Monoamine oxidase inhibitory constituents of propolis: kinetics and mechanism of inhibition of recombinant human MAO-A and MAO-B

Towards cost-effective drug discovery: Reusable immobilized enzymes for neurological disease research

Enzyme handling and utilization bears many challenges such as their limited stability, intolerance of organic solvents, high cost, or inability to reuse. Most of these limitations can be overcome by enzyme immobilization on the surface of solid support. In this work, the recombinant form of human cholinesterases and monoamine oxidases as important drug targets for neurological diseases were immobilized on the surface of magnetic non-porous microparticles by a non-covalent bond utilizing the interaction between a His-tag terminus on the recombinant enzymes and cobalt (Co2+) ions immobilized on the magnetic microparticles. This type of binding led to targeted enzyme orientation, which completely preserved the catalytic activity and allowed high reproducibility of immobilization. In comparison with free enzymes, the immobilized enzymes showed exceptional stability in time and the possibility of repeated use. Relevant Km, Vmax, and IC50 values using known inhibitors were obtained using particular immobilized enzymes. Such immobilized enzymes on magnetic particles could serve as an excellent tool for a sustainable approach in the early stage of drug discovery.

Apigenin attenuates depressive-like behavior via modulating monoamine oxidase A enzyme activity in chronically stressed mice

Chronic stress is a risk factor for depression and is characterized by elevated levels of brain monoamine oxidase A (MAOA). Mounting evidence has shown that MAOA is a biochemical link between stress and depression. Apigenin (API), a natural flavonoid, as demonstrated in vitro inhibitory effect on MAOA, is suggestive of antidepressant-like activity. However, the in vivo inhibitory effect of API on MAOA and how it affects depression still remain unclear. Here, we report the probable mechanisms of action of API in chronic unpredictable mild stress (CUMS)-induced depression in mice. Treatment with API reversed anhedonia, and reduced anxiety and immobility time in behavioral studies. API reduced brain corticosterone and malondialdehyde (MDA) levels but increased brain levels of glutathione and superoxide dismutase. Furthermore, interleukin-6 and tumor necrosis factor-α were attenuated by API. It also restored cell loss and inhibited the activity of MAOA in the hippocampal brain regions and prefrontal cortex. Comparative binding affinity of API for MAOA (-7.7 kcal/mol) through molecular docking studies was greater than that of reference compound, clorgyline (-6.8 kcal/mol). Favorable hydrophobic interactions important to API binding at MAOA binding cavity was revealed to include conventional hydrogen bond (Cys323 and Tyr444), π-Sulfur (Cys323), π-π Stacked (Tyr407), π-π T-shaped (Phe208), π-lone pair and π-alkyl (Ile335, Ile180) interactions. These results suggest that API is a potent, selective, reversible inhibitor of MAOA with capability of attenuating CUMS-induced depression via inhibiting MAOA enzyme activity and altering other pathomechanisms.

β-Carboline Alkaloids in Soy Sauce and Inhibition of Monoamine Oxidase (MAO)

Monoamine oxidase (MAO) oxidizes neurotransmitters and xenobiotic amines, including vasopressor and neurotoxic amines such as the MPTP neurotoxin. Its inhibitors are useful as antidepressants and neuroprotectants. This work shows that diluted soy sauce (1/3) and soy sauce extracts inhibited human MAO-A and -B isozymes in vitro, which were measured with a chromatographic assay to avoid interferences, and it suggests the presence of MAO inhibitors. Chromatographic and spectrometric studies showed the occurrence of the β-carboline alkaloids harman and norharman in soy sauce extracts inhibiting MAO-A. Harman was isolated from soy sauce, and it was a potent and competitive inhibitor of MAO-A (0.4 µM, 44 % inhibition). The concentrations of harman and norharman were determined in commercial soy sauces, reaching 243 and 52 μg/L, respectively. Subsequently, the alkaloids 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA) were identified and analyzed in soy sauces reaching concentrations of 69 and 448 mg/L, respectively. The results show that MTCA was a precursor of harman under oxidative and heating conditions, and soy sauces increased the amount of harman under those conditions. This work shows that soy sauce contains bioactive β-carbolines and constitutes a dietary source of MAO-A and -B inhibitors.

Assay of MAO Inhibition by Chromatographic Techniques (HPLC/HPLC-MS)

Monoamine oxidase (MAO) enzymes (MAO A and B) catalyze the oxidative deamination of biogenic amines, neurotransmitters, and xenobiotic amines and contribute to the regulation of the content of these active substances in mammalian organisms. The oxidation of biogenic amines by MAO produces hydrogen peroxide (H₂O₂) and aldehydes that represent risk factors for oxidative injury. The inhibitors of MAO are useful as antidepressants and neuroprotective agents. Usually, the assays of MAO determine amine deamination products or measure the H₂O₂ released by using direct spectrophotometric or fluorimetric methods. Direct methods are more prone to interferences and can afford inaccurate results. Those limitations can be avoided by using chromatographic techniques. This work describes a chromatographic method to assay MAO A and MAO B activity by using kynuramine as a nonselective substrate and the subsequent analysis of 4-hydroxyquinoline by RP-HPLC-DAD-fluorescence and mass spectrometry (MS). Alternatively, the assay uses the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin as a substrate of MAO that is oxidized (bioactivated) to neurotoxic pyridinium cations which are analyzed by HPLC. These methods are applied to assess the inhibition of MAO by bioactive β-carboline alkaloids occurring in foods, plants, and biological systems.

Dissecting the molecular mechanisms underlying the antidepressant activities of herbal medicines through the comprehensive review of the recent literatures

Depression is clinically defined as a mood disorder with persistent feeling of sadness, despair, fatigue, and loss of interest. The pathophysiology of depression is tightly regulated by the biosynthesis, transport and signaling of neurotransmitters [e.g., serotonin, norepinephrine, dopamine, or γ-aminobutyric acid (GABA)] in the central nervous system. The existing antidepressant drugs mainly target the dysfunctions of various neurotransmitters, while the efficacy of antidepressant therapeutics is undermined by different adverse side-effects. The present review aimed to dissect the molecular mechanisms underlying the antidepressant activities of herbal medicines toward the development of effective and safe antidepressant drugs. Our strategy involved comprehensive review and network pharmacology analysis for the active compounds and associated target proteins. As results, 45 different antidepressant herbal medicines were identified from various in vivo and in vitro studies. The antidepressant mechanisms might involve multiple signaling pathways that regulate neurotransmitters, neurogenesis, anti-inflammation, antioxidation, endocrine, and microbiota. Importantly, herbal medicines could modulate broader spectrum of the cellular pathways and processes to attenuate depression and avoid the side-effects of synthetic antidepressant drugs. The present review not only recognized the antidepressant potential of herbal medicines but also provided molecular insights for the development of novel antidepressant drugs.

