Effects of dexamethasone and dynamic loading on cartilage of human osteochondral explants challenged with inflammatory cytokines

Post-traumatic osteoarthritis (PTOA), characterized by articular cartilage degradation initiated in an inflammatory environment after traumatic joint injury, can lead to alterations in cartilage biomechanical properties. Low dose dexamethasone (Dex) shows chondroprotection in cartilage challenged with inflammatory cytokines, but little is known about the structural biomechanical response of human cartilage to Dex in such a diseased state. This study examined changes in the biomechanical properties and biochemical composition of the cartilage within human osteochondral explants in response to treatment with exogenous cytokines, Dex, and a regimen of cyclic loading at the start and end of culture. Osteochondral explants were harvested from five pairs of human ankle talocrural joints (Collins grade 0-1) and cultured for 10 days with/without exogenous cytokines (100 ng/ mL TNF alpha, 50 ng/mL IL-6, 250 ng/mL sIL-6R) +/- Dex (100 nM). Biomechanical testing on day-0 and day-10 enabled estimation of the unconfined compression equilibrium modulus (Ey), dynamic stiffness (Ed) and hydraulic permeability (kp) of cartilage excised from bone, accompanied by biochemical assessment of media and cartilage tissue. Dex preserved chondrocyte cell viability and decreased sulfated glycosaminoglycan (sGAG) loss and nitric oxide release, but did not alter Ey, Ed and kp (before or after loading) on day-10. In the cytokine/ cytokine+Dex treated groups, sGAG content exhibited a weaker correlation with Ey and Ed than at baseline, suggesting an important role for structural rather than biochemical changes in producing biomechanical alterations in response to cytokines and Dex. These findings aid in forming a more complete profile of potential clinical effects of Dex for use in OA/PTOA treatment regimens.