1,3,4-Oxadiazol-2-ylbenzenesulfonamides as privileged structures for the inhibition of monoamine oxidase B.

The present study investigates the monoamine oxidase (MAO) inhibition properties of a series of ten 5-aryl-1,3,4-oxadiazol-2-ylbenzenesulfonamides. The target compounds were synthesized by dehydration of the corresponding N,N'-diacylhydrazines with phosphorus oxychloride to yield the 1,3,4-oxadiazole cycle with concomitant transformation of the sulfonamide to the sulfonyl chloride group. Treatment with aqueous ammonia in acetonitrile regenerated the target sulfonamides. The results of the enzymology document that these compounds are potent and specific MAO-B inhibitors with the most potent compound exhibiting an IC50 value of 0.0027 µM. An analysis of the structure-activity relationships shows that the 4-benzenesulfonamides are significantly more potent MAO-B inhibitors than the corresponding 3-benzenesulfonamides, and that the corresponding N,N'-diacylhydrazine synthetic precursors are weak MAO inhibitors. Although MAO inhibition by oxadiazole compounds are known, this is the first report of nanomolar MAO inhibition potencies recorded for sulfonamide derivatives. MAO-B specific inhibitors such as those discovered here may be of interest in the treatment of neurodegenerative disorders such as Parkinson's disease.

Discovery, synthesis, biological evaluation and molecular docking study of (R)-5-methylmellein and its analogs as selective monoamine oxidase A inhibitors.

(R)-5-Methylmellein (5-MM), the major ingredient in the fermented mycelia of the medicinal fungus Xylaria nigripes (called Wuling Shen in Chinese)¸ was found to be a selective inhibitor against monoamine oxidase A (MAO-A) and might play an important role in the clinical usage of this edible fungus as an anti-depressive traditional Chinese medicine (TCM). Based on the discovery and hypothesis, a variety of (R)-5-MM analogs were synthesized and evaluated in vitro against two monoamine oxidase isoforms (MAO-A and MAO-B). Most synthetic analogs showed selective inhibition of MAO-A with IC50 values ranging from 0.06 to 29 µM, and compound 13aR is the most potent analog with high selectivity (IC50, MAO-A: 0.06 µM; MAO-B: >50 µM). Interestingly, the enzyme kinetics study of 13aR indicated that this ligand seemed to bind in the MAO-A active site according to so-called "tight-binding inhibition" mode. The molecular docking study of 13aR was thereafter performed in order to rationalize the obtained biological results.

Isoflavones prevent oxidative stress and inhibit the activity of the enzyme monoamine oxidase in vitro.

Oxidative stress occurs due to an imbalance between antioxidant defenses and pro-oxidant agents in brain. This condition has been associated to the pathogenesis of several brain diseases; therefore, increasing the use of compounds that exert antioxidant activity. Thus, the objective of this study was to evaluate, in vitro, the effect of isoflavones in: (1) lipid peroxidation, catalase activity and thiol groups in the presence of pro-oxidants: sodium nitroprusside or Fe2+/EDTA complex in rat brain homogenates; (2) the activity of the enzyme monoamine oxidase (MAO). As a result, the isoflavones reduced lipid peroxidation in a manner dependent on the concentration and protected against the reduction of catalase activity as well as the induced thiol oxidation in brain tissue. In addition, isoflavones inhibited MAO activity (MAO-A and MAO-B). Taken together, our results showed that isoflavones avoided oxidative stress and decreased the MAO activity, suggesting a promissory use in the treatment of neurodegenerative diseases.

Docking of Natural Products against Neurodegenerative Diseases: General Concepts.

BACKGROUND: Since antiquity, humanity has used medicinal plant preparations to cure its ills, and, as research has progressed, new technologies have enabled more investigations on natural compounds which originate from plants, fungi, and marine species. The health benefits that these natural products provide have become a motive for treatment studies of various diseases. OBJECTIVE: Among them, the neurodegenerative diseases like Alzheimer's and Parkinson's, a major age-related neurodegenerative disorder. Studies with natural products for neurodegenerative diseases (particularly through molecular docking) search for, and then focus on those ligands which offer effective inhibition of the enzymes monoamine oxidase and acetylcholinesterase. METHOD: This review introduces the main concepts involved in docking studies with natural products: and also in our group, which has conducted a docking study of natural products isolated from Tetrapterys mucronata for inhibition of acetylcholinesterase. RESULTS: We observed that compounds 4 and 5 formed more interactions than the theoretical ligand, but that ligands with greater activity also interacted with residues HIS 381 and GLN 527. CONCLUSION: We have reported on our docking study performed with AChE and alkaloids isolated from the plant Tetrapterys mucronata. Our docking results corroborate the experiments conducted, and emphasize the positive contribution that these theoretical studies involving natural products bring to the fight against neurodegenerative diseases.

