The Experimental Study On The Action Of Recruitment Of The Transplanted Stem Cells Into Infracted Myocardium Enhanced By Remote Ischemic Preconditioning

Background:Cell-based therapies have emerged as a potential therapeutic approach in ischemic heart disease. Intravenous delivery was preliminarily accepted in the clinical setting due to its prominsing characteristic of non-invasiveness and repeatable practise. However, the therapeutic efficacy is severely undermined by its low retention in myocardium resulted from lung entrapment. Stromal cell derived factor-la (SDF-la) played a pivotal role in the process of stem cell homing to acutely infarcted myocardium. But its induced synthesis returned to the baseline level within one week. Remote ischemic preconditioning (RIPC) was an endogenous protective procedure against ischemia-reperfusion (IR) injury by providing an intermittent ischemia stimulus in distant organ. Recruitment and mobilization of bone marrow stem cells was proposed mechanism of RIPC in its late stage. Thus, we assumed that RIPC activated SDF-1α synthesis expression in the myocardium which proceeded into sub-acute myocardial infarction (Ml) stage and could enhance the retention of the intravenously infused cells in the myocardium.Methods:MI of female Sprague-Dawley (SD) rats weighing250-300grams was induced by ligation of the left anterior descending (LAD) coronary artery. The eligible animals were included and divided into subgroups with reference to echocardiography (ECG) at1week later. RIPC was induced with4cycles of5minutes occlusion and reperfusion of the abdominal aorta (AA). The sham procedure was recognized as control which included laparotomy and exposure of AA. The changes of SDF-la in the serum and myocardium were compared between the RIPC group and sham group in a time-dependable manner. We further investigated whether RIPC has an impact on the transplantation efficacy of intravenously delivered mesenchymal stem cells (MSCs) at the time of maximum SDF-1α-dependable gradient between the myocardium and the blood. Male SD rat-derived MSCs were harvested from bone marrow and cultured to the third generation. A total of4×106MSCs were infused via femur vein into female MI rats which subject to RIPC, sham or void procedure. The media with same volume was given into another three groups as the counterparts, respectively. One month later, all the six groups underwent left ventricular function examination. The MSCs engraftment in the myocardium was evaluated by immunohistochemistry (IHC) examination and quantitative polymerase chain reaction (PCR) for SRY gene in Y chromosome. For determining whether SDF-1α play a pivotal role in the transplantation efficacy induced by RIPC, the CXCR4specific and nonspecific antibody was intraperitoneally administered immediately after RIPC procedure and the MSCs retention in myocardium was compared at the same time.Results:A total of135MI rats were recruited into experiments whose left ventricular function was eligible in the terms of cardiac function. For the sub-acute MI rats, RIPC induced an increase of SDF-1α in serum at1hour later (n=4,P<0.01), while, the SDF-la gene transcription enhanced during12hours to48hours (n=4, P<0.05) and protein synthesis raised only at24hours after the procedure in the myocardium (n=4, P<0.01). The time point of SDF maximum gradient between myocardium and serum was pinpointed at24hours after RIPC procedure, thereafter, it was designated as optimum time for intravenous MSC infusion. At1month after cell transplantation, both IHC examination for labeled infused cells and PCR analysis for Y chromosome demonstrated that RIPC significantly increased MSC retention in myocardium by79.1±12.3%(0.45±0.12%versus0.27±0.09%and0.25±0.07%, n=10, P<0.01) and thereby contributed to better cardiac function in comparison with that before cell transplantation (LVFS,24.14±4.59%:16.79±4.34%, m=10, P<0.05;LVESD,5.59±1.11mm:6.99±1.07mm, n=10, P<0.05) Furthermore, blockade with a CXCR4-specific antibody after RIPC markedly attenuated the enhancement of therapeutic efficacy (0.45±0.12%versus0.29±0.09%, n=10, P<0.05)Conclusions:RIPC activated the transcription and protein synthesis of the SDF-la at24hours later in the sub-acute infracted myocardium. The maximum gradient of SDF-la between the myocardium and serum was established by RIPC at24hours later after the procedure in the sub-acute MI stage. RIPC enhanced retention of the intravenously infused MSCs in the infarcted myocardium when cell injection was administered at1day after RIPC. SDF-1α played a pivotal role in the increased therapeutic efficacy induced by RIPC. Priming of the heart with RIPC might be a novel preconditioning approach for enhancing cell retention in myocardium via intravenous delivery.