1,4-Substituted 4-(1H)-pyridylene-hydrazone-type inhibitors of AChE, BuChE, and amyloid-β aggregation crossing the blood–brain barrier

Barbiturate-sulfonate hybrids as potent cholinesterase inhibitors: design, synthesis and molecular modeling studies

Aim: Design and synthesis of a series of 5-benzylidene(thio)barbiturates 3a-r.Methodology: Evaluation of the inhibitory activity of the new chemical entities on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) using Donepezil as the standard reference.Results & Conclusion: Compound 3r emerged as the most potent AChE inhibitor (IC50 = 9.12 μM), while compound 3q exhibited the highest inhibitory activity against BChE (IC50 = 19.43 μM). Toxicological bioassays confirmed the absence of cytotoxicity for the most potent compounds at the tested doses. Molecular docking analysis demonstrated that the tested derivatives effectively bind to the active sites of both enzymes. Overall, this study sheds light on the potential of barbiturate-sulfonate conjugates as promising drug candidates.

Novel multifunctional tacrine-donepezil hybrids against Alzheimer's disease: Design synthesis and bioactivity studies

A series of tacrine-donepezil hybrids were synthesized as potential multifunctional anti-Alzheimer's disease (AD) compounds. For this purpose, tacrine and the benzylpiperidine moiety of donepezil were fused with a hydrazone group to achieve a small library of tacrine-donepezil hybrids. In agreement with the design, all compounds showed inhibitory activity toward both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values in the low micromolar range. Kinetic studies on the most potent cholinesterase (ChE) inhibitors within the series showed a mixed-type inhibition mechanism on both enzymes. Also, the docking studies indicated that the compounds inhibit ChEs by dual binding site (DBS) interactions. Notably, tacrine-donepezil hybrids also exhibited significant neuroprotection against H2O2-induced cell death in a differentiated human neuroblastoma (SH-SY5Y) cell line at concentrations close to their IC50 values on ChEs and showed high to medium blood-brain barrier (BBB) permeability on human cerebral microvascular endothelial cells (HBEC-5i). Besides, the compounds do not cause remarkable toxicity in a human hepatocellular carcinoma cell line (HepG2) and SH-SY5Y cells. Additionally, the compounds were predicted to also have good bioavailability. Among the tested compounds, H4, H16, H17, and H24 stand out with their biological profile. Taken together, the proposed novel tacrine-donepezil scaffold represents a promising starting point for the development of novel anti-ChE multifunctional agents against AD.

Candidate drug molecule-DNA interaction and molecular modelling of candidate drug molecule

Aim: 1,4-dihydropyridine derivative, 1-(3-phenyl propyl)-4-(2-(2-hydroxybenzylidene) hydrazone)-1,4-dihydropyridine (abbreviated as DHP) was synthesized as potential agent for Alzheimer’s disease which is a progressive neurodegenerative brain disorder affecting millions of elderly people. With this study, the electrochemical properties of DHP were investigated and its interaction with DNA was analyzed by differential pulse voltammetry (DPV) and cyclic voltammetry (CV) measurements. In addition, this study aims to determine degradation mechanism of the DHP molecule by Density-functional theory (DFT) in gas and in aqueous phase. Material and Method: Experimental conditions such as immobilization time, the effect of the scan rate, concentration, and the effect of pH were optimized. The method was validated according to validation parameters such as range, precision, linearity, limit of detection (LOD), limit of quantitation (LOQ) and inter/intraday. Results: Linearity study for the calibration curve of DNA and DHP with DPV was calculated in the calibration range 10-100 µg/mL. The LOD and LOQ values were calculated as 3 and 10 µg/mL and intra-day and inter-day repeatability (RSD %) were 1.85 and 3.64 µg/mL, respectively. After the DHP-DNA interaction, the oxidation currents of guanine decreased as a proof of interaction. The activation energy of the most possible path of reaction was calculated, and their thermodynamically most stable state was determined in gas phase. Conclusion: We developed to improve a sensitive, fast and easy detection process for determination of interaction between DHP and DNA.

