Seal hole, heal heart
INDIA, a frontrunner as far as the incidence of heart attacks is concerned, will have to import the technique of mending damaged hearts. The repair kit, called 'cellular bandage', meant to seal holes in the heart occuring after an attack, was recently developed by researchers in the us (New Scientist, Vol 148, No 2004).
Developed on the basic understanding of hole creation that disruption of blood supply to cells creates holes in the outer membranes, forcing them to die, scientists at the Boston-based North- eastern University developed this novel patching technique. "Cell death occurs because the holes in the membrane allow critical enzymes and salts to wash out of the cells," says Ban-An Khaw, the leader of the research team.
When a person experiences a heart attack, the blood supply to the heart muscle is terminated, creating holes in the membrane of the cells. The chances of survival of any victim of a heart attack depends on the extent to which his or her heart muscle has incurred damage by the same. Scientists, therefore, set out to investigate if the damage sustained by the heart muscle could be limited by patching up the holes in time.
Interestingly, the patching technique involves little bundles of fat called liposomes, which are already being tested as a delivery system for drugs and genes. The liposomes in this case are coated with antibodies which are designed to bind with myosin. Myosin is a protein found in abundance inside the cells of the heart muscle, responsible for contraction of the muscle. Scientists believed that the affinity between the antibodies on the liposomes and the myosin inside the cell will draw the liposomes over holes in the cell's membrane. Antibodies would thus anchor liposomes into the gaps where they would eventually blend with the cell membrane containing fat.
The next step was to test this theory, Cultured heart muscle cells were first starved of oxygen. Following this, half of them were treated with liposomes and the other half were left untreated. The number of cells that survived were to indicate whether or not liposomes sealed holes. Significantly, with liposomes, almost 90 per cent of the oxygen starved cells survived. Without liposome treatment, just five per cent survived.
To trace how the cells got sealed, scientists used silver grains trapped inside the liposome molecules. "If the silver stays on the outside of the cells, we know they have been plugged. But if the silver grains end up inside the cells, the liposomes must have fused with the cell membrane," says Khaw. Further, by plugging the cellular holes and restoring blood supply by giving standard clot busting drugs, one could salvage up to 90 per cent of the heart muscle.
After successful laboratory trials, animal trials are on the anvil. While heart attack victims are sure to benefit from this technique, could the wonder kit seal broken hearts as well? Time will tell.