'Zombie cells' buildup in your body may play role in aging

By Malcolm Ritter
Call them zombie cells — they refuse to die.
As they build up in your body, studies suggest, they promote aging and the conditions that come with it like osteoporosis and Alzheimer's disease. Researchers are studying drugs that can kill zombie cells and possibly treat the problems they bring.
Basically the goal is to fight aging itself, which hopefully will in turn delay the appearance of age-related disease and disabilities as a group, says geriatrics specialist Dr. James Kirkland of the Mayo Clinic in Rochester, Minnesota. That's in contrast to playing a “whack-a-mole game" of treating one disease only to see another spring up, he said.
The research has been done chiefly in mice. Earlier this year, the first test in people was published and provided some tantalizing results.
Zombie cells are actually called senescent cells. They start out normal but then encounter a stress, like damage to their DNA or viral infection. At that point, a cell can choose to die or become a zombie, basically entering a state of suspended animation.
The problem is that zombie cells release chemicals that can harm nearby normal cells. That's where the trouble starts.
What kind of trouble? In mouse studies, drugs that eliminate zombie cells — so-called senolytics — have been shown to improve an impressive list of conditions, such as cataracts, diabetes, osteoporosis, Alzheimer's disease, enlargement of the heart, kidney problems, clogged arteries and age-related loss of muscle.
Drugs show promise
Mouse studies have also shown a more direct tie between zombie cells and aging. When drugs targeting those cells were given to aged mice, the animals showed better walking speed, grip strength and endurance on a treadmill. Even when the treatment was applied to very old mice, the equivalent of people ages 75 to 90, it extended lifespan by an average of 36 percent.
Researchers have also shown that transplanting zombie cells into young mice basically made them act older: their maximum walking speed slowed down, and their muscle strength and endurance decreased. Tests showed the implanted cells converted other cells to zombie status.
The field of zombie cells is still young. But Kirkland estimates at least a dozen companies have formed or have launched efforts to pursue treatments.
And what about giving them to healthy people who want to ward off aging? That's possible but a long way off, after studies have established that the drugs are safe enough, she said.
“We may not get there," Kirkland said.
In any case, experts are impressed by the research so far.
“I think this is very exciting," said Dr. George Kuchel of the University of Connecticut Center on Aging in Farmington. The results from animal studies are “very spectacular. It's very compelling data."