"Vermellogens" and the Development of CB[8]-Based Supramolecular Switches Using pH-Responsive and Non-Toxic Viologen Analogues

We present herein the "vermellogens", a new class of pH-responsive viologen analogues, which replace the direct linking between para-substituted pyridinium moieties within those by a hydrazone functional group. A series of such compounds have been efficiently synthesized in aqueous media by hydrazone exchange reactions, displaying a marked pH-responsivity. Furthermore, the parent N,N'-dimethylated "vermellogen": the "red thread", an analogue of the herbicide paraquat and used herein as a representative model of the series, showed anion-recognition abilities, non-reversible electrochemical behavior, and non-toxicity of the modified bis-pyridinium core. The host-guest chemistry for the "red thread" with the CB[7,8] macrocyclic receptors has been extensively studied experimentally and by dispersion corrected density functional theory methods, showing a parallel behavior to that previously described for the herbicide but, crucially, swapping the well-known redox reactive capabilities of the viologen-based inclusion complexes by acid-base supramolecular responsiveness.

“The red cage”: implementation of pH-responsiveness within a macrobicyclic pyridinium-based molecular host

The “red cage”, a new pyridinium-based macrobicyclic host, has been found to complex model aromatic substrates in aqueous media in a pH-responsive fashion.

Synthesis and Biological Activity of Hydrazones and Derivatives: A Review

Hydrazones and their derivatives are very important compounds in medicinal chemistry due to their reported biological activity for the treatment of several diseases, like Alzheimer's, cancer, inflammation, and leishmaniasis. However, most of the investigations on hydrazones available in literature today are directed to the synthesis of these molecules with little discussion available on their biological activities. With the purpose of bringing lights into this issue, we performed a revision of the literature and wrote this review based on some of the most current research reports of hydrazones and derivatives, making it clear that the synthesis of these molecules can lead to new drug prototypes. Our goal is to encourage more studies focused on the synthesis and evaluation of new hydrazones, as a contribution to the development of potential new drugs for the treatment of various diseases.

Thinking outside the "Blue Box": from molecular to supramolecular pH-responsiveness

We present herein the development of a new polycationic cyclophane: the "red box", second in a series of hydrazone-based analogues of the well-known organic receptor cyclobis(paraquat-p-phenylene)cyclophane ("blue box"). The macrocycle has been prepared in an excellent yield in aqueous media, and shows both a remarkable pH-responsiveness and unusual hydrolytic stability of the two hydrazone C[double bond, length as m-dash]N bonds, associated with charge delocalization of the amine lone pair. Whilst in aqueous media the "red box" is able to complex a variety of aromatic substrates, both in its acidic and basic form, in organic media the cyclophane is only able to capture those in the acidic form, resulting in supramolecular pH-responsiveness.

Protein-Protein Interactions and Aggregation Inhibitors in Alzheimer's Disease

BACKGROUND

Alzheimer's Disease (AD), a multifaceted disorder, involves complex pathophysiology and plethora of protein-protein interactions. Thus such interactions can be exploited to develop anti-AD drugs.

OBJECTIVE

The interaction of dynamin-related protein 1, cellular prion protein, phosphoprotein phosphatase 2A and Mint 2 with amyloid β, etc., studied recently, may have critical role in progression of the disease. Our objective has been to review such studies and their implications in design and development of drugs against the Alzheimer's disease.

METHODS

Such studies have been reviewed and critically assessed.

RESULTS

Review has led to show how such studies are useful to develop anti-AD drugs.

CONCLUSION

There are several PPIs which are current topics of research including Drp1, Aβ interactions with various targets including PrPC, Fyn kinase, NMDAR and mGluR5 and interaction of Mint2 with PDZ domain, etc., and thus have potential role in neurodegeneration and AD. Finally, the multi-targeted approach in AD may be fruitful and opens a new vista for identification and targeting of PPIs in various cellular pathways to find a cure for the disease.

