How Monoamine Oxidase A Decomposes Serotonin: An Empirical Valence Bond Simulation of the Reactive Step

Monoamine signaling and neuroinflammation: mechanistic connections and implications for neuropsychiatric disorders

Monoamines, including norepinephrine, serotonin, and dopamine, orchestrate a broad spectrum of neurophysiological and homeostatic events. Recent research shows a pivotal role for monoaminergic signaling in modulating neuroinflammation by regulating proinflammatory cytokines and chemokines within the central nervous system. Importantly, this modulation is not unidirectional; released proinflammatory cytokines markedly "feedback" to influence the metabolism of monoamine neurotransmitters, impacting their synthesis, release, and reuptake. This bidirectional interplay significantly links monoaminergic pathways and neuroinflammatory responses. In this review, we summarize current knowledge of the dynamic interactions between monoamine signaling and neuroinflammation, as well as their critical implications for the pathophysiology of neuropsychiatric disorders, including Parkinson's Disease, Major Depressive Disorder, and Alzheimer's Disease. By integrating recent findings, we shed light on potential therapeutic targets within these interconnected pathways, providing insights into novel treatment strategies for these devastating disorders.

Hesperidin in Chronic Fatigue Syndrome: An Integrated Analysis of Traditional Pharmacology and Machine Learning-Based Therapeutic Predictions

Hesperidin, a bioflavonoid abundantly found in citrus fruits, offers a myriad of health benefits. With the food industry extensively utilizing citrus fruits, particularly for juice production, substantial quantities of by-products such as peels, seeds, cells, and membrane residues accumulate. Remarkably, these by-products serve as a valuable source of hesperidin. Consequently, the extraction of hesperidin from these by-products has garnered significant scientific interest, aiming to harness its potential as a natural antioxidant. By shedding light on these aspects, this review provides a comprehensive review of hesperidin's role in enhancing human well-being, particularly in the context of chronic fatigue syndrome (CFS). By synthesizing current research, we elucidate the compound's antioxidant, anti-inflammatory, and neuroprotective effects, which may mitigate symptoms associated with CFS. Furthermore, we introduce machine learning methodologies to predict hesperidin's efficacy in clinical settings, offering a novel perspective on personalized nutrition strategies. Our findings underscore the need for further empirical studies to validate these predictions and explore hesperidin's mechanisms of action. This review not only bridges the gap between nutrition science and pharmacology but also highlights the promising future of hesperidin as a nutraceutical in combating chronic health conditions.

Investigation of Electrostatic Effects on Enyzme Catalysis: Insights from Computational Simulations of Monoamine Oxidase A Pathological Variants Leading to the Brunner Syndrome

Brunner syndrome is a rare genetic disorder characterized by impulsive aggressiveness and intellectual disability, which is linked to impaired function of the monoamine oxidase A (MAO-A) enzyme. Patients with specific point mutations in the MAOA gene have been reported to exhibit these symptoms, along with notably elevated serotonin levels, which suggest a decreased catalytic performance of the mutated MAO-A enzymes. In this study, we present multiscale molecular simulations focusing on the rate-limiting step of MAO-A-catalyzed serotonin degradation for the C266F and V244I variants that are reportedly associated with pathologies characteristic of the Brunner syndrome. We found that the C266F mutation causes an approximately 18,000-fold slowdown of enzymatic function, which is equivalent to a MAOA gene knockout. For the V244I mutant, a somewhat smaller, yet still significant 300-fold slowdown has been estimated. Furthermore, we conducted a comprehensive comparison of the impact of enzyme electrostatics on the catalytic function of the wild-type (WT) MAO-A and both aforementioned mutants (C266F and V244I), as well as on the E446K mutant investigated in one of our earlier studies. The results have shown that the mutation induces a noteworthy change in electrostatic interactions between the reacting moiety and its enzymatic surroundings, leading to a decreased catalytic performance in all of the considered MAO-A variants. An analysis of mutation effects supported by geometry comparison of mutants and the wild-type enzyme at a residue level suggests that a principal driving force behind the altered catalytic performance of the mutants is subtle structural changes scattered along the entire enzyme. These shifts in geometry also affect domains most relevant to catalysis, where structural offsets of few tenths of an Å can significantly change contribution to the barrier of the involved residues. These results are in full agreement with the reasoning derived from clinical observations and biochemical data. Our research represents a step forward in the attempts of using fundamental principles of chemical physics in order to explain genetically driven pathologies. In addition, our results support the view that the catalytic function of enzymes is crucially driven by electrostatic interactions.

Methods for Theoretical Treatment of Local Fields in Proteins and Enzymes

Electric fields generated by protein scaffolds are crucial in enzymatic catalysis. This review surveys theoretical approaches for detecting, analyzing, and comparing electric fields, electrostatic potentials, and their effects on the charge density within enzyme active sites. Pioneering methods like the empirical valence bond approach rely on evaluating ionic and covalent resonance forms influenced by the field. Strategies employing polarizable force fields also facilitate field detection. The vibrational Stark effect connects computational simulations to experimental Stark spectroscopy, enabling direct comparisons. We highlight how protein dynamics induce fluctuations in local fields, influencing enzyme activity. Recent techniques assess electric fields throughout the active site volume rather than only at specific bonds, and machine learning helps relate these global fields to reactivity. Quantum theory of atoms in molecules captures the entire electron density landscape, providing a chemically intuitive perspective on field-driven catalysis. Overall, these methodologies show protein-generated fields are highly dynamic and heterogeneous, and understanding both aspects is critical for elucidating enzyme mechanisms. This holistic view empowers rational enzyme engineering by tuning electric fields, promising new avenues in drug design, biocatalysis, and industrial applications. Future directions include incorporating electric fields as explicit design targets to enhance catalytic performance and biochemical functionalities.

