TNF blockers neutralize a protein, called tumor necrosis factor alpha (TNF), that is overproduced in inflammatory diseases like rheumatoid arthritis.
"Studies have shown that TNF is also elevated in the cerebrospinal fluid of Alzheimer's patients and that higher levels correlate with the progression of the disease," Chou tells WebMD.
To further explore the possible association between rheumatoid arthritis, Alzheimer's, and TNF blockers, Chou and colleagues combed through a medical and pharmacy claims database that included information on 8.5 million U.S. adults.
Chou presented his findings here at the annual meeting of the American College of Rheumatology.
TNF Blockers Linked to 55% Reduced Risk of Alzheimer's
The researchers identified 165 people who had both RA and newly diagnosed Alzheimer's disease. Each of these individuals was then compared with up to 10 people of the same age, sex, and duration of drug treatment who had arthritis but no dementia.
After taking into account known risk factors for Alzheimer's such as high cholesterol levels and diabetes, the researchers found that the use of TNF blockers was associated with a 55% lower risk of Alzheimer's disease in people with rheumatoid arthritis.
When they further analyzed the risk according to the three TNF blockers studied, the researchers found that Enbrel was associated with a nearly 70% reduced risk of Alzheimer's, Chou says.
The study does not prove cause and effect. It only shows there may be an association between TNF blockers, particularly Enbrel, and a lower risk of Alzheimer's disease, he says. RA patients who take the drugs may share some other risk factor that explains the link.
Enbrel May Cross Blood-Brain Barrier More Easily
Stressing that she is only speculating, Marcy Bolster, MD, tells WebMD that Enbrel may have had a greater effect because it is a smaller molecule than the other two TNF blockers studied.
"Theoretically, it may cross the blood-brain earlier more easily," says Bolster, director of the rheumatology training program at the Medical University of South Carolina in Charleston. Researchers have been searching for Alzheimer's drugs that are able to enter the brain, where plaques and tangles cause destruction in people with Alzheimer's disease.
"It could also be that by reducing inflammation in RA, there's a beneficial effect on what is going on in the brain of Alzheimer's patients," says Bolster, who moderated a news briefing to discuss the findings.
While provocative, the findings need to be validated in a more robust study in which people with RA on various drugs are followed over time, Bolster says.
Also, "we want to see if the association holds up in the general population. We only looked at RA patients," Chou says.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.