A coumarin-based multifunctional chemosensor for Cu2+/Al3+ as an AD theranostic agent: Synthesis, X-ray single crystal analysis and activity study

The pathogenesis of Alzheimer's disease (AD) is complex. So far there is no effective drug to treat the disease. The pathological changes of AD began 30 years before symptoms, so early diagnosis is considered to be important for AD treatment. Integrating diagnosis and therapy into a single regent has provided a new opportunity for AD treatment. Given that metal dyshomeostasis is thought to be one of the key factors to cause AD, a Schiff base substituted coumarin (probe 1) has been designed and synthesized as a selective metal chelator for multi-factor anti-AD in this work. The results of metal ions recognition showed that probe 1 had high selective fluorescent turn-on response to Al3+ and fluorescent turn-off response to Cu2+, due to intramolecular charge transfer (ICT) mechanism. Meanwhile, the results of both in vitro and in vivo bioactivities evaluation including metal chelation, reactive oxide species (ROS) elimination, self-/Cu2+-induced Aβ aggregation showed that 1 and 1-Cu(II) complex had excellent synergistic anti-AD activities. In addition, 1 had low cytotoxicity and was predicted to cross the blood-brain barrier (BBB). Noticeably, X-ray single crystal diffraction of 1-Cu(II) provided molecular level information to explain the structure and theranostic activity relationship. To sum up, 1 may be a promising candidate for the development of AD theranostic agent.

Antiradical and Antioxidant Activity of Compounds Containing 1,3-Dicarbonyl Moiety: An Overview

Free radicals and oxidants may cause various damages both to the lifeworld and different products. A typical solution for the prophylaxis of oxidation-caused conditions is the usage of various antioxidants. Among them, various classes are found-polyphenols, conjugated polyalkenes, and some sulfur and nitrogen derivatives. Regarding the active site in the molecules, a widely discussed group of compounds are 1,3-dicarbonyl compounds. Among them are natural (e.g., curcumin and pulvinic acids) and synthetic (e.g., 4-hydroxy coumarins, substituted Meldrum's acids) compounds. Herein, information about various compounds containing the 1,3-dicarbonyl moiety is covered, and their antiradical and antioxidant activity, depending on the structure, is discussed.

Discovery of Novel Coumarin-Schiff Base Hybrids as Potential Acetylcholinesterase Inhibitors: Design, Synthesis, Enzyme Inhibition, and Computational Studies

To discover anti-acetylcholinesterase agents for the treatment of Alzheimer's disease (AD), a series of novel Schiff base-coumarin hybrids was rationally designed, synthesized successfully, and structurally characterized using Fourier transform infrared (FTIR), Nuclear magnetic resonance (NMR), and High-Resolution Mass Spectrometry (HRMS) analyses. These hybrids were evaluated for their potential inhibitory effect on acetylcholinesterase (AChE). All of them exhibited excellent inhibitory activity against AChE. The IC₅₀ values ranged from 87.84 to 515.59 μg/mL; hybrids 13c and 13d with IC₅₀ values of 0.232 ± 0.011 and 0.190 ± 0.004 µM, respectively, showed the most potent activity as acetylcholinesterase inhibitors (AChEIs). The reference drug, Galantamine, yielded an IC₅₀ of 1.142 ± 0.027 µM. Reactivity descriptors, including chemical potential (μ), chemical hardness (η), electrophilicity (ω), condensed Fukui function, and dual descriptors are calculated at wB97XD/6-311++ G (d,p) to identify reactivity changes of the designed compounds. An in-depth investigation of the natural charge pattern of the studied compounds led to a deep understanding of the important interaction centers between these compounds and the biological receptors of AChE. The molecular electrostatic surface potential (MESP) of the most active site in these derivatives was determined using high-quality information and visualization. Molecular docking analysis was performed to predict binding sites and binding energies. The structure-activity-property relationship studies indicated that the proposed compounds exhibit good oral bioavailability properties. To explore the stability and dynamic behavior of the ligand-receptor complexes, molecular dynamics simulations (MDS) were performed for 100 ns on the two best docked derivatives, 13c and 13d, with the AChE (4EY7) receptor. A popular method for determining the free binding energies (MM/GBSA) is performed using snapshots taken from the systems' trajectories at 100 ns. These results revealed that the complex system of compound 13d acquired a relatively more stable conformation and exhibited better descriptors than the complex system of compound 13c and the Galantamine drug, suggesting its potential as an effective inhibiting drug. The binding free energy analysis revealed that the 13d-4EY7 complex exhibited greater stability with AChE receptors compared to other complexes.

