Hopes have been raised that diabetes drugs could be developed as treatments for Alzheimer's disease after scientists demonstrated the beneficial effect of insulin on the brain.
A US-led research team found the hormone, released by the pancreas to help control levels of sugar in the blood, protected memory-forming parts of the brain.
The study, published in the Proceedings of the National Academy of Sciences, concluded that insulin may slow or prevent the memory loss caused by toxic proteins which attack the brains of Alzheimer's sufferers.
It boosts theories the disease - characterised by progressively catastrophic dementia - could be due to a type of brain diabetes.
The team of researchers from Northwestern University in Illinois and the Federal University of Rio de Janeiro in Brazil carried out a study that involved treating neurons taken from one of the brain's memory centres - the hippocampus - with insulin and diabetes drug rosiglitazone.
Cells in the hippocampus are susceptible to damage caused by ADDLs, toxic proteins that build up in people with Alzheimer's disease.
ADDLs (amyloid beta-derived diffusible ligands) are known to attack memory-forming synapses, according to the scientists. After the proteins have attached, the synapses lose their capacity to respond to incoming information, resulting in memory loss.
The researchers discovered damage to neurons exposed to ADDLs was blocked by insulin, which stopped the proteins from attaching to the cells.
Senior author William Klein, a professor of neurobiology and physiology in the Weinberg College of Arts and Sciences and a researcher in Northwestern's Cognitive Neurology and Alzheimer's Disease Centre, said: "Therapeutics designed to increase insulin sensitivity in the brain could provide new avenues for treating Alzheimer's disease.
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"Sensitivity to insulin can decline with ageing, which presents a novel risk factor for Alzheimer's disease. Our results demonstrate that bolstering insulin signalling can protect neurons from harm."
