Design of small molecules that target metal-Aβ species and regulate metal-induced Aβ aggregation and neurotoxicity

Abstract

The accumulation of metal ions and amyloid-β (Aβ) aggregates found in the brain of patients with Alzheimer's disease (AD) has been suggested to be involved in AD pathogenesis. To investigate metal-Aβ-associated pathways in AD, development of chemical tools to target metal-Aβ species is desired. Only a few efforts, however, have been reported. Here, we report bifunctional small molecules, N-(pyridin-2-ylmethyl)aniline (L2-a) and N 1 ,N 1 -dimethyl-N 4 -(pyridin-2-ylmethyl)benzene-1,4-diamine (L2-b) that can interact with both metal ions and Aβ species, as determined by spectroscopic methods including high-resolution NMR spectroscopy. Using the bifunctional compound L2-b, metal-induced Aβ aggregation and neurotoxicity were modulated in vitro as well as in human neuroblastoma cells. Furthermore, treatment of human AD brain tissue homogenates containing metal ions and Aβ species with L2-b showed disassembly of Aβ aggregates. Therefore, our studies presented herein demonstrate the value of bifunctional compounds as chemical tools for investigating metal-Aβ-associated events and their mechanisms in the development and pathogenesis of AD and as potential therapeutics.amyloid-β peptide | copper | zinc | reactive oxygen species | rational structure-based design M ore than 24 million people worldwide have Alzheimer's disease (AD), a devastating and fatal form of dementia (1-3). The key pathological markers in AD are amyloid-β (Aβ) plaques and neurofibrillary tangles, the accumulation of which is accompanied by oxidative stress, inflammation, and neurodegeneration. The "amyloid hypothesis" in AD states that Aβ, generated via cleavage of the amyloid precursor protein (APP) by β-and γ-secretases, is a proximal causative agent (1-4). It is, however, still unclear which morphological Aβ species, from soluble small oligomers to large fibrils, are central to AD pathogenesis (1-5).In addition to Aβ aggregate deposits, dyshomeostasis and miscompartmentalization of metal ions such as Fe, Cu, and Zn ions clearly occur in AD brains (1-4, 6-10). Some studies suggest that highly concentrated metal ions play an important role in Aβ aggregate deposition and neurotoxicity including the formation of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) (1-4, 6-13). The role of metal ions in AD and molecular mechanisms of metal-Aβ-associated pathological pathways, however, are not fully understood. Using traditional metal chelating agents, potential regulation of metal-induced Aβ aggregation and neurotoxicity has been shown in vitro and in vivo (1-4, 6, 10, 13-17). Some compounds such as clioquinol (CQ) and an 8-hydroxyquinoline derivative (PBT2) have moved into clinical trials and showed improved cognition. Long-term use of CQ is, however, limited by an adverse side effect, subacute myelo-optic neuropathy (18). Although these traditional metal chelators have yet to be available as therapeutic agents, the studies using these compounds show the possible involvement of metal ions in AD pathogenesis.To elucidate the pathological ...

The use of multi-target drugs in the treatment of neurodegenerative diseases

“…Recently, Lim's group has developed compounds with structures that -based on known structure-activity relationship experience in MAO inhibition [44] -may possess MAO-inhibitory properties [45]. These compounds have emerged as bifunctional candidate small molecules that chelate Ab-associated metal species and regulate metal-induced Ab aggregation and oxidative stress-induced neurotoxicity.…”

“…Structurally similar to memantine (an uncompetitive NMDA receptor antagonist used clinically to treat AD), NGP1-01's favorably fast on-off binding kinetics should afford this compound an improved side-effect profile compared with powerfully binding NMDA antagonists such as MK-801 [55]. NGP1-01 was shown to also be an uncompetitive NMDA antagonist in murine whole-brain synaptoneurosomes [Geldenhuys WJ, Bloomquist JR, Van der Schyf CJ, Unpublished Data] and blocked NMDAmediated 45 Ca 2+ uptake with an IC 50 of 2.98 µM. This dual mechanism of modulating calcium entry into neuronal cells (via L-type calcium channels and the NMDA receptor) suggests that NGP1-01 may have utility as a neuroprotective agent in AD, stroke and other neurodegenerative diseases with cognitive decline [56].…”

Introduction of a Fluorescent Probe to Amyloid‐β to Reveal Kinetic Insights into Its Interactions with Copper(II)

“…L2-b is a bifunctional ligand designed to target both Ab and metal ions. [22] To quantify the relative efficiency, we introduce an efficacy index, defined as the reaction rate at 10 mm ligand concentration relative to that of EDTA. The efficacy index for CQ shows it more rapidly removes Cu 2+ from Ab ( Figure 4; Supporting Information and Table S2 therein).…”

Insights into antiamyloidogenic properties of the green tea extract (−)-epigallocatechin-3-gallate toward metal-associated amyloid-β species

“…The involvement of metal-Aβ species in AD pathogenesis, however, has not been clearly elucidated. To advance our understanding of the potential neurotoxicity of metal-Aβ species, efforts to develop chemical tools capable of interacting directly with metal-Aβ species and modulating their reactivity in vitro and in biological systems are under way (1,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). In particular, novel bifunctional compounds that contain elements for metal chelation and Aβ interaction have recently been prepared or identified via rational structure-based design strategies or systematic selection of natural products.…”