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Amylin Deposition in the Brain: A Second Amyloid in Alzheimer’s Disease?

Aug 9, 2013
Jackson K, Barisone G, Diaz E, Jin L, Decarli C, Despa F

Objectives: Hyperamylinemia, a common pancreatic disorder in obese and insulin resistant patients, is known to cause amylin oligmerization and cytotoxicity in pancreatic islets leading to β-cell mass depletion and development of type-2 diabetes. Recent data revealed that hyperamylinemia also affects the vascular system, heart and kidneys. We, therefore, hypothesized that oligomerized amylin might accumulate in cerebrovascular system and brain parenchyma of diabetic patients.

Methods: Amylin accumulation in the brain of diabetic patients with vascular dementia or Alzheimer’s disease (AD), non-diabetic patients with AD, and age-matched healthy controls was assessed by quantitative real-time PCR, immunohistochemistry, western blot and ELISA.

Results: Amylin oligomers and plaques were identified in the temporal lobe gray matter from diabetic patients, but not controls. In addition, extensive amylin deposition was found in blood vessels and perivascular spaces. Intriguingly, amylin deposition was also detected in blood vessels and brain parenchyma of patients with late-onset AD without clinically apparent diabetes. Mixed amylin and Aβ deposits were occasionally observed. However, amylin accumulation leads to amyloid formation independent of Aβ deposition. Tissues infiltrated by amylin show increased interstitial space, vacuolation, spongiform change, and capillaries bended at amylin accumulation sites. Unlike the pancreas, there was no evidence of amylin synthesis in the brain.

Interpretations: Metabolic disorders and aging promote accumulation of amylin amyloid in cerebrovascular system and gray matter altering microvasculature and tissue structure. Amylin amyloid formation in the wall of cerebral blood vessels may also induce failure of elimination of Aβ from the brain, thus contributing to the etiology of AD.

ANN NEUROL 2013. © 2013 American Neurological Association.