Thyroid Hormone Could One Day Treat Osteoporosis
MONDAY, March 10 -- In experiments with rats and mice, scientists have found that thyroid stimulating hormone can prevent the bone loss associated with osteoporosis and may even restore lost bone.
The finding raises the possibility that thyroid stimulating hormone (TSH) might one day provide treatment for women with severe cases of postmenopausal osteoporosis, the researchers said.
"We found that TSH, which is a hormone that was thought to be exclusively involved in the release of thyroid hormones, which are essential for the homeostasis of the body, can directly affect bone remodeling," said lead researcher Dr. Mone Zaidi, a professor of medicine and physiology and director of the Mount Sinai Bone Program at Mount Sinai School of Medicine in New York City.
TSH inhibits the process of bone reabsorption by the body, Zaidi said. "This is a process that is fundamental for the renewal of the skeleton. Throughout life, old bone is replaced by new bone," he said. "Osteoporosis occurs when this process is exaggerated, and bone removal outpaces bone replacement."
In earlier research with mice, Zaidi's group found that TSH could actually suppress bone reabsorption. For the new study, the researchers wanted to see if TSH could stop bone reabsorption when the reabsorption rates were as high as they are in osteoporosis.
To show the benefits of TSH in preventing bone loss, Zaidi's team studied rats whose ovaries had been removed, which induced menopause-related osteoporosis. The researchers then gave the rats injections of TSH often as far apart as two weeks.
The researchers found that injections of TSH prevented bone loss and actually increased bone strength. "In addition, in rats, TSH actually restored the lost bone," Zaidi said.
The findings were published in the March 10 issue of the Proceedings of the National Academy of Sciences.
There had been a fear that injections of TSH would release thyroid hormones, which could have unwanted effects. However, Zaidi and his colleagues found that this was not the case with the animals they studied.
Zaidi said TSH is already used in humans to treat thyroid disorders. "We might be able to use the same drug for different purposes, a much larger purpose than it has ever been employed for," he said.
Dr. Stephen Honig, director of the Osteoporosis Center at the Hospital for Joint Diseases in New York City, said the idea of treating the bone disease with TSH is intriguing. But, it's far from certain that the beneficial effects seen in rodents would apply to humans. And other problems related to the use of TSH would need to be solved, he said.
"This is a very interesting animal study that strongly suggests that thyroid stimulating hormone may have anti-reabsorption effects on bone," Honig said. However, he noted that TSH can cause hyperthyroidism -- an overactive thyroid gland -- that can unleash serious problems with the body's metabolism.
"One question for TSH will be how often will it induce hyperthyroidism and can dose adjustments minimize this without impacting its bone-strengthening effects," Honig said. "The [study] authors suggest that, so far, hyperthyroidism has not been a problem, at least in a group of postmenopausal women being treated with TSH for thyroid cancer."
For more on osteoporosis, visit the U.S. National Library of Medicine.
Posted: March 2008