From the Guidelines
Calcitonin acts by inhibiting osteoclast action, although it may also stimulate osteoblast function, as documented in studies such as 1. The mechanism of calcitonin involves binding to specific receptors on osteoclasts, the cells responsible for breaking down bone tissue, thereby inhibiting osteoclast activity and reducing bone resorption. Some key points about calcitonin's mechanism include:
- Inhibition of osteoclastic bone resorption, which leads to a decrease in serum calcium levels
- Increase in calcium excretion by the kidneys
- Reduction in calcium absorption in the intestines
- Potential stimulation of osteoblast function, as suggested by in vitro data
- Production by parafollicular C cells in the thyroid gland in response to elevated blood calcium levels, creating a negative feedback loop for calcium homeostasis The effects of calcitonin are generally short-lived and less potent than those of parathyroid hormone (PTH), which acts in opposition to raise blood calcium levels, as noted in the context of bone metabolism and disease in chronic kidney disease 1. In clinical settings, synthetic calcitonin is used to treat conditions characterized by excessive bone resorption, such as Paget's disease, hypercalcemia, and osteoporosis, with its efficacy documented in various studies, including those on patients with osteoporosis and those undergoing transplantation 1.
From the FDA Drug Label
Calcitonin acts primarily on bone, but direct renal effects and actions on the gastrointestinal tract are also recognized. The actions of calcitonin on bone and its role in normal human bone physiology are still not completely elucidated, although calcitonin receptors have been discovered in osteoclasts and osteoblasts. Single injections of calcitonin cause a marked transient inhibition of the ongoing bone resorptive process. With prolonged use, there is a persistent, smaller decrease in the rate of bone resorption Histologically, this is associated with a decreased number of osteoclasts and an apparent decrease in their resorptive activity. In vitro studies have shown that calcitonin-salmon causes inhibition of osteoclast function with loss of the ruffled osteoclast border responsible for resorption of bone.
The mechanism of calcitonin involves:
- Inhibition of bone resorption: Calcitonin inhibits the activity of osteoclasts, which are responsible for breaking down bone tissue.
- Decrease in osteoclast number and activity: Prolonged use of calcitonin leads to a decrease in the number of osteoclasts and their resorptive activity.
- Possible increase in bone formation: There is some evidence that calcitonin may also increase bone formation through increased osteoblastic activity. The mechanism of calcitonin is primarily related to its action on bone, although it also has effects on the renal and gastrointestinal systems 2, 2, 2.
From the Research
Mechanism of Calcitonin
The mechanism of calcitonin involves the inhibition of bone resorption, which leads to a decrease in calcium levels in the systemic circulation 3. This is achieved through the suppression of osteoclast activity, which are the cells responsible for bone resorption 4. Calcitonin has been shown to target the most active osteoclasts, reducing their resorption activity without decreasing their numbers 4.
Effects on Bone Turnover
Calcitonin has been found to have a positive effect on bone osteoblasts, which are the cells responsible for bone formation 3. However, recent studies have shown that calcitonin may also suppress osteoblast activity and bone turnover in genetically modified mice 3. In contrast, other peptides in the calcitonin family, such as amylin, have been shown to inhibit osteoclast activity 3.
Comparison with Other Treatments
Calcitonin has been compared to other treatments for osteoporosis, such as bisphosphonates 5, 6, 7. Bisphosphonates have been shown to increase bone mineral density and reduce fracture rates, but they may also have adverse effects such as suppressing bone formation 5, 6, 7. Calcitonin, on the other hand, has been shown to reduce vertebral fracture rates with minimal changes in bone density, and may also have a beneficial effect on bone pain associated with fractures 5.
Key Points
- Calcitonin inhibits bone resorption and decreases calcium levels in the systemic circulation 3
- Calcitonin targets the most active osteoclasts, reducing their resorption activity without decreasing their numbers 4
- Calcitonin has a positive effect on bone osteoblasts, but may also suppress osteoblast activity and bone turnover in some cases 3
- Calcitonin has been compared to other treatments for osteoporosis, such as bisphosphonates, and may have a beneficial effect on bone pain associated with fractures 5