Learning From Healthy Bears (You Mean We Should Hibernate?????)
ANCHORAGE — Gain a few hundred pounds and lie around in bed for months, and you are likely to develop a host of ailments, from diabetes and heart failure to muscle loss, osteoporosis and bedsores.
Unless, that is, you happen to be a bear.
Scientists
have puzzled for decades over the evolutionary tweaks that have allowed
bears and other hibernating animals to lie still through the winter,
forgoing food and water, yet emerge with their health intact come
spring. Researchers believed that if they could better understand how
the animals did it, they might apply the insights to humans, developing
new drugs or medical treatments, for example, or ways for astronauts to
survive long spaceflights in a hibernationlike state.
But
progress has been slow, the bear den holding its secrets tightly. And
in December, the field suffered a further setback, when a highly publicized hibernation study
was retracted after one of the authors was found to have manipulated
the data. Yet the advent of technologies like gene sequencing and
sophisticated imaging techniques over the last few decades has given
investigators hope that they will eventually be able to harness aspects
of the bear’s exceptional physiology for human use.
Last month, in a session on hibernation and human health at the 24th International Conference on Bear Research and Management
here, scientists presented more than a dozen studies, including
research on bears’ cardiovascular system, muscle chemistry, kidney
functioning, fat storage and metabolism.
“I
really think a lot is going on at the moment,” said Dr. Peter Godsk
Jorgensen, a cardiologist at Gentofte Hospital in Copenhagen, who in his
talk discussed studies that used ultrasound imaging and speckle tracking
— a method of quantifying the movement of heart muscle — to look at
heart function in bears during winter hibernation and summer activity.
Confirming
work by other researchers, Dr. Godsk Jorgensen and his colleagues found
that bears’ heart rate slowed sharply during hibernation, from about 75
beats a minute to as few as 10, with pauses that sometimes lasted 19
seconds or more.
“I
once had a patient with a pause of 13 seconds,” Dr. Godsk Jorgensen
said. “When you have that, you go around and you faint and hit your
head.”
A Bear’s Hibernating Heart
The
researchers also identified clusters of blood cells on the bear’s
ultrasound, called “smoke,” that are seen in humans who have severe
heart failure or atrial fibrillation, a condition that raises the risk of blood clots and stroke.
Dr.
Ole Frobert, a cardiologist at Orebro University Hospital in Sweden who
led the research team on the ultrasound study, said work on hibernation
in bears was attracting more interest at a time when some scientists
have grown disillusioned with studies using mice as subjects.
“Medical
research in a way is in a crisis,” Dr. Frobert said, “because we do a
lot of research and publish a lot of papers, but there are very few
breakthroughs.”
Mice
can be more easily kept in a laboratory than bears, of course, but they
are far from perfect as a model for humans and often fail to respond to
drugs or other treatments as humans do. Bears, although more difficult
to study, Dr. Frobert said, allow scientists to look at several
physiological systems at once, and provide a natural model of
evolutionary solutions to questions that continue to befuddle
scientists.
In six years of research, carried out in collaboration with the Scandinavian Brown Bear Research Project
and other researchers in Europe and the United States, Dr. Frobert and
his colleagues have found startling differences in bears’ physiology
during periods of hibernation and periods of activity.
Hibernating
bears, grown fat from summer feasting, do not eat, drink, urinate or
defecate while they are hibernating. But they lose no muscle mass from
inactivity. Platelets in the bears’ blood become less sticky, acting as a
natural blood thinner, the researchers found, perhaps to counteract
blood clots that could form during long periods of immobility. The
bears’ metabolism drops to 25 percent of its normal state and their
kidneys stop functioning, yet they do not have kidney failure.
The
research team collected blood and tissue samples for the studies from
free-ranging brown bears in Sweden in February and again in June. The
bears, all teenagers, were tranquilized, and although some of the
animals later changed dens, they seemed otherwise unaffected by the
research, Dr. Frobert said.
The new wave of hibernation research is of particular interest to scientists studying obesity, which has become epidemic in the United States over the last few decades.
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Obesity in humans is associated with resistance to insulin, a hormone that regulates glucose in the blood, and Type 2 diabetes. Bears also show insulin resistance, studies find, but do not develop diabetes in the classic sense.
“Obese
bears are healthier; in fact, they are more reproductively fit,” said
Heiko T. Jansen, a professor at the College of Veterinary Medicine at
Washington State University who presented at the meetings. “They have
all the advantages, which is so counterintuitive to human biology.”
In
research financed in part by the pharmaceutical company Amgen, Dr.
Jansen and his colleagues found that bears’ handling of insulin appears
to vary with the seasons, with resistance increasing during hibernation
and sensitivity increasing in summer.
Fat
cells of hibernating bears treated with a blood serum from “summer”
bears become more insulin sensitive, the researchers found.
“There’s clearly something important in serum that’s important for multiple things,” Dr. Jansen said.
He and other researchers said they hoped such studies would eventually lead to drugs to treat diabetes or cure obesity.
But
practical applications are still uncertain. And it may take some time
for researchers to figure out how bears do naturally what people cannot.
“We
have to learn and relearn and relearn that nature has solved these
problems,” Dr. Jansen said. “And it’s our job as primates to figure this
out.”