Why can’t we grow our limbs back? We are working on it!

This is about limb regeneration. It’s the kind of thing that salamanders can do. It is a very complicated process. Humans can’t do it but wouldn’t it be nice if we could? It would almost be the holy grail of medicine. Research on the regeneration of a frog’s limb gives the faintest of hope that humans might be able to achieve this in the future.

Frog leg limb regeneration has been made possible by a cocktail of drugs and a bioreactor dome
Frog leg regeneration has been made possible by a cocktail of drugs and a bioreactor dome. Image: Tufts University.

The Life Science website states that humans have the ability to regenerate. Humans can build entire organ systems in the womb just from genetic information. A complete person is built in nine months. And they say that the underlying genetic machinery in a human and a salamander is not that different. It is, therefore, believed that humans might be able to regenerate limbs. They don’t know the reason why at the moment but they’re looking at the mechanisms which would help to illuminate humankind’s failure in this regard.

Researchers employed a cocktail of drugs and a “bioreactor dome” around the stump of an amputated frog’s leg to see whether, in conjunction, they could initiate the body to regrow the missing leg. Frogs are not known to regenerate limbs. However, in this instance over a period of 18 months a skinnier than normal and slightly malformed limb had fully grown where there was once nothing.

Nirosha Murugan, from Tufts University in Massachusetts, said “It would be unrealistic to micromanage every molecular cascade”. What they hope to do is to find the “key to start the engine of the system”. The intention is that the body takes over by kickstarting it with this mixture of drugs.

The experiments on frogs have been published in the journal Science Advances. Five chemicals designed to promote cell bone growth were put over the stump and sealed inside a silicon cap. They called this a bioreactor dome. It was left on for 24 hours in the hope that the cells and the stump would be programmed to start regeneration of the limb.

Initially it didn’t work but after four months there was the faint vestige of a stump. After nine months there was a “finger-like projection”. This became a complex leg-like structure with webbed toes. The legs were imperfect. As mentioned, after 18 months it was fully grown but skinnier and malformed.

They hope to be able to achieve the same result with people although there is no guarantee of success. Frogs react differently and this is indicated by their ability to produce a featureless cartilaginous “spike” after the leg has been amputated. This tells us that frogs respond to a loss of a limb in a different way to people.

Next, they’re going to try to reproduce the process in a mammal. Even if the ability to regenerate a full limb is a long way off, the regeneration of nerve cells might at least help in resolving problems with the nervous system including such conditions as phantom limb pain.

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