Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease

Dual Inhibitors of Brain Carbonic Anhydrases and Monoamine Oxidase-B Efficiently Protect against Amyloid-β-Induced Neuronal Toxicity, Oxidative Stress, and Mitochondrial Dysfunction

We report here the first dual inhibitors of brain carbonic anhydrases (CAs) and monoamine oxidase-B (MAO-B) for the management of Alzheimer's disease. Classical CA inhibitors (CAIs) such as methazolamide prevent amyloid-β-peptide (Aβ)-induced overproduction of reactive oxygen species (ROS) and mitochondrial dysfunction. MAO-B is also implicated in ROS production, cholinergic system disruption, and amyloid plaque formation. In this work, we combined a reversible MAO-B inhibitor of the coumarin and chromone type with benzenesulfonamide fragments as highly effective CAIs. A hit-to-lead optimization led to a significant set of derivatives showing potent low nanomolar inhibition of the target brain CAs (KIs in the range of 0.1-90.0 nM) and MAO-B (IC50 in the range of 6.7-32.6 nM). Computational studies were conducted to elucidate the structure-activity relationship and predict ADMET properties. The most effective multitarget compounds totally prevented Aβ-related toxicity, reverted ROS formation, and restored the mitochondrial functionality in an SH-SY5Y cell model surpassing the efficacy of single-target drugs.

Potential of Tryptamine Derivatives as Multi-Target Directed Ligands for Alzheimer's Disease: AChE, MAO-B, and COX-2 as Molecular Targets

Extensive research has been dedicated to develop compounds that can target multiple aspects of Alzheimer's disease (AD) treatment due to a growing understanding of AD's complex multifaceted nature and various interconnected pathological pathways. In the present study, a series of biological assays were performed to evaluate the potential of the tryptamine analogues synthesized earlier in our lab as multi-target-directed ligands (MTDLs) for AD. To assess the inhibitory effects of the compounds, various in vitro assays were employed. Three compounds, SR42, SR25, and SR10, displayed significant AChE inhibitory activity, with IC50 values of 0.70 µM, 0.17 µM, and 1.00 µM, respectively. These values superseded the standard drug donepezil (1.96 µM). In the MAO-B inhibition assay, SR42 (IC50 = 43.21 µM) demonstrated superior inhibitory effects as compared to tryptamine and other derivatives. Moreover, SR22 (84.08%), SR24 (79.30%), and SR42 (75.16%) exhibited notable percent inhibition against the COX-2 enzyme at a tested concentration of 100 µM. To gain insights into their binding mode and to validate the biological results, molecular docking studies were conducted. Overall, the results suggest that SR42, a 4,5 nitro-benzoyl derivative of tryptamine, exhibited significant potential as a MTDL and warrants further investigation for the development of anti-Alzheimer agents.

Enzyme Inhibition Assays for Monoamine Oxidase

Monoamine oxidase (MAO) catalyzes the oxidative deamination of monoamines with two isoforms, namely, MAO-A and MAO-B, in mitochondrial outer membranes. These two types of MAO-A and MAO-B participate in changes in levels of neurotransmitter such as serotonin (5-hydroxytryptamine) and dopamine. Selective MAO-A inhibitors have been targeted for anti-depression treatment, while selective MAO-B inhibitors are targets of therapeutic agents for Alzheimer's disease and Parkinson's disease. For this reason, study on the development of MAO inhibitors has recently become important. Here, we describe methods of MAO activity assay, especially continuous spectrophotometric methods, which give relatively high accuracy. MAO-A and MAO-B can be assayed using kynuramine and benzylamine as substrates, respectively, at 316 nm and 250 nm, respectively, to measure their respective products, 4-hydroxyquinoline and benzaldehyde. Inhibition degree and pattern can be analyzed by using the Lineweaver-Burk and secondary plots in the presence of inhibitor, and reversibility of inhibitor can be determined by using the dialysis method.

Exploration of a library of piperonylic acid-derived hydrazones possessing variable aryl functionalities as potent dual cholinesterase and monoamine oxidase inhibitors

A library of piperonylic acid-derived hydrazones possessing variable aryl moiety was synthesized and investigated for their multifunctional properties against cholinesterases (ChEs) and monoamine oxidases (MAOs). The in vitro enzymatic assay results revealed that the tested hydrazones have exhibited excellent cholinesterase inhibition profile. Compound 4i, (E)-N'-(2,3-dichlorobenzylidene)benzo[d][1,3]dioxole-5-carbohydrazide showed promising dual inhibitory profile against AChE (0.048 ± 0.007 μM), BChE (0.89 ± 0.018 μM), and MAO-B (0.95 ± 0.12 μM) enzymes. SAR exploration revealed that the truncation of the linker connecting both the aryl binding sites of the semicarbazone scaffold, by one atom, has relatively suppressed the AChE inhibitory potential. Kinetic studies disclosed that the compound 4i reversibly inhibited AChE enzyme in a competitive manner (Ki = 8.0 ± 0.076 nM), while it displayed a non-competitive and reversible inhibition profile against MAO-B (Ki = 9.6 ± 0.021 µM). Moreover, molecular docking studies of synthesized compounds against ChEs and MAOs provided the crucial molecular features that enable their close association and interaction with the target enzymes. All atomistic simulation studies confirmed the stable association of compound 4i within the active sites of AChE and MAO-B. In addition, theoretical ADMET prediction studies demonstrated the acceptable pharmacokinetic profile of the dual inhibitors. In summary, the attempted lead simplification study afforded a potent dual ChE-MAO-B inhibitor compound that merits further investigation.

