Analysis of conserved active site residues in monoamine oxidase A and B and their three-dimensional molecular modeling

Network Pharmacology-Guided Evaluation of Ginger and Cornelian Cherry Extracts Against Depression and Metabolic Dysfunction in Estrogen-Deficient Chronic Stressed Rats

This study investigated the therapeutic effects of water extracts from Zingiber officinale Roscoe (ginger) and Cornus officinalis Siebold and Zucc. fruits (COF) water extracts on depression-like behavior and metabolic dysfunction in estrogen-deficient rats exposed to chronic mild stress (CMS). Network pharmacology analysis identified three bioactive compounds in ginger and four in COF, with 11 overlapping targets linked to both depression and metabolic pathways, primarily involving NR3C1, HTR2A, MAOA, and SLC6A4 genes associated with hypothalamic-pituitary-adrenal (HPA) axis regulation and neurotransmitter modulation. Ovariectomized rats received 200 mg/kg/day of ginger or COF extracts for 7 weeks, with a 4-week CMS protocol initiated at week 3. Both extracts significantly improved depression-like behaviors, memory performance, glucose tolerance, lipid profiles, and bone mineral density, normalized HPA axis markers (corticosterone and ACTH), and increased hippocampal serotonin and dopamine levels. Ginger demonstrated greater efficacy in improving memory and metabolic outcomes compared to COF. Molecular docking further validated these findings, revealing strong and stable interactions between key phytochemicals-such as hydroxygenkwanin and telocinobufagin-and target proteins MAOA, HTR2A, and NR3C1, supporting their mechanistic role in stress and mood regulation. These results support supplementing ginger and COF extracts as promising botanical interventions for estrogen-deficiency-related mood and metabolic disorders, with potential clinical application at a human-equivalent dose of 1.5 g/day.

Dynamic Model of Serotonin Presynapse and Its Application to Suicide Attempt in Patients with Bipolar Disorder

Suicide attempts are prevalent among patients with bipolar disorder (BD). Impaired serotonin (5-HT) system in the pathogenesis of suicide attempt is partially heritable. To quantify the combined effects of multiple genetic variants, we developed a dynamic model of the 5-HT presynapse with functionally integrated individual genetic variants. The model includes five genetic variants in 5-HT system genes (TPH2, SLC6A4, MAOA) and quantitatively assesses their influence on 5-HT synthesis, reuptake, and degradation. The model was validated on 140 unaffected individuals and tested on 101 BD patients. Predicted mean concentrations of 5-HT, 5-HT precursor, and degradation product were compared between BD patients with and without a history of attempted suicide, and unaffected individuals. The model consists of eight differential equations that describe the temporal concentration change of model outputs. Calculated concentrations in unaffected control individuals aligned with published experimentally measured values, validating our model. BD patients with a history of suicide attempt showed lower calculated concentrations of 5-HT degradation product 5-hydroxy-3-indolacetic acid (5-HIAA) compared to unaffected individuals (p = 0.044). Additionally, higher calculated concentrations of free cellular 5-HT (p = 0.048) and stored 5-HT (p = 0.047), with the effect size d = 0.35, were observed when comparing suicide attempters to non-attempters.. Our approach illuminated a complex interplay of genetic variants in 5-HT system genes that contributes to the risk of suicide attempt, with quantitative and personalized outputs unattainable through genetic association studies.

Advancing the understanding and management of Mpox: insights into epidemiology, disease pathways, prevention, and therapeutic strategies

Mpox, previously known as monkeypox, is a zoonotic viral disease caused by the Mpox virus (MPXV), a member of the Orthopoxvirus genus. This disease is of significant concern due to its zoonotic transmission, which can be challenging to control, its ability to spread easily from person to person, the potential for severe symptoms or even fatality, and its history of frequent global outbreaks. Despite the growing threat, there is still limited research on the pathophysiology of the disease and available disease-modifying treatments. To address this gap, the latest developments in Mpox epidemiology, viral variant detection, and advanced diagnostic tools for accurate MPXV detection have been reviewed. Ongoing preventive measures, including vaccination strategies, have also been examined. Additionally, the genomic and proteomic characteristics of MPXV have been explored, and network and pathway enrichment analyses have been performed to identify potential therapeutic targets. The findings presented in this manuscript suggest the potential for novel disease-modifying treatments. Moreover, emerging technologies, such as artificial intelligence and "big data," are playing a crucial role in advancing disease management and enhancing prevention strategies. This review emphasizes the evolving understanding of Mpox and MPXV variants and underscores the importance of continued research and public health initiatives to combat the disease and prevent future global outbreaks.

New phenylpiperazine-thiazolidine-2,4-dione hybrids targeting MAO inhibition: Synthesis, biological evaluation, kinetic study and in silico insights

Monoamine oxidase inhibitors are promising drug targets for many neurological diseases such as depression, Alzheimer's disease, and Parkinson's disease. The current study developed new hybrid compounds by merging phenyl piperazines, and 2,4-thiazolidinedione moieties based on their reported MAO inhibitory activities. The newly synthesized derivatives were screened for their MAOs inhibitory activity using in-vitro fluorometric assay. Most newly synthesized compounds elicited strong inhibitory activity against both hMAO isozymes. Hybrids 4a and 4c were the most potent hMAO-A inhibitors with IC50 values of 0.194 and 0.188 µM, respectively, compared to toloxatone as reference (IC50 = 1.080 µM), meanwhile, compound 4g exhibited the most potent inhibitory activity against MAO-B with an IC50 value of 0.330 µM. The kinetic study of compound 4c revealed that it exhibited a mixed inhibition mode with a Ki value of 3.4 nM. Compound 4c was evaluated against the normal SH-SY5Y cell line and found to be non-cytotoxic at its active inhibition concentration. ADME profiles of the most active hybrids 4a, 4c, 4j, and 4k revealed that they could serve as successful drug candidates showing good CNS penetration. Molecular docking simulations were executed for the most active motifs 4a and 4c to demonstrate the binding pattern with the target proteins explaining their potential inhibitory activity. Lastly, this study will significantly contribute to developing novel safe, effective medications for treating various neurological disorders in the foreseeable future.

Mechanism of nimodipine in treating neurodegenerative diseases: in silico target identification and molecular dynamic simulation

Aim

Nimodipine has shown neuroprotective effects in several studies; however, the specific targets and mechanisms remain unclear. This study aims to explore the potential targets and mechanisms of nimodipine in the treatment of neurodegenerative diseases (NDDs), providing a theoretical foundation for repurposing nimodipine for NDDs.

Methods

Drug-related targets were predicted using SwissTargetPrediction and integrated with results from CTD, GeneCards, and DrugBank. These targets were then cross-referenced with disease-related targets retrieved from CTD to identify overlapping targets. The intersecting targets were imported into STRING to construct a protein-protein interaction (PPI) network. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed using the R package ClusterProfiler. Molecular docking was carried out using AutoDock Vina, and the ligand-receptor complexes with the highest binding affinities were further simulated using GROMACS to assess the dynamic structural stability and interactions between the ligand and receptor in the dynamic system.

Results

A total of 33 intersecting drug-disease targets were identified. After constructing the PPI network and removing isolated targets, the network contained 28 nodes and 69 edges. Network degree analysis combined with enrichment analysis highlighted 12 key targets: CASP3, TNF, BAX, BCL2, IL1B, GSK3B, IL1A, MAOB, MAOA, BDNF, APP, and GFAP. Molecular docking analysis revealed binding energies greater than -6 kcal/mol for MAOA, GSK3B, MAOB, CASP3, BCL2, IL1B and APP. MAOA, with the highest binding energy of -7.343 kcal/mol, demonstrated a stable structure in a 100ns dynamic simulation with nimodipine, exhibiting an average dynamic binding energy of -52.39 ± 3.05 kcal/mol. The dynamic cross-correlation matrix (DCCM) of nimodipine resembled that of harmine, reducing the interactions between protein residues compared to the apo state (regardless of positive or negative correlations). Furthermore, nimodipine induced new negative correlations in residues 100-200 and 300-400.

