Insulin and memory

Behind the Headlines

Tuesday February 3 2009

Alzheimer's disease causes loss of memory and reasoning ability

“Alzheimer’s sufferers have been given fresh hope after scientists discovered insulin drugs for diabetes can prevent memory loss”, the Daily Express reported. The newspaper said that researchers had treated neurons (brain cells) from the hippocampus (part of the brain involved in memory) with insulin and the diabetes drug rosiglitazone. It said that damage to neurons exposed to toxins was blocked by insulin.

This laboratory study presents evidence that insulin is linked to Alzheimer’s and may have a role in treating it. It adds to evidence from other studies that have had the same conclusion.

The drug, Rosiglitazone, is currently being trialled in humans with Alzheimer’s disease. The results will provide a clearer picture of the potential of insulin in treating this condition.

Where did the story come from?

Dr Fernanda G De Felice, Marcelo NN Vieira, Theresa R Bomfim and colleagues from Northwestern University in Illinois and the Universidade Federal do Rio de Janeiro in Brazil carried out this study. It was supported by grants from research bodies including the American Health Assistance Foundation, the Alzheimer’s Association and the National Institutes of Health. The study was published in the peer-reviewed medical journal PNAS.

What kind of scientific study was this?

One of the characteristics of Alzheimer’s Disease is severe memory loss. The researchers say that this memory loss is caused by an accumulation in the brain of certain proteins called Aβ-derived diffusible ligands (ADDLs). These proteins bind to synapses (the junctions between brain cells) and cause oxidative stress. This damage affects neurological function.

The researchers wanted to investigate if the brain’s susceptibility to these proteins is affected by insulin treatment. Insulin plays an important role in the ability of the brain to adapt to injury. This laboratory study used cultures of brain cells from the hippocampus. These brain cells were used to see if insulin is involved in processes that protect the synapses from damage caused by ADDL proteins. The researchers say that previous research has shown that ADDLs cause a “major loss of insulin receptors” at the surface of nerve cells.

The study had several complex aspects to it, including an investigation of the effects of ADDLs on other enzymes and cellular chemical reactions. It also looked at how insulin affects ADDL-induced loss of insulin receptors, and whether the drug rosiglitazone (used to treat type II diabetes) enhances the activity of insulin. Laboratory methods were used to assess the levels of insulin receptors on the surface of the brain cells and the effects that different treatments had on them.

What were the results of the study?

The researchers found that an accumulation of ADDLs led to loss of insulin receptors in cultures of hippocampal brain cells. Various substances were able to protect against this, the most relevant for this story being insulin. This protective ability of insulin was enhanced by treatment with rosiglitazone.

What interpretations did the researchers draw from these results?

The researchers conclude that a combination of protecting synapses from the effects of ADDLs along with a reduction in ADDL concentration may be a good strategy for preventing memory loss.

They say their study shows that drugs involved in insulin use and uptake (such as rosiglitazone) may help protect synapses, and that other drugs, such as therapeutic antibodies, may be able to reduce the concentrations of ADDLs.

What does the NHS Knowledge Service make of this study?

This early laboratory study confirms that insulin receptors are affected by ADDL proteins in brain cells. It indicates that brain cells may be protected from these effects by treatment with insulin and drugs that help cells use insulin. The study adds further evidence to others that have found this link.

However, these experiments were carried out in the laboratory and should be viewed only as preliminary evidence of the effects of insulin on neurological function in humans. Further studies in people with Alzheimer’s disease will provide a clearer picture of the potential of these drugs in treating dementia-related memory loss. Towards this end, the authors report that rosiglitazone is currently being trialled in people with Alzheimer’s disease.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Insulin may be key to fighting Alzheimer's disease. The Times, February 03 2009

Diabetics’ drug may help Alzheimer’s victims

Alzheimer's 'is brain diabetes'. BBC News, February 03 2009

Links to the science

De Felice FG, Vieira MNN, Bomfim TR, et al. Protection of synapses against Alzheimer's-linked toxins: Insulin signaling prevents the pathogenic binding of Aβ oligomers. PNAS 2009; Published online before print February 2

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