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 started the search for an artificial option. As might be expected, finding a blood substitute has proved very hard, 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. .
Another research team headed by Douglas Lemon of Baxter Hemoglobin Therapeutics Inc, in Boulder, Colorado, attack the problem of hypertension. The problem seems to be caused by constriction of the blood vessels when they come into contact with the cell-free blood substitutes. To solve this problem the team needed to finding out exactly what makes them contract. .
The researchers have designed haemoglobin complexes that are less effective at binding nitric oxide, while maintaining their affinity for oxygen. Their haemoglobins do indeed seem to scavenge less nitric oxide, leaving the 'patient' (in this case rats) less prone to hypertension. .
Although we are still a long way from replacing donated blood with artificial blood substitutes, these findings should keep the research flowing.
