The team, led by Temple University Professor Domenico Pratic̣, also identified the mechanisms underlying the protective effects of extra-virgin olive oil (EVOO).
"We found that olive oil reduces brain inflammation but most importantly activates a process known as autophagy (a process by which cells break down and clear out intracellular debris and toxins, such as amyloid plaques and tau tangles)," Prof. Pratic̣ said.
"Brain cells from mice fed diets enriched with EVOO had higher levels of autophagy and reduced levels of amyloid plaques and phosphorylated tau."
"Phosphorylated tau protein is responsible for neurofibrillary tangles, which are suspected of contributing to the nerve cell dysfunction in the brain that is responsible for Alzheimer's memory symptoms."
In order to investigate the relationship between EVOO and dementia, Prof. Pratic̣ and co-authors used a well-established Alzheimer's disease mouse model.
Known as a triple transgenic model (3xTg), the animals develop three key characteristics of the disease: memory impairment, amyloid plagues, and neurofibrillary tangles.
The team divided the animals into two groups, one that received a chow diet enriched with EVOO and one that received the regular chow diet without it.
The olive oil was introduced into the diet when the mice were 6 months old, before symptoms of Alzheimer's disease begin to emerge in the animal model.
In overall appearance, there was no difference between the two groups of animals.
However, at age 9 months and 12 months, mice on the EVOO-enriched diet performed significantly better on tests designed to evaluate working memory, spatial memory, and learning abilities.
Studies of brain tissue from both groups of mice revealed dramatic differences in nerve cell appearance and function.
"One thing that stood out immediately was synaptic integrity," Prof. Pratic̣ said.
"The integrity of the connections between neurons, known as synapses, were preserved in animals on the EVOO diet."
"In addition, compared to mice on a regular diet, brain cells from animals in the olive oil group showed a dramatic increase in nerve cell autophagy activation, which was ultimately responsible for the reduction in levels of amyloid plaques and phosphorylated tau."
"This is an exciting finding for us. Thanks to the autophagy activation, memory and synaptic integrity were preserved, and the pathological effects in animals otherwise destined to develop Alzheimer's disease were significantly reduced," he said.
"This is a very important discovery, since we suspect that a reduction in autophagy marks the beginning of Alzheimer's disease."
The team now plans to investigate the effects of introducing EVOO into the diet of the same mice at 12 months of age, when they have already developed plaques and tangles.
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