Blood substitute from worms shows promise

HANNAH HOAG

Donated red cells are given to increase blood's oxygen carrying capacity. © GettyImages

Worms may help doctors get round the worldwide blood shortage. Preliminary tests hint that their haemoglobin might be a good red-cell alternative, say researchers¹.

Ageing populations, Europe's BSE outbreak and the worldwide HIV/AIDS epidemic have cut blood supplies. "There is a real need for a substitute - talk to any emergency room surgeon," says biochemist John Olson, of Rice University in Houston, Texas.

Haemoglobin in red cells carries oxygen from the lungs to the tissues. People who have lost a lot of blood are transfused with donated red cells to increase their blood's oxygen-carrying capacity.

Animal haemoglobins can cause allergic reactions and even damage the kidneys. But the haemoglobin from a common marine worm (Arenicola marina) has shown none of these effects, in mice at least. "The preclinical data are very exciting," says biologist Franck Zal of the Université Pierre et Marie Curie in Paris, "We don't have to modify anything, only collect it and purify it."

"The molecule's large size and natural cross-linking make it ideal," says Rhoda Elison Hirsch who works on the structure and dynamics of haemoglobin at the Albert Einstein College of Medicine in New York. "I'm thrilled that someone is working on this."

Being about 50 times larger than human haemoglobin, the worm protein cannot damage the kidneys. If human haemoglobin is transfused without the protection of the red blood cell, it breaks into smaller fragments, which clog the kidney's filtration system. "Bigger is generally better," says Olson.

The researchers still have to test whether free worm haemoglobin scavenges nitric oxide from blood vessel walls - this causes high blood pressure. In human blood, haemoglobin is packaged inside red blood cells. Other groups have tried to mimic this by encapsulating molecules in an artificial cell, or by modifying their structure.

I'm thrilled that someone is working on this Rhoda Elison Hirsch Albert Einstein College of Medicine, New York

Pharmaceutical companies have been developing oxygen-carrying red-blood substitutes for over 30 years. The most promising are synthetic derivatives of human or cow haemoglobin. None has approval from the US Food and Drug Administration yet, although one is being used in South Africa.

"Every few years a new one looks promising, but it fails when it reaches clinical trials," warns transfusion scientist Lorna Williamson of Britain's National Blood Service. Even if the molecule proves safe and effective, it may be difficult to produce in large quantities, adds Olson.

1. Zal, F., Lallier, F.. & Toulmond, A. Utilisation comme substitut sanguin d'une hémoglobine extracellulaire de poids moléculaire élevé. French Patent No. 00 07031, granted August 2, 2002.

© Nature News Service / Macmillan Magazines Ltd 2003