葡京官网

Technology : Pig cells keep cholesterol at bay

作者:司徒知革    发布时间:2019-02-27 02:07:03    

By Michael Day PEOPLE at risk of an early death from heart attacks brought on by very high inherited cholesterol levels could one day be treated with cells transplanted from pigs’ livers. According to American researchers, the pig cells would clear much of the clot-forming lipid from the blood. Familial hypercholesterolaemia is an inherited disease that leaves people unable to remove the LDL (low density lipoprotein) form of cholesterol from their blood. The liver cells of people with this condition lack the receptors that would normally scavenge the fatty substance from their bloodstreams. People with one faulty LDL receptor gene (heterozygotes) tend to have two to three times the normal level of cholesterol in their blood. When both LDL receptor genes are faulty, cholesterol levels are between 5 and 10 times as high as in normal people. In people with this severe form, heart attacks before the age of 20 are common. Cholesterol-lowering drugs do them little good because their serum cholesterol is so high that even a substantial reduction does not bring it down to within the normal range. The main treatment available is liver transplantation. But this is a drastic step to have to take, and there is also a serious shortage of organs for transplant. A team led by Albert Edge of the biotechnology firm Diacrin in Charlestown, Massachusetts, decided to test whether transplants of liver cells from another species could help instead. “The main advantage of xenotransplantation would be that it gets around the shortage of donated livers—and that’s a very real problem,” says Edge. The team tested the idea on rabbits that were suffering from a condition similar to familial hypercholesterolaemia. Using the immunosuppressant drug cyclosporin to prevent rejection, they introduced pig liver cells into the rabbits’ livers (Nature Medicine, vol 3, p 48). These cells became incorporated into the rabbits’ livers, providing them with functional LDL receptors that lowered cholesterol in the animals’ blood by between 30 and 60 per cent for over 100 days. “We didn’t expect it to be this effective,” Edge told New Scientist. The researchers were particularly surprised that the single drug, cyclosporin, prevented rejection of the foreign tissue so effectively. Transplant patients usually have to be given a cocktail of drugs. Some immunologists believe the liver may be “immunologically privileged”. They think the lining of blood vessels in the liver may protect liver cells from attack by antibodies. Another possibility is that liver tissue is intrinsically immunosuppressive. Edge predicts that if pig-liver cell transplants become possible in people, they will be used in patients with the less severe form of the disease—which involves only one faulty copy of the gene—who are not able to tolerate drug therapy. For people with the more severe form, even reductions in cholesterol of between 30 and 60 per cent would not be enough to improve their prospects. The continuing need to take immunosuppressant drugs could also be a problem. “Long-term cyclosporin use would be a potential concern,” says Jeffrey Platt, head of surgery, paediatrics and immunology at Duke University, North Carolina. People who take such drugs for long periods are more vulnerable to infection and some cancers. However, Platt says several groups are working on methods of inducing host tissue to accept transplants permanently,

 

Copyright © 网站地图