July 23, 2004
HIV-positive people may be at risk for developing chronic dementia similar to Alzheimer's disease, according to a study presented on Tuesday at the International Conference on Alzheimer's Disease by researchers from the University of California-San Francisco and the San Francisco Veterans Affairs Medical Center, the Oakland Tribune reports. Amyloid beta, a protein that is produced during the aging process that can damage brain cells, is normally broken down by the neprilysin enzyme. However, in HIV-positive people, the HIV-associated protein Tat blocks neprilysin and amyloid can then accumulate, according to the study. UCSF professor Lynn Pulliam and colleagues applied synthetic Tat to normal human brain cells that contained neprilysin and found a resulting 125% increase in amyloid. According to Pulliam, an accumulation of unchecked amyloid, in combination with factors such as genetics, can result in a "slow and devastating" memory loss similar to Alzheimer's. "What we're worried about is a kind of slow, chronic dementia we haven't seen before in HIV patients," Pulliam said. She added that even if HIV is not detected in the blood, the virus can remain in the brain where amyloid will accumulate as a patient ages. Dr. Kathleen Clanon, medical director of HIV services at the Alameda County Medical Center, said that aging HIV-positive people are "acquiring all the same problems that come with aging but at an accelerated rate." However, Clanon said that the slow memory loss is very different from the acute dementia seen in patients during the final months of life before the advent of antiretroviral drug treatment. Although new treatments such as Aricept can temporarily delay the onset of Alzheimer's, Pulliam said that it is unclear whether they would be effective in HIV-positive people (Vesely, Oakland Tribune, 7/21).
Antiretroviral drugs may block an enzyme that helps break down amyloid and insulin, according to another study presented at the conference (Burling, Philadelphia Inquirer, 7/23). Dr. Cristian Achim of the University of Pittsburgh and colleagues examined the brains of 160 people who had died of AIDS-related illnesses and who had used antiretroviral drugs. The researchers found that two-thirds of those studied had deposits of amyloid similar to the levels seen in people with Alzheimer's (Reuters, 7/22). The researchers found significant amounts of amyloid in the brains of patients who had used both older and newer antiretroviral drugs. Doctors treating HIV-positive people should be "especially careful" in monitoring patients for signs of dementia and diabetes, the researchers said (Philadelphia Inquirer, 7/23). "The current adult HIV patient population in the [United States] stands a good chance of surviving the virus, which means they will become affected by many of the disorders associated with later stages in life," Achim said, adding, "Although these results are preliminary, it is plausible to hypothesize that beta-amyloid brain deposits will only increase in the aging HIV population on prolonged anti-viral therapy." The researchers plan to test the hypothesis using brain imaging techniques to measure the accumulation of amyloid beta (Conference release, 7/22).