Scientists have found a drug that increases the normal lifespan of the nematode worm, paving the way for a drug to stop ageing.

A study in this week's journal Science by researchers at the Buck Institute found that worms treated with a drug that mimics natural antioxidant systems lived around 50% longer than untreated nematodes.

"Further studies on higher organisms in the near future will allow us to answer whether or not we have to reconsider aging as an inevitability," says lead author Dr Simon Melov.

The anti-ageing drug developed by the researchers is made up of synthetic versions of superoxide dismutase and catalase, two enzymes involved in converting cell-damaging free radicals into water.

The researchers were also able to normalise lifespan in a mutant nematode strain with a shortened life span linked to oxidative stress.

It appears that oxidative stress is a major determinant of life span and that it can be counteracted by pharmacological intervention, they say, adding their next priority is to move these compounds towards clinical trials.

"It has already been shown that fruit fly and nematodes can be genetically engineered to live longer by increasing the number of genes responsible for these enzymes," comments University of Queensland biochemist, Dr Paul Ebert. "But the idea that a pill could have the same effect is new".

Nematodes have been used for many years to study biological processes relevant to other species including humans.

"We're not much different from nematodes," says Dr Ebert."At a certain age, our mitochondria screw up and free radicals increase", although he adds there has been some debate about whether free radicals are the major determinant of ageing.

Dr Ebert's work includes studying insects which have grown resistant to the ageing process by repeated exposure to the pesticide phosphine which kills insects by causing them to undergo a rapid ageing process.

Asked about possible negative impacts of drugs that mimic antioxidants, Dr Ebert said that other parts of the body, for example, the immune system, used free radicals to fight diseases. While the Science study ruled out negative impacts of prolonged life on fertility or growth rate, there was no apparent investigation of immune system effects.

The Buck Institute is co-operating with Eukarion Inc., a private biopharmaceutical company located in Massachusettes which holds five US patents for technology of this kind and has been awarded over $2 million in grants from the US National Institutes of Health.