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

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

Old targets, new strategy: Apigenin-7-O-β-d-(-6″-p-coumaroyl)-glucopyranoside prevents endothelial ferroptosis and alleviates intestinal ischemia-reperfusion injury through HO-1 and MAO-B inhibition

With the increasing morbidity and mortality, intestinal ischemia/reperfusion injury (IIRI) has attracted more and more attention, but there is no efficient therapeutics at present. Apigenin-7-O-β-D-(-6″-p-coumaroyl)-glucopyranoside (APG) is a new flavonoid glycoside isolated from Clematis tangutica that has strong antioxidant abilities in previous studies. However, the pharmacodynamic function and mechanism of APG on IIRI remain unknown. This study aimed to investigate the effects of APG on IIRI both in vivo and in vitro and identify the potential molecular mechanism. We found that APG could significantly improve intestinal edema and increase Chiu's score. MST analysis suggested that APG could specifically bind to heme oxygenase 1 (HO-1) and monoamine oxidase b (MAO-B). Simultaneously, APG could attenuate ROS generation and Fe²⁺ accumulation, maintain mitochondria function thus inhibit ferroptosis with a dose-dependent manner. Moreover, we used siRNA silencing technology to confirm that knocking down both HO-1 and MAO-B had a positive effect on intestine. In addition, we found the HO-1 and MAO-B inhibitors also could reduce endothelial cell loss and protect vascular endothelial after reperfusion. We demonstrate that APG plays a protective role on decreasing activation of HO-1 and MAO-B, attenuating IIRI-induced ROS generation and Fe²⁺ accumulation, maintaining mitochondria function thus inhibiting ferroptosis.

Computationally Assisted Lead Optimization of Novel Potent and Selective MAO-B Inhibitors

A series of dietary flavonoid acacetin 7-O-methyl ether derivatives were computationally designed aiming to improve the selectivity and potency profiles against monoamine oxidase (MAO) B. The designed compounds were evaluated for their potential to inhibit human MAO-A and -B. Compounds 1c, 2c, 3c, and 4c were the most potent with a Ki of 37 to 68 nM against MAO-B. Compounds 1c–4c displayed more than a thousand-fold selectivity index towards MAO-B compared with MAO-A. Moreover, compounds 1c and 2c showed reversible inhibition of MAO-B. These results provide a basis for further studies on the potential application of these modified flavonoids for the treatment of Parkinson’s Disease and other neurological disorders.

Acetylcholinesterase and monoamine oxidase-B inhibitory activities by ellagic acid derivatives isolated from Castanopsis cuspidata var. sieboldii

Among 276 herbal extracts, a methanol extract of Castanopsis cuspidata var. sieboldii stems was selected as an experimental source for novel acetylcholinesterase (AChE) inhibitors. Five compounds were isolated from the extract by activity-guided screening, and their inhibitory activities against butyrylcholinesterase (BChE), monoamine oxidases (MAOs), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) were also evaluated. Of these compounds, 4'-O-(α-L-rhamnopyranosyl)-3,3',4-tri-O-methylellagic acid (3) and 3,3',4-tri-O-methylellagic acid (4) effectively inhibited AChE with IC₅₀ values of 10.1 and 10.7 µM, respectively. Ellagic acid (5) inhibited AChE (IC₅₀ = 41.7 µM) less than 3 and 4. In addition, 3 effectively inhibited MAO-B (IC₅₀ = 7.27 µM) followed by 5 (IC₅₀ = 9.21 µM). All five compounds weakly inhibited BChE and BACE-1. Compounds 3, 4, and 5 reversibly and competitively inhibited AChE, and were slightly or non-toxic to MDCK cells. The binding energies of 3 and 4 (- 8.5 and - 9.2 kcal/mol, respectively) for AChE were greater than that of 5 (- 8.3 kcal/mol), and 3 and 4 formed a hydrogen bond with Tyr124 in AChE. These results suggest 3 is a dual-targeting inhibitor of AChE and MAO-B, and that these compounds should be viewed as potential therapeutics for the treatment of Alzheimer's disease.

A Recent Look into Natural Products that have Potential to Inhibit Cholinesterases and Monoamine Oxidase B: Update for 2010-2019

With respect to the unknowns of pathophysiology of Alzheimer's Disease (AD)-, and Parkinson's Disease (PD)-like neurodegenerative disorders, natural product research is still one of the valid tools in order to provide alternative and/or better treatment options. At one hand, various extracts of herbals provide a combination of actions targeting multiple receptors, on the other hand, the discovery of active natural products (i.e., secondary metabolites) generally offers alternative chemical structures either ready to be employed in clinical studies or available to be utilized as important scaffolds for the design of novel agents. Regarding the importance of certain enzymes (e.g. cholinesterase and monoamine oxidase B), for the treatment of AD and PD, we have surveyed the natural product research within this area in the last decade. Particularly novel natural agents discovered within this period, concomitant to novel biological activities displayed for known natural products, are harmonized within the present study.

Evidence for 5-HT1A receptor-mediated antiallodynic and antihyperalgesic effects of apigenin in mice suffering from mononeuropathy

BACKGROUND AND PURPOSE

Neuropathic pain places a devastating health burden, with very few effective therapies. We investigated the potential antiallodynic and antihyperalgesic effects of apigenin, a natural flavonoid with momoamine oxidase (MAO) inhibitory activity, against neuropathic pain and investigated the mechanism(s).

EXPERIMENTAL APPROACH

The neuropathic pain model was produced by chronic constriction injury of sciatic nerves in male C57BL/6J mice, with pain-related behaviours being assayed by von Frey test and Hargreaves test. In this model the role of 5-HT and 5-HT_1A receptor-related mechanisms were investigated in vivo/in vitro.

KEY RESULTS

Apigenin repeated treatment (p.o., once per day for 2 weeks), in a dose-related manner (3, 10 and 30 mg·kg^-1 ), ameliorated the allodynia and hyperalgesia in chronic nerve constriction injury in mice. These effects seem dependent on neuronal 5-hydroxytryptamine, because (i) the antihyperalgesia and antiallodynia were attenuated by depletion of 5-HT with p-chlorophenylalanine and potentiated by 5-hydroxytryptophan and (ii), apigenin-treated chronic constriction injury mice caused an increased level of spinal 5-HT, associated with diminished MAO activity. In vivo administration, spinally or systematically, of the 5-HT_1A antagonist WAY-100635 inhibited the apigenin-induced antiallodynia and antihyperalgesia. In vitro, apigenin acted as a positive allosteric modulator to increase the efficacy (stimulation of [³⁵ S]GTPγS binding) of the 5-HT_1A agonist 8-OH-DPAT. Apigenin attenuated neuronal changes caused by chronic constriction of the sciatic nerve in mice, without causing a hypertensive crisis.

CONCLUSION AND IMPLICATIONS

Apigenin antiallodynic and antihyperalgesic actions against neuropathic pain crucially involve spinal 5-HT_1A receptors and indicate it could be used to treat neuropathic pain.

