This week it was announced that a blood substitute based on their alternative theories is looking promising in an early trial. Developing a suitable blood substitute for people has been a major effort for decades. An artificial blood would relieve shortages and prevent patients being infected by contaminated supplies.

Ideally, it could be given to anyone without triggering rejection, so accident victims could be given transfusions immediately without testing to see what blood group they are. And a long-lasting form that does not need to be kept cold would be ideal for use in disasters, wars and remote areas. But company after company has worked on substitutes only to abandon their efforts because of safety concerns.

Most blood substitutes are based on various forms of haemoglobin, the protein that carries oxygen in most animals. The guiding principles are that artificial blood should be thinner than real blood, so that it circulates easily, and have a low affinity for oxygen, so that it releases oxygen easily.

In the past decade, initial trials of several substitutes looked promising. But it turned out many had a disastrous effect- they made capillaries collapse, shutting off the oxygen supply to tissues.

The reason, most researchers think, is that the haemoglobin in artificial bloods is free-floating, instead of being enclosed in red blood cells.

This allows it to enter the spaces between cells, where it mops up nitric oxide- a molecule that helps keep blood vessels open. But Marcos Intaglietta of the University of California, San Diego, is one of a small number of scientists who think the physical characteristics of blood substitutes are to blame.

He argues that they thin the blood, reducing shear stress in the capillaries and leading to vasoconstriction. Creating a
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
10-Mar-2004