Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein (BGLAP), is a noncollagenous protein found in bone and dentin. In humans, the osteocalcin is encoded by the BGLAPgene.
Osteocalcin is secreted solely by osteoblasts and thought to play a role in the body's metabolic regulation and is pro-osteoblastic, or bone-building, by nature. It is also implicated in bone mineralization and calcium ion homeostasis. 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.
Current data suggests a possible role of osteocalcin in male fertility. Research from Columbia University Medical Center proposes that osteocalcin may enhance the synthesis of testosterone. Although these studies were initially performed by only a single laboratory, at least two other groups have independently confirmed the role of osteocalcin in insulin secretion. 
Use as a biochemical marker for bone formation
As osteocalcin is produced by osteoblasts, it is often used as a marker for the bone formation process. It has been 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 Teriparatide. In many studies, osteocalcin is used as a preliminary biomarker on the effectiveness of a given drug on bone formation. For instance, one study which aimed to study the effectiveness a glycoprotein called lactoferrin on bone formation used osteocalcin as a measure of osteoblast activity. 
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