Expression of cathepsin-K in gingival crevicular fluid of patients with periodontitis.

Cathepsin-K is a highly expressed cysteine protease, and it plays a key role in bone remodeling and cartilage breakdown in bone. Cathepsin-K is used as a well-known marker of osteoclast activity, because this enzyme is mainly derived from osteoclasts. The receptor activator for NF-kappaB ligand (RANKL) plays an important role in osteoclast formation. Although a recent study suggests the involvement of RANKL in the pathogenesis of periodontal disease, no one has previously examined the level of cathepsin-K in the body fluid of human subjects. If the presence of cathepsin-K, as well as RANKL, can be detected in body fluids, it would be indirect proof of the differentiation and/or activation of osteoclasts in the tissues bathed by these fluids. This communication reports on the in vivo concentrations of cathepsin-K and RANKL in the gingival crevicular fluid (GCF) of normal subjects and those patients with severe, moderate, and mild forms of the disease. Increased concentrations of cathepsin-K and RANKL were detected in the GCF from patients with periodontitis (P<0.005 versus control subjects). Also, there was a positive correlation between cathepsin-K and RANKL levels (r=0.726), suggesting that both of them contribute to osteoclastic bone destruction in periodontal disease.