Contact: Mark Shainblum
Forget the antioxidants? McGill researchers cast doubt on role of free radicals in aging
Some organisms live longer when their ability to rid themselves of free radicals is partially disabled
This release is available in French.
For more than 40 years, the prevailing explanation of why we get old
has been tied to what is called oxidative stress. This theory
postulates that when molecules like free radicals, oxygen ions and
peroxides build up in cells, they overwhelm the cells' ability to
repair the damage they cause, and the cells age.
of "alternative" antioxidant therapies -- such as Vitamin E or CoQ10
supplements in megadose format --has sprung up as the result of this
theory. However, clinical trials have not shown that these treatments
have statistically significant effects.
And now researchers at McGill University, in a study published in the February issue of the journal
are calling the entire oxidative stress theory into question. Their
results show that some organisms actually live longer when their
ability to clean themselves of this toxic molecule buildup is partially
disabled. Collectively, these molecules are known as reactive oxygen
species, or ROS for short.
Dr. Siegfried Hekimi of McGill's
Department of Biology, said most of the evidence for the oxidative
stress theory is circumstantial, meaning oxidative stress could just as
easily be a result of aging as its cause.
"The problem with
the theory is that it's been based purely on correlative data, on the
weight of evidence," explained Hekimi, McGill's Strathcona Chair of
Zoology and Robert Archibald & Catherine Louise Campbell Chair in
Developmental Biology. "It is true that the more an organism appears
aged, whether in terms of disease, or appearance or anything you care
to measure, the more it seems to be suffering from oxidative stress".
has really entrenched the theory," he continued, "because people think
correlation is causation. But now this theory really is in the way of
Hekimi and postdoctoral fellow Jeremy Van Raamsdonk
studied mutant Caenorhabditis elegans worms. They progressively
disabled five genes responsible for producing a group of proteins
called superoxide dismutases (SODs), which detoxify one of the main
ROS. Earlier studies seemed to show that decreased SOD production
shortened an organism's lifespan, but Hekimi and Van Raamsdonk did not
observe this. In fact, they found quite the opposite.
of their mutant worms showed decreased lifespan compared to wild-type
worms, even though oxidative stress was clearly raised. In fact, one
variety actually displayed increased lifespan, the researchers said.
mutation that increases longevity affects the main SOD found in
mitochondria inside the animals' cells," said Hekimi. "This is
consistent with earlier findings that mitochondria are crucial to the
aging process. It seems that reducing mitochondrial activity by
damaging it with ROS will actually make worms live longer."
The researchers hasten to point out that they are not suggesting that oxidative stress is good for you.
"ROS undoubtedly cause damage to the body," Hekimi said. "However, they do not appear to be responsible for aging."
ON THE WEB: http://dx.plos.org/10.1371/journal.pgen.1000361
ABOUT McGILL UNIVERSITY
University, founded in Montreal, Que., in 1821, is Canada's leading
post-secondary institution. It has two campuses, 11 faculties, 10
professional schools, 300 programs of study and more than 34,000
students. McGill attracts students from more than 160 countries around
the world. Almost half of McGill students claim a first language other
than English – including 6,000 francophones – with more than 6,200
international students making up almost 20 per cent of the student body.