How Are Alzheimer's Disease And Diabetes Linked?

An experiment has shown that diabetes is associated with the onset of Alzheimer's disease. The finding, published online in this week's issue of the Journal of Alzheimer's Disease, is a collaboration between researchers from New Jersey's University of Medicine and Dentistry (UMDNJ) and researchers from Northwestern University, and was based on an experimental model, which shows that diabetes can potentially be used as an important new tool for investigating Alzheimer's disease and developing new drugs to combat the disease.
The study was built on evidence from previous studies at Klein's lab, which suggested a close link between Alzheimer's disease and diabetes and decided to investigate whether untreated diabetes could be a physiological model of Alzheimer neuropathology.
Frederikse remarked: "The results were striking. Because we used diabetes as an instigator of the disease, our study shows - for the first time directly - the link between Alzheimer's and diabetes."
The team discovered that in both Alzheimer's disease and diabetes the amyloid beta peptide pathology in the brain cortex and hippocampus significantly increases at the same time. High levels of amyloid beta peptides are typical in those with Alzheimer's disease. They also discovered substantial amyloid beta pathology in the retina, whereas no observable pathology was found either in the brain or retina when diabetes was not present. Frederikse continued:

"Second, our study examined the retina, which is considered an extension of the brain, and is more accessible for diagnostic exams. Our findings indicate that scientists may be able to follow the onset and progression of Alzheimer's disease through retinal examination, which could provide a long sought after early-warning sign of the disease."

The team noted that their experimental model replicated spontaneous formation of amyloid beta "oligomer" assemblies in brain and retina. This may shed more light on explaining one of Alzheimer's most widely recognized symptoms.
Klein states: "This is exciting. Oligomers are the neurotoxins now regarded as causing Alzheimer's disease memory loss. What could cause them to appear and buildup in late-onset Alzheimer's disease has been a mystery, so these new findings with diabetes represent an important step."
According to earlier studies, the impact of insulin on the formation of memories is significant, given that once oligomers are attached to neurons, they evoke an elimination of insulin receptors from the surface membranes, and thus contribute to insulin resistance in the brain. This is the start of a vicious cycle, as diabetes induces oligomer accumulation, making neurons even more insulin resistant.