Roundworms test our progress on anti-ageing
Elixers of youth have often turned out to be snake oil. Worms could change all that. Elizabeth Finkel reports.
Over the past three decades, the quest for the fountain of youth has veered precariously between science and snake oil. All too often one lab has announced a miracle drug only to have that claim quashed by another.
Now three US research teams – from the Buck Institute for Research on Ageing, Rutgers University and the University of Oregon – have combined forces to find a surer footing. By meticulously adhering to the same protocols while using 22 genetically different types of roundworm (Caenorhabditis) to test new compounds, their work offers a robust, fast and inexpensive pathway to the most promising anti-ageing drugs.
So far the star performer across all the labs and types of worms is a compound called Thioflavin T, a dye widely used to detect clumps of amyloid protein in the brains of Alzheimer’s patients. Their findings are published in Nature Communications.
For many worm researchers, the results are a relief for a field plagued by the scourge of irreproducibility. “I’m very happy someone has bothered to do this,” says Lindsay Wu at the University of New South Wales.
One of the paper’s author, Gordon Lithgow of the Buck Institute, admits to having being traumatised by non-reproducible results. Back in 2000, he published a sensational paper in Science showing that antioxidants increased the life span of roundworms by 44%.
“I still have two boxes of newspaper clipping from that time,” he says. But two years later David Gems of University College London was unable to repeat the result.
It’s not an unusual tale. According to a recent estimate, more than 50% of pre-clinical studies have errors that mean they can’t be repeated.
But this problem hit ageing research particularly hard. For decades researchers had conscientiously steered the field – tainted by myths and snake oil – towards rigorous science. Their key to credibility was sticking to incontrovertible genetic studies. For instance in 1988, researchers found that if the roundworm C. elegans lacked a gene called age-1, the lifespan went up by 70%, and in 1993 they found that mutating a gene called daf-2 doubled the lifespan. Researchers couldn’t resist trying to see if chemical compounds could imitate the genetic tweak. That led to Lithgow’s 2000 paper in Science.
Beguiling as the worm is, many who have sought the fountain of youth using it have been burned. Studies on resveratrol, the much-touted life-extending compound famously found in red wine, for instance, have met a similar fate.
Nevertheless, funding agencies like the US National Institutes of Health are convinced of the merit of searching for compounds that might slow the ageing process and increase “health span”. Promising drugs like metformin and rapamycin are already in human trials. Lithgow says there are hundreds more on the shelves to test.
For the next cabs off the rank, the US National Institute on Ageing (NIA) has encouraged researchers to find a more rigorous way forward with its so-called Intervention Testing Program – a multi-institutional investigation of treatments with the potential to extend lifespan and delay disease and dysfunction in mice.
But trials in mice can cost millions of dollars and take years. So in 2013, three laboratories got together to form the worm version – the Caenorhabditis Intervention Testing Program, or CITP.
The first step was to compare lab protocols. “We got together and were shocked by the small differences,” Lithgow says. Once their methods were fully aligned, they tested 10 promising anti-ageing compounds. Besides aspirin, curcumin, valproic acid and Thioflavin T, there were three compounds thought to mimic the effects of dietary restriction – NP1, alpha-ketoglutarate, and resveratrol – and three with antioxidant properties – propyl gallate, alpha lipoic acid and quercetin. Each was tested on 9 varieties of worms belonging to three distinct species; the DNA variation between the worms was huge, Lithgow says, as much as between a worm and a human.
Following exactly the same protocols paid off: results between the labs were pretty consistent. The main disagreements were between the different varieties of worms. Some compounds like NP-1, resveratrol and propyl gallate extended life span in some strains but not others. Quercetin, alpha lipoic acid, aspirin, valproic acid and curcumin had little effect on any of the strains.
The clear winner across all the strains was Thioflavin T – the compound that Lithgow’s lab first reported in 2011 could extend the life of worms by 60%.
Lithgow’s team had worked on a hunch that since Thioflavin T was used to stain the abnormal brain deposits of Alzheimer’s disease, it might also interfere with the formation of those deposits. In worms it appears to be doing just that, not just with one type of protein but with many that form sticky deposits and contribute to the ageing-associated diseases.
So can we expect to see Thioflavin T in a human trial soon? Probably not. Though derivates of the compound are given to people with suspected Alzheimer’s to detect amyloid in their brain using PET scans, for now its use on people remains as a one-off dose. Its long-term toxicity and effectiveness has to be tested on mice first.
The CITP experiment may have sleuthed the source of much of the non-replicability that plagues worm researchers. But one big mystery remains: results could vary by 10% within the same lab and using the same worm types, especially if the experiment was performed weeks apart. “There is some variation that we just can’t explain”, Lithgow says. “We underestimated how intrinsically variable these worms are. Biology is messy stuff; we have to try harder.”