Conclusion

Nimodipine binds to the internal pocket of MAOA and shows potential inhibitory effects. Given its brain-enrichment characteristics and proven neuroprotective effects, it is hypothesized that nimodipine may exert therapeutic effects on NDDs by inhibiting MAOA activity and modulating cerebral oxidative stress. Thus, MAOA emerges as a promising new target for nimodipine in the treatment of NDDs.

Microwave-Assisted Synthesis of Morpholine-Based Chalcones as Reversible MAO-A Inhibitors in the Management of Mental Depression

Background: Depression is one of the most serious and common health problems among the youth population and is responsible for the initiation of many diseases. As per the World Health Organization, 3.8% of the population suffers from mental depression, globally. The monoamine oxidase-A (MAO-A) enzyme is responsible for the degradation of neurotransmitters leading to lower levels of neurotransmitters. Methods: Chalcones (C1-C15) were synthesized by reacting substituted acetophenone with various benzaldehydes in a basic ethanolic solvent at 80 °C under microwave irradiation conditions. To compare the reaction time and product yield, a conventional method of synthesis of chalcones was also performed. The synthesized chalcones (C1-C15) were spectroscopically characterized and screened initially for inhibitory activities against MAO-A and MAO-B. The best active compounds were undertaken for IC50 determination against MAO-A enzyme followed by the reversibility of inhibition analysis and the antioxidant assay. Moreover, in silico molecular docking and ADME pharmacokinetic investigations were accomplished. Results: Most of the compounds inhibited MAO-A, specifically, compounds C14 and C6 exhibited the highest inhibition at IC50 values of 7.91 ± 0.08 μM and 8.45 ± 0.19 μM, respectively. Both these compounds exhibited a reversible MAO-A inhibition displaying up to 60% recovery of enzymatic activity when diluted with substrate (Tyramine). The results of the in silico study indicated docking scores of -9.56 Kcal/mol (C14) and -9.45 Kcal/mol (C6) and exhibited a π-π stacking interaction with the crucial amino acid Trp-397. The compounds were determined to cross the blood-brain barrier (BBB) and displayed favorable gastrointestinal (GI) absorption. Further, the antioxidant assay results demonstrated that the synthesized compounds possess modest free radical scavenging potential. Conclusions: This study displayed the MAO-A inhibitory potential of morpholine-substituted chalcones as a promising pharmacophore for the development of novel antidepressant lead compounds.

Molecular pathways: the quest for effective MAO-B inhibitors in neurodegenerative therapy

Neurodegenerative diseases like Parkinson's and Alzheimer's are a global health challenge due to their progressive degeneration, leading to cognitive decline and motor dysfunction. Monoamine oxidase B (MAO-B) enzyme is implicated in neurodegeneration, and developing inhibitors could be a promising therapeutic strategy. This review explores MAO-B activity molecular pathways, evaluates MAO-B inhibitors in neurodegenerative therapy, identifies challenges, and suggests future research directions. This review synthesizes findings from a range of scientific literature, including experimental studies, clinical trials, and biochemical analyses that focus on the role of MAO-B in neurodegeneration. Information was gathered from databases such as PubMed, Scopus, and Web of Science, ensuring a comprehensive overview of recent advancements in MAO-B inhibition strategies. The review reveals several promising MAO-B inhibitors that have demonstrated efficacy in preclinical models, as well as some that have progressed to clinical trials. Compounds such as rasagiline and selegiline have shown neuroprotective effects and benefits in symptom management in patients with Parkinson's disease. Furthermore, the review discusses novel inhibitors that target specific molecular pathways, enhancing the potential for improved therapeutic outcomes. However, several inhibitors also present challenges regarding their selectivity, side effects, and long-term efficacy. Research on MAO-B inhibitors for neurodegenerative diseases is crucial, with ongoing studies aiming for selective, potent molecules with fewer side effects and multimodal therapies.

The potential of MAO inhibitors as chemotherapeutics in cancer: A literature survey

Drug resistance in cancer is determined by genetic mutations and adaptations of tumor cells to drug treatments, raising a challenge in the treatment of cancer. Factors such as prolonged drug exposure, genetic variability among patients, and tumor heterogeneity have been established as contributors to rising incidence of drug resistance, prompting ongoing research into alternative therapies and combination treatments to overcome this challenge. Monoamine oxidases (MAOs), including both isoforms MAO-A and MAO-B, are mitochondrial enzymes responsible for the catabolism of monoamine neurotransmitters such as dopamine, norepinephrine, and serotonin. While these enzymes play a pivotal role in the nervous system, their role in tumorigenesis has garnered increasing attention in the last years. Recent studies, in fact, have highlighted the potential of MAO inhibitors (MAOIs) as antitumor agents, emphasizing their use as standalone treatments or in synergy with traditional anticancer therapies, focusing on pathways involved in tumorigenesis. This review aims to provide a comprehensive overview of MAOIs currently under study for their potential antitumor activity, focusing on their structural characteristics, mechanisms of action, and efficacy in preclinical and clinical settings, referencing key articles in the field.

Targeting MAO-B with Small-Molecule Inhibitors: A Decade of Advances in Anticancer Research (2012-2024)

Monoamine oxidase B (MAO-B) is a key enzyme in the mitochondrial outer membrane, pivotal for the oxidative deamination of biogenic amines. Its overexpression has been implicated in the pathogenesis of several cancers, including glioblastoma and colorectal, lung, renal, and bladder cancers, primarily through the increased production of reactive oxygen species (ROS). Inhibition of MAO-B impedes cell proliferation, making it a potential therapeutic target. Various monoamine oxidase B inhibitors have shown promise in inhibiting tumor growth and inducing apoptosis across different cancer types. In this review, we investigate MAO-B network biology, which highlighted glycolysis pathways as notable links between MAO-B and cancer. Further molecular modeling analysis illustrated the basis of MAO-B ligand binding, revealing a hydrophobic binding pocket, with key residues such as Tyr398 and Tyr435 playing crucial roles in substrate oxidation. MAO-B inhibitors that were reportsed in the literature (2012-2024) and their potential application in cancer therapy were discussed, highlighting key molecular scaffolds, such as propargyl analogs of phenyl alkyl amines, hydrazine derivatives, cyclopropylamine derivatives, MAO-B activated pro-drugs, and natural phenylpropanoid derivatives. The reported literature underscores the therapeutic potential of MAO-B inhibitors as versatile anticancer agents, warranting further investigation to optimize their efficacy and specificity across various malignancies.

Structural Conversion of Serotonin into Amyloid-like Nanoassemblies Conceptualizes an Unexplored Neurotoxicity Risk

The neuromodulator 5-hydroxytryptamine, known as serotonin, plays a key regulatory role in the central nervous system and peripheral organs; however, several research revelations have indicated a direct link between the oxidation of serotonin and a plethora of detrimental consequences. Hence, the question of how several neuronal and non-neuronal complications originate via serotonin oxidation remains an important area of investigation. Here, we show the autoxidation-driven structural conversion of serotonin into hemolytic and cytotoxic amyloid-like nanoassemblies under physiological conditions. We also observed the catalysis of serotonin oxidation in the presence of Aβ1-42 amyloid fibrils and Cu(II) ions. The serotonin nanostructures generated from its spontaneous and amyloid-mediated oxidation exhibited typical structural and functional characteristics of amyloid entities, and their effective internalization in neuroblastoma cells caused cell-damaging effects via cytosolic aggregation, ROS generation and necrosis/apoptosis-mediated cell death. Since imbalance in the serotonin level is known to predispose diverse pathological conditions including serotonin syndrome, atherosclerosis, diabetes, and Alzheimer's diseases, our results on the formation of cytotoxic nanoassemblies via serotonin oxidation may provide important evidence for understanding the molecular mechanism of serotonin associated complications.

