MK-677 brought muscle mass, but long-term effects on vitality unclear, scientists say
THURSDAY, Nov. 6 (HealthDay News) -- An experimental drug can restore the amounts of muscle-linked growth hormone in seniors to youthful levels, a new study shows.
Those on the therapy also gained muscle mass over the two-year trial, scientists say. However, there's no clear indication that this led to significant improvements in their strength or function.
Still, it does raise the hope that by increasing natural growth hormone Americans might be able to beat back the ravages of age.
"As we all get older, our body composition changes," explained study author Dr. Michael O. Thorner, a teaching professor of internal medicine at the University of Virginia in Charlottesville. "So, people in their 80s and 90s all look the same: their fat is distributed in the center and the abdomen, and they lose a lot of muscle mass."
"This has become an increasing problem as life expectancy has increased from 45 at the turn of the century to now over 80," he continued. "Obviously people would like to remain independent and functional as long as possible, but these changes work against them."
The challenge is to stop or at least slow down those changes.
"Because this age-related reduction in muscle mass is associated with a decrease in growth hormone secretion, the rationale for the therapy we're studying is to try and address the problem by boosting the normal secretion of this hormone," Thorner said.
His team reported its findings in the Nov. 3 issue of the Annals of Internal Medicine.
Human growth hormone, produced naturally by the body's pituitary gland, is essential to healthy development and the maintenance of tissues and organs. But as people enter their 30s and 40s, levels of the hormone start to decline. The use of synthetic versions of human growth hormone has also become the focus of "sports doping" headlines, with well-known athletes allegedly turning to the drug for its reputed performance-enhancing properties.
Aging Americans are also showing an interest in synthetic human growth hormone as a hoped-for "elixir of youth." According to the American College of Physicians, it's estimated that some patients spend as much as $1,000 to $2,000 per month on the drug for anti-aging purposes.
But what if there were a way to jumpstart the aging body's natural supply of growth hormone?
In the current work, the authors had 65 healthy adults between the ages of 60 and 81 receive either a placebo or a so-called "oral ghrelin mimetic" called MK-677, over the course of one year. MK-677 is an experimental medication that prompts the body to release naturally produced growth hormone. The drug was ingested once daily in pill form.
After the end of the year, those who had been taking a placebo were switched to MK-677. At the same time, the group who had already been taking the drug either continued to take the medication or were taken off it.
Thorner's team found that patients who had received the therapy experienced an increase in growth hormone levels equivalent to levels seen among healthy young adults. Their lean, fat-free muscle mass also increased, as did overall body weight and the amount of fat distributed to the arms and legs.
"Whereas those who didn't get the growth-hormone boosting therapy lost about one pound of muscle in a year, those who got [the drug] gained about two pounds of muscle mass and experienced appetite stimulation," Thorner added. "Although fat increase was the same between the two groups, there was a difference in [fat] distribution, so that among those treated with the drug 50 percent of it was distributed to the limbs, rather than all to the center, as usual."
Patients who had been on MK-677 and then were taken off the medication saw all of the drug's beneficial effects dissipate, the authors reported. In contrast, those who stayed on the regimen maintained their gains throughout the total two-year period.
Insulin sensitivity decreased among those taking MK-677, while their blood sugar increased. The therapy did not have any observable effect on the muscularity of the thigh area -- a key source of mobility strength -- nor did it have any impact on overall muscle strength or activity function, the team noted.
"But the patients we studied were healthy to begin with," Thorner stressed. "So, we believe that we now need a longer-term study with possibly more frail individuals, to see if we can demonstrate any possible change or improvement in function as a result of the therapy."
Thorner noted that a person's growth hormone levels are highest during mid-puberty, but have dropped by about half by the time men and women turn 30. The decline continues with age, with levels diminishing at a rate of about 50 percent every 7 years.
Dr. Todd Schlifstein, an assistant professor of rehabilitation medicine at the New York University School of Medicine in New York City, called the study "very interesting" but agreed that more research is needed.
"I think it certainly enlightens an area where there certainly seems like there is a potential for a benefit for elderly patients," he said. "But now it needs to be looked at further in a functionality type of way, to see how an increase in appetite, body energy, and lean muscle mass actually translates into how a patient actually walks, for example, and how it impacts on their over well-being, which is much harder to test. But that's the next step."
There's more on maintaining muscle mass as you age at the U.S. National Institute on Aging.
SOURCES: Michael O. Thorner, MB, BS, Dsc, teaching professor, internal medicine, University of Virginia, Charlottesville, Va.; Todd Schlifstein, M.D., assistant professor, rehabilitation medicine, New York University School of Medicine, New York City; Nov. 3, 2008, Annals of Internal Medicine
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