Synthesis, Pharmacological Evaluation, and Molecular Modeling of Phthalimide Derivatives as Monoamine Oxidase and Cholinesterase Dual Inhibitors

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by dementia and cognitive decline, associated with synaptic loss and degeneration of cholinergic neurons. New multitarget inhibitors for monoamine oxidase (MAO) and cholinesterase (ChE) enzymes are emerging as a potential treatment strategy for AD. Herein, we synthesized a series of N-benzyl-substituted biaryl phthalimide derivatives (3a-3m) encompassing potentially therapeutically active arenes/heteroarenes to serve as multitarget compounds for treating AD. To improve their binding affinity as well as inhibitory activity against ChE and MAO target proteins, comparable molecular structures were synthesized bearing electron-donating, electron-withdrawing, heterocyclic, and fluorinated moieties for a comprehensive SAR. In vitro evaluation of synthesized compounds against cholinesterases (AChE/BChE) and monoamine oxidases (MAO-A/MAO-B) revealed that compound 3e had good potency against AChE (IC50 = 0.24 μM) and BChE (IC50 = 6.29 μM), while compound 3f had the highest inhibition of MAO-B (IC50 = 0.09 μM). Selected compounds (3e,f) showed no cytotoxicity against the neuroblastoma cell line (SH-SY5Y) and normal human embryonic HEK-293 cells. Moreover, they showed high blood-brain barrier penetration (PAMPA assay) and reversible MAO-B inhibitory activity (ex vivo). In molecular docking studies, compounds 3e and 3f displayed the highest binding affinity with ChEs and MAO-B, respectively. In silico ADMET studies and MD simulation studies were also carried out for the most potent derivatives (3e and 3f), suggesting their strong potential as anti-Alzheimer agents.

Identification of 17 novel epigenetic biomarkers associated with anxiety disorders using differential methylation analysis followed by machine learning-based validation

BACKGROUND

The changes in DNA methylation patterns may reflect both physical and mental well-being, the latter being a relatively unexplored avenue in terms of clinical utility for psychiatric disorders. In this study, our objective was to identify the methylation-based biomarkers for anxiety disorders and subsequently validate their reliability.

METHODS

A comparative differential methylation analysis was performed on whole blood samples from 94 anxiety disorder patients and 296 control samples using targeted bisulfite sequencing. Subsequent validation of identified biomarkers employed an artificial intelligence-based risk prediction models: a linear calculation-based methylation risk score model and two tree-based machine learning models: Random Forest and XGBoost.

RESULTS

Seventeen novel epigenetic methylation biomarkers were identified to be associated with anxiety disorders. These biomarkers were predominantly localized near CpG islands, and they were associated with two distinct biological processes: 1) cell apoptosis and mitochondrial dysfunction and 2) the regulation of neurosignaling. We further developed a robust diagnostic risk prediction system to classify anxiety disorders from healthy controls using the 17 biomarkers. Machine learning validation confirmed the robustness of our biomarker set, with XGBoost as the best-performing algorithm, an area under the curve of 0.876.

CONCLUSION

Our findings support the potential of blood liquid biopsy in enhancing the clinical utility of anxiety disorder diagnostics. This unique set of epigenetic biomarkers holds the potential for early diagnosis, prediction of treatment efficacy, continuous monitoring, health screening, and the delivery of personalized therapeutic interventions for individuals affected by anxiety disorders.

Preliminary Investigation Into the Antidepressant Effects of a Novel Curcumin Analogue (CACN136) In Vitro and In Vivo

The aim of this study was to develop a novel antidepressant with high activity. Based on the findings of molecular docking, eight novel curcumin analogues were evaluated in vitro to check for antidepressant efficacy. Among them, CACN136 had the strongest antidepressant effect. Firstly, CACN136 had a stronger 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) radical ion scavenging ability (IC50: 17.500 ± 0.267 μg/mL) compared to ascorbic acid (IC50: 38.858 ± 0.263 μg/mL) and curcumin (27.189 ± 0.192 μg/mL). Secondly, only CACN136 demonstrated clear protective effects on cells damaged by glutamate and oxidative stress at all concentrations. Finally, only CACN136 showed ASP + inhibition and was more effective than fluoxetine hydrochloride (FLU) at low concentrations. To further confirm the antidepressant effect of CACN136 in vivo, the CUMS model was established. Following 28 days of oral administration of CUMS mice, CACN136 increased the central area residence time in the open-field test, significantly increased the sucrose preference rate in the sucrose preference test (P < 0.001) and significantly reduced the immobility period in the tail suspension test (P < 0.0001), all of which were more effective than those of FLU. Subsequent research indicated that the antidepressant properties of CACN136 were linked to a decrease in the metabolism of 5-HT and the modulation of oxidative stress levels in vivo. In particular, the activation of the Keap1-Nrf2/BDNF-TrkB signaling pathway by CACN136 resulted in elevated levels of antioxidant enzymes, enhancing the antioxidant capability in mice subjected to CUMS. In conclusion, CACN136 has the potential to treat depression and could be an effective antidepressant.

Flavins and Flavoproteins in the Neuroimmune Landscape of Stress Sensitization and Major Depressive Disorder

Major Depressive Disorder (MDD) is a common and severe neuropsychiatric condition resulting in irregular alterations in affect, mood, and cognition. Besides the well-studied neurotransmission-related etiologies of MDD, several biological systems and phenomena, such as the hypothalamic-pituitary-adrenal (HPA) axis, reactive oxygen species (ROS) production, and cytokine signaling, have been implicated as being altered and contributing to depressive symptoms. However, the manner in which these factors interact with each other to induce their effects on MDD development has been less clear, but is beginning to be understood. Flavins are potent biomolecules that regulate many redox activities, including ROS generation and energy production. Studies have found that circulating flavin levels are modulated during stress and MDD. Flavins are also known for their importance in immune responses. This review offers a unique perspective that considers the redox-active cofactors, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), as vital substrates for linking MDD-related maladaptive processes together, by permitting stress-induced enhancement of microglial interleukin-1 beta (IL-1β) signaling.

