Blood Relatives

Article excerpt

First-generation artificial blood is about to hit the market

Last year, the tally of blood transfusions climbed to a record high. More people are donating blood than ever before, but a rapidly aging society is using it up even faster as the number of elective surgeries and medical treatments requiring blood transfusions continues to rise.

This year, things are starting out even worse. "We have in fact seen the worst ... in memory, in terms of blood availability," says Harvey G. Klein, president of the American Association of Blood Banks in Bethesda, Md.

In 1999, the U.S. Food and Drug Administration put a ban on blood donations from people who lived in the United Kingdom for more than 6 months between 1980 and 1996. Of concern was the spread of the human version of mad cow disease, Cruetzfeld-Jakob disease, that had hit the United Kingdom. More recently, an FDA advisory committee recommended adding people from France, Ireland, and Portugal to the ban. The spread of AIDS and other bloodborne diseases such as hepatitis has also diminished the blood supply by excluding potential donors.

If only there were substitutes that could fill some of blood's roles in the body, artificial substances that would be free of the supply constraints and contamination vulnerabilities of the real stuff. Besides the roles these substitutes could play in general surgery, such products could save lives during emergencies and major disasters in which blood isn't readily available. It could also be a medical boon to developing countries that don't bank blood.

For decades, researchers have sought to develop a partial replacement for blood. Now, several companies are about to release the first line of artificial blood products. "I've watched this field over the last 20 years, and this is the most promising that it's been," says George Nemo, head of the transfusion-medicine program at the National Heart, Lung, and Blood Institute in Bethesda, Md.

Half the blood supply could potentially be replaced with the new substitutes, claims Robert M. Winslow, president of Sangart, a San Diego-based company developing one of them. Although these products are far from perfect--and researchers are already developing a more sophisticated generation of artificial blood--they carry the oxygen that will keep people alive.

Blood is a wondrous concoction of red blood cells, white blood cells, platelets, and plasma--which is itself a cocktail of proteins, carbohydrates, hormones, and other biochemicals--that together fight infections, heal wounds, deliver oxygen, and remove wastes.

The molecular heart of blood's oxygen-carrying ability is the protein known as hemoglobin, which jam packs red blood cells. More than 250 million hemoglobin molecules can crowd inside a single cell. Each hemoglobin scoops up to four oxygen molecules from the lungs and carries them to all of the body's other tissues. Once depleted of its oxygen cargo, a hemoglobin molecule snatches up carbon dioxide made by cells and brings the gas to the lungs, where it's exhaled.

Hemoglobin has been a favorite starting point for developers of blood substitutes. For one thing, different blood types, such as type A and type B, are based on different sets of proteins, known as antigens, that cover the surfaces of red blood cells. If a doctor gives a patient the wrong type of blood, that person's immune system will reject the foreign cells.

In the 1960s, researchers tried to circumvent complications from cell-surface antigens by making a blood substitute using free hemoglobin extracted from cells. Surprisingly, the naked molecule turned out to be toxic. Normally, hemoglobin exists as a molecule of four tightly bound units. But outside the red blood cell, the units fall apart. In animal studies, the hemoglobin fragments caused kidney damage.

In the 1970s, the Department of Defense continued supporting the quest to develop free hemoglobin into a blood substitute for wounded troops. …