Contrary to the common belief that nicotine can treat the Alzheimer's disease, chronic nicotine exposure worsens some Alzheimer's-related brain abnormalities, US scientists reported Tuesday.

LOS ANGELES, Feb. 8 (Xinhuanet)-- Contrary to the common belief that nicotine can treat the Alzheimer's disease, chronic nicotine exposure worsens some Alzheimer's-related brain abnormalities, US scientists reported Tuesday.

    In the latest online edition of the Proceedings of the NationalAcademy of Sciences, the researchers at the University of California, Irvine(UCI), said that chronic nicotine exposure increases neurofibrillary tangles, namely the bundles of fibers that are one of the two neuropathological hallmarks of the disease.

    Alzheimer's disease is marked by the accumulation of two distinct brain lesions, beta-amyloid plaques and neurofibrillary tangles which accumulate in specific brain regions critical to learning and memory.

    Previous animal studies had suggested that nicotine reduces thenumber of amyloid plaques; however, this possible benefit is outweighed by the increase in tangles, according to UCI researchers.

    "In earlier work, we showed that plaques can induce tangles, but that is only one way in which tangles can form," said Salvatore Oddo, the first author of the paper.

    "There are other pathways independent of plaques that can lead to the formation of tangles. One of these is nicotine. It increases tangles independent of plaques, and therefore should notbe used as a treatment for Alzheimer's disease."

    To determine whether nicotine has a preventative effect on bothlesions of Alzheimer's disease, the researchers administered the drug in the drinking water of 20 mice that were genetically engineered to develop both the plaques and the tangles of Alzheimer's disease. They found that chronic nicotine exposure increased the tangles while having no significant effect on the plaques.

    In contrast to previous reports that nicotine has some marginally positive effects, these latest findings suggest that chronic nicotine exposure may actually be detrimental, enhancing certain Alzheimer's disease brain pathologies, said Frank LaFerla,associate professor at the UCI.

    "But these previous studies drew their conclusions after focusing only on plaque formation. Our paper stresses the importance of investigating Alzheimer's disease therapies in animal models that involve both types of pathologies, plaques and tangles, as it is possible for a compound to positively affect onelesion while worsening the other," he said.

    Starting with mild memory problems and ending with severe braindamage, Alzheimer's usually begins after the age of 60, the risk increasing with age. If no effective therapies are developed, by 2050 it is estimated that 13 million Americans will have the disease.

    In the United States, five percent of the population over age 65 and one-third of the population over age 85 are afflicted by Alzheimer's. It is the third most expensive disease to treat and is the third leading cause of death, trailing cancer and coronary heart disease. Enditem