IT MAY, after all, be possible to mend a broken heart. 快猫短视频s at Northeastern University in Boston have invented a 鈥渃ellular bandage鈥� which they hope will limit the amount of damage sustained by the heart after a heart attack.
If the blood supply is cut off to cells, they develop holes in their outer membrane and die. When a person has a heart attack this is exactly what happens; the blood supply to the muscle of the heart is disrupted, creating holes in the membranes of the cells. Whether people survive an attack depends on how much of their heart muscle has been damaged in this way.
Ban-An Khaw and his colleagues wanted to see if they could limit the damage sustained by heart muscle by trying to patch up the holes in time to prevent the cells dying (Nature Medicine, vol 1, p 1195). 鈥淐ell death occurs because the holes in the membrane allow critical enzymes and salts to wash out of the cells,鈥� says Khaw. 鈥淚t鈥檚 like a car engine which runs out of petrol 鈥� the tank needs to be filled up again if it is going to carry on working.鈥�
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The patching technique relies on little bundles of fat called liposomes, which in this case have antibodies attached. The antibodies Khaw has used so far are designed to bind to myosin, a protein which is plentiful inside heart muscle cells and which is responsible for the contraction of the muscle. The liposomes will be pulled over holes in the cell鈥檚 membrane because of the attraction between the antibodies on the liposome and the myosin inside the cell. Khaw believes the force of the attraction will pull the liposome into the hole, where it will eventually fuse with the cell membrane, which also consists of fat.
To test this theory, Khaw took cultured heart muscle cells that had been starved of oxygen and treated half of them with liposomes. The other half were left untreated. He reasoned that if the liposomes sealed the holes, the number of cells which survived would be a measure of success.
Without liposome treatment, only 5 per cent of the oxygen-starved cells survived. But with treatment, the survival rate increased to almost 90 per cent. Khaw also used silver grains trapped in the liposome to get an impression of how the cells were sealed. 鈥淚f the silver stays on the outside of the cells, we know they have been plugged,鈥� he says. But if the silver ends up inside the cells, the liposomes must have fused with the cell membranes.
For heart attack victims, Khaw estimates that plugging the cellular leaks and restoring the blood supply by administering standard clot-busting drugs could salvage up to 90 per cent of the heart muscle at risk of dying. Without plugging the holes, only around half the muscle is usually saved. Animal trials are due to start this week. If they are successful, Khaw says that human trials will follow.
Other researchers are already looking at liposomes as a delivery system for drugs and genes. Khaw also wants to explore this angle. 鈥淲e could use genes delivered by liposomes to convert fibroblast cells into muscle cells, so replacing scar tissue by real muscle,鈥� he says. (see Diagram)