Theoretical investigation of selective inhibitory activity of chromone-based compounds against monoamine oxidase (MAO)-A and -B

Monoamine oxidase (MAO) is crucial for the breakdown of monoamine neurotransmitters, making it a promising target for treating neurodegenerative disorders, such as depression, Alzheimer's disease, and Parkinson's disease. In this study, we investigated the selective inhibitory activity of chromone-based compounds against MAO-A and MAO-B for neurodegenerative disease treatment. In literary sources, thirty chromone derivatives have been identified as potential ligands for MAO-A and MAO-B inhibitors. We utilized molecular docking to evaluate how the most active compound interacted with the targeted MAO-A and MAO-B. Compound 2 g, the most active for MAO-A, demonstrated a lower CDOCKER energy compared to the co-crystallized ligand. Meanwhile, compound 2f, the most active for MAO-B, showed a CDOCKER energy similar to the co-crystallized ligand and exhibited similar binding patterns. Furthermore, we constructed a quantitative structure-activity relationship (QSAR) model to predict the properties and estimate IC50 values for 30 chromone derivatives functioning as MAO-A and MAO-B inhibitors. The model predictions were validated against experimental measurements. Our 2D QSAR model demonstrated robustness, with a statistically significant non-cross-validated coefficient (r2 < 0.9), cross-validated correlation coefficient (q2 < 0.6), and predictive squared correlation coefficient (r2pred < 0.8). Additionally, MD simulations confirmed the stable binding of compounds 2 g and 2f with MAO-A and MAO-B, respectively, displaying substantial binding energy. The most effective pharmacophore model identified key features, such as hydrogen bond acceptors and hydrophobic interactions, that contribute significantly to inhibitory potency. This study offers valuable insight into the selection of compounds with improved selectivity for MAO inhibition.

Targeting the p53-p21 axis in liver cancer: Linking cellular senescence to tumor suppression and progression

Liver cancer is a major health epidemic worldwide, mainly due to its high mortality rates and limited treatment options. The association of cellular senescence to tumorigenesis and the cancer hallmarks remains a subject of interest in cancer biology. The p53-p21 signalling axis is an important regulator in restoring the cell's balance by supporting tumor suppression and tumorigenesis in liver cancer. We review the novel molecular mechanisms that p53 and its downstream effector, p21, employ to induce cellular senescence, making it last longer, and halt the proliferation of damaged hepatocytes to become tumorous cells. We also examine how dysregulation of this pathway contributes to HCC pathogenesis, proliferation, survival, acquired resistance to apoptosis, and increased invasiveness. Furthermore, we comprehensively describe the molecular cross-talk between the p53-p21 signalling axis and major cell cycle signalling pathways, including Wnt/β-catenin, PI3K/Akt, and TGF-β in liver cancer and provide an overview of promising candidates for chemoprevention and future therapeutic strategies. This review article explores the roles of the p53-p21 pathway in liver cancer, examining its function in promoting cellular senescence under normal conditions and its potential role in cancer progression. It also highlights novel therapeutic drugs and drug targets within the pathway and discusses the implications for treatment strategies and prognosis in liver cancer.

A Conjugated Polymer-Based Portable Smartphone Platform for Sensitive and Point-Of-Care Detection of Monoamine Neurotransmitter

The precise and effective detection of neurotransmitters (NTs) is crucial for clinical investigation of neuronal processes, and timely monitoring of NT-related chronic diseases. However, sensitive detection of specific NT with unprecedented selectivity is highly challenging due to similarities in chemical and electronic structures of various interfering neurochemicals. Herein, an anionic conjugated polyelectrolyte Poly[(9,9-bis(4'-sulfonatobutyl)fluorene-co-alt-1,4-phenylene) sodium], PFPS was rationally designed and synthesized for amplified detection and point-of-care (PoC) determination of monoamine neurotransmitter, serotonin (5-Hydroxy tryptamine or 5-HT, also diagnostic biomarker of carcinoid tumor) in human blood plasma. The PFPS displayed a remarkable sensing response with an exceptionally high fluorescence quenching constant of 1.14×105 M-1 and an ultralow detection limit of 0.67 μM or 0.142 ppm, much below the clinical range. Furthermore, a smartphone-enabled portable platform was constructed for real-time onsite detection of 5-HT by quantification of visual fluorescence response of PFPS into RGB values using a color recognizer android application. The smartphone platform could be readily applied for convenient, non-invasive PoC testing of 5-HT levels in complex biological fluids accurately and is expected to revolutionize clinical diagnosis and personalized health care devices.

Computational Study on Flavin-Catalyzed Aerobic Dioxygenation of Alkenyl Thioesters: Decomposition of Anionic Peroxides

Flavin-dependent catalysts are widely applied to aerobic monooxygenation/oxidation reactions. In contrast, flavin-catalyzed aerobic dioxygenation reactions exhibit higher atomic economy but are less reported, not to mention the relevant mechanistic studies. Herein, a density functional theory study on flavin-catalyzed aerobic epoxidation-oxygenolysis of alkenyl thioesters was performed for the first time. Different from the previous mechanistic proposal, a pathway featuring two catalytic stages, monoanionic flavin-C(4a)-peroxide/oxide intermediates, and a reverse reaction sequence (epoxidation goes prior to oxygenolysis) was revealed. In comparison, the pathways involving dianionic flavin catalysts, monoanionic flavin-N(5)-(hydro)peroxide/C(10a)-peroxide, or neutral flavin-C(4a)-hydroperoxide/hydroxide/N(5)-oxide, and the pathways where oxygenolysis goes prior to epoxidation are less favored. Epoxidation goes through intramolecular substitution of the O-O bond of anionic flavin-C(4a)-peroxide by β-carbon, while the resulting flavin-C(4a)-oxide accomplishes the oxygenolysis. Furthermore, two other reaction modes, i.e., concerted O-O cleavage/1,2-shift of α-substituents and dyotropic rearrangement were discovered for the decomposition of other anionic peroxides, and preliminary rules were summarized for understanding the chemoselectivity for this process. This study sheds light on the different reaction features of numerous flavin-dioxygen derivatives, providing deeper insights into flavin-catalyzed dioxygenation reactions, and is expected to inspire experimental design based on unconventional anionic peroxides.

Development of a long term, ex vivo, patient-derived explant model of endometrial cancer

Incidence of endometrial cancer (EC) is rising in the developed world. The current standard of care, hysterectomy, is often infeasible for younger patients and those with high body mass index. There are limited non-surgical treatment options and a lack of biologically relevant research models to investigate novel alternatives to surgery for EC. The aim of the present study was to develop a long-term, patient-derived explant (PDE) model of early-stage EC and demonstrate its use for investigating predictive biomarkers for a current non-surgical treatment option, the levonorgestrel intra-uterine system (LNG-IUS). Fresh tumour specimens were obtained from patients with early-stage endometrioid EC. Tumours were cut into explants, cultured on media-soaked gelatin sponges for up to 21 days and treated with LNG. Formalin-fixed, paraffin embedded (FFPE) blocks were generated for each explant after 21 days in culture. Tumour architecture and integrity were assessed by haematoxylin and eosin (H&E) and immunohistochemistry (IHC). IHC was additionally performed for the expression of five candidate biomarkers of LNG resistance. The developed ex vivo PDE model is capable of culturing explants from early-stage EC tumours long-term (21 Days). This model can complement existing models and may serve as a tool to validate results obtained in higher-throughput in vitro studies. Our study provides the foundation to validate the extent to which EC PDEs reflect patient response in future research.

