New directions in monoamine oxidase A and B selective inhibitors and substrates

Characterization of structural, biochemical, pharmacokinetic, and pharmacodynamic properties of the LSD1 inhibitor bomedemstat in preclinical models

INTRODUCTION

Lysine-specific demethylase 1 (LSD1) is emerging as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Neuroendocrine prostate cancer (NEPC) is increasingly recognized as an adaptive mechanism of resistance in mCRPC patients failing androgen receptor axis-targeted therapies. Safe and effective LSD1 inhibitors are necessary to determine antitumor response in prostate cancer models. For this reason, we characterize the LSD1 inhibitor bomedemstat to assess its clinical potential in NEPC as well as other mCRPC pathological subtypes.

METHODS

Bomedemstat was characterized via crystallization, flavine adenine dinucleotide spectrophotometry, and enzyme kinetics. On-target effects were assessed in relevant prostate cancer cell models by measuring proliferation and H3K4 methylation using western blot analysis. In vivo, pharmacokinetic (PK) and pharmacodynamic (PD) profiles of bomedemstat are also described.

RESULTS

Structural, biochemical, and PK/PD properties of bomedemstat, an irreversible, orally-bioavailable inhibitor of LSD1 are reported. Our data demonstrate bomedemstat has >2500-fold greater specificity for LSD1 over monoamine oxidase (MAO)-A and -B. Bomedemstat also demonstrates activity against several models of advanced CRPC, including NEPC patient-derived xenografts. Significant intra-tumoral accumulation of orally-administered bomedemstat is measured with micromolar levels achieved in vivo (1.2 ± 0.45 µM at the 7.5 mg/kg dose and 3.76 ± 0.43 µM at the 15 mg/kg dose). Daily oral dosing of bomedemstat at 40 mg/kg/day is well-tolerated, with on-target thrombocytopenia observed that is rapidly reversible following treatment cessation.

CONCLUSIONS

Bomedemstat provides enhanced specificity against LSD1, as revealed by structural and biochemical data. PK/PD data display an overall safety profile with manageable side effects resulting from LSD1 inhibition using bomedemstat in preclinical models. Altogether, our results support clinical testing of bomedemstat in the setting of mCRPC.

Integrated Binary QSAR-Driven Virtual Screening and In Vitro Studies for Finding Novel hMAO-B-Selective Inhibitors

The increased activity of monoamine oxidase (MAO) enzymes may lead to serious consequences since they reduce the level of neurotransmitters and are associated with severe neurodegenerative diseases. The inhibition of this enzyme, especially the B isoform, plays a vital role in the treatment of Parkinson's disease (PD). This study is aimed to find novel human MAO-B (hMAO-B) selective inhibitors. A total of 256.750 compounds from the Otava small molecules database were virtually screened gradually by employing several screening techniques for this purpose. Initially, a high-throughput virtual screening (HTVS) method was employed, and 10% of the molecules having high docking scores were subjected to binary QSAR models for further screening of their therapeutic activities against PD, Alzheimer's disease (AD), and depression as well as for their toxicity and pharmacokinetic properties. Then, enzyme selectivity of the ligands towards the A and B forms that passed through all the filters were studied using the induced-fit docking method and molecular dynamics simulations. At the end of this exhaustive research, we identified two hit molecules ligand 3 (Otava ID: 7131545) and ligand 4 (Otava ID: 7566820). Based on the in vitro results, these two compounds (ligands 3 and 4) together with ligands 1 and 2 found in our previous study showed activity at the nanomolar (nM) level, and the results indicated that these four ligands inhibit hMAO-B better than the FDA-approved drug selegiline.

Single Heterocyclic Compounds as Monoamine Oxidase Inhibitors: From Past to Present

Inhibitors of monoamine oxidase (MAO) have shown therapeutic values in a variety of neurodegenerative diseases such as depression, Parkinson's disease and Alzheimer's disease. Heterocyclic compounds exhibit a broad spectrum of biological activities and vital leading compounds for the development of chemical drugs. Herein, we focus on the synthesis and screening of novel single heterocyclic derivatives with MAO inhibitory activities during the past decade. This review covers recent pharmacological advancements of single heterocyclic moiety along with structure- activity relationship to provide better correlation among different structures and their receptor interactions.

Mitochondrial ROS Formation in the Pathogenesis of Diabetic Cardiomyopathy

Diabetic cardiomyopathy is a result of diabetes-induced changes in the structure and function of the heart. Hyperglycemia affects multiple pathways in the diabetic heart, but excessive reactive oxygen species (ROS) generation and oxidative stress represent common denominators associated with adverse tissue remodeling. Indeed, key processes underlying cardiac remodeling in diabetes are redox sensitive, including inflammation, organelle dysfunction, alteration in ion homeostasis, cardiomyocyte hypertrophy, apoptosis, fibrosis, and contractile dysfunction. Extensive experimental evidence supports the involvement of mitochondrial ROS formation in the alterations characterizing the diabetic heart. In this review we will outline the central role of mitochondrial ROS and alterations in the redox status contributing to the development of diabetic cardiomyopathy. We will discuss the role of different sources of ROS involved in this process, with a specific emphasis on mitochondrial ROS producing enzymes within cardiomyocytes. Finally, the therapeutic potential of pharmacological inhibitors of ROS sources within the mitochondria will be discussed.

Role of Estradiol in the Expression of Genes Involved in Serotonin Neurotransmission: Implications for Female Depression

BACKGROUND

In women, changes in estrogen levels may increase the incidence and/or symptomatology of depression and affect the response to antidepressant treatments. Estrogen therapy in females may provide some mood benefits as a single treatment or might augment clinical response to antidepressants that inhibit serotonin reuptake.

OBJECTIVE

We analyzed the mechanisms of estradiol action involved in the regulation of gene expression that modulates serotonin neurotransmission implicated in depression.

METHOD

Publications were identified by a literature search on PubMed.

RESULTS

The participation of estradiol in depression may include regulation of the expression of tryptophan hydroxylase-2, monoamine oxidase A and B, serotonin transporter and serotonin-1A receptor. This effect is mediated by estradiol binding to intracellular estrogen receptor that interacts with estrogen response elements in the promoter sequences of tryptophan hydroxylase-2, serotonin transporter and monoamine oxidase-B. In addition to directly binding deoxyribonucleic acid, estrogen receptor can tether to other transcription factors, including activator protein 1, specificity protein 1, CCAAT/enhancer binding protein β and nuclear factor kappa B to regulate gene promoters that lack estrogen response elements, such as monoamine oxidase-A and serotonin 1A receptor.

CONCLUSION

Estradiol increases tryptophan hydroxylase-2 and serotonin transporter expression and decreases the expression of serotonin 1A receptor and monoamine oxidase A and B through the interaction with its intracellular receptors. The understanding of molecular mechanisms of estradiol regulation on the protein expression that modulates serotonin neurotransmission will be helpful for the development of new and more effective treatment for women with depression.

