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Platelets Chilled to Order

11 September 2003 (All day)
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Patchwork. A minor modification might allow refrigerated platelets to keep clotting once transfused.

Tackling a problem that hematologists and blood bankers long ago gave up on, a team of scientists has determined how to store platelets in the refrigerator instead of at room temperature. If upheld in further experiments, the technique could stabilize platelet supplies and reduce the risk of bacterial infections from transfusions.

Platelets are disk-shaped cells that help blood clot. Each year millions of units are transfused into people around the world to stem bleeding. But because platelets must be stored at warm temperatures, they last only 5 days after donation. (By contrast, red blood cells can be refrigerated for more than a month, and plasma can be frozen for a year.) They can also foster bacteria that are a leading cause of transfusion-borne infection. In January, Harvard scientists Thomas Stossel, Karin Hoffmeister, and their colleagues found that when platelets are chilled, certain protein receptors on their surfaces clump together, revealing a sugar molecule. That triggers a reaction in the liver: When the platelets are infused, liver cells yank them out of the bloodstream.

Now Hoffmeister's team has figured out a potential remedy, as reported in this week's issue of Science. Further experiments in test tubes showed which portion of the sugar molecule the liver cells were noticing. The scientists reasoned that if they threw a cloak over the sugar--in the form of another kind of sugar molecule, with a different chemistry, that covers up the first--the liver wouldn't recognize the platelets, and they'd circulate freely.

Hoffmeister and colleagues extracted platelets from the blood of mice, mixed them with a solution containing the second sugar, and refrigerated the concoction for 2 hours. They then injected the modified platelets into mice, and the cells seemed none the worse for wear. The group also studied human platelets with a similar sugary disguise. After chilling the platelets for up to 12 days and then examining them in a petri dish, Stossel's team found that their function seemed intact.

The technique "seems to offer real promise" not only for reducing pathogens but also for extending storage time, says Roger Dodd, executive director of biomedical safety for the American Red Cross in Rockville, Maryland. After more expansive testing, refrigerating modified cells may allow blood banks--and recipients--to start counting their savings.

Related sites
Thomas Stossel's lab
The American Association of Blood Banks
Backgrounder on blood, from PBS

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