Computational Modeling and Characterization of Peptides Derived from Nanobody Complementary-Determining Region 2 (CDR2) Targeting Active-State Conformation of the β2-Adrenergic Receptor (β2AR)

This study assessed the suitability of the complementarity-determining region 2 (CDR2) of the nanobody (Nb) as a template for the derivation of nanobody-derived peptides (NDPs) targeting active-state β2-adrenergic receptor (β2AR) conformation. Sequences of conformationally selective Nbs favoring the agonist-occupied β2AR were initially analyzed by the informational spectrum method (ISM). The derived NDPs in complex with β2AR were subjected to protein-peptide docking, molecular dynamics (MD) simulations, and metadynamics-based free-energy binding calculations. Computational analyses identified a 25-amino-acid-long CDR2-NDP of Nb71, designated P4, which exhibited the following binding free-energy for the formation of the β2AR:P4 complex (ΔG = -6.8 ± 0.8 kcal/mol or a Ki = 16.5 μM at 310 K) and mapped the β2AR:P4 amino acid interaction network. In vitro characterization showed that P4 (i) can cross the plasma membrane, (ii) reduces the maximum isoproterenol-induced cAMP level by approximately 40% and the isoproterenol potency by up to 20-fold at micromolar concentration, (iii) has a very low affinity to interact with unstimulated β2AR in the cAMP assay, and (iv) cannot reduce the efficacy and potency of the isoproterenol-mediated β2AR/β-arrestin-2 interaction in the BRET2-based recruitment assay. In summary, the CDR2-NDP, P4, binds preferentially to agonist-activated β2AR and disrupts Gαs-mediated signaling.

Role of Serotonylation and SERT Posttranslational Modifications in Alzheimer's Disease Pathogenesis

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) is implicated mainly in Alzheimer's disease (AD) and reported to be responsible for several processes and roles in the human body, such as regulating sleep, food intake, sexual behavior, anxiety, and drug abuse. It is synthesized from the amino acid tryptophan. Serotonin also functions as a signal between neurons to mature, survive, and differentiate. It plays a crucial role in neuronal plasticity, including cell migration and cell contact formation. Various psychiatric disorders, such as depression, schizophrenia, autism, and Alzheimer's disease, have been linked to an increase in serotonin-dependent signaling during the development of the nervous system. Recent studies have found 5-HT and other monoamines embedded in the nuclei of various cells, including immune cells, the peritoneal mast, and the adrenal medulla. Evidence suggests these monoamines to be involved in widespread intracellular regulation by posttranslational modifications (PTMs) of proteins. Serotonylation is the calcium-dependent process in which 5-HT forms a long-lasting covalent bond to small cytoplasmic G-proteins by endogenous transglutaminase 2 (TGM2). Serotonylation plays a role in various biological processes. The purpose of our article is to summarize historical developments and recent advances in serotonin research and serotonylation in depression, aging, AD, and other age-related neurological diseases. We also discussed several of the latest developments with Serotonin, including biological functions, pathophysiological implications and therapeutic strategies to treat patients with depression, dementia, and other age-related conditions.

Exploring the serotonin-probiotics-gut health axis: A review of current evidence and potential mechanisms

Modulatory effects of serotonin (5-Hydroxytryptamine [5-HT]) have been seen in hepatic, neurological/psychiatric, and gastrointestinal (GI) disorders. Probiotics are live microorganisms that confer health benefits to their host. Recent research has suggested that probiotics can promote serotonin signaling, a crucial pathway in the regulation of mood, cognition, and other physiological processes. Reviewing the literature, we find that peripheral serotonin increases nutrient uptake and storage, regulates the composition of the gut microbiota, and is involved in mediating neuronal disorders. This review explores the mechanisms underlying the probiotic-mediated increase in serotonin signaling, highlighting the role of gut microbiota in the regulation of serotonin production and the modulation of neurotransmitter receptors. Additionally, this review discusses the potential clinical implications of probiotics as a therapeutic strategy for disorders associated with altered serotonin signaling, such as GI and neurological disorders. Overall, this review demonstrates the potential of probiotics as a promising avenue for the treatment of serotonin-related disorders and signaling of serotonin.

Prion-like Aggregation of the Heptapeptide GNNQQNY into Amyloid Nanofiber Is Governed by Configuration Entropy

A major cause of prion infectivity is the early formation of small, fibril-like aggregates consisting of the heptapeptide GNNQQNY. The prion aggregates exhibit a unique stacking mode in which the hydrophobic tyrosine (Y) is exposed outward, forming a bilayer β-sheet-stacking zipper structure. This stacking mode of the prion peptides, termed "Y-outward" structure for convenience, goes against the common understanding that, for other amyloid-forming peptides, the hydrophobic residues should be hidden within the peptide fibril, referred to as "Y-inward" structure. To explore the extraordinary stacking behaviors of the prion GNNQQNY peptides, two fibril models are constructed in a fashion of "Y-outward" and "Y-inward" stackings and then studied in silico to examine their thermodynamic stabilities and disaggregation pathways. The "Y-inward" structure indeed exhibits stronger thermodynamic stability than the "Y-outward" structure, according to potential energy and stacking energy calculations. To show how the peptide fibrils dissociate, we illustrated two disaggregation pathways. A dihedral-based free energy landscape was then calculated to examine the conformational degrees of freedom of the GNNQQNY chains in the "Y-outward" and "Y-inward" structures. Peptide chains lose more configurational entropy in the "Y-inward" structure than in the "Y-outward" structure, indicating that the prion peptides are prone to aggregate in a fashion of "Y-outward" stacking pattern due to its low conformational constraints. The prion-like aggregation of the GNNQQNY peptides into amyloid fibrils is primarily governed by the configuration entropy.