Analysis of monoamine oxidase (MAO) enzymatic activity by high-performance liquid chromatography-diode array detection combined with an assay of oxidation with a peroxidase and its application to MAO inhibitors from foods and plants.

Monoamine oxidase (MAO) enzymes catalyze the oxidative deamination of biogenic amines and neurotransmitters and produce ammonia, aldehydes, and hydrogen peroxide which is involved in oxidative processes. Inhibitors of MAO-A and -B isozymes are useful as antidepressants and neuroprotectants. The assays of MAO usually measure amine oxidation products or hydrogen peroxide by spectrophotometric techniques. Those assays are often compromised by interfering compounds resulting in poor results. This research describes a new method that combines in the same assay the oxidative deamination of kynuramine to 4-hydroxyquinoline analyzed by HPLC-DAD with the oxidation of tetramethylbenzidine (TMB) (or Amplex Rex) by horseradish peroxidase (HRP) in presence of hydrogen peroxide. The new method was applied to study the inhibition of human MAO-A and -B by bioactive compounds including ß-carboline alkaloids and flavonoids occurring in foods and plants. As determined by HPLC-DAD, ß-carbolines, methylene blue, kaempferol and clorgyline inhibited MAO-A and methylene blue, 5-nitroindazole, norharman and deprenyl inhibited MAO-B, and all of them inhibited the oxidation of TMB in the same extent. The flavonoids catechin and cyanidin were not inhibitors of MAO by HPLC-DAD but highly inhibited the oxidation of TMB (or Amplex Red) by peroxidase whereas quercetin and resveratrol were moderate inhibitors of MAO-A by HPLC-DAD, but inhibited the peroxidase assay in a higher level. For some phenolic compounds, using the peroxidase-coupled assay to measure MAO activity led to mistaken results. The new method permits to discern between true inhibitors of MAO from those that are antioxidants and which interfere with peroxidase assays but do not inhibit MAO. For true inhibitors of MAO, inhibition as determined by HPLC-DAD correlated well with inhibition of the oxidation of TMB and this approach can be used to assess the in vitro antioxidant activity (less hydrogen peroxide production) resulting from MAO inhibition.

Characterization of the binding site for d-deprenyl in human inflamed synovial membrane.

AIMS: d-Deprenyl when used as a positron emission tomography tracer visualizes peripheral inflammation. The major aim of the current study was to identify and investigate the properties of the binding target for d-deprenyl in synovial membrane explants from arthritic patients. MAIN METHODS: Thirty patients diagnosed with arthritis or osteoarthritis were enrolled into the study. Homologous and competitive radioligand binding assays utilizing [3H]d-deprenyl were performed to investigate the biochemical characteristics of the binding site and assess differences in the binding profile in synovial membranes exhibiting varying levels of inflammation. KEY FINDINGS: The [3H]d-deprenyl binding assay confirmed the existence of a single, saturable population of membrane-bound protein binding sites in synovial membrane homogenates. The macroscopically determined level of inflammation correlated with an increase in [3H]d-deprenyl binding affinity, without significant alterations in binding site density. Selective monoamine oxidase B inhibitor, selegiline competed for the same site as [3H]d-deprenyl, but failed to differentiate the samples with regard to their inflammation grade. A monoamine oxidase A inhibitor, pirlindole mesylate showed only weak displacement of [3H]d-deprenyl binding. No significant alterations in monoamine oxidase B expression was detected, thus it was not confirmed whether it could serve as a marker for ongoing inflammation. SIGNIFICANCE: Our study was the first to show the biochemical characteristics of the [3H]d-deprenyl binding site in inflamed human synovium. We confirmed that d-deprenyl could differentiate between patients with varying severity of synovitis in the knee joint by binding to a protein target distinct from monoamine oxidase B.

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.

Bioactive properties of commercialised pomegranate (Punica granatum) juice: antioxidant, antiproliferative and enzyme inhibiting activities.

