Smoking does not prevent Alzheimer's, study concludes

• The final excuse for smoking -- that it might reduce the risk of developing Alzheimer's disease -- has just been stubbed out, findings from an animal study suggest.
• Past animal and human studies have indicated that nicotine exposure inhibits the formation of amyloid plaque, a key feature of Alzheimer's disease.
• However, the new study shows that chronic nicotine use appears to worsen the effects of a brain protein called tau, which is responsible for the fibrous tangles that are the other hallmark of the disease.
• So, at best, the effects of nicotine are probably canceled out, according to the researchers.
• Dr. Frank M. LaFerla, from the University of California at Irvine, and colleagues administered nicotine to a genetically engineered strain of mice that develops Alzheimer's disease.
• Nicotine treatment produced an increase in nicotine receptors in the animals' brains that correlated with a dramatic rise in the aggregation and activity of the tau protein.
• This indicates that the disease-causing effects of tau were worsened, the team reports in the Proceedings of the National Academy of Sciences.
• Moreover, in these experiments, chronic nicotine administration had no effect on levels of soluble amyloid, the researchers point out.
• The results emphasize the importance of assessing nicotine's affects on all aspects of the disease, they write.
• "Our findings suggest that the use of nicotine as a potential therapy for Alzheimer's disease should be reevaluated."