Some Bear Facts That Could Help Prevent Human Strokes
Long periods of immobility can put people at risk of dangerous blood clots — yet hibernating bears lie around for months without any problem. Now scientists think they've figured out why.
The researchers hope the insight can eventually lead to new drugs for preventing life-threatening blood clots — the kind that begin in the legs but can travel to the brain and cause a stroke, or to the lungs and cause a pulmonary embolism.
In their new study, the researchers found that in hibernating bears, a particular protein — called heat shock protein 47 (HSP47) — is substantially dialed down from its normal activity level. And that appears to prevent blood clots from forming while the animals are in months-long slumber.
Even more importantly, the investigators found, that phenomenon also occurs in other species, including humans. Specifically, HSP47 activity is low in people paralyzed by spinal cord injuries.
That may sound counterintuitive, since temporary immobility — recovering from an injury or surgery, or taking a long-haul flight — can promote blood clots in some people. But it's known that people with paralysis have no higher blood clot risk than mobile people do.
And the new findings suggest that HSP47 may be the key, the study authors said.
The hope is that the finding will lead to new ways to prevent blood clots in vulnerable people, according to Dr. Tobias Petzold, one of the researchers on the study.
"We would like to further study the mechanism by which HSP47 works in preventing (blood clots) in more detail," said Petzold, of Ludwig-Maximilians-University in Munich, Germany.
Some long-used medications are already used for preventing blood clots in at-risk people, including old-fashioned aspirin. But, Petzold said, they have side effects, such as an increased risk of bleeding. So there is still a need to keep hunting for medications that are highly effective but safer.
"We think that a ‘natural' blood thinner that the body is capable of mobilizing spontaneously could help tackle that unmet clinical need," Petzold said.
Why turn to bears in that quest?
"We believe that the bear is a walking library of solutions to our sedentary lifestyle," Petzold said.
After all, he pointed out, hibernating bears spend a large portion of their waking lives feasting and packing on huge amounts of weight, only to then spend half the year lying around doing nothing. For humans, that's a virtual recipe for obesity, muscle loss, thinning bones, type 2 diabetes and many other health problems — including blood clots.
Yet bears emerge from their hibernation unscathed. Understanding what, exactly, protects them could theoretically point to completely new treatments for various human diseases related to "modern lifestyles," Petzold said.
Other researchers are studying bears for that very reason.
A study published last year by a Washington State University team identified specific proteins that seem to help shield hibernating grizzlies from diabetes.
Humans, it turns out, have counterparts to those protective proteins.
For the new study, Petzold and his colleagues studied not only brown bears, but also pigs that were either cooped-up or free-roaming, and people who were mobile or paralyzed by spinal cord injuries.
The researchers found that, on average, HSP47 from hibernating bears' blood cells was reduced by 55 times, versus active-season bears. A similar pattern was seen in both pigs and people.
It all suggests that HSP47 could be a good target for new medications for people at high risk of blood clots during shorter periods of immobility, according to an editorial published with the study.
At the moment, researchers know a lot more about the things that trigger clots than what protects against them, wrote Mirta Schattner, who studies blood clotting mechanisms at the National Academy of Medicine in Buenos Aires, Argentina.
According to Schattner, the new study "shows that looking at nature can be a good way to learn about human biology."
Blood clots, however, do not only form when people are immobilized, Schattner pointed out. Chronic health conditions like diabetes and various cancers can raise the risk, too. So, she added, one question going forward is whether this heat shock protein is important to blood clotting in those cases, too.
The findings were published online April 13 in the journal Science.
The American Heart Association has more on preventing and treating blood clots.
SOURCES: Tobias Petzold, MD, department of cardiology, Ludwig-Maximilians-University, Munich, Germany; Science, April 13, 2023, online