Technology : Fruit and veg make for safer blood

时间:2019-02-27 04:13:02166网络整理admin

By Andy Coghlan CHEMICALS found in figs, parsnips and celery can reduce the risk of infections being transmitted in blood transfusions. When exposed to ultraviolet light, the carbohydrate compounds—called psoralens—purge plasma and blood cells known as platelets of life-threatening bacteria and viruses. The Cerus Corporation based in Concord, California, is using synthetic psoralens in its sterilising treatment. In experiments reported in the journal Transfusion (vol 7, p 423), Cerus showed that psoralens can destroy infectious agents such as HIV and hepatitis viruses, and bacteria that would cause blood poisoning if transfused. Platelets were left unscathed. The psoralens penetrate platelets and bind loosely with the DNA or RNA of microorganisms that have infected them. When a sample is exposed to ultraviolet light the bond between the psoralen and the genetic material becomes permanent. The microorganism dies because it cannot replicate. “It gums up the works,” says Lily Lin, director of platelet development at Cerus. Blood cells have no genetic material, so they are unaffected. So far the cleansing technique only works with platelets and plasma—the fluid component of blood which is often transfused when people have suffered massive blood loss. It does not work on red blood cells because haemoglobin blocks ultraviolet light. Cerus is currently working out how to solve this problem. But even with this limitation, Peter Gibson of Britain’s Blood Transfusion Service says the discovery that platelets survived the treatment marks a significant breakthrough. In 1995/96 patients in Britain were given more than 200 000 transfusions of platelets. People who are undergoing chemotherapy often require platelets to prevent haemorrhaging, as do those who have received organ transplants. “Platelets have a shelf life of just five days, so the psoralen treatment could be given immediately after collection to stop these infectious agents proliferating,” says Lin. This could be the first reliable system for decontaminating platelets, she says. The only alternative is to screen donations for antibodies to particular viruses or bacteria and discard contaminated samples. But because antibodies can take weeks (or months for HIV) to appear after infection, contaminated blood can quite easily slip through the net. The Cerus technique kills all microorganisms, even those for which there is no current screening test. “Wherever there’s a centre for collection of blood, you could use this system for decontaminating platelets before shipping them out,” says Lin. Cerus has permission from the US Food and Drug Administration to run clinical trials with the platelet and plasma-purging system. There are no plans to conduct trials in Britain as yet. The procedure is expected to be safe because it is applied outside the body. The psoralens and dead microorganisms remain in the blood, but neither is likely to pose risks to the recipients of transfusions, says Lin. Although the role of blood cleaner is a new one for psoralens,