Inhibition of monoamine oxidase–A activity in rat brain by synthetic hydrazines: Structure-activity relationship (SAR)

A series of hydrazine derivatives was synthesized in order to evaluate their monoamine oxidase A (MAO-A) inhibitory effects. MAO-A inhibitory activity of 4-tosyl benzoic acid carbohydrazide was quite potent, similarly to that of the corresponding 4-benzyloxy-benzoic acid carbohydrazide and its N-cyanoethylated derivative. Structural variations of these compounds, such as the replacement of the 4-substitutent, of the aromatic ring on which the carbohydrazide moiety is grafted, as well as cyclization of the hydrazide moiety in five- or six-membered rings caused either significant decline or complete loss of MAO inhibitory properties. The most active compound (4-tosyl benzoic acid carbohydrazide) was also subjected to the forced swim test, an animal model of depression, eliciting a marked reduction in immobility time in rats, without affecting the locomotor activity, implying that it possesses anti-depressant properties due to inhibition of MAO type-A.     

干酪乳杆菌JH23代谢产物对单胺氧化酶的抑制作用

本文旨在分离干酪乳杆菌JH-23中具有抑制单胺氧化酶(MAO)活性的代谢产物.用乙酸乙酯对干酪乳杆菌JH23发酵液进行抽提,得到的脂溶性成分和水溶性成分在一定浓度范围内对MAO的抑制活性呈较好的量效关系.其中,脂溶性成分对MAO-A、MAO-B抑制作用的IC50分别为1.97和5.67 mg/mL;水溶性成分对MAO-A、MAO-B抑制作用的IC50分别为1.59和4.83 mg/mL.抑制特征曲线显示,两者对MAO-A与MAO-B的抑制作用均呈竞争性抑制.从水溶性成分中分离得到的活性组分W1对MAO-A、MAO-B抑制作用的IC50分别为0.33和1.13 mg/mL.通过进一步分离,以及红外和质谱分析,确定了组分W1中具有较强MAO抑制作用的物质为琥珀酸.     

Inhibition of Monoamine Oxidase by 3,4-Dihydroxyphenylserine

The effects of diastereomers of 3,4-dihydroxyphenylserine (DOPS) on the enzyme activity of monoamine oxidase (MAO) in human placenta and liver mitochondria were examined. Both L- and D-threo-DOPS were found to inhibit MAO-A in human placental mitochondria in competition with the substrate, and the Ki values for L- and D-threo-DOPS obtained were 68.3 and 125 microM, respectively. The inhibitory effect of L-threo-DOPS on both MAO-A and -B activity was confirmed in human liver mitochondria, and MAO-A was found to be more sensitive to the inhibitor. Other isomers of DOPS, L- and D-erythro-DOPS, were found to inhibit MAO activity, but the inhibition was noncompetitive with the substrate. The inhibitory effects of DOPS isomers were not affected by the presence of NSD-1055, an inhibitor of aromatic L-amino acid decarboxylase, suggesting that the inhibition is the direct effect of DOPS, and not of norepinephrine produced by the decarboxylase.     

Inhibition of Type A Monoamine Oxidase by Methylquinolines and Structurally Related Compounds

Abstract: A series of methylquinolines (MQ) were found to inhibit markedly type A monoamine oxidase (MAO) in human brain synaptosomal mitochondria. 4-MQ and 6-MQ inhibited type A MAO (MAO-A) competitively and 7- and 8-MQ inhibited MAO-A noncompetitively. Among these four isomers of MQ, 6-MQ was the most potent inhibitor; the K _i value toward MAO-A was 23.4 ± 1.8 μ M , which was smaller than the K _m value toward kynuramine, ± amine substrate, 46.2 ± 2.8 μ M . On the other hand, MQ were very weak inhibitors of type B MAO (MAO-B) and 8-MQ did not inhibit MAO-B in brain synaptosomal mitochondria. The inhibition of MAO-A proved to be reversible; by dialysis the inhibition of MQ was completely reversible. The affinity of these isomers of MQ toward MAO-A or -B was confirmed further with human liver mitochondria as sources of MAO-A and -B and with human placental mitochondria and rat pheochromocytoma PC12h cell line as sources of MAO-A. The relationship of the chemical structure of structurally related quinoline and isoquinoline derivatives to inhibition of the activity of type A or B MAO was examined.     

