Transforming growth factor-beta in calcium alginate beads for the treatment of articular cartilage defects in the rabbit

Abstract

Purpose: Articular cartilage has only limited capability for intrinsic repair. The use of growth factors has been suggested to improve the repair of cartilage after injury. Reliable delivery systems for these agents are needed. In this study we tested calcium alginate for the delivery of TGF-beta in the treatment of osteochondral defects in the rabbit knee.

Type of study: Randomized trial animal study and basic science study.

Methods: In vitro, to establish the kinetics of TGF-beta release from the alginate, 125I- labeled TGF-beta was suspended in 1.2% sodium alginate at concentrations of 1 microg/mL and 10 microg/mL. Beads were formed from 50 microL aliquots and placed into standard culture medium by immersion in calcium chloride solution and incubated at 37 degrees C. A gamma counter was used to measure the amount of TGF-beta that was released into the medium at various time points. In vivo, osteochondral defects were created in the trochlear grooves of 32 New Zealand White rabbits. Defects were treated with plain alginate or with alginate containing TGF-beta at 20 ng/mL or 2,000 ng/mL. Untreated defects served as a control. Animals were killed after 6 and 12 weeks. Knee joints were evaluated grossly with a 12-point grading scale. Histologic sections of the repair tissue were stained with Safranin O and evaluated using a 24-point grading scale by 2 independent blinded observers. Mean scores and standard deviations were calculated. P values were determined using the Student t test.

Results: The TGF-beta was released at a surprisingly slow but steady rate. Release rates extrapolated from the gamma counter measurements were 0.25% per hour and 0.33% per hour, for the 1 microg/mL and 10 microg/mL beads, respectively. Gross analysis scores at 6 and 12 weeks resulted in higher scores for both TGF-beta groups without reaching statistical significance. The lower TGF-beta concentration reached the highest scores, whereas the higher concentration (2,000 ng/mL) resulted in increased osteophyte formation. Histologic analysis at 6 weeks resulted in average scores ranging from 14.5 for empty defects and 18.1 for alginate-treated defects, to 20.0 and 20.3 for the 2,000 ng/mL and 20 ng/mL TGF-beta groups, respectively (P <.05). At 12 weeks, histologic scores ranged from 14.9 for empty and 14.5 for alginate to 20.1 and 20.5 for the 2,000 ng/mL and 20 ng/mL TGF-beta groups, respectively (P <.05). These results indicate a significant improvement of the quality of the repair tissue at 6 and 12 weeks with TFG-beta treatment, especially at the lower concentration.

Conclusions: The use of alginate allows the controlled delivery of TGF-beta selectively to the site of injury, potentially avoiding systemic side effects. Furthermore, treatment with TGF-beta appears to improve the repair of articular cartilage defects. Longer-term studies are needed to assess whether the benefits of the TGF-beta treatment can be sustained.