Pomegranate juice and related products have long been used either in traditional medicine or as nutritional supplements claiming beneficial effects. Although there are several studies on this food plant, only a few studies have been performed with pomegranate juice or marketed products. The aim of this work is to evaluate the antioxidant effects of pomegranate juice on cellular models using hydrogen peroxide as an oxidizing agent or DPPH and superoxide radicals in cell free systems. The antiproliferative effects of the juice were measured on HeLa and PC-3 cells by the MTT assay and pharmacologically relevant enzymes (cyclooxygenases, xanthine oxidase, acetylcholinesterase and monoamine oxidase A) were selected for enzymatic inhibition assays. Pomegranate juice showed significant protective effects against hydrogen peroxide induced toxicity in the Artemia salina and HepG2 models; these effects may be attributed to radical scavenging properties of pomegranate as the juice was able to reduce DPPH and superoxide radicals. Moderate antiproliferative activities in HeLa and PC-3 cancer cells were observed. However, pomegranate juice was also able to inhibit COX-2 and MAO-A enzymes. This study reveals some mechanisms by which pomegranate juice may have interesting and beneficial effects in human health.

Plant secondary metabolites- potent inhibitors of monoamine oxidase isoforms.

Target of monoamine oxidase inhibitions are considered as the treatment of depressive states and neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. Many medicinal chemistry research groups are actively working in this area for the development of most promising selective MAO inhibitors. Many plant isolates also showed remarkable MAO inhibition in recent years. The objective of this review is to identify the major MAO inhibitors secondary metabolites from plants like flavonoids, alkaloids and xanthones class of compounds.

Development of a novel fluorine-18 labeled deuterated fluororasagiline ([(18)F]fluororasagiline-D2) radioligand for PET studies of monoamino oxidase B (MAO-B).

The objective of this study was to synthesize and evaluate a novel fluorine-18 labeled deuterium substituted analogue of rasagiline (9, [(18)F]fluororasagiline-D2) as a potential PET radioligand for studies of monoamine oxidase B (MAO-B). The precursor compound (6) and reference standard (7) were synthesized in multi-step syntheses. Radiolabeling of 9 was accomplished by a two-step synthesis, compromising a nucleophilic substitution followed by hydrolysis of the sulfamidate group. The incorporation radiochemical yield from fluorine-18 fluoride was higher than 30%, the radiochemical purity was >99% and the specific radioactivity was >160GBq/µmol at the time of administration. In vitro compound 7 inhibited the MAO-B activity with an IC50 of 173.0±13.6nM. The MAO-A activity was inhibited with an IC50 of 9.9±1.1µM. The fluorine-18 version 9 was characterized in the cynomolgus monkey brain where a high brain uptake was found (275% SUV at 4min). There was a higher uptake in the striatum and thalamus compared to the cortex and cerebellum. A pronounced blocking effect (50% decrease) was observed in the specific brain regions after administration of l-deprenyl (0.5mg/kg) 30min prior to the administration of 9. Radiometabolite studies demonstrated 40% of unchanged radioligand at 90min post injection. An efficient radiolabeling of 9 was successfully established and in the monkey brain 9 binds to MAO-B rich regions and its binding is blocked by the selective MAO-B compound l-deprenyl. The radioligand 9 is a potential candidate for human PET studies.

Monoamine reuptake inhibition and mood-enhancing potential of a specified oregano extract.

A healthy, balanced diet is essential for both physical and mental well-being. Such a diet must include an adequate intake of micronutrients, essential fatty acids, amino acids and antioxidants. The monoamine neurotransmitters, serotonin, dopamine and noradrenaline, are derived from dietary amino acids and are involved in the modulation of mood, anxiety, cognition, sleep regulation and appetite. The capacity of nutritional interventions to elevate brain monoamine concentrations and, as a consequence, with the potential for mood enhancement, has not been extensively evaluated. The present study investigated an extract from oregano leaves, with a specified range of active constituents, identified via an unbiased, high-throughput screening programme. The oregano extract was demonstrated to inhibit the reuptake and degradation of the monoamine neurotransmitters in a dose-dependent manner, and microdialysis experiments in rats revealed an elevation of extracellular serotonin levels in the brain. Furthermore, following administration of oregano extract, behavioural responses were observed in mice that parallel the beneficial effects exhibited by monoamine-enhancing compounds when used in human subjects. In conclusion, these data show that an extract prepared from leaves of oregano, a major constituent of the Mediterranean diet, is brain-active, with moderate triple reuptake inhibitory activity, and exhibits positive behavioural effects in animal models. We postulate that such an extract may be effective in enhancing mental well-being in humans.

[Inhibition of liver mitochondrial monoamine oxidase activity by alkaloids isolated from Chelidonium and Macleaya and by their derivative drugs]. / Ingibirovanie aktivnosti mitokhondrial'noi monoaminoksidazy alkaloidami iz chistotela i makleii i lekarstvami na ikh osnove.