Synthesis and inhibitory effect of piperine derivates on monoamine oxidase

A series of piperine derivates (1-19) have been designed, synthesized and evaluated in vitro for their monoamine oxidase (MAO) A and B inhibitory activity and selectivity. It is worth noting that most of the small amine moieties substituted on the piperidine ring proved to be potent and selective inhibitors of MAO-B rather than of MAO-A. 5-(3,4-methylenedioxyphenyl)-2E,4E-pentadienoic acid n-propyl amide (3) showed the greatest MAO-B inhibitory activity (IC(50)(MAO-B)=0.045 μM) and good selectivity (IC(50)(MAO-A)=3.66 μM). The conjugated double bond and carbonyl group of piperine are proved to be an essential feature for piperine and related alkylamides to exhibit MAO-inhibitory activity. Binding mode of the titled compounds was predicted using FlexX algorithm. The design and optimization of novel small molecule monoamine oxidase inhibitors will be guided by the results of this report.     

Inhibition of monoamine oxidase by 8-[(phenylethyl)sulfanyl]caffeine analogues

In a previous study we have investigated the monoamine oxidase (MAO) inhibitory properties of a series of 8-sulfanylcaffeine analogues. Among the compounds studied, 8-[(phenylethyl)sulfanyl]caffeine (IC₅₀ = 0.223 μM) was found to be a particularly potent inhibitor of the type B MAO isoform. In an attempt to discover potent MAO inhibitors and to further examine the structure–activity relationships (SAR) of MAO inhibition by 8-sulfanylcaffeine analogues, in the present study a series of 8-[(phenylethyl)sulfanyl]caffeine analogues were synthesized and evaluated as inhibitors of human MAO-A and -B. The results document that substitution on C3 and C4 of the phenyl ring with alkyl groups and halogens yields 8-[(phenylethyl)sulfanyl]caffeine analogues which are potent and selective MAO-B inhibitors with IC₅₀ values ranging from 0.017 to 0.125 μM. The MAO inhibitory properties of a series of 8-sulfinylcaffeine analogues were also examined. The results show that, compared to the corresponding 8-sulfanylcaffeine analogues, the 8-sulfinylcaffeins are weaker MAO-B inhibitors. Both the 8-sulfanylcaffeine and 8-sulfinylcaffeine analogues were found to be weak MAO-A inhibitors. This study also reports the MAO inhibition properties of selected 8-[(phenylpropyl)sulfanyl]caffeine analogues.     

Synthesis and evaluation of aplysinopsin analogs as inhibitors of human monoamine oxidase A and B

Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms. Previous studies have shown aplysinopsin analogs to possess a variety of biological activities, including modulation of neurotransmissions. A series of fifty aplysinopsin analogs was synthesized and assayed for monoamine oxidase A and B inhibitory activity. Three compounds displayed significant MAO inhibitory activity and selectivity. The compound (E)-5-[(6-bromo-1H-indol-3-yl)methylene]-2-imino-1,3-dimethylimidazolidin-4-one (3x) possessed an IC(50) of 5.6 nM at MAO-A and had a selectivity index of 80.24. An SAR study revealed that multiple N-methylations, one of which should be at position N-2', and bromination at C-5 or C-6 are important factors for MAO-A potency and selectivity.     

Azure B and a synthetic structural analogue of methylene blue,ethylthioninium chloride,present with antidepressant-like properties

Aims

The phenothiazinium compound, methylene blue (MB), possesses diverse pharmacological actions and is attracting attention for the treatment of bipolar disorder and Alzheimer's disease. MB acts on both monoamine oxidase (MAO) and the nitric oxide (NO)-cGMP pathway, and possesses antidepressant activity in rodents. The goal of this study was to synthesise a structural analogue of MB, ethylthioninium chloride (ETC), and to evaluate the effects of the structural changes on the MAO inhibitory and antidepressant properties of MB. This study also investigated the antidepressant properties of azure B, the major metabolite of MB, versus MB and imipramine as active comparators.

