Space mice pioneer bone research

Astronauts, like Endeavour spacewalker Daniel Tani, lose bone mass after being exposed to the weightlessness of space.

By Amanda Barnett
CNN

(CNN) -- Space shuttle Endeavour has mice. Two dozen of them, in fact. But these mice aren't pests, they're invited guests.

The pioneering mice are part of an experiment on a bone-regulating protein called osteoprotegerin, or OPG. Scientists predict that OPG will protect against bone loss caused by the weightless environment of space. It's also a potential treatment for millions of ground-based Earthlings who have osteoporosis.

OPG was discovered in 1995 by researchers for Amgen, a biotechnology firm based in Thousand Oaks, California.

"It appears to be really safe," said primary investigator Paul Kostenuik, a research scientist with Amgen. The company is testing OPG in partnership with NASA's BioServe Space Technologies at the University of Colorado.

Did you know? In the United States, 8 million women and 2 million men have osteoporosis. Another 18 million people have low bone mass, putting them at increased risk for osteoporosis. One in two women and one in eight men over age 50 will have an osteoporosis-related fracture in their lifetimes. While osteoporosis is frequently considered an older person's disease, it can strike at any age. Osteoporosis causes more than 1.5 million bone fractures annually. Source: National Osteoporosis Foundation RESOURCES Message board: Space exploration

Twelve of the shuttle mice have been treated with OPG; the other 12 were given a placebo.

The mice are in a special animal enclosure module in the shuttle's middeck called the Commercial Biomedical Testing Module. The container automatically provides food and water, and shuttle crew members check in on them. But mostly, the mice just hang out and float.

After the shuttle lands, the mice are to be returned to the scientists, who will examine the effects of spaceflight.

Weighty dilemma for space travelers

An astronaut or cosmonaut may lose 1 to 2 percent of his or her bone density per month in space, said Kostenuik. If astronauts are to someday travel to Mars, or stay on the space station for lengthy missions, they could be at risk for bone fractures when they return to Earth's gravity.

Current osteoporosis treatments have serious downsides for space travelers.

For example, when astronauts swallow pills, the lack of gravity makes them stick in the esophagus, said Kostenuik. And drugs that include estrogen aren't appropriate for male crew members, according to Kostenuik. OPG is injected and does not include estrogen.

"We already know OPG prevents bone loss in a variety of disease states," said Kostenuik. He said scientists predict it also will be safe and effective in near-zero gravity.

OPG still is in early stages of clinical development and Kostenuik said it may be several years before it's available on Earth or in space.