Transfer of Copper from an Amyloid to a Natural Copper-Carrier Peptide with a Specific Mediating Ligand

Proteomics Evidence of the Role of TDMQ20 in the Cholinergic System and Synaptic Transmission in a Mouse Model of Alzheimer's Disease

The interaction between copper ions and amyloid peptide Aβ has been reported to be involved in Alzheimer's disease (AD) pathology. Based on copper coordination biochemistry, we designed specific copper chelators [tetradentate monoquinolines (TDMQs)] in order to regulate copper homeostasis in the AD brain and inhibit the deleterious oxidative stress catalyzed by copper-Aβ complexes. We previously reported that TDMQ20, a highly selective copper chelator selected as a drug candidate, was able to extract copper from the Cu-Aβ_1-16 complex and restore cognitive and behavioral deficits in AD mouse models. For a better understanding of the mechanism of action of TDMQ20, we decided to investigate the change of profile of proteins expressed in 5xFAD mice after an oral treatment of TDMQ20 (dose = 10 mg/kg, once every two days for 3 months, in total 45 times). Clioquinol (CQ), a non-specific chelator, has been used as a comparator. Here, we report the proteomic alterations in the cortex of 5xFAD mice using iTRAQ (isobaric tags for relative and absolute quantification) proteomics technology. The results indicated that 178 differentially expressed proteins (DEPs) have been identified in the AD mouse group with respect to wild type (WT) animals (AD/WT). After treatment by TDMQ20, 35 DEPs were found common in AD/WT and TDMQ20/AD groups in an opposite change manner (up- or down-regulated, respectively). In addition, among the 35 DEPs mentioned above, 10 common target proteins have been identified in AD/WT, TDMQ20/AD, and CQ/AD groups, among which 3 target proteins were successfully validated by western blot analysis. In particular, the expression levels of ChAT and CHRM4 are significantly increased upon TDMQ20 treatment with respect to 5xFAD mice, while CQ did not significantly change the expression of these proteins. Our study suggests the involvement of the copper chelator TDMQ20 on the cholinergic system, a feature that may explain the improved cognitive and behavioral performance in AD mice upon oral treatment of TDMQ20.

Effect of metal ions on Alzheimer's disease

Alzheimer's disease (AD) is a degenerative disease of the nervous system. The typical pathological changes of AD are Aβ deposition, neurofibrillary tangles, neuron loss, and chronic inflammation. The balance of metal ions is essential for numerous physiological functions, especially in the central nervous system. More studies showed that metal ions participate in the development of AD. However, the involvement of metal ions in AD is controversial. Thus, we reviewed articles about the relationship between metal ions and AD and discussed some contradictory reports in order to better understand the role of metal ions in AD.

TDMQ20, a Specific Copper Chelator, Reduces Memory Impairments in Alzheimer's Disease Mouse Models

Besides targeting amyloid or tau metabolisms, regulation of redox metal ions is a recognized therapeutic target for Alzheimer's disease (AD). Based on the bioinorganic chemistry of copper, we designed specific chelators of copper(II) (TDMQs) insight to regulate copper homeostasis in the brain and to inhibit the deleterious oxidative stress catalyzed by copper-amyloid complexes. An oral treatment by TDMQ20 was able to fully reverse the cognitive and behavioral impairment in three different murine models, two nontransgenic models mimicking the early stage of AD and a transgenic model representing a more advanced stage of AD. To our knowledge, such a comparative study using the same molecule has never been performed. Regular C57BL/6 mice received a single injection of human Cu-Aβ_1-42 in the lateral ventricles (icv-CuAβ) or in the hippocampus (hippo-CuAβ). In both cases, mice developed a cognitive impairment similar to that of transgenic 5XFAD mice. Oral administration of TDMQ20 to icv-CuAβ or hippo-CuAβ mice within a 16-day period resulted in a significant improvement of the cognitive status. The 3-month treatment of transgenic 5XFAD mice with TDMQ20 also resulted in behavioral improvements. The consistent positive pharmacological results obtained using these different AD models correlate well with previously obtained physicochemical data of TDMQ20. The short-term novel object recognition (NOR) test was found particularly relevant to evaluate the rescue of declarative memory impairment. TDMQ20 was also able to reduce the oxidative stress in the mouse cortex. Due to its reliability and facile use, the hippo-CuAβ model can be considered as a robust nontransgenic model to evaluate the activity of potential drugs on the early stages of memory deficits.