Monoamine oxidase-B inhibitors as potential neurotherapeutic agents: An overview and update

Monoamine oxidase (MAO) inhibitors have made significant contributions and remain an indispensable approach of molecular and mechanistic diversity for the discovery of antineurodegenerative drugs. However, their usage has been hampered by nonselective and/or irreversible action which resulted in drawbacks like liver toxicity, cheese effect, and so forth. Hence, the search for selective MAO inhibitors (MAOIs) has become a substantial focus in current drug discovery. This review summarizes our current understanding on MAO-A/MAO-B including their structure, catalytic mechanism, and biological functions with emphases on the role of MAO-B as a potential therapeutic target for the development of medications treating neurodegenerative disorders. It also highlights the recent developments in the discovery of potential MAO-B inhibitors (MAO-BIs) belonging to diverse chemical scaffolds, arising from intensive chemical-mechanistic and computational studies documented during past 3 years (2015-2018), with emphases on their potency and selectivity. Importantly, readers will gain knowledge of various newly established MAO-BI scaffolds and their development potentials. The comprehensive information provided herein will hopefully accelerate ideas for designing novel selective MAO-BIs with superior activity profiles and critical discussions will inflict more caution in the decision-making process in the MAOIs discovery.

An amine oxidase gene from mud crab, Scylla paramamosain, regulates the neurotransmitters serotonin and dopamine in vitro

Amine oxidase, which participates in the metabolic processing of biogenic amines, is widely found in organisms, including higher organisms and various microorganisms. In this study, the full-length cDNA of a novel amine oxidase gene was cloned from the mud crab, Scylla paramamosain, and termed SpAMO. The cDNA sequence was 2,599 bp in length, including an open reading frame of 1,521 bp encoding 506 amino acids. Two amino acid sequence motifs, a flavin adenine dinucleotide-binding domain and a flavin-containing amine oxidoreductase, were highly conserved in SpAMO. A quantitative real-time polymerase chain reaction analysis showed that the expression level of SpAMO after quercetin treatment was time- and concentration-dependent. The expression of SpAMO tended to decrease and then increase in the brain and haemolymph after treatment with 5 mg/kg/d quercetin; after treatment with 50 mg/kg/d quercetin, the expression of SpAMO declined rapidly and remained low in the brain and haemolymph. These results indicated that quercetin could inhibit the transcription of SpAMO, and the high dose (50 mg/kg/d) had a relatively significant inhibitory effect. SpAMO showed the highest catalytic activity on serotonin, followed by dopamine, β-phenylethylamine, and spermine, suggesting that the specific substrates of SpAMO are serotonin and dopamine. A bioinformatics analysis of SpAMO showed that it has molecular characteristics of spermine oxidase, but a quercetin test and enzyme activity study indicated that it also functions like monoamine oxidase. It is speculated that SpAMO might be a novel amine oxidase in S. paramamosain that has the functions of both spermine oxidase and monoamine oxidase.

Proposing Novel MAO-B Hit Inhibitors Using Multidimensional Molecular Modeling Approaches and Application of Binary QSAR Models for Prediction of Their Therapeutic Activity, Pharmacokinetic and Toxicity Properties

Monoamine oxidase (MAO) enzymes MAO-A and MAO-B play a critical role in the metabolism of monoamine neurotransmitters. Hence, MAO inhibitors are very important for the treatment of several neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). In this study, 256 750 molecules from Otava Green Chemical Collection were virtually screened for their binding activities as MAO-B inhibitors. Two hit molecules were identified after applying different filters such as high docking scores and selectivity to MAO-B, desired pharmacokinetic profile predictions with binary quantitative structure-activity relationship (QSAR) models. Therapeutic activity prediction as well as pharmacokinetic and toxicity profiles were investigated using MetaCore/MetaDrug platform which is based on a manually curated database of molecular interactions, molecular pathways, gene-disease associations, chemical metabolism, and toxicity information. Particular therapeutic activity and toxic effect predictions are based on the ChemTree ability to correlate structural descriptors to that property using recursive partitioning algorithm. Molecular dynamics (MD) simulations were also performed to make more detailed assessments beyond docking studies. All these calculations were made not only to determine if studied molecules possess the potential to be a MAO-B inhibitor but also to find out whether they carry MAO-B selectivity versus MAO-A. The evaluation of docking results and pharmacokinetic profile predictions together with the MD simulations enabled us to identify one hit molecule (ligand 1, Otava ID: 3463218) which displayed higher selectivity toward MAO-B than a positive control selegiline which is a commercially used drug for PD therapeutic purposes.

Privileged scaffolds as MAO inhibitors: Retrospect and prospects

This review aims to be a comprehensive, authoritative, critical, and readable review of general interest to the medicinal chemistry community because it focuses on the pharmacological, chemical, structural and computational aspects of diverse chemical categories as monoamine oxidase inhibitors (MAOIs). Monoamine oxidases (MAOs), namely MAO-A and MAO-B represent an enormously valuable class of neuronal enzymes embodying neurobiological origin and functions, serving as potential therapeutic target in neuronal pharmacotherapy, and hence we have coined the term "Neurozymes" which is being introduced for the first time ever. Nowadays, therapeutic attention on MAOIs engrosses two imperative categories; MAO-A inhibitors, in certain mental disorders such as depression and anxiety, and MAO-B inhibitors, in neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). The use of MAOIs declined due to some potential side effects, food and drug interactions, and introduction of other classes of drugs. However, curiosity in MAOIs is reviving and the recent developments of new generation of highly selective and reversible MAOIs, have renewed the therapeutic prospective of these compounds. The initial section of the review emphasizes on the detailed classification, structural and binding characteristics, therapeutic potential, current status and future challenges of the privileged pharmacophores. However, the chemical prospective of privileged scaffolds such as; aliphatic and aromatic amines, amides, hydrazines, azoles, diazoles, tetrazoles, indoles, azines, diazines, xanthenes, tricyclics, benzopyrones, and more interestingly natural products, along with their conclusive SARs have been discussed in the later segment of review. The last segment of the article encompasses some patents granted in the field of MAOIs, in a simplistic way.

Design, synthesis, and pharmacological evaluation of 2-amino-5-nitrothiazole derived semicarbazones as dual inhibitors of monoamine oxidase and cholinesterase: effect of the size of aryl binding site