Challenges and Opportunities of Metal Chelation Therapy in Trace Metals Overload-Induced Alzheimer's Disease

Essential trace metals like zinc (Zn), iron (Fe), and copper (Cu) play an important physiological role in the metabolomics and healthy functioning of body organs, including the brain. However, abnormal accumulation of trace metals in the brain and dyshomeostasis in the different regions of the brain have emerged as contributing factors in neuronal degeneration, Aβ aggregation, and Tau formation. The link between these essential trace metal ions and the risk of AD has been widely studied, although the conclusions have been ambiguous. Despite the absence of evidence for any clinical benefit, therapeutic chelation is still hypothesized to be a therapeutic option for AD. Furthermore, the parameters like bioavailability, ability to cross the BBB, and chelation specificity must be taken into consideration while selecting a suitable chelation therapy. The data in this review summarizes that the primary intervention in AD is brain metal homeostasis along with brain metal scavenging. This review evaluates the impact of different trace metals (Cu, Zn, Fe) on normal brain functioning and their association with neurodegeneration in AD. Also, it investigates the therapeutic potential of metal chelators in the management of AD. An extensive literature search was carried out on the "Web of Science, PubMed, Science Direct, and Google Scholar" to investigate the effect of trace elements in neurological impairment and the role of metal chelators in AD. In addition, the current review highlights the advantages and limitations of chelation therapies and the difficulties involved in developing selective metal chelation therapy in AD patients.

A rapid responsive coumarin-naphthalene derivative for the detection of cyanide ions in cell culture

Cyanide ion (CN^-) is widely used in many industrial processes; however, it causes several diseases in humans. Therefore, rapid and accurate detection of CN^- is very important and urgent. In this study, a CN^- sensor (MH-2) which was capable of detecting CN^- ions in living cell was developed. MH-2 gives a rapid color change, absorbance and fluorescence response to CN^- in the presence of the anions tested in the working system. The binding ratio between the sensor and CN^- was demonstrated by some spectrophotometric methods and the sensing mechanism was investigated by NMR titration experiments, suggesting that MH-2 gives response to CN^- via the nucleophilic addition reaction. The fluorescence detection limit and the absorbance detection limit were calculated as 0.056 μM and 0.11 μM, respectively. Both of these detection limits are below the tolerable limit recommended by WHO for CN^- in the drinking water (1.9 μM). MH-2 was also applied to living cells for bio-imaging and the results showed that the sensor penetrates the cells and can detect cyanide ions in living cells.

Synthesis, physicochemical characterization and neuroprotective evaluation of novel 1-hydroxypyrazin-2(1H)-one iron chelators in an in vitro cell model of Parkinson's disease

Iron dysregulation, dopamine depletion, cellular oxidative stress and α-synuclein protein mis-folding are key neuronal pathological features seen in the progression of Parkinson's disease. Iron chelators endowed with one or more therapeutic modes of action have long been suggested as disease modifying therapies for its treatment. In this study, novel 1-hydroxypyrazin-2(1H)-one iron chelators were synthesized and their physicochemical properties, iron chelation abilities, antioxidant capacities and neuroprotective effects in a cell culture model of Parkinson's disease were evaluated. Physicochemical properties (log β, log D7.4, pL0.5) suggest that these ligands have a poorer ability to penetrate cell membranes and form weaker iron complexes than the closely related 1-hydroxypyridin-2(1H)-ones. Despite this, we show that levels of neuroprotection provided by these ligands against the catecholaminergic neurotoxin 6-hydroxydopamine in vitro were comparable to those seen previously with the 1-hydroxypyridin-2(1H)-ones and the clinically used iron chelator Deferiprone, with two of the ligands restoring cell viability to ≥89% compared to controls. Two of the ligands were endowed with additional phenol moieties in an attempt to derive multifunctional chelators with dual iron chelation/antioxidant activity. However, levels of neuroprotection with these ligands were no greater than ligands lacking this moiety, suggesting the neuroprotective properties of these ligands are due primarily to chelation and passivation of intracellular labile iron, preventing the generation of free radicals and reactive oxygen species that otherwise lead to the neuronal cell death seen in Parkinson's disease.

Biphenylpiperazine Based MAO Inhibitors: Synthesis, Biological Evaluation, Reversibility and Molecular Modeling Studies

In this study, 21 new 1,4-biphenylpiperazine derivatives were designed, synthesized and evaluated as monoamine oxidase (MAO) inhibitors by in vitro fluorometric method. All these compounds exhibited inhibitory activity against hMAO enzymes, 17 analogues of them showed selectivity towards hMAO-B over hMAO-A enzyme. Compound 20 exhibited the best activity and selectivity towards hMAO-B with IC₅₀ value of 53 nM and selectivity index of 1122 folds over MAO-A, compared to the reference drugs rasagiline (IC₅₀ = 66 nM) and selegiline (IC₅₀ = 40 nM). Kinetic study and reversibility test of the most potent compound (20) revealed that it is reversible and mixed competitive inhibitor (K_i value is 17 nM for the inhibition of hMAO-B). Compound 20 was evaluated against normal NIH/3T3 mouse embryonic fibroblast cell lines and it was found that it is non-cytotoxic at its effective concentration against hMAO-B. Moreover, compound 20 and the most potent compounds have acceptable ADME properties and good pharmacokinetics profiles. Molecular docking simulations were performed for explanation and elucidation for the biological activity of compounds 19 and 20. Accordingly, 1,4- biphenylpiperazine derivatives can be considered as a promising lead to produce more potent and safer MAO inhibitors for management of various neurological disorders.

