Responsiveness of bovine chondrocytes to growth factors in medium with different serum concentrations

Autologous transplantation of chondrocytes is currently under investigation as a potential therapy to stimulate intrinsic repair in articular cartilag e defects. The quality of the repair tissue may benefit from the preservati on of the characteristic chondrocytic phenotype of the transplanted cells t ogether with the production of a new extracellular matrix composed of colla gen type ii and larger proteoglycans. A number of growth factors are believ ed to play an important role in the process of generating new cartilage rep air tissue. In this study, the dose-dependent response of bovine chondrocyt es to recombinant human insulin-like growth factor-1, recombinant human tra nsforming growth factor-beta 2, and recombinant human bone morphogenetic pr otein-2 was studied in an alginate culture system under different culture c onditions. The chondrocytes were cultured in medium with increasing concent rations of fetal calf serum. The cultures were assessed by the total amount of DNA, quantitative and qualitative synthesis of proteoglycan, production of nitric oxide, and histology. Cells cultured in the presence of each gro wth factor had an equal, nonsignificant stimulation of DNA synthesis compar ed with those cultured in basal medium alone. Recombinant human insulin-lik e growth factor-1 and recombinant human transforming growth factor-beta 2 s timulated proteoglycan synthesis in a dose-dependent and reversed dose-depe ndent fashion, respectively. Recombinant human bone morphogenetic protein-2 stimulated proteoglycan synthesis significantly only in the absence of fet al call serum or in the presence of small amounts of the serum. Overall, pr oteoglycan synthesis dramatically decreased with the addition of each growt h factor as the concentration of fetal calf serum in the medium decreased. and the dose-dependent stimulation pattern, as observed for recombinant hum an insulin-like growth factor-1 and recombinant human transforming growth f actor-beta 2. disappeared. Apart from a moderate increase in mRNA for aggre can and decorin, the growth factors did not greatly affect the type of prot eoglycans synthesized. Histological examination confirmed the presence of a dense pericellular matrix deposition, especially when the chondrocytes wer e cultured in the presence of recombinant human insulin-like growth factor- 1 or recombinant human transforming growth factor-beta 2. The results indic ate that these growth factors can stimulate qualitatively superior matrix p roduction and that the responsiveness of the chondrocytes to the growth fac tors changes with the culture conditions. Further knowledge about the inter action between chondrocytes, growth factors, and the external environment i s important to stimulate chondrocytes to produce adequate repair tissue in cartilage defects in vivo. Insulin-like growth factor-1 especially seems ca pable of stimulating, in the most consistent and predictable fashion. quali tatively superior proteoglycan synthesis by differentiated chondrocytes. Ad ditional in vivo studies are needed to evaluate the potential of these grow th factors as stimulators in cartilage repair.