Protective effect of the phosphodiesterase III inhibitor cilostazol on amyloid β-induced cognitive deficits associated with decreased amyloid β accumulation

Alzheimer's disease (AD), which is characterized by progressive cognitive impairment, is the most common neurodegenerative disease. Here, we investigated the preventive effect of a phosphodiesterase III inhibitor, cilostazol against cognitive decline in AD mouse model. In vitro studies using N2a cells stably expressing human amyloid precursor protein Swedish mutation (N2aSwe) showed that cilostazol decreased the amyloid β (Aβ) levels in the conditioned medium and cell lysates. Cilostazol attenuated the expression of ApoE, which is responsible for Aβ aggregation, in N2aSwe. Intracerebroventricular injection of Aβ_25-35 in C57BL/6J mice resulted in increased immunoreactivity of Aβ and p-Tau, and microglia activation in the brain. Oral administration of cilostazol for 2weeks before Aβ administration and once a day for 4weeks post-surgery almost completely prevented the Aβ-induced increases of Aβ and p-Tau immunoreactivity, as well as CD11b immunoreactivity. However, post-treatment with cilostazol 4weeks after Aβ administration, when Aβ was already accumulated, did not prevent the Aβ-induced neuropathological responses. Furthermore, cilostazol did not affect the neprilysin and insulin degrading enzymes involved in the degradation of the Aβ peptide, but decreased ApoE levels in Aβ-injected brain. In addition, cilostazol significantly improved spatial learning and memory in Aβ-injected mice. The findings suggest that a phosphodiesterase III inhibitor, cilostazol significantly decreased Aβ accumulation and improved memory impairment induced by Aβ_25-35. The beneficial effects of cilostazol might be explained by the reduction of Aβ accumulation and tau phosphorylation, not through an increase in Aβ degradation but via a significant decrease in ApoE-mediated Aβ aggregation. Cilostazol may be the basis of a novel strategy for the therapy of AD.