VEGF-neutralized platelet-rich plasma with adipose-derived stromal vascular fraction enhanced osteochondral repair in a point-of-care goat model.

BACKGROUND/OBJECTIVE: Focal articular cartilage defects do not heal spontaneously. Platelet-rich plasma (PRP) is as an autologous source of growth factors that has been reported to promote tissue healing. However, PRP contains angiogenic factors such as vascular endothelial growth factor (VEGF) that are known to inhibit chondrogenesis and promote osteoarthritis progression. Mesenchymal stem cells (MSCs) have also shown promise in promoting focal cartilage repair, but MSC therapies typically require cell isolation and expansion before implantation in a second surgery. Adipose-derived stromal vascular fraction (SVF) is rich in MSCs and can be harvested and delivered in a single procedure. The purpose of this study was to determine the effect of VEGF-neutralized PRP on in vitro chondrogenesis and in vivo osteochondral repair when combined with an MSC-rich SVF in a single-stage point-of-care goat model. It was hypothesized that VEGF-neutralized PRP would enhance in vitro chondrogenesis and improve in vivo osteochondral repair when combined with SVF. METHODS: Adipose-derived MSCs (ASCs) were encapsulated in photocrosslinkable hydrogels supplemented with (1) Hanks' Balanced Salt Solution (HBSS), (2) PRP, (3) VEGF-neutralized PRP, or (4) transforming growth factor- β3 (TGF-β3) for in vitro experiments. Cell viability and gene expression were determined on days 3, 7, and 21. For in vivo experiments, ASC-rich SVF was procured and delivered in the aforementioned hydrogels to an osteochondral defect in a single-stage point-of-care goat model. At 6 months, osteochondral regeneration was characterised by gross appearance, histological grading, immunohistochemistry, biomechanical testing, and quantitative MRI. RESULTS: In vitro cell viability remained high, with no differences across groups. TGF-β upregulated chrondrogenic, fibrogenic, and hypertrophic gene expression. VEGF-neutralized PRP, as compared to native PRP, preferentially upregulated chondrogenesis while inhibiting fibrogenesis. In the point-of-care in vivo goat model, VEGF-neutralized PRP tended to best recapitulate native osteochondral macroscopic appearance, histology, immunohistochemical content, biomechanical properties (i.e., elastic modulus), and biochemical content on quantitative MRI, although results did not consistently reach statistical significance. By comparison, TGF-β upregulated hypertrophic markers with evidence of ectopic bone formation on histology, increased Collagen I and X on immunohistochemistry, supraphysiological elastic modulus, and overly dense biochemical content on quantitative MRI. CONCLUSION: Neutralization of VEGF in PRP enhanced in vitro chondrogenesis of adipose-derived MSCs and tended to best improve in vivo osteochondral regeneration when combined with stromal vascular fraction obtained in a single-stage point-of-care procedure in a clinically relevant goat model. VEGF neutralization in PRP tended to produce superior results compared to whole PRP, consistent with the known deleterious effect of angiogenic factors on cartilage integrity. Furthermore, VEGF-neutralized PRP promoted a hyaline cartilage phenotype as compared to TGF-β supplementation, which promoted a hypertrophic cartilage phenotype. THE TRANSLATIONAL POTENTIAL OF THE ARTICLE: This study suggests that tailoring PRP composition for specific pathologies may yield superior clinical effects. Notably, neutralization of angiogenic factors in PRP, such as VEGF, may enhance the efficacy of PRP in promoting osteochondral regeneration. Additional in vivo studies confirming the mechanisms underlying VEGF(-) PRP are needed. Clinical trials in which PRP composition is altered to either enrich or deplete components of known importance in specific disease pathogenesis should be considered but should comply with national and international regulatory standards.