Inhibitory mechanism of vortioxetine on CYP450 enzymes in human and rat liver microsomes

Vortioxetine is a novel anti-major depression disorder drug with a high safety profile compared with other similar drugs. However, little research has been done on drug-drug interactions (DDI) about vortioxetine. In this paper, the inhibitory effect of vortioxetine on cytochrome P450 (CYP450) and the type of inhibitory mechanism were investigated in human and rat liver microsomes. We set up an in vitro incubation system of 200 μL to measure the metabolism of probe substrates at the present of vortioxetine at 37°C. The concentrations of the metabolites of probe substrates were all measured by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method. It was found no time-dependent inhibition (TDI) of vortioxetine through determination of half-maximal inhibitory concentration (IC50) shift values. The enzymes and metabolites involved in this experiment in human and rats were as follows: CYP3A4/CYP3A (midazolam); CYP2B6/CYP2B (bupropion); CYP2D6/CYP2D (dextromethorphan); CYP2C8/CYP2C-1 (amodiaquine); CYP2C9/CYP2C-2 (losartan); and CYP2C19/CYP2C-3 (mephenytoin). We found that vortioxetine competitively inhibited CYP2C19 and CYP2D6 in human liver microsomes (HLMs) with inhibition constant (Ki) values of 2.17 μM and 9.37 μM, respectively. It was noncompetitive inhibition for CYP3A4 and CYP2C8, and its Ki values were 7.26 μM and 6.96 μM, respectively. For CYP2B6 and CYP2C9, vortioxetine exhibited the mixed inhibition with Ki values were 8.55 μM and 4.17 μM, respectively. In RLMs, the type of vortioxetine inhibition was uncompetitive for CYP3A and CYP2D (Ki = 4.41 and 100.9 μM). The inhibition type was competitive inhibition, including CYP2B and CYP2C-2 (Ki = 2.87 and 0.12 μM). The inhibition types of CYP2C-1 and CYP2C-3 (Ki = 39.91 and 4.23 μM) were mixed inhibition and noncompetitive inhibition, respectively. The study of the above mechanism will provide guidance for the safe clinical use of vortioxetine so that the occurrence of DDI can be avoided.

A Concise Review of the Recent Structural Explorations of Chromones as MAO-B Inhibitors: Update from 2017 to 2023

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that catalyze the oxidative deamination of a wide range of endogenous and exogenous amines. Multiple neurological conditions, including Parkinson's disease (PD) and Alzheimer's disease (AD), are closely correlated with altered biogenic amine concentrations in the brain caused by MAO. Toxic byproducts of this oxidative breakdown, including hydrogen peroxide, reactive oxygen species, and ammonia, can cause oxidative damage and mitochondrial dysfunction in brain cells. Certain MAO-B blockers have been recognized as effective treatment options for managing neurological conditions, including AD and PD. There is still a pressing need to find potent therapeutic molecules to fight these disorders. However, the focus of neurodegeneration studies has recently increased, and certain compounds are now in clinical trials. Chromones are promising structures for developing therapeutic compounds, especially in neuronal degeneration. This review focuses on the MAO-B inhibitory potential of several synthesized chromones and their structural activity relationships. Concerning the discovery of a novel class of effective chromone-based selective MAO-B-inhibiting agents, this review offers readers a better understanding of the most recent additions to the literature.

Microbial Metabolites of 3-n-butylphthalide as Monoamine Oxidase A Inhibitors

Novel compounds with antidepressant activity via monoamine oxidase inhibition are being sought. Among these, derivatives of 3-n-butylphthalide, a neuroprotective lactone from Apiaceae plants, may be prominent candidates. This study aimed to obtain the oxidation products of 3-n-butylphthalide and screen them regarding their activity against the monoamine oxidase A (MAO-A) isoform. Such activity of these compounds has not been previously tested. To obtain the metabolites, we used fungi as biocatalysts because of their high oxidative capacity. Overall, 37 strains were used, among which Penicillium and Botrytis spp. were the most efficient, leading to the obtaining of three main products: 3-n-butyl-10-hydroxyphthalide, 3-n-butylphthalide-11-oic acid, and 3-n-butyl-11-hydroxyphthalide, with a total yield of 0.38-0.82 g per g of the substrate, depending on the biocatalyst used. The precursor-3-n-butylphthalide and abovementioned metabolites inhibited the MAO-A enzyme; the most active was the carboxylic acid derivative of the lactone with inhibitory constant (K_i) < 0.001 µmol/L. The in silico prediction of the drug-likeness of the metabolites matches the assumptions of Lipinski, Ghose, Veber, Egan, and Muegge. All the compounds are within the optimal range for the lipophilicity value, which is connected to adequate permeability and solubility.

Platelet Serotonin (5-HT) Concentration, Platelet Monoamine Oxidase B (MAO-B) Activity and HTR2A, HTR2C, and MAOB Gene Polymorphisms in Asthma

The complex role of the serotonin system in respiratory function and inflammatory diseases such as asthma is unclear. Our study investigated platelet serotonin (5-HT) levels and platelet monoamine oxidase B (MAO-B) activity, as well as associations with HTR2A (rs6314; rs6313), HTR2C (rs3813929; rs518147), and MAOB (rs1799836; rs6651806) gene polymorphisms in 120 healthy individuals and 120 asthma patients of different severity and phenotypes. Platelet 5-HT concentration was significantly lower, while platelet MAO-B activity was considerably higher in asthma patients; however, they did not differ between patients with different asthma severity or phenotypes. Only the healthy subjects, but not the asthma patients, carrying the MAOB rs1799836 TT genotype had significantly lower platelet MAO-B activity than the C allele carriers. No significant differences in the frequency of the genotypes, alleles, or haplotypes for any of the investigated HTR2A, HTR2C and MAOB gene polymorphisms have been observed between asthma patients and healthy subjects or between patients with various asthma phenotypes. However, the carriers of the HTR2C rs518147 CC genotype or C allele were significantly less frequent in severe asthma patients than in the G allele carriers. Further studies are necessary to elucidate the involvement of the serotonergic system in asthma pathophysiology.