Hibiscus sabdariffa L.: A potent natural neuroprotective agent for the prevention of streptozotocin-induced Alzheimer's disease in mice

Hibiscus sabdariffa L. (Malvaceae) is one of the well-known traditionally used remedy worldwide. It exhibited numerous pharmacological properties including antioxidant, antidepressant, sedative, anti-inflammatory, antiproliferative, antimicrobial and neuroprotective activities. The aim of this study is to highlight the mechanisms underlying the neuroprotective effects of anthocyanin-enriched extracts of two Hibiscus varieties (white and red calyces) in the management of Alzheimer's disease (AD) in addition to their metabolic profiling. The anthocyanin contents were determined quantitatively using the pH-differential technique and qualitatively by LC/MS/MS. The extracts were tested in vitro for their antioxidant potential as well as acetylcholinesterase inhibition activity and both showed promising activities. The LC/MS/MS analysis allowed the tentative identification of 26 and 24 metabolites in red and white calyces, respectively, represented by anthocyanins, flavonoids, aliphatic and phenolic acids. In vivo, streptozotocin induced AD in mice model was established and Hibiscus extracts were tested at a dose of 200 mg kg^-1 compared to celecoxib (30 mg/kg). Histopathology of cerebral cortex and hippocampus, immunohistochemistry for tau- protein and caspase-3 with behavioral tests and measurement of several biochemical parameters were done. Hibiscus prevented memory impairment, and this could be attributed to the amelioration of STZ-induced neuroinflammation and amyloidogenesis. Consequently, Hibiscus represents a promising safe agent that can be repurposed for AD through exerting anti-inflammatory, anti-acetylcholinesterase, antioxidant, and anti-amyloidogenic activities.

Synthesis and pharmacological evaluation of novel chromone derivatives as balanced multifunctional agents against Alzheimer's disease

In a continuing effort to develop multitargeted compounds as potential treatment agents against Alzheimer's disease (AD), a series of chromone derivatives were designed, synthesized and evaluated. In vitro assay indicated that most of the target compounds have both MAOs inhibition activities, antioxidant activity and biometal chelating ability. Especially, compound s19 exhibits good inhibitory potency for inhibition of MAOs (IC₅₀ value of 5.12μM for hMAO-A and 0.816μM for hMAO-B), moderate inhibition of Aβ aggregation (75.1% at 20μM), metal chelation, control of ROS generation and antioxidant activity (ORAC=3.62). In addition, s19 could reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Taken together, these results suggested that s19 might be a promising multitargeted compound for AD treatment.

Development of multifunctional heterocyclic Schiff base as a potential metal chelator: a comprehensive spectroscopic approach towards drug discovery

Amyloid-β peptides and their metal-associated aggregated states have been implicated in the pathogenesis of Alzheimer's disease. The present paper epitomises the design and synthesis of a small, neutral, lipophilic benzothiazole Schiff base (E)-2-((6-chlorobenzo[d]thiazol-2-ylimino)methyl)-5-diethylamino)phenol (CBMDP), and explores its multifunctionalty as a potential metal chelator/fluorophore using UV-visible absorption, steady-state fluorescence, single molecule fluorescence correlation spectroscopic (FCS) techniques which is further corroborated by in silico studies. Some pharmaceutically relevant properties of the synthesized compound have also been calculated theoretically. Steady-state fluorescence and single molecule FCS reveal that the synthesized CBMDP not only recognizes oligomeric Aβ40, but could also be used as an amyloid-specific extrinsic fluorophore as it shows tremendous increase in its emission intensity in the presence of Aβ40. Molecular docking exercise and MD simulation reveal that CBMDP localizes itself in the crucial amyloidogenic and copper-binding region of Aβ40 and undergoes a strong binding interaction via H-bonding and π-π stacking. It stabilizes the solitary α-helical Aβ40 monomer by retaining the initial conformation of the Aβ central helix and mostly interacts with the hydrophilic N-terminus and the α-helical region spanning from Ala-2 to Val-24. CBMDP exhibits strong copper as well as zinc chelation ability and retards the rapid copper-induced aggregation of amyloid peptide. In addition, CBMDP shows radical scavenging activity which enriches its functionality. Overall, the consolidated in vitro and in silico results obtained for the synthesized molecule could provide a rational template for developing new multifunctional agents.