Boning up on bone loss
Binghamton University researcher fractures myths around osteoporosis
Osteoporosis is not a disease, and neither weight-bearing exercise nor calcium supplements-not even a combination of the two-is capable of triggering the growth of new bone, says Kenneth McLeod, chair of the bioengineering department at Binghamton University and a leading researcher in the field of tissue development, healing and adaptation.
But dont throw in the towel and plan your wardrobe and life around a dowagers hump or broken hip just yet.
A past president of Bioelectromagnetics Society and the Society for Physical Regulation in Biology & Medicine, McLeod says its time for engineers and biologists alike to give up fractured approaches to studying osteoporosis and recognize that the loss of bone mass is a natural, arguably "normal," adaptive response to systemic changes in the body.
"Osteoporotics are, in most cases, perfectly healthy people," he said. "This is not a disease, but an adaptive condition signaling some change in the internal environment. Bone is adaptive, and the bones of osteoporotics are adapting to their environment."
Recognizing this fact is key to enhancing our understanding of what is really going on in the body, he said, and an approach that targets the mechanism for bone loss probably offers the most realistic hope of learning to avoid or reverse the inarguably devastating effects of this increasingly "predictable" adaptation, he said.
A major public health threat affecting more than 44 million Americans, osteoporosis affects women disproportionately. Eighty percent of those with the condition are women. Estimated national expenditures for hospital and nursing home care associated with osteoporotic and related fractures was $17 billion in 2001, or $47 million a day.
Though osteoporosis is not age dependent, 55 percent of the population 50 years of age and older have low bone mass and face an increased risk of developing osteoporosis and related fractures, according to the National Institutes of Health. Characterized by low bone mass and structural deterioration of bone tissue, osteoporosis leads to bone fragility and an increased susceptibility to fractures of the hip, spine, and wrist.
McLeods research interests are many, but he makes no bones about his keen interest in osteoporosis and the need for a bioengineering approach to the issue.
"Biologists might want to look for the gene for osteoporosis and engineers tend to treat osteoporotic bones as if they are parts of a failed mechanical system, but you are not going to understand osteoporosis by either of these approaches as there is not necessarily anything wrong with the bone." McLeod said. "What we need to know is what has changed in the environment, what is the mechanism for bone loss?"
What researchers know for sure, McLeod said, is that an individual with a dietary calcium deficiency cannot make bone.
"But just because you take calcium doesnt mean youre going to make bone," he added. "Calcium is necessary but not sufficient. There has to be a signal to make bone, and it turns out that if you dont have adequate fluid flow across your bone, youre not going to have adequate cell metabolism to trigger bone formation."
The limitations of calcium in addressing bone loss have been made most apparent by the space program, McLeod noted.
"Astronauts have a very serious problem with osteoporosis. They go up in space and there is no signal to make bone, so they start dumping bone. They have all sorts of calcium in their blood, so much so that they are likely to form kidney stones, which are a major problem for astronauts. So clearly you can overdose on calcium to the point where you have kidney stones and still have osteoporosis."
The only way to maintain bone mass is to maintain adequate fluid flow across your bone tissue, which requires adequate muscle activity, which affects lymphatic flow and cardiovascular activity, McLeod said. But that doesnt mean that weightlifting, jumping jacks, running or long walks will help to reverse osteoporosis by triggering bone growth or even slowing its deterioration, he said.
"It could well be that there are certain exercise regimens that will turn out to be very important in managing osteoporosis," he said.
"But right now, weve tried all sorts of things-Tai Chi, aerobics, walking, and none of these work effectively in adults to increase bone mass in osteoporotics."
McLeods research suggests that a key to reversing bone loss and triggering bone growth is training up one type of human muscle fiber, Type II A fibers. These fibers, also called fast oxidative fibers, contain many mitochondria and are surrounded by many blood capillaries.
Type II A fibers are pink, have a medium contraction velocity and are resistant to fatigue as compared to either the Type I fiber which are red, contract slowly, and are highly resistant to fatigue, or the more common II B fibers, which are white, and contract at high velocity but fatigue quickly.
With the appropriate stimulus, Type II B fibers, also called fast twitch or fast glycolytic fibers, can be trained into Type II A muscles, McLeod said. Toward that end, McLeod has developed a device that sends low-level vibrations into the body to stimulate II A muscle fiber development, enhance fluid flow through the bones, and stimulate bone growth. The device is in clinical testing in advance of seeking approval from the Food and Drug Administration.
Meanwhile, he said, while walking is good for you for many other reasons, if you think you are growing bone for your effort, forget it. "We are pretty confident now that walking has little influence on bone growth in adults."
McLeod and his research group are also tackling a variety of other health related issues from a bioengineering perspective. Working with support from the National Institutes of Health, for instance, McLeod has discovered a way to study in vitro the formation of extracellular matrix molecules, such as fibronectin and elastin, into fibers. With funding from Estee-Lauder, his laboratory is now trying to discover the mechanism by which UV inhibits normal elastin fiber formation and will then try to develop ways to prevent it. This work on extracellular matrix formation could be most important for people of European descent who are living in equatorial climates. In Australia, for instance, skin cancer rates are over 50 percent among those of European descent, McLeod said.
Some other examples of his many collaborative projects include:
An epidemiological study on breast cancer on Long Island and Cape Cod.
A cardiovascular study with Westchester Medical Center.
An exploration of the regulation of gene expression using electromagnetic exposure with Memorial Sloan-Kettering in New York City.
Susan Barker | EurekAlert!