The Potential Protective Effects of Calcitonin Involved in Coordinating Chondrocyte Response, Extracellular Matrix, and Subchondral Trabecular Bone in Experimental Osteoarthritis

Previous reports indicate a potential role for calcitonin (CT) in the treatment of osteoarthritis (OA). To evaluate this potential therapeutic role, we investigated the effect of CT pretreatment on the activation of mitogen-activated protein kinase (MAPK) signaling and the expression of matrix metalloproteinase-13 (MMP-13) in interleukin-1 beta (IL-1 beta)-induced chondrocytes, and further assessed its protective effect in a rat model of anterior cruciate ligament transection (ACLT), using sham-operated and saline-treated controls. Using western blotting in vitro, we found that CT pretreatment inhibited the IL-1 beta-induced phosphorylation of 38,000-dalton protein (p38) and extracellular regulated protein 1/2 (ERK1/2) and reduced the expression of MMP-13 protein. For the in vivo experiment, 30 male rats were randomly divided into three groups of 10, subjected to bilateral ACLT or sham surgery, and then treated for 12 weeks with subcutaneous injections of CT or normal saline. Histological observations showed that CT treatment reduced the severity of the cartilage lesions stemming from the ACLT surgery and provided a lower Mankin score when compared with that determined for rats in the saline-treated ACLT group. Immunohistochemical staining revealed that CT treatment increased type II collagen expression and decreased MMP-3 and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) expression when compared with the saline-treated group. Subchondral bone analysis indicated that CT treatment inhibited the reduction in bone mineral density observed in the saline-treated ACLT group and reduced the ACLT-induced destruction to the subchondral trabecular microstructure. Our data demonstrate that CT induces its protective effects by reducing the chondrocyte response to inflammatory stimuli, cartilage extracellular matrix degradation, and subchondral trabecular microstructure damages brought on by OA.