Team of scientists, including U of G researcher, finds toxin linked to neurological diseases more widespread than believed
BY ANDREW VOWLES
A Guelph scientist is part of an international research team that has found a link between a common bacterium found worldwide and neurological disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS).
Although the group doesn't claim to have pinpointed the cause of these and related neurological diseases in humans, the researchers — including Susan Murch, a U of G graduate and research associate in the Department of Plant Agriculture — have found that the same toxin believed to cause an ASL-like disease among indigenous people on Guam exists in the brain tissue of Canadians with Alzheimer's.
Having found a toxic amino acid called BMAA (beta-methylamino-L-alanine) in 95 per cent of cyanobacteria, or blue-green algae, in Sweden, Scotland and Hawaii, the scientists are now calling on authorities to monitor for the toxin in drinking-water supplies.
Their work was published April 3 in the online edition of the Proceedings of the National Academy of Sciences.
Until recently, BMAA was known only in cycads. These plants, resembling small palm trees, grow in warm parts of the world and are eaten by some indigenous people. Among them are inhabitants of the Pacific island of Guam, who contract an ALS-like disease up to 100 times more often than anywhere else in the world. The affliction has been the leading cause of death among adult Chamorros since the 1950s.
The Chamorro people use cycad seeds to make flour for tortillas. Scientists have known since the 1960s that the flour contains the neurotoxin. But analysis showed that amounts in the flour were far below concentrations needed to cause neurological damage in animals and people.
More recently, a team of scientists that includes neurologist Oliver Sacks and Paul Cox, director of the Institute for Ethnomedicine at Hawaii's National Tropical Botanical Garden, wondered whether the substance might be present in another food.
That led them to investigate a delicacy made from a species of fruit bat that the Chamorro boil in coconut milk thickened with cycad flour. The bat, which is called a flying fox, also eats the cycad seeds. Three years ago, the team, including Murch, found that BMAA bioaccumulates in the bats. Eating a single flying fox would expose a person to as much BMAA as in about 1,000 kilograms of cycad flour, she says.
Magnified in the human body, the substance is believed to work as a slow-acting toxin that leads to a complex of neurological diseases. On Guam, the disease peaked in the mid-1900s at about 400 deaths per 100,000 people.
As the bats have been hunted nearly to extinction, the death rate among the Chamorro has fallen to about 22 per 100,000. (The scientists don't know whether flying foxes themselves suffer neurological damage from eating cycads.)
“It's a hard process,” says Murch, who has witnessed the effects of the disease during research trips to Guam. “One of the real challenges with progressive neurological diseases is that they're long-term diseases.”
They found the substance in Chamorro brain tissue analyzed at the Kinsmen Neurological Institute at the University of British Columbia. They also found BMAA in the brain tissue of two Alzheimer's sufferers who had died in Canada but had presumably never visited Guam. None was found in 13 other people who had died of unrelated causes. (BMAA affects a neurotransmitter that has been implicated in several diseases, including ALS, Parkinson's and Alzheimer's.)
Looking more closely, the team found that BMAA is actually produced by a species of cyanobacteria in the roots of the cycad trees. Their new paper describes their discovery that the same toxin is produced by diverse species of cyanobacteria common in oceans, lakes and soils around the world.
Their work is also featured this month in a New Yorker article about neurological diseases written by science writer Jonathan Weiner, whose books include the Pulitzer Prize-winning The Beak of the Finch and His Brother's Keeper, about a family affected by ALS. (Sacks, the author of Awakenings, wrote about the Chamorros in his 1996 book, The Island of the Colour Blind.)
Murch says links between toxins produced by cyanobacteria and neurological disorders need to be studied more closely, including everything from toxicity studies to large-scale population screening. “Our idea and approach are quite controversial and take the research in a new direction.”
She spent two years working at the National Tropical Botanical Garden, which conserves tropical plants and identifies plant-derived medicines, on the island of Kauai. She studied uses of molecular biology and plant breeding to rescue endangered plants, work that was featured last fall in two articles in Science News and in other media reports.
Those earlier articles also described research by Prof. Praveen Saxena, Plant Agriculture, in developing propagation techniques for endangered plants and plants used as a source of herbal medicines.
“In vitro conservation of plants is a valuable tool for the study of endangered species such as cycads,” says Murch.
She studied tissue culture with Saxena for her PhD, completed in 2000, following master's studies in horticultural science and a B.Sc. in chemistry, also at Guelph. Originally from Cambridge, Ont., she returned to Canada from Hawaii last fall.
In the Bovey Building, Murch is turning her interest in tropical plants into growing breadfruit from various Pacific Islands; she plans to develop tissue culture protocols for a germplasm bank for these plants.
“Working on interesting scientific questions is what's important,” she says. “I love the feeling of being among the first people to learn something.”
