VOA标准英语2011--Pythons Unlock Human Heart Health Secrets

Pythons Unlock Human Heart Health Secrets

Studying snakes might seem like an unlikely way to help people with heart disease, but a python’s remarkable ability to quickly enlarge its heart during digestion has Colorado medical researchers looking toward surprising new therapies to treat human heart conditions.

Young Burmese pythons coil in plastic boxes at a science lab at the University of Colorado in Boulder. Each one is well over a meter long, but they can grow to seven meters.

The snakes' “extreme” physiology is why molecular biologist Leslie Leinwand studies them. For instance, she says, even a big python never needs a mid-day dinner or even a weekly meal.

“They can go for months and months without eating anything, and nothing terrible happens to them.”

When these giant serpents do finally show up for supper, they prefer rats, pigs or even a deer. And, unlike people, pythons never nibble. They swallow their prey whole, in one gulp. After that, Leinwand says, things get even stranger.

“Right after they eat a meal, the bulk of their organs in the body get bigger.”

To speed digestion after that monstrous meal, the python’s heart also gets bigger - 40 percent larger than normal - and it can take two weeks for a python to finish digesting its dinner. After that, the heart and digestive organs gradually return to their normal size.

Dramatic changes

The key to this unusual process appears to be the python’s blood. When scientists filter out the red blood cells of a resting python, the remaining plasma is clear, like human plasma. However, python plasma changes dramatically during the first days of digestion.

“Their blood is actually milky white, and that milkiness, what’s making it white, is actually the fat in the blood,” CU student Ryan Doptis explains.

That fat gives the python energy to digest its meal, says Leinwand, just as blood fats fuel our bodies. However, she says, the strange, milky blood coursing through a python’s body during the digestion process contains 50 times more fat than normal. In people, high blood fat can increase the risk of heart attack, but that's not the case for these snakes.

“In the python, it isn’t toxic at all. What happens is the pythons have evolved a way of burning that fat, that’s in the blood, very efficiently and without harmful byproducts," says Leinwand. "There’s what we would call cardio-protection or heart protection that the python has.”

Heart protection

She adds that people, too, sometimes need cardio-protection. When someone suffers from high blood pressure or has a heart attack, heart cells can die. Over time, the weakened heart may grow flabbier in a way that increases damage. While exercise can strengthen some hearts, Leinwand warns it’s not for everyone.

“Some people with such severe heart disease can’t exercise enough to get that benefit, so our idea is that we could use what we’ve learned in the python perhaps to treat heart disease.”

According to Leinwand, when the python’s heart grows to help the snake digest its meal, it’s doing something that also happens, to a much lesser extent, to a human athlete’s heart. Each individual heart cell is getting larger and stronger.

Impact on mammals

Post-graduate student, lead researcher Cecilia Riquelme, wondered if the fatty snake blood could produce similar changes to a mammal’s heart. So she followed a hunch.

“There has to be a factor in the blood that was inducing all the organs to grow in a concerted manner. So how can we prove that?" Riquelme says. "I decided maybe I can just try the python blood on cardiac cells in the laboratory.”

So Riquelme bathed heart cells from a rat in python plasma. The cells grew bigger and stronger.

The results, published online in Science, astonished Leinwand. “That was the first eureka moment of this project. Because, it still would be of academic interest if this was something specific to snakes. But when she showed that you could promote this type of cellular growth in the heart cells of a mammal, that motivated us to really push on this project.”

Heart drug for humans?

The researchers zeroed in on three key fatty acids in the python’s milky blood, fats which are also found in foods such as coconut oil, animal fat and butter.

“So it’s myristic, palmitic and palmitoleic," Leinwand says. "I want to emphasize it needs to be those three and in a particular combination that’s found in the python.”

These fatty acids are only a fraction of the many fats in a python’s blood. Still, in the right proportions, even small amounts of them have proven powerful at strengthening the heart of a healthy, live mouse.

If further testing shows that these fatty acids can also strengthen a sick mammalian heart - possibly a diseased human heart, Leinwand envisions a new drug for treating heart disease.

“Those three fatty acids would be the drug,” she says.