Alzheimer's disease: An evolving understanding of noradrenergic involvement and the promising future of electroceutical therapies

Alzheimer's disease (AD) poses a significant global health concern over the next several decades. Multiple hypotheses have been put forth that attempt to explain the underlying pathophysiology of AD. Many of these are briefly reviewed here, but to-date no disease-altering therapy has been achieved. Despite this, recent work expanding on the role of noradrenergic system dysfunction in both the pathogenesis and symptomatic exacerbation of AD has shown promise. The role norepinephrine (NE) plays in AD remains complicated but pre-tangle tau has consistently been shown to arise in the locus coeruleus (LC) of patients with AD decades before symptom onset. The current research reviewed here indicates NE can facilitate neuroprotective and memory-enhancing effects through β adrenergic receptors, while α2A adrenergic receptors may exacerbate amyloid toxicity through a contribution to tau hyperphosphorylation. AD appears to involve a disruption in the balance between these two receptors and their various subtypes. There is also a poorly characterized interplay between the noradrenergic and cholinergic systems. LC deterioration leads to maladaptation in the remaining LC-NE system and subsequently inhibits cholinergic neuron function, eventually leading to the classic cholinergic disruption seen in AD. Understanding AD as a dysfunctional noradrenergic system, provides new avenues for the use of advanced neural stimulation techniques to both study and therapeutically target the earliest stages of neuropathology. Direct LC stimulation and non-invasive vagus nerve stimulation (VNS) have both demonstrated potential use as AD therapeutics. Significant work remains, though, to better understand the role of the noradrenergic system in AD and how electroceuticals can provide disease-altering treatments.

Selective Interactions of O-Methylated Flavonoid Natural Products with Human Monoamine Oxidase-A and -B

A set of structurally related O-methylated flavonoid natural products isolated from Senecio roseiflorus (1), Polygonum senegalense (2 and 3), Bhaphia macrocalyx (4), Gardenia ternifolia (5), and Psiadia punctulata (6) plant species were characterized for their interaction with human monoamine oxidases (MAO-A and -B) in vitro. Compounds 1, 2, and 5 showed selective inhibition of MAO-A, while 4 and 6 showed selective inhibition of MAO-B. Compound 3 showed ~2-fold selectivity towards inhibition of MAO-A. Binding of compounds 1-3 and 5 with MAO-A, and compounds 3 and 6 with MAO-B was reversible and not time-independent. The analysis of enzyme-inhibition kinetics suggested a reversible-competitive mechanism for inhibition of MAO-A by 1 and 3, while a partially-reversible mixed-type inhibition by 5. Similarly, enzyme inhibition-kinetics analysis with compounds 3, 4, and 6, suggested a competitive reversible inhibition of MAO-B. The molecular docking study suggested that 1 selectively interacts with the active-site of human MAO-A near N5 of FAD. The calculated binding free energies of the O-methylated flavonoids (1 and 4-6) and chalcones (2 and 3) to MAO-A matched closely with the trend in the experimental IC_50's. Analysis of the binding free-energies suggested better interaction of 4 and 6 with MAO-B than with MAO-A. The natural O-methylated flavonoid (1) with highly potent inhibition (IC₅₀ 33 nM; Ki 37.9 nM) and >292 fold selectivity against human MAO-A (vs. MAO-B) provides a new drug lead for the treatment of neurological disorders.

Propolis: A useful agent on psychiatric and neurological disorders? A focus on CAPE and pinocembrin components

Propolis consists of a honeybee product, with a complex mix of substances that have been widely used in traditional medicine. Among several compounds present in propolis, caffeic acid phenethyl ester (CAPE), and pinocembrin emerge as two principal bioactive compounds, with benefits in a variety of body systems. In addition to its well-explored pharmacological properties, neuropharmacological activities have been poorly discussed. In an unprecedented way, the present review addresses the current finding on the promising therapeutic purposes of propolis, focusing on CAPE and pinocembrin, highlighting its use on neurological disturbance, as cerebral ischemia, neuroinflammation, convulsion, and cognitive impairment, as well as psychiatric disorders, such as anxiety and depression. In addition, we provide a critical analysis, discussion, and systematization of the molecular mechanisms which underlie these central nervous system effects. We hypothesize that the pleiotropic action of CAPE and pinocembrin, per se or associated with other substances present in propolis may result in the therapeutic activities reported. Inhibition of the pro-inflammatory cascade, antioxidant activity, and positive neurotrophic modulatory effects consist of the main molecular targets attributed to CAPE and pinocembrin in health benefits.

Apitherapy for Parkinson's Disease: A Focus on the Effects of Propolis and Royal Jelly

The vast increase of world's aging populations is associated with increased risk of age-related neurodegenerative diseases such as Parkinson's disease (PD). PD is a widespread disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra, which encompasses a wide range of debilitating motor, emotional, cognitive, and physical symptoms. PD threatens the quality of life of millions of patients and their families. Additionally, public welfare and healthcare systems are burdened with its high cost of care. Available treatments provide only a symptomatic relief and produce a trail of noxious side effects, which increase noncompliance. Hence, researchers have recently focused on the use of nutraceuticals as safe adjunctive treatments of PD to limit its progress and associated damages in affected groups. Propolis is a common product of the beehive, which possesses a large number of therapeutic properties. Royal jelly (RJ) is a bee product that is fed to bee queens during their entire life, and it contributes to their high physical fitness, fertility, and long lifespan. Evidence suggests that propolis and RJ can promote health by preventing the occurrence of age-related debilitating diseases. Therefore, they have been used to treat various serious disorders such as diabetes mellitus, cardiovascular diseases, and cancer. Some evolving studies used these bee products to treat PD in animal models. However, a clear understanding of the collective effect of propolis and RJ as well as their mechanism of action in PD is lacking. This review evaluates the available literature for the effects of propolis and RJ on PD. Whenever possible, it elaborates on the underlying mechanisms through which they function in this disorder and offers insights for fruitful use of bee products in future clinical trials.

Identification of Novel Phyto-chemicals from Ocimum basilicum for the Treatment of Parkinson's Disease using In Silico Approach

BACKGROUND

Parkinson's disease is characterized by decreased level of dopaminergic neurotransmitters and this decrease is due to the degradation of dopamine by protein Monoamine Oxidase B (MAO-B). In order to treat Parkinson's disease, MAO-B should be inhibited.

OBJECTIVE

To find out the novel phytochemicals from plant Ocimum basilicum that can inhibit MAO-B by using the in silico methods.

METHODS

The data of chemical constituents from plant Ocimum basilicum was collected and inhibitory activity of these phytochemicals was then predicted by using the Structure-Based (SB) and Ligand-Based Virtual Screening (LBVS) methods. Molecular docking, one of the common Structure-Based Virtual Screening method, has been used during this search. Traditionally, molecular docking is used to predict the orientation and binding affinity of the ligand within the active site of the protein. Molegro Virtual Docker (MVD) software has been used for this purpose. On the other hand, Random Forest Model, one of the LBVS method, has also been used to predict the activity of these chemical constituents of Ocimum basilicum against the MAO-B.

RESULTS

During the docking studies, all the 108 compounds found in Ocimum basilicum were docked within the active site of MAO-B (PDB code: 4A79) out of which, 57 compounds successfully formed the hydrogen bond with tyr 435, a crucial amino acid for the biological activity of the enzyme. Rutin (-182.976 Kcal/mol), Luteolin (-163.171 Kcal/mol), Eriodictyol-7-O-glucoside (- 160.13 Kcal/mol), Rosmarinic acid (-133.484 Kcal/mol) and Isoquercitrin (-131.493 Kcal/mol) are among the top hits with the highest MolDock score along with hydrogen interaction with tyr 435. Using the RF model, ten compounds out of 108 chemical constituent of Ocimum basilicum were predicted to be active, Apigenin (1.0), Eriodictyol (1.0), Orientin (0.876), Kaempferol (0.8536), Luteolin (0.813953) and Rosmarinic-Acid (0.7738095) are predicted to be most active with the highest RF score.