A series of 2-amino-5-nitrothiazole derived semicarbazones were designed, synthesised and investigated for MAO and ChE inhibition properties. Most of the compounds showed preferential inhibition towards MAO-B. Compound 4, (1-(1-(4-Bromophenyl)ethylidene)-4-(5-nitrothiazol-2-yl)semicarbazide) emerged as lead candidate (IC₅₀ = 0.212 µM, SI = 331.04) against MAO-B; whereas compounds 21 1-(5-Bromo-2-oxoindolin-3-ylidene)-4-(5-nitrothiazol-2-yl)semicarbazide (IC₅₀ = 0.264 µM) and 17 1-((4-Chlorophenyl) (phenyl)methylene)-4-(5-nitrothiazol-2-yl)semicarbazide (IC₅₀ = 0.024 µM) emerged as lead AChE and BuChE inhibitors respectively; with activity of compound 21 almost equivalent to tacrine. Kinetic studies indicated that compound 4 exhibited competitive and reversible MAO-B inhibition while compounds 21 and 17 showed mixed-type of AChE and BuChE inhibition respectively. Docking studies revealed that these compounds were well-accommodated within MAO-B and ChE active sites through stable hydrogen bonding and/or hydrophobic interactions. This study revealed the requirement of small heteroaryl ring at amino terminal of semicarbazone template for preferential inhibition and selectivity towards MAO-B. Our results suggest that 5-nitrothiazole derived semicarbazones could be further exploited for its multi-targeted role in development of anti-neurodegenerative agents. [Formula: see text] A library of 2-amino-5-nitrothiazole derived semicarbazones (4-21) was designed, synthesised and evaluated for in vitro MAO and ChE inhibitory activity. Compounds 4, 21 and 17 (shown) have emerged as lead MAO-B (IC₅₀:0.212 µM, competitive and reversible), AChE (IC₅₀:0.264 µM, mixed and reversible) and BuChE (IC₅₀:0.024 µM, mixed and reversible) inhibitor respectively. SAR studies disclosed several structural aspects significant for potency and selectivity and indicated the role of size of aryl binding site in potency and selectivity towards MAO-B. Antioxidant activity and neurotoxicity screening results further suggested their multifunctional potential for the therapy of neurodegenerative diseases.

Novel 1-(2-pyrimidin-2-yl)piperazine derivatives as selective monoamine oxidase (MAO)-A inhibitors

In the present study, a new series of 2-[4-(pyrimidin-2-yl)piperazin-1-yl]-2-oxoethyl 4-substituted piperazine-1-carbodithioate derivatives (2a-n) were synthesized and screened for their monoamine oxidase A and B inhibitory activity. The structures of compounds were elucidated using spectroscopic methods and some physicochemical properties of new compounds were predicted using Molinspiration and MolSoft programs. Compounds 2-[4-(pyrimidin-2-yl)piperazin-1-yl]-2-oxoethyl 4-(4-nitrophenyl)piperazine-1-carbodithioate (2j) and 2-[4-(pyrimidin-2-yl)piperazin-1-yl]-2-oxoethyl 4-benzhydrylpiperazine-1-carbodithioate (2m) exhibited selective MAO-A inhibitory activity with IC₅₀=23.10, 24.14 µM, respectively. Some of the biological results were found in accordance with the obtained in silico data based on Lipinski’s fule of five.

Androgen metabolites impact CSF amines and axonal serotonin via MAO-A and -B in male macaques

A number of studies have shown that mutations or deletions of the monoamine oxidase-A (MAO-A) gene cause elevated CNS serotonin and elevated impulsive aggression in humans and animal models. In addition, low cerebrospinal fluid (CSF) 5-hydroxyindole acetic acid (5HIAA) has been documented in a limited number of violent criminal populations and in macaques that exhibit impulsive aggression. To reconcile these different analyses, we hypothesized that CSF 5HIAA reflected degradation of serotonin by the activity of MAO-A; and that low MAO-A activity would result in lower CSF 5HIAA, but overall higher serotonin in the CNS. To test this hypothesis, male Japanese macaques (Macaca fuscata) were castrated, rested for 5-7months, and then treated for 3months with [1] placebo, [2] testosterone (T), [3] dihydrotestosterone (DHT; non-aromatizable androgen) and 1,4,6-androstatriene-3,17-dione (ATD) (steroidal aromatase inhibitor), or [4] flutamide (FLUT; androgen antagonist) and ATD (n=5/group). These treatments enable isolation of androgen and estrogen activities. In the dorsal raphe, MAO-A and MAO-B expressions were determined with in situ hybridization (ISH) and protein expression of aromatase was determined with immunohistochemistry (IHC). CSF concentrations of 5HIAA, 3-methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) were determined with liquid chromatography/mass spectrometry (LC/MS). From the same animals, previously published data on serotonin axon density were used as a proxy for CNS serotonin. Aromatase conversion of T to estrogen (E) suppressed MAO-A (positive pixel area, p=0.0045), but androgens increased MAO-B (positive pixel area, p=0.014). CSF 5HIAA was suppressed by conversion of T to E (Cohen's d=0.6). CSF 5HIAA was positively correlated with MAO-A-positive pixel area (r(2)=0.78). CSF 5HIAA was inversely correlated with serotonin axon-positive pixel area (r(2)=0.69). In summary, CSF 5HIAA reflects MAO-A activity rather than global serotonin. Low CSF 5HIAA may, in this paradigm, reflect higher serotonin activity. Androgens lower MAO-A activity via metabolism to E, thus elevating CNS serotonin and decreasing CSF 5HIAA. Since androgens increase certain types of aggression, these data are consistent with studies demonstrating that lower MAO-A activity is associated with elevated serotonin and increased aggression.

Monoamine Oxidases as Potential Contributors to Oxidative Stress in Diabetes: Time for a Study in Patients Undergoing Heart Surgery

Oxidative stress is a pathomechanism causally linked to the progression of chronic cardiovascular diseases and diabetes. Mitochondria have emerged as the most relevant source of reactive oxygen species, the major culprit being classically considered the respiratory chain at the inner mitochondrial membrane. In the past decade, several experimental studies unequivocally demonstrated the contribution of monoamine oxidases (MAOs) at the outer mitochondrial membrane to the maladaptative ventricular hypertrophy and endothelial dysfunction. This paper addresses the contribution of mitochondrial dysfunction to the pathogenesis of heart failure and diabetes together with the mounting evidence for an emerging role of MAO inhibition as putative cardioprotective strategy in both conditions.

Update on the pharmacology of selective inhibitors of MAO-A and MAO-B: focus on modulation of CNS monoamine neurotransmitter release

Inhibitors of monoamine oxidase (MAO) were initially used in medicine following the discovery of their antidepressant action. Subsequently their ability to potentiate the effects of an indirectly-acting sympathomimetic amine such as tyramine was discovered, leading to their limitation in clinical use, except for cases of treatment-resistant depression. More recently, the understanding that: a) potentiation of indirectly-acting sympathomimetic amines is caused by inhibitors of MAO-A but not by inhibitors of MAO-B, and b) that reversible inhibitors of MAO-A cause minimal tyramine potentiation, has led to their re-introduction to clinical use for treatment of depression (reversible MAO-A inhibitors and new dose form MAO-B inhibitor) and treatment of Parkinson's disease (MAO-B inhibitors). The profound neuroprotective properties of propargyl-based inhibitors of MAO-B in preclinical experiments have drawn attention to the possibility of employing these drugs for their neuroprotective effect in neurodegenerative diseases, and have raised the question of the involvement of the MAO-mediated reaction as a source of reactive free radicals. Despite the long-standing history of MAO inhibitors in medicine, the way in which they affect neuronal release of monoamine neurotransmitters is still poorly understood. In recent years, the detailed chemical structure of MAO-B and MAO-A has become available, providing new possibilities for synthesis of mechanism-based inhibitors. This review describes the latest advances in understanding the way in which MAO inhibitors affect the release of the monoamine neurotransmitters dopamine, noradrenaline and serotonin (5-HT) in the CNS, with an accent on the importance of these effects for the clinical actions of the drugs.

