Link between chronic bacterial inflammation and Alzheimer disease

Alzheimer's disease (AD) is a degenerative disease of brain that is associated with dementia, brain atrophy, accumulation of hyperphosphorylated tau protein and amyloid-beta peptide in hippocampus and cortex region of the brain. The development of AD is a multifactorial process that may also involve infection with bacterial pathogens. Recent studies suggest that bacteria including spirochetes have the potential to initiate cascade of events, leading to inflammatory condition of the central nervous system. Bacteria and spirochetes are activators of proinflammatory cytokines, generate free radicals, nitric oxide and further induction of apoptosis. Infection with these microbes may be considered as a risk factor for pathophysiology of AD or to cognitive changes. Recent studies have revealed that exposure to these microorganisms induces Aβ accumulation and tau protein phosphorylation, and chronic infections with these pathogenic bacteria can possibly contribute to progression of AD. In this article, we update and review the role of bacteria in the pathogenesis of AD resulting from initiation of cascade events in chronic inflammations and amyloidogenesis. Controlling these chronic infections with antibacterial or anti-inflammatory drugs will allow preventing inflammation, a risk factor for AD.