Extracellular Matrix Bioscaffold Augmented with Human Stem Cells for Cardiovascular Repair
An estimated 16.3 million Americans suffer from coronary heart disease. Every 25 seconds, someone has a coronary event and every minute, someone dies from one. Treatment for coronary heart disease has improved greatly in recent years, yet 1 in 6 deaths in the US in 2007 was still caused by this terrible disease. Stem cells have been used as an supplemental form of treatment but they have been most effective for patients treated immediately after their first heart attack. Unfortunately, stem cell therapy for chronic heart disease and heart failure has been less successful. With current delivery methods for stem cells into the heart, most are washed away quickly, whereas our device will hold them in the area that needs repair. With this project we are testing a novel approach to improve the benefits of stem cell therapy for patients suffering from chronic heart disease. By applying a type of bone marrow stem cells known to enhance tissue repair (mesenchymal stem cells) to a biological scaffold, we hope to greatly amplify the beneficial properties of both the stem cells and the biological scaffold. This device will be implanted onto an appropriate preclinical model that have been treated so as to mirror the chronic heart disease seen in humans. We predict that this novel device will heal the damaged heart and improve its function to pave the way for a superior treatment option for the thousands of Americans for whom the unlikely prospect of a heart transplant is currently the only hope.
Heart disease is the number one cause of death and disability in California and in the US as a whole. An estimated 16.3 million Americans over the age of 20 suffer from coronary heart disease (CHD) with an estimated associated cost of $177.5 billion and CHD accounted for 1 in 6 deaths in the US in 2007. Advances in treatment have decreased early mortality but consequently lead to an increase in the incidences of heart failure (HF). Patients with HF have a 50 percent readmission rate within six months, which is a heavy cost both in terms of quality of life and finances. The high cost of caring for patients with HF results primarily from frequent hospital readmissions for exacerbations. The need for efficient treatment strategies that address the underlying cause, massive loss of functional myocardium, is yet to be met. We believe that present project proposal, development of a combined mesenchymal stem cell and extra cellular matrix scaffold device, will lead to improved standards of care for patients suffering from chronic myocardial infarction who are thus at risk of developing HF. By not only retarding disease progression but by actually restoring cardiac function, we believe that the proposed project will have a tremendous impact on both the cost of care as well as the quality of life for large groups of Californians and patients worldwide for whom the improbable prospect of heart transplantation is the only curative treatment option available.
Heart disease is a major cause of death and disability in the US, accounting for 1 in every 4 deaths and costing more than 100 billion annually. While significant improvements have been made towards treating and managing heart disease, we are still not able to effectively return the heart to a healthy state and cure the patients. With our project we have set out to develop a novel strategy for not only halting the disease progression but to reverse the devastating effect on the function of the heart. By combining bone marrow mesenchymal stromal cells with a biological scaffold material, we hope to create a patch for the heart that will support and regenerate the diseased tissue to the point where the patient will be relieved of the burden of their disease and have a markedly improve quality of life. We have in the past year made significant advances toward establishing an animal disease model in which we can study novel ways of treating heart disease. We have in the same time isolated and characterized cells that reside in the bone marrow and that have the potential to heal the diseased tissue by improving blood flow, minimize scarring and generally promoting recovery of the heart function. We have studies these cells under when grown under different conditions and found their ability to mediate tissue regeneration to be highly dependent on their local environments. We are currently trying to identify the optimal combination of cells and microenvironment that may achieve maximal regenerative effect in our disease model and ultimately help our patient combat their heart disease.
Cardiovascular diseases remain the leading cause of death and disability in the United States. Even with optimal intervention, patients that suffer from an initial coronary event are prone to development of ischemic heart disease (IHD). Current therapies for IHD such medication, percutaneous coronary intervention, anticoagulants, and coronary artery bypass grafting are incapable of rescuing necrotic tissue and recovering normal cardiac function. The only current curative therapy is heart transplantation; however donor organ supply is severely limited and the vast majority of patients die from congestive heart failure while on the transplant waiting list.
Cellular therapies are being explored as a potential cure for IHD. In the majority of these trials, cells are injected in suspension into either vasculature or directly into the ischemic myocardium. Clinical outcomes have clearly demonstrated the safety of these cell based therapies. However, clinical improvements have been modest at best, ostensibly due to poor long term donor cells survival and retention.
Mesenchymal stem cells (MSCs) are an attractive allogeneic stem cell source for cardiac regenerative therapies. MSCs are considered to be immunoprivileged in that they modulate and evade the host immune microenvironment, thus making them ideal candidates for allogeneic transplantation. MSCs also facilitate regeneration by secreting angiogenic and chemotactic factors that facilitate new blood vessel formation and recruitment of host stem and progenitor cells.
Porcine small intestinal submucosa extracellular matrix (SIS-ECM) is a bioscaffold produced from the small intestine of pigs. It has been found to exert a variety of beneficial pro-regenerative functions, hereunder modulating the chemotactic and immune response and releasing large amounts of pro-angiogenic factors. SIS-ECM is ideal in surgical applications as a replacement for synthetic materials in that it facilitates site specific regeneration and resorbs into native tissue without a need for later removal.
The overall goal of this project is to generate a MSC seeded SIS-ECM device for the treatment of IHD. The hypothesis is that the combination of MSCs and SIS-ECM will produce a device with regenerative properties that exceed either component alone. We will with this project develop a porcine myocardial infarct (MI) model that mimics the hallmarks of the human disease. We will then test the proposed device in this model and monitor functional improvement as compared to control animals and animals receiving cells or SIS-ECM alone. We will also verify in vitro that human and porcine MSCs are phenotypically and functionally equivalent to confirm that the results obtained in our porcine model are relevant for the human setting with a high probability. Finally, we will explore mechanisms of action in vitro in relevant assay and in vivo in rat myocardial infarct models.
Major accomplishments in this reporting period:
1. We successfully established a reproducible porcine chronic MI model (CMI) and an acute myocardial infarct (AMI) model. We tested two routes of delivery, epicardial patch and intramyocardial injection. We also optimized orientation and seeding density of the device as well as telemetry implantation in a non-injury porcine sternotomy model. We conclude that the CMI model is well suited for the upcoming studies where we will transplantation our device as an epicardial patch with the MSC seeded side facing the epicardium and seeded below maximal capacity to be the favored approach.
2. We found that MSCs from human and porcine bone marrow samples can readily be isolated, expanded and banked using identical methodology. We created master cell banks from three donors for each species. We additionally generated working cell banks of eGFP and Luciferase overexpressing MSCs for both species. We furthermore confirmed, again using identical methodology that both human and porcine MSCs are analogous with respect to tri-lineage potential, cells surface marker expression and karyotype. Moreover, these major MSC hallmarks are not altered in response to seeding onto SIS-ECM. Finally, we are completing similar studies for rat MSCs
3. We have confirmed that human and porcine MSCs are analogous in the expression pattern of angiogenic factors. We also found that the migratory effect of culture supernatants from human or porcine MSCs seeded onto plastic or SIS-ECM is comparable. Additionally, we found that secretion levels of inflammatory cytokines and in vitro tube formation from culture supernatant was comparable for human MSCs seeded on plastic or SIS-ECM. We furthermore established an AMI model in both immune competent and immune deficient rats. Using these models we have demonstrated significant disease modifying effects of the rat DC analogue as compared to SIS-ECM or MSCs alone. Finally we found improved cell retention at the site of implant for our human DC in the immune deficient SCID rat AMI model.