Astrogliosis marker 11C-SL25.1188 PET in traumatic brain injury with persistent symptoms

Traumatic brain injury (TBI) is common but little is known why up to a third of patients have persisting symptoms. Astrogliosis, a pathophysiological response to brain injury, may be a potential therapeutic target, but demonstration of astrogliosis in the brain of humans with TBI and persistent symptoms is lacking. Astroglial marker monoamine oxidase B (MAO-B) total distribution volume (11C-SL25.1188 VT), an index of MAO-B density, was measured in 29 TBI and 29 similarly aged healthy control cases with 11C-SL25.1188 PET, prioritizing prefrontal cortex (PFC) and cortex proximal to cortical convexity. Correlations of PFC 11C-SL25.1188 VT with psychomotor and processing speed; and serum blood measures implicated in astrogliosis were determined. 11C-SL25.1188 VT was greater in TBI in PFC (P = 0.00064) and cortex (P = 0.00038). PFC 11C-SL25.1188 VT inversely correlated with Comprehensive Trail Making Test psychomotor and processing speed (r = -0.48, P = 0.01). In participants scanned within 2 years of last TBI, PFC 11C-SL25.1188 VT correlated with serum glial fibrillary acid protein (r = 0.51, P = 0.037) and total tau (r = 0.74, P = 0.001). Elevated 11C-SL25.1188 VT argues strongly for astrogliosis and therapeutics modifying astrogliosis towards curative phenotypes should be tested in TBI with persistent symptoms. Given substantive effect size, astrogliosis PET markers should be applied to stratify cases and/or assess target engagement for putative therapeutics targeting astrogliosis.

Screening of Monoamine Oxidase Inhibitors from Seeds of Nigella glandulifera Freyn et Sint. by Ligand Fishing and Their Neuroprotective Activity

Nigella glandulifera is a traditional medicinal plant used to treat seizures, insomnia, and mental disorders among the Tibetan and Xinjiang people of China. Recent pharmacological research indicates that the seeds of this plant have a neuroprotective effect; however, the chemical components responsible for this effect are unknown. Monoamine oxidase B (MAO-B) has been recognized as a target for developing anti-Parkinson's disease drugs. In this work, MAO-B functionalized magnetic nanoparticles were used to enrich the enzyme's ligands in extracts of N. glandulifera seeds for rapid screening of MAO-B inhibitors coupled with HPLC-MS. Tauroside E and thymoquinone were found to inhibit the enzyme with IC₅₀ values of 35.85 μM and 25.54 μM, respectively. Both compounds exhibited neuroprotective effects on 6-OHDA-induced PC-12 cells by increasing the cell viability to 52% and 58%, respectively, compared to 50% of the injured cells. Finally, molecular docking indicated strong interactions of both inhibitors with the enzyme. This work shows that MAO-B functionalized magnetic nanoparticles are effective for rapid screening of anti-PD inhibitors from complex herbal mixtures and, at the same time, shows the promising potential of this plant's seeds in developing anti-PD drugs.

Current Drug Targets in Alzheimer's Associated Memory Impairment: A Comprehensive Review

Alzheimer's disease (AD) is the most prevalent form of dementia among geriatrics. It is a progressive, degenerative neurologic disorder that causes memory and cognition loss. The accumulation of amyloid fibrils and neurofibrillary tangles in the brain of AD patients is a distinguishing feature of the disease. Therefore, most of the current therapeutic goals are targeting inhibition of beta-amyloid synthesis and aggregation as well as tau phosphorylation and aggregation. There is also a loss of the cholinergic neurons in the basal forebrain, and first-generation therapeutic agents were primarily focused on compensating for this loss of neurons. However, cholinesterase inhibitors can only alleviate cognitive symptoms of AD and cannot reduce the progression of the disease. Understanding the molecular and cellular changes associated with AD pathology has advanced significantly in recent decades. The etiology of AD is complex, with a substantial portion of sporadic AD emerging from unknown reasons and a lesser proportion of early-onset familial AD (FAD) caused by a mutation in several genes, such as the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2) genes. Hence, efforts are being made to discover novel strategies for these targets for AD therapy. A new generation of AChE and BChE inhibitors is currently being explored and evaluated in human clinical trials for AD symptomatic treatment. Other approaches for slowing the progression of AD include serotonergic modulation, H3 receptor antagonism, phosphodiesterase, COX-2, and MAO-B inhibition. The present review provides an insight into the possible therapeutic strategies and their molecular mechanisms, enlightening the perception of classical and future treatment approaches.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, “general chemicals,” natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10–15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

An updated patent review on monoamine oxidase (MAO) inhibitors

INTRODUCTION

: Monoamine oxidase (MAO) inhibitors are currently used as antidepressants (selective MAO-A inhibitors) or as co-adjuvants for neurodegenerative diseases (selective MAO-B inhibitors). The research within this field is attracting attention due to their crucial role in the modulation of brain functions, mood and cognitive activity, and monoamine catabolism.

AREAS COVERED

MAO inhibitors (2018-2021) are discussed according to their chemotypes. Structure-activity relationships are derived for each chemical scaffold (propargylamines, chalcones, indoles, benzimidazoles, (iso)coumarins, (iso)benzofurans, xanthones, and tetralones), while the chemical entities were divided into newly synthesized molecules and natural metabolites. The mechanism of action and type of inhibition are also considered. Lastly, new therapeutic applications are reported, which demonstrates the clinical potential of these inhibitors as well as the possibility of repurposing existing drugs for a variety of diseases.

EXPERT OPINION

MAO inhibitors here reported exhibit different potencies (from the micro- to nanomolar range) and isoform selectivity. These compounds are clinically licensed for multi-faceted neurodegenerative pathologies due to their ability to also act against other relevant targets (cholinesterases, inflammation, and oxidative stress). Moreover, the drug repurposing approach is an attractive strategy by which MAO inhibitors may be applied for the treatment of prostate cancer, inflammation, vertigo, and type 1 diabetes.

Biologically Active Compounds Present in Tobacco Smoke: Potential Interactions Between Smoking and Mental Health

Tobacco dependence remains one of the major preventable causes of premature morbidity and mortality worldwide. There are well over 8,000 compounds present in tobacco and tobacco smoke, but we do not know what effect, if any, many of them have on smokers. Major interest has been on nicotine, as well as on toxic and carcinogenic effects and several major and minor components of tobacco smoke responsible for the negative health effects of smoking have been elucidated. Smokers themselves report a variety of positive effects from smoking, including effects on depression, anxiety and mental acuity. Smoking has also been shown to have protective effects in Parkinson’s Disease. Are the subjective reports of a positive effect of smoking due to nicotine, of some other components of tobacco smoke, or are they a manifestation of the relief from nicotine withdrawal symptoms that smoking provides? This mini-review summarises what is currently known about the components of tobacco smoke with potential to have positive effects on smokers.

