Human mesenchymal stem cells are advantageous in both basic and applied research. The use of this adult cell type overpasses ethical issues-compared to the use of embryonic or other cells-being one of the most promising areas of study in autologous tissue regeneration engineering and cell therapy1, such as the neoplastic area, the treatment of degenerative diseases, and therapeutic applications in the reconstructive surgery area2,3,4,5. It has been previously reported that there is an abundant source of mesenchymal multipotent and pluripotent stem cells in the stromal vascular cell fraction of adipose tissue6,7. These ADSC are considered great candidates for use in cell therapy and transplantation/infusion since a considerable number of cells with a strong capacity for expansion ex vivo can be easily obtained with a high yield from a minimal invasive procedure5,8.
It was also demonstrated that adipose tissue presents a greater capacity to provide mesenchymal stem cells than two other sources (bone marrow and umbilical cord tissue)9. Besides being poorly immunogenic and having a high ability to integrate into the host tissue and to interact with the surrounding tissues4,10, ADSC has a multipotent capacity of differentiation into cell lines, with reports of chondrogenic, osteogenic, and myogenic differentiation under appropriate culture conditions11,12,13, and into cells, such as pancreatic, hepatocytes, and neurogenic cells14,15,16.
The scientific community agrees that the mesenchymal stem cells' immunomodulatory effect is a more relevant mechanism of action for cell therapy17,18,19 than their differentiation property. One of the most significant merits of the ADSC use is the possibility of autologous infusion or grafting, becoming an alternative treatment for several diseases. For regenerative medicine, ADSC have already been used in cases of liver damage, reconstruction of cardiac muscle, regeneration of nervous tissue, improvement of skeletal muscle function, bone regeneration, cancer therapy, and diabetes treatment20,21.
To this date, there are 263 registered clinical trials for the evaluation of ADSC's potential, listed on the website of the United States National Institutes of Health22. Different protocols to harvest adipose tissue have been established, but there is no consensus in the literature about a standardized method to isolate ADSC for clinical use23,24. Lipoaspirate processing methods during and after surgery can directly affect cell viability, the final cellular yield25, and the quality of the ADSC population20. Regarding the surgical pre-treatment, it is not well established which surgical pre-treatment technique yields a more significant number of viable cells after isolation or whether the anesthetic solution injected into adipose tissue affects cell yield and its functions26. Similarly, the difference between techniques for obtaining adipose cells can lead to as much as a 70% decrease in the number of viable ADSC20. According to the literature, mechanical treatments to obtain cell populations with high viability-including ultrasound-should be avoided, for they can break down the adipose tissue20. However, the manual fat aspiration method with syringes is less harmful, causing less cell destruction, with tumescent liposuction yielding a significant number of cells with the best quality26.
This technique uses a saline solution with lidocaine and epinephrine that is injected into the liposuction area. For each 3 mL volume of solution injected, 1 mL is aspirated. In this study, the wet liposuction technique was performed, in which for each 1 mL of adrenaline and saline solution injected, 0.2 mL of adipose tissue is aspirated. The use of digestive enzymes, especially collagenase, is common for the process of isolating ADSC.
After the first isolation step in the laboratory, the final pellet is called stromal vascular fraction (SVF). It contains different cell types27, including endothelial precursor cells, endothelial cells, macrophages, smooth muscle cells, lymphocytes, pericytes, pre-adipocytes, and ADSCs, which are capable of adhesion. Once the final isolation is concluded from in vitro cultures, cells that did not adhere to the plastic are eliminated in medium exchanges. After eight weeks of expansion, medium changes, and passages, ADSCs represent most of the cell population in the flasks20. One of the most significant advantages of using isolated adipose-derived stem cells for a possible future therapy is the possibility of cryopreservation. It was demonstrated that cryopreserved lipoaspirate is a potential source of SVF cells even after 6 weeks of freezing28, with biological activity even after 2 years of cryopreservation29, and full capability to grow and differentiate in culture30. However, during the thawing process, a considerable percentage of cells is usually lost31. Therefore, the lipoaspirate removal process and the following methods of cell isolation must ensure the highest cell yield.
This study describes a faster methodology for collecting and isolating ADSC, demonstrating high cellular yield and viability for better efficiency of cellular therapeutics. Furthermore, the effect of this improved technique after long-term SVF cryopreservation was evaluated.