ARLINGTON, Va., Oct. 1, 2003 -- Although they may be known more for preventing forest fires, stealing “pic-i-nic” baskets or harassing lost little girls with gold locks, bears may teach us a thing or two about having strong, healthy bones.

Biomedical engineers at Michigan Technological University are looking to the beloved Ursus americanus, the American black bear, and particularly its hibernating ability, for clues to help prevent osteoporosis in humans.

During hibernation, a bear’s metabolism changes; its heart rate and body temperature decrease and it recycles wastes while asleep. After several months of inactivity, bears emerge from hibernation with a huge appetite and bones almost as strong as when they first entered the den. Biomedical engineering researchers want to find out how bears do this, then use that knowledge to help people in situations similar to hibernating bears, such as people immobilized for long periods of time due to illness or injury and people at risk for osteoporosis.

Normally, our bones undergo a constant but perfectly balanced process of bone building and bone breakdown; osteoblasts build bone tissue as fast as osteoclasts resorb it. This constant recycling, along with the stress of normal activities, keeps our bones healthy and strong. This process becomes unbalanced in favor of the bone-resorbing osteoclasts whenever the physical demands of our bodies decrease, such as when someone is confined to a wheelchair or bed or when an astronaut spends months in space, and in cases of osteoporosis.

Osteoporosis is progressive thinning of bone characterized by low bone mass and structural deterioration of bone tissue. It leads to bone fragility and an increased susceptibility to fractures of the hip, spine, and wrist, and it affects more than 44 million Americans, about 80 percent of whom are women.

In 2001, this nation spent an estimated $17 billion, or $47 million a day, for hospital and nursing home care associated with osteoporosis and related fractures.

Though osteoporosis is not age dependent, 55 percent of the population 50 years of age and older have low bone mass and face an increased risk of developing osteoporosis and related fractures, according to the National Institutes of Health. According to the National Osteoporosis Foundation, osteoporosis is responsible for more than 1.5 million fractures annually. Public health officials expect all these figures to climb as the numbers of elderly rise.

Bears maintain bone by recycling their calcium with almost total efficiency, says Seth Donahue, Ph.D, an assistant professor in the Department of Biomedical Engineering and a leader of the Michigan Tech team. As a result, bears – even female bears, which often give birth and nurse their cubs during hibernation – don’t lose bone density.

In studies conducted while at Pennsylvania State University, Donahue analyzed blood samples from bears during and after hibernation, looking for markers that indicate the processes for both bone formation and bone loss. Donahue found that during hibernation, the bears showed increased bone resorption markers, but no change in bone formation markers. Also, bears just emerging from their dens showed dramatic increases in the marker for bone formation, which suggests they’re regaining bone much faster than other animals, including humans. Results were published earlier this year in the journal Clinical Orthopedics and Related Research.

The next step, says Donahue, is to find out how the bears make more efficient use of calcium, which may lie in their hormones or other molecules. If that is the case, it might be possible to produce those hormones or other material synthetically and prescribe it to osteoporosis patients.

But don’t think avoiding osteoporosis is as simple as increasing your calcium intake. "Just because you take calcium doesn't mean you're going to make bone," says Kenneth McLeod, chair of the bioengineering department at Binghamton University and a leading researcher in the field of tissue development, healing and adaptation. "Calcium is necessary but not sufficient. There has to be a signal to make bone, and it turns out that if you don't have adequate fluid flow across your bone, you're not going to have adequate cell metabolism to trigger bone formation."

McLeod says that osteoporosis is not a disease but a normal, adaptive response by our body to its environment and that neither weight-bearing exercise nor calcium supplements -- nor even a combination of the two -- are capable of triggering the growth of new bone. He believes that the only way to avoid bone loss is to maintain adequate fluid flow across your bone tissue, which requires adequate muscle activity.

McLeod's research suggests that a key to reversing bone loss and triggering bone growth is training up one type of human muscle fiber, Type II A fibers. These fibers, also called fast oxidative fibers, contain many mitochondria and are surrounded by many blood capillaries. McLeod has developed a device that sends low-level vibrations into the body to stimulate Type II A muscle fiber development, enhance fluid flow through the bones, and stimulate bone growth. The device is in clinical testing in advance of seeking approval from the Food and Drug Administration.

In 1990, The Whitaker Foundation awarded McLeod a research grant, which helped him lay the foundation for his current research. Last year, the foundation awarded Donahue a research grant to model and measure the effects of microcracks on fluid flow in bone. The long-term goal of the project is to increase the understanding of the mechanical and biological processes that regulate changes in bone.

Contact:
Mark Bowman (703) 528-2430