The Bones of the Matter: Reversing the Loss of Bone Mass in Space

Without the influence of gravity, astronauts experience bone loss and it takes research in space to figure out how to reverse that.

MOFFETT FIELD, Calif. (NASA PR) — Spaceflight is hard on the human body. Adapted over generations to meet the rigors of an environment with gravity, all of the normal rules about staying healthy on Earth don’t apply in zero gravity. Long-term space exploration depends on knowing how to keep humans strong and well, so NASA has been studying the consequences of short-term trips in space for years, with the International Space Station contributing significantly to the understanding of how to keep astronauts healthy.

Some of the things learned thus far include the fact that multiple sunrises and sunsets every single day disrupt circadian rhythms and that the lack of gravity causes bone-density and muscle loss. Figuring out how to counteract these otherworldly conditions is yielding positive results—for example, special lighting helps induce sleep, and rigorous exercise schedules help keep bodies healthy. However, one persistent and troubling issue is bone loss.

Jacob Cohen, chief scientist at NASA’s Ames Research Center in California’s Silicon Valley, says NASA scientists and other researchers know this loss is driven by loading and unloading, or the absence of gravity’s pull on the body. Understanding how the body responds to the space environment will make it possible to develop more effective countermeasures for long-duration missions—and help fight bone diseases encountered on Earth.

“As scientists, we want to know, what are the mechanisms that effect bone loss, what are the mechanisms that effect muscle loss,” Cohen says. “We want to make sure we keep the crew as healthy as possible so when they come back, they have a normal life.”

A Model of Success

The final Space Shuttle, launched in 2011, carried mice into space to study the effects of the sclerostin antibody by Amgen. The goal was to see if it could help protect astronauts’ bone health, but the research has also helped people suffering from osteoporosis here on Earth. (Credit: NASA)

Amgen, a biotechnology company based in Thousand Oaks, California, was already working on new treatments for terrestrial osteoporosis. Teaming up with Louis Stodieck, a research professor at the University of Colorado at Boulder and director of BioServe Space Technologies, Amgen worked with NASA to devise a rodent-based experiment that could benefit astronauts and Earthbound humans alike.

With humans, a six-month or yearlong stint in microgravity can only yield so much information on the effects of living in space. But with rodents, whose lifespan is so much shorter, even a two-week trip can reveal biological trends and effects that can be scaled into useful data on what might happen in the human body over a longer period of time.

“The idea is, you can assess how things might occur in humans if you have good animal models that can predict what the human response is going to be, both to the environment as well as to any countermeasure you might want to test to mitigate any issues of that environment,” Stodieck explains.

During three separate Space Shuttle flights, groups of 15 mice, all about 10 weeks old, were sent into microgravity for two-week stints. Each time, one group was treated with a molecule designed to mitigate the loss of bone density and muscle strength, while a second group was given a placebo. Other mice got the same treatments but remained on Earth as a control group.

RX for Astronauts

Some basic mechanisms in humans and mice are similar enough for conducting research studies. Because mice have a much shorter lifespans, researchers learn more about the potential effects of new treatments at different ages. (Credit: NASA)

One experiment focused on sclerostin, a naturally secreted protein that tells the body to dial down the formation of new bone. The mice were injected with an antibody that blocks sclerostin, essentially telling the body to “let up on the brake,” explains Chris Paszty, Amgen’s research lead on the project.

That stimulated the rodent bodies to keep regenerating bone tissue, resulting in increased mineral density and improved bone structure and strength.

The hypothesis was that the bones of the mice injected with the sclerostin antibody before going into space wouldn’t be as negatively affected by the two-week exposure to microgravity as the control groups that had received placebos. The results were encouraging.

“What we found was that the mice that had received our sclerostin antibody had increased bone formation and improved bone structure, and even increased bone strength,” Paszty says. “That’s exactly what we’ve found here on Earth. We were very pleased to see we had gotten the same results in space.”

The mouse house, also called a rodent habitat, was developed to serve as a short-term home away from home for mice on the International Space Station. The mini-research subjects are helping NASA learn what it takes to make astronauts healthy during long-term space exploration.(Credit: NASA)

Humans or animals in microgravity will rapidly lose muscle and bone. Bone loss in particular is much faster than a patient on Earth suffering from osteoporosis—approximately 10 times faster in space.

Paszty and Stodieck both note that although space-based experiments aren’t a requirement for the clinical trials and FDA approval process for new treatments, much can be learned about basic biology using space-based experimentation.

Another of the molecules tested by Amgen on the space flights is already approved in a drug, helping women with osteoporosis prevent broken bones. Marketed as Prolia, the drug was developed in part using mice data from Amgen’s first space experiment.

The company’s work on bone health treatments is of interest to NASA as it continues to explore ways to protect astronauts’ health in space, but the research has benefits for people suffering from osteoporosis here on Earth.