Neuroprotective effects of linarin through activation of the PI3K/Akt pathway in amyloid-β-induced neuronal cell death

Linarin, a natural occurring flavanol glycoside derived from Mentha arvensis and Buddleja davidii is known to have anti-acetylcholinesterase effects. The present study intended to explore the neuroprotective effects of linarin against A beta(25-35)-induced neurotoxicity with cultured rat pheochromocytoma cells (PC12 cells) and the possible mechanisms involved. For this purpose, PC12 cells were cultured and exposed to 30 mu M A beta(25-35) in the absence or presence of linarin (0.1, 1.0 and 10 mu M). In addition, the potential contribution of the PI3K/Akt neuroprotective pathway in linarin-mediated protection against A beta(25-35)-induced neurotoxicity was also investigated. The results showed that linarin dose-dependently increased cell viability and reduced the number of apoptotic cells as measured by MTT assay, Annexin-V/PI staining, JC-1 staining and caspase-3 activity assay. Linarin could also inhibit acetylcholinesterase activity induced by A beta(25-35) in PC12 cells. Further study revealed that linarin induced the phosphorylation of Akt dose-dependently. Treatment of PC12 cells with the PI3K inhibitor LY294002 attenuated the protective effects of linarin. Furthermore, linarin also stimulated phosphorylation of glycogen synthase kinase-3 beta (GSK-3 beta), a downstream target of PI3K/Akt. Moreover, the expression of the anti-apoptotic protein Bcl-2 was also increased by linarin treatment. These results suggest that linarin prevents A beta(25-35)-induced neurotoxicity through the activation of PI3K/Akt, which subsequently inhibits GSK-3b and up-regulates Bcl-2. These findings raise the possibility that linarin may be a potent therapeutic compound against Alzheimer's disease acting through both acetylcholinesterase inhibition and neuroprotection. (C) 2011 Elsevier Ltd. All rights reserved.