Mice lifespan extended by 35% following 'elixir of youth' treatment
Elixir of youth treatments that prevent ageing could be in prospect after an extraordinary experiment in which the lifespan of mice was extended by up to 35%.
The secret is simply to remove worn-out "senescent" cells that accumulate with age and have a destructive effect on the body, scientists found.
When this was done using a drug to activate a "suicide gene" in genetically modified mice, the effects were dramatic. Treated animals not only lived 25% to 35% longer, but in many respects they were healthier too.
The mice remained more active and their hearts and kidneys functioned better than mice left to age naturally.
Their body tissues and organs also bore less evidence of damaging inflammation, and they grew fewer tumours.
Scientists are still not sure to what extent humans stand to benefit from the discovery. But a number of research groups are already on the hunt for senescent cell-targeting compounds that could form the basis of lucrative treatments.
US scientist Dr Darren Baker, who led the Mayo Clinic team behind the mouse study, said: "It is not a far fetched idea to think that there will be things coming down the pipeline that influence or remove these senescent cells."
Senescent cells are potentially dangerous defective old cells that are prevented from dividing and enter a state of suspended animation.
But even though they no longer reproduce, they can still do harm by secreting molecules that damage adjacent tissues and trigger chronic inflammation.
For this reason, senescent cells are closely associated with age-related diseases and frailty.
Although the immune system sweeps them away on a regular basis, this process becomes less effective with time and they are allowed to accumulate.
The Mayo Clinic team wanted to see what would happen if middle-aged mice were protected against the effects of senescent cells.
A strain of transgenic mouse was created with a "suicide gene" that targeted and killed off senescent cells when activated by a particular drug.
Even though senescent cells only made up a small fraction of the animals' total cell population, their removal had far-reaching effects.
Describing the research in a podcast interview with the journal Nature, which published the results, Dr Baker said: "All of the mice that were treated to remove their senescent cells had a life span extension neighbouring from 25 to 35%.
"In all cases we found there is significant health and lifespan extension."
The treatment had no obvious negative side effects, the scientists reported.
Since the research technique relied on genetic engineering it could not directly be applied to humans, said Dr Baker.
But he knew of "a variety of groups" that were trying to track down compounds which selectively wiped out senescent cells.
He added: "The advantage of targeting senescent cells is that clearance of just 60 - 70% can have significant therapeutic effects.
"If translatable, because senescent cells do not proliferate rapidly, a drug could efficiently and quickly eliminate enough of them to have profound impacts on healthspan and lifespan."
Although removing senescent cells overcame many of the effects of ageing, it did not have an impact on them all, the research showed.
Declines in motor performance, muscle strength and memory remained unaltered.
This might reflect the limitations of the genetically engineered mouse strain used in the experiment, or it could be evidence that senescent cells are linked to some aspects of ageing but not others, scientists said.
All the mice used in the study aged at a normal rate, unlike others in previous research which were bred to undergo accelerated ageing.