Main methods

ETC and azure B were firstly evaluated as inhibitors of human MAO, and secondly for antidepressant-like activity in the acute forced swim test (FST) in rats, and compared to saline, imipramine and MB.

Key findings

The results document that ETC is a reversible inhibitor of MAO-A and MAO-B with IC₅₀ values of 0.510 μM and 0.592 μM, respectively, and that it is a weaker MAO-A inhibitor than MB and azure B. ETC and azure B were more effective than imipramine and MB in reversing immobility in the FST without inducing locomotor effects, with evidence supporting a serotonergic action. Of interest is the finding that ETC is more toxic for cultured cells than MB.

Conclusion

Azure B may therefore be a contributor to the antidepressant effect of MB. Small structural changes made to MB retain its antidepressant effect, even though the resulting phenothiazinium compound possesses reduced MAO-A inhibitory potency.     

Plasma 5-Hydroxyindoleacetic Acid as an Indicator of Monoamine Oxidase-A Inhibition in Rat Brain and Peripheral Tissues

We have examined the changes induced by the monoamine oxidase (MAO; EC 1.4.3.4) inhibitors tranylcypromine, clorgyline, and deprenyl on MAO activity and 5-hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content in rat brain and blood (plasma and whole blood). The decreases of MAO-A activity observed in the liver and lungs after different doses of clorgyline or tranylcypromine correlated significantly (r > 0.80 in all cases) with the decline of plasma 5-HIAA. This was unaffected by 0.25 and 5 mg kg^?1 of deprenyl, indicating that 5-HT was deaminated exclusively in the periphery by MAO-A. It is interesting that very potent and significant correlations (r > 0.75) were found between plasma 5-HIAA and MAO-A activity, 5-HIAA and 5-HT content in brain tissue. These results suggest that plasma 5-HIAA can be used confidently as a peripheral indicator of the inhibition of MAO-A in brain. This may represent a favorable alternative to the analysis of 5-HIAA in CSF in psychiatric patients undergoing antidepressant treatment with nonspecific MAO inhibitors or with the new selective MAO-A inhibitors.     

MAO inhibitory activity modulation: 3-Phenylcoumarins versus 3-benzoylcoumarins

With the aim of finding the structural features for the human MAO inhibitory activity and selectivity, in the present communication we report the synthesis, pharmacological evaluation and a comparative study of a new series of 3-phenylcoumarins (compounds 1-4) and 3-benzoylcoumarins (compounds 5-8). A bromo atom and a methoxy/hydroxy substituent were introduced in these scaffolds, at six and eight positions of the coumarin moiety, respectively. The synthesized compounds 1-8 were evaluated as MAO-A and B inhibitors using R-(−)-deprenyl and iproniazide as reference compounds. The presence or absence of a carbonyl group between the coumarin and the phenyl substituent in 3 position remarks, respectively, the MAO-A or MAO-B inhibitory activity. Some of the new compounds showed MAO-B inhibitory activities in the low nanomolar range. Compound 2 (IC₅₀ = 1.35 nM) showed higher inhibitory activity than the R-(−)-deprenyl (IC₅₀ = 19.60 nM) and higher MAO-B selectivity, with more than 74,074-fold inhibition level, respecting to the MAO-A isoform.     

Characterization of monoamine oxidase isoforms in human islets of Langerhans.

In this paper, we describe the characterization of the expression of monoamine oxidase (MAO) in whole pancreas and in isolated islets of Langerhans from human. Classical monamine oxidase activity assays reveal that both isoforms A & B are present in human pancreas. Two complementary approaches indicated that both MAO A and B are expressed in isolated islet: RT-PCR using specific primers revealed amplification products with the expected size for MAO-A and MAO-B: two peptides corresponding to MAO A (approximately 61 kDa) and B (approximately 55 kDa) were detected using a polyclonal anti MAO-A/MAO-B antiserum. Western blotting and subsequent densitometric analysis indicate that whole and endocrine pancreas express the two isoforms with different relative proportions. Islets appear to express almost twice as much MAO protein as whole pancreas, in near equal proportions of the two isoforms, whereas whole pancreas expresses more MAO-A than the B isoform. The expression of MAO A and B in islets could be the first step toward the characterization of the functional properties of these enzymes in the endocrine pancreas.     

