Although growth factor therapy could be an attractive method for stimulating the repair of damaged cartilage matrix, there is evidence that with aging and/or with the development of osteoarthritis (OA), articular chondrocytes may become unresponsive to growth factor stimulation. The aim of the current study was to compare the ability of insulin-like growth factor+(IGF-1) and osteogenic protein+(OP-1), alone and in combination, to stimulate human normal and OA chondrocytes in culture.
Chondrocytes isolated by enzymatic digestion of cartilage obtained from subjects undergoing knee replacement for OA (n = 6) or from normal ankle joints of tissue donors (n = 7) were cultured in alginate beads in serum-free medium and treated for 21 days with 100 ng/ml IGF-1, 100 ng/ml OP-1, or both. Controls were treated with vehicle alone. The cultures were evaluated for cell survival, cell number by DNA analysis, matrix production by particle exclusion assay, and level of accumulated proteoglycan by dimethylmethylene blue assay.
After 21 days in serum-free alginate culture, survival of cells from OA cartilage was 65 ± 2% (mean ± SEM), while survival of cells from normal cartilage was significantly greater (82 ± 3%). Treatment with either IGF-1 or OP-1 alone minimally improved survival, while the combination IGF +OP significantly improved survival, to 87 ± 2% for OA cells and 95±1% for normal cells. Cell proliferation was noted only in the IGF+OP group; this was significant for both normal and OA cells (∼2-fold increase in DNA levels). Matrix production, assessed by particle exclusion and by proteoglycan accumulation, was greatest in the cells treated with IGF + OP in both normal and OA cultures. When proteoglycan levels were corrected for cell numbers (mg proteoglycan/ng DNA), a significant increase over control was noted with OP-1 alone and IGF IGF-1 alone, in both normal and OA cultures, with the greatest levels in the combination group (3-fold increase over control).
OP-1 was more potent than IGF-1 in stimulating proteoglycan production in both normal and OA cells. However, the best results were obtained with the combination, suggesting that combined therapy with IGF-1 and OP-1 may be an effective strategy for treating OA cartilage damage.