It has been shown that the major alkaloids from plants Chelidonium majus L. and Macleaya (Bocconia) cordata and microcarpa, namely, berberine, sanguinarine, chelidonine, and drugs "Ukrain" (thiophosphoric acid derivative of a sum of the alkaloids isolated from Ch. majus L.) and "Sanguirythrine" (a mixture of the alkaloids sanguinarine and chelerythrine, w/w 3:7, isolated from Macleaya), are irreversible inhibitors of oxidative deamination reaction of serotonin and tyramine as substrates, catalyzed by rat liver mitochondrial monoamine oxidase (MAO). At the same time these substances do not influence the oxidative deamination reaction of benzylamine as substrate (in concentration 1 mM or less). The substrate specificity of this inhibition manifests that mainly the oxidative deamination reactions catalyzed by MAO form A are inhibited by the agents studied. Among the examined agents, alkaloid chelidonine and drug "Ukrain" are the strongest inhibitors of the reaction. Alkaloids berberine and sanguinarine and drug "Sanguirythrine" exhibit a weaker action. Judging from the data obtained, sanguinarine and chelerythrine appear to exert similar inhibitory effects in this reaction, since sanguinarine and "Sanguirythrine" have similar values of bimolecular rate constants of their interaction with mitochondrial MAO. As it is well known, the MAO inhibitors appear to be, as a rule, pronounced antidepressants. The combination of malignotoxicity and antidepressive activity in drug "Ukrain" seems to be favourable for its clinical applications.

Neuroprotection in the MPTP Parkinsonian C57BL/6 mouse model by a compound isolated from tobacco.

Epidemiological evidence suggests a lower incidence of Parkinson's disease in smokers than in nonsmokers. This evidence, together with the lower levels of brain monoamine oxidase (MAO) activity in smokers and the potential neuroprotective properties of MAO inhibitors, prompted studies which led to the isolation and characterization of 2,3,6-trimethyl-1,4-naphthoquinone (TMN), an MAO-A and MAO-B inhibitor which is present in tobacco and tobacco smoke. Results of experiments reported here provide evidence that this compound protects against the MPTP-mediated depletion of neostriatal dopamine levels in the C57BL/6 mouse. These results support the hypothesis that the inhibition of MAO by constituents of tobacco smoke may be related to the decreased incidence of Parkinson's disease in smokers.

Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental study.

The roots of Withania somnifera (WS) are used extensively in Ayurveda, the classical Indian system of medicine, and WS is categorized as a rasayana, which are used to promote physical and mental health, to provide defence against disease and adverse environmental factors and to arrest the aging process. WS has been used to stabilize mood in patients with behavioural disturbances. The present study investigated the anxiolytic and antidepressant actions of the bioactive glycowithanolides (WSG), isolated from WS roots, in rats. WSG (20 and 50 mg/kg) was administered orally once daily for 5 days and the results were compared by those elicited by the benzodiazepine lorazepam (0.5 mg/kg, i.p.) for anxiolytic studies, and by the tricyclic anti-depressant, imipramine (10 mg/kg, i.p.), for the antidepressant investigations. Both these standard drugs were administered once, 30 min prior to the tests. WSG induced an anxiolytic effect, comparable to that produced by lorazepam, in the elevated plus-maze, social interaction and feeding latency in an unfamiliar environment, tests. Further, both WSG and lorazepam, reduced rat brain levels of tribulin, an endocoid marker of clinical anxiety, when the levels were increased following administration of the anxiogenic agent, pentylenetetrazole. WSG also exhibited an antidepressant effect, comparable with that induced by imipramine, in the forced swim-induced 'behavioural despair' and 'learned helplessness' tests. The investigations support the use of WS as a mood stabilizer in clinical conditions of anxiety and depression in Ayurveda.

Selective inhibitors of monoamine oxidase (MAO). 5. 1-Substituted phenoxathiin inhibitors containing no nitrogen that inhibit MAO A by binding it to a hydrophobic site.

It is believed that a monoamine oxidase (MAO) inhibitor specific for MAO A, which is reversibly bound to this enzyme and displaceable by tyramine, will be an antidepressant which will not cause a rise in blood pressure when tyramine-containing foods are ingested. Some linear tricyclic compounds with a larger and a smaller group forming the central ring and with a lipophilic group ortho to the larger group (here mostly the SO2 function of phenoxathiin 10,10-dioxide) are reported to have the sought properties. Potency appears to require short length and relatively small cross section for the substituent. The 1-ethyl (13), 1-vinyl (22), 1-trifluoromethyl (27), and 1-iodo (76) phenoxathiin dioxides had the best profiles. Structure-activity relationships, syntheses, and a possible rationale for the selectivity of these compounds and related tricyclics are given. Compound 13 was selected for further development. A summary of pharmacological data for 13 is given.