Monoamine oxidase is a major determinant of redox balance in human atrial myocardium and is associated with postoperative atrial fibrillation

Background

Onset of postoperative atrial fibrillation (POAF) is a common and costly complication of heart surgery despite major improvements in surgical technique and quality of patient care. The etiology of POAF, and the ability of clinicians to identify and therapeutically target high‐risk patients, remains elusive.

Methods and Results

Myocardial tissue dissected from right atrial appendage (RAA) was obtained from 244 patients undergoing cardiac surgery. Reactive oxygen species (ROS) generation from multiple sources was assessed in this tissue, along with total glutathione (GSHt) and its related enzymes GSH‐peroxidase (GPx) and GSH‐reductase (GR). Monoamine oxidase (MAO) and NADPH oxidase were observed to generate ROS at rates 10‐fold greater than intact, coupled mitochondria. POAF risk was significantly associated with MAO activity (Quartile 1 [Q1]: adjusted relative risk [ARR]=1.0; Q2: ARR=1.8, 95% confidence interval [CI]=0.84 to 4.0; Q3: ARR=2.1, 95% CI=0.99 to 4.3; Q4: ARR=3.8, 95% CI=1.9 to 7.5; adjusted P_trend=0.009). In contrast, myocardial GSHt was inversely associated with POAF (Quartile 1 [Q1]: adjusted relative risk [ARR]=1.0; Q2: ARR=0.93, 95% confidence interval [CI]=0.60 to 1.4; Q3: ARR=0.62, 95% CI=0.36 to 1.1; Q4: ARR=0.56, 95% CI=0.34 to 0.93; adjusted P_trend=0.014). GPx also was significantly associated with POAF; however, a linear trend for risk was not observed across increasing levels of the enzyme. GR was not associated with POAF risk.

Conclusions

Our results show that MAO is an important determinant of redox balance in human atrial myocardium, and that this enzyme, in addition to GSHt and GPx, is associated with an increased risk for POAF. Further investigation is needed to validate MAO as a predictive biomarker for POAF, and to explore this enzyme's potential role in arrhythmogenesis.

The protective role of Bax inhibitor-1 against chronic mild stress through the inhibition of monoamine oxidase A

The anti-apoptotic protein Bax inhibitor-1 (BI-1) is a regulator of apoptosis linked to endoplasmic reticulum (ER) stress. It has been hypothesized that BI-1 protects against neuron degenerative diseases. In this study, BI-1⁻/⁻ mice showed increased vulnerability to chronic mild stress accompanied by alterations in the size and morphology of the hippocampi, enhanced ROS accumulation and an ER stress response compared with BI-1⁺/⁺ mice. BI-1⁻/⁻ mice exposed to chronic mild stress showed significant activation of monoamine oxidase A (MAO-A), but not MAO-B, compared with BI-1⁺/⁺ mice. To examine the involvement of BI-1 in the Ca²⁺-sensitive MAO activity, thapsigargin-induced Ca²⁺ release and MAO activity were analyzed in neuronal cells overexpressing BI-1. The in vitro study showed that BI-1 regulates Ca²⁺ release and related MAO-A activity. This study indicates an endogenous protective role of BI-1 under conditions of chronic mild stress that is primarily mediated through Ca²⁺-associated MAO-A regulation.

Monoamine Oxidases Are Mediators of Endothelial Dysfunction in the Mouse Aorta

Monoamine oxidases (MAOs) generate H 2 O 2 as a by-product of their catalytic cycle. Whether MAOs are mediators of endothelial dysfunction is unknown and was determined here in the angiotensin II and lipopolysaccharide-models of vascular dysfunction in mice. Quantitative real-time polymerase chain reaction revealed that mouse aortas contain enzymes involved in catecholamine generation and MAO-A and MAO-B mRNA. MAO-A and -B proteins could be detected by Western blot not only in mouse aortas but also in human umbilical vein endothelial cells. Ex vivo incubation of mouse aorta with recombinant MAO-A increased H 2 O 2 formation and induced endothelial dysfunction that was attenuated by polyethylene glycol-catalase and MAO inhibitors. In vivo lipopolysaccharide (8 mg/kg IP overnight) or angiotensin II (1 mg/kg per day, 2 weeks, minipump) treatment induced vascular MAO-A and -B expressions and resulted in attenuated endothelium-dependent relaxation of the aorta in response to acetylcholine. MAO inhibitors reduced the lipopolysaccharide- and angiotensin II–induced aortic reactive oxygen species formation by 50% (ferrous oxidation xylenol orange assay) and partially normalized endothelium-dependent relaxation. MAO-A and MAO-B inhibitors had an additive effect; combined application completely restored endothelium-dependent relaxation. To determine how MAO-dependent H 2 O 2 formation induces endothelial dysfunction, cyclic GMP was measured. Histamine stimulation of human umbilical vein endothelial cells to activate endothelial NO synthase resulted in an increase in cyclic GMP, which was almost abrogated by MAO-A exposure. MAO inhibition prevented this effect, suggesting that MAO-induced H 2 O 2 formation is sufficient to attenuate endothelial NO release. Thus, MAO-A and MAO-B are both expressed in the mouse aorta, induced by in vivo lipopolysaccharide and angiotensin II treatment and contribute via the generation of H 2 O 2 to endothelial dysfunction in vascular disease models.

Neurobehavioral assessment of hydroalcoholic extract of Trigonella foenum-graecum seeds in rodent models of Parkinson's disease

CONTEXT

Neuroprotective therapy to rescue dopaminergic neurons is an important trait in the management of Parkinson's disease (PD).

OBJECTIVE

The present study identified and evaluated SFSE-T, a standardized hydroalcoholic extract of Trigonella foenum-graecum L. seeds (Fabaceae), in animal models of PD.

MATERIALS AND METHODS

The identification of SFSE-T was carried out by high-performance liquid chromatography for the marker compound trigonelline (TGN). The effects of single dose oral treatment of SFSE-T (10, 30 or 100 mg/kg) were studied using animal models of PD, namely, 6-hydroxydopamine (6-OHDA)-induced unilateral lesions in rats, and 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration in C57BL/6 mice. The effects of SFSE-T on monoamino oxidase (MAO) enzyme in vitro as well as possible side effects of SFSE-T in vivo were also evaluated.

RESULTS

The concentration of TGN in a test sample of SFSE-T was found to be 82%. SFSE-T (30 mg/kg, oral) showed a significant increase in the number of ipsilateral rotations (45.67 rotations in 30-min period) as compared with vehicle control group (no rotations) when tested in 6-OHDA-induced unilateral lesioned rats. SFSE-T (30 mg/kg, oral) showed significant reversal of motor dysfunction (spontaneous motor activity scores, speed, distance traveled and number of square crossed) caused by MPTP induced lesions in C57BL/6 mice in pretreatment (1 h) schedule but not in post-treatment (1 h) schedule. SFSE-T neither showed anticholinergic effects nor showed selective MAO-B enzyme inhibition in vitro.

