In Vitro and in Vivo Growth Factor Delivery to Chondrocytes and Bone-Marrow-Derived Stromal Cells in Cartilage and in Self-Assembling Peptide Scaffolds

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Abstract

The inability of articular cartilage to repair itself after acute injury has been implicated in the development of osteoarthritis. The objective of this work was to develop methods for delivering growth factors to cartilage and to test the ability of a selfassembling peptide scaffold, (KLDL)3, with or without growth factors to augment repair. Delivery methods included growth factor adsorption, scaffold-tethering, and modification of growth factor structure.

(KLDL)3 was modified to deliver IGF-1 and TGF-β1 to chondrocytes and bone-marrow-derived stromal cells (BMSCs), respectively, by adsorption and by biotinstreptavidin tethering. This study showed that while TGF-β1 can be effectively delivered by adsorption, IGF-1 can not. Additionally, while tethering these factors provided longt-erm sequestration, tethering did not stimulate proteoglycan production in vitro.

A full-thickness, critically sized, rabbit cartilage defect model was used to test the ability of (KLDL)3 with or without chondrogenic factors (TGF-β1, dexamethasone, and IGF-1) and BMSCs to stimulate cartilage regeneration in vivo. (KLDL)3 alone showed the greatest repair after 12 weeks with significantly higher Safranin-O, collagen II immunostaining, and cumulative histology scores compared to untreated contralateral controls. Ongoing studies include the evaluation of (KLDL)3 in a clinically relevant sized equine defect co-treated with microfracture and subjected to strenuous exercise.

A fusion protein was created by adding a heparin-binding domain to IGF-1 (HBIGF-1), converting IGF-1 from a short-acting growth factor to one that can be retained and locally delivered in articular cartilage in vivo. It was shown that HB-IGF-1 is retained in cartilage through binding to negatively charged glycosaminoglycan chains, with chondroitin sulfate the most prevalent type in cartilage. HB-IGF-1 was shown to bind adult human cartilage and to be preferentially delivered and retained in rat articular cartilage after intra-articular injection. In contrast, unmodified IGF-1 was not detectable after intra-articular injection. These results suggest that modification of growth factors with heparin-binding domains may be a clinically relevant strategy for local delivery to cartilage.

Taken together, these results show that (KLDL)3 self-assembling peptide hydrogels are customizable for growth factor delivery and can promote cartilage repair in vivo. In addition, the fusion protein HB-IGF-1 is preferentially retained in cartilage tissue compared to un-modified IGF-1.

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