Copper link to Alzheimer's disease
Copper may increase the growth of the protein clumps in the brain that are a trademark of Alzheimer's disease, according to a new US study on rabbits.
Researchers first noticed that the rabbits they use to model Alzheimer's disease developed fewer plaques in their brains when they drank distilled water rather than tap water. These insoluble plaques, generated in the rabbits via a high-cholesterol diet, are a trademark of the degenerative illness.
The tap water contained significant amounts of copper, so Larry Sparks, at the Sun Health Institute in Sun City, Arizona, and Bernard Schreurs, at West Virginia University, then gave the rabbits distilled water spiked with copper supplements.
These rabbits developed significantly more plaques than those drinking only distilled water. They also suffered dramatically poorer memories in complex tests.
"We believe that this is a two-step process," Sparks told New Scientist. "Cholesterol causes overproduction of Alzheimer's proteins and then copper inhibits the clearance of beta-amyloid [a plaque-inducing protein] from the brain to the blood."
"The most striking thing was probably the fact we got full blown plaques in the brains of [these rabbits] which were regionally distributed similarly to Alzheimer's," he says.
Harriet Millward, deputy chief executive of the UK's Alzheimer's Research Trust, says a link between copper and Alzheimer's has been suggested before but that research so far has been contradictory.
"These are certainly interesting results - but we still need more research," she told New Scientist. She also notes that using cholesterol-fed rabbits as a model for Alzheimer's disease is a "very novel".
In the latest experiments, the cholesterol-fed rabbits were given water laced with 0.12 parts per million copper, one tenth of US safety limit for humans. Three-quarters of the rabbits showed senile plaque-like deposits in their brains after 10 weeks. These rabbits also showed an 80 per cent deficit in memory in complex conditioning tests.
The plaques were not found in the brains of animals given pure distilled water and were rare among those drinking tap water.
"Although we can only speculate about how the effects of copper consumption in cholesterol-fed rabbits relate to those in humans, it is of note that the levels of copper ... that induced beta-amyloid and senile plaque-like structures are well below those considered safe for humans," Sparks and Schreurs write in Proceedings of the National Academy of Sciences:
Sparks says the pair are now working on understanding the mechanism by which copper might cause beta-amyloid to accumulate in the brain.
Ashley Bush and colleagues at Harvard Medical School have previously proposed a different mechanism by which metals like copper and zinc could cause Alzheimer's (New Scientist print edition, 3 August 2002). They have suggested that the metals may cause beta-amyloid to turn into a rogue enzyme, catalysing the production of hydrogen peroxide, which then damages brain cells.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.1832769100)
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