<<返回上一页

Body builder

发布时间:2019-03-07 13:02:01来源:未知点击:

By Robert Adler A CURE for osteoporosis, the condition that weakens bone and cripples millions of elderly people worldwide could be in sight. Researchers developing a new understanding of how one hormone keeps bone cells alive certainly think so. Scientists have known for 50 years that animals develop more massive bones if given repeated injections of parathyroid hormone (PTH), a substance that controls the level of calcium in the blood. But because they didn’t understand how PTH worked, researchers have concentrated on developing other treatments for osteoporosis. These include hormones and other drugs that slow the rate of bone loss, and some that also increase bone density. But in severe cases, the treatments fail to prevent broken bones, which can be lethal in elderly people. Now researchers at the University of Arkansas for Medical Sciences in Little Rock have found out just how PTH rebuilds bone. As they report in the current Journal of Clinical Investigation (vol 104, p 439), PTH keeps osteoblasts, specialised cells that lay down new bone, from committing cellular suicide. Called apoptosis, programmed cell death is part of the normal turnover of cells. And the researchers found that giving mice daily doses of PTH cut the osteoblast suicide rate tenfold. That led to a bigger cellular workforce and more healthy bone tissue. “In the past, we’ve been talking about preventing bone loss, but this is increasing bone mass,” says Stavros Manolagas, the director of the university’s osteoporosis centre. “For the first time, you can talk about reversing the process—a cure.” The researchers gave daily injections of human PTH to normal mice and to a strain of mice with weak bones. They used X-rays to measure bone density before and during treatment. Under the microscope, they could see healthy, newly formed bone along with more bone-forming osteoblasts in the treated mice than in mice given hormone-free injections. When they grew the osteoblasts in dishes, the researchers could see that far fewer cells died by apoptosis in bone samples taken from the treated mice. Manolagas and Robert Jilka, also at the University of Arkansas, say that human osteoblasts are also programmed to commit suicide. So PTH or the other substances they’ve studied should strengthen human bones by keeping the cells working longer. In fact, several small recent studies have shown that PTH rebuilds bone in people with age-related and steroid-induced bone loss very effectively. David Dempster, who directs the Regional Bone Centre at Helen Hayes Hospital, in New York state, has studied PTH treatment in osteoporosis patients. He points out that other treatments slow down both the removal and rebuilding of bone. But PTH speeds up the bone-remodelling process and tips the balance towards greater bone mass. “That’s the best you can get,” he says. Only large clinical trials can prove that any new osteoporosis drugs are safe and prevent broken bones, Dempster says. Such trials could take five to ten years. “I think this mechanism is a very exciting finding,