Comparison of Efficacy of Endogenous and Exogenous IGF-I in Stimulating Matrix Production in Neonatal and Mature Chondrocytes.

OBJECTIVE: The goal of this study was to compare the efficacy of endogenous upregulation of IGF-I by gene therapy and exogenous addition of insulin-like growth factor I (IGF-I) in enhancing proteoglycan synthesis by skeletally mature and neonatal chondrocytes. Chondrocyte transplantation therapy is a common treatment for focal cartilage lesions, with both mature and neonatal chondrocytes used as a cell source. Additionally, gene therapy strategies to upregulate growth factors such as IGF-I have been proposed to augment chondrocyte transplantation therapies. METHODS: Both skeletally mature and neonatal chondrocytes were exposed to either an adeno-associated virus-based plasmid containing the IGF-I gene or exogenous IGF-I. RESULTS: Analysis of IGF-I and glycosaminoglycan production using a 4-parameter dose-response model established a clear connection between the amount of IGF-I produced by cells and their biosynthetic response. Both neonatal and mature chondrocytes showed this relationship, but the sensitivities were quite different, with EC50 of 0.57 ng/mL for neonatal chondrocytes and EC50 of 8.70 ng/mL IGF-I for skeletally mature chondrocytes. CONCLUSIONS: These data suggest that IGF-I gene therapy may be more effective with younger cell sources. Both cell types were less sensitive to exogenous IGF-I than endogenous IGF-I.