Reply: Comparison of Endothelial Differentiation Capacities of Human and Rat Adipose-Derived Stem Cells

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We would like to thank Bertrand et al. for their interest in our study.1 The use of xenogeneic materials in clinical grade cell cultures has long been discussed, and serum-free culture media have been produced to mitigate this problem.2,3 Moreover, differentiation of adipose-derived stem cells into endothelial cells in a serum-free medium has also been described.4 We believe the same serum-free culture medium can be used as a replacement for the basal medium that we have used in our study.
The final ratio of human adipose-derived stem cells differentiating into endothelial cells was unexpectedly low in our study (especially when compared to 11.5 percent in rat adipose-derived stem cells). However, considering the abundance of adipose tissue in the human body and the high yield of adipose-derived stem cells (10- to 100-fold more than bone marrow–derived stem cells),5 adipose-derived stem cells still hold the potential to be an important source of endothelial cells for clinical tissue-engineering applications. We agree with Bertrand et al. that a more complex differentiation protocol, such as increased vascular endothelial growth factor concentrations, hypoxia, and shear stress, may significantly increase the endothelial cell differentiation of adipose-derived stem cells as reported by Planat-Benard et al.6 Our purpose was to evaluate the clinical potential of the only commercially available endothelial cell differentiation medium; thus, we did not use a more complicated differentiation protocol. Evaluation of the effects of such protocols on endothelial cell differentiation of adipose-derived stem cells will be a topic of our future research.
Isolation of endothelial cells from lipoaspirates by means of magnetic-activated cell sorting is an attractive idea. Our flow cytometric results also confirmed the presence of endothelial cells in the stromal vascular fraction in varying amounts. However, the number of endothelial cells is prone to fluctuate depending on the donor site and amount of lipoaspirate. In addition, in our own experience, magnetic-activated cell sorting reduces the viability of the cells significantly. To obtain a clinically relevant endothelial cell population, the stromal vascular fraction to be sorted by magnetic-activated cell sorting should be a considerably large one. We agree with Bertrand et al. that the combined use of adipose-derived stem cells and endothelial cells would be a promising approach for regenerative therapy, but future studies are necessary to compare the functional aspects of microvascular endothelial cells derived from stromal vascular fraction and endothelial cells derived from adipose-derived stem cells.
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