MAO Isoforms Research Articles

Discovery, Biological Evaluation, and Structure–Activity and −Selectivity Relationships of 6′-Substituted (E)-2-(Benzofuran-3(2H)-ylidene)-N-methylacetamides, a Novel Class of Potent and Selective Monoamine Oxidase Inhibitors

The use of selective inhibitors of monoamine oxidase A (MAO-A) and B (MAO-B) holds a therapeutic relevance in the treatment of depressive disorders and Parkinson's disease (PD), respectively. Here, the discovery of a new class of compounds acting as monoamine oxidase inhibitors (MAO-Is) and bearing a 6'-substituted (E)-2-(benzofuran-3(2H)-ylidene)-N-alkylacetamide skeleton is reported. 6'-Sulfonyloxy derivatives exhibited outstanding affinities to MAO-A (7.0 nM < IC50 < 49 nM, much higher than moclobemide) and a pronounced MAO-A/B selectivity. The corresponding 6'-benzyloxy derivatives showed potent MAO-B inhibition and inverted selectivity profile. The rigid E-geometry of the exocyclic double bond allowed a more efficient binding conformation compared to more flexible and less active 2-(1-benzofuran-3-yl)-N-methylacetamide isomers and 4-N-methylcarboxamidomethylcoumarin analogues. Focused structural modifications and docking simulations enabled the identification of key molecular determinants for high affinity toward both MAO isoforms. These novel MAO-Is may represent promising hits for the development of safer therapeutic agents with a potential against depression, PD, and other age-related neurodegenerative pathologies.

Synthesis, molecular modeling, and in vitro screening of monoamine oxidase inhibitory activities of some novel hydrazone derivatives

Thirteen 2-[2-(5-methyl-2-benzoxazolinone-3-yl)acetyl]-3/4/5-substituted benzylidenehydrazine derivatives were synthesized by reacting 2-(5-methyl-2-benzoxazolinone-3-yl)acetylhydrazine and substituted benzaldehydes in neutral and acid/base catalyzed conditions, and a comparison was made in terms of their yields and reaction times. The structures of all compounds were confirmed by IR, (1)H NMR, (13)C NMR, mass spectral data, and elemental analyses. All the compounds were investigated for their ability to selectively inhibit MAO isoforms by in vitro tests and were found to inhibit recombinant human MAO-B selectively and reversibly in a competitive manner. Among the compounds examined, compound 16 was found to be more selective than selegiline, a known MAO-B inhibitor, in respect to the K i values experimentally found. Additionally, compounds 9 and 15 showed moderate MAO-B inhibitor activity. The interaction of compounds with MAO isoforms was investigated by molecular docking studies using recently published crystallographic models of MAO-A and MAO-B. The results obtained from the docking studies were found to be in good agreement with the experimental values.

Investigation of the neuroprotective action of saffron (Crocus sativus L.) in aluminum-exposed adult mice through behavioral and neurobiochemical assessment

In the present study, the possible reversal effects of saffron against established aluminum (Al)-toxicity in adult mice, were investigated. Control, Al-treated (50mg AlCl3/kg/day diluted in the drinking water for 5weeks) and Al+saffron (Al-treatment as previously plus 60mg saffron extract/kg/day intraperitoneally for the last 6days), groups of male Balb-c mice were used. We assessed learning/memory, the activity of acetylcholinesterase [AChE, salt-(SS)/detergent-soluble(DS) isoforms], butyrylcholinesterase (BuChE, SS/DS isoforms), monoamine oxidase (MAO-A, MAO-B), the levels of lipid peroxidation (MDA) and reduced glutathione (GSH), in whole brain and cerebellum. Brain Al was determined by atomic absorption spectrometry, while, for the first time, crocetin, the main active metabolite of saffron, was determined in brain after intraperitoneal saffron administration by HPLC. Al intake caused memory impairment, significant decrease of AChE and BuChE activity, activation of brain MAO isoforms but inhibition of cerebellar MAO-B, significant elevation of brain MDA and significant reduction of GSH content. Although saffron extract co-administration had no effect on cognitive performance of mice, it reversed significantly the Al-induced changes in MAO activity and the levels of MDA and GSH. AChE activity was further significantly decreased in cerebral tissues of Al+saffron group. The biochemical changes support the neuroprotective potential of saffron under toxicity.

Exploring Nitrostyrene as a Scaffold for a New Class a of Monoamine Oxidase Inhibitors

With the ultimate purpose of finding out the structural features that are relevant for MAO inhibitory activity and selectivity towards MAO-B isoform, a series of compounds encompassing a β-nitrostyrene moiety was designed and the in vitro inhibitory activity was evaluated. In the present work, we report the synthesis and the pharmacological evaluation of a series of functionalized derivatives of β-methyl-β-nitrostyrene with distinct substitution patterns in the phenyl ring, namely hydroxyl, methoxy, benzyloxy and methylenedioxy. All the studied compounds were substituted in meta and para positions of the phenyl ring related to the nitrovinyl side chain. The synthesized compounds were evaluated towards both human MAO isoforms, displaying some of them activities in the low micromolar range. Particularly compound 6 (a methylenedioxy derivative) exhibits high potency and selectivity towards MAO-B.