Translating pharmacology models effectively to predict therapeutic benefit

Many in vitro and in vivo models are used in pharmacological research to evaluate the role of targeted proteins in a disease. Understanding the translational relevance and limitation of these models for analyzing the disposition, pharmacokinetic/pharmacodynamic (PK/PD) profile, mechanism, and efficacy of a drug, is essential when selecting the most appropriate model of the disease of interest and predicting clinically efficacious doses of the investigational drug. Here, we review selected animal models used in ophthalmology, infectious diseases, oncology, autoimmune diseases, and neuroscience. Each area has specific challenges around translatability and determination of an efficacious dose: new patient-specific dosing methods could help overcome these limitations.

Amelioration of Alzheimer's Disease by Gut-Pancreas-Liver-Brain Interaction in an App Knock-In Mouse Model

In this study, we observed disease progression, changes in the gut microbiota, and interactions among the brain, liver, pancreas, and intestine in a mouse model of Alzheimer's disease (AD), in addition to attempting to inhibit disease progression through the dietary supplementation of L-arginine and limonoids. Wild-type mice (WC) and AD mice were fed a normal diet (AC), a diet supplemented with L-arginine and limonoids (ALA), or a diet containing only limonoids (AL) for 12-64 weeks. The normal diet-fed WC and AC mice showed a decrease in the diversity of the gut microbiota, with an increase in the Firmicutes/Bacteroidetes ratio, and bacterial translocation. Considerable bacterial translocation to the pancreas and intense inflammation of the pancreas, liver, brain, and intestinal tissues were observed in the AC mice from alterations in the gut microbiota. The ALA diet or AL diet-fed mice showed increased diversity of the bacterial flora and suppressed oxidative stress and inflammatory responses in hepatocytes and pancreatic cells, bacterial translocation, and neurodegeneration of the brain. These findings suggest that L-arginine and limonoids help in maintaining the homeostasis of the gut microbiota, pancreas, liver, brain, and gut in AD mice.

Unraveling the metabolic pathway of choline-TMA-TMAO: Effects of gypenosides and implications for the therapy of TMAO related diseases

Trimethylamine-N-oxide (TMAO) has emerged as a promising new therapeutic target for the treatment of central nervous system diseases, atherosclerosis and other diseases. However, its origin in the brain is unclear. Gynostemma pentaphyllum (Thunb.) Makino can reduce the increase of TMAO level caused by a high fat diet. But its effective chemical composition and specific mechanism have not been reported. The study confirmed that TMA was more easily to penetrate blood brain barrier than TMAO, the MAO enzyme was partly involved in the transformation of the TMA in brain, which further supplemented the choline-TMA-TMAO pathway. Based on the above metabolic pathway, using multi-omics approaches, such as microbiodiversity, metagenomics and lipidomics, it was demonstrated that the reduction of plasma TMAO levels by gypenosides did not act on FMO3 and MAO in the pathway, but remodeled the microbiota and affected the trimethylamine lyase needed in the conversion of choline to TMA in intestinal flora. At the same time, gypenosides interfered with enzymes associated with TCA and lipid metabolism, thus affecting TMAO and lipid metabolism. Considering the bidirectional transformation of phosphatidycholine and choline, lipid metabolism and TMAO metabolism could affected each other to some extent. In conclusion, our study revealed the intrinsic correlation between long-term application of gypenosides to lipid reduction and nervous system protection, and explained why gypenosides were used to treat brain diseases, even though they had a poor ability to enter the brain. Besides, it provided a theoretical basis for clinical application of gypenosides and the development of new drugs.

Insights into the Mechanism of the Therapeutic Potential of Herbal Monoamine Oxidase Inhibitors in Neurological Diseases

Monoamine oxidase (MAO) is an enzyme that catalyzes the deamination of monoamines and other proteins. MAO's hyperactivation results in the massive generation of reactive oxygen species, which leads to a variety of neurological diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and depression-like disorders. Although synthetic MAO inhibitors are clinically available, they are associated with side effects such as hepatotoxicity, cheese reaction, hypertensive crisis, and so on, necessitating the investigation of alternative MAO inhibitors from a natural source with a safe profile. Herbal medications have a significant impact on the prevention of many diseases; additionally, they have fewer side effects and serve as a precursor for drug development. This review discusses the potential of herbal MAO inhibitors as well as their associated mechanism of action, with an aim to foster future research on herbal MAO inhibitors as potential treatment for neurological diseases.

Cyanobiphenyls: Novel H3 receptor ligands with cholinesterase and MAO B inhibitory activity as multitarget compounds for potential treatment of Alzheimer's disease

Alzheimer's disease (AD) is a complex and incurable illness that requires the urgent approval of new effective drugs. However, since 2003, no new molecules have shown successful results in clinical trials, thereby making the common "one compound - one target" paradigm questionable. Recently, the multitarget-directed ligand (MTDL) approach has gained popularity, as compounds targeting at least two biological targets may be potentially more effective in treating AD. On the basis of these findings, we designed, synthesized, and evaluated through biological assays a series of derivatives of alicyclic amines linked by an alkoxy bridge to an aromatic lipophilic moiety of [1,1'-biphenyl]-4-carbonitrile. The research results revealed promising biological activity of the obtained compounds toward the chosen targets involved in AD pathophysiology; the compounds showed high affinity (mostly low nanomolar range of K_i values) for human histamine H₃ receptors (hH₃R) and good nonselective inhibitory potency (micromolar range of IC₅₀ values) against acetylcholinesterase from electric eel (eeAChE) and equine serum butyrylcholinesterase (eqBuChE). Moreover, micromolar/submicromolar potency against human monoamine oxidase B (hMAO B) was detected for some compounds. The study identified compound 5 as a multiple hH₃R/eeAChE/eqBuChE/hMAO B ligand (5: hH₃R K_i = 9.2 nM; eeAChE IC₅₀ = 2.63 µM; eqBuChE IC₅₀ = 1.30 µM; hMAO B IC₅₀ = 0.60 µM). Further in vitro studies revealed that compound 5 exhibits a mixed type of eeAChE and eqBuChE inhibition, good metabolic stability, and moderate hepatotoxicity effect on HepG2 cells. Finally, compound 5 showed a beneficial effect on scopolamine-induced memory impairments, as assessed by the passive avoidance test, thus revealing the potential of this compound as a promising agent for further optimization for AD treatment.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Three -(pyridin-2-yl)-2-(pyridin-2-ylimino)thiazolidin-4-one as a novel inhibitor of cerebral MAO-B activity with antioxidant properties and low toxicity potential