Mechanisms involved in the antidepressant-like action of orally administered 5-((4-methoxyphenyl)thio)benzo[c][1,2,5]thiadiazole (MTDZ) in male and female mice

RATIONALE

The compound 5-((4-methoxyphenyl)thio)benzo[c][1,2,5]thiadiazole (MTDZ) has recently been shown to inhibit in vitro acetylcholinesterase activity, reduce cognitive damage, and improve neuropsychic behavior in mice, making it a promising molecule to treat depression.

OBJECTIVES

This study investigated the antidepressant-like action of MTDZ in mice and its potential mechanisms of action.

RESULTS

Molecular docking assays were performed and suggested a potential inhibition of monoamine oxidase A (MAO-A) by MTDZ. The toxicity study revealed that MTDZ displayed no signs of toxicity, changes in oxidative parameters, or alterations to biochemistry markers, even at a high dose of 300 mg/kg. In behavioral tests, MTDZ administration reduced immobility behavior during the forced swim test (FST) without adjusting the climbing parameter, suggesting it has an antidepressant effect. The antidepressant-like action of MTDZ was negated with the administration of 5-HT1A, 5-HT1A/1B, and 5-HT3 receptor antagonists, implying the involvement of serotonergic pathways. Moreover, the antidepressant-like action of MTDZ was linked to the NO system, as L-arginine pretreatment inhibited its activity. The ex vivo assays indicated that MTDZ normalized ATPase activity, potentially linking this behavior to its antidepressant-like action. MTDZ treatment restricted MAO-A activity in the cerebral cortices and hippocampi of mice, proposing a selective inhibition of MAO-A associated with the antidepressant-like effect of the compound.

CONCLUSIONS

These findings suggest that MTDZ may serve as a promising antidepressant agent due to its selective inhibition of MAO-A and the involvement of serotonergic and NO pathways.

The Benzoxazole Heterocycle: A Comprehensive Review of the Most Recent Medicinal Chemistry Developments of Antiproliferative, Brain-Penetrant, and Anti-inflammatory Agents

The benzoxazole is one of the most widely exploited heterocycles in drug discovery. Natural occurring and synthetic benzoxazoles show a broad range of biological activities. Many benzoxazoles are available for treating several diseases, and, to date, a few are in clinical trials. Moreover, an ever-increasing number of benzoxazole derivatives are under investigation in the early drug discovery phase and as potential hit or lead compounds. This perspective is an attempt to thoroughly review the rational design, the structure-activity relationship, and the biological activity of the most notable benzoxazoles developed during the past 5 years (period 2019-to date) in cancers, neurological disorders, and inflammation. We also briefly overviewed each target and its role in the disease. The huge amount of work examined suggests the great potential of the scaffold and the high interest of the scientific community in novel biologically active compounds containing the benzoxazole core.

Tyrosinase deficiency impairs social novelty preference in mice

OBJECTIVE

Tyrosinase is a rate-limiting enzyme for the biosynthesis of melanin pigment in peripheral tissues, such as skin and the retina. We recently reported the expression and enzymatic activity of tyrosinase as well as its protective effects against oxidative stress-induced protein damage in the mouse brain. The functional role of tyrosinase in the central nervous system, however, remains largely unknown. In the present study, we investigated the involvement of tyrosinase in social behavior in mice.

METHODS

Pigmented C57BL/10JMsHir (B10) and tyrosinase-deficient albino B10.C- Tyr c /Hir (B10-c) mice were subjected to the three-chamber sociability test to assess sociability and social novelty preference. In addition, we measured the mRNA expression of genes involved in catecholamine metabolism in the hippocampus by real-time quantitative PCR analysis.

RESULTS

The results obtained showed that tyrosinase deficiency impaired social novelty preference, but not sociability in mice. We also found that the hippocampal expression of genes involved in catecholamine metabolism, such as monoamine oxidase A and catechol-O-methyltransferase , were significantly decreased in tyrosinase-deficient B10-c mice.

CONCLUSION

These results suggest that tyrosinase activity is functionally involved in the phenotypic expression of social behavior, particularly social novelty preference, in mice. The present study will advance our understanding of the functional role of tyrosinase in the central nervous system.

Synthesis and Monoamine Oxidase Inhibitory Activity of Halogenated Flavones

Small molecule neurotransmitters containing amines are metabolized by monoamine oxidase (MAO) in the nervous system. Monoamine oxidase inhibitors are a valuable class of drugs prescribed for the management of neurological disorders, including depression. A series of halogenated flavonoids similar to the dietary flavonoid acacetin were designed as selective MAO-B inhibitors. MAO-A and -B inhibition of 36 halogenated flavones were tested. The halogens (fluorine and chlorine) were placed at positions 5 and 7 on ring A of the flavone scaffold. All compounds were selective MAO-B inhibitors with micro- and nanomolar IC50 values. Compounds 9f, 10a-c, 11a-c, 11g,h, and 11l displayed inhibitory activity toward MAO-B with IC50 values between 16 to 74 nM. We conclude that halogenated flavonoids are promising molecules in pursuit of developing new agents for neurological disorders.

Stromal-derived MAOB promotes prostate cancer growth and progression

Prostate cancer (PC) develops in a microenvironment where the stromal cells modulate adjacent tumor growth and progression. Here, we demonstrated elevated levels of monoamine oxidase B (MAOB), a mitochondrial enzyme that degrades biogenic and dietary monoamines, in human PC stroma, which was associated with poor clinical outcomes of PC patients. Knockdown or overexpression of MAOB in human prostate stromal fibroblasts indicated that MAOB promotes cocultured PC cell proliferation, migration, and invasion and co-inoculated prostate tumor growth in mice. Mechanistically, MAOB induces a reactive stroma with activated marker expression, increased extracellular matrix remodeling, and acquisition of a protumorigenic phenotype through enhanced production of reactive oxygen species. Moreover, MAOB transcriptionally activates CXCL12 through Twist1 synergizing with TGFβ1-dependent Smads in prostate stroma, which stimulates tumor-expressed CXCR4-Src/JNK signaling in a paracrine manner. Pharmacological inhibition of stromal MAOB restricted PC xenograft growth in mice. Collectively, these findings characterize the contribution of MAOB to PC and suggest MAOB as a potential stroma-based therapeutic target.

Monoamine Oxidase-A (MAO-A) Inhibitors Screened from the Autodisplayed Fv-Antibody Library

Serotonin-like mimotopes were screened from the Fv-antibody library to be used as inhibitors against monoamine oxidase A (MAO-A). The Fv-antibody [corresponding to the VH region of immunoglobulin G (IgG)] consists of three complementarity-determining regions and four frame regions. The Fv-antibody library was prepared by site-directed mutagenesis of CDR3, which consists of 11 amino acid residues. Three target clones were screened from the Fv-antibody library, and the binding affinity of the screened clones to the monoclonal anti-serotonin antibody was analyzed using fluorescence-activated cell sorting. The screened Fv-antibodies were expressed as soluble proteins fused with green fluorescence protein. Additionally, the screened CDR3 regions (11 residues) of the selected Fv-antibodies were synthesized as peptides with linking amino acid residues. The binding constants (KD) of the three serotonin-like mimotopes (Fv-antibodies and peptides) were estimated using a surface plasmon resonance biosensor. The inhibitory activity (IC50) of the serotonin-like mimotopes (Fv-antibodies and peptides) was estimated separately for MAO-A and MAO-B enzymes and compared with that of conventional inhibitors. Finally, the screened serotonin-like mimotopes were used to treat a cell line (SH-SY5Y, ATCC code: CRL-2266) expressing serotonin receptors. This was done to confirm the following two aspects: (1) the binding of mimotopes to the serotonin receptors on the cell surface and (2) the inhibitory activity of mimotopes against MAO-A enzymes in the cell lysates.

