December 29, 2008
A slow but persistent lack of nutrients in the brain may be a critical factor in causing some forms of Alzheimer's disease, a new study suggests. The findings appeared in the scientific journal Neuron.
"What we are talking about here is a slow, insidious process over many years where people have a low level of cardiovascular disease or atherosclerosis in the brain," said study leader Dr. Robert Vassar, of the Feinberg School of Medicine at Northwestern University in Chicago. "It's so mild, they don't even notice it, but it has an effect over time because it's producing a chronic reduction in the blood flow."
As we age, blood flow to the brain slowly decreases because of atherosclerosis, or hardening of the arteries; damage to blood vessels from high blood pressure; and other factors. Levels of nutrients carried in the blood, like blood sugar, also decrease.
Blood sugar, or glucose, is critical for providing energy to cells throughout the body, including in the brain. The net effect of diminished blood flow is a slow and persistent starvation of the brain, researchers from the Feinberg School of Medicine at Northwestern University in Chicago suggest.
The researchers found that when the brain doesn't get enough glucose, it launches a biochemical process that may lead to the accumulation of the sticky clumps of protein, or beta-amyloid plaques, that characterize Alzheimer's disease. They found that when blood sugar levels decrease, a protein called elF2alpha changes form, leading to the buildup of the toxic protein clumps.
"This finding is significant because it suggests that improving blood flow to the brain might be an effective therapeutic approach to prevent or treat Alzheimer's," said Dr. Vassar, a professor of cell and molecular biology at the Feinberg School.
To keep blood vessels healthy and blood flow to the brain strong, experts recommend a heart-healthy diet that will help to keep cholesterol levels low and high blood pressure in check. Regular exercise is also critical for a healthy cardiovascular system and for keeping blood vessels in the brain open and flexible. And the earlier you start, the healthier your blood vessels will stay into old age.
"If people start early enough, maybe they can dodge the bullet," Dr. Vassar said. For people who already have symptoms, medications that increase blood flow and keep hypertension in check may also help the delivery of oxygen and glucose to the brain, he added.
Ten years ago, Dr. Vassar discovered an enzyme called BACE1 that involved in the accumulation of sticky plaques in the brains of people with Alzheimer's. He believes that energy deprivation in the brain may increase levels of BACE1, which may be a protective adaptive response in the short term. But over the long haul, persistent elevation of the enzyme may lead to damaging plaque buildup and the loss of brain function characteristic of Alzheimer's disease.
While not enough blood sugar may be damaging to the brain, excess levels of glucose in the blood may be a sign of diabetes and also be harmful to the brain, researchers at Columbia University in New York recently showed. Keeping blood sugar levels in check, through healthy diet, regular exercise and maintaining weight, is key to keeping the brain sharp into old age.
Source: Neuron, December 26, 2008.