What is the mechanism of action of denosumab in bone remodeling?

• A. Denosumab binds RANKL, inhibiting osteoclast formation and activity
• B. Denosumab stimulates osteoblast activity
• C. Denosumab increases calcium resorption in kidneys
• D. Denosumab degrades collagen in bone matrix

Answer: (A)

Denosumab works by binding RANKL, preventing it from activating the RANK receptor on osteoclast precursors and mature osteoclasts. Without RANKL signaling, osteoclast formation, maturation, and bone-resorbing activity drop, so bone resorption slows. In normal bone remodeling, RANKL produced by osteoblasts and stromal cells promotes osteoclast development, and osteoprotegerin serves as a natural decoy receptor to keep this in check. Denosumab mimics that decoy effect, tilting the balance toward reduced osteoclast-mediated resorption and helping to preserve or increase bone density. It’s not promoting osteoblast activity, nor is it increasing renal calcium reabsorption or degrading collagen in the bone matrix.