According to research appearing in this week's issue of the Proceedings of the National Academy of Sciences, the chemical seems to protect mice brain cells in lab cultures from the effects of nerve damage. Why it has this effect is still an open question and the potential impact for humans isn't known.

Mifepristone used to be known by the brand name RU486 and is now known as Mifeprex.

"[It] clearly has some kind of effect on the brain, so people are trying to find out the basic biology," explains Dr. Beverly Winikoff, president of Gynuity Health Projects in New York City. Gynuity works to increase women's access to new technologies for reproductive health.

"But this is very basic biology. We're talking about rats," Winikoff adds. "We're talking about things that we have no idea whether they extrapolate to humans and whether they could be clinically useful."

"There are a million observations you can make in tissue culture, but very, very, very rarely does that ever end up meaning much to treating humans," says Dr. Kevin McKinley, chairman of the department of neurology at the Ochsner Clinic Foundation in New Orleans. "This may help us better understand why certain brain cells die, but right now this is just the observation that this particular [compound] may affect the survival of cells."

The U.S. Food and Drug Administration (FDA) approved mifepristone in September 2000 as an alternative to surgical abortion in women who have been pregnant for 49 days or less (measured from the beginning of the last period). The drug blocks the hormone progesterone, which would normally prepare the lining of the uterus to receive a fertilized egg and which also helps maintain a pregnancy. The drug has to be administered by a physician and may call for as many as three visits to the doctor's office, during which time the patient may also take misoprostol, which causes the muscles of the uterus to contract. According to the FDA, the combination of drugs ends a pregnancy in 92 percent to 95 percent of all women.

However, more recent research has shown that mifepristone may also protect brain cells during traumatic brain injury and that it can relieve some symptoms of psychotic depression.

The authors of the new study set out to determine why this might be happening. They added mifepristone to Purkinje cells, which are isolated from newborn mice and normally undergo automatic, programmed cell death in tissue culture, a process called apoptosis.

Adding mifepristone extended the life of these cells. "This may interrupt that process," McKinley says.

The researchers have not been able to pinpoint the exact mechanism except to say it is not the inhibition of progesterone or steroid receptors or the compound's antioxidant activity. It could possibly be other steroid-related effects, or something else altogether.

"The signals for apoptosis and what keeps certain things alive and why other things die is really one of the big targets for research of this decade," McKinley says. "Something about mifepristone keeps them alive, and it could be steroid effects. It may help us understand the molecular mechanisms of cell death and may lead to more specific treatments."

There may also be another lesson to be gained from the research. "We can't demonize chemicals because some people don't like their politics," Winikoff says. "The point is that various technologies can be useful to human beings in many ways..."

More information

Get more information on emergency contraception from Princeton University or the Planned Parenthood Federation of America. The Population Council has more on Mifeprex.