Bioequivalence and Dose-Response of Adipose Derived Cells in Augmentation of Random Pattern Skin Flap Survival

Purpose: Adipose derived cells have demonstrated proangiogeneic potential in skin flap survival^1-2. However, many questions are left unanswered and impede easy translation to clinical practice. No study to-date has compared the relative efficacy of subtypes of adipose derived cells or demonstrated dose-response relationships for optimal dosing. This preclinical study seeks to compare and demonstrate dose-dependent effect of different adipose derived cells in promoting survival of random pattern flap in a rodent dorsal skin flap model, and to investigate the potential differences in mechanism involved in their efficacy.

Methods and materials: Thirty-five adult Sprague-Dawley rats were randomized into one control and six treatment groups. Allogeneic rat adipose-derived stem cells (rADSCs) characterized using differentiation assays and flow cytometric analysis were used in three dosage groups (ie. 0.4x10⁶, 2x10⁶, 10x10⁶cells respectively), and autologous stromal vascular fraction (rSVF) were isolated from the inguinal fat pads and used in another three dosage groups (ie. 0.4x10⁶, 2x10⁶, 10x10⁶cells respectively). A caudally based 3x10cm dorsal skin flap was raised in each animal. Control medium or adipose-derived cells (ie. rADSC or rSVF) were injected sub-dermally into the panniculus carnosus distal to the mid-length of the flaps before inset. Animals were observed to postoperative day 7 before image recording of flap for flap necrosis and harvest of tissue for quantitative polymerase chain reaction (qPCR) analysis and immunohistofluorescence (IHF) analysis.

Results: The rADSC were immunophenotyped to be CD31-, CD34-, CD45-, CD73+, and CD90+ and the cells can be induced into the chondrogenic, osteogenic and adipogenic lineages. Dose-dependent trends of flap necrosis were observed in both rADSC and rSVF. The 2x10⁶cells treatment groups demonstrated optimal efficacy in the dose range (ie. control group 45.3% necrosis versus 29.2% and 26.6% flap necrosis in rADSC and rSVF groups respectively). The 10x10⁶ cells treatment groups were noted to have a possible adverse effect on flap survival (ie. rADSC with 47.4% and rSVF with 47.3% flap necrosis). qPCR and IHF analyses demonstrated upregulation of proangiogeneic, lymphangiogeneic and antiapoptotic factors in treatment groups, and differences between rADSC and rSVF groups.

Conclusion: This study reports the dose-dependent effect of adipose derived cells in promoting random pattern flap survival and more importantly the bioequivalence in efficacy between allogeneic rADSC and autologous rSVF. An optimal dose for promotion of flap survival probably exist with higher doses being counterproductive. The mechanisms of action between rADSC and rSVF in promoting flap survival may differ and requires further investigation to elucidate.

References:

1. Lu F, Mizuno H, Uysal CA, Cai X, Ogawa R, Hyakusoku H. Improved viability of random pattern skin flaps through the use of adipose-derived stem cells. Plast. Reconstr. Surg. 2008; 121: 50-58.
2. Foroglou P, Karathanasis V, Demiri E, Koliakos G, Papadakis M. Role of adipose-derived stromal cells in pedicle skin flap survival in experimental animal models. World J Stem Cells 2016; 8(3): 101-105.