MONDAY, Oct. 30, 2006 (HealthDay News) -- Studies in mice are shedding light on how depression helps eat away at human bone.
Scientists have longed noted links between depression and lowered bone mass. In fact, the bone density of depressed people is up to 15 percent less than that of happier folk.
Now, researchers from Jerusalem and Hungary say they slowed bone loss in "depressed" mice by giving the rodents an antidepressant. Their study is providing clues to how depression weakens bones, as well as new ways to stop it.
The study is published in the Nov. 7 issue of the Proceedings of the National Academies of Science.
The findings may help in the fight against the osteoporosis, said one expert who's done similar work.
"These results are a nice complement to our research," said Ricardo Battaglino, assistant member of the staff in the department of cytokine biology at the Forsyth Institute in Boston.
In the study, a team led by Raz Yirmiya of Hebrew University of Jerusalem, first induced depression in mice by exposing them to chronic stress. They then gave them the antidepressant imipramine (Tofranil).
The drug improved both the rodents' behavior and their bones, the researchers said.
Battaglino wasn't surprised by the finding, since his own group had found that the antidepressant drug Prozac increased bone mass in adult mice.
Battaglino said he tried the drug after noticing serotonin receptors on the surface of bone cells. Serotonin receptors regulate the entry of serotonin, a molecule that facilitates communication between brain cells and is implicated in anxiety and depression. Prozac is one of a group of drugs known as selective serotonin reuptake inhibitors (SSRIs) that act on this receptor.
Battaglino's team decided to see if the Prozac could influence bone cells and bone mass. They found that it did. His team is publishing the results in the Journal of Cellular Biochemistry.
Yirmiya and his colleagues gave the mice imiprimaine and found that some responded by a reversal in bone loss. "Imipramine is a tricyclic antidepressant that acts on both the norepinephrine (also called noradrenaline) and serotonin reuptake systems," Battaglino explained.
Yirmiya found that the animals' bone loss was associated with an increase in the neurotransmitter norepinephrine. So, they decided to treat the animals with a drug known as a beta blocker, propranolol (Inderal), which works by inhibiting norepinephrine.
They found the drug reduced bone loss without affecting the rodents' behavior.
"They found a new mediator for depression-induced bone loss, norepinephrine," Battaglino said.
Bone remodeling is a constant process of new bone formation and bone degradation. If not enough new bone is made or too much existing bone is degraded, the net result is low bone mass.
Battaglino said his research, as well as the results of this new study, both suggest that depression most likely affects the bone-forming cells, the osteoblasts, rather than the bone-degrading cells, the osteoclasts.
While there is no immediate reward for patients stemming from the new research, Battaglino said, "I think it's important to raise awareness that these drugs could potentially be used as drugs to increase bone formation."
What is not yet known, he said, is whether the drugs would work better than the current bone-building drugs or if they should be used in combination with them.
More information
To learn more about bone health, visit the National Osteoporosis Foundation.
