Alzheimer's impairs insulin signalling in the portion of the brain responsible for regulating metabolism, making a person with the disease more likely to develop diabetes, a new study in mice suggests.
The findings by researchers from Icahn School of Medicine at Mount Sinai in the US also indicate that an increase of a particular group of amino acids in the blood could serve as a biomarker of impaired brain insulin signalling.
The study, conducted in mice, is part of ongoing research to better understand the link between Alzheimer's disease (AD) and diabetes.
It is the first study to show that mice with AD have insulin resistance (a precursor to type II diabetes) in the hypothalamus, the area of the brain that regulates metabolism of nutrients such as fatty acids, glucose and amino acids in tissues including muscle, liver and fat.
The mice with AD also showed elevated levels of branched chain amino acids (BCAA) in the blood.
A previous study from the same team of researchers had demonstrated that brain insulin signalling regulates BCAA levels in blood, and hence BCAAs could be a novel biomarker of hypothalamic insulin action in patients with Alzheimer's, which still needs to be confirmed in humans.
"This is the first study to suggest that Alzheimer's disease pathology increases susceptibility to diabetes due to impaired insulin signalling in the hypothalamus," said Christoph Buettner from Icahn School of Medicine.
"Our research provides a rationale that therapies developed to improve insulin signalling in the brain may reduce the likelihood that a patient with Alzheimer's disease develops diabetes," Buettner said.
AD is a progressive and fatal brain disorder that gradually destroys a person's memory and ability to learn, reason, make judgements, communicate and carry out daily activities.
Diabetes is a metabolic disease that results in high blood sugar levels because the body does not produce enough insulin for proper function.
Ageing is known to be one of the top risk factors for both diseases, and several previous epidemiological studies have supported the hypothesis that diabetes increases a person's risk for AD, researchers said.
"Our findings represent a turning point in the understanding of the relationship between Alzheimer's disease, type II diabetes and insulin resistance," said Sam Gandy from Icahn School of Medicine.
The study was published in the journal Alzheimer's and Dementia.