CONCLUSION

The comparison of the two screening methods show that the ten compounds that were predicted to be active by the RF model, are also found in top hits of docking studies with the highest score. The top hits obtained during this study are predicted to be the inhibitor of MAO-B, thus, could be used further for the development of drugs for the treatment of Parkinson's disease (PD).

The Antiproliferative Effects of Flavonoid MAO Inhibitors on Prostate Cancer Cells

Prostate cancer (PCa) patients commonly experience clinical depression. Recent reports indicated that monoamine oxidase-A (MAO-A) levels elevate in PCa, and antidepressant MAO-Is show anti-PCa properties. In this work, we aimed to find potential drugs for PCa patients suffering from depression by establishing novel anti-PCa reversible monoamine oxidase-A inhibitors (MAO-AIs/RIMA); with an endeavor to understand their mechanism of action. In this investigation, twenty synthesized flavonoid derivatives, defined as KKR compounds were screened for their inhibitory potentials against human MAO-A and MAO-B isozymes. Meanwhile, the cytotoxic and antiproliferative effects were determined in three human PCa cell lines. MAO-A-kinetics, molecular docking, SAR, cell morphology, and cell migration were investigated for the most potent compounds. The screened KKRs inhibited MAO-A more potently than MAO-B, and non-toxically inhibited LNCaP cell proliferation more than the DU145 and PC3 cell lines, respectively. The results showed that the three top MAO-AI KKRs compounds (KKR11, KKR20, and KKR7 (IC₅₀s 0.02-16 μM) overlapped with the top six antiproliferative KKRs against LNCaP (IC₅₀s ~9.4 μM). While KKR21 (MAO-AI) and KKR2A (MAO-I) were ineffective against the PCa cells. Furthermore, KKR21 and KKR11 inhibited MAO-A competitively (K_is ≤ 7.4 nM). Molecular docking of the two compounds predicted shared hydrophobic and distinctive hydrophilic interactions-between the KKR molecule and MAO-A amino acid residues-to be responsible for their reversibility. The combined results and SAR observations indicated that the presence of specific active groups-such as chlorine and hydroxyl groups-are essential in certain MAO-AIs with anti-PCa effects. Additionally, MAO-A inhibition was found to be associated more with anti-PCa property than MAO-B. Distinctively, KKR11 [(E)-3-(3,4-dichlorophenyl)-1-(2-hydroxy-4,6-dimethoxyphenyl)prop-2-en-1-one] exhibited anti-metastatic effects on the DU145 cell line. The chlorine substitution groups might play vital roles in the KKR11 multiple actions. The obtained results indicated that the flavonoid derivative KKR11 could present a novel candidate for PCa patients with depression, through safe non-selective potent inhibition of MAOs.

Flavonoids Isolated from Vitex grandifolia, an Underutilized Vegetable, Exert Monoamine A & B Inhibitory and Anti-inflammatory Effects and Their Structure-activity Relationship

Objectives

Vitex grandifolia belongs to family Lamiaceae; it consists of flowering plants and it is also called the mint family. The Yoruba people of southwest Nigeria called it "Oriri" or "Efo oriri". This plant is classified as an underutilized vegetable and little is known about its phytochemistry or its biological evaluations.

Materials and Methods

Methanol extracts of the dried leaves and stem of the plant were subjected to fractionation and isolation using vacuum layer and column chromatography methods. The structures of the compounds were elucidated using spectroscopic techniques including IR, 1D-, and 2D-NMR and by comparison with the data reported in the literature. They were evaluated in vitro for the inhibition of monoamine recombinant human MAO-A and -B and anti-inflammatory activities.

Results

Three known flavonoids were isolated from the methanolic extract of the leaves of V. grandifolia for the first time to the best of our knowledge, i.e. isoorientin (1), orientin (2), and isovitexin (3). Most of the isolated compounds showed selective inhibition of monoamine oxidase B, inhibition of MAO-B by isoorientin (1) and orientin (2) were 9-fold more potent (IC₅₀ (μg/mL) of 11.08 and 11.04) compared to the inhibition of MAO-A (IC₅₀ (μg/mL) of ˃100), while clorgyline and deprenyl were used as positive standards. The isolated flavonoids displayed good activity against the NF-ﭏb assay with IC₅₀ (μg/mL) of 8.9, 12, and 18. This study establishes a link between the structure and the biological activities on the basis of the different patterns of substitution, particularly the C2=C3 double bond and the position of glucose moiety.

Conclusion

This study is the first to establish the phytochemistry of the polar part of V. grandifolia and the anti-inflammatory and neuroprotective role of these isolated compounds.

Novel approaches to the discovery of selective human monoamine oxidase-B inhibitors: is there room for improvement?

Introduction: Selective monoamine oxidase-B (MAO-B) inhibitors are currently used as coadjuvants for the treatment of early motor symptoms in Parkinson's disease. They can, based on their chemical structure and mechanism of inhibition, be categorized into reversible and irreversible agents. Areas covered: This review provides a comprehensive update on the development state of selective MAO-B inhibitors describing the results, structures, structure-activity relationships (SARs) and Medicinal chemistry strategies as well as the related shortcomings over the past five years. Expert opinion: Researchers have explored and implemented new and old chemical scaffolds achieving high inhibitory potencies and isoform selectivity. Most of them were characterized and proposed as multitarget agents able to act at different levels (including AChE inhibition, H3R or A_2AR antagonism, antioxidant and chelating properties, Aβ_1-42 aggregation reduction) in the network of aetiologies of neurodegenerative disorders. These results can also be used to avoid 'cheese-reaction' effects and the occurrence of serotonergic syndrome in patients.

The Therapeutic Potential of Apigenin

Several plant bioactive compounds have exhibited functional activities that suggest they could play a remarkable role in preventing a wide range of chronic diseases. The largest group of naturally-occurring polyphenols are the flavonoids, including apigenin. The present work is an updated overview of apigenin, focusing on its health-promoting effects/therapeutic functions and, in particular, results of in vivo research. In addition to an introduction to its chemistry, nutraceutical features have also been described. The main key findings from in vivo research, including animal models and human studies, are summarized. The beneficial indications are reported and discussed in detail, including effects in diabetes, amnesia and Alzheimer's disease, depression and insomnia, cancer, etc. Finally, data on flavonoids from the main public databases are gathered to highlight the apigenin's key role in dietary assessment and in the evaluation of a formulated diet, to determine exposure and to investigate its health effects in vivo.

Marker-based standardization and investigation of nutraceutical potential of Indian propolis

OBJECTIVE

Propolis, a resinous material collected by honey bees from various plants, has been explored globally for its medicinal and nutritional properties. However, research over Indian propolis is at infancy. This study was designed to investigate nutraceutical potential of Indian propolis.

METHODS

In the present study, propolis extract was standardized with respect to markers caffeic acid phenethyl ester, caffeic acid, galangin, luteolin, curcumin, apigenin, pinocembrin and quercetin by new high-performance thin-layer chromatographic (HPTLC) methods. The physico-chemical analysis, residues analysis and in vitro antioxidant activity analysis were performed. Nutraceutical value was examined in terms of fats, fibers, minerals, proteins, polysaccharides, total carbohydrates, and energy value.

