| Objective:To observe whether or not the allogeneic MSCs can migrate to the site of myocardial infarction, survive and differentiate into cardiomyocytes, then to serve as a reference for the clinical application of MSCs to treat AMI.Materials and Methods MSCs from ten-day-old suckling pigs were isolated and cultured in vitro.AMI was performed by transcatheter embolization of the distal of left anterior descending artery or left circumflex artery using thread segment. Before and 24 hours after operation, myocardial enzymes and troponin were tested, as well as echocardiography and MRI, to detect whether or not the model was successfully established.Eleven pigs were performed MRI before operation, eight of them were performed postoperation. The MR scanning was performed with both non-enhanced and perfusion weighted MR imaging. The non-enhanced MR imaging sequences included FIESTA, Fiesta, Tags, Double and Triple. Perfusion weighted MR imaging was performed with fast GRE ET pulse sequence with TR=8.2ms, TE=2.6ms, TI=167.4ms. The perfusion weighted imaging was started at the time of administration of 0.1mmol/kg of Gd-DTPA. Five to ten minutes after PWI performed, the delayed sequence was started. The morphology, signal intensity and function of the hearts on MR imaging before operation were compared with those after operation. From PWI imaging, the signal intensity-time(SI-T) curve was generated, the highest slope rate value, peak signal, peak-time were calculated.Eight AMI models were successfully established. Two of them were served as control group, six of them were chosen as treatment group in which three for coronary artery graft group, another three for the vein graft group. The second passage MSCs labeled with SPIO was transplanted through intracoronary arterial injection or intravenous administration, respectively. In the treatment group, each pig received 1×107 MSCs. Seven to ten days after embolization was chosen as the time of transplantation. Control group did not receive treatment.The pigs were killed in control group after five weeks of embolization, while four weeks after transplantation in treatment group. The morphology, location and extent of infarction were compared with MR imaging. With HE staining, MVD (microvessel density) in the infarct scar area of control group were compared with that of treatment group. With Prussian blue staining,presumed MSCs were observed in the scar area of treatment group. Potential transdifferentiation of myocardial-like cells from implanted MSCs was identified by antibody immunostaning for troponin.ResultsIsolation and culture of MSCs was performed by the characteristics of its adherent. The purity of MSCs was improved by exchanging culture medium for several times.Eleven pigs underwent surgical intervention, three of them were excluded because one was dead due to occurrence of ventricular fibrillation during the surgery, the second was dead the next day after operation, the third failed because of the femoral artery spasm. The value of myocardial enzymes, troponin, ejection fraction and fractional shortening was significantly different between preoperation and postoperation (P<0.05).All pigs showed normal on non-enhanced MR imaging and perfusion weighted imaging before operation. Eight successful AMI models were performed non-enhanced MR imaging and perfusion weighted imaging after operation. The morphology of heart had no significant change in all sequence. In FIESTA sequence, the signal intensity was slightly increased in infarct site in three cases. On Fiesta and Tags images, the motion in infarct region significantly decreased. In non-enhanced Double and Triple sequence, all cases showed slightly higher signal intensity. On perfusion weighted images, the first-pass myocardial perfusion showed low perfusion and delayed myocardial enhancement were found in all cases. Compared with those of preparation, the highest slope value and peak-signal intensity reduced but the peak-time increased. On delayed Double and Triple images, the signal intensity significantly increased compared with those of non-enhanced sequences. The location and extent of infarction were consistent with the general pathology.In scar area, HE staining showed marked augmentation of neovascularization in the treatment group. The capillary density was greater in coronary graft group than in the vein graft group. The control group showed only a small amount of neovascularity. With Prussian blue staining, there were blue granules within the cytoplasm of cells in scar area of the treatment group in which coronary graft group were much more than vein graft group. There were no such cells in the control group. Immunohistochemistry verified the expression of Troponin: scattered cells showing strong positive expression were observed in treatment group. Positive expression in coronary graft group was higher than vein graft group. No positive cells were present in control group. Conclusion :Allogeneic (suckling pig) MSCs were transplanted to pigs with AMI through intracoronary arterial injection or intravenous administration. Some of the MSCs which homing to the infarct site can survive, transdifferentiate into cardiomyocytes and promote angiogenesis. The means by intracoronary arterial injection was superior to that by intravenous administration.
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