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  • 5/30/2007

Blood Marker Could Point to Alzheimer"s Risk


Scientists have zeroed in on blood biomarkers that could someday help doctors predict who"s at risk for Alzheimer"s disease. They might even help guide treatment, the U.S. researchers added.

These biomarkers, called cytokines, are all hallmarks of heightened inflammatory responses. Cytokines specific to Alzheimer"s disease were found in greater numbers on white blood cells called mononuclear cells.

Higher concentrations of inflammatory markers in the blood have been linked to Alzheimer"s disease before. But other conditions of old age, such as heart disease and arthritis, can also trigger inflammation, the researchers pointed out.

However, the newly discovered markers point specifically at Alzheimer"s disease-linked inflammation in the brain, the scientists said.

That"s important, because right now "there"s no single blood test or neuroimaging study -- CT scan or MRI -- that can reliably predict whether somebody has Alzheimer"s disease, much less whether someone is at risk of developing the illness," explained lead researcher Dr. Zaldy Tan, director of the Memory Disorders Clinic at Beth Israel Deaconess Medical Center, in Boston.

"So, if this finding is validated in other studies and larger samples, it might become a test for future risk of Alzheimer"s disease," he said.

There are currently no effective treatments for Alzheimer"s disease, which now affects more than 5 million Americans, according to the Alzheimer"s Association. Scientists project that unless new ways are found to prevent or treat the disease, that total could climb to 16 million by mid-century.

The exact role of inflammatory processes in Alzheimer"s remains a mystery, although numerous studies support the notion that they are at least associated with the mind-robbing illness.

"The data has been conflicting," Tan said. "Most of the studies out there are population-based, looking at the use of anti-inflammatory drugs, for example, on the incidence of Alzheimer"s disease." Those studies have found no good evidence that taking steroids or nonsteroidal anti-inflammatories (for example, aspirin or ibuprofen) cuts Alzheimer"s risk.

Tougher still has been the search for a blood marker that might precisely indicate the presence of, or risk for, Alzheimer"s disease in a particular patient.

A number of studies with elderly patients have correlated a high number of cytokines in red blood cells with Alzheimer"s, but "since this population is significantly older, there are other reasons someone might have inflammation -- arthritis, for example," Tan said.

The new study, published in the May 29 issue of Neurology, focused on a particular type of white blood cell, the mononuclear cell. Tan"s team focused on these cells because they have the ability -- unlike many other cells -- to cross the blood-brain barrier.

Taking advantage of the ongoing Framingham Heart Study, Tan and his colleagues periodically tested the blood of 691 healthy elderly participants averaging 79 years of age. Then they tracked the volunteers" mental health for the next seven years.

Over that period of time, 44 of the participants developed Alzheimer"s disease.

The researchers found that individuals with the highest levels of mononuclear cell-derived inflammatory cytokines were twice as likely to develop the illness as those with the lowest levels of the inflammatory markers.

"So, our hypothesis now is that it is possible to indirectly measure [Alzheimer"s-linked] brain inflammation by looking at the amount of inflammatory markers released by these blood cells, cells that may eventually make it to the brain," Tan said.

One expert agreed the finding could someday lead to a real advance in the care and understanding of Alzheimer"s disease.

"What this study does is take us to another level in terms of diagnostics," said Paul Sanberg, director of the Center of Excellence for Aging and Brain Repair at the University of South Florida College of Medicine, in Tampa. "They are finding a more consistent result when they look at the inflammatory markers in mononuclear cells."

He said the jury is still out on whether treating inflammation might prevent or treat Alzheimer"s, since no one is sure whether inflammation helps cause the disease or is simply a product of the illness.

But if it turns out that dampening inflammation can help, a blood test measuring these cytokines might be of great use to doctors, Sanberg said. "If you can find a consistent marker, then maybe some patients might be treated by anti-inflammatories better than others, depending on the [blood] level of these markers," he said.

Tan agreed that it"s too early to talk about treatments, but he believes the new finding brings effective diagnostics and therapy that much closer.

"This is another piece of the puzzle in the mechanism of Alzheimer"s disease," he said.


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