Bone
That Grows Back (6.19.03) - Suppose you break a bone, and go to the emergency
room. Imagine that a doctor there could start growing your bone back.
Growing
Stronger Bones (5.11.00) - Women aged 50 and over who garden at least
once a week showed higher bone density readings than women who engage in almost
any other form of exercise.
For osteoporosis sufferers a cure might come down to bear bones research now
underway at Michigan Technological University. As this ScienCentral News video
reports, scientists there are studying how bear hormones could help strengthen
human bones.
Bear with Them
When black bears hunker down to sleep away winter, something unique happens.
Instead of emerging from slumber with weaker bones, bears wake with stronger
skeletons than ever.
Humans can't pull off this kind of inactivity without our bones becoming as
brittle as kindling. So, what do they have that we don't? New research indicates
that it's all in the bears' hormones. Understanding these hormones might be
the key to preserving human bone density and preventing the bone disease
osteoporosis,
a study published in the Journal
of Experimental Biology suggests.
In humans and other mammals, lack of physical activity causes bone production
to slow as bone breakdown speeds up. But the black bear is different. To thwart
breakdown, the burly animals have developed a unique biological method to
control calcium levels even as they sleep. "We're most interested in
how bears recycle calcium," explains Seth
Donahue, the study's lead researcher and an assistant professor at
Michigan
Technological University. "That's most likely regulated by specific
hormones."
image: Virginia Tech
Not much is known about exactly how these hormones
work, but researchers do know that the hormones regulate the resorption
cells that break bone down, the forming cells that build bone up, and
the calcium
levels that sustain bone building.
Donahue theorizes that because bears don't urinate or defecate while hibernating
(unlike other hibernators), they store the calcium that builds as they hold
in waste. This unique trait enabled bears to evolve "a unique recycling
mechanism for dealing with these waste products," says Donahue. And it's
this recycling mechanism that Donahue believes helps bears forming cells work
overtime to replace lost bone, something that happens very slowly in humans.
At work in this rebuilding process are two hormones common to bears and
people—calcitonin
and parathormone.
In bears, the two seem to have a slightly different sequence of amino acids
or proteins that enable bears to maintain steady levels of calcium even as
they sleep, Donahue says.
Finding out why bear bones are s strong could lead to new therapies for osteoporosis. image: Virginia Tech
Humans don't have this ability. When we experience
long periods of inactivity, and as we age, our bones naturally break down.
While this process is a part of growing older, it can be compounded by the
degenerative bone disease osteoporosis. The disease makes bones more fragile
and subject to fracture. After taking a synthetic version of parathormone,
osteoporosis patients say they've experienced some relief. But Donahue hopes
to do more. He'd like to use his research to manufacture a synthetic drug
that mimics what bear hormones do. "If we can identify which specific
growth factors or hormones regulate calcium in bears, it might give us some
insight for developing pharmaceutical therapies for osteoporosis in humans,"
he says.
Donahue first began exploring black bears, known scientifically as Ursus
americanus, after reading a study that showed bears don't lose muscle
mass while hibernating He teamed up with Dr. Michael Vaughan, a professor
of wildlife sciences at Virginia
Tech, who also studies bear physiology. Vaughn collected blood samples
for Donahue, who then began to explore the hormones at work in bear bone formation.
All this could change the way doctors treat osteoporosis. Rarely seen hundreds
of years ago, the disease is striking more people as the U.S. population survives
into its seventies and eighties, a time when the effects of osteoporosis become
severe. Last year, the disease caused 1.5 million fractures, with fifty percent
of women and twenty five percent of men over the age of fifty suffering a
broken bone related to osteoporosis.
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