More successes for the "plasticine cells"
3.4.2001
By: By Nicholas Wade, New York Times
Three studies in which bone marrow stem cells were used to repair heart tissue in animals lay the groundwork for a possible revolution in the treatment of heart patients.
In one of the studies, heart tissue developed from the injected cells that appeared to be functioning - the first success of its kind after about two decades of effort. In another study, the stem cells became new blood vessels that rescued the heart cells surrounding the damaged area from the normal course of overgrowth and death. The third study used stem cells to strengthen the hearts of pigs.
According to the three groups of researchers - from Columbia University, the New York Medical College in Valhalla, the "National Institutes of Health" and "Osiris Therapeutics" in Baltimore - in a year or more it will be possible to conduct such experiments on humans.
If these techniques also prove themselves in humans, the researchers say, the treatment for heart attack sufferers will be as follows: cells will be extracted from their bone marrow, these cells will undergo a sorting and culture process and then will be injected directly into the heart, or perhaps into the bloodstream, from where they will settle on the damaged heart tissue and cells The proliferating heart muscle that will soon grow around.
It is also possible - although the idea has not yet been tested and has not been proven possible - that the entire treatment will consist of injecting a cytokine - a natural protein that stimulates the stem cells of the bone marrow to multiply - to heart patients. The cells will settle on the heart tissue. Biologists say it's too early to know whether the bone marrow stem cells are also the heart's own stem cells, which researchers have searched in vain for years, or whether their extraordinary ability to repair the heart is actually a general property of stem cells.
Stem cells are cells that have not yet differentiated into one of the body's specific cell types. That is, they can become the adult cells of the body. At the same time they multiply to maintain a constant source for the creation of new cells. The cells used in the new studies are called adult stem cells, and they are different from embryonic stem cells, the use of which is controversial.
The new studies are a product of recent findings, according to which the stem cells of the bone marrow are much more versatile than thought, and that they are able to create other tissues besides the red and white blood cells, their most familiar function. From this point of view, it seems that the cells are a kind of universal plasticine that responds to local signals. If they are placed in the heart they will develop into heart tissue instead of blood cells.
According to Dr. Silvio Itasco and his colleagues from Columbia University, the editors of one of the studies published in the March issue of "Medicine" they isolated a special type of stem cells from human bone marrow. The cells, which they call "angioblasts", are part of the stem cells from which the blood system cells are formed. The angioblasts form the delicate blood vessel cells. Although these cells had previously been assumed to exist, they had not been isolated before, Dr. Itasco said.
After a heart attack, caused by a blockage in one of the heart's arteries, the muscle cells deprived of oxygen die en masse. The surrounding cells multiply four or five times to compensate for the damaged tissue. This is why most people survive the heart attack. But the cells that multiplied also die after a while and are replaced by scar tissue. Then heart failure appears.
Dr. Itasco and his team hypothesized that the overproliferated muscle cells die due to a lack of blood supply. This was what motivated them to try to isolate the angioblast cells.
Then they injected human angioblasts into rats that gave them heart attacks. For reasons that are not yet understood, the rejection reaction of the immune system is less acute in the case of stem cells compared to other foreign cells. The angioblasts injected into the rats' circulation settled on the damaged heart tissue.
In the second study, the researchers sorted cells from mouse bone marrow to isolate the primitive stem cells and sift out those that had already taken the first steps towards becoming blood cells. The primitive stem cells were injected directly into the hearts of mice that caused a heart attack.
The researchers found that the stem cells created new heart tissue by maturing into different cells, including heart muscle cells, the smooth muscle cells in the walls of the arteries, and the cells that line the walls of blood vessels. The functional efficiency of the left ventricle of the mice was about 40% greater than that of untreated mice. This is the first time, said Dr. Donald Orlick, one of the authors of the study, that new heart tissue has been formed from injected cells.
New York Times