DISCUSSION AND CONCLUSION

SFSE-T showed reversal of motor symptoms in an animal model of PD probably through neuroprotective properties.

Mechanism of polyamine toxicity in cultured cardiac myocytes

The goal of this study was to investigate the mechanism of polyamine-mediated injury to the cardiac myocytes isolated from neonatal rat hearts. The myocytes, cultured in Dulbecco's minimal essential medium-1% foetal calf serum (FBS), were exposed to spermidine or spermine. The toxicity to myocytes was determined by (a) increased release of creatine kinase (CPK) into the media and (b) decline in cell viability or functional activity. Spermidine, above 10 mum, increased the release of CPK into media, decreased cell viability and decreased the functional activity of the myocytes. The FBS exhibited polyamine oxidase activity and semicarbazide-sensitive amine oxidase activity. Aminoguanidine, MDL72,527 or semicarbazide, are the inhibitors of amine oxidases, polyamine oxidase (PAO) and semicarbazide-sensitive amine oxidase (SSAO), respectively. The addition of these inhibitors to the medium protected the myocytes from spermidine toxicity. To determine whether myocyte PAO is involved in polyamine toxicity, we used horse serum that contained high SSAO activity and negligible PAO activity. The myocyte extracts had negligible SSAO activity but high PAO activity. When myocytes were cultured in horse serum in lieu of FBS, spermine caused toxicity at above 100 mum. In horse serum, MDL72,527 and semicarbazide protected the myocytes from spermine toxicity. These observations show that extracellular amine oxidases and myocyte PAO are significant in mediation of polyamine toxicity.

2-(Cyclohexylamino)-1-(4-cyclopentylpiperazin-1-yl)-2-methylpropan-1-one, a novel compound with neuroprotective and neurotrophic effects in vitro

Focusing on development of novel drug candidates for the treatment of neurodegenerative diseases, we developed and synthesized a new compound, 2-(cyclohexylamino)-1-(4-cyclopentylpiperazin-1-yl)-2-methylpropan-1-one (amido-piperizine 1). The compound demonstrated robust neuroprotective properties after both glutamate excitotoxicity and peroxide induced oxidative stress in primary cortical cultures. Furthermore, amido-piperizine 1 was found to significantly induce neurite outgrowth in vitro which could suggest central reparative and regenerative potential of the compound. With these potential beneficial effects in CNS, the ability of the amido-piperizine 1 to penetrate the blood-brain barrier was tested using MDR1-MDCK cells. Amido-piperizine 1 was found not to be a P-gp substrate and to have a high blood-brain barrier penetration potential, indicating excellent availability to the CNS. Moreover, amido-piperizine 1 had a fast metabolic clearance rate in vitro, suggesting that parenteral in vivo administration seems preferable. As an attempt to elucidate a possible mechanism of action, we found that amido-piperizine 1 bound in nano-molar range to the sigma-1 receptor, which could explain the observed neuroprotective and neurotrophic properties, and with a 100-fold lower affinity to the sigma-2 receptor. These results propose that amido-piperizine 1 may hold promise as a drug candidate for the treatment of stroke/traumatic brain injury or other neurodegenerative diseases.

Alterations in striatal oxidative stress level produced by pharmacological manipulation of dopamine as shown by a novel synthetic marker molecule

Oxidative stress (OS) is thought to participate in neurodegenerative diseases such as Parkinson's disease, but the contribution of dopamine metabolism and auto-oxidation to OS in Parkinson's and other diseases is not clear. Oxidative stress in rat striatum was measured by microdialysis using a novel synthetic compound composed of tyrosine and linoleic acid (LT), and determination of the oxidation products LT-OOH and LT-epoxy by HPLC-MS. Since LT is non-diffusible through the microdialysis membrane, the oxidized products formed in microdialyzate reflect oxidation state in the extracellular compartment. The extracellular oxidative stress (OS(ec)) was compared with intracellular oxidative stress (OS(ic)) as measured by tissue levels of oxidized and reduced glutathione and 7-ketocholesterol. Reserpinization caused an increase in OS(ic) but a reduction in OS(ec). Inhibition of both subtypes of monoamine oxidase (MAO-A and MAO-B) with tranylcypromine caused a reduction in both OS(ic) and OS(ec) whereas selective inhibition of MAO-A with clorgyline caused a reduction in Os(ic) but no change in OS(ec). A high dose (10 mg/kg) of amphetamine caused an increase in OS(ec) whereas a smaller dose (4 mg/kg) caused a reduction in OS(ec). Both doses of amphetamine reduced OS(ic). The present findings are consistent with a role of monoamine oxidase as well as dopamine auto-oxidation in production of striatal OS.

Homoisoflavonoids: natural scaffolds with potent and selective monoamine oxidase-B inhibition properties

A series of homoisoflavonoids [(E)-3-benzylidenechroman-4-ones 1a-w, 3-benzyl-4H-chromen-4-ones 2a-g, and 3-benzylchroman-4-ones 3a-e] have been synthesized and tested in vitro as inhibitors of human monoamine oxidase isoforms A and B (hMAO-A and hMAO-B). Most of the compounds were found to be potent and selective MAO-B inhibitors. In general, the (E)-3-benzylidenechroman-4-ones 1a-w showed activities in the nano- or micromolar range coupled with high selectivity against hMAO-B. The reduction of the exocyclic double bond results in compounds 3a-e selective against isoform B and active in the micromolar range. In contrast, the endocyclic migration of the double bond (compounds 2a-g) generally produces the loss of the inhibitory activity or a marked reduction in potency. (E)-3-(4-(Dimethylamino)benzylidene)chroman-4-one (1l) and (E)-5,7-dihydroxy-3-(4-hydroxybenzylidene)chroman-4-one (1h) were the most interesting compounds of the entire series of inhibitors, showing hMAO-B affinity better than the selective inhibitor selegiline. Molecular modeling studies have been carried out to explain the selectivity of the most active homoisoflavonoids 1h and 1l.

Molecular mechanisms in exercise-induced cardioprotection

Physical inactivity is increasingly recognized as modifiable behavioral risk factor for cardiovascular diseases. A partial list of proposed mechanisms for exercise-induced cardioprotection include induction of heat shock proteins, increase in cardiac antioxidant capacity, expression of endoplasmic reticulum stress proteins, anatomical and physiological changes in the coronary arteries, changes in nitric oxide production, adaptational changes in cardiac mitochondria, increased autophagy, and improved function of sarcolemmal and/or mitochondrial ATP-sensitive potassium channels. It is currently unclear which of these protective mechanisms are essential for exercise-induced cardioprotection. However, most investigations focus on sarcolemmal KATP channels, NO production, and mitochondrial changes although it is very likely that other mechanisms may also exist. This paper discusses current information about these aforementioned topics and does not consider potentially important adaptations within blood or the autonomic nervous system. A better understanding of the molecular basis of exercise-induced cardioprotection will help to develop better therapeutic strategies.

