Articulating motion decreases IL-1B induced cartilage extracellular matrix wear

Purpose: The cytokine interleukin-1β (IL-1β) stimulates a catabolic response in cartilage and has been used in vitro to model the extracellular matrix degradation seen in osteoarthritis (OA). Several groups have shown a protective effect of mechanical load and compression on IL-1β induced matrix damage in chondrocyte cultures and scaffold constructs. Torzilli et al. have demonstrated in multiple papers that this same effect is seen when applying compressive loads to cartilage explants. Our laboratory utilizes a novel in vitro cartilage loading simulator that better replicates the complex motions of loading, compression, and articulation of both the femoral condyles and tibial plateau that are seen in vivo joint articulation. Therefore, we aimed to evaluate the combined effects of articulating motion and of IL-1β on cartilage integrity in an in vitro dual-rotating system. We hypothesized that articulation would decrease the effects of IL-1β on matrix degradation as observed through the loss of glycosaminoglycans. Methods: Fresh twenty-four week old bovine stifle joints were obtained from a local abattoir. Full thickness (∼3 mm) oval cartilage explants were removed by custom punch from the femoral trochlear groove. Explants were randomized into four test groups (n = 4 each): articulation + IL-1β, articulation only, no articulation + IL-1β, and control (no articulation, no IL-1β). Explants underwent a five-day pre-culture in media (DMEM: F12+ITS). Groups exposed to IL-1β (100 ng/mL) experienced a one day pretreatment condition before testing, and IL-1β exposure was continued throughout the three day period. Testing was conducted in the four station joint motion simulator, housed in an incubator with 95% humidity, 5% CO2 and 37°C [Fig. 1]. Explants were laterally confined in porous polyethylene platens and loaded to 40N (∼2 MPa) while articulated against a ceramic ball for three hours per day for three days (ball rotation: ±30° at 0.1 Hz, explant rotation: ±15° at 0.5 Hz). Culture media was individually collected and replenished at the end of each test and rest period. Immediately after test completion on day three, explants were qualitatively examined for cell viability with LIVE/DEAD® assay. The collected wear media from the three test days were examined for total glycosaminoglycan (GAG) content using the DMMB assay. A two-way ANOVA was used for statistical analysis of cumulative GAG release while student t-tests were used for analysis of daily GAG release with p-value less than 0.05 being significant. Results: There were no visual differences in cell viability of non-articulated explants, regardless of exposure to IL-1β. However, articulation against the ceramic ball caused increased superficial zone cell death, regardless of exposure to IL-1β. As expected, there was a significant increase in cumulative GAG release due to the presence of IL-1β versus the absence of IL-1β (p = 0.003) [Fig. 2]. There was a trend towards a decrease in GAG release due to articulation (p = 0.087). However, no interaction between articulating motion and IL-1β was detected (p = 0.8311). Significant differences in media GAG content were observed after day three of testing [Fig. 3]. The media GAG content of the IL-1 treatment alone group was significantly higher than that of the other groups (p < 0.01); while the articulation alone group had a significantly lower media GAG content when compared to the other groups (p < 0.05). Conclusions: This study uses a novel model of joint movement to address the effects of articulating load and motion on IL-1β induced cartilage matrix damage. The data showed that the in vitro articulating motion applied in this tribosystem may be promising for minimizing the effects of IL-1β, which follows previous findings in the literature that mechanical loading decreases IL-1β matrix degradation. Based on the daily GAG release, we suspect that a longer time period would show more significant differences between the interactions of articulation and IL-1β. Future studies shall include extending the testing period as well as more extensive analysis of the media and cartilage for markers of GAG and collagen damage.