We herewith have shown that freshly isolated SVF

We herewith have shown that freshly isolated SVF improve cardiac outcome comparable to cultured ASCs in an immunocompetent rat model of AMI with reperfusion. Our data are comparable to data of Bai et al., who have also shown that both fresh SVF buy Pyridoxal isonicotinoyl hydrazone and cultured ASCs improved cardiac function in a comparable way (Bai et al., 2010). However, we now have additionally shown that these stem cells truly reduced scar size, which was not analyzed by Bai et al. directly. In addition, we have applied intravenous delivery of these cells, which makes the application of this technique in patients easier, compared to intramyocardial injection. Notwithstanding, both studies demonstrate that these mesenchymal stem cells truly have the potential of homing to the infarcted heart. In addition we have used fully immunocompetent rats, which was possible since we used cells from syngeneic animals, which is more comparable to a clinical setting than the immunodeficient mice Bai et al. have used in their study. In contrast to the study of Bai et al., we did find one important difference between injection of fresh SVF cells and cultured ASCs, namely that in the ASC group three animals showed severe shortness of breath directly following injection of ASC, and one of these animals died within several minutes after treatment, due to thrombo-emboli of the lung, which was not found in the SVF-treated group. This detrimental effect of cultured ASC on the pulmonary circulation was probably caused by the entrapment of ASCs in the lungs, related to increased size of ASCs due to the culturing procedure, also shown in this study. It indeed has been described previously that culturing of stem cells increases cell size and also increases the expression of adhesion molecules, which may lead to complications during transplantation (McIntosh et al., 2006; Zhu et al., 2008). Furthermore, it is known that respiratory failure is the most common complication after bone marrow transplant (Gao et al., 2001). Since the results in cardiac outcome between fresh SVF cells and cultured ASCs is comparable, and culturing is time consuming, expensive, and leads to more complications, our study seems to indicate that the use of SVF cells is clinically more favorable. In this study we also found a trend towards improved stroke volume and fractional shortening after stem cell treatment, compared to the vehicle-treated group, although this was not statistically significant. However, it should be pointed out that infarct size was relatively small. We however deliberately induced non-aneurysmatic infarcts by placing the suture approximately 2mm below the origin of the coronary artery, since in patients most infarcts are non-aneurysmatic, because of the widespread use of immediate reperfusion therapy. This might explain its small effect on heart function after AMI and in turn also the small effect of stem cell treatment on the reduced function (Ndrepepa et al., 2007; Pfeffer et al., 1979; Schaer et al., 1990). Another important finding of this study is that stem cells were detected in the infarcted area 28days after AMI, using CM-DiI labeling, a label that is not exchanged between cells, and can be traced up to 6weeks in vivo, also after fixation (Andrade et al., 1996; Weir et al., 2008). Even more importantly, we found that all detected stem cells showed cardiomyogenic differentiation. However, the number of detected stem cells was relatively low, suggesting that the improvement of infarction is most likely not explained by any differentiation of ASCs into cardiomyocytes. Reduction in infarct size might partly be explained by improved angiogenesis (Mazo et al., 2008; Miyahara et al., 2006; Zhang et al., 2007). We indeed did find trends of increased numbers of total vessels and arterioles in the infarction area after treatment with stem cells, although this was borderline statistically significant. Several other studies have described in small animal models that the effect of ASC transplantation after AMI can be explained by differentiation towards endothelial cells (Mazo et al., 2008; Miyahara et al., 2006; Zhang et al., 2007). However, we did not find differentiation of SVF cells or ASCs towards endothelial cells. Strem et al. (2005) also only found differentiation of stem cells towards cardiomyocytes, but no differentiation towards endothelial cells, in a mouse model in which SVF cells were transplanted directly after reperfusion (Strem et al., 2005). Differences in studies might be explained by the time point of injection, resulting in altered differentiation signals for the cells. These studies namely transplanted ASCs late after infarction (>3weeks). While both in the study of Strem et al. and in our study, cells were transplanted within 1week after infarction.