Low levels of brain oxygen may boost Alzheimer’s risk, a new study in mice shows.

The study compared mice that were kept in cages with low-oxygen air with mice exposed to normal levels of oxygen and found that the mice who were deprived of oxygen developed more of the plaque believed to cause Alzhiemer's in their brains. .

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Researchers included Weihong Song, MD, PhD, of the psychiatry department and Brain Research Centre at Canada’s University of British Columbia.

Song’s team studied mice that had a gene tied to Alzheimer’s disease.

The researchers kept some mice in cages with low-oxygen air for 16 hours a day for a month.

They kept the other mice in cages with normal oxygen levels.

In humans, conditions such as stroke that hamper blood flow in the brain can limit the brain's oxygen supply.

After the month, the researchers tested both sets of mice on a memory test in which they were timed while swimming through a water maze to reach a hidden platform.

The mice that had lived in low oxygen performed worse.

Those mice also had more amyloid beta plaque -- a hallmark of Alzheimer’s disease -- in their brains, compared to the mice with normal brain oxygen levels.

Song and colleagues also studied the mice’s genes.

Under the influence of low brain oxygen levels, the BACE1 gene upped production of amyloid beta, the key protein in Alzheimer’s brain plaque.

Even a “slight” rise in BACE1 activity “could lead to a dramatic increase in [amyloid beta] production,” the researchers write.

Low brain oxygen levels might also affect other genes and may spur brain cell death, worsening memory in Alzheimer’s disease, Song’s team notes.

Boosting brain oxygen levels may benefit Alzheimer’s patients, the researchers say. However, their study did not test that theory.

The report appears in Proceedings of the National Academy of Sciences’ online early edition.

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By Miranda Hitti, reviewed By Louise Chang, MD

SOURCES: Sun, X. Proceedings of the National Academy of Sciences of the United States of America, week of Nov. 20-24, 2006; online early edition. News release, Proceedings of the National Academy of Sciences of the United States of America.