Mitochondrial monoamine oxidase-A-mediated hydrogen peroxide generation enhances 5-hydroxytryptamine-induced contraction of rat basilar artery

BACKGROUND AND PURPOSE

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

EXPERIMENTAL APPROACH

Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies.

KEY RESULTS

Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC(50) : 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca(2+) -activated K(+) (BK(Ca) ) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF(-1) vs. 2.61 ± 0.66 pA·pF(-1) ). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK(Ca) amplitude than in those from WKY.

CONCLUSIONS AND IMPLICATIONS

5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK(Ca) gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.

A Simple One-Pot, Three Component Synthesis of 3-Arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones and their Sulfur Analogues as Potential Monoamine Oxidase Inhibitors

Several new 3-arylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones and 3-aryl-5-oxo-7-thioxo-7,8-dihydropyrimido[4,5-c]pyridazin-5(6H)-ones have been synthesized by a three-component reaction of barbituric acid or thiobarbituric acid with arylglyoxals in the presence of a catalytic amount of pyridine and hydrazine hydrate at room temperature in water.

Monoamine oxidase A-mediated enhanced catabolism of norepinephrine contributes to adverse remodeling and pump failure in hearts with pressure overload

RATIONALE

Monoamine oxidases (MAOs) are mitochondrial enzymes that catabolize prohypertrophic neurotransmitters, such as norepinephrine and serotonin, generating hydrogen peroxide. Because excess reactive oxygen species and catecholamines are major contributors to the pathophysiology of congestive heart failure, MAOs could play an important role in this process.

OBJECTIVE

Here, we investigated the role of MAO-A in maladaptive hypertrophy and heart failure.

METHODS AND RESULTS

We report that MAO-A activity is triggered in isolated neonatal and adult myocytes on stimulation with norepinephrine, followed by increase in cell size, reactive oxygen species production, and signs of maladaptive hypertrophy. All of these in vitro changes occur, in part, independently from alpha- and beta-adrenergic receptor-operated signaling and are inhibited by the specific MAO-A inhibitor clorgyline. In mice with left ventricular dilation and pump failure attributable to pressure overload, norepinephrine catabolism by MAO-A is increased accompanied by exacerbated oxidative stress. MAO-A inhibition prevents these changes, and also reverses fetal gene reprogramming, metalloproteinase and caspase-3 activation, as well as myocardial apoptosis. The specific role of MAO-A was further tested in mice expressing a dominant-negative MAO-A (MAO-A(neo)), which were more protected against pressure overload than their wild-type littermates.

CONCLUSIONS

In addition to adrenergic receptor-dependent mechanisms, enhanced MAO-A activity coupled with increased intramyocardial norepinephrine availability results in augmented reactive oxygen species generation, contributing to maladaptive remodeling and left ventricular dysfunction in hearts subjected to chronic stress.

Role of monoamine oxidases in the exaggerated 5-hydroxytryptamine-induced tension development of human isolated preeclamptic umbilical artery

We investigated the role(s) of monoamine oxidases (MAOs) on the altered 5-hydroxytryptamine (5-HT, serotonin)-induced tension development of the isolated umbilical artery of preeclamptic pregnancy of Chinese women. An enhanced 5-HT-induced tension development of the umbilical artery of preeclamptic pregnancy was observed when compared with that of normal pregnancy. The enhanced component of 5-HT-induced tension development was eradicated by clorgyline (a MAO-A inhibitor). Blockade of eNOS (endothelial isoform nitric oxide synthase) (N(omega)-nitro-L-arginine methyl ester), 5-HT transporter (citalopram), 5-HT receptor subtypes (5HT2B, SB 204741; 5-HT2C, RS 102221; 5-HT7, SB 269970), and endothelium denudation of the umbilical artery of normal pregnancy mimicked the enhanced 5-HT-induced tension development as observed in the preeclamptic tissues. In contrast, no apparent changes in 5-HT-induced tension development of the umbilical artery of preeclamptic pregnancy were observed with the same pharmacological manipulations. A decreased protein expression levels of MAO-A and eNOS (no iNOS and MAO-B expression was detected) and no change in caveolin-1 and 5-HT transporter expression were demonstrated in the umbilical artery (endothelium intact) lysate of preeclamptic pregnancy, compared to that of the umbilical artery of normal pregnancy. Thus, in the umbilical artery of preeclamptic pregnancy, a decrease of MAO-A and eNOS protein expression levels are probably associated with, or responsible for, the exaggerated 5-HT-induced tension development.

The biochemistry of drug metabolism--an introduction: Part 2. Redox reactions and their enzymes

This review continues a general presentation of the metabolism of drugs and other xenobiotics started in a recent issue of Chemistry & Biodiversity. This Part 2 presents the numerous oxidoreductases involved, their nomenclature, relevant biochemical properties, catalytic mechanisms, and the very diverse reactions they catalyze. Many medicinally, environmentally, and toxicologically relevant examples are presented and discussed. Cytochromes P450 occupy a majority of the pages of Part 2, but a large number of relevant oxidoreductases are also considered, e.g., flavin-containing monooxygenases, amine oxidases, molybdenum hydroxylases, peroxidases, and the innumerable dehydrogenases/reductases.

New insights on receptor-dependent and monoamine oxidase-dependent effects of serotonin in the heart

Biogenic amines like serotonin (5-HT) and catecholamines usually act through stimulation of G-protein coupled receptors (GPCRs). We now have strong evidence that they can signal through receptor-independent mechanisms. One well described pathway is the degradation of biogenic amine by monoamine oxidases (MAOs) after transport into the cells by selective transporters. The oxidation of biogenic amines generates hydrogen peroxide, H(2)O(2), that can act as a signalling intermediate in the cell. This original mechanism of action of 5-HT is relevant in the heart since it is responsible for both cardiomyocyte hypertrophy and apoptosis. Moreover, in vivo experiments indicate a physiological significance for MAO in the damage during ischemia-reperfusion in the heart. Since functional 5-HT receptors are present in the heart and have also been demonstrated to contribute to cardiomyocyte growth and apoptosis, it is of major interest to evaluate respective contribution and cross-regulations between 5-HT receptors and MAO in cardiac function.

