Summary

This work provides initial evidence that healthy synovium might have a protective effect on injured cartilage, thus suggesting a new avenue in exploring prevention of PTOA.

Abstract

Normal synovium plays an important protective role for cartilage, while inflamed synovium can lead to degenerative changes. However, the effect of normal synovium on damaged cartilage remains unknown. The purpose of this study is to investigate whether normal synovium has a protective effect on damaged cartilage.

Fresh human tali and femoral condyles were collected through the Gift of Hope Organ and Tissue Donor Network (Itasca, IL) from 7 human donors with no history of joint disease (mean age; 39.0 year-old, 4 males and 3 females). Only specimens with normal gross morphology were used. Two cartilage damage models were introduced: 1) the treatment with high dose of IL-1ß (10ng/ml); or 2) damage created by mechanical impaction using the pneumatic pressure controlled impactor (600 N within 2 ms). IL-1ß was added to cartilage explants for 48 hours before co-culture. The mechanical impaction was performed when cartilage was still attached to subchondral bone. Grossly normal cartilage explants (8 mm) and synovium (8 mm) from both joints were harvested and randomly assigned to one of six treatment groups (n = 5 in each group): non-treated cartilage without or with synovium (Group 1 or 2), IL-1ß-treated cartilage without or with synovium (Group 3 or 4), impacted cartilage without or with synovium (Group 5 or 6). Samples were collected at 0, 2, and 14 days after co-culture and assessed for the percentage of live cells and histology with Safranin O staining. The percentage of live cells was counted in the superficial zone and the middle/deep zone. Histological grading was conducted based on modified Mankin score.

There were no significant differences in the percentage of live cells between Group 1 and 2. Damaged cartilage in both models displayed elevated cell death especially in the superficial layer at 0, 2, and 14 days (Group 3: 56.4 ± 20.0%, 44.5 ± 11.5%, and 57.6 ± 16.3%; Group 5: 14.8 ± 5.3%, 12.8 ± 13.2%, and 20.1 ± 4.1%, respectively). In the presence of synovium, chondrocyte survival significantly increased at 2 and 14 days (Group 4: 75.3 ± 4.7% and 77.8 ± 7.8%, P< 0.01 and P<0.02: Group 6: 31.8 ± 13.7% and 33.4 ± 14.3%, P = 0.03 and 0.04, respectively). For histological analysis, non-treated cartilage (Group 1 and 2) had a normal structure through 14 days culture. Mankin score progressively increased in damaged cartilage (Group 3: 1.0 ± 1.41, 2.2 ± 1.8, and 3.25 ± 1.64; Group 5: 3.0 ± 1.2, 3.6 ± 1.1, and 4.6 ± 0.5 at 0, 2, and 14 days). In the presence of synovium, Mankin score was decreased at 2 and 14 days (Group 4: 0.8 ± 1.3, and 0.8 ± 0.8, P = 0.087 and P< 0.01: Group 6: 1.0 ± 0.0 and 1.6 ± 0.5, P =0.02 and < 0.01, respectively).

In conclusion, the results of this study demonstrate that healthy synovium exhibits a protective effect on damaged cartilage in two injury models as evidenced by increased cell survival and improved histological appearance, thus providing new insight into a potential for preventing PTOA.