RESULTS

The developed HPTLC methods were found to be simple, reliable accurate, and the validation parameters were within the limits of the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use guidelines. Macerated ethanolic extract of propolis (MEEP) was found to have polyphenolic content of (20.99 ± 0.24) mg/g and flavonoids content of (8.39 ± 0.04) mg/g. MEEP was found to comprise of (283.33 ± 51.31) g/kg fats, (30.07 ± 7.30) g/kg fibers, (102.56 ± 2.84) g/kg proteins and (389.36 ± 57.50) g/kg carbohydrate with a calorie value of (38 409.33 ± 6 169.80) kJ/kg. It was found that Indian propolis exhibited high nutraceutical value and showed absence of pesticides and heavy metals. The MEEP showed in vitro antioxidant activity with inhibitory concentration of (12.24 ± 4.64) μg/mL.

CONCLUSION

The present work explores Indian propolis as a potential nutritious candidate. The proposed analytical methods can be applied in future screening of the quality of Indian propolis.

Isoform selectivity of harmine-conjugated 1,2,3-triazoles against human monoamine oxidase

AIM

There is little information available on the monoamine oxidase isoform selectivity of N-alkyl harmine analogs, which exhibit a myriad of activities including MAO-A, DYRK1A and cytotoxicity to several select cancer cell lines.

RESULTS

Compounds 3e and 4c exhibited an IC₅₀ of 0.83 ± 0.03 and 0.43 ± 0.002 μM against MAO-A and an IC₅₀ of 0.26 ± 0.04 and 0.36 ± 0.001 μM against MAO-B, respectively. Molecular docking studies revealed π-π interactions between the synthesized molecules and aromatic amino acid residues. Conclusion & future perspective: The current study delineates the structural requirements for MAO-A selectivity and such information may be helpful in designing selective analogs for kinase, DYRK1A and harmine-based cytotoxics without apparent MAO enzyme inhibition.

Nutraceutical Potential of Phenolics from 'Brava' and 'Mansa' Extra-Virgin Olive Oils on the Inhibition of Enzymes Associated to Neurodegenerative Disorders in Comparison with Those of 'Picual' and 'Cornicabra'

The increasing interest in the Mediterranean diet is based on the protective effects against several diseases, including neurodegenerative disorders. Polyphenol-rich functional foods have been proposed to be unique supplementary and nutraceutical treatments for these disorders. Extra-virgin olive oils (EVOOs) obtained from 'Brava' and 'Mansa', varieties recently identified from Galicia (northwestern Spain), were selected for in vitro screening to evaluate their capacity to inhibit key enzymes involved in Alzheimer's disease (AD) (acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and 5-lipoxygenase (5-LOX)), major depressive disorder (MDD) and Parkinson's disease (PD) (monoamine oxidases: hMAO-A and hMAO-B respectively). 'Brava' oil exhibited the best inhibitory activity against all enzymes, when they are compared to 'Mansa' oil: BuChE (IC50 = 245 ± 5 and 591 ± 23 mg·mL-1), 5-LOX (IC50 = 45 ± 7 and 106 ± 14 mg·mL-1), hMAO-A (IC50 = 30 ± 1 and 72 ± 10 mg·mL-1) and hMAO-B (IC50 = 191 ± 8 and 208 ± 14 mg·mL-1), respectively. The inhibitory capacity of the phenolic extracts could be associated with the content of secoiridoids, lignans and phenolic acids.

Isolation and Biological Evaluation of Prenylated Flavonoids from Maclura pomifera

Phytochemical analysis of the ethanolic extract of Maclura pomifera fruits yielded four new compounds (I-IV) along with eleven known compounds (V-XV). The crude extract exhibited significant activity towards cannabinoid receptors (CB1: 103.4% displacement; CB2: 68.8% displacement) and possibly allosteric interaction with δ and μ opioid receptors (-49.7 and -53.8% displacement, resp.). Compound I was found to be possibly allosteric for κ and μ opioid receptors (-88.4 and -27.2% displacement, resp.) and showed moderate activity (60.5% displacement) towards CB1 receptor. Compound II exhibited moderate activity towards cannabinoid receptors CB1 and CB2 (47.9 and 42.3% displacement, resp.). The known compounds (V-VIII) exhibited prominent activity towards cannabinoid receptors: pomiferin (V) (IC50 of 2.110 and 1.318 μM for CB1 and CB2, resp.), auriculasin (VI) (IC50 of 8.923 μM for CB1), warangalone (VII) (IC50 of 1.670 and 4.438 μM for CB1 and CB2, resp.), and osajin (VIII) (IC50 of 3.859 and 7.646 μM for CB1 and CB2, resp.). The isolated compounds were also tested for inhibition of human monoamine oxidase-A and monoamine oxidase-B enzymes activities, where all the tested compounds showed fewer inhibitory effects on MAO-A compared to MAO-B activities: auriculasin (VI) (IC50 of 1.91 and 45.98 μM for MAO-B and MAO-A, resp.).

Design, Synthesis and Biological Evaluation of Novel N-Pyridyl-Hydrazone Derivatives as Potential Monoamine Oxidase (MAO) Inhibitors

A new series of N-pyridyl-hydrazone derivatives was synthesized by using a simple and efficient method. The final compounds obtained were screened for their inhibitory potency against monoamine oxidase (MAO) A and B. The newly synthesized compounds 2a-2n specifically inhibited monoamine oxidases, displaying notably low IC₅₀ values. Compounds 2i and 2j, with a CF₃ and OH group on the 4-position of the phenyl ring, respectively, showed considerable MAO-A and MAO-B inhibitory activities. Compounds 2k, 2l and 2n, with N-methylpyrrole, furan and pyridine moieties instead of the phenyl ring, were the most powerful and specific inhibitors of MAO-A, with IC₅₀ values of 6.12 μM, 10.64 μM and 9.52 μM, respectively. Moreover, these active compounds were found to be non-cytotoxic to NIH/3T3 cells. This study supports future studies aimed at designing MAO inhibitors to obtain more viable medications for neurodegenerative disorders, such as Parkinson's disease.

Evaluation of Anxiolytic and Antidepressant-like Activity of Aqueous Leaf Extract of Nymphaea Lotus Linn. in Mice

The search for psychoactive plants possessing therapeutic potential in the treatment of anxiety and depression has attracted growing interest. One such plant, Nymphaea lotus (commonly known as water lily), is used in traditional medicine for analgesic and sedative effects. The present study sought to assess the anti-anxiety and antidepressant activities of crude leaf extract of N. lotus and determine possible mechanisms of action. Barbiturate sleep induction, rota-rod, light/dark box, elevated plus maze, forced swimming test (FST) and open field test (OFT) were conducted. Male Albino Swiss mice were treated orally with vehicle 10 mL/kg, imipramine 15 mg/kg (reference drug in the FST), diazepam 1 or 5 mg/kg (reference drug in the OFT) or N. lotus extract (CEN) 20, 60 or 180 mg/kg. Mice were pretreated with p-chlorophenylalanine methyl ester (PCPA) 100 mg/kg, α-methyl-p-tyrosine (AMPT) 100 mg/kg, prazosin (PRAZ) 0.5 mg/kg or yohimbine (YOH) 1 mg/kg prior to oral administration of vehicle 10 mL/kg or CEN 20 mg/kg to determine potential mechanisms of action. Monoamine oxidase (MAO) assay and quantification of brain derived neurotrophic factor (BDNF) were performed. CEN potentiated sodium pentobarbital-induced hypnotic effect and anxiolytic-like effect without altering immobility time in FST. Both MAO activity and BDNF level remained unchanged. These results suggest anxiolytic-like effect of CEN and involvement of noradrenergic mechanism due to the blockade of anxiolytic-like effect by AMPT and PRAZ.