Cardioprotective Role of Tinospora cordifolia against Trimethylamine-N-Oxide and Glucose Induced Stress in Rat Cardiomyocytes

BACKGROUND

Type 2 diabetes has become a concern issue that affects the quality of life and can increase the risk of cardiac insufficiency elevating the threat to the life safety of patients. A recognized cause of cardiac insufficiency is diabetic cardiomyopathy, chronic hyperglycemia, and myocardial lipotoxicity which can reduce the myocardial contractile performance, and enhance the cardiomyocyte hypertrophy and interstitial fibrosis. The cause of diabetic cardiomyopathy is multi-factorial which includes oxidative stress, insulin resistance, inflammation, apoptosis, and autophagy. Recent clinical studies have suggested the dysbiosis of gut microbiota, secretion of metabolites, and their diffusion in to the host as to have direct detrimental effects on the cardiac contractility.

MATERIALS AND METHODS

In the present paper, we have done in silico studies including molecular interaction of phytoconstituents of Tinospora cordifolia against reactive oxygen species producing proteins. Whereas, in vitro studies were conducted on H9C2 cardiac cells including cell morphological examination, level of reactive oxygen species, cell count-viability, apoptotic status, in the presence of high glucose, trimethylamine-n-oxide, and plant extracts which were determined through cell analyzer and microscopic assays.

RESULTS

The treatment of high glucose and trimethylamine-n-oxide was found to be increase the cardiac stress approximately two fold by attenuating hypertrophic conditions, oxidative stress, and apoptosis in rat cardiomyocytes, and Tinospora cordifolia was found to be a cardioprotective agent.

CONCLUSION

Conclusively, our study has reported that the Indian medicinal plant Tinospora cordifolia has the ability to treat diabetic cardiomyopathy. Our study can open up a new herbal therapeutic strategy against diabetic cardiomyopathy.

Protective effects of niacin following high fat rich diet: an in-vivo and in-silico study

Niacin had long been understood as an antioxidant. There were reports that high fat diet (HFD) may cause psychological and physical impairments. The present study was aimed to experience the effect of Niacin on % growth rate, cumulative food intake, motor activity and anxiety profile, redox status, 5-HT metabolism and brain histopathology in rats. Rats were administered with Niacin at a dose of 50 mg/ml/kg body weight for 4 weeks following normal diet (ND) and HFD. Behavioral tests were performed after 4 weeks. Animals were sacrificed to collect brain samples. Biochemical, neurochemical and histopathological studies were performed. HFD increased food intake and body weight. The exploratory activity was reduced and anxiety like behavior was observed in HFD treated animals. Activity of antioxidant enzymes was decreased while oxidative stress marker and serotonin metabolism in the brain of rat were increased in HFD treated animals than ND fed rats. Morphology of the brain was also altered by HFD administration. Conversely, Niacin treated animals decreased food intake and % growth rate, increased exploratory activity, produced anxiolytic effects, decreased oxidative stress and increased antioxidant enzyme and 5-HT levels following HFD. Morphology of brain is also normalized by the treatment of Niacin following HFD. In-silico studies showed that Niacin has a potential binding affinity with degradative enzyme of 5-HT i.e. monoamine oxidase (MAO) A and B with an energy of ~ - 4.5 and - 5.0 kcal/mol respectively. In conclusion, the present study showed that Niacin enhanced motor activity, produced anxiolytic effect, and reduced oxidative stress, appetite, growth rate, increased antioxidant enzymes and normalized serotonin system and brain morphology following HFD intake. In-silico studies suggested that increase 5-HT was associated with the binding of MAO with Niacin subsequentially an inhibition of the degradation of monoamine. It is suggested that Niacin has a great antioxidant potential and could be a good therapy for the treatment of HFD induced obesity.

Modified Tacrine Derivatives as Multitarget-Directed Ligands for the Treatment of Alzheimer's Disease: Synthesis, Biological Evaluation, and Molecular Modeling Study

To develop multitarget-directed ligands (MTDLs) as potential treatments for Alzheimer's disease (AD) and to shed light on the effect of the chromene group in designing these ligands, 35 new tacrine-chromene derivatives were designed, synthesized, and biologically evaluated. Compounds 5c and 5d exhibited the most desirable multiple functions for AD; they were strong hAChE inhibitors with IC₅₀ values of 0.44 and 0.25 μM, respectively. Besides, their potent BuChE inhibitory activity was 10- and 5-fold more active than rivastigmine with IC₅₀ = 0.08 and 0.14 μM, respectively. Moreover, they could bind to the peripheral anionic site (PAS), influencing Aβ aggregation and decreasing Aβ-related neurodegeneration, especially compound 5d, which was 8 times more effective than curcumin with IC₅₀ = 0.74 μM and 76% inhibition at 10 μM. Compounds 5c and 5d showed strong BACE-1 inhibition at the submicromolar level with IC₅₀ = 0.38 and 0.44 μM, respectively, which almost doubled the activity of curcumin. They also showed single-digit micromolar inhibitory activity against MAO-B with IC₅₀ = 5.15 and 2.42 μM, respectively. They also had antioxidant activities and showed satisfactory metal-chelating properties toward Fe⁺², Zn⁺², and Cu⁺², inhibiting oxidative stress in AD brains. Furthermore, compounds 5c and 5d showed acceptable relative safety upon normal cells SH-SY5Y and HepG2. It was shown that 5c and 5d were blood-brain barrier (BBB) penetrants by online prediction. Taken together, these multifunctional properties highlight that compounds 5c and 5d can serve as promising candidates for the further development of multifunctional drugs against AD.

Structure-Based Design of Novel MAO-B Inhibitors: A Review

With the significant growth of patients suffering from neurodegenerative diseases (NDs), novel classes of compounds targeting monoamine oxidase type B (MAO-B) are promptly emerging as distinguished structures for the treatment of the latter. As a promising function of computer-aided drug design (CADD), structure-based virtual screening (SBVS) is being heavily applied in processes of drug discovery and development. The utilization of molecular docking, as a helping tool for SBVS, is providing essential data about the poses and the occurring interactions between ligands and target molecules. The current work presents a brief discussion of the role of MAOs in the treatment of NDs, insight into the advantages and drawbacks of docking simulations and docking software, and a look into the active sites of MAO-A and MAO-B and their main characteristics. Thereafter, we report new chemical classes of MAO-B inhibitors and the essential fragments required for stable interactions focusing mainly on papers published in the last five years. The reviewed cases are separated into several chemically distinct groups. Moreover, a modest table for rapid revision of the revised works including the structures of the reported inhibitors together with the utilized docking software and the PDB codes of the crystal targets applied in each study is provided. Our work could be beneficial for further investigations in the search for novel, effective, and selective MAO-B inhibitors.

2,1-Benzothiazine - (quinolin/thiophen)yl hydrazone frameworks as new monoamine oxidase inhibitory agents; synthesis, in vitro and in silico investigation

Two series of new 2,1-benzothiazine derivatives have been synthesized by condensation of 4-hydrazono-1-methyl-3,4-dihydro-1H-benzo[c][1,2]thiazine 2,2-dioxide (5) with 2-chloroquinoline-3-carbaldehydes and acetylthiophenes to acquire new heteroaryl ethylidenes 7(a-f) and 9(a-k) in excellent yields. After characterization by FTIR, ¹H NMR, ¹³C NMR and elemental analyses, the newly synthesized analogues were investigated against monoamine oxidase enzymes (MAO A and MAO B). The titled compounds exhibited activity in the lower micromolar range among which 9e was the most potent compound against MAO A with IC₅₀ of 1.04 ± 0.01 μM whereas 9h proved to be the most potent derivative against MAO B with an IC₅₀ value of 1.03 ± 0.17 μM. Furthermore, in vitro results were further endorsed by molecular docking studies to determine the interaction between the potent compounds and the enzyme active site. These newly synthesized compounds represent promising hits for the development of safer and potent lead molecules for therapeutic use against depression and other neurological diseases.

