The Effects of Graded Densities of Lipoaspirate on Fat Graft Survival
Robert J. Allen, Jr., MD, Orlando Canizares, MD, Phuong D. Nguyen, MD, Carrie Scharff, BA, Vishal D. Thanik, MD, Stephen M. Warren, MD, Pierre B. Saadeh, MD, Sydney R. Coleman, MD, Alexes Hazen, MD.
New York University Langone Medical Center, New York, NY, USA.
Autologous fat represents perhaps the ideal filler for use in plastic surgery; however, the results of microstructural fat grafting have been conflicting and equivacol. Up to this point, the mechanisms responsible for fat graft survival have not been clearly elucidated, and much debate has arisen over the possible role of adipocytes, progenitor cells, and cytokines in this process. Whereas recent studies have focused on the effects that different harvesting and processing techniques have on the cellularity of fat grafts, in this study, we hypothesize that the graded densities of fat grafts that result from centrifugation have different cellular and biological characteristics that influence the amount of fat graft survival following injection.
Syringe-assisted lipoaspirate was harvested from human subjects undergoing routine liposuction. 10cc of this lipoaspirate was then centrifuged for 3 minutes at 300(x)g. The bloody fraction was drained, and the oil was decanted and wicked from the top. Of the resulting processed lipoaspirate, 1.5cc of the highest density (HD) and lowest density (LD) fat was separated for either injection or cellular and biological analysis. The relative number of functional adipocytes in each fraction prior to injection was measured using a glycerol-3-phosphate dehydrogenase (G3PDH) assay. Additionally, the number of progenitor cells and the levels of a variety of proteins were analyzed in each fraction. HD or LD fat that was injected into the dorsal subcutaneous tissues of adult FVB mice was harvested and weighed at 4 and 6 weeks post-injection to determine the amount of fat graft survival.
Low density fractions had increased G3PDH activity (4.37 vs. 1.55 mUnits/mL), indicating an increased number of functional adipocytes in this fraction at baseline. Greater percentages of HD fat grafts survived at both 4 and 6 weeks post-injection compared to LD fat grafts (81.0% vs. 76.4% and 67.4% vs. 63.0%, respectively). Vascular endothelial growth factor (VEGF) concentrations were elevated in HD fractions over LD fractions at all time points studied: 33% at baseline, 1,510% at 4 weeks, and 43% at 6 weeks post-injection. Stromal cell-derived factor-1α (SDF) concentrations were similar in both fractions except at the 6 week time point, when [SDF] were 298% greater in the HD grafts. Additionally, HD fat grafts were found to have more progenitor cells/g than LD fat grafts at baseline (6.45 x 104 vs. 3.65 x 104).
Our results demonstrate that HD fractions of lipoaspirate are superior to LD fractions in terms of fat graft survival. The mechanism responsible for this finding appears to be vasculogenic in nature, as HD fractions contained fewer functional adipocytes, more progenitor cells, and increased concentrations of several vasculogenic mediators (VEGF, SDF). This work is the first of its kind, revealing that centrifugation of lipoaspirate creates densities of fat with varying biological characteristics that may lead to improved fat graft survival clinically.