Cytotoxic Activity of Propolis Extracts from the Stingless Bee Trigona Sirindhornae Against Primary and Metastatic Head and Neck Cancer Cell Lines

Background:

Propolis, a resinous substance produced by the honeybee, has a wide spectrum of potent biological activities. However, anti-cancer activity of propolis obtained from Trigona sirindhornae, a new species of stingless bee, has not yet been reported. This study concerned cytotoxicity of propolis extracts from T. sirindhornae against two head and neck squamous cell carcinoma (HNSCC) cell lines.

Materials and Methods:

A dichloromethane extract of propolis (DMEP) was prepared generating 3 fractions: DMEP-A, DMEP-B, and DMEP-C. Genetically-matched HNSCC cell lines derived from primary (HN30) and metastatic sites (HN31) in the same patient were used to study cytotoxic effects of the DMEPs by MTT assays. The active compounds in the DMEPs were analyzed by reverse-phase high performance liquid chromatography.

Results:

DMEP-A exhibited cytotoxic activity on HN30 cells with significantly decreased viability at 200 µg/ml compared with the control (p<0.05). However, no significant cytotoxic effect was evident in HN31 cells. DMEP-B and DMEP-C significantly decreased the viability of both cell lines from 100–200 µg/ml and 50–200 µg/ml, respectively (p<0.05). Interestingly, HN31 cells were more toxically sensitive compared with the HN30 cells when treated with DMEP-B and DMEP-C. IC₅₀ values for DMEP-B with HN30 and HN31 cells were more than 200 µg/ml and 199.8±1.05 µg/ml, respectively. The IC₅₀ of DMEP-C to HN30 and HN31 cells was found to be 114.3±1.29 and 76.33±1.24 µg/ml, respectively. Notably, apigenin, pinocembrin, p-coumaric acid, and caffeic acid were not detected in our propolis extracts.

Conclusion:

T. sirindhornae produced propolis displays cytotoxic effects against HNSCC cells s. Moreover, DMEP-B and DMEP-C differentially inhibited the proliferation of a metastatic HNSCC cell line.

Monoamine Oxidase Inhibitory Activity of Biflavonoids from Branches of Garcinia gardneriana (Clusiaceae)

Garcinia gardneriana is chemically characterized by the presence of biflavonoids. Taking into account that flavonoids are able to inhibit monoamine oxidase (MAO) activity, in the present study, the chemical composition of the branches’ extract of the plant is described for the first time and the MAO inhibitory activity of the isolated biflavonoids was evaluated. Based on spectroscopic and spectrometric data, it was possible to identify volkesiflavone, morelloflavone (1), Gb-2a (2) and Gb-2a-7- O-glucoside (3) in the ethyl acetate fraction from ethanol extract of the branches. Compounds 1-3 were evaluated in vitro and demonstrated the capacity to inhibit MAO-A activity with an IC50 ranging from 5.05 to 10.7 μM, and from 20.7 to 66.2 μM for MAO-B. These inhibitions corroborate with previous IC50 obtained for monomeric flavonoids, with a higher selectivity for MAO-A isoform. The obtained results indicate that biflavonoids might be promising structures for the identification of new MAO inhibitory compounds.

Patients on psychotropic medications and herbal supplement combinations: clinical considerations

Populations using herbs and herbal preparations are widespread and growing. As many herbal ingredients exert actions on psychotropic drug targets, psychiatrists should be well informed and aware of potential drug-drug interactions in clinical practice. Reliable and clinically useful information in this area, however, is fragmented, if not deficient. This paper reviewed the clinical aspects of herb-drug interactions, focusing in particular on the monoamine oxidase enzyme and P450 cytochrome enzyme-inhibitory properties of herbs and their potential interference with psychotropic drug actions and clinical judgement.

Ciproxifan, a histamine H3 receptor antagonist, reversibly inhibits monoamine oxidase A and B

Ciproxifan is a well-investigated histamine H₃ receptor (H3R) inverse agonist/antagonist, showing an exclusively high species-specific affinity at rodent compared to human H3R. It is well studied as reference compound for H3R in rodent models for neurological diseases connected with neurotransmitter dysregulation, e.g. attention deficit hyperactivity disorder or Alzheimer’s disease. In a screening for potential monoamine oxidase A and B inhibition ciproxifan showed efficacy on both enzyme isoforms. Further characterization of ciproxifan revealed IC₅₀ values in a micromolar concentration range for human and rat monoamine oxidases with slight preference for monoamine oxidase B in both species. The inhibition by ciproxifan was reversible for both human isoforms. Regarding inhibitory potency of ciproxifan on rat brain MAO, these findings should be considered, when using high doses in rat models for neurological diseases. As the H3R and monoamine oxidases are all capable of affecting neurotransmitter modulation in brain, we consider dual targeting ligands as interesting approach for treatment of neurological disorders. Since ciproxifan shows only moderate activity at human targets, further investigations in animals are not of primary interest. On the other hand, it may serve as starting point for the development of dual targeting ligands.

The Benzopyrone Biochanin-A as a reversible, competitive, and selective monoamine oxidase B inhibitor

Background

Monoamine oxidase-B (MAO-B) inhibitors are widely used in the treatment of Parkinson’s disease. They increase vital monoamine neurotransmitters in the brain. However, there is a need for safer natural reversible MAO inhibitors with MAO-B selectivity. Our previous studies showed that Psoralea corylifolia seeds (PCS) extract contains compounds that inhibit monoamine oxidase-B.

Methods

In this study, six of PCS constituents sharing a benzopyrone structure were investigated. The compounds Biochanin-A (BIO-A), isopsoralen, 6-prenylnaringenin, neobavaisoflavone, psoralen, and psoralidin, were tested for their ability to inhibit recombinant human MAO-A and B (hMAO-A and hMAO-B) isozymes. The ability of these compounds to inhibit MAO-A and MAO-B were compared to that of PCS ethanolic extract (PCSEE) using spectrophotometric assays and confirmed by luminescence assays. The highly potent and selective MAO-B inhibitor, BIO-A, was further investigated for both isozymes reversibility and enzyme kinetics. Molecular docking studies were used to predict the bioactive conformation and molecular interactions of BIO-A with both isozymes.