Special Issue: Amine oxidases: structures, mechanisms and therapeutic targets

On 18 July 2010, more than 60 researchers from 15 different countries gathered at the University of Alberta in Edmonton, Canada, to participate in the 14th International Amine Oxidase Workshop: AO 2010. The inaugural conference, held in 1984, was the result of the persuasive powers of Keith Tipton and Moussa Youdim, who convinced Brian Callingham to host the first official meeting of the unofficial ‘‘Amine Oxidase Club’’. The workshop was therefore held at Queens’ College, Cambridge, and was organized by Callingham and assisted by Tipton, Youdim and Lars Oreland. Several amine oxidase meetings had been organized sporadically over a 13-year period leading up to the 1984 Cambridge workshop; the first was held 40 years ago, in Cagliari, Sardinia (1971), and four more meetings took place during the following decade, in London (1975), Midland, Michigan (1979), Hakone (1981) and Heidelberg (1982). These meetings were, for the most part, organized as unique events on behalf of institutions or companies, but the increased interest in the area following the discovery of separate MAO isoforms highlighted a need for a more regular exchange of information. Thus, the International Amine Oxidase Workshop was born, and the decision was made during the Cambridge meeting that future workshops should be held every two years. Previous meetings have generally focused upon monoamine oxidase (MAO; EC 1.4.3.4) and semicarbazidesensitive amine oxidase/diamine oxidase (EC 1.4.3.6; recently reclassified separately as EC 1.4.3.21, primary amine oxidase [PrAO], and EC 1.4.3.22, diamine oxidase). MAO and PrAO were covered extensively in Edmonton, with the expanding influence of MAO in various neuropathologies, as well as emerging links between PrAO and several cardiovascular and metabolic conditions, leading to much discussion. Furthermore, given the recent resurgence in interest in trace amines—neuromodulatory substrates for amine oxidases—and in their receptors, a tradition was continued by including a session covering trace amine research in the Edmonton workshop program. Discussion of the lysyl oxidase field was also introduced to the scientific program for the first time. Though lysyl oxidase (EC 1.4.3.13) is typically thought of with regard to its role in cross-linking connective tissue, significant breakthroughs in the past decade have revealed a potential involvement for this enzyme in metastatic cancers, cellular differentiation and chemotaxis. As a potential novel drug target, the development of selective therapeutics targeting lysyl oxidase would be facilitated by comparing its structure and mechanism with those of other copper-containing amine oxidases, as well as with MAOs. Similarly, the development of ideas proposing a role for PrAO in connective tissue architecture would benefit from an understanding of what has been done with lysyl oxidase in this regard, and it was with these thoughts in mind that Herb Kagan was invited to assist in introducing lysyl oxidase to the Amine Oxidase Workshop. It is hoped that these new links forged in Edmonton between related fields will be strengthened through continued participation in future workshops. A major objective of the Edmonton meeting was to provide an opportunity for trainees and young scientists new to the field to present their work to an audience of internationally renowned experts in a relaxed and collegial setting. It is safe to say that this objective was achieved; the quality of presentations from numerous junior scientists in A. Holt (&) G. B. Baker Edmonton, Canada e-mail: aholt@pmcol.ualberta.ca

Synthesis of new 3-aryl-4,5-dihydropyrazole-1-carbothioamide derivatives. An investigation on their ability to inhibit monoamine oxidase

Some differently substituted 3-aryl-4,5-dihydropyrazoles-1-carbothioamides have been synthesised with the aim to investigate their monoamine oxidase inhibitory activity. The chemical structures of the compounds have been characterized by means of their IR, 1H NMR, 13C NMR spectroscopic data and elemental analyses. All the active compounds showed a selective activity towards the B isoform of the enzyme, regardless of the substitution on the heterocyclic ring. The inhibition of the enzymatic activity was measured on human recombinant MAO isoforms, expressed in baculovirus infected BTI insect cells. Docking experiments were carried out with the aim to rationalize the mechanism of inhibition of the most active and selective compound.

Chromone-2- and -3-carboxylic acids inhibit differently monoamine oxidases A and B

Chromone carboxylic acids were evaluated as human monoamine oxidase A and B ( hMAO-A and hMAO-B) inhibitors. The biological data indicated that only chromone-3-carboxylic acid is a potent hMAO-B inhibitor, with a high degree of selectivity for hMAO-B compared to hMAO-A. Conversely the chromone-2-carboxylic acid resulted almost inactive against both MAO isoforms. Docking experiments were performed to elucidate the reasons of the different MAO IC 50 data and to explain the absence of activity versus selectivity, respectively.

