People on antidepressants might have something to feel good about--stronger bones. New research shows that generic Prozac builds bone density in mice. Although the results are at odds with other work that shows Prozac decreases bone density, experts hope the conundrum might reveal the genetic underpinnings of the drug's influence.
Researchers believe depression results from too little of the neurotransmitter serotonin bathing certain neurons. Antidepressants known as selective serotonin reuptake inhibitors (SSRIs) prevent serotonin from getting cleared out from the space between neurons, allowing it to stick around and work its magic. But SSRIs work on other parts of the body as well. Studies have shown that the drugs can interfere with the cellular machinery that helps build and break down bone, although the net effect on overall bone density has remained unclear.
To gauge the impact of SSRIs on the bones of live animals, molecular biologist Ricardo Battaglino of the Forsyth Institute in Boston and colleagues injected adult mice daily for 6 weeks with generic Prozac--or fluoxetine--at doses approximating what people would take. The researchers then measured the density of the femur and a spinal bone. They found that treated mice had about 60% more spongy bone--the part of bone most affected by bone loss--than did control animals.
To find out if fluoxetine could protect against bone loss, the team injected the drug, along with lipopolysaccharride (LPS), directly into skull bone. LPS induces inflammation and subsequent bone turnover. About twice as much new bone was seen in animals that received both the drug and LPS versus those given no fluoxetine or those given LPS alone, the team reports in an upcoming issue of the Journal of Cellular Biochemistry.
The results contradict a 2005 finding by a group led by endocrinologist Michael Bliziotes at Oregon Health and Science University in Portland, who showed that twice as much fluoxetine as used in this study lowered overall bone mass in a different strain of mice. "At this point, we can say it's possible that we get different responses to Prozac in the bone," says Bliziotes, adding that a genetic explanation would be a "very exciting." Understanding the genetic underpinnings of why fluoxetine helps bone in some circumstances and not in others could lead to better treatment plans, Bliziotes says.