Influence of chondroitin sulfate on the biochemical, mechanical and frictional properties of cartilage explants in long-term culture

A recent study [Basalo et al., 2007. Chondroitin sulfate reduces the friction coefficient of articular cartilage. J. Biomech. 40(8), 1847–1854] has shown that the friction coefficient of bovine articular cartilage is reduced significantly by the supplementation of chondroitin sulfate (CS) at a concentration of 100 mg/ml. This result suggests that intra-articular injection of CS may be used as a prophylactic treatment against the progression of osteoarthritis. The objective of this study was to test the hypothesis that long-term culture of cartilage explants in CS produces no adverse mechanical, biochemical, or cytotoxic effects, while reducing the friction coefficient relative to the control group. Long-term cultures of live bovine articular cartilage explants were performed with incubation in media containing CS of three different concentrations (0, 10 and 100 mg/ml). Frictional tests (cartilage-on-glass) were performed under constant stress (0.5 MPa) for 3600 s and the time-dependent friction coefficient was measured. Samples incubated in a 100 mg/ml of CS solution exhibited a significantly lower equilibrium friction coefficient than the control (0.05±0.01 vs. 0.18±0.02 on Day 0, 0.04±0.01 vs. 0.14±0.04 on Day 7 and 0.04±0.01 vs. 0.15±0.06 on Day 14). Samples incubated in 10 mg/ml of CS did not exhibit any significant decrease in the friction coefficient. Cell viability and DNA content were maintained in all groups. However, after 28 days of culture, the Young's modulus and glycosaminoglycan content of explants incubated in 100 mg/ml of CS decreased to 5% and 40% of their initial levels, respectively. Based on this adverse outcome the hypothesis of this study is rejected, dampening our enthusiasm for the use of intra-articular CS injections as a prophylactic treatment in osteoarthritis.