established an acellular scaffold that was shown to be free of native cells and returned to a biocompatible state, to serve as a scaffold for cell culture. Primary P7 mCherry expressing cardiomyocytes were isolated and introduced by perfusion into the embryonic ECM heart. The same cells were also plated, and the performance of the two culture modalities was compared at 3 and 28 days. Histologic comparison demonstrated the maintenance of the rod cellular morphology. Analysis of cellular contractile performance by video microscopy demonstrated improved contractile performance of CMs when cultured on ECM and paced at 1 Hz (3 Day plated contraction velocity/relaxation velocity (μm/sec) 1.18±0.3/0.91±0.2 and ECM contraction velocity/relaxation velocity (μm/sec) 6.65±1.0/4.52±0.7). At 28 days plated contraction velocity/relaxation velocity was (μm/sec) 2.71±0.2/1.59±0.1 and ECM contraction velocity/relaxation velocity was (μm/sec) 8.83±4.2/6.20±2.6). Conclusion: Biocompatible, acellular morphologically preserved embryonic ECM can be extracted from E13.5 murine embryos. By E13.5 the structural integrity of the acellular matrix can sustain vascular perfusion for delivery of P7 cardiomyocytes to internal organoid structures. These ECM preparations support the maturation and physiologic performance of cardiomyocytes.

Clinical and Echocardiographic Factors Associated with Right Ventricular Systolic Dysfunction in Hemodialysis Patients

Background: Chronic kidney disease is a disorder of epidemic proportions that impairs cardiac function. Cardiovascular diseases are the leading cause of death in hemodialysis patients, and the understanding of new nontraditional predictors of mortality could improve their outcomes. Right ventricular systolic dysfunction (RVSD) has recently been recognized as a predictor of cardiovascular death in heart failure and hemodialysis patients. However, the factors contributing to RVSD in hemodialysis patients remain unknown. The aim of this study was to evaluate the clinical and echocardiographic factors associated with RVSD in hemodialysis patients. Methods: A cross-sectional study was conducted in which 100 outpatients with end-stage renal disease on chronic hemodialysis were evaluated. A transthoracic echocardiographic examination was performed at optimal dry weight. Right ventricular systolic function was evaluated using tricuspid annular plane systolic excursion (TAPSE). Clinical and echocardiographic data were recorded for each patient. A multivariate linear logistic regression was created using RVSD (TAPSE <14 mm) as the dependent variable. Results: Fifteen patients with RVSD and 85 patients without RVSD were analyzed. TAPSE had a positive correlation with left ventricular ejection fraction (LVEF) and myocardial relaxation velocity. Independent contributors to RVSD were LVEF (OR 1.14, 95% CI 1.05-1.26), left ventricular mass index (OR 1.02, 95% CI 1.00-1.04), and myocardial relaxation velocity (OR 1.81, 95% CI 1.18-3.19). Conclusions: Echocardiographic factors were significant contributors to RVSD. These measurements could be included as part of the routine workup in all end-stage renal disease patients on hemodialysis.

AdE-1, a new inotropic Na+ channel toxin from Aiptasia diaphana, is similar to, yet distinct from, known anemone Na+ channel toxins

Heart failure is one of the most prevalent causes of death in the western world. Sea anemone contains a myriad of short peptide neurotoxins affecting many pharmacological targets, several of which possess cardiotonic activity. In the present study we describe the isolation and characterization of AdE-1 (ion channel modifier), a novel cardiotonic peptide from the sea anemone Aiptasia diaphana, which differs from other cnidarian toxins. Although AdE-1 has the same cysteine residue arrangement as sea anemone type 1 and 2 Na+ channel toxins, its sequence contains many substitutions in conserved and essential sites and its overall homology to other toxins identified to date is low (<36%). Physiologically, AdE-1 increases the amplitude of cardiomyocyte contraction and slows the late phase of the twitch relaxation velocity with no induction of spontaneous twitching. It increases action potential duration of cardiomyocytes with no effect on its threshold and on the cell's resting potential. Similar to other sea anemone Na+ channel toxins such as Av2 (Anemonia viridis toxin II), AdE-1 markedly inhibits Na+ current inactivation with no significant effect on current activation, suggesting a similar mechanism of action. However, its effects on twitch relaxation velocity, action potential amplitude and on the time to peak suggest that this novel toxin affects cardiomyocyte function via a more complex mechanism. Additionally, Av2's characteristic delayed and early after-depolarizations were not observed. Despite its structural differences, AdE-1 physiologic effectiveness is comparable with Av2 with a similar ED50 value to blowfly larvae. This finding raises questions regarding the extent of the universality of structure–function in sea anemone Na+ channel toxins.