Adipose Stem Cells Incorporated in Fibrin Clot Modulate Expression of Growth Factors

Abstract

Purpose: To evaluate the platelet capture rate of whole blood fibrin clots and the expression, secretion, and retention of the growth factors vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and basic fibroblast growth factor (bFGF) from fibrin clots and to determine how these levels may be modulated by allogeneic adipose-derived stem cells (ASCs).

Methods: Whole blood from 10 human volunteers was transferred to a clotting device and the platelet capture rate determined. Two experimental conditions and 1 control were evaluated over 2 weeks in vitro. Clots made from human whole blood without ASCs, clot(−)ASC, were compared with clots with ASCs incorporated, clot(+)ASC, and a control group of synthetic polyethylene glycol gels with ASCs incorporated, control(+)ASCs. All conditions were examined for secretion and retention of VEGF, PDGF, and bFGF via enzyme-linked immunosorbent assay and immunohistochemistry. The analysis of platelet retention for clots made with this device was performed.

Results: Enzyme-linked immunosorbent assay analysis showed significantly higher (P < .001) secretion of VEGF in clot(+)ASC compared with clot(−)ASC or control(+)ASC. In contrast, clot(−)ASC produced soluble PDGF, and the addition of ASCs results in decreased soluble PDGF with concomitant increases in PDGF immunoreactivity of ASCs. Soluble bFGF levels were low in clot(−)ASC, and were found to increase at early time points in clot(+)ASC. Furthermore, bFGF immunoreactivity could be detected in clot(+)ASC, whereas no bFGF immunoreactivity is present in clot(−)ASC or control(+)ASC. Control(+)ASC displayed a spike in bFGF secretion at day 0, which may be due to a stress response elicited by the encapsulation process. Approximately 98% of available platelets in whole blood were concentrated in the clot on formation.

Conclusions: Fibrin clots made by this method retain high concentrations of platelets, and when incorporated with ASCs show modulated secretion and immunoreactivity of VEGF, PDGF, and bFGF.

Clinical Relevance: Whole blood fibrin clots capture platelets and release growth factors, and the addition of ASCs increases VEGF release for up to 2 weeks after clot formation. This suggests that whole blood fibrin clots may be a viable scaffold and delivery vehicle for future stem cell treatments.