ABSTRACT
Cathepsin K plays an essential role in bone remodeling and resorption in diseases such as osteoporosis, osteolytic bone metastasis and rheumatoid arthritis. Cathepsin K is a cystein protease that plays a pivotal role in osteoclast function and in the degradation of protein components of the bone matrix by cleaving proteins such as collagen type I, collagen type II and osteonectin. Our study aimed at measuring cathepsin K in the serum of rheumatoid arthritis patients. Our study group consisted of 50 patients with active longstanding rheumatoid arthritis and 50 age and sex matched healthy controls. Standardized clinical examination was performed for each patient, with stress on tender joint count, pain on motion, soft tissue swelling, swollen joint count and swollen proximal interphalangeal score. We found increased levels of cathepsin K compared with the control group and a significant correlation with radiological destruction measured by the Larsen score. Inhibition of cathepsin K may therefore be a new target for preventing bone erosion and joint destruction in rheumatoid arthritis. However, further studies have to be performed to prove that cathepsin K is a valuable parameter for bone metabolism in patients with early rheumatoid arthritis