Adipose tissue-derived stem cells in a fibrin implant enhance neovascularization in a peritoneal grafting site: a potential way to improve ovarian tissue transplantation.

STUDY QUESTION: Do two different concentrations of human adipose tissue-derived stem cells (ASCs) embedded inside a fibrin scaffold have the potential to differentiate into vessels and aid vascularization in a peritoneal grafting site intended for ovarian tissue transplantation? SUMMARY ANSWER: Human ASCs in low and high concentrations differentiated into vessels when transplanted to mouse peritoneum inside a fibrin matrix, but only high ASC concentrations significantly increased human vessel area 14 days after transplantation. WHAT IS KNOWN ALREADY: ASCs have multilineage differentiation potential, including proangiogenic properties and have been used in tissue engineering to enhance vascularization in transplanted tissues. Fibrin has been studied and used as an ASC-compatible biomaterial. STUDY DESIGN, SIZE, DURATION: In vivo experimental model using 22 severe combined immunodeficient mice. In total, 16 mice (eight per group) were intraperitoneally grafted with a fibrin scaffold loaded with two different human ASC concentrations (either 150 000 [L-ASC] or 1 500 000 [H-ASC] cells) and lithium phthalocyanine (LiPc) crystals as oxygen-sensitive probes. Six mice were grafted with an empty fibrin (EF) implant containing only LiPc and served as controls. Levels of partial pressure of oxygen (pO2) in implants were monitored in vivo by electron paramagnetic resonance oximetry (EPR). ASC identification, proliferation, and host and human vascularization were analyzed by immunohistochemistry (IHC). All analyses were performed on post-grafting Days 3, 7 and 14. PARTICIPANTS/MATERIALS, SETTING,
METHODS: Prospective experimental study conducted at the Gynecology Research Unit, Université Catholique de Louvain. All materials were used to perform pO2 measurements (EPR oximetry), as well as histological (hematoxylin-eosin staining) and IHC (anti-human vimentin, anti-human Ki67, anti-mouse and human double CD34) analyses. MAIN RESULTS AND THE ROLE OF CHANCE: A significant increase in pO2 in implants was observed in all groups between Days 3 and 7 (P < 0.001). ASC-loaded implants displayed a tendency towards increased pO2 levels from Days 7 to 14, not observed in EF implants. ASC-loaded implants showed differentiation into human CD34-positive vessels. Total CD34-positive endothelial area was correlated to pO2 values obtained by EPR oximetry (r = 0.6506, P = 0.0019). In the H-ASC group, a greater human CD34-positive vascular surface area was found compared to the L-ASC group 14 days after transplantation (P < 0.0049). LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: As demonstrated by our results, ASCs transplanted inside a fibrin matrix can differentiate into CD34-positive human vessels. However, other possible mechanisms involved in ASC angiogenic behavior remain to be investigated. WIDER IMPLICATIONS OF THE
FINDINGS: High concentrations of ASCs loaded inside a fibrin scaffold could serve as a substrate to prepare a peritoneal grafting site over 14 days, in order to enhance vascularization once human ovarian tissue is grafted. Our proposed preparation of the grafting site would not only benefit ovarian tissue transplantation, but also other experimental avascular grafting procedures. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS-PDR Convention T.0077.14, Télévie Grant no. 7.6515.16F awarded to DDM and Grant 5/4/150/5 awarded to M.M.D. [CAA is FRS-FNRS research associate]), Fonds Spéciaux de Recherche, and Fondation St Luc, Foundation Against Cancer, and donations from the Ferrero family. None of the authors have any competing interests to declare.