Supplementation with Extracellular Vesicles Derived from Adipose-Derived Stem Cells Increases Fat Graft Survival and Browning in Mice: A Cell-Free Approach to Construct Beige Fat from White Fat Grafting

Sir: We read with great interest the article entitled “Supplementation with Extracellular Vesicles Derived from Adipose-Derived Stem Cells Increases Fat Graft Survival and Browning in Mice: A Cell-Free Approach to Construct Beige Fat from White Fat Grafting” by Zhu et al.1 in Plastic and Reconstructive Surgery. The authors confirmed that extracellular vesicles derived from adipose-derived stem cells promoted fat graft survival and browning using a murine model of fat grafting. The authors’ work provided new evidence for the role of extracellular vesicles in regenerative medicine. As the media of intercellular communication, extracellular vesicles contain macromolecules that regulate biological behaviors, including miRNA, mRNA, long noncoding RNA, and DNA. Because of the advantages of low immunogenicity, stable viability, and availability of mass production, research on extracellular vesicles is a hot topic in regenerative medicine. Thus, we would like to ask for some detailed information about the design of this study, namely, how was the dose and frequency (0.2 ml of extracellular vesicles, 100 μg/ml once per week for 12 weeks) of extracellular vesicle injection determined? In addition, for extracellular vesicle preparation, why did the authors use human lipoaspirates rather than adipose tissue from the mice? In the discussion section, the authors mentioned that the graft survival was less satisfactory in this study, possibly because of the mechanical damage to the grafts. Mechanical damage could occur in the cutting of inguinal fat and fat injection. The authors injected fat particles with a 19-gauge needle. We usually use a 16-gauge rather than a 19-gauge needle based on the following considerations: on the one hand, the fine needle produces high shear force, which impairs graft viability.2 On the other hand, the fat particles need to be cut smaller to pass through the fine needle, leading to long extracorporeal ischemia time. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Zhongyang Sun, M.D.Hongyi Zhao, M.D.Department of Plastic SurgeryBeijing HospitalNational Center of GerontologyInstitute of Geriatric MedicineChinese Academy of Medical SciencesBeijing, People’s Republic of China