The brains of chimpanzees and other primates may get clogged with the same protein plaques that plague Alzheimer's sufferers. But they do not get the disease, a "curious phenomenon" that has long baffled researchers. Now, thanks to research conducted by scientists from the Yerkes National Primate Research Center at Emory University in Atlanta, the medical community now has a clue into the reason why primates are not afflicted with Alzheimer's.

Understanding that the amino acid sequence of human amyloid protein is different in humans than in monkey brains, the Emory University scientists hypothesized that the structure of the plague might also be different. Study author Rebecca Rosen, a neuroscience doctoral candidate at the primate research center, and her colleagues put this theory to the test. According to their report, which was published in the latest issue of the journal of Neurobiology of Aging, they took Pittsburgh Compound B (PIB), a compound widely used in clinical trials to diagnose Alzheimer's. PIB binds to amyloid deposits in live human brains, thereby "lighting up" the plaques on positron-emission tomography (PET) scans. PIB in brain tissue was taken from several sources, including deceased rhesus monkeys, deceased squirrel monkeys, deceased chimpanzees, nine deceased humans with end-stage Alzheimer's and three deceased older but healthy humans. "We were able to show that, similar to what has been seen in mouse brains, PIB does not bind with high affinity to plaque in monkey or ape brains," says Rosen.

Having identified that a "tag" molecule used to track plaque build-up easily latches onto plaques in human brains, but not in primates, the researchers believe there is a basic structural difference between the two types of plaque. Determining the nature of that difference could ultimately lead scientists to render plaques as harmless in human brains as they are in the brains of other primates. "What this tells us, first of all, is that plaques are structurally distinct in human vs. non-human primates," says Rosen. "Why that is is a huge question, but now we have a tool we can use to differentiate the structure of amyloid plaques between humans and non-human primates. We can use this tagging compound to characterize the toxic nature of the amyloid plaques in the human brain in order to understand them better. It also confirms the usefulness of the PIB for diagnosing Alzheimer's," she adds.

News Release: Why chimps, monkeys don't develop Alzheimer's: www.news.yahoo.com, May 25, 2009