Some brain diseases are associated with oxidative stress and altered monoamine oxidase (MAO) activity. The objective of this study was to evaluate the antioxidant and neuroprotective actions through MAO inhibition of 3-(pyridin-2-yl)-2-(pyridine-2-ylimino) thiazolidin-4-one (PPIT, a synthetic molecule containing a thiazolidinone nucleus), as well as its effects on toxicity parameters in Swiss female mice. Five in vitro assays were carried out to verify the PPIT antioxidant capacity: protein carbonylation (PC), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picryl-hydrazil (DPPH), ferric ion (Fe³⁺ ) reducing antioxidant power (FRAP), and superoxide dismutase (SOD)-like activity. The results showed that PPIT reduced the level of PC in the homogenate of the brain. This compound did not demonstrate SOD mimetic activity, but it acted as a free radical scavenger (ABTS and DPPH) and exhibited reducing activity in the FRAP assay. In addition, the effects of PPIT on cerebral MAO activity (MAO-A and B isoforms) were investigated in vitro. Our data revealed inhibition of the MAO-B activity by PPIT with no effects on MAO-A. Lastly, an acute oral toxicity test was conducted in mice. No changes in food intake, body weight, and biochemical markers of kidney and liver damage were detected in mice treated with a high dose of PPIT (300 mg/kg). In conclusion, the present study demonstrated that PPIT exhibits antioxidant activity and selectively inhibits the MAO-B isoform without causing apparent toxicity. These findings suggest PPIT as a potential therapeutic candidate to be tested in preclinical models of brain diseases involving perturbations of MAO-B activity and redox status.

Elucidating the Multi-Targeted Role of Nutraceuticals: A Complementary Therapy to Starve Neurodegenerative Diseases

The mechanisms underlying multifactorial diseases are always complex and challenging. Neurodegenerative disorders (NDs) are common around the globe, posing a critical healthcare issue and financial burden to the country. However, integrative evidence implies some common shared mechanisms and pathways in NDs, which include mitochondrial dysfunction, neuroinflammation, oxidative stress, intracellular calcium overload, protein aggregates, oxidative stress (OS), and neuronal destruction in specific regions of the brain, owing to multifaceted pathologies. The co-existence of these multiple pathways often limits the advantages of available therapies. The nutraceutical-based approach has opened the doors to target these common multifaceted pathways in a slow and more physiological manner to starve the NDs. Peer-reviewed articles were searched via MEDLINE and PubMed published to date for in-depth research and database collection. Considered to be complementary therapy with current clinical management and common drug therapy, the intake of nutraceuticals is considered safe to target multiple mechanisms of action in NDs. The current review summarizes the popular nutraceuticals showing different effects (anti-inflammatory, antioxidant, neuro-protectant, mitochondrial homeostasis, neurogenesis promotion, and autophagy regulation) on vital molecular mechanisms involved in NDs, which can be considered as complementary therapy to first-line treatment. Moreover, owing to its natural source, lower toxicity, therapeutic interventions, biocompatibility, potential nutritional effects, and presence of various anti-oxidative and neuroprotective constituents, the nutraceuticals serve as an attractive option to tackle NDs.

Discovery of N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide: a novel, selective, and competitive indole-based lead inhibitor for human monoamine oxidase B

Herein, two new series of N-substituted indole-based analogues were rationally designed, synthesized via microwave heating technology, and evaluated as noteworthy MAO-B potential inhibitors. Compared to the reported indazole-based hits VI and VII, compounds 4b and 4e exhibited higher inhibitory activities over MAO-B with IC₅₀ values of 1.65 and 0.78 µM, respectively. When compared to the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), both 4b and 4e also showed better selectivity indices (SI > 60 and 120, respectively). A further kinetic evaluation of the most potent derivative (4e) displayed a competitive mode of inhibition (inhibition constant (K_i)/MAO-B = 94.52 nM). Reasonable explanations of the elicited biological activities were presented via SAR study and molecular docking simulation. Accordingly, the remarkable MAO-B inhibitory activity of 4e (N-(1-(3-fluorobenzoyl)-1H-indol-5-yl)pyrazine-2-carboxamide), with its selectivity and competitive inhibition, advocates its potential role as a promising lead worthy of further optimization.

Insight into Inhibitory Mechanism of PDE4D by Dietary Polyphenols Using Molecular Dynamics Simulations and Free Energy Calculations

Phosphodiesterase 4 (PDE4), mainly present in immune, epithelial, and brain cells, represents a family of key enzymes for the degradation of cyclic adenosine monophosphate (cAMP), which modulates inflammatory response. In recent years, the inhibition of PDE4 has been proven to be an effective therapeutic strategy for the treatment of neurological disorders. PDE4D constitutes a high-interest therapeutic target primarily for the treatment of Alzheimer’s disease, as it is highly involved in neuroinflammation, learning ability, and memory dysfunctions. In the present study, a thorough computational investigation consisting of molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations based on the linear response approximation (LRA) method was performed to study dietary polyphenols as potential PDE4D inhibitors. The obtained results revealed that curcumin, 6-gingerol, capsaicin, and resveratrol represent potential PDE4D inhibitors; however, the predicted binding free energies of 6-gingerol, capsaicin, and resveratrol were less negative than in the case of curcumin, which exhibited the highest inhibitory potency in comparison with a positive control rolipram. Our results also revealed that the electrostatic component through hydrogen bonding represents the main driving force for the binding and inhibitory activity of curcumin, 6-gingerol, and resveratrol, while the van der Waals component through shape complementarity plays the most important role in capsaicin’s inhibitory activity. All investigated compounds form hydrophobic interactions with residues Gln376 and Asn602 as well as hydrogen bonds with nearby residues Asp438, Met439, and Ser440. The binding mode of the studied natural compounds is consequently very similar; however, it significantly differs from the binding of known PDE4 inhibitors. The uncovered molecular inhibitory mechanisms of four investigated natural polyphenols, curcumin, 6-gingerol, capsaicin, and resveratrol, form the basis for the design of novel PDE4D inhibitors for the treatment of Alzheimer’s disease with a potentially wider therapeutic window and fewer adverse side effects.

