APP and Alzheimer disease: GLP-1 crosses BBB to exert neuroprotective benefits through decreasing the levels of APP and glycogen synthase kinase- 3β (GSK-3β), reducing Aβ deposition and tau phosphorylation, which are hallmarks of AD, as well as increasing insulin secretion and insulin receptor sensitivity and restoring insulin signaling pathway (Siddiqui et al., 2021).