Effect of extract of Rhazya stricta, a traditional medicinal plant, on rat brain tribulin.

Rhazya stricta leaves, which have both antidepressant and sedative properties in animal models, are widely used in folk medicine in the Arabian peninsula. In this study, the effects of oral administration of leaf extracts on rat brain tribulin levels [endogenous monoamine oxidase (MAO) A and B inhibitory activity], were determined. In an acute study, low doses brought about an increase in MAO A inhibitory activity, while intermediate doses caused a significant reduction. The highest doses had no significant effects on activity. There were no significant effects on MAO B inhibitory activity at any dose. Subchronic administration (21 days) caused a significant decrease in MAO A inhibitory activity, most prominent at low dosage, and an increase in MAO B inhibitory activity. Acute intramuscular administration also resulted in a similar pattern. Such paradoxical effects were at least partially explained when different extracts of the leaves were used; a weakly basic chloroform fraction caused an increase in MAO A inhibitory activity, whereas butanol extracts brought about a decrease. These fractions had no significant effects on MAO B inhibitory activity. The findings show that Rhazya stricta leaves contain at least two different components that affect MAO inhibitory activity in opposite directions. It may be that the antidepressant and sedative actions of the plant are explicable in terms of these different components.

Anxiolytic activity of Panax ginseng roots: an experimental study.

The putative anxiolytic activity of the white and red varieties of ginseng, the root of Panax ginseng, was investigated in rats and mice using a number of experimental paradigms of anxiety and compared with that of diazepam. Pilot studies indicated that single-dose administration of ginseng had little to no acute behavioural effects, hence the two varieties of ginseng were administered orally at two dose levels twice daily for 5 days, while diazepam (1 mg/kg, i.p.) was administered acutely. White and red varieties of ginseng (20 and 50 mg/kg) showed positive results when tested against several paradigms of experimental anxiety. Both were effective in the open-field and elevated plus-maze tests and reduced conflict behaviour in thirsty rats and footshock-induced fighting in paired mice. Ginseng also attenuated pentylenetetrazole-induced decrease in rat brain MAO activity, confirming its anxiolytic activity since this has been proposed to be an endogenous marker for anxiety. The effects induced by white and red ginseng (50 mg/kg x 5 days) were comparable to those induced by diazepam (1 mg/kg).

Serotonergic effects of isatin: an endogenous MAO inhibitor related to tribulin.

A study of the acute effects of isatin, an endogenous MAO inhibitor related to tribulin, on rat brain serotonergic function was undertaken. A single dose of isatin significantly increased 5-HT concentrations in the hypothalamus and cortex but did not significantly alter 5-HIAA concentrations. Synaptosomal 5-HT uptake was unaffected but there was a trend for the number of 3H-ketanserin binding sites was to be decreased. The results of the study are discussed in terms of the relationship of isatin to tribulin and their possible causal role in stress.

Failure to detect any transport of the irreversible monoamine oxidase inhibitor N-cyclopropyl-4-chloroamphetamine by the carrier of 5-hydroxytryptamine in the brain of the rat in vivo.

N-Cyclopropyl-4-chloroamphetamine (LY 93716) was examined for its potential preference for inhibiting the activity of monoamine oxidase (MAO) within serotonergic nerve terminals in the hypothalamus of the rat. Such an effect should support the hypothesis of Fuller and Perry (1977) (Neuropharmacology 16: 495-497) that this compound is transported by the uptake mechanism for 5-hydroxytryptamine (5-HT). By using a small (0.1 microM) substrate concentration of [14C]5-HT and a synaptosomal preparation incubated in the absence and presence of a selective inhibitor of the uptake of 5-HT (citalopram) it is possible to measure the activity of MAO in serotonergic nerve terminals. It was found that LY 93716 caused greater inhibition outside than inside the serotonergic nerve terminals when the activity of MAO was analysed 24 hr after the injection, but an inverted relationship was observed when analysed 72 hr after administration. Inhibition of uptake did not cause any change in the inhibition of MAO within the serotonergic nerve terminals at the former time but antagonized the inhibition observed 72 hr after the injection. It is concluded that the latter effect was due to antagonism of the neurotoxic action of LY 93716 and that no evidence was found that LY 93716 is transported by the uptake carrier for 5-HT.