Monoamine oxidase A and B inhibiting effect and molecular modeling of some synthesized coumarin derivatives

New series of bioactive 7-oxycoumarin derivatives were synthesized and tested for their in vitro and in vivo monoamine oxidase (MAO) A and B inhibitory effect. In vitro studies revealed exceptionally potent and selective MAO-A inhibitors with K_i values on a picomolar range. The acetohydrazide (3b) and the dioxopyrrolidine derivative (7b) showed the most potent in vitro and in vivo MAO inhibition activity. Moreover, molecular modeling study of the synthesized compounds into MAO-A (PDB: 2Z5X) and MAO-B (PDB: 2XFN) binding sites exhibited direct correlation between AutoDock binding affinity and% inhibition MAO-A (pM) and MAO-B (μM). In addition, the results of in vivo MAO inhibiting properties (ED₅₀) of the tested compounds revealed better direct correlation.     

Hydroxycoumarins as selective MAO-B inhibitors

A series of 3-aryl-4-hydroxycoumarin derivatives was synthesized with the aim to find out the structural features for the MAO inhibitory activity and selectivity. Methoxy and/or chloro substituents were introduced in the 3-phenyl ring, whereas the position 6 in the coumarin moiety was not substituted or substituted with a methyl group or a chloro atom due to their different electronic, steric and/or lipophilic properties. Most of the synthesized compounds presented MAO-B inhibitory activity. The presence of methoxy and chloro groups, respectively in the para and meta positions of the 3-phenyl ring, have an important influence on the inhibitory activity. Moreover, the presence of a chloro atom in the six position of the moiety (compound 7) improved the inhibitor activity as well as its selectivity against MAO-B compared with iproniazide, used as reference compound. Docking experiments were carried out to understand which are the most energetically preferred orientations adopted by compounds 5, 6 and 7 inside the MAO-B binding pocket.     

Modification of substrate-inhibitor affinities of human platelet monoamine oxidase B in vitro

The rate of benzylamine utilization by monoamine oxidase (MAO)-B from human blood platelets was 2-4 times higher than that for octopamine. Both activities were inhibited 100% by 10(-7) M deprenyl (a specific MAO-B inhibitor) and were not affected by clorgyline (a specific MAO-A inhibitor) or by polyclonal antibodies to MAO-A. The preincubation of platelet MAO-B with purified MAO-A from mitochondrial membranes of human placenta resulted in appearance of excess octopamine activity. This additional activity was not precipitated by antibodies to MAO-A or inhibited by deprenyl but was inhibited by clorgyline. Incubation of the MAO-A preparation from placenta at 45 degrees C for 15 min before its preincubation with MAO-B caused 50% loss of both activities. Protease inhibitors had no effect on the modification of MAO. These data indicate that MAO-A or a factor tightly bound to it can modify MAO-B yielding a form of the enzyme with both MAO-A and MAO-B substrate and inhibitor affinities and MAO-B immunospecificity.     

