APP and Alzheimer disease: In previous studies with choroid plexus homogenates with different cases with AD in the different stages (I/0, III-IV, and V-VI), we demonstrated that in AD patients, amyloid-beta peptide also accumulates in choroid plexus [15], there is an oxidation of carboxymethyl-lysine (CML), and N-carboxyethyl-lysine (CEL) may result in impaired protein interactions, protein folding, and protein kinase activity; abnormal function of endothelial and vascular smooth muscle cells; impaired HDL-cholesterol metabolism in the choroid plexus in advanced stages of AD [16].