Binding of Cu2+ to Aβ1-29 causes aggregation and toxicity in SH-SY5Y cells

The accumulation and aggregation of amyloid-β (Aβ) are critical factors in the pathogenesis of Alzheimer's disease (AD). Several studies have indicated that metal ions such as Cu²⁺and Zn²⁺ play a key role in the formation and stabilization of neurotoxic Aβ aggregates, however the molecular mechanisms underlying Aβ cytotoxicity have not yet been fully elucidated. Previously, we showed that the Aβ-derived fragment peptide (Aβ-FrP), Aβ1-19, altered conformation in the presence of Cu²⁺, inhibiting its digestion by metalloproteinase-7 (MMP-7). In this study we demonstrated that Aβ1-19 did not form aggregates in the presence of Cu²⁺. Therefore, we synthesized a new Aβ-FrP, Aβ1-29, which displayed Cu²⁺-dependent conformational conversion and aggregate formation. Aβ1-29 was cleaved by MMP-7, however this reaction was inhibited in the presence of Cu²⁺ in a similar way to Aβ1-19. Interestingly, Aβ1-29 showed conformational conversion and aggregate formation in the presence of Zn²⁺, however this did not confer resistance against MMP-7 cleavage. Moreover, Aβ1-29 induced the apoptotic cell death of neural SH-SY5Y cells in the presence of Cu²⁺ but not Zn²⁺. These results suggest that Cu²⁺, unlike Zn²⁺, may play an important role in the aggregation mechanism of Aβ and thus in the pathology of AD.

Critical evaluation of current Alzheimer's drug discovery (2018-19) & futuristic Alzheimer drug model approach

Alzheimer's disease (AD), a neurodegenerative disease responsible for death of millions of people worldwide is a progressive clinical disorder which causes neurons to degenerate and ultimately die. It is one of the common causes of dementia wherein a person's incapability to independently think, behave and decline in social skills can be quoted as major symptoms. However the early signs include the simple non-clinical symptoms such as forgetting recent events and conversations. Onset of these symptoms leads to worsened conditions wherein the AD patient suffers severe memory impairment and eventually becomes unable to work out everyday tasks. Even though there is no complete cure for AD, rigorous research has been going on to reduce the progress of AD. Currently, a very few clinical drugs are prevailing for AD treatment. So this is the need of hour to design, develop and discovery of novel anti-AD drugs. The main factors for the cause of AD according to scientific research reveals structural changes in brain proteins such as beta amyloid, tau proteins into plaques and tangles respectively. The abnormal proteins distort the neurons. Despite the high potencies of the synthesized molecules; they could not get on the clinical tests up to human usage. In this review article, the recent research carried out with respect to inhibition of AChE, BuChE, NO, BACE1, MAOs, Aβ, H3R, DAPK, CSF1R, 5-HT4R, PDE, σ₁R and GSK-3β is compiled and organized. The summary is focused mainly on cholinesterases, Aβ, BACE1 and MAOs classes of potential inhibitors. The review also covers structure activity relationship of most potent compounds of each class of inhibitors alongside redesign and remodeling of the most significant inhibitors in order to expect cutting edge inhibitory properties towards AD. Alongside the molecular docking studies of the some final compounds are discussed.

Metal Ions in Alzheimer's Disease: A Key Role or Not?

Despite tremendous research efforts in universities and pharmaceutical companies, effective drugs are still lacking for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease have not yet been clearly understood. Besides a small percentage of cases with early onset disease having a genetic origin (<5%, familial AD), most cases develop in the elderly as a sporadic form due to multiple and complex parameters of aging. Consequently, AD is spreading in all countries with a long life expectancy. AD is characterized by deposition of senile plaques made of β-amyloid proteins (Aβ) and by hyperphosphorylation of tau proteins, which have been considered as the main drug targets up to now. However, antibodies targeting amyloid aggregates, as well as enzyme inhibitors aiming to modify the amyloid precursor protein processing, have failed to improve cognition in clinical trials. Thus, to set up effective drugs, it is urgent to enlarge the panel of drug targets. Evidence of the link between AD and redox metal dysregulation has also been supported by post-mortem analyses of amyloid plaques, which revealed accumulation of copper, iron, and zinc by 5.7, 2.8, and 3.1 times, respectively, the levels observed in normal brains. Copper-amyloid complexes, in the presence of endogenous reductants, are able to catalyze the reduction of dioxygen and to produce reduced, reactive oxygen species (ROS), leading to neuron death. The possibility of using metal chelators to regenerate normal trafficking of metal ions has been considered as a promising strategy in order to reduce the redox stress lethal for neurons. However, most attempts to use metal chelators as therapeutic agents have been limited to existing molecules available from the shelves. Very few chelators have resulted from a rational design aiming to create drugs with a safety profile and able to cross the blood-brain barrier after an oral administration. In the human body, metals are handled by a sophisticated protein network to strictly control their transport and reactivity. Abnormal concentrations of certain metals may lead to pathological events due to misaccumulation and irregular reactivity. Consequently, therapeutic attempts to restore metal homeostasis should carefully take into account the coordination chemistry specificities of the concerned redox-active metal ions. This Account is focused on the role of the main biologically redox-active transition metals, iron and copper. For iron, the recent debate on the possible role of magnetite in AD pathogenesis is presented. The section devoted to copper is focused on the design of specific copper chelators as drug candidates able to regulate copper homeostasis and to reduce the oxidative damage responsible for the neuron death observed in AD brains. A short survey on non-redox-active metal ions is also included at the beginning, such as aluminum and its controversial role in AD and zinc which is a key metal ion in the brain.

