Plastic particles from takeout containers and other day-to-day products are making their way into the brain and triggering Alzheimer’s-like symptoms, a new study warns.
A growing body of studies warns that tiny micro- and nanoplastic particles are prevalent in the environment and routinely enter the human body through the food and water we consume, as well as the air we breathe.
These particles have been detected in all systems of the body, including the brain, where they can accumulate and trigger Alzheimer's-like conditions, according to a new study published Environmental Research Communications.
Previous research has shown that such microplastic particles infiltrate the blood-brain barrier, which protects the brain from harmful foreign substances, including viruses and bacteria.
The latest study assessed the brain health impacts of such plastic toxins that cross the blood-brain barrier.
It found that the accumulation of such plastic particles in the brain can lead to cognitive decline and even Alzheimer's disease, especially in those who carry genetic risk factors.
In the study, scientists examined mice that had been genetically modified to include the naturally occurring gene APOE4 – a strong indicator of Alzheimer's risk.
The gene is known to make people 3.5 times more likely to develop Alzheimer’s than those who carry the APOE3 variant of the gene that is passed from parents to offspring.
"In these mice, like in people, it's not a guarantee that you're going to see any changes in cognition. You could have identical twins both carrying APOE4, one totally cognitively healthy, and the other could develop Alzheimer's disease," said study co-author Jaime Ross from the University of Rhode Island College of Pharmacy.
"So that tells us there's something about lifestyle, something about the environment going on. There are modifiable factors we're studying related to Alzheimer's - diet, exercise, vitamins, and especially environmental toxins like microplastics,” Dr Ross explained.
Researchers sought to understand the level of Alzheimer's disease risk one had if they carried the APOE4 gene, and also happened to consume a lot of microplastics accidentally from the environment.
To study this, they exposed two groups of mice – one with the APOE4 variant and one with APOE3 – to micro- and nanoplastics in their drinking water over a period of three weeks.
These tiny particles, found in Styrofoam take-out containers, plastic cups and more, infiltrated the mice’s organs, including the brain.
There were also a control group of mice carrying each APOE gene variety that was not subject to the microplastic exposure.
Scientists then examined the cognitive ability of each of the mice, beginning with an open-field test, in which a mouse is put in a chamber and allowed to explore it at will for 90 minutes.
While typically, in this test, mice hug the walls to hide from potential predators, the APOE4 mice exposed to microplastics – especially the male ones – tended to wander and spend time in open space, leaving themselves vulnerable to predators, researchers found.
In another test, the ability of mice to recognise new objects was assessed.
Female mice with the APOE4 gene that were exposed to microplastics were slow to recognise the novel objects, hinting at a sign of cognitive decline, researchers said.
"In the first test, you can see the males are spending more time and resting more in the centre of the arena. In females, we saw changes in novel object recognition," Dr Ross said.
"In human Alzheimer's patients, men tend to experience more changes in apathy; they care less. Women experience more changes in memory. So the memory and the apathy connection are pretty clear,” she explained.
The findings indicate that animals carrying the largest known risk factor for developing Alzheimer's are exposed to micro- and nanopastics, their behaviour changes in a sex-dependent manner similar to what is seen in human Alzheimer's patients, scientists said.
Researchers call for further study into the cognitive decline caused by exposure to micro- and nanoplastics, which are among the most prominent environmental toxins to which people are routinely exposed.
"It's interesting that what we're seeing in mice is similar to what we're seeing in the real world. We want to encourage further research into the scourge of micro- and nanoplastics,” Dr Ross said.
