Bone sialoprotein (BSP) is a phosphorylated glycoprotein that makes up approximately 12% of the total non-collagenous proteins in bone and plays a key role in bone mineralization and remodeling. The native polypeptide chain of BSP has a molecular weight of around 35 kDa, but posttranslational glycosylation modifications increase its apparent molecular weight to 70–80 kDa. BSP is primarily synthesized by bone-associated cells, including osteoblasts, osteoclasts, osteocytes, fibroblasts, hypertrophic chondrocytes, and even trophoblasts, underscoring its importance in skeletal development and maintenance.
In both research and clinical settings, BSP is an important biomarker for bone metabolism and pathology. Elevated BSP expression is associated with cancers that metastasize to bone, such as breast and prostate cancers, where it is commonly overexpressed in an underglycosylated form. This altered expression pattern is also seen in other cancers including lung, thyroid, multiple myeloma, and neuroblastoma—particularly those prone to bone metastasis. BSP levels may also correlate with the presence of microcalcifications, providing further diagnostic relevance in oncology and skeletal disease assessment.
Quantification of BSP is achieved through an immunoassay method based on the interaction between sample antigens and antibodies coated on microtiter wells. A peroxidase-conjugated secondary antibody is used to enable detection via a colorimetric reaction with tetramethylbenzidine (TMB), which is halted by an acidic stop solution. The absorbance, measured at 450 nm, is plotted against a standard curve to determine BSP concentration in samples. This assay format supports sensitive and specific detection of BSP, making it a valuable tool in both bone research and the evaluation of bone-involved malignancies.
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