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The animal that never gets cancer

The naked mole rat may not be pretty, but it doesn't feel pain, get dementia, osteoporosis, or cancer. Dr Karl gets under the skin of this very special animal.

The animals called rodents make up about 40 per cent of all mammals. They're very widespread and live in all kinds of extreme environments worldwide.

But one rodent called the naked mole rat is very special - it doesn't seem to age, it doesn't feel some kinds of pain, it lives in communities like bees and ants, and it never gets cancer.

First of all, the name 'naked mole rat' is dead wrong. It's not naked (it's mostly covered with naked skin but it does have about 100 hairs), it's not a mole and even though it's a rodent, it's not a rat. It's closer to porcupines and guinea pigs than rats.

The naked mole rat lives in the dry, high plateaus of East Africa. It's about 8 to 10 centimetres long and weighs about 30 grams. They live in groups of about 20 to 300 individuals — though usually about 70 or so.

They dig with their teeth underground tunnels that are kilometres long. In fact, about one-third of all their muscles are in their jaw. For humans the corresponding part is our leg.

As in a bee colony, there are many females but only one has sex and makes babies. She is serviced by between one and three males. And, again as in a bee hive, all the other naked mole rats in the burrow are organised in castes. So some dig tunnels, some are warriors, some look after the babies, some forage for food, and so on.

Naked mole rats are vegetarians — apart from eating their own dead babies and their faeces.

Another odd thing about them is that they don't feel chemical pain, such as from acid or capsaicin — that's the stuff that makes chilli hot. This is probably because their underground tunnels are not well ventilated so the carbon dioxide level is not the 400 parts per million we currently enjoy, but 50,000 parts per million or five per cent. We humans can only function for about four hours in levels that high. But naked mole rats do it all their lives.

The problem is that the carbon dioxide dissolves in water to make acid, which both disrupts normal physiological functioning as well as being painful. But the naked mole rat has evolved to not feel any pain and function normally for their whole life.

And speaking of lives, they're incredibly long-lived. Animals of their size and weight usually live for only a few years. Naked mole rats have lived for over 30 years. And during that long life they don't show any signs of ageing - no osteoporosis, no muscular frailty, no mental decline and no slowing down of various organ systems. They stay strong and robust until the end.

And speaking of the end. They don't get cancer. Cancers account for about 10 to 15 per cent of all human deaths, and about 90 per cent of all mice and rat deaths — providing they can avoid cats and the like. Naked mole rats — zero cancer deaths. They simply don't get any cancers.

We've found several different pathways or adaptations they use to avoid cancer. One is called early contact inhibition. The 'contact' refers to cells touching or contacting each other. Normally the cells in your body are always dying and always regenerating. And normally they regenerate and grow to a certain stage. Once they have replaced what was there originally they stop growing. Cancer cells do not stop growing in most animals. But they do in the naked mole rat.

If you get a bunch of normal human cells and grow them on a culture plate they'll grow until they form a single thin mono layer on that plate then stop. But cells from the naked mole rat won't even get to the single thin mono-layer stage. Once they sense another naked mole rat cell nearby, they'll stop growing. So inside a naked mole rat, if a cell turns cancerous it will try to keep on growing without limit, but naked mole rat cells have the so-called early contact inhibition. As soon as they get too close in contact with each other, they inhibit growth. The cancerous cell just withers on the vine.

In terms of living longer and more robustly, how to bypass certain types of pain, and how to foil cancers, naked mole rats have so much to teach us.

And that's a bare fact ....

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