Fecal transplants from young mice are like a 'fountain of youth' for old mice, study finds

It might not be the fountain of youth we've dreamed of, but experiments in mice suggest one possible, if distasteful, path to rejuvenation: a dose of the microbial ecosystem from the gut of a healthy youngster.

In a study, researcher John Cryan and his team took feces from young mice and turned it into a kind of slurry, and delivered into the guts of older mice through a feeding tube.

He said the fecal transplant had a number of surprising effects.

We're basically getting a rewinding, (...) rejuvenating effect.- John Cryan, neuroscience professor

It reversed age-related inflammation in the body and the brains of older mice, and changed the chemistry of their brain's hippocampus — the region involved in learning and memory — to resemble that of younger mice. The transplant also led to improvements in the older mice's memory, learning and anxiety levels, all of which are affected negatively with age.

"We're basically getting a rewinding, (...) rejuvenating effect," Cryan told Quirks & Quarks host Bob McDonald. 

The study's results were published in the journal Nature Aging.

Previous studies have shown how the diversity of microbes in our gut declines as we age and is associated with poorer health outcomes in humans and in elderly mice. The changes were also associated with with deficits in memory, learning, and immune response.

"We wanted to go one step further and really prove that it was the microbes that were actually causing the effects," said Cryan, a professor of neuroscience and the vice president for research and innovation at University College Cork in Ireland.

Linking gut health with the brain

Cryan said the team is hoping to follow up on this study by investigating how the microbes affect the way the gut communicates with the brain.

One way he thinks this could be happening is via the vagus nerve, which connects the gut and the brain.

"We showed some years ago with colleagues at McMaster University in Hamilton that when we cut the vagus nerve, all of the effects [on the brain] of specific bacteria were gone," Cryan explained.

If people can keep their cognitive function better for longer, if people are less sensitive to infections and less sensitive to immune effects, that would have a huge impact on their everyday quality of life.- Cryan

He described how the ecosystem of different microbes that co-exist in the gut, known as the microbiome "is like a little factory producing all kinds of weird and wonderful chemicals that our bodies couldn't make otherwise." 

Those chemicals may be getting into the blood and passing through the blood-brain barrier into our brains or could be affecting neurons in the gastrointestinal tract that are indirectly connected to the brain, resulting in changes in memory and cognition. 

What this could mean for us

Cryan said they also want to figure out if their findings in lab mice could be applied in some way to humans. People already undergo fecal transplants to treat gut infections. They could investigate whether those transplants could produce aging-related benefits as well.

"If people can keep their cognitive function better for longer, if people are less sensitive to infections and less sensitive to immune effects, that would have a huge impact on their everyday quality of life," he said.

He pointed to another recent study from Europe that showed how elderly people eating a Mediterranean-style diet rich in fruits, vegetables, nuts, legumes, olive oil and fish and low in red meat and saturated fats was associated with beneficial changes to the gut microbiome and slowed down the cognitive effects of aging.

And while fecal transplants as a rejuvenation therapy for humans may be a dubious, or even repellant prospect, the experiments in mice may still provide valuable information about the relationship between our gut microbes and aging, said Cryan.

"I have a gut feeling about all of this that it's telling us that the microbiome is playing such a crucial role in brain function across the lifespan, but in particular, as we age."

Produced and written by Sonya Buyting. Click on the link at the top of the page to hear the interview with John Cryan.