Hyperoxic or hypoxic environment

: We read the article by Khan et al. (2017) in a recent issue of this journal with great interest. We would like to congratulate the authors for this report. In the article, the authors focused primarily on the characteristics of adiposederived mesenchymal stem cells (Ad-MSCs) by altering culture environment. The results of the study showed that culture medium containing 0.5% gelatin enhanced the proliferation rate, induced immunosuppression, and activated BMP-7 and the wnt/AXIN/β-catenin pathway in Ad-MSCs. However, we believe there is a misunderstanding in the introduction section of the article. A review of the literature shows that certain characteristics of MSCs can be modified with altered culture environments or preconditioned incubation processes. Khan et al. also cited a review published by Song et al. in 2010, as mentioned in the Introduction. This study indicated that preconditioning MSCs under hypoxic conditions enhanced the activity of the MSCs, suggesting a new perspective for the cellular treatment of cardiac tissue damages. In this review, hypoxic conditions were shown to have cytoprotective effects for MSCs, regulated paracrine factors, and increased the VEGF secretion (Song et al., 2010). Likewise, several studies with different designs in the literature yielded similar results (Kadle et al., 2016; Ciria et al., 2017). Therefore, we believe that the term "hyperoxic conditions" mentioned in the introduction of Khan et al.'s article (in citation to the study of Song et al.) is confusing. We recommend that this erroneous term be corrected to prevent any misunderstanding for the readers. We believe that the authors of the article would regard our opinion as a contribution.