Results

The data obtained indicate that benzopyrones inhibited hMAO-A and hMAO-B with different degrees as confirmed with the luminescence assay. BIO-A inhibited hMAO-B with high potency and selectivity in the present study (IC₅₀ = 0.003 μg/mL) and showing 38-fold more selectivity than PCSEE (hMAO-B IC₅₀ = 3.03 μg/mL, 17-fold selectivity) without affecting hydrogen peroxide. Furthermore, BIO-A reversibly and competitively inhibited both hMAOs with significantly lower inhibitory constant (K_i) in hMAO-B (3.8 nM) than hMAO-A (99.3 nM). Our docking studies indicated that the H-bonds and hydrophobic interactions at the human MAO-A and MAO-B active sites contributed to the reversibility and selectivity of BIO-A.

Conclusions

The data obtained indicate that BIO-A is a potent, reversible and selective MAO-B inhibitor and may be recommended for further investigation in its possible use in the therapeutic management of Parkinson’s and Alzheimer’s diseases.

Phytochemical and ethnomedicinal study of Huperzia species used in the traditional medicine of Saraguros in Southern Ecuador; AChE and MAO inhibitory activity

ETHNOBOTANICAL AND ETHNOMEDICINAL RELEVANCE

This study concerns seven Huperzia species (Lycopodiaceae), namely H. brevifolia, H. columnaris, H. compacta, H. crassa, H. espinosana, H. tetragona, H. weberbaueri, which are considered sacred plants by the Saraguro community, living in the Southern Andes of Ecuador; these plants are widely used in traditional medicine and ritual ceremonies.

MATERIAL AND METHODS

The plants were selected on the basis of written interviews with 10 visionary healers (yachak) (2 women, 8 men), indicated as the most credible by the Saraguro Healers Council. The Informant Consensus Factor (F_ic) was determined. The first phytochemical study of the plants was performed by standard procedures, while the AChE and MAO-A inhibition by fractions enriched in high MW alkaloids, was measured in vitro.

AIMS OF THE STUDY

i) to investigate the uses of some Huperzia plants in healing and magical-religious practices of Saraguros; ii) to identify the main components of plant hydromethanolic extracts; iiì) to test the effects of alkaloidal fractions on the activity of two enzymes linked to mental health.

RESULTS

All the interviewed Saraguro yachak showed a high consensus about the uses of the seven Huperzia plants as purgatives and against supernatural diseases, such as the "espanto" (startle). In admixtures with other plants, some species also induce a state of trance or hallucinations in participants in magical-religious rituals. GC-MS of the volatile alkaloid fractions allowed the identification of some lycodine-type and lycopodine-type alkaloids (1-5) in H. compacta, H. columnaris, and H. tetragona. The flavones selgin) (6) and tricin (7) were isolated from H. brevifolia and H. espinosana. Tricin (7) was also detected in the other five species. The rare serratene triterpenes serratenediol (8) serratenediol-3-O-acetate (9), 21-episerratenediol (10), and 21-episerratenediol-3-O-acetate (11) were isolated from H. crassa. In addition, the presence of an unprecedented group of high molecular weight alkaloids has been determined. Alkaloid fractions of H. brevifolia, H. compacta, H. espinosana, and H. tetragona significantly inhibited AChE and MAO-A activities in vitro.

CONCLUSIONS

The first phytochemical and ethnopharmacological study of seven Huperzia plants, widely used by Saraguro healers, led to the identification of several alkaloids and triterpenoids with different remarkable biological activities. In addition, alkaloid fractions exhibited a significant AChE and MAO-A inhibitory activity. These results may support the use of these plants in brews prepared for inducing psychoactive effects in participants in magical-religious ceremonies. This study confirms the rich traditional medical knowledge of Saraguro healers which must be documented and preserved for future generations.

Inhibition of Human Monoamine Oxidase: Biological and Molecular Modeling Studies on Selected Natural Flavonoids

Naturally occurring flavonoids display a plethora of different biological activities, but emerging evidence suggests that this class of compounds may also act as antidepressant agents endowed with multiple mechanisms of action in the central nervous system, increasing central neurotransmission, limiting the reabsorption of bioamines by synaptosomes, and modulating the neuroendocrine and GABA_A systems. Due to their presence in foods, food-derived products, and nutraceuticals, we established their role and structure-activity relationships as reversible and competitive human monoamine oxidase (MAO) inhibitors. In addition, molecular modeling studies, which evaluated their modes of MAO inhibition, are presented. These findings could provide pivotal implications in the quest of novel drug-like compounds and for the establishment of harmful drug-dietary supplement interactions commonly reported in the therapy with antidepressant agents.

Isolation of Acacetin from Calea urticifolia with Inhibitory Properties against Human Monoamine Oxidase-A and -B

Calea urticifolia (Asteraceae: Asteroideae) has long been used as a traditional medicine in El Salvador to treat arthritis and fever, among other illnesses. The chloroform extract of the leaves of C. urticifolia showed potent inhibition of recombinant human monoamine oxidases (MAO-A and -B). Further bioassay-guided fractionation led to the isolation of a flavonoid, acacetin, as the most prominent MAO inhibitory constituent, with IC₅₀ values of 121 and 49 nM for MAO-A and -B, respectively. The potency of MAO inhibition by acacetin was >5-fold higher for MAO-A (0.121 μM vs 0.640 μM) and >22-fold higher for MAO-B (0.049 μM vs 1.12 μM) as compared to apigenin, the closest flavone structural analogue. Interaction and binding characteristics of acacetin with MAO-A and -B were determined by enzyme-kinetic assays, enzyme-inhibitor complex binding, equilibrium-dialysis dissociation analyses, and computation analysis. Follow-up studies showed reversible binding of acacetin with human MAO-A and -B, resulting in competitive inhibition. Acacetin showed more preference toward MAO-B than to MAO-A, suggesting its potential for eliciting selective pharmacological effects that might be useful in the treatment of neurological and psychiatric disorders. In addition, the binding modes of acacetin at the enzymatic site of MAO-A and -B were predicted through molecular modeling algorithms, illustrating the high importance of ligand interaction with negative and positive free energy regions of the enzyme active site.

Kinetics of Inhibition of Monoamine Oxidase Using Curcumin and Ellagic Acid

Background:

Curcumin and ellagic are the natural polyphenols having a wide range of pharmacological actions. They have been reported to have their use in various neurological disorders.

Objective:

This study was aimed to evaluate the effect of curcumin and ellagic acid on the activity of monoamine oxidase (MAO), the enzyme responsible for metabolism of monoamine neurotransmitters which are pivotal for neuronal development and function.

Materials and Methods:

The in vitro effects of these selected polyphenols on MAO activities in mitochondria isolated from rat brains were examined. Brain mitochondria were assayed for MAO type-B (MAO-B) using benzylamine as substrates. Rat brain mitochondrial MAO preparation was used to study the kinetics of enzyme inhibition using double reciprocal Lineweaver–Burk plot.

Results:

MAO activity was inhibited by curcumin and ellagic acid; however, higher half maximal inhibitory concentrations of curcumin (500.46 nM) and ellagic acid (412.24 nM) were required compared to the known MAO-B inhibitor selegiline. It is observed that the curcumin and ellagic acid inhibit the MAO activity with both the competitive and noncompetitive type of inhibitions.

Conclusions:

Curcumin and ellagic acid can be considered a possible source of MAO inhibitor used in the treatment of Parkinson's and other neurological disorders.