Multiple genes and factors associated with bipolar disorder converge on growth factor and stress activated kinase pathways controlling translation initiation: implications for oligodendrocyte viability

Famine and viral infection, as well as interferon therapy have been reported to increase the risk of developing bipolar disorder. In addition, almost 100 polymorphic genes have been associated with this disease. Several form most of the components of a phosphatidyl-inositol signalling/AKT1 survival pathway (PIK3C3, PIP5K2A, PLCG1, SYNJ1, IMPA2, AKT1, GSK3B, TCF4) which is activated by growth factors (BDNF, NRG1) and also by NMDA receptors (GRIN1, GRIN2A, GRIN2B). Various other protein products of genes associated with bipolar disorder either bind to or are affected by phosphatidyl-inositol phosphate products of this pathway (ADBRK2, HIP1R, KCNQ2, RGS4, WFS1), are associated with its constituent elements (BCR, DUSP6, FAT, GNAZ) or are downstream targets of this signalling cascade (DPYSL2, DRD3, GAD1, G6PD, GCH1, KCNQ2, NOS3, SLC6A3, SLC6A4, SST, TH, TIMELESS). A further pathway relates to endoplasmic reticulum-stress (HSPA5, XBP1), caused by problems in protein glycosylation (ALG9), growth factor receptor sorting (PIK3C3, HIP1R, SYBL1), or aberrant calcium homoeostasis (WFS1). Key processes relating to these pathways appear to be under circadian control (ARNTL, CLOCK, PER3, TIMELESS). DISC1 can also be linked to many of these pathways. The growth factor pathway promotes protein synthesis, while the endoplasmic reticulum stress pathway, and other stress pathways activated by viruses and cytokines (IL1B, TNF, Interferons), oxidative stress or starvation, all factors associated with bipolar disorder risk, shuts down protein synthesis via control of the EIF2 alpha and beta translation initiation complex. For unknown reasons, oligodendrocytes appear to be particularly prone to defects in the translation initiation complex (EIF2B) and the convergence of these environmental and genomic signalling pathways on this area might well explain their vulnerability in bipolar disorder.

Oxidative stress-dependent sphingosine kinase-1 inhibition mediates monoamine oxidase A-associated cardiac cell apoptosis

The mitochondrial enzyme monoamine oxidase (MAO), its isoform MAO-A, plays a major role in reactive oxygen species-dependent cardiomyocyte apoptosis and postischemic cardiac damage. In the current study, we investigated whether sphingolipid metabolism can account for mediating MAO-A- and reactive oxygen species-dependent cardiomyocyte apoptosis. In H9c2 cardiomyoblasts, MAO-A-dependent reactive oxygen species generation led to mitochondria-mediated apoptosis, along with sphingosine kinase-1 (SphK1) inhibition. These phenomena were associated with generation of proapoptotic ceramide and decrease in prosurvival sphingosine 1-phosphate. These events were mimicked by inhibition of SphK1 with either pharmacological inhibitor or small interfering RNA, as well as by extracellular addition of C(2)-ceramide or H(2)O(2). In contrast, enforced expression of SphK1 protected H9c2 cells from serotonin- or H(2)O(2)-induced apoptosis. Analysis of cardiac tissues from wild-type mice subjected to ischemia/reperfusion revealed significant upregulation of ceramide and inhibition of SphK1. It is noteworthy that SphK1 inhibition, ceramide accumulation, and concomitantly infarct size and cardiomyocyte apoptosis were significantly decreased in MAO-A-deficient animals. In conclusion, we show for the first time that the upregulation of ceramide/sphingosine 1-phosphate ratio is a critical event in MAO-A-mediated cardiac cell apoptosis. In addition, we provide the first evidence linking generation of reactive oxygen species with SphK1 inhibition. Finally, we propose sphingolipid metabolites as key mediators of postischemic/reperfusion cardiac injury.

An evaluation of potential mechanism-based inactivation of human drug metabolizing cytochromes P450 by monoamine oxidase inhibitors, including isoniazid

AIMS

To characterize potential mechanism-based inactivation (MBI) of major human drug-metabolizing cytochromes P450 (CYP) by monoamine oxidase (MAO) inhibitors, including the antitubercular drug isoniazid.

METHODS

Human liver microsomal CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A activities were investigated following co- and preincubation with MAO inhibitors. Inactivation kinetic constants (KI and kinact) were determined where a significant preincubation effect was observed. Spectral studies were conducted to elucidate the mechanisms of inactivation.

RESULTS

Hydrazine MAO inhibitors generally exhibited greater inhibition of CYP following preincubation, whereas this was less frequent for the propargylamines, and tranylcypromine and moclobemide. Phenelzine and isoniazid inactivated all CYP but were most potent toward CYP3A and CYP2C19. Respective inactivation kinetic constants (KI and kinact) for isoniazid were 48.6 microm and 0.042 min-1 and 79.3 microm and 0.039 min-1. Clorgyline was a selective inactivator of CYP1A2 (6.8 microm and 0.15 min-1). Inactivation of CYP was irreversible, consistent with metabolite-intermediate complexation for isoniazid and clorgyline, and haeme destruction for phenelzine. With the exception of phenelzine-mediated CYP3A inactivation, glutathione and superoxide dismutase failed to protect CYP from inactivation by isoniazid and phenelzine. Glutathione partially slowed (17%) the inactivation of CYP1A2 by clorgyline. Alternate substrates or inhibitors generally protected against CYP inactivation.

CONCLUSIONS

These data are consistent with mechanism-based inactivation of human drug-metabolizing CYP enzymes and suggest that impaired metabolic clearance may contribute to clinical drug-drug interactions with some MAO inhibitors.

Synthesis and Molecular Modelling of Novel Substituted-4,5-dihydro-(1H)-pyrazole Derivatives as Potent and Highly Selective Monoamine Oxidase-A Inhibitors

This report describes novel pyrazoline derivatives investigated for their ability to selectively inhibit the activity of the A and B isoforms of monoamine oxidase. These new synthetic compounds proved to be reversible, potent, and selective inhibitors of monoamine oxidase-A rather than of monoamine oxidase-B, and are promising candidates to further advance drug discovery efforts. The most active compounds show inhibitory activity on monoamine oxidase-A in the 1.0x10(-8)-8.6x10(-9) M range. Moreover, it should be pointed out that for some compounds a high IC50>or=10(-9) M value is associated with a high A-selectivity (Selectivity Index monoamine oxidase-B/monoamine oxidase-A in the 10,000-12,500 range). Further insight to understand enzyme-inhibitor molecular interaction was obtained by docking experiments with the monoamine oxidase-A and monoamine oxidase-B isoforms.

The antioxidant anethole dithiolethione inhibits monoamine oxidase-B but not monoamine oxidase A activity in extracts of cultured astrocytes

Anethole dithiolethione (ADT) is a clinically available, pluripotent antioxidant proposed as a neuroprotectant for Parkinson's disease (PD). Here, using extracts from cultured astrocytes, containing both monoamine oxidase (MAO) A and B activity, we demonstrate that ADT concentration-dependently inhibits MAO-B activity in a clinically relevant concentration range (0.03-30 microM, IC-50 = 0.5 microM) without affecting MAO A activity. Considering the alleged contribution of MAO activity in general, and MAO-B in particular, to oxidative stress and neurodegeneration in PD, our data further support the neuroprotective potential of ADT.

