A Breath of Fresh Fructose?

naked mole rat

Described by some as looking like “bratwurst with teeth,” naked mole rats live in communities with social structures resembling beehives, are coldblooded like reptiles, and now are known to get energy from fructose, like a plant. (Photo credit: Ger Bosma/Alamy)

It’s difficult to find an odder animal than the naked mole rat (Heterosphalus glaber). A native of east African deserts, these mammals live more like bees, in complex, underground societies complete with a queen who gives birth to worker offspring who will never reproduce. Also, unlike other mammals, they don’t regulate their body temperatures and so are essentially cold blooded, like reptiles.

In recent years, scientists have come to learn more and more about these curious creatures. They’ve discovered that they’re oblivious to most types of pain, are pretty much cancer resistant, and can live for up to 32 years under the right conditions. Contrast this to the average three-year lifespan for most other rodents, many of which are ideal subjects for study precisely because they do contract cancer readily. It’s easy to see why the naked mole rat has gained popularity among scientists hoping to find ways to improve the quality of life as humans age. Recently, however, scientists have uncovered what may be perhaps the strangest “ability” yet of the naked mole rat, one that makes it similar to plants: the ability to use fructose as a source of energy.

Plants make glucose. Using oxygen as fuel, mammals metabolize glucose to get energy. The oxygen, of course, comes from the air, which is approximately 21% oxygen. Only a few percentage points below this level, air is deemed oxygen poor, and humans stop functioning in air with only 10% oxygen. Scientists always suspected the naked mole rat was especially adapted to low-oxygen environments. They burrow deep into the ground where air naturally would be especially scarce and so have developed “ultra sticky” hemoglobin which allows their blood cells to transport oxygen far more effectively. What the scientists weren’t expecting was how far the naked mole rat could take this. Test subjects placed for hours in a chamber with only 5% oxygen showed no obvious signs of distress. Taking it still further, when the chamber was made completely oxygen-free, the naked mole rats went into a sort of suspended animation state, with their heart rate dropping from 200 to 50 beats per minute. And even after 18 minutes of being completely oxygen starved, the animals could be revived and showed no ill effects. While surviving the oxygen-poor environments made some sense, researchers at the University of Illinois, Chicago, where the study was conducted, couldn’t think of a reason for the naked mole rat’s ability to survive so long without oxygen.

Analyzing the blood of the oxygen-starved rats, something really significant stood out: high levels of fructose and sucrose as well as the chemical GLUT5, a glucose transporter. The fructose had reached all the organs, including the brain. Where it was coming from is still unknown, and the possibility that the rats are actually manufacturing it has not been dismissed. What is clear is that naked mole rats are able to use fructose as fuel when there’s no oxygen present.

“The naked mole rat has simply rearranged some basic building blocks of metabolism to make it super-tolerant to low-oxygen conditions,” said Thomas Park, one of the study’s co-authors, in a report about the research.

And while humans are able to store and use fructose in the liver and kidneys, we are not able to get energy from it. We lack the correct enzymes. Fructose instead gets turned into fat cells, and our bodies need to turn it into glucose before we can use it. This is, of course, the same chemical found in “high fructose corn syrup,” one that has been linked to numerous health problems.

Why the naked mole rat developed such an ability isn’t hard to understand. Worker rats especially spend much of their days burrowing tunnels. They go deeper and deeper, get more and more exhausted and oxygen deprived, and so the ability to “switch” to another pathway for generating energy would only be to their benefit. The question now is, do human beings have the same ability? Can this pathway be “switched on” in our cells to give our bodies another way to produce energy, potentially eliminating the harmful effects from strokes and heart attacks, when the body’s organs suffer from a lack of oxygen? It’s all speculation now, and Park and his colleagues don’t know the answer, and they admit it’s one that others need to answer.

More to Explore
Naked mole-rats are now even weirder: Without oxygen, they live like plants
What can we learn from naked mole rats and eusocial living? – tech podcast
Naked Mole Rat — National Geographic

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