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Osteoprotegerin

OPG (Osteoprotegerin; also called Osteoclastogenesis Inhibitory Factor or TNFRSF11B) is a secreted member of the TNF (Tumor necrosis factor) receptor superfamily of proteins [1]. OPG, composed of 380 amino acids, is expressed as monomer and secreted as disulphide-homodimeric protein [2]. OPG is produced by numerous cell types and tissues and its expression pattern targets three main biological : the skeletal, immune, and vascular systems. Produced by osteoblasts, it protects the skeleton from excessive bone resorption by acting as a decoy receptor for the ligand nuclear factor-kB ligand (RANKL), preventing it from interacting with its receptor RANK [3]. OPG/RANK/RANKL molecular triumvirat plays a pivotal function in the regulation of the immune system through dendritic cells [4]. OPG-deficient mice exhibit severe osteoporosis and vascular calcification of the aorta and renal arteries [5]. Defects in TNFRSF11B are the cause of juvenile Paget disease (JPD), a bone disease [6]. OPG also functions as a soluble receptor for the TNF ligand TRAIL (TNF-related apoptosis-inducing ligand) preventing it to activate apoptotic signaling cascase and therefore providing cells with a survival advantage [7].

Free Osteoprotegerin (human) Detection Set (APO-54N-028)

Summary of features

	For the quantitative determination of free OPG (human)(not complexed to RANKL and TRAIL) from biological fluids (serum, plasma and cell culture supernatant)
	Detection limit: 2 pg/ml
	Range: 0-250 pg/ml
	Specificity : Detects only human OPG
	Format: sufficient materials to run ELISAs on 5 x 96-well plates

Principle of the Kit

This assay is a sandwich Enzyme Linked-Immuno-Sorbent Assay (ELISA) developed for the direct measurement of human OPG (hOPG) in biological fluids. A monoclonal antibody specific for hOPG (COAT) is coated onto the wells of the microtiter plate. Samples and standards of hOPG are pipetted into the wells for binding to the coated antibody. After extensive washing to remove unbound compounds, hOPG is recognized by the addition of a biotinylated polyclonal antibody specific for hOPG (DET). After removal of excess biotinylated antibody, streptavidine-peroxidase is added. Following a final washing, peroxidase activity is quantified using the substrate 3,3’,5,5’-tetramethylbenzidine (TMB). The intensity of the color reaction is measured at 450 nm after acidification and is directly proportional to the concentration of hOPG in the samples.

Figure: Linearity of the STD curve.

LITERATURE OVERVIEW:

1. Boyce, B.F., and Xing, L. (2007). Biology of RANK, RANKL, and osteoprotegerin. Arth. Res. & Therapy 9 Suppl 1, S1.

2. Simonet, W.S., Lacey, D.L., Dunstan, C.R., Kelley, M., Chang, M.S., Luthy, R., Nguyen, H.Q., Wooden, S., Bennett, L., Boone, T., et al. (1997). Osteoprotegerin: a novel secreted protein involved in the regulation of bone density. Cell 89, 309-319.

3. Lacey, D.L., Timms, E., Tan, H.L., Kelley, M.J., Dunstan, C.R., Burgess, T., Elliott, R., Colombero, A., Elliott, G., Scully, S., et al. (1998). Osteoprotegerin ligand is a cytokine that regulates osteoclast differentiation and activation. Cell 93, 165-176.

4. Baud'huin, M., Lamoureux, F., Duplomb, L., Redini, F., and Heymann, D. (2007). RANKL, RANK, osteoprotegerin: key partners of osteoimmunology and vascular diseases. Cell Mol Life Sci 64, 2334-2350.

5. Min, H., Morony, S., Sarosi, I., Dunstan, C.R., Capparelli, C., Scully, S., Van, G., Kaufman, S., Kostenuik, P.J., Lacey, D.L., et al. (2000). Osteoprotegerin reverses osteoporosis by inhibiting endosteal osteoclasts and prevents vascular calcification by blocking a process resembling osteoclastogenesis. J. Exp.Med. 192, 463-474.

6. Whyte, M.P. (2006). Paget's disease of bone and genetic disorders of RANKL/OPG/RANK/NF-kappaB signaling. Annals of the New York Academy of Sciences 1068, 143-164.

7. Emery, J.G., McDonnell, P., Burke, M.B., Deen, K.C., Lyn, S., Silverman, C., Dul, E., Appelbaum, E.R., Eichman, C., DiPrinzio, R., et al. (1998). Osteoprotegerin is a receptor for the cytotoxic ligand TRAIL. J. Biol. Chem. 273, 14363-14367.