Molecular characterization of monoamine oxidase in zebrafish (Danio rerio)

Monoamine oxidase (MAO) is responsible for the degradation of a number of neurotransmitters and other biogenic amines. In terrestrial vertebrates, two forms of the enzyme, named MAO A and B, were found in which mammals are coded by two similar but distinct genes. In teleosts, the biochemical data obtained so far indicate that enzyme activity is due to a single form, whose sequence, obtained for trout, displays 70% identity with mammal MAO A and B. In this paper, we carried out an investigation of zebrafish MAO (Z-MAO) to shed further light on the nature of the MAO form present in aquatic vertebrates. Sequencing studies have revealed an open reading frame 522-amino-acids long with MW 58.7 kDa, displaying 84% identity with trout MAO and about 70% identity with mammal MAO A and MAO B. Analysis of the sequence and of the predicted secondary structure shows that also in Z-MAO principal domains characterizing the MAOs are present. The domain linking the FAD is very well conserved, while the transmembrane domain sequence linking the enzyme to the external mitochondrial membrane does not appear to be conserved even with respect to trout MAO. Comparison with the amino acids which, according to the human MAO B and rat MAO A models, line the substrate-binding site shows that in Z-MAO, several residues (V172, N173, F200, L327) differ from MAO B but are similar or identical to the corresponding ones present in rat MAO A, as well as in trout MAO. A three-dimensional model is reported of the substrate-binding site of Z-MAO obtained by comparative modeling. Our observations support the hypothesis that the MAO form present in aquatic vertebrates is a MAO A-like form. Experiments performed to test the effect of selective MAO A (clorgyline) and MAO B (deprenyl) inhibitors on the enzyme's activity in liver and brain confirm the presence of a single form of MAO in zebrafish.

Metabolism of Homovanillamine to Homovanillic Acid in Guinea Pig Liver Slices

BACKGROUND/AIMS

Homovanillamine is a biogenic amine that it is catalyzed to homovanillyl aldehyde by monoamine oxidase A and B, but the oxidation of its aldehyde to the acid derivative is usually ascribed to aldehyde dehydrogenase and a potential contribution of aldehyde oxidase and xanthine oxidase is usually ignored.

METHODS

The present investigation examines the metabolism of homovanillamine to its acid derivative by concurrent incubation with monoamine oxidase and aldehyde oxidase. In addition, the metabolism of homovanillamine in freshly prepared and cryopreserved liver slices is examined and the relative contribution of aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase activity by using specific inhibitors of each oxidizing enzyme is compared.

RESULTS

Homovanillamine was rapidly converted mainly to homovanillic acid when incubated with both momoamine oxidase and aldehyde oxidase. Homovanillic acid was also the main metabolite in the incubations of homovanillamine with freshly prepared or cryopreserved liver slices, via the intermediate homovanillyl aldehyde. The acid formation was 70-75 % inhibited by disulfiram (specific inhibitor of aldehyde dehydrogenase), whereas isovanillin (specific inhibitor of aldehyde oxidase) inhibited acid formation to a lesser extent (50-55 %) and allopurinol (specific inhibitor of xanthine oxidase) had almost no effect.

CONCLUSIONS

Homovanillamine is rapidly oxidized to its acid, via homovanillyl aldehyde, by aldehyde dehydrogenase and aldehyde oxidase with little or no contribution from xanthine oxidase.

A new hypertrophic mechanism of serotonin in cardiac myocytes: receptor‐independent ROS generation

Reactive oxygen species (ROS) play a critical role in cardiac hypertrophy. We have recently shown that the serotonin-degrading enzyme monoamine oxidase A (MAO A) is an important source of hydrogen peroxide in rat heart. In the present study, we investigated the potential role of hydrogen peroxide generated by MAO A in cardiomyocyte hypertrophy by serotonin. Serotonin (5 microM, 48 h) induced hypertrophy in cultured adult rat ventricular myocytes, as reflected by increased 3H-leucine incorporation (+43%, P<0.001) and total protein content (+22%, P<0.001). Serotonin also increased intracellular hydrogen peroxide and oxidative stress production, measured respectively by DCF fluorescence intensity and GSH/GSSG ratio, and promoted ERK1/2 phosphorylation (P<0.001). Serotonin effects were only partially inhibited by the 5-HT2B receptor antagonist SB 206553. In contrast, they were extensively (>80%) prevented by the amine uptake inhibitor imipramine, the MAO inhibitor pargyline and the MEK inhibitor PD 98059. Cardiomyocyte hypertrophy and ERK activation were also inhibited by decreasing intracellular ROS by adenoviral overexpression of catalase or cardiomyocytes treatment with the iron chelator deferoxamine. These data suggest that part of cardiac hypertrophic effect of serotonin requires hydrogen peroxide production by MAO A and ERK1/2 activation. This newly recognized, receptor-independent mechanism of serotonin may contribute to myocardial remodeling and failure.

Liquid chromatographic and tandem mass spectrometric assay for evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors: application of biomarkers in drug discovery

A simple and selective assay for the evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors was developed through the simultaneous determination of endogenous 5-hydroxy tryptamine, 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophane, and 2-phenethylamine (PEA) in rat brain using liquid chromatography-tandem mass spectrometry (LC/MS/MS). These analytes were separated on a Zorbax SB-C18 column using a gradient elution with acetonitrile and 0.2% formic acid and detected on an electrospray ionization mass spectrometer in positive-ion multiple-reaction-monitoring mode. The susceptibility and variability of these analytes as potential biomarkers in response to MAO inhibition in vivo were evaluated after application to three MAO inhibitors, tranylcypromine, clorgyline, and pargyline. A dramatic increase (about 40-fold) in PEA brain level and a decrease in 5-HIAA by more than 90% were observed after administration of 15 mg/kg of the nonselective MAO inhibitor tranylcypromine. As expected, the brain level of PEA escalated to about 6-fold, while the 5-HIAA level remained unchanged following a dose of the MAO B inhibitor pargyline at 2mg/kg. In contrast, the brain level of 5-HIAA reduced by approximately 53%, but the PEA level was unaffected following the same dose of the MAO A inhibitor clorgyline. The results indicated that 5-HIAA and PEA were susceptible and effective biomarkers in the rat brain in response to MAO A and B inhibition, respectively. The LC/MS/MS method is useful not only for the determination of inhibitory potency but also for the differentiation of the selectivity of a MAO inhibitor against rat brain MAO A and B in vivo.

Inactivation of acetylcholinesterase by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride

The neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to reversibly inhibit the activity of acetylcholinesterase. The inactivation of the enzyme was detected by monitoring the accumulation of yellow color produced from the reaction between thiocholine and dithiobisnitrobenzoate ion. The kinetic parameter, Km for the substrate (acetylthiocholine), was found to be 0.216 mM and Ki for MPTP inactivation of acetylcholinesterase was found to be 2.14 mM. The inactivation of enzyme by MPTP was found to be dose-dependent. It was found that MPTP is neither a substrate of AChE nor the time-dependent inactivator. The studies of reaction kinetics indicate the inactivation of AChE to be a linear mixed-type inhibition. The dilution assays indicate that MPTP is a reversible inhibitor for AChE. These data suggest that once MPTP enters the basal ganglia of the brain, it can inactivate the acetylcholinesterase enzyme and thereby increase the acetylcholine level in the basal ganglia of brain, leading to potential cell dysfunction. It appears that the nigrostriatal toxicity by MPTP leading to Parkinson's disease-like syndrome may, in part, be mediated via the acetylcholinesterase inactivation.