Most researchers believe Alzheimer's is caused by one of two proteins, one called tau, the other beta-amyloid, but a new UCLA study suggests a third possible cause: iron accumulation. The surprising new research appears in the Journal of Alzheimer's Disease.
For the study, the researchers looked at two areas of the brain in patients with Alzheimer's. They compared the hippocampus, which is known to be damaged early in the disease, and the thalamus, an area that is generally not affected until the late stages. Using brain-imaging techniques, they found that iron is increased in the hippocampus and is associated with tissue damage in that area. But increased iron was not found in the thalamus.
While most Alzheimer's researchers focus on the buildup of tau or beta-amyloid that results in the signature plaques associated with the disease, researcher George Bartzokis has long argued that the breakdown begins much further "upstream." The destruction of myelin, the fatty tissue that coats nerve fibers in the brain, he says, disrupts communication between neurons and promotes the buildup of the plaques. These amyloid plaques in turn destroy more and more myelin, disrupting brain signaling and leading to cell death and the classic symptoms of Alzheimer's.
Bartzokis explained that myelin is produced by cells called oligodendrocytes. These cells, along with myelin, have the highest levels of iron of any cells in the brain, and circumstantial evidence has long supported the possibility that brain iron levels might be a risk factor for age-related diseases like Alzheimer's. Although iron is essential for cell function, too much of it can promote oxidative damage, to which the brain is especially vulnerable.
In the new study, Bartzokis and his colleagues tested their hypothesis that elevated tissue iron caused the tissue breakdown associated with Alzheimer's disease. They targeted the vulnerable hippocampus, a key area of the brain involved in the formation of memories, and compared it to the thalamus, which is relatively spared by Alzheimer's until the very late stages of disease.
The researchers used an MRI technique that can measure the amount of brain iron in ferritin, a protein that stores iron. "We found that the amount of iron is increased in the hippocampus and is associated with tissue damage in patients with Alzheimer's but not in the healthy older individuals - or in the thalamus. So the results suggest that iron accumulation may indeed contribute to the cause of Alzheimer's disease," said Bartzokis.
But it's not all bad news, he added. "The accumulation of iron in the brain may be influenced by modifying environmental factors, such as how much red meat and iron dietary supplements we consume and, in women, having hysterectomies before menopause."
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Source: University of California - Los Angeles