Inhibition of monoamine oxidase by 8-benzyloxycaffeine analogues

Based on recent reports that several ( E)-8-styrylcaffeinyl analogues are potent reversible inhibitors of monoamine oxidase B (MAO-B), a series of 8-benzyloxycaffeinyl analogues were synthesized and evaluated as inhibitors of baboon liver MAO-B and recombinant human MAO-A and -B. The 8-benzyloxycaffeinyl analogues were found to inhibit reversibly both MAO isoforms with enzyme–inhibitor dissociation constants ( K i values) ranging from 0.14 to 1.30 μM for the inhibition of human MAO-A, and 0.023–0.59 μM for the inhibition of human MAO-B. The most potent MAO-A inhibitor was 8-(3-methylbenzyloxy)caffeine while 8-(3-bromobenzyloxy)caffeine was the most potent MAO-B inhibitor. The analogues inhibited human and baboon MAO-B with similar potencies. A quantitative structure–activity relationship (QSAR) study indicated that the MAO-B inhibition potencies of the 8-benzyloxycaffeinyl analogues are dependent on the Hansch lipophilicity (π) and Hammett electronic ( σ) constants of the substituents at C-3 of the benzyloxy ring. Electron-withdrawing substituents with a high degree of lipophilicity enhance inhibition potency. These results are discussed with reference to possible binding orientations of the inhibitors within the active site cavities of MAO-A and -B.

Development of Spin-Labeled Pargyline Analogues as Specific Inhibitors of Human Monoamine Oxidases A and B

Three TEMPO-conjugated pargyline analogues (ParSL-1, ParSL-2, and ParSL-3) have been synthesized and their inhibitory properties tested for the two human monoamine oxidase isoforms (hMAOA and hMAOB). The three analogues differ in flexibility and substituent positions (para or meta) of the linkers connecting the TEMPO group to the pargyline phenyl ring. ParSL-1 contains a flexible acetamido (-CH(2)-CO-NH-) linker connecting the two moieties at the para position. In contrast, the TEMPO moieties in ParSL-2 and ParSL-3 are attached with rigid amido (-CO-NH-) linkers to the para or meta positions of the pargyline phenyl ring, respectively. These variations in conformational flexibility and substituent position are shown to have profound effects in tuning the specificities of these analogues toward the two MAO isoforms. ParSL-1 irreversibly inhibits either MAOA and MAOB, ParSL-2 inhibits only MAOB (K(i) = 15 +/- 5 microM), and ParSL-3 is found to be specific for MAOA (K(i) = 268 +/- 72 microM). These results thus provide additional insights into the role of conformational flexibility and structural properties of MAO inhibitors in tuning their isoform specificities. These active site probes have been used to determine the topological orientation of these enzymes in the mitochondrial membrane. Studies with intact mitochondria show MAOA is topologically on the cytosolic face of the outer membrane in human placenta but recombinant MAOA is situated on the opposite inner face in Pichia mitochondria. Recombinant MAOB is found to be situated on the cytosolic face of the outer membrane in Pichia mitochondria.

Pyrazoline-based mycobactin analogues as MAO-inhibitors

3,5-Diaryl carbothioamide pyrazolines designed as mycobactin analogs (mycobacterial siderophore) were reported to be potent antitubercular agents under iron limiting condition in our earlier study. Clinical complications of newly introduced antibiotic Linezolid, due its MAO inhibitory activity, prompted us to evaluate our compounds for their MAO-inhibitory activity against rat liver MAO-A and MAO-B as pyrazolines were reported to be antidepressants and MAO inhibitors. The present study carried out with this pilot library of 32 compounds will provide us with necessary information for designing antitubercular molecules with reduced MAO-inhibitory activity and also help us in identifying a selective MAO-B inhibitor which has potential clinical utility in neurodegenerative disorders. Thirty-two compounds analyzed has shown spectrum of activity from selective to nonselective against two isoforms of rat liver MAO-A and MAO-B and also as competitive, reversible to non-competitive, irreversible. It is also interesting to note that anti-tubercular compound 11, 14 and 16 were also found to be selective inhibitors of rat liver MAO-B. Docking studies with human MAO shows that compound 11 interacts with the catalytic site of both the isoforms, suggesting compound 11 as nonselective inhibitor of human MAO isoforms.

MAO inhibition by arylisopropylamines: the effect of oxygen substituents at the β-position

Twenty-nine arylisopropylamines, substituted at the β-position of their side chain by an oxo, hydroxy, or methoxy group, were evaluated in vitro as MAO-A and MAO-B inhibitors. The oxo derivatives (`cathinones') were in general less active as MAO-A inhibitors than the corresponding arylisopropylamines, but exhibited an interesting MAO-B inhibiting activity, which was absent in the hydroxy, methoxy, and β-unsubstituted analogues. These results suggest that selective affinity for the two MAO isoforms in this family of compounds is modulated not only by the aryl substitution pattern but also by the side-chain substituents on the arylalkylamine scaffold.

Binding of the imidazoline ligand 3H-2-benzofuranyl-2-imidazoline (BFI) to human brain and platelets. Potentiation by tranylcypromine and role of MAO isoforms.

Binding of the imidazoline ligand 3H-2-benzofuranyl-2-imidazoline (BFI) to human brain and platelets. Potentiation by tranylcypromine and role of MAO isoforms.