Design, synthesis, and biological evaluation of new urolithin amides as multitarget agents against Alzheimer's disease

A series of urolithin amide (i.e., URO-4-URO-10 and THU-4-THU-10) derivatives was designed and synthesized, and their chemical structures were confirmed with spectroscopic techniques and elemental analysis. The title compounds and synthesis intermediates (THU-1-THU-10 and URO-1-URO-10) were evaluated for their potential to inhibit acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and monoamine oxidase B (MAO-B). Compounds THU-4 and THU-8 were found to be the most potent inhibitors for the cholinesterases and MAO-B, respectively. The docking studies were also employed to evaluate the binding modes of the most active compounds with AChE, BuChE, and MAO-B. Furthermore, the moderate-to-strong activities of the compounds were also displayed in amyloid-beta inhibition and antioxidant assay systems. The results pointed out that the urolithin scaffold can be employed in drug design studies for the development of multitarget ligands acting on various cascades shown to be important within the pathophysiology of Alzheimer's disease.

Monoamine Oxidase Inhibitors: From Classic to New Clinical Approaches

Monoamine oxidases (MAOs) are involved in the oxidative deamination of different amines and neurotransmitters. This pointed them as potential targets for several disorders and along the last 70 years a wide variety of MAO inhibitors have been developed as successful drugs for the treatment of complex diseases, being the first drugs approved for depression in the late 1950s. The discovery of two MAO isozymes (MAO-A and B) with different substrate selectivity and tissue expression patterns led to novel therapeutic approaches and to the development of new classes of inhibitors, such as selective irreversible and reversible MAO-B inhibitors and reversible MAO-A inhibitors. Significantly, MAO-B inhibitors constitute a widely studied group of compounds, some of them approved for the treatment of Parkinson's disease. Further applications are under development for the treatment of Alzheimer's disease, amyotrophic lateral sclerosis, and cardiovascular diseases, among others. This review summarizes the most important aspects regarding the development and clinical use of MAO inhibitors, going through mechanistic and structural details, new indications, and future perspectives. Monoamine oxidases (MAOs) catalyze the oxidative deamination of different amines and neurotransmitters. The two different isozymes, MAO-A and MAO-B, are located at the outer mitochondrial membrane in different tissues. The enzymatic reaction involves formation of the corresponding aldehyde and releasing hydrogen peroxide (H₂O₂) and ammonia or a substituted amine depending on the substrate. MAO's role in neurotransmitter metabolism made them targets for major depression and Parkinson's disease, among other neurodegenerative diseases. Currently, these compounds are being studied for other diseases such as cardiovascular ones.

Synthesis of novel 4-methylthiocoumarin and comparison with conventional coumarin derivative as a multi-target-directed ligand in Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial disorder characterized by cognitive deficit and memory loss. The pathological feature of the disease involves β-amyloid senile plaques, reduced levels of acetylcholine neurotransmitter, oxidative stress and neurofibrillary tangles formation within the brain of AD patients. The present study aims to screen the inhibitory activity of newly synthesized and existing novel 4-methylthiocoumarin derivative against acetylcholinesterase, butyrylcholinesterase, BACE1, β-amyloid aggregation and oxidative stress involved in the AD pathogenesis. The in vitro assays used in this study were Ellman's assay, FRET assays, Thioflavin T, transmission electron microscopy, circular dichroism, FRAP, and TEAC. Molecular docking and dynamics studies were performed to correlate the results. C3 and C7 (thiocoumarin derivatives) were found to be the most potent inhibitors of acetylcholinesterase (IC50-5.63 µM) and butyrylcholinesterase (IC50-3.40 µM) using Ellman's assays. Enzyme kinetic studies showed that C3 and C7 compounds followed by the mixed mode of inhibition using LB plot. C3 also moderately inhibited the BACE1 using FRET assay. C3 inhibited the fibrillization of β-amyloid peptides in a concentration-dependent manner as observed by Thioflavin T, TEM studies and Circular dichroism data. Molecular modeling studies were performed to understand the probable mode of binding of C3 and C7 in the binding pocket of acetylcholinesterase, butyrylcholinesterase, BACE1 and amyloid β peptides. This indicates the important role of hydrophobic interactions between C3 and acetylcholinesterase. C3 also exhibited significant antioxidant potential by FRAP and TEAC assays. Hence, C3 might serve as a promising lead for developing novel multi target-directed ligand for the treatment of AD.

Severe reactive astrocytes precipitate pathological hallmarks of Alzheimer's disease via H2O2- production

Although the pathological contributions of reactive astrocytes have been implicated in Alzheimer's disease (AD), their in vivo functions remain elusive due to the lack of appropriate experimental models and precise molecular mechanisms. Here, we show the importance of astrocytic reactivity on the pathogenesis of AD using GiD, a newly developed animal model of reactive astrocytes, where the reactivity of astrocytes can be manipulated as mild (GiDm) or severe (GiDs). Mechanistically, excessive hydrogen peroxide (H₂O₂) originated from monoamine oxidase B in severe reactive astrocytes causes glial activation, tauopathy, neuronal death, brain atrophy, cognitive impairment and eventual death, which are significantly prevented by AAD-2004, a potent H₂O₂ scavenger. These H₂O₂^--induced pathological features of AD in GiDs are consistently recapitulated in a three-dimensional culture AD model, virus-infected APP/PS1 mice and the brains of patients with AD. Our study identifies H₂O₂ from severe but not mild reactive astrocytes as a key determinant of neurodegeneration in AD.