Alterations of mitochondrial electron transport chain and oxidative stress induced by alkaloid-like α-aminonitriles on Aedes aegypti larvae

Aedes aegypti mosquitoes are responsible for dengue, chikungunya, and Zika virus transmission in tropical and subtropical areas around the world. Due to the absence of vaccines or antiviral drugs for human treatment, the majority of control strategies are targeted at Ae. aegypti elimination. Our research on mosquito control insecticidal agents has previously shown that the alkaloid girgensohnine and its analogues (α-aminonitriles) present in vitro acetylcholinesterase inhibition and in vivo insecticidal activity against Ae. aegypti. However, acetylcholinesterase inhibition may not be the only mechanism of action behind these effects. On this basis, the principal aim of this study was to elucidate the possible action mode of four α-aminonitriles on Ae. aegypti by studying other important enzymatic targets, such as mitochondrial electron transport chain complexes, catalase, and superoxide dismutase, key oxidative stress enzymes. Mitochondria were isolated from Ae. aegypti larvae by differential centrifugation, stored at -70°C, and fragmented using ultrasound for 10min. The effects of α-aminonitriles (1 to 4) over enzymatic activities were evaluated using concentrations of 8nM, 2μM, 8μM, and 40μM. Results indicated that α-aminonitriles caused significant NADH dehydrogenase and succinate oxidase inhibition (~44% at the highest concentration tested). Succinate dehydrogenase and cytochrome c oxidase activities were found to increase (162% and 106% at 40μM, respectively). It was also observed that these compounds produced catalase inhibition and thus prevented H₂O₂ reduction, which induced the formation of reactive oxygen species (ROS). Moreover, NBT assay showed that compounds 3 and 4 (with 2-(pyrrolidin-1-yl) acetonitrile as substituent) increased by approximately 50% the O₂^●- concentration in the mitochondrial respiratory chain. It was concluded that the tested compounds act as complex I inhibitors by blocking electron transport and causing electron leak, possibly between complex I and III. Furthermore, α-aminonitriles inhibited catalase activity; compounds 1 and 2 (with piperidine fragment) inhibited glutathione reductase activity and further promoted the accumulation of ROS, which probably induced oxidative stress.

Underlying mechanisms and chemical/biochemical therapeutic approaches to ameliorate protein misfolding neurodegenerative diseases

Protein misfolding and inclusion body formations are common events in neurodegenerative diseases characterized by deposition of misfolded proteins inside or outside of neurons, and are commonly referred to as "protein misfolding neurodegenerative diseases" (PMNDs). These phenotypically diverse but biochemically similar aggregates suggest a highly conserved molecular mechanism of pathogenesis. These challenges are magnified by presence of mutations that render individual proteins subject to misfolding and/or aggregation. Cell proteostasis network and molecular chaperoning are maintaining cell proteome to preserve the protein folding, refolding, oligomerization, or disaggregation, and play formidable tasks to maintain the health of organism in the face of developmental changes, environmental insults, and rigors of aging. Maintenance of cell proteome requires the orchestration of major pathways of the cellular proteostasis network (heat shock response (HSR) in the cytosol and the unfolded protein response (UPR) in the endoplasmic reticulum). Proteostasis responses culminate in transcriptional and post-transcriptional programs that up-regulate the homeostatic mechanisms. Proteostasis is strongly influenced by the general properties of individual proteins for folding, misfolding, and aggregation. We examine a growing body of evidence establishing that when cellular proteostasis goes awry, it can be reestablished by deliberate chemical and biological interventions. We first try to introduce some new chemical approaches to prevent the misfolding or aggregation of specific proteins via direct binding interactions. We then start with approaches that employ chemicals or biological agents to enhance the general capacity of the proteostasis network. We finish with evidence that synergy is achieved with the combination of mechanistically distinct approaches to reestablish organ proteostasis. © 2016 BioFactors, 43(6):737-759, 2017.

Synthesis and anticholinesterase activity of new substituted benzo[d]oxazole-based derivatives

A series of novel benzo[d]oxazole derivatives (6a-n) have been synthesized and biologically evaluated as potential inhibitors of acetylcholinesterases (AChE) and butyrylcholinesterase (BChE). The chemical structures of all final compounds were confirmed by spectroscopic methods. In vitro studies showed that most of the synthesized compounds are potent acetylcholinesterase and butyrylcholinesterase inhibitors. Among them, compounds 6a and 6j strongly inhibited AChE and BChE activities with IC₅₀ values of 1.03-1.35 and 6.6-8.1 μm, respectively. Docking studies also provided the binding modes of action and identified hydrophobic pi forces as the main interaction.

