Treatment with insulin-like growth factor-1 increases chondrogenesis by periosteum in vitro.

The repair of defects in articular cartilage with hyaline tissue that is resilient to wear is a challenging problem. Fibrocartilaginous tissue forms in response to injury through the articular surface and degenerates under mechanical load. Because periosteum contains cells, which are capable of synthesizing cartilage matrix proteins, it has been used to repair defects in articular surfaces. Treatment of periosteal grafts with growth factors, particularly those that elicit chondrocyte gene expression, may improve tissue regeneration. Gene expression by periosteal explants in vitro was measured. Expression of type II collagen and aggrecan mRNA was increased in response to treatment with IGF-I. Furthermore, IGF-I treatment caused an increase in type II collagen and aggrecan mRNA that was time and concentration dependent. The effect of short and long-term (continuous) incubations was compared to determine if a pretreatment could be used to condition a graft for subsequent surgical use. Short-term incubation in vitro with IGF-I followed by incubation without IGF-I was nearly as effective at increasing expression of type II collagen and aggrecan mRNA as incubation for the same length of time with IGF-I present continuously in the culture media. Treatment with IGF-I also produced cell clustering and nodule formation which are indicative of chondrogenesis. These results suggest that pretreatment with IGF-I in vitro may enhance the effectiveness of a graft to produce hyaline cartilage in vivo. Whether the cellular and molecular changes we have observed can lead to the formation of tissue that withstands the mechanical forces exerted by weight bearing remains to be determined.

Marrow stromal cells embedded in alginate for repair of osteochondral defects.

Articular cartilage defects of sufficient size ultimately degenerate with time, leading to arthritic changes. Numerous strategies have been used to address full-thickness cartilage defects, yet none thus far has been successful in restoring the articular surface to its preinjury state. We compared the effects of agarose, alginate, and type I collagen gels on the expression of cartilage-specific markers from rabbit marrow stromal cells and then assessed the in vivo effects of cells seeded in alginate beads on the repair of full-thickness osteochondral defects in the rabbit model. Marrow aspirates from rabbits were cultured and the stromal population selected. Marrow stromal cells were then placed in either 1.2% w/v alginate, type I collagen gels (3 mg/mL), or 0.5% agarose suspension culture. After 2, 5, 10, and 20 days in culture, the RNA was extracted and analyzed by reverse transcription polymerase chain reaction for the cartilage-specific markers aggrecan and type II collagen. The strongest increase in aggrecan and type II collagen gene expression was found in the agarose suspension followed by alginate; type I collagen gels induced the lowest levels. Alginate beads were chondrogenic and maintained their size and consistency over time in culture, whereas the cell-seeded collagen gels invariably contracted. Full-thickness defects measuring 3 x 6 mm x 3 mm deep were then created in the medial femoral condyles of rabbit knees and filled with alginate beads, alginate beads seeded with stromal cells, or left empty. Alginate beads containing stromal cells remained within the defects and progressively filled the defects with regenerate tissue. Histologic analysis showed viable, phenotypically chondrogenic cells in the defects. The matrix stained positive with safranin O, indicating proteoglycan synthesis, and bonding between the regenerate and host tissue was excellent. We have shown quantitative differences in the chondrogenic effects of the biomaterials tested. Alginate induces the chondrogenic phenotype in marrow stromal cells in vitro, and possesses the necessary physical characteristics and handling properties to support cells and serve as a carrier to fill full-thickness osteochondral defects in vivo.