Development of Phthalimide-Donepezil Hybrids as Potent Multitarget- Directed Ligands for the Treatment of Alzheimer’s Disease

Background:

Due to the complex etiology of AD, multi-target-directed ligands (MTDLs), combining two or more distinct pharmacological moieties, have been developed in both symptomatic and disease-modifying efficiencies and are considered as an effective way for the treatment of AD.

Methods:

To test their biological activities, including AChE/BChE inhibitory activity and MAOA/ MAO-B inhibitory activity. In addition, molecular modeling studies were performed to afford insight into the binding mode.

Results:

The results displayed that compound 4c showed the best AChE inhibitory activity with an IC50 value of 4.2 μM, which was supported by the kinetic study and docking study. Compound 4c was also a selective MAO-B inhibitor (IC50 = 8.2 μM). Moreover, compound 4c could cross the blood-brain barrier in vitro.

Conclusion:

Compound 4c deserved to further study as a potential multifunctional agent for the treatment of Alzheimer’s disease.

Embryonic proteoglycans regulate monoamines in the rat frontal cortex and hippocampus in Alzheimer's disease-like pathology

Using the rat Alzheimer's disease (AD)-like model we have analyzed the hippocampal short-term potentiation, levels of monoamines, and morphological changes in the hippocampal and cortical neurons after the administration of proteoglycans of embryonic origin (PEG). Results showed that the levels of monoamines and especially norepinephrine in the target AD brain structures were found elevated, except serotonin, which was unaffected in the hippocampus, but decreased in the frontal cortex. These changes were accompanied by the substantial structural damage of cortical and hippocampal neurons. PEG was able to reverse most of these changes. In addition, PEG administration had regime-dependent effects on a short-term potentiation pattern of hippocampal neurons. The elevated levels of key elements of brain monoaminergic system in the model of AD support the hypothesis of the important role of monoamines in the excessive synaptic excitation resulting in cognitive dysfunction in AD brain. The neuroprotective effect of PEG, as manifested by the recovery of the monoaminergic system, suggests this bioactive substance as a perspective therapeutic agent for the treatment of AD.

Multitarget Therapeutic Strategies for Alzheimer's Disease: Review on Emerging Target Combinations

Neurodegenerative diseases represent nowadays one of the major health problems. Despite the efforts made to unveil the mechanism leading to neurodegeneration, it is still not entirely clear what triggers this phenomenon and what allows its progression. Nevertheless, it is accepted that neurodegeneration is a consequence of several detrimental processes, such as protein aggregation, oxidative stress, and neuroinflammation, finally resulting in the loss of neuronal functions. Starting from these evidences, there has been a wide search for novel agents able to address more than a single event at the same time, the so-called multitarget-directed ligands (MTDLs). These compounds originated from the combination of different pharmacophoric elements which endowed them with the ability to interfere with different enzymatic and/or receptor systems, or to exert neuroprotective effects by modulating proteins and metal homeostasis. MTDLs have been the focus of the latest strategies to discover a new treatment for Alzheimer's disease (AD), which is considered the most common form of dementia characterized by neurodegeneration and cognitive dysfunctions. This review is aimed at collecting the latest and most interesting target combinations for the treatment of AD, with a detailed discussion on new agents with favorable in vitro properties and on optimized structures that have already been assessed in vivo in animal models of dementia.

Vital Role of Monoamine Oxidases and Cholinesterases in Central Nervous System Drug Research: A Sharp Dissection of the Pathophysiology

BACKGROUND

Monoamine oxidase and cholinesterase enzymes are very critical enzymes that regulate the level of neurotransmitters such as acetylcholine and monoamines. Monoamine neurotransmitters and acetylcholine play a very important role in many physiological events. An increase or decrease in the amount of these neurotransmitters is observed in a wide range of central nervous system pathologies. Balancing the amount of these neurotransmitters is important in improving the progression of these diseases. Inhibitors of monoamine oxidase and cholinesterase enzymes are important in symptomatic therapy and delaying progression of a group of central nervous system disease manifested with memory loss, cognitive decline and psychiatric disturbances like depression.

OBJECTIVE

In this article, the relationship between central nervous system diseases and the vital role of the enzymes, monoamine oxidase and cholinesterase, is discussed on the pathophysiologic basis, focusing on drug research.

CONCLUSION

Monoamine oxidase and cholinesterase enzymes are still a good target for the development of novel drug active substances with optimized pharmacokinetic and pharmacodynamic properties, which can maximize the benefits of current therapy modalities.

Synthesis of natural product-like polyprenylated phenols and quinones: Evaluation of their neuroprotective activities

Twenty-seven natural product-like polyprenylated phenols and quinones were synthesized and their neuroprotective activity was tested using human monoamine oxidase B (MAO-B) and SH-SY5Y cells. Eight compounds inhibited MAO-B (IC₅₀ values < 25 μM) and the inhibition mode and molecular docking of two (8c and 16c) were investigated. Compounds inhibiting MAO-B activity were additionally tested for their ability to protect SH-SY5Y cells from peroxide injury. Three derivatives (3c, 8c and 16c) exhibited both MAO-B inhibitory and neuroprotective activity. A structure activity-relationship study showed that a phenolic hydroxyl group and a longer side chain are important for both activities.

Danshensu attenuates scopolamine and amyloid-β-induced cognitive impairments through the activation of PKA-CREB signaling in mice

Alzheimer's disease (AD) is an important chronic neurodegenerative disorder and is mainly associated with cognitive dysfunction. At present, bioactive compounds from traditional medicinal plants have received much attention for the enhancement of cognitive function. Danshensu, a phenolic acid isolated from herbal medicines, has various pharmacological activities in the central nervous system, including anxiolytic-like and neuroprotective properties. The present study aimed to investigate the ameliorating effects of danshensu on scopolamine- and amyloid-β (Aβ) protein-induced cognitive impairments in mice. Danshensu (3 and 10 mg/kg, p.o.) effectively ameliorated scopolamine-induced cognitive dysfunction in mice, as measured in passive avoidance and Y-maze tasks. In a mechanistic study, danshensu inhibited monoamine oxidase A (MAO-A) activity but not MAO-B. Additionally, danshensu treatment increased the dopamine level and the phosphorylation levels of protein kinase A (PKA) and cAMP response element binding protein (CREB), in the cortex of the brain. Furthermore, the ameliorating effect of danshensu against scopolamine-induced cognitive impairment was fully blocked by H89, a PKA inhibitor. Finally, danshensu also ameliorated Aβ-induced cognitive impairments in an animal model of AD. The results revealed that danshensu treatment significantly improved scopolamine and Aβ-induced cognitive impairments in mice by facilitation of dopamine signaling cascade such as PKA and CREB due to MAO-A inhibition. Thus, danshensu could be used as a promising therapeutic agent for preventing and treating AD.