Study of early stages of amyloid Aβ13-23 formation using molecular dynamics simulation in implicit environments

β-amyloid aggregation and formation of senile plaques is one of the hallmarks of Alzheimer's disease (AD). It leads to degeneration of neurons and decline of cognitive functions. The most aggregative and toxic form of β-amyloid is Aβ1-42 but in experiments, the shorter forms able to form aggregates are also used. The early stages of amyloid formation are of special interest due to the influence of this peptide on progression of AD. Here, we employed nine helices of undecapeptide Aβ13-23 and studied progress of amyloid formation using 500ns molecular dynamics simulation and implicit membrane environment. The small β-sheets emerged very early during simulation as separated two-strand structures and a presence of the membrane facilitated this process. Later, the larger β-sheets were formed. However, the ninth helix which did not form paired structure stayed unchanged till the end of MD simulation. Paired helix-helix interactions seemed to be a driving force of β-sheet formation at early stages of amyloid formation. Contrary, the specific interactions between α-helix and β-sheet can be very stable and be stabilized by the membrane.

Acetylcholinesterase inhibitors with photoswitchable inhibition of β-amyloid aggregation

Photochromic cholinesterase inhibitors were obtained from cis-1,2-α-dithienylethene-based compounds by incorporating one or two aminopolymethylene tacrine groups. All target compounds are potent acetyl- (AChE) and butyrylcholinesterase (BChE) inhibitors in the nanomolar concentration range. Compound 11b bearing an octylene linker exhibited interactions with both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Yet upon irradiation with light, the mechanism of interaction varied from one photochromic form to another, which was investigated by kinetic studies and proved "photoswitchable". The AChE-induced β-amyloid (Aβ) aggregation assay gave further experimental support to this finding: Aβ1-40 aggregation catalyzed by the PAS of AChE might be inhibited by compound 11b in a concentration-dependent manner and seems to occur only with one photochromic form. Computational docking studies provided potential binding modes of the compound. Docking studies and molecular dynamics (MD) simulations for the ring-open and -closed form indicate a difference in binding. Although both forms can interact with the PAS, more stable interactions are observed for the ring-open form based upon stabilization of a water molecule network within the enzyme, whereas the ring-closed form lacks the required conformational flexibility for an analogous binding mode. The photoswitchable inhibitor identified might serve as valuable molecular tool to investigate the different biological properties of AChE as well as its role in pathogenesis of AD in in vitro assays.

Pharmacogenomics of Alzheimer's disease: novel therapeutic strategies for drug development

Alzheimer's disease (AD) is a major problem of health and disability, with a relevant economic impact on our society. Despite important advances in pathogenesis, diagnosis, and treatment, its primary causes still remain elusive, accurate biomarkers are not well characterized, and the available pharmacological treatments are not cost-effective. As a complex disorder, AD is a polygenic and multifactorial clinical entity in which hundreds of defective genes distributed across the human genome may contribute to its pathogenesis. Diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena, together with structural and functional genomic dysfunctions, lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death, the major neuropathological hallmarks of AD. Future perspectives for the global management of AD predict that genomics and proteomics may help in the search for reliable biomarkers. In practical terms, the therapeutic response to conventional drugs (cholinesterase inhibitors, multifactorial strategies) is genotype-specific. Genomic factors potentially involved in AD pharmacogenomics include at least five categories of gene clusters: (1) genes associated with disease pathogenesis; (2) genes associated with the mechanism of action of drugs; (3) genes associated with drug metabolism (phase I and II reactions); (4) genes associated with drug transporters; and (5) pleiotropic genes involved in multifaceted cascades and metabolic reactions. The implementation of pharmacogenomic strategies will contribute to optimize drug development and therapeutics in AD and related disorders.