Blood & Laboratory Values

Osteocalcin – Function & Diseases

Osteocalcin

Osteocalcin is a peptide hormone found in the bones with various functions. It is significantly involved in bone metabolism and serves as a marker for various bone diseases in the blood . But it also plays a major role in carbohydrate and fat metabolism .

What is osteocalcin?

Osteocalcin is a peptide hormone produced in the osteoblasts of bones or the odontoblasts of teeth. As part of the extracellular bone matrix, it binds to the mineral hydroxyapatite . There it is about one to two percent.

By binding to the mineral ‘s calcium , osteocalcin inhibits the unrestrained mineralization of bone. It is encoded by a gene on chromosome 1q25q31. In studies on mice, mutations of this gene led to increased mineralization of the bones and thus to the development of marble bone disease. This resulted in increased bone formation and increased brittleness at the same time. The synthesis of the hormone depends on the vitamin D metabolite calcitriol (1,25(OH)2D3).

Binding to calcium is in turn catalyzed by the enzyme glutamyl carboxylase. Vitamin K acts as a cofactor. Osteocalcin acts as a marker of bone formation. It has already been isolated from surviving Neanderthal bones. It is measured in the blood for diagnostic purposes.

Function, effect & tasks

Osteocalcin fulfills several functions in the organism. It is a hormone that is only synthesized in the osteoblasts of bones or the odontoblasts of teeth . 

There it is significantly involved in bone metabolism. Bone-building and bone-breaking processes are constantly taking place within the skeletal system. When bone-degrading processes predominate, what is known as osteoporosis occurs . While the hormone does not prevent osteoporosis, it does act as an important marker for certain bone diseases. Inside the bone, it has the task of restricting the mineralization of the bones. It binds to the hydroxyapatite of the extracellular non-collagenous bone matrix. The bones form normally and acquire the necessary strength against fractures. In the matrix it is contained up to two percent. In order to be able to bind to the calcium atoms of the mineral, however, the glutamyl residues contained in osteocalcin must first be removed using an enzyme .

This enzyme is glutamyl carboxylase, which in turn is activated with the cofactor vitamin K. According to the latest findings, osteocalcin also lowers blood sugar and breaks down fat. Blood sugar reduction occurs in two ways. Osteocalcin stimulates the synthesis of the hormone insulin directly by stimulating the “islets of Langerhans” in the pancreas . Furthermore, it also increases insulin effectiveness indirectly by stimulating the hormone adiponectin . In recent years it has been found that [[insulin resistance is caused by reduced production of adiponectin.

The more fat is stored in the adipocytes , the lower the adiponectin synthesis. This in turn reduces the effectiveness of the insulin. In addition, it was also found in animal experiments that osteocalcin stimulates fat burning. Mice with high levels of osteocalcin did not develop obesity or diabetes . Based on this research, future approaches could emerge to combat obesity and type II diabetes more effectively with the help of osteocalcin.

Formation, Occurrence, Properties & Optimal Values

As already mentioned, osteocalcin is synthesized in the osteoblasts of bones and in the odontoblasts of teeth. Its production rate depends on vitamin K and is stimulated by vitamin D. After its formation, it is then mainly incorporated as a component in the extracellular bone matrix. Only there is it stable.

In free form, it has a short half-life. Half of it is broken down in the blood plasma by the proteases contained there within four minutes. It is released during bone turnover and enters the blood. The concentrations measured in blood and urine provide information about the metabolic activity of the bones and are therefore a good marker for certain bone diseases.

Diseases & Disorders

Blood and urine levels of osteocalcin depend on many factors. In general, they characterize the bone turnover rate. Bone is constantly being broken down and rebuilt during bone turnover.

When bone-degrading processes predominate, bone density decreases over the long term and fragility increases. Of course, substances that are involved in bone formation are also increasingly released. This includes osteocalcin. High levels in the blood always mean increased degradation processes. Too high levels of osteocalcin in the blood are found in osteoporosis with a high metabolic rate, hyperparathyroidism , bone metastases in malignancies, Paget’s disease , osteomalacia , hyperthyroidism or renal insufficiency . Osteocalcin levels that are too low occur with prolonged cortisone therapy , osteoporosis with low bone turnover, rheumaticarthritis or hypoparathyroidism. Osteoporosis in particular can be caused by many different causes. Therefore, bone turnover can be high or low.

What all forms of osteoporosis have in common is that bone resorption outweighs bone formation. Hormone disorders based on an overactive parathyroid hormone cause the osteocalcin levels in the blood to rise sharply. The parathyroid hormone regulates the calcium level in the blood by breaking down the bones. Conversely, too low parathyroid hormone concentrations also lead to low osteocalcin levels in the blood. In the context of Paget’s disease, there are irregular remodeling processes in the skeletal system , which also leads to increased osteocalcin concentrations.

Of course, with generally increased metabolic rates in the context of an overactive thyroid , bone turnover also increases with increased osteocalcin levels. Cortisone therapy slows bone turnover. The blood values ​​are typical for certain diseases. However, the osteocalcin determination provides only one finding within the framework of the overall diagnosis .

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.