Elevated levels of cholesterol may play an even greater role in the development of Alzheimer's disease than was first thought.

Researchers from Georgetown University Medical Center examined the link between cholesterol and a protein called APP.

We are paving the way for possible new therapie

Dr Vassilios Papadopoulos

APP is found in several major organs including the brain and heart.

Nobody knows what role it plays in normal circumstances, but in people with Alzheimer's APP is processed in an abnormal way and is converted to beta amyloid protein.

When fragments of this protein break off, they form the plaques that are one of the characteristic structural abnormalities found in the brains of people suffering from Alzheimer's.

Past research has shown that high cholesterol levels appear to increase APP levels.

However, the latest study has found that high cholesterol also increases the rate at which the amyloid beta peptides break off and form plaques.

Toxic

Not only that, but elevated levels of cholesterol were found to stimulate a chemical reaction which puts nerve cells at risk by increasing the amount of cholesterol that floats free from the body's cells.

This free cholesterol is toxic to human nerve cells.

This research adds weight to calls for people in mid life to ensure they know what their cholesterol levels are

Dr Richard Harvey

The researchers have identified another protein that can reduce this problem by binding to the free cholesterol, and transporting it to the liver where it can be broken down.

Researcher Dr Vassilios Papadopoulos said: "By giving the dangerous free cholesterol something to bind to, we are paving the way for possible new therapies.

"Our study adds to the growing body of evidence implicating high cholesterol as a significant risk factor in Alzheimer's disease, and breaks new ground in showing the damage caused by excessive levels of cholesterol."

Dr Richard Harvey, medical director the UK Alzheimer's Society, told BBC News Online the research presented a "very neat theory".

"However, the research is test-tube based, and has to be interpreted with caution. It is also important that this research is properly published and subjected to scientific scrutiny.

"This research doesn't at present point to any new treatments for Alzheimer's disease, but it does add additional weight to calls for people in mid life to ensure that they know what their cholesterol levels are, and to seek treatment if the levels are high."

Long way to go

Rebecca Wood, chief executive of the UK Alzheimer's Research Trust, said: "This is interesting research and backs up previous work into possible links between raised cholesterol levels and an increased risk of Alzheimer's disease.

"As it is not known what causes Alzheimer's, it is hoped that identifying risk factors for the disease will help to find a way of preventing it.

"There are many exciting areas of Alzheimer's research at present, but there is a long way to go in the fight against the disease."

The research will be presented at a meeting of the US Endocrine Society.