In Silico Evaluation and In Vitro Determination of Neuroprotective and MAO-B Inhibitory Effects of Pyrrole-Based Hydrazones: A Therapeutic Approach to Parkinson's Disease

Parkinson's disease is a huge burden in modern medicinal practice. A serious drawback of current antiparkinsonian therapy is its symptomatic nature. This directed our investigations in the search for new more potent derivatives, affecting not only the loss of dopaminergic neurons but also the oxidative damage of neuronal cells. Thus in vitro neurotoxicity and neuroprotective analysis on a group of N-pyrrolyl hydrazide-hydrazones were performed. The neurotoxicity of the target derivatives was determined on a subcellular level in isolated rat synaptosomes, mitochondria and microsomes determining their effect on cellular vitality, GSH depletion and MDA production. The neuroprotective effects of the evaluated hydrazones were measured in three models of induced oxidative stress: 6-OHDA, t-BuOOH and Fe²⁺/AA-induced lipid peroxidation. Molecular docking simulations along with in vitro evaluation of MAO-B inhibitory potential of the target molecules were also performed. The results identified the ethyl 5-(4-bromophenyl)-1-(3-hydrazinyl-3-oxopropyl)-2-methyl-1H-pyrrole-3-carboxylate (12) as the most promising compound with the lowest neurotoxicity and highest neuroprotection on all evaluated parameters and inhibiting the hMAOB enzyme by 50%, comparable with the activity of the reference, Selegiline. The compatibility of the in silico and in vitro evaluations is a good prerequisite for these methods to be applied in future assessment of pyrrole-based compounds as anti-Parkinson agents.

Phytoestrogen Coumestrol Selectively Inhibits Monoamine Oxidase-A and Amyloid β Self-Aggregation

Pueraria lobata leaves contain a variety of phytoestrogens, including flavonoids, isoflavonoids, and coumestan derivatives. In this study, we aimed to identify the active ingredients of P. lobata leaves and to elucidate their function in monoamine oxidase (MAO) activation and Aβ self-aggregation using in vitro and in silico approaches. To the best of our knowledge, this is the first study to elucidate coumestrol as a selective and competitive MAO-A inhibitor. We identified that coumestrol, a coumestan-derivative, exhibited a selective inhibitory effect against MAO-A (IC₅₀ = 1.99 ± 0.68 µM), a key target protein for depression. In a kinetics analysis with 0.5 µg MAO-A, 40–160 µM substrate, and 25 °C reaction conditions, coumestrol acts as a competitive MAO-A inhibitor with an inhibition constant of 1.32 µM. During an in silico molecular docking analysis, coumestrol formed hydrogen bonds with FAD and pi–pi bonds with hydrophobic residues at the active site of the enzyme. Moreover, based on thioflavin-T-based fluorometric assays, we elucidated that coumestrol effectively prevented self-aggregation of amyloid beta (Aβ), which induces an inflammatory response in the central nervous system (CNS) and is a major cause of Alzheimer’s disease (AD). Therefore, coumestrol could be used as a CNS drug to prevent diseases such as depression and AD by the inhibition of MAO-A and Aβ self-aggregation.

In Vitro and In Silico Characterization of Kurarinone as a Dopamine D1A Receptor Antagonist and D2L and D4 Receptor Agonist

Alterations in the expression and/or activity of brain G-protein-coupled receptors (GPCRs) such as dopamine D₁R, D_2LR, D₃R, and D₄R, vasopressin V_1AR, and serotonin 5-HT_1AR are noted in various neurodegenerative diseases (NDDs). Since studies have indicated that flavonoids can target brain GPCRs and provide neuroprotection via inhibition of monoamine oxidases (hMAOs), our study explored the functional role of kurarinone, an abundant lavandulated flavonoid in Sophora flavescens, on dopamine receptor subtypes, V_1AR, 5-HT_1AR, and hMAOs. Radioligand binding assays revealed considerable binding of kurarinone on D₁R, D_2LR, and D₄R. Functional GPCR assays unfolded the compound's antagonist behavior on D₁R (IC₅₀ 42.1 ± 0.35 μM) and agonist effect on D_2LR and D₄R (EC₅₀ 22.4 ± 3.46 and 71.3 ± 4.94 μM, respectively). Kurarinone was found to inhibit hMAO isoenzymes in a modest and nonspecific manner. Molecular docking displayed low binding energies during the intermolecular interactions of kurarinone with the key residues of the deep orthosteric binding pocket and the extracellular loops of D₁R, D_2LR, and D₄R, validating substantial binding affinities to these prime targets. With appreciable D_2LR and D₄R agonism and D₁R antagonism, kurarinone might be a potential compound that can alleviate clinical symptoms of Parkinson's disease and other NDDs.

High-Throughput Screening and Molecular Dynamics Simulation of Natural Product-like Compounds against Alzheimer's Disease through Multitarget Approach

Alzheimer’s disease (AD) is a progressive neurological disorder that affects 50 million people. Despite this, only two classes of medication have been approved by the FDA. Therefore, we have planned to develop therapeutics by multitarget approach. We have explored the library of 2029 natural product-like compounds for their multi-targeting potential against AD by inhibiting AChE, BChE (cholinergic pathway) MAO-A, and MOA-B (oxidative stress pathway) through in silico high-throughput screening and molecular dynamics simulation. Based on the binding energy of these target enzymes, approximately 189 compounds exhibited a score of less than −10 kcal/mol against all targets. However, none of the control inhibitors exhibited a binding affinity of less than −10 kcal/mol. Among these, the top 10 hits of compounds against all four targets were selected for ADME-T analysis. As a result, only F0850-4777 exhibited an acceptable range of physicochemical properties, drug-likeness, pharmacokinetics, and suitability for BBB permeation with high GI-A and non-toxic effects. The molecular dynamics study confirmed that F0850-4777 remained inside the binding cavity of targets in a stable conformation throughout the simulation and Prime-MM/GBSA study revealed that van der Waals’ energy (ΔG_vdW) and non-polar solvation or lipophilic energy (ΔG_{Sol_Lipo}) contribute favorably towards the formation of a stable protein–ligand complex. Thus, F0850-4777 could be a potential candidate against multiple targets of two pathophysiological pathways of AD and opens the doors for further confirmation through in vitro and in vivo systems.

Navigating into the Chemical Space of Monoamine Oxidase Inhibitors by Artificial Intelligence and Cheminformatics Approach

The monoamine oxidase (MAO) enzyme class is a prevalent target for many neurodegenerative and depressive disorders. Even though scrutinization of many promising drugs for the treatment of MAO inhibition has been carried out in recent times, a conclusive structural requirement for potent activity needs to be developed. Numerous approaches have been examined for the identification of structural features for potent MAO inhibitors (MAOIs) that mainly involve an array of computational studies, synthetic approaches, and biological evaluation. In this paper, we have analyzed ∼2200 well-known MAOIs to expand perceptions in the chemical space of MAOIs. The physicochemical properties of the MAOIs disclosed a discernible hydrophobic feature making a bunch discrete from the central nervous system (CNS) acting drugs, as exposed using the principal component analysis (PCA). The Murcko scaffold structure study revealed unfavorable and favorable scaffold structures, in both data sets, with the highest biological activity shown by the 3-phenyl-2H-chromen-2-one scaffold. This scaffold showed a polypharmacological effect. R-group disintegration and automatic structure-activity relationship (SAR) study resulted in identification of substructures responsible for the inhibitory bioactivity of the MAO-A and MAO-B enzymes. Moreover, with activity cliff analysis, significant biological activity was detected by simple molecular conversion in the chemical compound structure. In addition, we used the machine learning tool to generate a hypothesis wherein pyrazole, benzene ring, and amide containing structural functionalities can exhibit potential biological activities. This hypothesis revealed that CNS target drugs, C4155, C13390, C21265, C43862, C31524, C24810, C37100, C42075, and C43644, could be repurposed as valuable candidates for the MAO-B enzyme. For researchers, this study will bring new perceptions in the discovery and development of MAOIs and direct lead and hit optimization for the progress of small molecules beneficial for MAO-targeting associated diseases.