Selective Deuteration Improves the Affinity of Adenosine A2A Receptor Ligands: A Computational Case Study with Istradefylline and Caffeine

We used a range of computational techniques to assess the effect of selective C-H deuteration on the antagonist istradefylline affinity for the adenosine A_2A receptor, which was discussed relative to its structural analogue caffeine, a well-known and likely the most widely used stimulant. The obtained results revealed that smaller caffeine shows high receptor flexibility and exchanges between two distinct poses, which agrees with crystallographic data. In contrast, the additional C8-trans-styryl fragment in istradefylline locks the ligand within a uniform binding pose, while contributing to the affinity through the C-H···π and π···π contacts with surface residues, which, together with its much lower hydration prior to binding, enhances the affinity over caffeine. In addition, the aromatic C8-unit shows a higher deuteration sensitivity over the xanthine part, so when both of its methoxy groups are d₆-deuterated, the affinity improvement is -0.4 kcal mol^-1, which surpasses the overall affinity gain of -0.3 kcal mol^-1 in the perdeuterated d₉-caffeine. Yet, the latter predicts around 1.7-fold potency increase, being relevant for its pharmaceutical implementations, and also those within the coffee and energy drink production industries. Still, the full potential of our strategy is achieved in polydeuterated d₁₉-istradefylline, whose A_2A affinity improves by -0.6 kcal mol^-1, signifying a 2.8-fold potency increase that strongly promotes it as a potential synthetic target. This knowledge supports deuterium application in drug design, and while the literature already reports about over 20 deuterated drugs currently in the clinical development, it is easily foreseen that more examples will hit the market in the years to come. With this in mind, we propose that the devised computational methodology, involving the ONIOM division of the QM region for the ligand and the MM region for its environment, with an implicit quantization of nuclear motions relevant for the H/D exchange, allows fast and efficient estimates of the binding isotope effects in any biological system.

NMR-Based Metabolomics to Analyze the Effects of a Series of Monoamine Oxidases-B Inhibitors on U251 Cells

Alzheimer’s disease (AD) is a typical progressive neurodegenerative disorder, and with multiple possible pathogenesis. Among them, coumarin derivatives could be used as potential drugs as monoamine oxidase-B (MAO-B) inhibitors. Our lab has designed and synthesized coumarin derivatives based on MAO-B. In this study, we used nuclear magnetic resonance (NMR)-based metabolomics to accelerate the pharmacodynamic evaluation of candidate drugs for coumarin derivative research and development. We detailed alterations in the metabolic profiles of nerve cells with various coumarin derivatives. In total, we identified 58 metabolites and calculated their relative concentrations in U251 cells. In the meantime, the outcomes of multivariate statistical analysis showed that when twelve coumarin compounds were treated with U251cells, the metabolic phenotypes were distinct. In the treatment of different coumarin derivatives, there several metabolic pathways changed, including aminoacyl-tRNA biosynthesis, D-glutamine and D-glutamate metabolism, glycine, serine and threonine metabolism, taurine and hypotaurine metabolism, arginine biosynthesis, alanine, aspartate and glutamate metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, glutathione metabolism and valine, leucine and isoleucine biosynthesis. Our work documented how our coumarin derivatives affected the metabolic phenotype of nerve cells in vitro. We believe that these NMR-based metabolomics might accelerate the process of drug research in vitro and in vivo.

Brunner syndrome caused by point mutation explained by multiscale simulation of enzyme reaction

Brunner syndrome is a disorder characterized by intellectual disability and impulsive, aggressive behavior associated with deficient function of the monoamine oxidase A (MAO-A) enzyme. These symptoms (along with particularly high serotonin levels) have been reported in patients with two missense variants in MAO-A (p.R45W and p.E446K). Herein, we report molecular simulations of the rate-limiting step of MAO-A-catalyzed serotonin degradation for these variants. We found that the R45W mutation causes a 6000-fold slowdown of enzymatic function, whereas the E446K mutation causes a 450-fold reduction of serotonin degradation rate, both of which are practically equivalent to a gene knockout. In addition, we thoroughly compared the influence of enzyme electrostatics on the catalytic function of both the wild type MAO-A and the p.R45W variant relative to the wild type enzyme, revealing that the mutation represents a significant electrostatic perturbation that contributes to the barrier increase. Understanding genetic disorders is closely linked to understanding the associated chemical mechanisms, and our research represents a novel attempt to bridge the gap between clinical genetics and the underlying chemical physics.

The catalytic mechanism of the mitochondrial methylenetetrahydrofolate dehydrogenase/cyclohydrolase (MTHFD2)

Methylenetetrahydrofolate dehydrogenase/cyclohydrolase (MTHFD2) is a new drug target that is expressed in cancer cells but not in normal adult cells, which provides an Achilles heel to selectively kill cancer cells. Despite the availability of crystal structures of MTHFD2 in the inhibitor- and cofactor-bound forms, key information is missing due to technical limitations, including (a) the location of absolutely required Mg2+ ion, and (b) the substrate-bound form of MTHFD2. Using computational modeling and simulations, we propose that two magnesium ions are present at the active site whereby (i) Arg233, Asp225, and two water molecules coordinate MgA2+, while MgA2+ together with Arg233 stabilize the inorganic phosphate (Pi); (ii) Asp168 and three water molecules coordinate MgB2+, and MgB2+ further stabilizes Pi by forming a hydrogen bond with two oxygens of Pi; (iii) Arg201 directly coordinates the Pi; and (iv) through three water-mediated interactions, Asp168 contributes to the positioning and stabilization of MgA2+, MgB2+ and Pi. Our computational study at the empirical valence bond level allowed us also to elucidate the detailed reaction mechanisms. We found that the dehydrogenase activity features a proton-coupled electron transfer with charge redistribution connected to the reorganization of the surrounding water molecules which further facilitates the subsequent cyclohydrolase activity. The cyclohydrolase activity then drives the hydration of the imidazoline ring and the ring opening in a concerted way. Furthermore, we have uncovered that two key residues, Ser197/Arg233, are important factors in determining the cofactor (NADP+/NAD+) preference of the dehydrogenase activity. Our work sheds new light on the structural and kinetic framework of MTHFD2, which will be helpful to design small molecule inhibitors that can be used for cancer treatment.