Inhibition of monoamine oxidase activity by antidepressants and mood stabilizers

OBJECTIVE: Monoamine oxidase (MAO), the enzyme responsible for metabolism of monoamine neurotransmitters, has an important role in the brain development and function, and MAO inhibitors have a range of potential therapeutic uses. We investigated systematically in vitro effects of pharmacologically different antidepressants and mood stabilizers on MAO activity. Methods: Effects of drugs on the activity of MAO were measured in crude mitochondrial fraction isolated from cortex of pig brain, when radiolabeled serotonin (for MAO-A) or phenylethylamine (for MAO-B) was used as substrate. The several antidepressants and mood stabilizers were compared with effects of well known MAO inhibitors such as moclobemide, iproniazid, pargyline, and clorgyline. Results: In general, the effect of tested drugs was found to be inhibitory. The half maximal inhibitory concentration, parameters of enzyme kinetic, and mechanism of inhibition were determined. MAO-A was inhibited by the following drugs: pargyline > clorgyline > iproniazid > fluoxetine > desipramine > amitriptyline > imipramine > citalopram > venlafaxine > reboxetine > olanzapine > mirtazapine > tianeptine > moclobemide, cocaine > lithium, valproate. MAO-B was inhibited by the following drugs: pargyline > clorgyline > iproniazid > fluoxetine > venlafaxine > amitriptyline > olanzapine > citalopram > desipramine > reboxetine > imipramine > tianeptine > mirtazapine, cocaine > moclobemide, lithium, valproate. The mechanism of inhibition of MAOs by several antidepressants was found various. Conclusions: It was concluded that MAO activity is acutely affected by pharmacologically different antidepressants at relatively high drug concentrations; this effect is inhibitory. There are differences both in inhibitory potency and in mechanism of inhibition between both several drugs and the two MAO isoforms. While MAO inhibition is not primary biochemical effect related to their therapeutic action, it can be supposed that decrease of MAO activity may be concerned in some effects of these drugs on serotonergic, noradrenergic, and dopaminergic neurotransmission.     

4-(O-Benzylphenoxy)-N-Methylbutylamine (Bifemelane) and Other 4-(O-Benzylphenoxy)-N-Methylalkylamines as New Inhibitors of Type A and B Monoamine Oxidase

4-(O-Benzylphenoxy)-N-methylbutylamine (Bifemelane, BP-N-methylbutylamine), a new psychotropic drug, was found to inhibit monoamine oxidase (MAO) in human brain synaptosomes. It inhibited type A MAO (MAO-A) competitively and type B (MAO-B) noncompetitively. BP-N-methylbutylamine had a much higher affinity to MAO-A than an amine substrate, kynuramine, and it was a more potent inhibitor of MAO-A than of MAO-B. The Ki values of MAO-A and -B were determined to be 4.20 and 46.0 microM, respectively, while the Km values of MAO-A and -B with kynuramine were 44.1 and 90.0 microM, respectively. The inhibition of MAO-A and -B by BP-N-methylbutylamine was found to be reversible by dialysis of the incubation mixture. MAO-A in human placental and liver mitochondria and in a rat clonal pheochromocytoma cell line, PC12h, was inhibited competitively by BP-N-methylbutylamine, while MAO-B in human liver mitochondria was inhibited noncompetitively, as in human brain synaptosomes. BP-N-methylbutylamine was not oxidized by MAO-A and -B. The effects of other BP-N-methylalkylamines, such as BP-N-methylethylamine, -propylamine, and -pentanylamine, on MAO activity were examined. BP-N-methylbutylamine was the most potent inhibitor of MAO-A, and BP-N-methylethylamine and -propylamine inhibited MAO-B competitively, whereas BP-N-methylbutylamine and -pentanylamine inhibited it noncompetitively. Inhibition of these BP-N-methylalkylamines on MAO-A and -B is discussed in relation to their chemical structure.     

Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). II. Distribution of MAO in different tissues

Monoamine oxidase (MAO) activity was measured fluorometrically in liver, kidney, intestine and brain of adult male and female ring doves. Liver MAO was inhibited in a concentration-related fashion by clorgyline and harmaline (MAO type A inhibitors) where a plateau in the inhibition curve occurred with about 15% activity remaining, and also by the type B inhibitor deprenyl, which produced a plateau when about 85% activity remained. Kidney, intestine and brain MAO were inhibited in a biphasic manner by harmaline. Results with inhibitors suggest that 85% of liver MAO, 86% of kidney MAO, 88% of intestine and 75% of brain MAO is type A. Using 10(-6) M harmaline to differentiate between MAO-A and MAO-B type activities, the apparent maximal velocities (Vmax) and Michaelis constants (Km) were determined in different tissues. Most activity occurred in the intestine, with proportionally lesser amounts of kidney, liver and brain. The majority of MAO present was in the A form. Except for kidney, Km of MAO-B was higher than that of MAO-A. Both MAO-A and -B activities were higher in the intestines of male birds, although sex differences in content and type of MAO activity were not observed in other tissues of the ring dove.     

