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Magnetic聽cells can be used to rebuild damaged tissue after a heart attack, research in mice suggests.

Heart attacks occur when the supply of blood to the heart is blocked, usually by a blood clot, causing heart muscle cells to die. Many patients develop chronic heart failure, in which the heart has trouble pumping enough blood to the rest of the body.

An obvious solution is to replace the damaged heart muscle cells with new ones, such as those derived from stem cells. But studies have found that less than 5 per cent of new cells stay in place when injected directly into the heart. Most leak out of the injection site or flow into circulation.

To overcome this problem,聽聽at the University of Bonn in Germany and his colleagues engineered聽magnetic聽muscle cells that could be retained in the heart using magnets.

First, they took heart muscle cells from mouse embryos and made them聽magnetic聽by loading them with iron oxide nanoparticles. The nanoparticles have a silica coating that stops them from being rejected by the immune system.

Next, they injected the magnetised cells directly into the hearts of mice with heart injuries. They hovered a magnet 5 millimetres above the heart surface of half the mice for 10 minutes to hold the cells in place.

The trial was a success: seven times more magnetic cells grafted to the heart tissue when the magnet was applied. 鈥淲e think the cells are kept in place by the magnet or they become like small magnets themselves and stick together,鈥� says Roell.

Pump it up

The additional muscle cells largely restored cardiac function 鈥� eight weeks later, the hearts of treated mice could pump almost double the amount of blood as untreated mice.

No signs of toxicity were observed. The聽magnetic聽nanoparticles did not affect cell viability when tested in heart muscle cells in a dish, and did not cause noticeable side-effects in live mice. After injection, they mostly remained in the heart muscle or were excreted via the liver and kidneys.

Previous research has found that iron oxide nanoparticles can be toxic in humans, but at significantly higher doses than those used in this study, says Roell.

聽at the University of Washington in Seattle says the approach is promising. 鈥淚t nicely addresses this real-world problem we have in trying to deliver cells to the heart, which at the moment is an incredibly inefficient business,鈥� he says. 鈥淚 would say so far, so good, although of course there are always challenges moving from mice to humans.鈥�

The聽magnetic聽nanoparticle approach is one of several being explored for healing heart attack damage. For example, some groups are experimenting with using gels to help cells stick to existing tissue, while others are trying to create heart muscle tissue that can be inserted directly.

One advantage of the聽magnetic聽nanoparticle approach is that it would not require open heart surgery, says Roell.聽Magnetic聽muscle cells derived from stem cells could potentially be injected into the heart via a long, narrow tube, while a magnet on the outside of the chest could hold them in place, he says.

Roell is now planning to test the聽magnetic聽nanoparticles in pigs, which have similar circulatory systems to humans. 鈥淲e鈥檙e hoping we can replicate these exciting mouse results in bigger animals,鈥� he says.