|Ph.D Thesis||Department of Medicine|
|Supervisor:||Prof. Gepstein Lior|
|Full Thesis text|
Heart transplantation is the only definitive treatment for progressive heart failure. However, due to the shortage in donor organs for heart transplantation, a search for new therapeutic paradigms for heart failure has become imperative. Myocardial cell-replacement techniques were demonstrated to alter the remodeling process responsible for the functional deterioration after myocardial infarction in the acute setting. In order to address this issue in the chronic setup, infarcted rat hearts, one month following surgical induction of myocardial infarction, were randomized to injection of human embryonic stem cell derived cardiomyocytes (hESC-CMs) or saline. Immunostaining confirmed the presence of the transplanted hESC-CMs in the infarcted left ventricular wall. Serial echocardiography studies revealed a typical course of post-infarction LV remodeling in the saline-injection control group, while transplantation of hESC-CMs prevented the aforementioned deterioration in fractional shortening.
Given the challenges associated with direct cell transplantation strategies we shifted our attention to the potential of the emerging tissue-engineering discipline. Two different technologies based on the discipline of tissue engineering technology were developed.
In the first study, we assessed the ability of a three-dimensional tissue-engineered human, vascularized, cardiac-muscle to engraft in the in-vivo rat heart and to promote functional vascularization. For this purpose, hESC-CMs alone or in combination with human endothelial cells and embryonic fibroblasts (tri-culture constructs) were seeded on degradable biopolymer-scaffolds. Synchronously contracting cardiac tissue-constructs were formed in-vitro that contained a dense vessel-network. Grafting of the engineered tissue in the rat heart resulted in the formation of long-term stable grafts showing cardiomyocyte structural maturation and formation of functional human and rat-derived vasculature within the scaffold.
In the second tissue-engineering approach, a photopolymerizable, biodegradable, PEGylated-fibrinogen hydrogel was developed and proven to be an effective carrier for cardiomyocytes [neonatal rat ventricular cardiomyocytes (NRVCMs) and hESC-CMs] both in-vitro and in-vivo. To determine the functional consequences of the combined in-situ cell-delivery/tissue-engineering strategy, infarcted rat hearts were randomized to injection of saline, NRVCMs, biopolymer, or combined delivery of the biopolymer and NRVCMs. Echocardiography revealed typical post-infarction functional deterioration in the saline-injected control group. Injection of NRVCMs or biopolymer alone significantly altered this remodeling process. Co-injection of the biopolymer and NRVCMs resulted in the best functional outcome. Similar improvements in other remodeling parameters were also noted in the combined group. Finally, feasibility studies demonstrated the ability of the biopolymer to act as an effective carrier of hESC-CMs and to significantly alter the remodeling process.