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Background
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Osteocalcin (OT) is the most abundant noncollagenous protein in mature bone where it constitutes 1% to 2% of the total protein. Synthesized by osteoblasts, it is incorporated into the bone matrix. Osteocalcin is a 49-residue protein with three gamma-carboxyglutamic acid residues, at positions 17, 21 and 24. These three residues confer on it a very strong ability to bind to hydroxyapatite. Osteocalcin is a noncollagenous protein found in bone and dentin. It is secreted by osteoblasts and thought to play a role in mineralization and calcium ion homeostasis. It has been stipulated that osteocalcin may also function as a negative regulator of bone formation, although its exact role is unknown. It was reported that osteocalcin acts as a hormone in the body, causing beta cells in the pancreas to release more insulin, and at the same time directing fat cells to release the hormone adiponectin, which increases sensitivity to insulin. As osteocalcin is manufactured by osteoblasts, it is often used as a biochemical marker, or biomarker, for the bone formation process. It has been routinely observed that higher serum-osteocalcin levels are relatively well correlated with increases in bone mineral density (BMD) during treatment with anabolic bone formation drugs for osteoporosis, such as Forteo. In many studies, Osteocalcin is used as a preliminary biomarker on the effectiveness of a given drug on bone formation.
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