A continuous supply of donated blood is vital for modern medicine. But the ever-increasing worry over blood-borne diseases such as HIV and hepatitis has fuelled the search for an artificial alternative. As might be expected, finding a blood substitute has proved incredibly hard, but in the July issue of the journal Nature Biotechnology, two research teams report how some of the biggest remaining problems might be overcome.
Most attempts to find a suitable alternative to blood have concentrated on cell-free haemoglobin solutions. Haemoglobin, the oxygen-carrying complex, is usually packaged safely inside red blood cells. This makes a huge difference to the rate of oxygen delivery to the tissues, but there are other problems to be overcome too. The cell membrane contains enzymes that protect the haemoglobin from degradation, allowing it to function in the blood stream for about 3 months. A lack of enzymes in the cell-free substitute leaves the body at risk from oxidative damage by escaped haem molecules. One other problem is the unexplained rise in ?blood? pressure (hypertension) when cell-free haemoglobin is used.
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