A multifunctional bis-(-)-nor-meptazinol-oxalamide hybrid with metal-chelating property ameliorates Cu(II)-induced spatial learning and memory deficits via preventing neuroinflammation and oxido-nitrosative stress in mice

Excess copper exposure is a risk factor of neurodegeneration related to Alzheimer's disease (AD). Evidence indicates that, besides promoting amyloid β aggregation, activation of neuroinflammation and oxido-nitrosative stress (two key pathophysiological processes of AD) may also play important roles in Cu(II)-induced neuronal injury. Therefore, the copper-chelating strategy has gained attention in search for new anti-AD drugs. We previously reported a novel multifunctional compound N¹,N²-bis(3-(S)-meptazinol-propyl) oxalamide (ZLA), a bis-(-)-nor-meptazinol-oxalamide hybrid with properties of dual binding site acetylcholinesterase (AChE) inhibition and Cu(II)/Zn(II) chelation. The present study was aimed to explore its effect on cognitive deficits caused by intrahippocampal injection of Cu(II) in mice. Results showed that ZLA (2, 5 mg/kg; i.p.) treatment significantly ameliorated the Cu(II)-induced impairment of hippocampus-dependent learning and memory, whereas rivastigmine, an AChE inhibitor showing a similar potency of enzyme inhibition to ZLA, had no obvious effect. Immunohistochemical and Western blot analyses revealed that ZLA attenuated the decrease in hippocampal expression of microtubule-associated protein 2 (MAP2, a dendritic marker) in Cu(II)-challenged mice. Further analysis showed that ZLA suppressed the Cu(II)-evoked microglial activation. Moreover, it inhibited the Cu(II)-evoked production of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β and expression of inducible nitric oxide synthase in the hippocampus. The Cu(II)-induced oxidative and nitrosative stress in the hippocampus was also attenuated after ZLA treatment. Collectively, these results suggest that ZLA ameliorates the Cu(II)-caused cognitive deficits. Inhibition of neuroinflammation and oxido-nitrosative stress, and thus ameliorating neuronal injury, may be the potential mechanism for the anti-amnesic effect of ZLA.

N4 -Tetradentate Chelators Efficiently Regulate Copper Homeostasis and Prevent ROS Production Induced by Copper-Amyloid-β1-16

The disruption of copper homeostasis and the oxidative stress induced by Cu-amyloids are crucial features of Alzheimer's disease pathology. The copper specific N₄ -tetradendate ligands TDMQ20 and 1 are able to fully inhibit in vitro the aerobic oxidation of ascorbate induced by Cu-Aβ_1-16 , even in the presence of 100 molar equivalents of Zn^II with respect to Cu^II , whereas other ligands with N₂ O₂ or N₃ O₂ coordination spheres failed to do so. This essential result indicates that, in addition to metal selectivity, the coordination sphere of copper chelators should exhibit a N₄ -tetradendate motif to be able to reduce an oxidative stress in the zinc-rich physiological environment of brain. The N₄ -scaffolds of these two aminoquinoline-based ligands, TDMQ20 or 1, suitable for a square-planar coordination of copper(II), allowed them to enhance both the selectivity for copper and the ability to reduce the oxidative stress induced by copper-amyloid in a zinc-rich environment.

Developing drugs targeting transition metal homeostasis

Metal dyshomeostasis is involved in the pathogenesis and progression of diseases including cancer and neurodegenerative diseases. Metal chelators and ionophores are well known modulators of transition metal homeostasis, and a number of these molecules are in clinical trials. Metal-binding compounds are not the only drugs capable of targeting transition metal homeostasis. This review presents recent highlights in the development of chelators and ionophores for the treatment of cancer and neurodegenerative disease. Moreover, we discuss the development of small molecules that alter copper and iron homeostasis by inhibiting metal transport proteins. Finally, we consider the emergence of metal regulatory factor 1 as a drug target in diseases where it mediates zinc-induced signalling cascades leading to pathogenesis.