Lead author Rashid Deane, a research professor in the University of Rochester Medical Center Department of Neurosurgery, says copper is found in drinking water carried by copper pipes, nutritional supplements and in food such as red meat, shellfish, nuts and many fruits and vegetables.
It plays an important and beneficial role in nerve conduction, bone growth, the formation of connective tissue and hormone secretion, Deane says.
However, the study shows copper can also accumulate in the brain and cause the system that controls what enters and exits the brain to break down, resulting in the toxic accumulation of the protein amyloid beta, a byproduct of cellular activity.
Using both mice and human brain cells, Deane and colleagues conducted a series of experiments that have pinpointed the molecular mechanisms by which copper accelerates the pathology of Alzheimer's disease.
Under normal circumstances, amyloid beta is removed from the brain by the protein lipoprotein receptor-related protein 1 (LRP1), which lines capillaries that supply the brain with blood. They bind with the amyloid beta found in the brain tissue and escort them into the blood vessels where they are removed from the brain.
The research team "dosed" normal mice with copper over a three month period equivalent to what people would consume in a normal diet, Deane says.
The researchers found copper made its way into the blood system and accumulated in the vessels that feed blood to the brain, specifically in the cellular "walls" of the capillaries and over time the metal can accumulate in these cells with toxic effect.
The researchers observed the copper disrupted the function of LRP1 through a process called oxidation which, in turn, inhibited the removal of amyloid beta in both mouse and human brain cells.
"Copper is an essential metal and it is clear that these effects are due to exposure over a long period of time," Deane said in a statement. "The key will be striking the right balance between too little and too much copper consumption. Right now we cannot say what the right level will be, but diet may ultimately play an important role in regulating this process."
The findings are published in the journal Proceedings of the National Academy of Sciences.