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.

Monoamine Oxidase Inhibition by Major Tanshinones from Salvia miltiorrhiza and Selective Muscarinic Acetylcholine M4 Receptor Antagonism by Tanshinone I

Monoamine oxidases (MAOs) and muscarinic acetylcholine receptors (mAChRs) are considered important therapeutic targets for Parkinson's disease (PD). Lipophilic tanshinones are major phytoconstituents in the dried roots of Salvia miltiorrhiza that have demonstrated neuroprotective effects against dopaminergic neurotoxins and the inhibition of MAO-A. Since MAO-B inhibition is considered an effective therapeutic strategy for PD, we tested the inhibitory activities of three abundant tanshinone congeners against recombinant human MAO (hMAO) isoenzymes through in vitro experiments. In our study, tanshinone I (1) exhibited the highest potency against hMAO-A, followed by tanshinone IIA and cryptotanshinone, with an IC50 less than 10 µM. They also suppressed hMAO-B activity, with an IC50 below 25 µM. Although tanshinones are known to inhibit hMAO-A, their enzyme inhibition mechanism and binding sites have yet to be investigated. Enzyme kinetics and molecular docking studies have revealed the mode of inhibition and interactions of tanshinones during enzyme inhibition. Proteochemometric modeling predicted mAChRs as possible pharmacological targets of 1, and in vitro functional assays confirmed the selective M4 antagonist nature of 1 (56.1% ± 2.40% inhibition of control agonist response at 100 µM). These findings indicate that 1 is a potential therapeutic molecule for managing the motor dysfunction and depression associated with PD.

Evaluation of monoamine oxidase A and B type enzyme occupancy using non-radiolabelled tracers in rat brain

Monoamine oxidase (MAO) enzymes, type A and B metabolise the amine neurotransmitters of the body. Selective inhibition of either enzyme is an approach for treating neurodegenerative and stress-induced disorders, and inhibition of an enzyme is proportional to the binding of the MAO inhibitor. Conventionally, the binding of test compounds to enzymes is assessed by radiolabelled ligands in ex vivo and in vivo occupancy assays. Regulatory restrictions and turnaround time are the limitations of the methods that use radiolabelled ligands. But the use of non-radiolabelled tracers and sensitive mass spectrometry (LC-MS/MS) based assays accelerated the determination of target occupancy in pre-clinical species. A report on use of non-radiolabelled ligand in in vivo MAO occupancy assay is not available. The objectives of the present study were to optimise non-radiolabelled harmine and deprenyl as selective tracers in MAO-A and MAO-B occupancy assays and evaluate MAO occupancy of test compounds in rat brain. Tracer optimisation resulted in a detectable, stable, and low ratio (<3.0) of tracer concentrations between any two brain tissues. In occupancy assay, tracer was intravenously administered (10 μg/kg, harmine or 60 μg/kg, L-deprenyl) after the treatment with test compound (clorgyline or tranylcypromine or pargyline or phenelzine or thioperamide). Specific brain tissues were isolated at a defined interval and tracer concentrations were quantified using LC-MS/MS method. Pre-treatment with MAO inhibitors resulted in a decrease (maximum, 80-85%) in harmine or an increase (maximum, 85-300%) in L-deprenyl concentrations. But we considered the change in tracer concentration, relative to the vehicle and positive control groups to calculate MAO occupancy. The observed selectivity and ratio of occupancies (ED₅₀) of test compound towards MAO-A and MAO-B are comparable with the results from in vitro radiolabelled ligand-based inhibition assay. The results demonstrated the application of these non-radiolabelled tracers as suitable pre-clinical tools to determine MAO occupancy.

Evaluation of the inhibition of monoamine oxidase A by bioactive coffee compounds protecting serotonin degradation

Monoamine oxidase A (MAO-A) is a major enzyme responsible for the deamination of neurotransmitters such as serotonin (5-HT) in the central nervous system. The decrease in 5-HT levels is accompanied by disorders at the affective and somatic levels, leading to depression and disorders of the satiety center. The aim of this study was to evaluate the degree of MAO-A inhibition by chlorogenic acids, as well as green, light-, and dark-roasted coffee extracts and bioactive compounds from beans of the species Coffea canephora and Coffea arabica. Data for analysis was obtained using isothermal titration calorimetry and molecular docking. The results showed that caffeine and ferulic acid, as well as green Robusta coffee, demonstrated the greatest inhibition of MAO-A activity, which may increase the bioavailability of serotonin. We believe that green coffee shows potential antidepressant activity by inhibiting MAO-A, and may be used for treating depression and potentially, type 2 diabetes.

Synthesis of 2′-(1,2,3-triazoyl)-acetophenones: molecular docking and inhibition of in vitro monoamine oxidase activity

The synthesis of 2′-(1,2,3-triazoyl)-acetophenones by a CuAAC using thiourea as a ligand, molecular docking and MAO activity analyses were performed.

Virtual screening and drug repurposing experiments to identify potential novel selective MAO-B inhibitors for Parkinson's disease treatment

The main study's purpose is to detect novel natural products (NPs) that are potentially selective MAO-B inhibitors and, additionally, to computationally reposition the marketed drugs with a new therapeutic role for Parkinson's disease. To reach the goals, 3D similarity search, docking, ADMETox, and drug repurposing approaches were employed. Thus, an unbiased benchmarking dataset was built including selective and nonselective inhibitors for MAO-B compliant with both ligand- and structure-based virtual screening approaches. A retrospective and prospective mining scenario was applied to SPECS NP and DrugBank databases to detect novel scaffolds with potential benefits for Parkinson's disease patients. Out of the three best selected natural products, cardamomin showed excellently predicted drug-like properties, superior pharmacological profile, and specific interactions with MAO-B active site, indicating a potential selectivity over MAO-B. Two marketed drugs, fenamisal and monobenzone, were proposed as promising candidates repurposed for Parkinson's disease. The application of shape, physicochemical, and electrostatic similarity searches protocol emerged as a plausible solution to explore MAO-B inhibitors selectivity. This protocol might serve as a rewarding tool in early drug discovery and can be extended to other protein targets.

Bioinformatic Analysis of the Flavin-Dependent Amine Oxidase Superfamily: Adaptations for Substrate Specificity and Catalytic Diversity

The flavin-dependent amine oxidase (FAO) superfamily consists of over 9000 nonredundant sequences represented in all domains of life. Of the thousands of members identified, only 214 have been functionally annotated to date, and 40 unique structures are represented in the Protein Data Bank. The few functionally characterized members share a catalytic mechanism involving the oxidation of an amine substrate through transfer of a hydride to the FAD cofactor, with differences observed in substrate specificities. Previous studies have focused on comparing a subset of superfamily members. Here, we present a comprehensive analysis of the FAO superfamily based on reaction mechanism and substrate recognition. Using a dataset of 9192 sequences, a sequence similarity network, and subsequently, a genome neighborhood network were constructed, organizing the superfamily into eight subgroups that accord with substrate type. Likewise, through phylogenetic analysis, the evolutionary relationship of subgroups was determined, delineating the divergence between enzymes based on organism, substrate, and mechanism. In addition, using sequences and atomic coordinates of 22 structures from the Protein Data Bank to perform sequence and structural alignments, active-site elements were identified, showing divergence from the canonical aromatic-cage residues to accommodate large substrates. These specificity determinants are held in a structural framework comprising a core domain catalyzing the oxidation of amines with an auxiliary domain for substrate recognition. Overall, analysis of the FAO superfamily reveals a modular fold with cofactor and substrate-binding domains allowing for diversity of recognition via insertion/deletions. This flexibility allows facile evolution of new activities, as shown by reinvention of function between subfamilies.