Rutin alleviates cadmium-induced neurotoxicity in Wistar rats: involvement of modulation of nucleotide-degrading enzymes and monoamine oxidase

Rutin is a flavonoid commonly found in many vegetables, fruits and other plant species. Thus, this study investigated the protective role of rutin on cognitive function and impairment of ectonucleotidase, monoamine oxidase (MAO) and antioxidant enzymes activities in the cortex and hippocampus of cadmium-induced rats. Cognitive impairment was induced by an oral administration of 5 mg/kg Cadmium chloride for 14 consecutive days. Rutin was dissolved in 2% dimethyl sulfoxide (DMSO) and administered orally at the doses of 25 and 50 mg/kg for 14 days. Thereafter, animals were divided into six groups (n = 6) as follows: control, rutin 25 mg/kg, rutin 50 mg/kg, cadmium, cadmium plus rutin 25 mg/kg, cadmium plus rutin 50 mg/kg. After treatment period of 14 days, animals were sacrificed and the brain was dissected into cortex and hippocampus. Results showed that cadmium caused a significant increase in ectonucleotidases, adenosine deaminase (ADA) and MAO activities, with a concomitant decrease in thiol levels and antioxidant enzymes activities. However, treatment with rutin decreased ectonucleotidase, ADA and MAO activities in cadmium-induced rats. In addition, rutin reduced residual level of cadmium ion in the brain of cadmium-induced rats. Conclusively, present findings revealed that rutin could prevent/restored the impairment of the enzymes that regulate the purinergic and monoaminergic extracellular signaling and restore antioxidant status in cognitive impairment caused by prolonged cadmium exposure.

Identification of a Novel Peptide from β-Casein That Enhances Spatial and Object Recognition Memory in Mice

An increase in the aging population has spurred recent efforts to identify diet and lifestyle changes that help prevent cognitive decline. Several epidemiological investigations and clinical studies have indicated that consuming fermented dairy products prevents cognitive decline. Some peptides from whey including β-lactolin improve memory impairment; the intake of Camembert cheese has been shown to prevent Alzheimer's in mouse models. To elucidate the molecular mechanisms underlying these preventive effects, we screened peptides from digested casein protein for their ability to improve spatial memory in a scopolamine-induced amnesia mouse model. Administration of KEMPFPKYPVEP peptide from β-casein at 0.5 mg/kg (54.8 ± 2.5) and 2 mg/kg (57.9 ± 3.7) improved memory impairment in the amnesia mice in comparison with control (44.9 ± 3.4; p = 0.031 and p = 0.042, respectively) and increased dopamine (5.9 ± 3.8 [control] and 12.4 ± 6.2 [KEMPFPKYPVEP peptide]) and norepinephrine (7.7 ± 0.8 [control] and 9.9 ± 2.0 [KEMPFPKYPVEP peptide]) levels in the frontal cortex (p = 0.039 and p = 0.031, respectively). Collectively, our findings suggest that peptides in fermented dairy products prevent cognitive decline and support previously reported observations.

Monoamine Oxidases (MAOs) as Privileged Molecular Targets in Neuroscience: Research Literature Analysis

Background: Monoamine oxidases (MAOs) were discovered nearly a century ago. This article aims to analyze the research literature landscape associated with MAOs as privileged class of neuronal enzymes (neuroenzymes) with key functions in the processes of neurodegeneration, serving as important biological targets in neuroscience. With the accumulating publications on this topic, we aimed to evaluate the publication and citation performance of the contributors, reveal the popular research themes, and identify its historical roots. Methods: The electronic database of Web of Science (WoS) Core Collection was searched to identify publications related to MAOs, which were analyzed according to their publication year, authorship, institutions, countries/regions, journal title, WoS category, total citation count, and publication type. VOSviewer was utilized to visualize the citation patterns of the words appearing in the titles and abstracts, and author keywords. CRExplorer was utilized to identify seminal references cited by the MAO publications. Results: The literature analysis was based on 19,854 publications. Most of them were original articles (n = 15,148, 76.3%) and reviews (n = 2,039, 10.3%). The top five WoS categories of the analyzed MAO publications were Pharmacology/Pharmacy (n = 4,664, 23.5%), Neurosciences (n = 4,416, 22.2%), Psychiatry (n = 2,906, 14.6%), Biochemistry/Molecular Biology (n = 2,691, 13.6%), and Clinical Neurology (n = 1,754, 8.8%). The top 10 institutions are scattered in the United States, UK, France, Sweden, Canada, Israel, and Russia, while the top 10 countries/regions with the most intensive research on the field of MAOs are the United States, followed by European and Asian countries. More highly cited publications generally involved neurotransmitters, such as dopamine (DA), serotonin, and norepinephrine (NE), as well as the MAO-A inhibitors moclobemide and clorgyline, and the irreversible MAO-B inhibitors selegiline and rasagiline. Conclusion: Through decades of research, the literature has accumulated many publications investigating the therapeutic effects of MAO inhibitors (MAOIs) on various neurological conditions, such as Alzheimer's disease (AD), Parkinson's disease (PD), and depression. We envision that MAO literature will continue to grow steadily, with more new therapeutic candidates being tested for better management of neurological conditions, in particular, with the development of multi-target acting drugs against neurodegenerative diseases.

