675. Enhanced Survival of Chondrocytes over Expressing Insulin like Growth Factor I in Equine Cartilage Repair

Abstract

Top of pageAbstract Recent studies have shown that insulin-like growth factor (IGF-I) plays a powerful role in cell survival and prevention of programmed cell death. When recombinant IGF-I is combined with chondrocyte transplants, local upregulation of matrix production occurs in experimentally induced full-thickness cartilage defects resulting in morphological improvement of cartilage at the site of cartilage injury. This study was designed to test whether genetic modification of chondrocytes to over express IGF-I could enhance cartilage repair by improving chondrocyte survival. Sixteen horses arthroscopically had a 15 mm cartilage defect made in both femoropatellar joints. The defects were repaired with AdIGF-I transduced chondrocytes in one limb and na|[iuml]|ve chondrocytes in the opposite limb. Four horses were necropsied at 4 and 9 weeks and 8 horses at 8 months postoperative. Ten 10 mg of DNA was harvested from the repair tissue and Taqman|[trade]| quantitative real-time polymerase chain reaction (PCR) was used to assess the number of copies of the Y-chromosome marker SRY. A standard curve for the SRY was constructed using genomic DNA from male chondrocytes. A conversion factor of 6.6pg of DNA per diploid cell was used to calculate percentage of cell survival. A paired t test was used to compare cell survival between IGF-I-treated and control groups at each time point. Significance was set at P|[le]|0.05. Average percentage of SRY-positive (male, donor) cells present in the defects at 4 weeks, 9 weeks and 8 months was 4.8%, 0%, and 0.9% respectively (Figure 1). At 4 weeks there was a significantly greater cell survival after repair with AdIGF-I-modified cells when compared with control (P|[le]|0.05). At 8 months there was a trend towards greater cell survival in defects repaired with IGF-I expressing chondrocytes (P=.06). Chondrocyte survival in this study was positively influenced by genetic modification with AdIGF-I. While the range of percentage donor cells surviving (0-8%) is low, it is consistent with other studies quantifying perichondrial cell or chondrocyte survival in articular cartilage defects. Previously we have reported an average 4% survival of chondrocytes at 8 months following repair using this equine model and this PCR technique. While in that study, no differences were detected between BMP7-treated and control chondrocytes, the current study clearly shows a correlation between IGF-I treatment and cell survival, especially at the early time point.