In line with this, intranasal insulin administration in AD patients slows down cognitive decline [59,96], and insulin-sensitizing antidiabetic medications such as metformin and PPAR-γ agonists (peroxisome proliferator-activated receptors) [10], as well as other treatments such as GLP-1 (glucagon-like peptide-1) analogues and DPP4 (dipeptidyl peptidase 4) inhibitors [126,146], prevent neurodegeneration in T2D models. Here, DPP4 is linked to type 2 diabetes mellitus.