SUMMARY

Monoamine oxidase (MAO) is involved in a variety of neurological disorders including Parkinson's disease (PD)

Curcumin and ellagic acid inhibit the monoamine oxidase activity

Ellagic acid revealed more potent MAO type-B (MAO-B) inhibitory activity than curcumin

Kinetic studies of MAO inhibition using different concentrations of curcumin and ellagic acid were plotted as double reciprocal Lineweaver–Burk plot

The mode of inhibition of both compounds toward MAO-B is mixed (competitive and uncompetitive) type of inhibition with both the competitive and noncompetitive type of inhibitions.

Abbreviations used: MAO: Monoamine oxidase, IC₅₀: Higher half maximal inhibitory concentrations, PD: Parkinson's disease, LB: Lewy bodies, SNpc: Substantia nigra pars compacta, ROS: Reactive oxygen species, SG: Selegiline, DMC: demethoxycurcumin, BDMC: Bisdemethoxycurcumin.

Evaluation of the Isoflavone Genistein as Reversible Human Monoamine Oxidase-A and -B Inhibitor

Monoamine oxidases inhibitors (MAOIs) are effective therapeutic drugs for managing Parkinson's disease (PD) and depression. However, their irreversibility may lead to rare but serious side effects. As finding safer and reversible MAOIs is our target, we characterized the recombinant human (h) MAO-A and MAO-B inhibition potentials of two common natural isoflavones, genistein (GST) and daidzein (DZ) using luminescence assay. The results obtained showed that DZ exhibits partial to no inhibition of the isozymes examined while GST inhibited hMAO-B (IC₅₀ of 6.81 μM), and its hMAO-A inhibition was more potent than the standard deprenyl. Furthermore, the reversibility, mode of inhibition kinetics, and tyramine oxidation of GST were examined. GST was a time-independent reversible and competitive hMAO-A and hMAO-B inhibitor with a lower K_i of hMAO-B (1.45 μM) than hMAO-A (4.31 μM). GST also inhibited hMAO-B tyramine oxidation and hydrogen peroxide production more than hMAO-A. Docking studies conducted indicated that the GST reversibility and hMAO-B selectivity of inhibition may relate to C5-OH effects on its orientation and its interactions with the threonine 201 residue of the active site. It was concluded from this study that the natural product GST has competitive and reversible MAOs inhibitions and may be recommended for further investigations as a useful therapeutic agent for Parkinson's disease.

Kaempferol as Selective Human MAO-A Inhibitor: Analytical Detection in Calabrian Red Wines, Biological and Molecular Modeling Studies

The purpose of this work was to determine the kaempferol content in three red wines of Calabria, a southern Italian region with a great number of certified food products. Considering that wine cultivar, climate, and soil influence the qualitative and quantitative composition in flavonoids of Vitis vinifera L. berries, the three analyzed samples were taken from the 2013 vintage. Moreover, the Gaglioppo samples, with assigned Controlled Origin Denomination (DOC), were also investigated in the production of years 2008, 2010, and 2011. In addition to the analysis of kaempferol, which is present in higher concentration than in other Italian wines, in vitro assays were performed to evaluate, for the first time, the inhibition of the human monoamine oxidases (hMAO-A and hMAO-B). Molecular recognition studies were also carried out to provide insight into the binding mode of kaempferol and selectivity of inhibition of the hMAO-A isoform.

Natural polyphenols: Influence on membrane transporters

Accumulated evidence has focused on the use of natural polyphenolic compounds as nutraceuticals since they showed a wide range of bioactivities and exhibited protection against variety of age-related disorders. Polyphenols have variable potencies to interact, and hence alter the activities of various transporter proteins, many of them classified as anion transporting polypeptide-binding cassette transporters like multidrug resistance protein and p-glycoprotein. Some of the efflux transporters are, generally, linked with anticancer and antiviral drug resistance; in this context, polyphenols may be beneficial in modulating drug resistance by increasing the efficacy of anticancer and antiviral drugs. In addition, these effects were implicated to explain the influence of dietary polyphenols on drug efficacy as result of food-drug interactions. However, limited data are available about the influence of these components on uptake transporters. Therefore, the objective of this article is to review the potential efficacies of polyphenols in modulating the functional integrity of uptake transporter proteins, including those terminated the effect of neurotransmitters, and their possible influence in neuropharmacology.

Evaluation of the Inhibitory Effects of Bavachinin and Bavachin on Human Monoamine Oxidases A and B

Monoamine oxidase B inhibitors (MAO-BIs) are used in the early management of Parkinson's disease (PD). Long-term suspected side effects of MAO-B classical inhibitors established the need for safer alternative therapeutic agents. In our study, the flavanone bavachinin (BNN) and its analog bavachin (BVN) found in the seeds of Psoralea corylifolia L. ethanolic extract (PCSEE) were investigated for their human MAO-A and MAO-B (hMAO-A and hMAO-B) inhibition. Both PCSEE and BNN effectively reduced hMAO-B activity more than hMAO-A while BVN had activating effects. BNN showed selective hMAO-B inhibition (IC₅₀ ~ 8.82 μM) more than hMAO-A (IC₅₀2009;~ 189.28 μM). BNN in the crude extract was determined by HPLC, also validated by TLC showing a yield of 0.21% PCSEE dry weight. BNN competitively inhibited hMAO-A and hMAO-B, with a lower hMAO-B K_i than hMAO-A K_i by 10.33-fold, and reduced hMAO-B K_m/V_max efficiency ratio to be comparable to the standard selegiline. Molecular docking examination of BNN and BVN predicted an indirect role of BNN C7-methoxy group for its higher affinity, selectivity, and reversibility as an MAO-BI. These findings suggest that BNN, which is known to be a potent PPAR-γ agonist, is a selective and competitive hMAO-B inhibitor and could be used in the management of PD.

Oleanolic acid acrylate elicits antidepressant-like effect mediated by 5-HT1A receptor

The development of new drugs for the treatment of depression is strategic to achieving clinical needs of patients. This study evaluates antidepressant-like effect and neural mechanisms of four oleanolic acid derivatives i.e. acrylate (D1), methacrylate (D2), methyl fumarate (D3) and ethyl fumarate (D4). All derivatives were obtained by simple one-step esterification of oleanolic acid prior to pharmacological screening in the forced swimming (FS) and open field (OF) tests. Pharmacological tools like α-methyl-p-tyrosine (AMPT, catecholamine depletor), p-chlorophenylalanine (serotonin depletor), prazosin (PRAZ, selective α1-receptor antagonist), WAY-100635 (selective serotonin 5-HT_1A receptor antagonist) as well as monoamine oxidase (MAO) and functional binding assays were conducted to investigate possible neural mechanisms. In the FS test, D1 showed the most promising antidepressant-like effect without eliciting locomotor incoordination. Unlike group of mice pretreated with AMPT 100 mg/kg, PCPA 100 mg/kg or PRAZ 1 mg/kg, the effect of D1 was attenuated by WAY-100635 0.3 mg/kg pretreatment. D1 demonstrated moderate inhibition of MAO-A (IC₅₀ = 48.848 ± 1.935 μM), potency (pEC₅₀ = 6.1 ± 0.1) and intrinsic activity (E_max = 26 ± 2.0%) on 5-HT_1A receptor. In conclusion, our findings showed antidepressant-like effect of D1 and possible involvement of 5-HT_1A receptor.