Osteoporosis: When ‘Clasts’ Beat the ‘Blasts’

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Category: Metabolic Bone Disease Published on Monday, 01 August 2005 Written by Yong Tsai, MD
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As mentioned in a previous column, our bones contain two different cell groups that, when working as a team, can keep bones healthy. But, when one out-performs the other, the results could be unhealthy.

One cell group is called “osteoclasts”, which break down bone, creating microscopic pits. The other is “osteoblasts”, which form new bone to fill these holes. However, when the “clasts” best the “blasts”, bone density decreases, possibly causing osteoporosis and fractures.

Preventing and treating osteoporosis means increasing bone mass and strength, by either decreasing bone absorption (osteoclasts) with drugs such as estrange, selective estrogen receptor modulators (SERMs), Calcitonin or Bisphosphonates, or to increase bone formation (osteoblasts) with drugs such as Forteo. These drugs can increase bone mass and improve bone structure, thus preventing fractures.

Estrogen replacement therapy for women, prescribed to prevent, but not treat osteoporosis, lasts only as long as it is continued. In other words, when treatment is stopped, bone loss resumes. Furthermore, estrogen should not be taken when a history of blood clots (venous thromboembolitic event) or personal or immediate family history of breast cancer exits. However, Raloxifene, used to treat osteoporosis, binds itself to estrogen receptors in bones, but not in the breasts or uterus. What this means is that Raloxifene can reduce bone absorption without increasing the risk of breast or uterine cancer. Common side effects include hot flashes, leg cramps, and an increases risk of thromboembolism.

For people with mild osteoporosis and who are unable to tolerate other anti-absorptive drugs, a synthetic polypeptide hormone similar to a salmon’s calcitonin is available. This drug – called “Miacalcin”, which is available in nasal spray form – can be rapidly absorbed by the nasal mucosa as treatment, but cannot prevent osteoporsis.

In addition, a class of drugs (called “bisphosphonates”, such as alendronate (Fosamax) and risedronate (Actonel), can provide significant increase in bone mass while reducing the risk of new vertebral fractures, even just after one year of treatment. To inhibit osteoclasts, bisphosphonates attach themselves to bone, thus becoming part of the bone. Therefore, bisphosphonates can maintain bone mass for a significant period after being stopped. For patients with moderate to severe osteoporosis or a history of hip fracture, bisphosphonates are the drug of choice. Even though bisphosphonates are safe and tolerable, a few patients may experience side effects such as indigestion, heartburn, nausea, vomiting, or esophageal ulcers.

Lastly, Forteo (teriparatide injection) has similar biologic effects on bone as does the function of our parathyroid gland. Currently used for patients with osteoporosis who do not respond to anti-absorption treatment, Forteo enhances osteoblast activity to increase bone mass. The only downfalls are the fact that it is more expensive than other anti-osteoporosis drugs and that it must be administered daily.

Thanks to medical advances anti-osteoporosis drugs that not only increase bone mass, but also improve bone quality, are readily available. A daughter’s osteoporosis can be prevented, while a mother’s can be reversed.

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