Selective Inhibition of Human Monoamine Oxidase B by Acacetin 7-Methyl Ether Isolated from Turnera diffusa (Damiana)

The investigation of the constituents that were isolated from Turnera diffusa (damiana) for their inhibitory activities against recombinant human monoamine oxidases (MAO-A and MAO-B) in vitro identified acacetin 7-methyl ether as a potent selective inhibitor of MAO-B (IC₅₀ = 198 nM). Acacetin 7-methyl ether (also known as 5-hydroxy-4′, 7-dimethoxyflavone) is a naturally occurring flavone that is present in many plants and vegetables. Acacetin 7-methyl ether was four-fold less potent as an inhibitor of MAO-B when compared to acacetin (IC₅₀ = 50 nM). However, acacetin 7-methyl ether was >500-fold selective against MAO-B over MAO-A as compared to only two-fold selectivity shown by acacetin. Even though the IC₅₀ for inhibition of MAO-B by acacetin 7-methyl ether was ~four-fold higher than that of the standard drug deprenyl (i.e., Selegiline^TM or Zelapar^TM, a selective MAO-B inhibitor), acacetin 7-methyl ether’s selectivity for MAO-B over MAO-A inhibition was greater than that of deprenyl (>500- vs. 450-fold). The binding of acacetin 7-methyl ether to MAO-B was reversible and time-independent, as revealed by enzyme-inhibitor complex equilibrium dialysis assays. The investigation on the enzyme inhibition-kinetics analysis with varying concentrations of acacetin 7-methyl ether and the substrate (kynuramine) suggested a competitive mechanism of inhibition of MAO-B by acacetin 7-methyl ether with Ki value of 45 nM. The docking scores and binding-free energies of acacetin 7-methyl ether to the X-ray crystal structures of MAO-A and MAO-B confirmed the selectivity of binding of this molecule to MAO-B over MAO-A. In addition, molecular dynamics results also revealed that acacetin 7-methyl ether formed a stable and strong complex with MAO-B. The selective inhibition of MAO-B suggests further investigations on acacetin 7-methyl as a potential new drug lead for the treatment of neurodegenerative disorders, including Parkinson’s disease.

Tryptophan-Tyrosine Dipeptide, the Core Sequence of β-Lactolin, Improves Memory by Modulating the Dopamine System

Tryptophan-tyrosine (WY)-related peptides including the β-lactopeptide of the glycine-threonine-tryptophan-tyrosine peptide, β-lactolin, improve spatial memory. However, whether and how the WY dipeptide as the core sequence in WY-related peptides improves memory functions has not been investigated. This study assessed the pharmacological effects of the WY dipeptide on memory impairment to elucidate the mechanisms. Here, we showed that oral administration of dipeptides of WY, tryptophan-methionine (WM), tryptophan-valine, tryptophan-leucine, and tryptophan-phenylalanine improved spontaneous alternation of the Y-maze test in scopolamine-induced amnesic mice. In contrast, tyrosine-tryptophan, methionine-tryptophan, tryptophan, tyrosine, and methionine had no effect. These results indicated that the conformation of dipeptides with N-terminal tryptophan is required for their memory improving effects. WY dipeptide inhibited the monoamine oxidase B activity in vitro and increased dopamine levels in the hippocampus and frontal cortex, whereas tryptophan did not cause these effects. In addition, the treatment with SCH-23390, a dopamine D1-like receptor antagonist, and the knockdown of the hippocampal dopamine D1 receptor partially attenuated the memory improvement induced by the WY dipeptide. Importantly, WY dipeptide improved the spontaneous alternations of the Y-maze test in aged mice. These results suggest that the WY dipeptide restores memory impairments by augmenting dopaminergic activity. The development of supplements rich in these peptides might help to prevent age-related cognitive decline.

Synthesis and biological assessment of KojoTacrines as new agents for Alzheimer's disease therapy

In view of the multifactorial nature of Alzheimer’s disease (AD), multitarget small molecules (MTSM) represent the most potent and attractive therapeutic strategy to design new drugs for Alzheimer’s disease therapy. The new MTSM KojoTacrines (KTs) were designed and synthesized by juxtaposition of selected pharmacophoric motifs from kojic acid and tacrine. Among them, 11-amino-2-(hydroxymethyl)-12-(3-methoxyphenyl)-7,9,10,12-tetrahydropyrano [2',3':5,6] pyrano[2,3-b]quinolin-4(8H)-one (KT2d) was identified as less-hepatotoxic than tacrine, at higher concentration, a moderate, but selective human acetylcholinesterase inhibitor (IC₅₀ = 4.52 ± 0.24 µM), as well as an antioxidant agent (TE = 4.79) showing significant neuroprotection against Aβ_1–40 at 3 µM and 10 µM concentrations. Consequently, KT2d is a potential new hit-ligand for AD therapy for further biological exploration.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Action of Hydrogen Peroxide on Synaptic Transmission at the Mouse Neuromuscular Junction

Hydrogen peroxide (H₂O₂) is one of the reactive oxygen species (ROS), endogenously produced during metabolism, which acts as a second messenger. In skeletal muscles, hypoxia- or hyperthermia-induced increase in H₂O₂ might affect synaptic transmission by targeting the most redox-sensitive presynaptic compartment (Giniatullin et al., 2006). However, the effects of H₂O₂ as a signal molecule have not previously been studied in different patterns of the synaptic activity. Here, using optical and microelectrode recording of synaptic vesicle exocytosis, we studied the use-dependent action of low concentrations of H₂O₂ and other oxidants in the mouse neuromuscular junction. We found that: (i) H₂O₂ at low micromole concentrations inhibited both spontaneous and evoked transmitter releases from the motor nerve terminals in a use-dependent manner, (ii) the antioxidant N-acetylcysteine (NAC) eliminated these depressant effects, (iii) the influence of H₂O₂ was not associated with lipid oxidation suggesting a pure signaling action, (iv) the intracellular oxidant Chloramine-T or (v) the glutathione depletion produced similar to H₂O₂ depressant effects. Taken together, our data revealed the effective inhibition of neurotransmitter release by ROS, which was proportional to the intensity of synaptic activity at the neuromuscular junction. The combination of various oxidants suggested an intracellular location for redox-sensitive sites responsible for modulation of the synaptic transmission in the skeletal muscle.