Quinoline and quninaldine as naturally occurring inhibitors specific for type A monoamine oxidase

Type A monoamine oxidase (MAO-A) in human placental mitochondria was competitively inhibited by naturally occurring substances, quinoline and quinaldine, using kynuramine as substrate. Quinoline had a higher affinity for MAO than kynuramine. MAO-A in human brain synaptosomal mitochondria was also competitively inhibited by quinoline, while type B MAO (MAO-B) was reversibly and non-competitively inhibited by quinoline. Quinoline inhibited MAO-A much more potently than MAO-B. Of several compounds structurally similar to quinoline, isoquinoline noncompetitively inhibited MAO-A and -B activity.     

Umbelliferone derivatives exert neuroprotective effects by inhibiting monoamine oxidase A,self-amyloidβ aggregation,and lipid peroxidation

Umbelliferone has been demonstrated to have a wide range of biological activities. However, the effect of incorporating a formyl moiety in the umbelliferone scaffold has not been investigated. In this paper, we investigated the inhibitory activity of six coumarins, namely umbelliferone (1), 6-formyl umbelliferone (2), 8-formyl umbelliferone (3), umbelliferone-6-carboxylic acid (4), esculetin (5), and scopoletin (6) against human monoamine oxidases (hMAOs), self-amyloid β (Aβ) aggregation, and lipid peroxidation. We found that all compounds had high selectivity for hMAO-A in comparison with hMAO-B. Among the compounds, 2 exhibited the highest hMAO inhibitory activity with an IC₅₀ value of 3.23 µM for hMAO-A and 15.31 µM for hMAO-B. Enzyme kinetic analysis showed that 2 and 3 were competitive hMAO inhibitors. In silico hydrated molecular docking simulations revealed that the coumarins interacted with substrate-binding site residues of the enzymes and the isoalloxazine ring of FAD. In addition, formyl coumarins 2 and 3 significantly inhibited lipid peroxidation in rat brain homogenates and self-Aβ_25-35 aggregation compared to other derivatives. These represent the first experimental and modelling data for hMAO-A/B inhibition by umbelliferone derivatives. Together, the data suggest that introduction of a formyl moiety in the 7-hydroxycoumarin scaffold, especially at the 6 position, plays an important role in the inhibition of hMAOs, Aβ self-aggregation, and lipid peroxidation. Umbelliferone derivative 2 is a promising therapeutic lead scaffold for developing anti-neuropsychiatric disorder drugs that function via selective hMAO-A inhibition.     

Differences in monoamine oxidase activity between cultured noradrenergic and cholinergic sympathetic neurons

Two types of monoamine oxidase activity (MAO-A and MAO-B) help regulate the levels of biogenic amines such as catecholamines and serotonin. Although MAO-A has greater activity toward most catecholamines than MAO-B, no direct experiments have determined the types and levels of MAO activity that are normally expressed in noradrenergic neurons. Noradrenergic neurons from neonatal rat superior cervical ganglia were isolated and cultured under conditions that permit either continued expression of the noradrenergic phenotype or promote a transition to a predominantly cholinergic phenotype. After 14-21 days in vitro, neurons from both types of cultures were assayed for the type and amount of monoamine oxidase activity using tryptamine, a common substrate for both MAO-A and MAO-B. Neurons cultured under noradrenergic conditions expressed sevenfold greater MAO activity than neurons cultured under cholinergic conditions. Essentially all MAO activity in the noradrenergic cultures was inhibited by preincubation with 10(-8)-10(-9) M clorgyline, which indicated that this activity was primarily MAO-A. Cultures grown under cholinergic conditions exhibited 6- to 10-fold lower MAO-A activity and an 8- to 10-fold lower level of catecholamine synthesis from labeled precursors compared to neurons grown under noradrenergic conditions. These results directly demonstrate that high MAO-A activity is expressed in noradrenergic neurons in vitro. The corresponding decreases in both MAO-A specific activity and catecholamine synthesis as neurons become cholinergic in vitro suggest that the expression of the noradrenergic phenotype involves the coordinate regulation of degradative as well as synthetic enzymes involved in catecholamine metabolism.