Discoveries: Space sheep

Colorado State University, NASA and a herd of sheep have teamed up to make human space travel safer.

The federal space agency hopes to send astronauts to Mars by 2030, but it needs more information about the impact of weightlessness on the body first. Christopher Puttlitz, associate professor of mechanical engineering and head of the CSU research team, is responsible for landing a $1.2 million grant from NASA to fund the study.

“It is estimated that it could take anywhere from nine to 12 months to travel to Mars and back depending how long [the astronauts] stay when they get there,” Puttlitz said. “Two big risk factors that could affect them psychologically and physiologically are prolonged exposure to microgravity and radiation. We’ve identified the knowledge gaps and are working toward providing answers.”

According to NASA’s Human Research Roadmap, astronauts can lose 1 percent to 2 percent of their bone density each month in space. This loss, coupled with the high-impact forces astronauts may encounter, can put them at risk of fracturing bones. So Puttlitz and Ross Palmer, a CSU professor and veterinary orthopedic surgeon,  are using living sheep to mimic the impact of space travel on bones to better understand bone health and healing.

The study began in 2011 and focuses on three distinct areas of research: developing a model to simulate bone-density loss, determining how bone fractures heal in space and identifying methods to treat broken bones in a microgravity atmosphere. The project is in its third and final year. NASA’s grant covers the duration of the study, providing about $400,000 per year.
“The systematic approach that Dr. Puttlitz and his team are taking greatly enhances the value of the study,” said Dr. Jean Sibonga, bone-discipline lead for the human research program at NASA.

The first year primarily was spent developing a new ground-based computer model to imitate bone density loss that astronauts may experience in space. The model simulated 12 months of space-travel-related bone loss in five to six weeks.

The model was developed by observing the results of placing a protection frame, or brace, on the back leg of a sheep and isolating the metatarsal bone from the impact of normal daily activity over an eight-week period. The brace kept the sheep from bearing weight, simulating the effects of microgravity. Because the bone was isolated from any gravitational forces, the research team was able to discern that the sheep’s bone density decreased – as did the load required to fracture the bone. The weakened bone could break more easily, Puttlitz reported in the Journal of Biomedical Engineering.

With the knowledge of bone density loss in microgravity revealed in the first phase of the study, the second phase focused on bone regeneration in the absence of gravity. In the second phase, the protective frame was placed on a new set of sheep for three weeks. At that time, veterinary orthopedic surgeons removed a 3-millimeter section of bone in the sheep’s isolated metatarsal.

“A fracture requires blunt force, whereas we’re removing a small piece of bone,” Palmer said.
“With this surgical process, we don’t have to work to restore ‘normal,’ because there’s no regional damage.”
They reaffixed the brace to the sheep’s leg and monitored fracture healing in simulated microgravity for another four weeks.

“We found that it definitely does slow down the healing and alters cellular mechanisms,” Palmer said. “We know the bone is already weakened when it’s isolated. This is significant in that – whether it’s an astronaut or my mother – if osteoporosis is present, they’re at risk of a fracture.”

Puttlitz also noted that in simulated microgravity, bone does not heal well because factors such as weight, which stimulates the cell growth that is crucial to healing and bone regeneration, are absent.

The use of sheep in these studies has been important for the researchers to determine how the results could translate to astronauts, and eventually to older people and others with osteoporosis.

Adult ovines, or sheep, have bones that are similar in size and skeletal architecture to humans, making them desirable candidates for investigating orthopedic-related conditions. Traditionally, mice and rats have been used in research experiment, but the findings are not as readily translatable to human outcomes because of major anatomic and physiologic differences between the two species, such as bone microarchitecture and healing rates.
Use of animals in a research study, though, is not taken lightly.

“We have to provide extensive literature research to establish that the use of animals for a research project is the only reasonable way and practical means to get the information necessary,” Palmer said. “It’s easy to look at it from an outside angle, until the information we discovered with animal research can be used for yourself or a family member.”

At federal and local levels, a multitude of overseers and protocols are in place to ensure humane treatment and specific procedures regarding use of animals for research.
Twenty-three sheep were used in phase 1 and approximately 20 in both phases 2 and 3. The sheep were selected according to the approved Institutional Animal Care and Use Committee (IACUC) protocol, said Puttlitz. IACUC is a self-regulating entity that, according to federal law, must be established by institutions that use laboratory animals for research or instructional purposes to oversee and evaluate all aspects of the institution’s animal care and use program. Additionally, CSU animal laboratories must abide by U.S. Department of Agriculture regulations.

The laboratory vet and flock manager, as well as other vets, provide daily assessment of the animals, Palmer said. Puttlitz added that orthopedic surgeons monitor the sheep at least twice a day and provide pain relief when necessary.

“It’s important to note that we recognize we’re causing discomfort to an animal, and that we take every measure to minimize or relieve that daily,” said Wayne Jensen, a CSU professor and associate head of the College of Veterinary Medicine and Biomedical Sciences.

The importance of animal use in research studies is that scientists can produce more exact findings before moving on to human trials. In this case, that includes pseudo-astronauts, complete with fluffy wool, beady eyes and bleating.

NASA’s Sibonga said the use of sheep in this project has been critical to its success. “The devil is in the details,” she said. “We are able to pin down those details using animals, especially larger animals. The tissue more resembles a human and allows us to translate the findings to terrestrial medicine.”

Even though the sheep are helping NASA determine the safety of space travel, the results of this study could extend to other populations with bone-density issues as well.

“Although this project is a niche application for NASA, there’s also a massive potential benefit for the greater population,” Palmer said. “For instance, one in five men over 50 in their lifetime will have a fracture induced by osteoporosis. In women, it’s one in three. This is debilitating because it causes someone to lose their lifestyle independence.”

The third and final phase is under way and will be conducted through this year.

Understanding that bone fractures do not heal well without gravitational forces, the research team is trying to identify the most effective methods to regenerate bone and heal fractures for astronauts in space.

“We’re working with non-invasive, FDA-approved treatments to enhance bone healing,” Puttlitz said. “We’re currently focusing on ultrasounds and the effects that a pulsed ultrasound unit would have when placed against the fracture site.”

The research team will test a number of theories later this year.

“Our emphasis is on alternative mechanical stimuli,” Palmer said. “We want to use something that’s adaptable and practical for a number of situations and people. To me, that’s the true benefit.”

For Palmer, being able to translate animal research to human practice is nothing short of remarkable.

“I grew up thinking all I was going to do was benefit animals,” he said. “This job took a huge turn working for the benefit of people. To be part of something that can impact the population this dramatically would be the ‘high five’ of my career.”

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