APP and Alzheimer disease: Therefore, as confirmed by the current results, Se-Met treatment reduced the expression of Aβ oligomers and Aβ deposition in the Gl, Epl, Ipl, MT, and Grl layers of the OB in 3× Tg-AD mice, which was exerted through the inhibition of the production of Aβ by downregulating the level of APP and BACE1.