New role for crinamine as a potent, safe and selective inhibitor of human monoamine oxidase B: In vitro and in silico pharmacology and modeling

ETHNOPHARMACOLOGICAL RELEVANCE

The development of selective inhibitors of monoamine oxidase B (MAO-B) has been essential in treating Parkinson's disease. However, the apparent hepatotoxicity and drug-drug interactions of current inhibitors accentuate the need for the development of novel pharmacotherapies. Crossyne guttata (L.) D. & U. Müll-Doblies is used frequently by Rastafarian bush doctors to treat alcoholism, a disorder which is also accentuated by MAO.

OBJECTIVE

The study sought to isolate, identify and characterise the biologically active constituents of C. guttata based on their ability to inhibit the MAO enzymes.

MATERIALS AND METHODS

Column chromatography was used to isolate the biologically active alkaloids of C. guttata. The ability of the alkaloids to inhibit the biotransformation of 4-aminoantipyrine by the MAO enzymes was evaluated in vitro. In silico docking was conducted using AutoDock Vina server while the pharmacokinetic properties of the compounds were evaluated using SwissADME.

RESULTS

Chromatographic separation of an ethanolic fraction of C. guttata yielded the alkaloids crinamine 1 and epibuphanisine 2. 1 and 2 along with structurally related alkaloids haemanthamine 3 and haemanthidine 4 were evaluated for their ability to inhibit the action of isozymes of MAO in vitro. Alkaloids effected submicromolar IC₅₀ values against MAO-B, the most potent of which being crinamine 1 (0.014 μM) > haemanthidine 4 (0.017 μM) > epibuphanisine 2 (0.039 μM) > haemanthamine 3 (0.112 μM). Binding energies of the alkaloids correlated well with their inhibitory potential with crinamine displaying the best binding efficacy and binding energy score with MAO-B.

DISCUSSION AND CONCLUSION

Crinamine and epibuphanisine exhibited potent and selective inhibitory activity towards MAO-B. After comprehensive in silico investigations encompassing robust molecular docking analysis, the drug-like attributes and safety of the alkaloids suggest the crinamine is a potentially safe drug for human application.

In Vitro and in Silico Human Monoamine Oxidase Inhibitory Potential of Anthraquinones, Naphthopyrones, and Naphthalenic Lactones from Cassia obtusifolia Linn Seeds

In recent years, Cassia seed extract has been reported as a neuroprotective agent in various models of neurodegeneration, mainly via an antioxidant mechanism. However, no one has previously reported the effects of Cassia seed extract and its phytochemicals on human monoamine oxidase (hMAO) enzyme activity. The seed methanol extract, the solvent-soluble fractions, and almost all isolated compounds displayed selective inhibition of hMAO-A isozyme activity. Interestingly, compounds obtusin (3), alaternin (8), aloe-emodin (9), questin (12), rubrofusarin (13), cassiaside (15), toralactone 9-O-β-gentiobioside (26), and (3S)-9,10-dihydroxy-7-methoxy-3-methyl-1-oxo-3,4-dihydro-1H-benzo[g]isochromene-3-carboxylic acid 9-O-β-d-glucopyranoside (38) showed the most promising inhibition of the hMAO-A isozyme with IC₅₀ values of 0.17-11 μM. The kinetic study characterized their mode of inhibition and molecular docking simulation predicted interactions with Ile-335 and Tyr-326 in support of the substrate/inhibitor selectivity in respective isozymes. These results demonstrate that Cassia seed extract and its constituents inhibit hMAO-A enzyme activity with high selectivity and suggest that they could play a preventive role in neurodegenerative diseases, especially anxiety and depression.

Computational Insight into the Mechanism of the Irreversible Inhibition of Monoamine Oxidase Enzymes by the Antiparkinsonian Propargylamine Inhibitors Rasagiline and Selegiline

Monoamine oxidases (MAOs) are flavin adenine dinucleotide containing flavoenzymes that catalyze the degradation of a range of brain neurotransmitters, whose imbalance is extensively linked with the pathology of various neurological disorders. This is why MAOs have been the central pharmacological targets in treating neurodegeneration for more than 60 years. Still, despite this practical importance, the precise chemical mechanisms underlying the irreversible inhibition of the MAO B isoform with clinical drugs rasagiline (RAS) and selegiline (SEL) remained unknown. Here we employed a combination of MD simulations, MM-GBSA binding free energy evaluations, and QM cluster calculations to show the MAO inactivation proceeds in three steps, where, in the rate-limiting first step, FAD utilizes its N5 atom to abstracts a hydride anion from the inhibitor α-CH₂ group to ultimately give the final inhibitor-FAD adduct matching crystallographic data. The obtained free energy profiles reveal a lower activation energy for SEL by 1.2 kcal mol^-1 and a higher reaction exergonicity by 0.8 kcal mol^-1, with the former being in excellent agreement with experimental ΔΔG^‡_EXP = 1.7 kcal mol^-1, thus rationalizing its higher in vivo reactivity over RAS. The calculated ΔG_BIND energies confirm SEL binds better due to its bigger size and flexibility allowing it to optimize hydrophobic C-H···π and π···π interactions with residues throughout both of enzyme's cavities, particularly with FAD, Gln206 and four active site tyrosines, thus overcoming a larger ability of RAS to form hydrogen bonds that only position it in less reactive orientations for the hydride abstraction. Offered results elucidate structural determinants affecting the affinity and rates of the inhibition reaction that should be considered to cooperate when designing more effective compounds devoid of untoward effects, which are of utmost significance and urgency with the growing prevalence of brain diseases.

Exposing the Interplay Between Enzyme Turnover, Protein Dynamics, and the Membrane Environment in Monoamine Oxidase B

There is an increasing realization that structure-based drug design may show improved success by understanding the ensemble of conformations accessible to an enzyme and how the environment affects this ensemble. Human monoamine oxidase B (MAO-B) catalyzes the oxidation of amines and is inhibited for the treatment of both Parkinson's disease and depression. Despite its clinical importance, its catalytic mechanism remains unclear, and routes to drugging this target would be valuable. Evidence of a radical in either the transition state or the resting state of MAO-B is present throughout the literature and is suggested to be a flavin semiquinone, a tyrosyl radical, or both. Here we see evidence of a resting-state flavin semiquinone, via absorption redox studies and electron paramagnetic resonance, suggesting that the anionic semiquinone is biologically relevant. On the basis of enzyme kinetic studies, enzyme variants, and molecular dynamics simulations, we find evidence for the importance of the membrane environment in mediating the activity of MAO-B and that this mediation is related to the protein dynamics of MAO-B. Further, our MD simulations identify a hitherto undescribed entrance for substrate binding, membrane modulated substrate access, and indications for half-site reactivity: only one active site is accessible to binding at a time. Our study combines both experimental and computational evidence to illustrate the subtle interplay between enzyme activity and protein dynamics and the immediate membrane environment. Understanding key biomedical enzymes to this level of detail will be crucial to inform strategies (and binding sites) for rational drug design for these targets.

Inhibitor structure-guided design and synthesis of near-infrared fluorescent probes for monoamine oxidase A (MAO-A) and its application in living cells and in vivo

A series of near-infrared fluorescent probes based on inhibitor (clorgyline) structure-guided design were synthesized for the specific detection of MAO-A in cells and in vivo.

