Inhibition of Alzheimer's β-Amyloid Induced Vasoactivity and Proinflammatory Response in Microglia by a cGMP-Dependent Mechanism

β-amyloid (Aβ) peptides are the major protein components of senile plaques in Alzheimer's disease (AD) brains. Vascular damage and reactive gliosis are found colocalized with amyloid deposits in AD brains, suggesting that the vasculature may be a clinically significant site of AD pathology. Our results show that freshly solubilized Aβ1–40enhances the vasoconstriction induced by endothelin-1 (ET-1) and increases resistance to relaxation triggered by nitric oxide (NO), suggesting that Aβ may oppose the NO/cGMP pathway. Using specific inhibitors and activators of the NO/cGMP pathway, we show that Aβ vasoactivity is not due to a modulation of nitric oxide synthase (NOS) or soluble guanylyl cyclase (sGC). However, we find that a selective cGMP phosphodiesterase (cGMP-PDE) inhibitor (dipyridamole) is able to interactively block the enhanced vasoconstriction as well as the opposition to relaxation induced by Aβ, suggesting that Aβ could effect the activity of this enzyme. Cyclic GMP levels, but not cAMP concentrations, are reduced after Aβ treatment of rat aortic rings, further substantiating this hypothesis. Moreover, in examination of this pathway in another cell type pertinent to AD, we find that Aβ induces a proinflammatory response in microglia as evidenced by increased leukotriene B4 release. We show that both dipyridamole and compounds which increase cGMP levels prevent Aβ-induced microglial inflammation. Our results suggest that therapeutic intervention aimed at reduction of microglial-mediated inflammation via inhibition of cGMP-PDE or elevation of cGMP may be beneficial in the treatment of AD.