Ionophoric polyphenols are permeable to the blood–brain barrier, interact with human serum albumin and Calf Thymus DNA, and inhibit AChE enzymatic activity

Abstract

Alzheimer’s disease (AD) is the most common form of dementia that affects more than 40 million people around the world. The incidence is expected to rapidly increase due to the lack of any effective treatment. In previous work we synthesized a family of five ionophoric polyphenols (compounds 1–5) that targeted important aspects related to AD, such as the toxic aggregation of amyloid-β peptides, the production of reactive oxygen species, or the excessive presence of Cu2+ ions. Here, in order to gain insights into their potential therapeutic value, we have tested the ability of compounds 1–5 to cross the blood–brain barrier (BBB), to interact with human serum albumin (HSA) and Calf Thymus (ct) DNA, and to inhibit acetylcholinesterase (AChE). We performed BBB permeability and efflux mechanisms studies by means of the in vitro parallel artificial membrane permeability assay (PAMPA-BBB) and several in silico methods, while fluorescence, UV–visible, and circular dichroism spectroscopies were used to determine their ability to interact with HSA and ctDNA. Our results show that all five ionophoric polyphenols can effectively cross the BBB, and can form adducts with both HSA and ctDNA through one binding site and with association constants ranging from 104 to 106 M−1, while still maintaining levels of unbound drug to protein within therapeutic range. Docking and molecular dynamics simulations show that the ionophoric polyphenols preferably bind the hydrophobic cavities of the subdomain IIA of HSA, as many other pharmaceuticals do, with predicted affinities that correlate well with experimental results obtained by spectroscopic techniques. In addition, structurally related compounds 1, 2, and 4 were found to be moderate in vitro AChE inhibitors by interacting with several residues of the active site of the enzyme, as revealed by docking and molecular dynamics simulations. Overall, our results suggest that HSA could be an efficient transport mechanism of the compounds in the bloodstream until reaching the brain, where they could effectively cross the BBB and exert their anti-AD activity, including AChE inhibition. DNA interactions similar to natural resveratrol could in part explain the previously reported nontoxic behavior of the compounds.