Vascularization of prevascularized and non-prevascularized fibrin-based human adipose tissue constructs after implantation in nude mice

Abstract

Adipose regeneration strategies have been hampered by the inability to supply an adequate vascular supply following implantation. Vascularization in vitro, also called prevascularization, is a promising method that could promote the vascularization of engineered adipose tissue constructs upon implantation. In this study we compared the ability of prevascularized-to-non-prevascularized fibrin-based human adipose tissue to promote vascularization. Human adipose tissue-derived stromal cells (ASCs) and different mixtures (1:1, 1:2 and 1:5) of ASCs with human umbilical vein endothelial cells (HUVECs) were cultured in fibrin at two different densities (1.0 × 10(6) and 10 × 10(6) cells/ml) for 7 days. Histological analysis revealed that prevascular structures formed in 1:5 ASC/HUVEC fibrin-based constructs seeded with a total of 10 × 10(6) cells/ml. These constructs and ASC-only constructs were implanted subcutaneously in athymic mice for 7 days and generated lipid-containing grafts. The numbers and densities of blood vessels within the ASC/HUVEC constructs were similar to those of ASC-only constructs. Furthermore, immunostaining studies demonstrated human-derived vasculature within a few of the ASC/HUVEC and ASC-only constructs. A subset of this human-derived vasculature contained erythrocytes, indicating integration with the host vasculature. In conclusion, our study indicated no difference in the rate of vascularization of prevascularized ASC/HUVEC and non-prevascularized ASC-only fibrin-based constructs, suggesting that prevascularization of these fibrin-based constructs does not promote vascularization. Our results further indicated that not only endothelial cells, but also ASCs may contribute to the formation of vascular lumina upon implantation. This finding is interesting, since it demonstrates the possibility of vascularized adipose tissue engineering from a single cell source.

Coculture of Stem Cells from Apical Papilla and Human Umbilical Vein Endothelial Cell Under Hypoxia Increases the Formation of Three-Dimensional Vessel-Like Structuresin Vitro

“…Such strategies include the provision of various proangiogenic factors, 21,22 genetic modification of cells to overproduce growth factors, 23,24 specific biomaterial design to mimic the extracellular matrix with high porosities, 25 and embedding ECs into engineered tissue constructs. 26,27 However, the time required for EC migration, angiogenic sprouting, and vasculogenesis is still too long to guarantee the viability of bioengineered tissue after implantation and for it to merge and fuse with host tissue. 28 It has been reported that extensive networks are formed at day 5 when engineered replacements are prevascularized with HUVEC before implantation.…”

In situ vascularization of injectable fibrin/poly(ethylene glycol) hydrogels by human amniotic fluid‐derived stem cells

“…Based on our in vitro data in similar hydrogels, [25] we had hypothesized that the development of robust vasculature would require the presence of both exogenous endothelial and perivascular cell sources; however, in similar subcutaneous mouse studies, vascularization was not significantly different between fibrin-based constructs seeded with MSC/HUVEC co-cultures compared to those seeded with MSC only. [18] Recent insight in to the secretome of AFSCs may help explain these results. Paracrine factors produced by AFSCs, including vascular endothelial growth factor, stromal cell-derived factor 1, interleukin 8, and monocyte chemotactic protein 1, were isolated and shown to be capable of enhancing vasculogenesis in a murine model.…”

“…[10,12,15] While some studies have shown that seeding endothelial cells into tissue constructs before implantation may improve in vivo perfusion and cell viability, [1,16,17] others have shown no difference between the rate of in vivo blood vessel formation in hydrogels pre-vascularized with endothelial cells in vitro compared to mesenchymal stem cell (MSC)-seeded hydrogels relying on in situ vascularization alone. [18] Studies have also shown that combining both endothelial cells and a perivascular cell source, such as MSCs or fibroblasts, is essential in the generation of robust functional vascular networks in vivo. [19][20][21] F o r P e e r R e v i e w 4 One potential source of both endothelial and perivascular cell types is amniotic fluidderived stem cells (AFSC).…”

Biomaterials to Prevascularize Engineered Tissues

“…Examples of endpoints include the time to blood perfusion of the implant with host circulation after implantation, changes in endothelial-cell-specific marker expression, total vessel length per unit area (e.g., centimeters per square centimeter) based on bright field microscopy or endothelial cell surface antibody staining (e.g., anti-human CD31), vessel density per unit crosssection area (e.g., vessel per square centimeter) after histology staining, and even evidence of new collagen synthesis in the implant [20][21][22].…”