Osteoprotegerin and RANKL regulate bone resorption, density, geometry and strength.

Osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand (RANKL) are dominant regulators of bone resorption. Many hormones, cytokines and growth factors mediate bone resorption by altering the ratio of RANKL to OPG. RANKL and OPG expression is also altered in numerous bone diseases, and these changes can reflect disease etiology or compensatory responses to disease. RANKL stimulates osteoclast formation, function and survival, and each of these effects is inhibited by OPG. OPG suppresses bone resorption and increases the density, area and strength of both cancellous and cortical bone. Denosumab (AMG 162), a fully human monoclonal antibody to RANKL, shares the pharmacologic attributes of OPG but has a significantly longer half-life that allows less frequent administration.