BioEd Online

A drug that prevents bone loss could permit astronauts to make long journeys in space, according to results from a study of spinal injury patients.

The two biggest persistent health problems in space flight are radiation exposure and bone loss, says Jay Shapiro, a bone researcher at the Uniformed Services University in Bethesda, Maryland. "They have to be solved before we launch a manned Mars mission."

Shapiro leads a team that has studied the effects of zoledronate in spinal injury patients over the course of a year. The drug is normally used to prevent secondary bone tumours developing in cancer patients, and has shown early promise in retarding the effects of the bone-wasting disease osteoporosis.

But spinal injury patients provide a much better model than those with osteoporosis for the weightless conditions in space, says Shapiro, because such patients lose bone at a similar rate to astronauts. "If grandma has osteoporosis, she loses about 2-3% of her bone mass every decade. Astronauts lose about 2% every month, and exercise has little impact on that," he says.

In the study, eight patients who did not take the drug lost 16-18% of their femur bone mass over a year, while seven patients using the drug lost only 6%. "The drug significantly reduced bone loss," says Shapiro. "It's very much a first step, but it seems the most reasonable drug to use to allow trips to Mars."

Shapiro presented the results last week at the annual meeting of the American Society for Bone and Mineral Research in Seattle, Washington. The research has been submitted for publication in the Journal of Bone and Mineral Research.

Space tests

The National Space Biomedical Research Institute, based in Houston, Texas, investigates how space flight affects the human body. Jeanne Becker, associate director of the institute, is trying to arrange for an astronaut on the International Space Station to take the drug. But she says that, as the space shuttle's schedule is not certain, it may be years before zoledronate gets a zero-gravity test.

"We need to look at this in the only lab that counts: space," agrees Shapiro. While waiting for that opportunity, he is planning a more intensive study with 36 patients to understand exactly how the drug works to prevent bone loss.

The research could also benefit spinal injury patients, whose limbs fracture easily after bone loss. Even though they do not use their legs, this weakness can make life extremely difficult, says Shapiro. "It's not easy to be transferred from a chair to a bath with a broken leg," he says. His recent study is the first test of the drug in those with spinal injuries.

Clever combinations

Drugs such as zoledronate could certainly play a key role in long space missions, says Colin McGuckin, a stem-cell scientist at Kingston University, UK, who is working with NASA to develop a way to use cell transplants to limit an astronaut's bone loss.

"It's six months to Mars, a year doing experiments on the surface and then six months back. Over that time, bone loss is going to be a major problem," he says.

But he adds that a mission to Mars will probably still need to provide the astronauts with an artificial gravity area, generated by a rotating section of the ship. "The solution will be a combination of clever medicine and clever spacecraft," he says.