A Plant Derived Therapeutic Factor For The Treatment Of Myocardial Infarction

Background:Ischemic heart diseases (IHD) including chronic coronary heart disease (cCHD) and myocardial infarction (MI) are leading causes of death in humans. Although many advanced strategies for the treatments of cCHD and MI have been developed in recent years, such as percutaneous transluminal coronary angioplasty, coronary artery stenting and coronary artery bypass grafting, these invasive procedures have significantly increased risks of many cardiovascular complications. Furthermore, none of these invasive revascularization procedures provide a substantial treatment of the disease. Current available therapies can only slow down the worsening of IHD and there are no drugs or therapies that can provide pathology modifying treatment of the IHD. Although it was considered that regeneration of sufficient and functional cardiac myocytes to replace the infacrted heart tissues in MI would result in substantial treatment of MI, replacing the dead heart tissues with regenerating myocardium from endogenous progenitor cells or from exogenously transplanted stem cells remains a therapeutic ideal mainly due to the low cardiogenic differentiation efficiency in these progenitor cells. In our previous studies with myocardial infarction rat and rabbit animal models, we have demonstrated the therapeutic effect of the active fraction isolated from Geum japonicum (EGJ), with the clear evidence of myocardial regeneration. Our recent studies have shown the isolation of an active compound (cardiogenin) from EGJ and investigation of the therapeutic effect of cardiogenin on MI in rat animal models, in which the cardiogenin induced trans-differentiation of the transplanted mesenchymal stem cells (MSCs) down to cardiogenic differentiation pathway forming functional myocardium in the infarct zone were implied.Objectives:Although transplantation of exogenous MSCs pretreated with the EGJ or cardiogenin through intra-myocardial injections to the multi-loci of the infarct region in MI heart resulted in significant regeneration of cardiac myocytes, the evidence for the endogenous cellular origin of the newly regenerated cardiac myocytes induced by cardiogenin is deficient. Furthermore, although multi-loci injections of the cardiogenin to the infarct heart can significantly induce myocardial regeneration in infarcted region of the MI hearts, replacement of the difficult and danger delivery of the cardiogenin by heart loci-injections with a safer and easier administration remains challenging. Therefore, the objectives of the current studies were (i) to demonstrate whether intragastric administration of the cardiogenin is able to replace the risky heart loci-injections, (ii) to investigate whether the endogenous MSCs can significantly contribute to the cellular source of the cardiogenin-induced regenerating myocardium, and (iii) to study the possible molecular mechanism underlying cardiogenin-mediated repair of infarcted hearts.Methodology and experimental design:Bone marrow transplantation (BMT) with labeled exogenous MSCs was performed in rats. The experimental rats with the implanted labeled MSCs were subsequently subject to a permanent ligation of left anterior descending coronary artery (LAD) one week after the BMT to produce MI, so that the fate of the bone marrow derived MSCs could be traced. By this animal model, the in vivo cardiogenic differentiation from bone marrow derived MSCs in response to intragastric administration of cardiogenin could be demonstrated.One week after LAD ligation, the experimental rats received their first daily treatment. Cardiogenin (0.5mg) dissolved in water (2.5ml/rat/day) was delivered by gastric gavage daily for 2 weeks. Water alone (2.5ml/rat/day) was administered to rats in the vehicle treated control and sham-operated group. Echocardiography was employed for evaluation of the therapeutic effect of cardiogenin treatment through assessing cardiac function prior to and post treatment. Morphological study and immunohistochemistry were used to determine the coronary vascular density, the cardiac regeneration, the infarct volume and the cellular origin of the regenerating myocytes in the experimental hearts.Results:It was shown that a number of DiI positive cells, which is an indicator of their bone marrow MSC origin, and many newly formed capillaries were found distributed in the whole infarct zone of the MI hearts in cardiogenin-treated animals 7 days post treatment but not in the vehicle treated controls. Numerous MEF2-positive cells were detected and the sizes of these MEF2 positive cells were bigger on day 14 post treatment, an indication of their growth and cardiogenic differentiation with time. The colocalization of the numerous Dil (orange) positive cells with MEF2 (red) positive nuclei implied their bone marrow MSCs origin (DiI-positive) and cardiomyogenic differentiation (MEF2-positive), confirming that the intragastric administration of cardiogenin could also induce significant cardiogenic differentiation of bone marrow derived MSCs in vivo leading to a substantial repair of infarcted hearts. Most of the DiI and MEF2 positive cells clustered together forming myocardial-like tissues, but their sizes were smaller than those of the viable pre-existing cardiomyocytes. These regenerating myocytes occupied on average 60.2±8.66% of the total infarct volume upon 2 weeks cardiogenin treatment. By contrast, in vehicle treated control hearts, only a few MEF2 and DiI positive cells were found, which scattered around the infarct rim and the whole infarct area was mainly occupied by fibrous scar. These results implied that sufficient in vivo cardiogenic differentiation of endogenous bone marrow derived MSCs could be induced by cardiogenin through intragastric administration for significant treatment of MI.Conclusions:In this study, we not only demonstrated the therapeutic effects of cardiogenin through intragastric administration on MI in rat model evidenced by the time-dependent functional improvement, but also provided the direct evidence that the endogenous bone marrow derived MSCs could be the major cellular source of the regenerating myocardium. Our preliminary study on the possibly involved underlying signaling pathways suggested that G protein signaling pathway and miR-9 may play a crucial role in cardiogenin-mediated cardiogenic differentiation of MSCs and myocardial regeneration. It was therefore concluded that the intragastric administration of the cardiogenin can also provide effective treatment on MI through promoting cardiogenic differentiation of endogenous bone marrow derived MSCs leading to substantial repair of MI, which should enable new treatment strategies for MI to be developed immediately.