[Alzheimer's disease and Helicobacter pylori infection: a possible link?]

Alzheimer's disease (AD) is associated with Aß peptide and Tau protein deposits, but the initial process inducing the disease and ultimately neurodegeneration has not yet been elucidated. An infectious hypothesis is suggested by the alteration of the blood-brain barrier and the activation of neuroinflammation in the brain, which could play a role, especially in the decrease of Aß peptide clearance. Several viral or bacterial agents have been incriminated, including Helicobacter pylori. Infection by H. pylori is acquired during childhood and often lifetime persisting, inducing a chronic gastric inflammation, which remains asymptomatic in approximately 80% of cases. However H. pylori infection can induce systemic inflammation and increase homocysteine levels, contributing to worsen AD lesions. Association between H. pylori and AD is suggested by 1) epidemiologic studies, which show higher AD prevalence and more pronounced cognitive impairment in infected than in non-infected subjects; 2) experimental studies in murine models: a) in a first study we evaluated the impact of H. pylori infection on the brain of non-AD predisposed C57BL/6J mice. After an 18-month infection, H. pylori induced a significant gastric inflammation but no brain Aβ deposit nor increased neuroinflammation was observed in their brain; b) we currently study the impact of Helicobacter species infection on behavior and cerebral lesions of AD transgenic (APPswe/PS1dE9) mice and their wild type littermate. The results of these studies do not allow to conclude a significant association between AD and H. pylory infection but may contribute to a better understanding of the role of brain neuroinflammation in AD.