(HealthDay News) -- Could a widely used treatment for depression be a remedy for osteoporosis?
Researchers have discovered that the drug Prozac also increases bone mass, at least in adult mice.
"Treating animals for six weeks with Prozac resulted in an increase in trabecular bone mass," said study lead author Ricardo Battaglino, assistant member of the staff in the department of cytokine biology at the Forsyth Institute in Boston. "It was a pretty significant 60 percent increase."
Trabecular bone is one of two main types of bone and makes up most of the spongy interior of the majority of bones.
Although it's way too early to advocate popping Prozac to reverse or stop bone loss, experts say it's a tantalizing lead for future research.
"For several reasons, people need to be cautious because fluoxetine [the generic name for Prozac] has central nervous system effects," said Dr. Grant Mitchell, chief of psychiatry at Northern Westchester Hospital Center in Mount Kisco, N.Y. "But it is interesting that current treatments for bone loss in osteoporosis do not take this approach, so the idea that we could at some point have another approach to reducing bone loss or even rebuilding new bone is actually exciting. Having more options would be great."
The study, which was funded by the U.S. National Institute of Dental and Craniofacial Research, is expected to be published in an upcoming issue of the Journal of Cellular Biochemistry.
Previous research, some of it by the same team, had found that serotonin receptors were commonly expressed on the surface of bone cells. Serotonin receptors govern the entry of serotonin -- a molecule that helps transmit signals between neurons and is implicated in anxiety and depression -- into cells.
Prozac is a member of a group of antidepressants called "selective serotonin reuptake inhibitors" (SSRIs) that act on this receptor.
The fact that these receptors populated bone cells "was surprising for us," Battaglino said, "because we were taking bone cells and serotonin, two molecules that apparently didn't have much to do with each other."
The next question was whether Prozac, which has an effect on serotonin, also exerted an influence on bone cells and, ultimately, bone mass.
For this study, laboratory mice were treated with Prozac for six weeks. The investigators were specifically interested in seeing if the drug stimulated new bone formation under normal conditions and if it blocked bone loss caused by inflammation or by loss of estrogen after taking out the ovaries.
Prozac both spurred the formation of new bone under normal conditions and reversed overall bone loss triggered by inflammation.
The drug was administered both systemically (like taking a pill) and locally (directly to the bone), and the effects were observed with both delivery methods, the researchers reported.
"They developed a way to deliver locally to the bone, which makes more sense," Mitchell pointed out. "The idea there would be to avoid the [potential] brain effects."
Oddly, a prior study using Prozac found that the drug actually hindered bone growth. The discrepancy may have been due to the way bone mass or density was measured and also to the fact that it involved children, not adults, Battaglino said.
In the new study, Prozac was not effective in female mice without circulating estrogen (i.e. after their ovaries had been removed). In those cases, Prozac "did not prevent bone loss associated with estrogen deficiency," Mitchell said. "It looks like, to be effective in relation to bone loss, Prozac needs to be in the presence of estrogen." This has implications for women moving into menopause who lose estrogen and have an increased risk of osteoporosis, he said.
The findings need to be replicated and, of course, tried in humans, but, given the number of people taking Prozac, the implications could be enormous.
"Fluoxetine is one of the most widely prescribed psychoactive drugs in this country and most likely the world, and it's been like that for at least 15 or 20 years," Battaglino said. "From the public health point of view, this would be pretty relevant."
The jury is still out on whether other SSRIs -- such as Celexa, Paxil and Zoloft -- might have the same effect on bone, Battaglino added, since similar tests on those drugs haven't yet been performed.
"This could be a class effect for SSRIs," he said. "However, it is known that in addition to blocking the serotonin transporter, Prozac can target other molecules -- for instance, some nicotinic acetylcholine receptors and even some serotonin receptors. So, this effect could be specific for Prozac. The experiments will have to be done to answer the question."
To find out more about bone loss, visit the National Osteoporosis Foundation.