Biaryl scaffold-focused virtual screening for anti-aggregatory and neuroprotective effects in Alzheimer's disease

Background

Alzheimer’s disease (AD) is a primary cause of dementia in ageing population affecting more than 35 million people around the globe. It is a chronic neurodegenerative disease caused by defected folding and aggregation of amyloid beta (Aβ) protein. Aβ is formed by the cleavage of membrane embedded amyloid precursor protein (APP) by using enzyme ‘transmembrane aspartyl protease, β-secretase’. Inhibition of β-secretase is a viable strategy to prevent neurotoxicity in AD. Another strategy in the treatment of AD is inhibition of acetylcholinesterase. This inhibition reduces the degradation of acetylcholine and temporarily restores the cholinergic function of neurons and improves cognitive function. Monoamine oxidase and higher glutamate levels are also found to be linked with Aβ peptide related oxidative stress. Oxidative stress leads to reduced activity of glutamate synthase resulting in significantly higher level of glutamate in brain. The aim of this study is to perform in silico screening of a virtual library of biaryl scaffold containing compounds potentially used for the treatment of AD. Screening was done against the primary targets of AD therapeutics, acetylcholinesterase, β-secretase (BACE1), Monoamine oxidases (MAO) and N-Methyl-D-aspartate (NMDA) receptor. Compounds were screened for their inhibitory potential by employing molecular docking approach using AutoDock vina. Binding energy scores were embodied in the heatmap to display varies strengths of interactions of the ligands targeting AD.

Results

Several ligands showed notable interaction with at least two targets, but the strong interaction with all the targets is shown by very few ligands. The pharmacokinetics of the interacting ligands was also predicted. The interacting ligands have good drug-likeness and brain availability essential for drugs with intracranial targets.

Conclusion

These results suggest that biaryl scaffold may be pliable to drug development for neuroprotection in AD and that the synthesis of further analogues to optimize these properties should be considered.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0472-6) contains supplementary material, which is available to authorized users.

Curcumin-based pyrazoline analogues as selective inhibitors of human monoamine oxidase A

A series of 2-methoxy-4-(5-phenyl-4,5-dihydro-1H-pyrazol-3-yl)phenol (pyrazoline) derivatives (2-6) have been synthesized and tested for human monoamine oxidase (hMAO) inhibitory activity. The most active derivative (2) behaved as a competitive hMAO-A inhibitor, with an inhibition constant value of 0.08 μM and a strong hMAO-A selectivity (K_i(hMAO-B)/K_i(hMAO-A) > 1751). In addition, 2 exhibited little to no cytotoxic effects up to a 25 μM concentration and provided the best blood-brain barrier permeability among the derivatives synthesized. Molecular dynamics simulations revealed that a chlorine substituent at the para-position of the phenyl ring in 2 enabled a π-π stacking interaction with Tyr407 and Tyr444 that resulted in the formation of an "aromatic sandwich" structure. Consequently, this tight-binding aromatic cage culminated in a dramatically reduced active site volume that is believed to be the origin of the observed selectivity between the hMAO-A and hMAO-B isozymes. Removal of the chlorine from 2 disrupted the favorable intermolecular interactions and resulted in a selectivity change towards hMAO-B.

Privileged scaffolds as MAO inhibitors: Retrospect and prospects

This review aims to be a comprehensive, authoritative, critical, and readable review of general interest to the medicinal chemistry community because it focuses on the pharmacological, chemical, structural and computational aspects of diverse chemical categories as monoamine oxidase inhibitors (MAOIs). Monoamine oxidases (MAOs), namely MAO-A and MAO-B represent an enormously valuable class of neuronal enzymes embodying neurobiological origin and functions, serving as potential therapeutic target in neuronal pharmacotherapy, and hence we have coined the term "Neurozymes" which is being introduced for the first time ever. Nowadays, therapeutic attention on MAOIs engrosses two imperative categories; MAO-A inhibitors, in certain mental disorders such as depression and anxiety, and MAO-B inhibitors, in neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). The use of MAOIs declined due to some potential side effects, food and drug interactions, and introduction of other classes of drugs. However, curiosity in MAOIs is reviving and the recent developments of new generation of highly selective and reversible MAOIs, have renewed the therapeutic prospective of these compounds. The initial section of the review emphasizes on the detailed classification, structural and binding characteristics, therapeutic potential, current status and future challenges of the privileged pharmacophores. However, the chemical prospective of privileged scaffolds such as; aliphatic and aromatic amines, amides, hydrazines, azoles, diazoles, tetrazoles, indoles, azines, diazines, xanthenes, tricyclics, benzopyrones, and more interestingly natural products, along with their conclusive SARs have been discussed in the later segment of review. The last segment of the article encompasses some patents granted in the field of MAOIs, in a simplistic way.

Review: biologically active pyrazole derivatives

Nitrogen-containing heterocyclic compounds and their derivatives have historically been invaluable as a source of therapeutic agents.

Why p-OMe- and p-Cl-β-Methylphenethylamines Display Distinct Activities upon MAO-B Binding

Despite their structural and chemical commonalities, p-chloro-β-methylphenethylamine and p-methoxy-β-methylphenethylamine display distinct inhibitory and substrate activities upon MAO-B binding. Density Functional Theory (DFT) quantum chemical calculations reveal that β-methylation and para-substitution underpin the observed activities sustained by calculated transition state energy barriers, attained conformations and key differences in their interactions in the enzyme’s substrate binding site. Although both compounds meet substrate requirements, it is clear that β-methylation along with the physicochemical features of the para-substituents on the aromatic ring determine the activity of these compounds upon binding to the MAO B-isoform. While data for a larger set of compounds might lend generality to our conclusions, our experimental and theoretical results strongly suggest that the contrasting activities displayed depend on the conformations adopted by these compounds when they bind to the enzyme.

Recent developments on the structure–activity relationship studies of MAO inhibitors and their role in different neurological disorders

Development of MAO inhibitors as effective drug candidates for the management and/or treatment of different neurological disorders.

Revealing Monoamine Oxidase B Catalytic Mechanisms by Means of the Quantum Chemical Cluster Approach

Two of the possible catalytic mechanisms for neurotransmitter oxidative deamination by monoamine oxidase B (MAO B), namely, polar nucleophilic and hydride transfer, were addressed in order to comprehend the nature of their rate-determining step. The Quantum Chemical Cluster Approach was used to obtain transition states of MAO B complexed with phenylethylamine (PEA), benzylamine (BA), and p-nitrobenzylamine (NBA). The choice of these amines relies on their importance to address MAO B catalytic mechanisms so as to help us to answer questions such as why BA is a better substrate than NBA or how para-substitution affects substrate's reactivity. Transition states were later validated by comparison with the experimental free energy barriers. From a theoretical point of view, and according to the our reported transition states, their calculated barriers and structural and orbital differences obtained by us among these compounds, we propose that good substrates such as BA and PEA might follow the hydride transfer pathway while poor substrates such as NBA prefer the polar nucleophilic mechanism, which might suggest that MAO B can act by both mechanisms. The low free energy barriers for BA and PEA reflect the preference that MAO B has for hydride transfer over the polar nucleophilic mechanism when catalyzing the oxidative deamination of neurotransmitters.

Monoamine oxidase A mediates prostate tumorigenesis and cancer metastasis

Tumors from patients with high-grade aggressive prostate cancer (PCa) exhibit increased expression of monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines. Despite the association between MAOA and aggressive PCa, it is unclear how MAOA promotes PCa progression. Here, we found that MAOA functions to induce epithelial-to-mesenchymal transition (EMT) and stabilize the transcription factor HIF1α, which mediates hypoxia through an elevation of ROS, thus enhancing growth, invasiveness, and metastasis of PCa cells. Knockdown and overexpression of MAOA in human PCa cell lines indicated that MAOA induces EMT through activation of VEGF and its coreceptor neuropilin-1. MAOA-dependent activation of neuropilin-1 promoted AKT/FOXO1/TWIST1 signaling, allowing FOXO1 binding at the TWIST1 promoter. Importantly, the MAOA-dependent HIF1α/VEGF-A/FOXO1/TWIST1 pathway was activated in high-grade PCa specimens, and knockdown of MAOA reduced or even eliminated prostate tumor growth and metastasis in PCa xenograft mouse models. Pharmacological inhibition of MAOA activity also reduced PCa xenograft growth in mice. Moreover, high MAOA expression in PCa tissues correlated with worse clinical outcomes in PCa patients. These findings collectively characterize the contribution of MAOA in PCa pathogenesis and suggest that MAOA has potential as a therapeutic target in PCa.