If you’re already genetically predisposed to Alzheimer’s disease, consuming microplastics could trigger cognitive decline, according to a new study in mice from researchers at the University of Rhode Island.
The researchers wanted to see how microplastics might interact with genetic Alzheimer’s risk to make brain dysfunction more likely – a combination of both the genes we’re born with and the environment we live in.
Two groups of mice were used, one with the APOE4 gene variant that increases Alzheimer’s risk, and one with the APOE3 variant that doesn’t affect risk. In each group, some of the mice had microplastics added to their drinking water, and some didn’t.
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“There are modifiable factors we’re studying related to Alzheimer’s – diet, exercise, vitamins, and especially environmental toxins like microplastics,” says neuroscientist Jaime Ross.
“If you carry the APOE4, and you happen to consume a lot of microplastics, will this contribute to Alzheimer’s disease?”
Using tests designed to measure cognition, the researchers found that mice with APOE4 that consumed microplastics did begin showing signs of cognitive decline.
Mice with the APOE3 gene, and APOE4 mice that hadn’t been exposed to microplastics, behaved normally, suggesting that the combination of genetic risk and microplastics was driving the changes in the animals.
Intriguingly, the researchers noted sex differences in affected mice. The male APOE4 mice given microplastics showed signs of cognitive decline through apathetic behavior, while the female APOE4 mice given microplastics seemed to have impaired memories.
This actually matches what we see in humans with Alzheimer’s: men with the disease often show signs of apathy, while women often experience issues with memory. That makes the microplastics link worth investigating further.
“When you expose animals that are carrying the largest known risk factor in humans for developing Alzheimer’s disease to micro and nanoplastics, lo and behold, their behavior changes in a sex-dependent manner similar to the sex-dependent differences we see with Alzheimer’s patients,” says Ross.
The researchers also found that some signs of inflammation in the APOE4 microplastics mice matched what would be expected from Alzheimer’s. The mice didn’t develop the disease itself, but did show some changes associated with it.
While a single APOE4 gene does raise the risk of Alzheimer’s in people quite considerably, it’s still not a guarantee of the disease developing – many people with this genetic risk don’t get Alzheimer’s. That points to other factors being involved too, and scientists are making progress in understanding what those factors are.
Based on these study results, it seems as though exposure to plastic pollution could be one of these additional factors. We know microplastics can potentially get into the brain, but it’s still not clear exactly how harmful this exposure could be.
As is often the case with Alzheimer’s, it’s tricky to work out which brain alterations might be happening as a result of the disease, and which might be driving it in the first place. While this study only involved mice, it could be significant that Alzheimer’s-like changes were seen in a short period of time.
“It’s interesting that what we’re seeing in mice is similar to what we’re seeing in the real world,” says Ross.
“We want to encourage further research into the scourge of micro and nanoplastics.”
The research has been published in Environmental Research Communications.