Chronic exposure to a toxin found in some lakes and desert topcrusts contributes to neurological problems commonly associated with ALS, Alzheimer’s and other neurodegenerative diseases, a new study shows – but at least in certain animals the damage appeared to be offset by increasing an amino acid in the diet.
The study, published Wednesday by the Royal Society of London, found that vervets chronically exposed to the neurotoxin BMAA developed neurofibrillary tangles and amyloid plaque deposits in the brain.
The finding stunned researchers, who were looking for preliminary signs of disease, but were not expecting to find advanced tangles and plaques.
“They looked identical to what you see in Alzheimer’s Disease, to the point that Dr. Robert Switzer (one of the neuropatholigists) mistakenly thought we had been looking at Alzheimer’s slides,” said Paul Alan Cox, the study’s lead author and an ethnobotanist at the Institute for Ethnomedicine in Jackson Hole, Wyoming. “No-one had seen tangles in an animal before...and the higher the exposure, the denser the tangles.”
The plaques and tangles were similar in structure and density to those found in the brains of Chamorro villagers in Guam, who ate flour made from seeds containing BMAA and who suffered unusually high rates of dementia and symptoms similar to ALS and Parkinson’s disease.
After a link between BMAA in the cycad seeds was discovered in the 1960s, use of the seeds declined and so did the incidence of disease.
A similar study done in the 1980s using macaques found that BMAA caused acute neurological symptoms, but the amounts fed to those monkeys were far more concentrated than an equivalent human dose.
The vervets in the new study did not show clinical signs of disease, but even those given low doses of BMAA were found to have plaques and tangles in their brains. It is not clear whether the findings would be replicated in humans, though studies of people with Alzheimer’s and ALS have found the presence of BMAA in some.
The study also found that feeding the dietary amino acid L-serine to the vervets significantly reduced the number of tangles in their brains. Further human trials are underway to determine whether L-serine could help prevent cognitive impairment.
BMAA is produced by cyanobacteria, which are found in many algal blooms. It has been identified in sharks, bottom-dwelling fish, and shellfish; in desert dust in the Middle East, and in water containing toxic blue-green algae blooms, which data suggests are becoming more prevalent worldwide.
ALS clusters have been found among people living near lakes in northern New England, and researchers suspect they may be related to people inhaling airborne BMAA, engaging in recreational activities in the water, drinking the water, or eating fish.
Relatively high levels of BMAA have been found in oysters in the south of France, in blue crabs in the Chesapeake Bay, and in shrimp and crab in southern Florida.
Elijah Stommel, a neuroglogy professor at Dartmouth who studied the New England ALS clusters, said the new study “raises the ante quite a bit. If you can produce a disease that looks like Alzheimer’s or like the ALS-Parkinsons-dementia complex seen in Guam by exposing them to a toxin that has been linked to it, then you’re showing a very strong correlation. There’s certainly more work to be done, but it is very important data.”
Ron Petersen, director of the Mayo Clinic Study of Aging and the Mayo Alzheimer’s Research Center, called the vervet study interesting but cautioned that more research would be necessary to understand the implications for human diseases. He also urged people not to rush out and buy the amino acid L-serine before further studies are done.
The vervet study “certainly may give us insight into other neurogenerative diseases,” he said, adding that Alzheimer’s disease is likely caused by a combination of genetic and environmental interactions.
“If you take a garden-variety Alzheimer’s patient walking around Washington, DC, have they been exposed to this toxin? Probably not, but it doesn’t mean there aren’t some other unexplained toxins that may be contributing to it.”