An Alarming Link
New studies say diabetes leads to Alzheimer's. Still, that raises hope for novel brain treatments
Internal junk. But just how can diabetes drive up the risk of Alzheimer's? "There are a number of possible ways, and many of them have to do with how cells use energy," says Petersen. Energy comes from blood sugar, and insulin is the body's sugar ferry. If cells don't let it in--that's what happens in type 2, the most common form of diabetes--those cells start to starve. The same thing happens to neurons in the brain. The weakened neurons can't clear away internal junk, like clumps of amyloid protein, something that's seen in Alzheimer's. And then they die.
Another pathway may involve the cell's internal energy factories, called mitochondria. They become damaged in Alzheimer's, suggests Allen Roses, a noted dementia scientist who runs genetics research for drug maker GlaxoSmithKline in Research Triangle Park, N.C. "Fragments of proteins called APOEs, found in Alzheimer's, poison mitochondria," he says. Over years, this weakens the cell and kills it. Other researchers have suggested that if insulin problems are added on top of this, as in diabetes, it's an "extra hit" on the neurons, hastening their death.
This could explain the apparent antidementia abilities of drugs that improve a cell's ability to utilize insulin. Boston's Miller reports at the meeting about a protective effect in a huge study of 142,000 diabetic patients. Those who got insulin-sensitizing drugs such as Avandia had much lower rates of Alzheimer's than did patients taking a different drug class.
Then there's the effect of extra insulin on those with Alzheimer's like Clarence Miller, who took the hormone for three weeks. "Overall, they could recall stories a little better and had better attention," says Suzanne Craft, the VA neuroscientist who led the study. "Their families also reported a change, saying they just seemed brighter, a little bit more with it."
But the effects were small, and everyone in Madrid worries that healthy people, terrified of Alzheimer's, will rush out to try these drugs. "That's a big mistake. We have no proof they work in the general population," says Mark Sager, director of the Wisconsin Alzheimer's Institute in Madison. "I wouldn't prescribe it." But, Sager adds, this week's reports are prompting him to look closer at the insulin connection. If the link between the two diseases keeps getting stronger, he might start prescribing these drugs after all.
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