Stroke victims could be more vulnerable to Alzheimer's

Jun 5 2007

University of Leeds scientists have shown how stroke victims could be more vulnerable to Alzheimer's disease – years or even decades after making a full recovery.

It has been known for some time that the two conditions were linked, but now the Leeds team has shown how an incident of reduced oxygen to the brain – caused by the stroke – can leave the patient vulnerable to the gradual build-up of toxic chemicals which can cause Alzheimer’s.

The research was led by Professor Chris Peers of the University’s school of medicine, who explained: “Our research is looking into what happens when oxygen levels in the brain are reduced by a number of factors, from long-term conditions like emphysema and angina, to sudden incidents such as a heart attack, stroke or even head trauma. Even though the patient may outwardly recover, the hidden cell damage may be irreversible.

“It could even be an issue for people who snore heavily, whose sleep patterns are such that there will be times in the night when their brain is hypoxic – deprived of sufficient oxygen. It can be anything that stops the heart and lungs working together to their optimal capabilities.”

The research centred on the damage done by these low-oxygen incidents to a group of brain cells called astrocytes. When the brain is functioning normally, it makes connections through the release of tiny amounts of chemical across the synapses. Once the chemical has been transmitted, it is “mopped up” by the astrocytes.

The Leeds team – which also includes Dr John Boyle in the Faculty of Medicine and Health and Dr Hugh Pearson of the Faculty of Biological Sciences – has shown that if at some point the astrocytes have become hypoxic, they are less able to mop up these transmitters, allowing the residual chemicals to accumulate and become toxic.

“This is an important factor in what’s going on in hypoxic brains,” said Prof Peers, whose work received funding from the Alzheimer’s Society and the Alzheimer’s Research Trust. “Astrocytes are just as essential as neurones for normal brain function – and we have ten times as many of them.”

Professor Susanne Sorensen, head of research at the Alzheimer's Society, added: "The team examined the role of cells that support neurones in the brain. This is exciting because rather than focussing on neurones they looked at processes in the brain, which until now have not be researched in so much detail."

In another project, the team is investigating two key signalling molecules which are very sensitive to fluctuations in oxygen levels. The scientists suspect that in low oxygen conditions these molecules could begin the increased production of a toxic protein called amyloid which builds up in the brains of people with Alzheimer’s.

The work at Leeds is part of a network of research projects nationally and internationally, which are adding to the sum of knowledge about a disease which costs the UK more than cancer, heart disease and stroke combined.

There are around 700,000 people in the UK currently suffering with dementia – a figure that is set to more than double by 2050, simply because we are living longer. And the disparity between funding levels for research into different conditions is stark, as Prof Peers explained: “For every cancer patient in this country, between £300 and £400 is spent every year on research. For Alzheimer’s sufferers it is closer to £15, yet sufferers can need full-time care for the last 20 to 30 years of their lives, so any research into intervention can be really cost-effective in the long term.”

Around 700,000 people in the UK – including 20 per cent of those aged over 80 – have a form of dementia. Alzheimer’s disease accounts for more than half of these. Alzheimer’s is not a normal, unavoidable part of getting older, but a fatal and incurable brain disease. It can take 30 years to develop. Beyond the age of 65, your chance of developing Alzheimer’s doubles every five years.