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Diabetes and Alzheimer's: An Emerging Relationship

Diabetes and Alzheimer's disease relationship

Evidence of a relationship between diabetes and Alzheimer's disease has been seen in previous research, and now a team of investigators say they have direct experimental proof. The new study indicates that diabetes is linked to the onset of Alzheimer's disease (AD), a relationship that has implications for both diseases.

The uneasy relationship between diabetes and Alzheimer's

In a study reported earlier this year in the International Journal of Alzheimer's Disease, investigators noted that characteristics of type 2 diabetes, including abnormal glucose use, metabolic dysregulation, and insulin resistance or deficiency, are seen in the early stage of Alzheimer's disease independent of type 2 diabetes.

Therefore, they noted Alzheimer's "has been considered as type 3 diabetes," and type 2 diabetes "is a risk factor for AD." In that study, the researchers focused on the inflammation factors in both diseases and pointed out the "potential synergism" in these factors when individuals had both diseases.

This latest study from researchers at the University of Medicine and Dentistry of New Jersey (UMDNJ) and Northwestern University in Illinois utilized a mouse model to provide new insight into the relationship between diabetes and the onset of Alzheimer's disease.

Specifically, scientists used diabetes to instigate Alzheimer's and noted the following findings:

  • Significant increases in amyloid beta peptide pathology in the brain cortex and hippocampus in both diabetes and Alzheimer's disease at the same time. Amyloid beta peptides are a typical sign of Alzheimer's disease
  • Substantial amyloid beta pathology in the retina (which is considered to be an extension of the brain) but none in the brain or retina when diabetes was not present. This is important because the retina is easily accessible for observation and is considered to be an extension of the brain.

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According to Peter Frederikse, PhD, of UMDNJ, "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."

Another link between diabetes and Alzheimer's has been noted previously: the role of insulin in the formation of memories. It appears that when amyloid beta configurations called oligomers, which are believed to cause memory loss in Alzheimer's disease, attach to neurons in the brain, this action ultimately contributes to insulin resistance in the brain. This then triggers a cycle in which diabetes causes oligomers to accumulate, which in turn makes neurons more insulin resistant.

In the new study, the model used by the scientists replicated spontaneous formation of oligomer configurations in the brain and retina, which may help researchers explain one of the most common symptoms of Alzheimer's disease--memory loss. William Klein, PhD, of Northwestern University, pointed out that the activity of oligomers "has been a mystery, so these new findings with diabetes represent an important step."

Thus this new study provides new information for scientists regarding the relationship between diabetes and Alzheimer's disease. Co-author Chinnaswamy Kasinathan, PhD, of UMDNJ noted that their discovery "allows us to identify a potential biomarker for Alzheimer's disease and may also make important contributions to Alzheimer drug testing and development."

Bitel CL et al. Amyloid-B and tau pathology of Alzheimer's disease induced by diabetes in an animal model. Journal of Alzheimer's Disease 2012 / UMDNJ

Image: Wikimedia Commons