Life of Donated Platelets May Be Prolonged

Protein shields crucial but fragile blood product from destruction

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HealthDay Reporter

THURSDAY, Sept. 11, 2003 (HealthDayNews) -- Researchers report a promising technique for prolonging the blood bank life of platelets, the non-cell bodies that are essential for clotting and that now must be thrown away after just a few days.

Just a spoonful of protein helps the platelets hang around, says a report in the Sept. 12 issue of Science by researchers in the United States, Sweden, and Denmark.

It's a special kind of protein, one that shields stored platelets from the body's mechanism of destroying them when they are transfused, says Dr. Thomas P. Stossel, professor of medicine at Harvard Medical School and a leader of the study.

Platelets are cell fragments that are essential in blood clotting. When blood is exposed to air, platelets react with a protein called fibrinogen to form a temporary plug. They then bind to each other and recruit other platelets, a process that forms fibrin, a stringy protein that forms the final clot to seal an injured blood vessel.

Platelet transfusions are important in cancer treatment, transplantation, and a number of other medical procedures. More than 12 million platelet donations are done each year in the United States.

But many of those donations ultimately are wasted, because platelets cannot be refrigerated. At low temperatures, receptors on the surface of platelets form clusters that contain a distinctive sugar molecule. Macrophages, the cells that remove impurities from the blood, detect that sugar and destroy the platelets.

So platelets now must be stored at room temperature. The threat of bacterial contamination and degraded performance limits their shelf life to five days.

What the researchers have done is to add a protein from a family called lectins to a supply of platelets. The lectin binds to the macrophage-attracting sugar, protecting refrigerated platelet clusters from destruction -- for up to 12 days in test tube experiments, the researchers say.

A lot of work must be done before blood banks could think of using the method, Stossel says. Almost all the work so far has been done in mice, with only a few limited studies of human platelets. All aspects of blood transfusion are "highly regulated by the Food and Drug Administration, and we would have to prove that it meets their requirements," he says.

But it is possible that one important proof of principle could be done within a year, Stossel says -- an autologous transfusion, in which platelets would be taken from an individual, refrigerated using the new method, and then transfused into the donor.

"The proof of the pudding would be an autologous transfusion," he says. "If it works, we would have a platelet of better quality, with a much lower risk of bacterial contamination that we could store for two or three times longer."

In addition to the benefit for patients, the method could save a lot of money, Stossel adds. "One estimate of the cost of platelet wastage is in the hundreds of millions of dollars," he says.

While large-scale human trials would be needed, says Dr. Karin M. Hoffmeister, professor of medicine at Harvard and another member of the research team, "we would hope that the method could be put to use in the next five years, if all goes as anticipated."

If the method does work, it would be "very, very important," says Dr. Louis M. Katz, president of Blood Banks of America and medical director of the Mississippi Valley Regional Blood Center in Davenport, Iowa.

The current short shelf life means that platelets often must be shipped long distances, Katz says. A longer life "would give us enormously more flexibility," he says.

And while any assessment of work done in the laboratory must be cautious, "this is very elegant work that looks to be very simple and, if it goes well, could move into clinical research quickly," Katz says.

More information

You can learn about the importance of platelets in cancer treatment and how to donate them from the Dana-Farber Cancer Institute, while the American Red Cross explains how blood products in general are used.

SOURCES: Thomas P. Stossel, M.D., and Karin M. Hoffmeister, M.D., professors of medicine, Harvard Medical School, Boston; Louis M. Katz, M.D., medical director, Mississippi Valley Regional Blood Center, Davenport, Iowa; Sept. 12, 2003, Science

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