Osteoprotegerin (OPG) is a member of the TNFR (tumor necrosis factor receptor) superfamily that can act as a decoy receptor for RANKL (receptor activator of nuclear factor κ-B ligand) and TRAIL (tumor necrosis factor-related apoptosis-inducing ligand). The primary structure of OPG protein consists of seven distinct domains, four of which corresponds to the extracellular cysteine-rich domains of TNFR proteins and constitutes the soluble OPG. OPG is expressed in a wide variety of tissues including adult heart, lung, kidney and liver. It is secreted both as a monomeric and a dimeric protein.

Binding of soluble osteoprotegerin (OPG) to sRANKL (soluble receptor activator of nuclear factor κ-B ligand) inhibits osteoclastogenesis by interrupting the signaling between stromal cells and osteoclastic progenitor cells, thereby leading to excess accumulation of bone and cartilage. Changes in the level of serum OPG are associated with atherosclerosis and cardiovascular disorders. It might also be associated with malignancy and plays a regulatory role in multiple myeloma, prostate, breast, bladder and gastric carcinoma. OPG plays a vital role in bone metabolism and is involved in inhibition of ovariectomy-associated bone loss in rats.

OPG is a soluble secreted member of the tumor necrosis factor receptor superfamily that lacks any apparent cell-association motifs. It regulates the formation of osteoclasts and is involved in the regulation of bone resorption and remodeling. Human and mouse OPG share approximately 84% and 94% amino acid sequence identity, respectively, with rat OPG.

Soluble secreted member of the tumor necrosis factor receptor superfamily that lacks any apparent cell-association motifs; regulates the formation of osteoclasts and is involved in the regulation of bone resorption and remodeling.

Lyophilized from a 0.2 μm filtered solution in phosphate buffered saline.

The biological activity is measured by its ability to neutralize apoptosis of mouse L-929 cells treated with 50 ng/ml recombinant human TRAIL.