Saturday, August 15, 2009

Oxygen Treatment Hastens Memory Loss In Alzheimer's Mice

ScienceDaily (Aug. 13, 2009) — A 65-year-old women goes into the hospital for routine hip surgery. Six months later, she develops memory loss and is later diagnosed with Alzheimer's Disease. Just a coincidence? Researchers at the University of South Florida and Vanderbilt University don't think so. They suspect that the culprit precipitating Alzheimer's disease in the elderly women may be a routine administration of high concentrations of oxygen for several hours during, or following, surgery – a hypothesis borne out in a recent animal model study.

Dr. Gary Arendash of the Florida Alzheimer's Disease Research Center at USF and Dr. L. Jackson Roberts II at Vanderbilt University used mice genetically altered to develop abnormal levels of the protein beta amyloid, which deposits in the brain as plaques and eventually leads to Alzheimer's-like memory loss as the mice age. They found that young adult Alzheimer's mice exposed to 100-percent oxygen during several 3-hour sessions demonstrated substantial memory loss not otherwise present at their age. Young adult Alzheimer's mice exposed to normal air had no measurable memory loss, and neither did normal mice without any genetic predisposition for Alzheimer's disease.

The authors suggest that people genetically predisposed to Alzheimer's disease or with excessive amounts of beta amyloid in their brains are at increased risk of developing the disease earlier if they receive high concentrations of oxygen, known as hyperoxia. Their study is published online this month in NeuroReport.

"Although oxygen treatment beneficially increases the oxygen content of blood during or after major surgery, it also has several negative effects that we believe may trigger Alzheimer's symptoms in those destined to develop the disease," said USF neuroscientist Arendash, the study's lead author. "Our study suggests that the combination of brain beta amyloid and exposure to high concentrations of oxygen provides a perfect storm for speeding up the onset of memory loss associated with Alzheimer's Disease."

While postoperative confusion and memory problems are common and usually transient in elderly patients following surgery, some patients develop permanent Alzheimer's-like cognitive impairment that remains unexplained. Recent studies have indicated that general anesthesia administered during surgery may increase a patient's risk of Alzheimer's disease, but the laboratory studies did not use animals or people predisposed to develop the disease.

"Postoperative memory loss can be a fairly common and devastatingly irreversible problem in the elderly after major surgical procedures," said Roberts, an MD who holds an endowed chair in Pharmacology at Vanderbilt University School of Medicine. "There has been much speculation as to the cause of this memory loss, but the bottom line is that no one really knows why it happens. If all it takes to prevent this is reducing the exposure of patients to unnecessarily high concentrations of oxygen in the operating room, this would be a major contribution to geriatric medicine."


The authors caution that the study in mice may or may not accurately reflect the effects of hyperoxia in human surgery patients.

"Nonetheless, our results call into question the wide use of unnecessarily high concentrations of oxygen during and/or following major surgery in the elderly," Roberts said. "These oxygen concentrations often far exceed that required to maintain normal hemoglobin saturation in elderly patients undergoing surgery."

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