CineCT imaging platform for in-vivo and ex-vivo measurement of myocardial biomechanics post myocardial infarction and following intramyocardial delivery of theranostic hydrogel

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Institute of Health (NIH) Purpose Myocardial infarction (MI) induces acute regional changes in myocardial strain and stiffness in the infarct and the remote areas of the left ventricle (LV), which lead to adverse changes in LV geometry and function. We hypothesize that cineCT imaging could evaluate these biomechanical changes along with the effects of intramyocardial delivery of theranostic hydrogels. Introduction We present an experimental platform to assess changes in the deformation of the LV myocardium using contrast cineCT (CCT) imaging of the beating porcine heart (active deformation) before and after acute MI and intramyocardial delivery of an imageable theranostic hydrogel. We then assess the acute effects of hydrogel delivery early post-MI on biomechanics (passive deformation) using an ex vivo perfused heart preparation. Methods Contrast cineCT imaging was performed using 64-slice CT on 5 Yorkshire pigs without MI (n = 3) or with MI (n = 2). MI pigs had serial imaging performed before and 1 hour after acute surgical coronary occlusion to induce anterolateral MI. One MI pig was also imaged 1 hour after intramyocardial injection of a novel imageable theranostic iodinated hydrogel within the MI region. Post euthanasia, excised hearts were flushed with chilled UW cardioplegic solution and mounted on a custom inflation apparatus for cineCT imaging during LV inflation by external pump. LV pressure was cycled between 10 and 60 mmHg at 35 bpm. Dilute iohexol was injected into aortic root and UW perfusate (15 ml, 1 ml/sec). CineCT image series were reconstructed, contrast enhanced, resampled to the LV long axis (Z), and exported as a series of 10 CT volumes covering 0-90% of the cardiac/inflation cycle. Volumes were registered incrementally using nonlinear image registration (BioImageSuite) and the calculated displacement at each time point was exported at a resolution of 1 mm. A custom Matlab program was used to fit the displacement field to local trilinear polynomials and then calculate the displacement gradients and 3D Lagrangian strains. To estimate the accuracy of this approach, cardiac volumes were also numerically deformed using a 10 pixel translation and 5% triaxial stretch. Results We successfully acquired serial in-vivo and ex-vivo 3D CineCT images for assessment of the active and passive LV myocardial deformation and tracked deformation through the full cardiac/inflation cycle (Figure 2). Numerical deformation tests showed average tracking errors of < 0.2 mm (1/4 pixel) in the X,Y,Z directions of the volume. These resulted in Lagrangian strain errors of < 0.47% for the in-plane strains EXX and EYY (radial and circumferential plane) and < 0.5% for EZZ (long axis). Conclusions We have developed a novel CineCT imaging platform that allows for high resolution in-vivo and ex-vivo measurement of myocardial biomechanics post-MI and following intramyocardial delivery of imageable theranostic hydrogels, which may improve early active and passive biomechanics.

Hydrojet-based delivery of footprint-free iPSC-derived cardiomyocytes into porcine myocardium

The reprogramming of patient´s somatic cells into induced pluripotent stem cells (iPSCs) and the consecutive differentiation into cardiomyocytes enables new options for the treatment of infarcted myocardium. In this study, the applicability of a hydrojet-based method to deliver footprint-free iPSC-derived cardiomyocytes into the myocardium was analyzed. A new hydrojet system enabling a rapid and accurate change between high tissue penetration pressures and low cell injection pressures was developed. Iron oxide-coated microparticles were ex vivo injected into porcine hearts to establish the application parameters and the distribution was analyzed using magnetic resonance imaging. The influence of different hydrojet pressure settings on the viability of cardiomyocytes was analyzed. Subsequently, cardiomyocytes were delivered into the porcine myocardium and analyzed by an in vivo imaging system. The delivery of microparticles or cardiomyocytes into porcine myocardium resulted in a widespread three-dimensional distribution. In vitro, 7 days post-injection, only cardiomyocytes applied with a hydrojet pressure setting of E20 (79.57 ± 1.44%) showed a significantly reduced cell viability in comparison to the cells applied with 27G needle (98.35 ± 5.15%). Furthermore, significantly less undesired distribution of the cells via blood vessels was detected compared to 27G needle injection. This study demonstrated the applicability of the hydrojet-based method for the intramyocardial delivery of iPSC-derived cardiomyocytes. The efficient delivery of cardiomyocytes into infarcted myocardium could significantly improve the regeneration.

In vivo combinatory gene therapy synergistically promotes cardiac function and vascular regeneration following myocardial infarction

Since myocardial infarction (MI) excessively damage the myocardium and blood vessels, the therapeutic approach for treating MI hearts should simultaneously target these two major components in the heart to achieve comprehensive cardiac repair. Here, we investigated a combinatory platform of ETV2 and Gata4, Mef2c and Tbx5 (GMT) transcription factors to develop a strategy that can rejuvenate both myocardium and vasculatures together in MI hearts. Previously ETV2 demonstrated significant effects on neovascularization and GMT was known to directly reprogram cardiac fibroblasts into cardiomyocytes under in vivo condition. Subsequently, intramyocardial delivery of a combination of retroviral GMT and adenoviral ETV2 particles into the rat MI hearts significantly increased viable myocardium area, capillary density compared to ETV2 or GMT only treated hearts, leading to improved heart function and reduced scar formation. These results demonstrate that this combinatorial gene therapy can be a promising approach to enhance the cardiac repair in MI hearts.

Epicardial Transplantation of Cardiac Progenitor Cells Based Cells Sheets is More Promising Method for Stimulation of Myocardial Regeneration, Than Conventional Cell Injections

Today, transplantation of stem / progenitor cells is a promising approach for the treatment of heart diseases. The therapeutic potential of transplanted cells directly depends on the method of delivery to the myocardium, which determines their regenerative properties. It is important for the development of effective methods of cell therapy. In this paper, we performed a comparative study of efficacy of cardiac progenitor cell (CPC) transplantation by intramyocardial needle injections and by tissue engineering constructs (TEC) – “cell sheets” consisting of cells and their extracellular matrix. It has been shown, that transplantation of TEC in comparison with the intramyocardial delivery provides more extensive distribution and retains more proliferating cellular elements in the damaged myocardium, attenuates the negative cardiac remodeling of the left ventricle and promotes its vascularization.