Could Alzheimer's be a form of diabetes? That is the tantalizing suggestion raised by a new study that found that insulin production in the brain declines as Alzheimer's disease advances.
The Study
Senior researcher Suzanne M. de la Monte, a neuropathologist at Rhode Island Hospital and a professor of pathology at Brown University Medical School, and her team autopsied the brain tissue of 45 patients who had been diagnosed with different degrees of Alzheimer's disease. They compared those tissues to samples taken from individuals who had no history of the disease.
The team analyzed insulin and insulin-receptor function in the frontal cortex of the brain, a major area affected by Alzheimer's. The discovery that the brain produces insulin at all is a recent one. The researchers found that as the severity of Alzheimer's increased, the levels of insulin as well as the brain's ability to respond to insulin decreased.
"Insulin disappears early and dramatically in Alzheimer's disease," says de la Monte. "We're able to show that insulin impairment is linked to abnormalities that contribute to the tangles [that are] characteristic of advanced Alzheimer's disease. This work ties several concepts together and demonstrates that Alzheimer's disease is quite possibly a type J diabetes," she says. (To understand the differences between type 1 and type 2 diabetes, see page 76)
This study may have treatment implications, such as using certain types of anti diabetes drugs to treat and/or prevent Alzheimer's.
Other Factors
Dr. Hugh C. Hendrie, professor of psychiatry and codirector of the Center for Alzheimer's Disease and Related Neuropsychiatric Disorders at Indiana University Center for Aging Research, believes that declining insulin levels may be an important feature of Alzheimer's, but not the whole story.
"There is now increasing evidence, primarily from observational studies, that diabetes, its predecessor metabolic syndrome and insulin resistance are implicated in increasing the risk for Alzheimer's disease," he says.
"However there are many other factors also implicated in Alzheimer's disease, such as hypertension and inflammation, so I think it's a bit of a stretch, at the moment, to describe Alzheimer's disease as an endocrinological disorder like diabetes," Hendrie says.
Another expert thinks that insulin and insulin-like growth factors may be the key to slowing the progression of Alzheimer's.
"'We have shown that insulin-like growth factors regulate learning and memory," says Douglas N. Ishii, professor in the department of biomedical sciences at Colorado State University in Fort Collins. "The clinical potential is that by injecting insulin-like growth factors into patients, one might be able to prevent the loss of learning and memory."