Witches, potions, and metabolites: an overview from a medicinal perspective

Witches were popularly imagined as older women (above middle age), with large warty noses, whose clothes were shabby and used pointy hats. They are usually associated with a cauldron and the presence of a black cat that accompany them in this imagery projection. The fact is that, historically, many women have suffered countless physical and emotional acts of violence, for which different analysis can be made from the perspective of the Human Sciences. Of the historical narratives that deal with this violence, the Salem witch trials stand out as the biggest witch hunt in history, where a series of hearings and trials of people accused of witchcraft took place in colonial Massachusetts, between February 1693 and May of 1694, episodes in which more than two hundred people were accused of practices of heresy. However, it is necessary to recognize that many of these women considered witches were, in fact, profound connoisseurs of plant species with biological properties, even though there was not precise information about the active compounds of these plants. With the development of characterization techniques for organic compounds, like spectrometric and spectroscopic analyses, most of the metabolites present in the "potions" had their structures elucidated, allowing a more appropriate knowledge of the possible metabolic pathways. In this article, we report a study of the structure-activity relationships for two of the most famous potions in history: the sleep potion and the love potion, with the aim of presenting new discussions within the scope of medicinal chemistry that can contribute to the process of science diffusion.

Pairing structural reconstruction with catalytic competence to evaluate the mechanisms of key enzymes in the folate-mediated one-carbon pathway

Mammalian metabolism comprises a series of interlinking pathways that include two major cycles: the folate and methionine cycles. The folate-mediated metabolic cycle uses several oxidation states of tetrahydrofolate to carry activated one-carbon units to be readily used and interconverted within the cell. They are required for nucleotide synthesis, methylation and metabolism, and particularly for proliferation of cancer cells. Based on the latest progress in genome-wide CRISPR loss-of-function viability screening of 789 cell lines, we focus on the most cancer-dependent enzymes in this pathway, especially those that are hyperactivated in cancer, to provide new insight into the chemical basis for cancer drug development. Since the complete 3D structure of several of these enzymes of the one-carbon pathway in their active form are not available, we used homology modelling integrated with the interpretation of the reaction mechanism. In addition, have reconstructed the most likely scenario for the reactions taking place paired with their catalytic competence that provides a testable framework for this pathway.

Why Monoamine Oxidase B Preferably Metabolizes N-Methylhistamine over Histamine: Evidence from the Multiscale Simulation of the Rate-Limiting Step

Histamine levels in the human brain are controlled by rather peculiar metabolic pathways. In the first step, histamine is enzymatically methylated at its imidazole N^τ atom, and the produced N-methylhistamine undergoes an oxidative deamination catalyzed by monoamine oxidase B (MAO-B), as is common with other monoaminergic neurotransmitters and neuromodulators of the central nervous system. The fact that histamine requires such a conversion prior to oxidative deamination is intriguing since MAO-B is known to be relatively promiscuous towards monoaminergic substrates; its in-vitro oxidation of N-methylhistamine is about 10 times faster than that for histamine, yet this rather subtle difference appears to be governing the decomposition pathway. This work clarifies the MAO-B selectivity toward histamine and N-methylhistamine by multiscale simulations of the rate-limiting hydride abstraction step for both compounds in the gas phase, in aqueous solution, and in the enzyme, using the established empirical valence bond methodology, assisted by gas-phase density functional theory (DFT) calculations. The computed barriers are in very good agreement with experimental kinetic data, especially for relative trends among systems, thereby reproducing the observed MAO-B selectivity. Simulations clearly demonstrate that solvation effects govern the reactivity, both in aqueous solution as well as in the enzyme although with an opposing effect on the free energy barrier. In the aqueous solution, the transition-state structure involving histamine is better solvated than its methylated analog, leading to a lower barrier for histamine oxidation. In the enzyme, the higher hydrophobicity of N-methylhistamine results in a decreased number of water molecules at the active side, leading to decreased dielectric shielding of the preorganized catalytic electrostatic environment provided by the enzyme. This renders the catalytic environment more efficient for N-methylhistamine, giving rise to a lower barrier relative to histamine. In addition, the transition state involving N-methylhistamine appears to be stabilized by the surrounding nonpolar residues to a larger extent than with unsubstituted histamine, contributing to a lower barrier with the former.

Ancestral Food Sources Rich in Polyphenols, Their Metabolism, and the Potential Influence of Gut Microbiota in the Management of Depression and Anxiety

The relationship between a population's diet and the risk of suffering from mental disorders has gained importance in recent years, becoming exacerbated due to the COVID-19 lockdown. This review concentrates relevant literature from Scopus, PubMed, and Google Scholar analyzed with the aim of rescuing knowledge that promotes mental health. In this context, it is important to highlight those flowers, seeds, herbaceous plants, fungi, leaves, and tree barks, among other ancestral matrices, that have been historically part of the eating habits of human beings and have also been a consequence of the adaptation of collectors, consuming the ethnoflora present in different ecosystems. Likewise, it is important to note that this knowledge has been progressively lost in the new generations. Therefore, this review concentrates an important number of matrices used particularly for food and medicinal purposes, recognized for their anxiolytic and antidepressant effects, establishing the importance of metabolism and biotransformation mainly of bioactive compounds such as polyphenols by the action of the gut microbiota.

On the Nature of the Bonding in Coinage Metal Halides

This article analyzes the nature of the chemical bond in coinage metal halides using high-level ab initio Valence Bond (VB) theory. It is shown that these bonds display a large Charge-Shift Bonding character, which is traced back to the large Pauli pressure arising from the interaction between the bond pair with the filled semicore d shell of the metal. The gold-halide bonds turn out to be pure Charge-Shift Bonds (CSBs), while the copper halides are polar-covalent bonds and silver halides borderline cases. Among the different halogens, the largest CSB character is found for fluorine, which experiences the largest Pauli pressure from its σ lone pair. Additionally, all these bonds display a secondary but non-negligible π bonding character, which is also quantified in the VB calculations.

Serotonergic Regulation of Hepatic Energy Metabolism

The liver is a vital organ that regulates systemic energy metabolism and many physiological functions. Nonalcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease and end-stage liver failure. NAFLD is primarily caused by metabolic disruption of lipid and glucose homeostasis. Serotonin (5-hydroxytryptamine [5-HT]) is a biogenic amine with several functions in both the central and peripheral systems. 5-HT functions as a neurotransmitter in the brain and a hormone in peripheral tissues to regulate systemic energy homeostasis. Several recent studies have proposed various roles of 5-HT in hepatic metabolism and inflammation using tissue-specific knockout mice and 5-HT-receptor agonists/antagonists. This review compiles the most recent research on the relationship between 5-HT and hepatic metabolism, and the role of 5-HT signaling as a potential therapeutic target in NAFLD.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

Questions in the Chemical Enzymology of MAO

We have structure, a wealth of kinetic data, thousands of chemical ligands and clinical information for the effects of a range of drugs on monoamine oxidase activity in vivo. We have comparative information from various species and mutations on kinetics and effects of inhibition. Nevertheless, there are what seem like simple questions still to be answered. This article presents a brief summary of existing experimental evidence the background and poses questions that remain intriguing for chemists and biochemists researching the chemical enzymology of and drug design for monoamine oxidases (FAD-containing EC 4.1.3.4).

