Stress Hormone Associated with Alzheimer's disease

Researchers have found that stress hormone corticosteroid is linked with Alzheimer's disease.

The latest study on Alzheimer's disease and stress was conducted by researchers at Temple University. Previous studies have shown that patients with AD have some two to three times higher levels of corticosteroid than other people without the condition.

Alzheimer's disease is an irreversible and progressive brain disease that slowly destroys memory and thinking skills which in turn lead to the affected person being unable to carry out simple tasks essential for daily living. In most people with Alzheimer's, symptoms first appear after the age 60.

In their study, researchers carried out a series of experiments in which they tested the association between the disease and stress.

The study was conducted on a group of genetically altered mice who developed amyloid beta and the tau protein- characteristics of AD. Researchers then injected one subset of mice with corticosteroid that mimicked body's response to stress.

The experimental mice didn't lose memory, but researchers found that they had significantly higher levels of tau than earlier. Also, in the synapses that connect neuronal cells in mice with corticosteroid injections were extensively damaged.

"Stress is an environmental factor that looks like it may play a very important role in the onset of Alzheimer's disease. When the levels of corticosteroid are too high for too long, they can damage or cause the death of neuronal cells, which are very important for learning and memory," said Domenico Praticò, professor of pharmacology and microbiology and immunology in Temple's School of Medicine, lead author of the study.

"This was surprising because we didn't see any significant memory impairment, but the pathology for memory and learning impairment was definitely visible," said Pratico in a news release. "So we believe we have identified the earliest type of damage that precedes memory deficit in Alzheimer's patients."

There was also a third set of mice that was altered such that it no longer produced a brain enzyme called 5-lipoxygenase. This set of mice no longer showed any response to corticosteroid.

Previous research has shown that higher levels of 5-lipoxygenase are associated with higher levels of tau in the brain. According to researchers, stress hormone increases the levels of 5-lipoxygenase which in turn lead to higher levels of tau that damage the brain.

'Corticosteroid uses the 5-lipoxygenase as a mechanism to damage the synapse, which results in memory and learning impairment, both key symptoms for Alzheimer's. So that is strong support for the hypothesis that if you block 5-lipoxygenase, you can probably block the negative effects of corticosteroid in the brain," said Pratico.

The study, "Knockout of 5-lipoxygenase prevents dexamethasone-induced tau pathology in 3xTg mice," published in the journal Aging Cell.