A study has found long-term exposure to environmental toxin
beta-Methylamino-L-alanine (BMAA) produced by blue-green algal blooms may be associated
with the development of beta-amyloid plaques and tau tangles – hallmarks of
Alzheimer’s disease – in the brain.
Researchers have suspected a connection between
environmental triggers and Alzheimer's disease since the discovery of an
unknown illness that included features of dementia, Parkinson's disease and amyotrophic
lateral sclerosis (ALS), which affected Chammoro villagers from the Pacific
island of Guam in the 1960s. [Read more Can Turmeric Prevent Alzheimer’s?]
The toxin, BMAA is produced by cyanobacteria - a type of
blue-green algae that are found in oceans, soil and lakes. The toxin is present
in various marine lives, including sharks and shellfish, which ingest
cyanobacteria and can also be found in plants, such as cycads.
The seeds of cycads are eaten by flying foxes, so BMAA is
often present in these animals. Chamorro villagers use the seeds from this
plant to make flour and also fish and flying foxes form a key component of
their diet. Therefore, their diet is highly contaminated with BMAA.
The team led by Paul Alan Cox, PhD, an ethnobotanist at the
Institute for EthnoMedicine in Provo, UT, had previously identified
beta-amyloid plaques and tau tangles in the brains of Chamorro villagers who
had died of paralytic illness. These villagers were exposed to high levels of
dietary BMAA, as a result of consuming flying foxes.
The team, for the latest study, aimed to prove whether there
is a link between dietary BMAA and development of neurodegenerative diseases. [Read more Art-making can reduce stress, even if you aren’t artistic]
To emulate the conditions experienced by the Chammoro
villagers, Dr. Cox and his colleagues decided to expose the same toxin to
vervet monkeys.
They conducted two experiments on the monkeys, in which they
fed the animals various doses of dietary BMAA over 140 days.
The researchers conducted two experiments on vervet monkeys (Image: Creative commons) |
The first experiment
The researchers divided the monkeys into 3 groups. The first
group was fed fruit containing BMAA, the second group was fed fruit containing
equal levels of BMAA and L-serine - a dietary amino acid – while the third group
was fed fruit containing a placebo.
Upon analyzing the brain tissue of the monkeys, researchers
found that those fed fruit containing only BMAA showed development of tau
tangles and beta-amyloid plaques.
The group of monkeys who ate equal amounts of BMAA and
L-serine, however, showed reduced tangles, while the group that were fed the
placebo did not develop tangles and plaques at all.
Studies coauthor Deborah Mash, PhD, director of the
University of Miami Brain Endowment Bank in Florida notes:
"The tangles and amyloid deposits produced were nearly
identical to those found in the brain tissue of the Pacific Islanders who died
from the Alzheimer's-like disease.”
Second experiment
The findings from the first experiment were replicated in
the second experiment, in which the monkeys were divided into four groups. [Read more Changes in brain occur 20 years before Alzheimer’s onset]
The first group of monkeys was fed fruit containing BMAA at
a dose similar to that consumed by Chamorro villagers. The second group ate
fruit that contained a tenth of that dose. The third group received fruit
containing equal amounts of BMAA and L-serine. The fourth group was given fruit
containing placebo.
At the end of the 140 days, the researchers found all
monkeys that consumed BMAA had developed tau tangles and beta-amyloid plaques.
Dr. Cox explained the results:
"Our findings show that chronic exposure to BMAA can
trigger Alzheimer's-like brain tangles and amyloid deposits.”
“As far as we are aware, this is the first time researchers
have been able to successfully produce brain tangles and amyloid deposits in an
animal model through exposure to an environmental toxin."
Role of amino acid in preventing
Alzheimer’s
As seen in the first experiment, monkeys that consumed an
equal amount of L-serine alongside BMAA showed a significant reduction in tau
tangles, suggesting the amino acid may hold promise for the treatment of
Alzheimer's.
Dr Dunlop said the focus of research now was to investigate
whether or not the amino L-serine that reduced the development of brain tangles
in the experiment could help slow down the early stage of Alzheimer's disease
in humans.
They also note that the US Food and Drug Administration
(FDA) have not approved L-serine for the treatment of neurodegenerative
conditions. [এই ৭টি খাবার আপনাকে ওজন কমাতে সাহায্য করবে]
But first, she said, scientists needed to work out if the
supplement was safe. She cautioned:
"We cannot recommend that people start taking it."
"We are currently starting phase 1 trials in the US looking
at the safety of this particular supplement in humans."
In the meantime, she said people could take simple steps to
avoid exposure to the toxin.
"We're not suggesting people stop eating certain foods
but ... if you're surfing or swimming or doing recreational activities in lakes
that have green scum, it's probably not a good idea," she said.
Researchers however are working on the findings. The
Institute for EthnoMedicine is conducting a phase 1 clinical trial alongside
Dartmouth Medical School in Hanover, NH, in which they are evaluating the
effects of L-serine among patients diagnosed with mild cognitive impairment
(MCI) or Alzheimer's.
The study was published in the journal Proceedings of the Royal Society B.