'Spare part heart' beats in lab

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The stripped-out shell of a heart has been made to work again - using brand new cells planted inside it.

Scientists removed all the muscle cells in a rat heart, leaving just a "scaffold" of other tissues such as blood vessels and valves.

When the University of Minnesota team added heart cells, they quickly grew and produced a pumping action.

It is hoped the Nature Medicine study will ultimately mean human or animal hearts can be crafted for transplant.

It opens a door to this notion that you can make any organ: kidney, liver, lung, pancreas - you name it and we hope we can make it Dr Doris TaylorUniversity of Minnesota

Experts believe that failing organs in humans could in theory be replaced by new versions grown using stem cells.

These are the body's master cells, which have the potential to be transformed into any cell type in the body.

Any organ constructed in this way would have a significant advantage over donor organs for transplantation because they could be made to match the patient, and face a much smaller risk of rejection by the immune system.

However, one of the biggest obstacles to developing three-dimensional organs is finding a way to persuade cells to form the complex structures needed.

The Minnesota researchers decided that the best template would be another heart.

They took an adult rat heart, bathed it in detergents which removed all the cardiac cells, leaving a "frame" of other heart tissues forming the basic shape of the organ.

This frame was then "seeded" with cardiac cells taken from a newborn rat, and kept in lab conditions designed to simulate the growing heart.

'Speechless'

In just four days, the cells had multiplied and spread to such an extent that the researchers could see contractions in the new muscle tissue.

By the eight day, the home-grown hearts were capable of pumping, albeit at only 2% of the power of a normal rat heart.

This isn't something that we will see in man for at least a decade, I believe Dr Peter WeissbergBritish Heart Foundation

Dr Doris Taylor, who led the experiment, suggested that it might change the way scientists think about producing artificial organs.

"It opens a door to this notion that you can make any organ: kidney, liver, lung, pancreas - you name it and we hope we can make it."

Another researcher, Dr Harald Ott, said: "When we saw the first contractions we were speechless."

Pig transplant

Professor Sian Harding, from Imperial College London, who is working on ways to repair failing human hearts with new heart cell "patches", described the technique as "potentially a real advance".

She said that it might be possible in the future to remove the cells from a pig heart - which is very similar in scale and function to a human heart. Human stem cells could then be seeded to produce an organ capable of being transplanted into humans.

She said: "Heart muscle cells need so much oxygen, that each of them has to be virtually touching a blood vessel, and achieving that kind of level of blood supply is a challenge.

"If you could use the existing blood vessel structure from another heart, that would be really useful."

Dr Peter Weissberg of the British Heart Foundation said that the research was "important", but cautioned that it would be some time before the technique could be use for human transplant organs.

"This isn't something that we will see in man for at least a decade, I believe," he said.

"First we have to find a way of getting hold of the patient's own stem cells so that the new heart is not rejected."

Dr Jon Frampton Wellcome Trust Senior Fellow at the University of Birmingham said: "Although this is only a first step requiring considerable follow-up development, the study nevertheless represents an exciting breakthrough that will eventually make the prospect of repairing damaged hearts a reality and will also be an approach that can be extended to other organs."