Induction of monoamine oxidase A-mediated oxidative stress and impairment of NRF2-antioxidant defence response by polyphenol-rich fraction of Bergenia ligulata sensitizes prostate cancer cells in vitro and in vivo

Prostate cancer (PCa) is a major cause of mortality and morbidity in men. Available therapies yield limited outcome. We explored anti-PCa activity in a polyphenol-rich fraction of Bergenia ligulata (PFBL), a plant used in Indian traditional and folk medicine for its anti-inflammatory and antineoplastic properties. PFBL constituted of about fifteen different compounds as per LCMS analysis induced apoptotic death in both androgen-dependent LNCaP and androgen-refractory PC3 and DU145 cells with little effect on NKE and WI38 cells. Further investigation revealed that PFBL mediates its function through upregulating ROS production by enhanced catalytic activity of Monoamine oxidase A (MAO-A). Notably, the differential inactivation of NRF2-antioxidant response pathway by PFBL resulted in death in PC3 versus NKE cells involving GSK-3β activity facilitated by AKT inhibition. PFBL efficiently reduced the PC3-tumor xenograft in NOD-SCID mice alone and in synergy with Paclitaxel. Tumor tissues in PFBL-treated mice showed upregulation of similar mechanism of cell death as observed in isolated PC3 cells i.e., elevation of MAO-A catalytic activity, ROS production accompanied by activation of β-TrCP-GSK-3β axis of NRF2 degradation. Blood counts, liver, and splenocyte sensitivity analyses justified the PFBL safety in the healthy mice. To our knowledge this is the first report of an activity that crippled NRF2 activation both in vitro and in vivo in response to MAO-A activation. Results of this study suggest the development of a novel treatment protocol utilizing PFBL to improve therapeutic outcome for patients with aggressive PCa which claims hundreds of thousands of lives each year.

Monoamine Oxidase Inhibitors: A Review of Their Anti-Inflammatory Therapeutic Potential and Mechanisms of Action

Chronic inflammatory diseases are debilitating, affect patients' quality of life, and are a significant financial burden on health care. Inflammation is regulated by pro-inflammatory cytokines and chemokines that are expressed by immune and non-immune cells, and their expression is highly controlled, both spatially and temporally. Their dysregulation is a hallmark of chronic inflammatory and autoimmune diseases. Significant evidence supports that monoamine oxidase (MAO) inhibitor drugs have anti-inflammatory effects. MAO inhibitors are principally prescribed for the management of a variety of central nervous system (CNS)-associated diseases such as depression, Alzheimer's, and Parkinson's; however, they also have anti-inflammatory effects in the CNS and a variety of non-CNS tissues. To bolster support for their development as anti-inflammatories, it is critical to elucidate their mechanism(s) of action. MAO inhibitors decrease the generation of end products such as hydrogen peroxide, aldehyde, and ammonium. They also inhibit biogenic amine degradation, and this increases cellular and pericellular catecholamines in a variety of immune and some non-immune cells. This decrease in end product metabolites and increase in catecholamines can play a significant role in the anti-inflammatory effects of MAO inhibitors. This review examines MAO inhibitor effects on inflammation in a variety of in vitro and in vivo CNS and non-CNS disease models, as well as their anti-inflammatory mechanism(s) of action.

Light-Induced Change of Arginine Conformation Modulates the Rate of Adenosine Triphosphate to Cyclic Adenosine Monophosphate Conversion in the Optogenetic System Containing Photoactivated Adenylyl Cyclase

We report the first computational characterization of an optogenetic system composed of two photosensing BLUF (blue light sensor using flavin adenine dinucleotide) domains and two catalytic adenylyl cyclase (AC) domains. Conversion of adenosine triphosphate (ATP) to the reaction products, cyclic adenosine monophosphate (cAMP) and pyrophosphate (PPi), catalyzed by ACs initiated by excitation in photosensing domains has emerged in the focus of modern optogenetic applications because of the request in photoregulated enzymes that modulate cellular concentrations of signaling messengers. The photoactivated AC from the soil bacterium Beggiatoa sp. (bPAC) is an important model showing a considerable increase in the ATP to cAMP conversion rate in the catalytic domain after the illumination of the BLUF domain. The 1 μs classical molecular dynamics simulations reveal that the activation of the BLUF domain leading to tautomerization of Gln49 in the chromophore-binding pocket results in switching of the position of the side chain of Arg278 in the active site of AC. Allosteric signal transmission pathways between Gln49 from BLUF and Arg278 from AC were revealed by the dynamical network analysis. The Gibbs energy profiles of the ATP → cAMP + PPi reaction computed using QM(DFT(ωB97X-D3/6-31G**))/MM(CHARMM) molecular dynamics simulations for both Arg278 conformations in AC clarify the reaction mechanism. In the light-activated system, the corresponding arginine conformation stabilizes the pentacoordinated phosphorus of the α-phosphate group in the transition state, thus lowering the activation energy. Simulations of the bPAC system with the Tyr7Phe replacement in the BLUF demonstrate occurrence of both arginine conformations in an equal ratio, explaining the experimentally observed intermediate catalytic activity of the bPAC-Y7F variant as compared with the dark and light states of the wild-type bPAC.

Recent advances of small molecule fluorescent probes for distinguishing monoamine oxidase-A and monoamine oxidase-B in vitro and in vivo

Monoamine oxidases (MAO-A and MAO-B) are the two flavin adenine dinucleotide (FAD) enzymes that play an important role in neurotransmitter homeostasis and in protection against biogenic amines. The two MAO enzymes are related to various diseases such as neurological disorders, cancer or other systemic diseases. It is crucial to distinguish these two subtypes in order to explore the pathogenesis and pathophysiology of different diseases. In this review, the relationship between MAOs and related diseases is briefly introduced. Additionally, we summarize the recent advances in small molecule fluorescent probes for specific detection of MAO-A and MAO-B.