Selective inhibitors of monoamine oxidase type B and the "cheese effect"

Novel tetrahydronaphthalen-1-yl-phenethyl ureas: synthesis and dual antibacterial-anticancer activities

Cancer and antibiotic-resistant bacterial infections are significant global health challenges. The resistance developed in cancer treatments intensifies therapeutic difficulties. In addressing these challenges, this study synthesised a series of N,N'-dialkyl urea derivatives containing methoxy substituents on phenethylamines. Using isocyanate for the efficient synthesis yielded target products 14-18 in 73-76% returns. Subsequently, their antibacterial and anticancer potentials were assessed. Cytotoxicity tests on cancer cell lines, bacterial strains, and a healthy fibroblast line revealed promising outcomes. All derivatives demonstrated robust antibacterial activity, with MIC values ranging from 0.97 to 15.82 µM. Notably, compounds 14 and 16 were particularly effective against the HeLa cell line, while compounds 14, 15, and 17 showed significant activity against the SH-SY5Y cell line. Importantly, these compounds had reduced toxicity to healthy fibroblast cells than to cancer cells, suggesting their potential as dual-functioning agents targeting both cancer and bacterial infections.

Targeting monoamine oxidase A: a strategy for inhibiting tumor growth with both immune checkpoint inhibitors and immune modulators

Monoamine oxidase A (MAOA) is a membrane-bound mitochondrial enzyme present in almost all vertebrate tissues that catalyzes the degradation of biogenic and dietary-derived monoamines. MAOA is known for regulating neurotransmitter metabolism and has been implicated in antitumor immune responses. In this review, we retrospect that MAOA inhibits the activities of various types of tumor-associated immune cells (such as CD8+ T cells and tumor-associated macrophages) by regulating their intracellular monoamines and metabolites. Developing novel MAOA inhibitor drugs and exploring multidrug combination strategies may enhance the efficacy of immune governance. Thus, MAOA may act as a novel immune checkpoint or immunomodulator by influencing the efficacy and effectiveness of immunotherapy. In conclusion, MAOA is a promising immune target that merits further in-depth exploration in preclinical and clinical settings.

Classics in Chemical Neuroscience: Selegiline, Isocarboxazid, Phenelzine, and Tranylcypromine

The discovery of monoamine oxidase inhibitors (MAOIs) in the 1950s marked a significant breakthrough in medicine, creating a powerful new category of drug: the antidepressant. In the years and decades that followed, MAOIs have been used in the treatment of several pathologies including Parkinson's disease, Alzheimer's disease, and various cancers and as anti-inflammatory agents. Despite once enjoying widespread use, MAOIs have dwindled in popularity due to side effects, food-drug interactions, and the introduction of other antidepressant drug classes such as tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs). The recently published prescriber's guide for the use of MAOIs in treating depression has kindled a resurgence of their use in the clinical space. It is therefore timely to review key aspects of the four "classic" MAOIs: high-dose selegiline, isocarboxazid, phenelzine, and tranylcypromine. This review discusses their chemical synthesis, metabolism, pharmacology, adverse effects, and the history and importance of these drugs within the broader field of chemical neuroscience.

New Insights on the Activity and Selectivity of MAO-B Inhibitors through In Silico Methods

To facilitate the identification of novel MAO-B inhibitors, we elaborated a consolidated computational approach, including a pharmacophoric atom-based 3D quantitative structure-activity relationship (QSAR) model, activity cliffs, fingerprint, and molecular docking analysis on a dataset of 126 molecules. An AAHR.2 hypothesis with two hydrogen bond acceptors (A), one hydrophobic (H), and one aromatic ring (R) supplied a statistically significant 3D QSAR model reflected by the parameters: R² = 0.900 (training set); Q² = 0.774 and Pearson's R = 0.884 (test set), stability s = 0.736. Hydrophobic and electron-withdrawing fields portrayed the relationships between structural characteristics and inhibitory activity. The quinolin-2-one scaffold has a key role in selectivity towards MAO-B with an AUC of 0.962, as retrieved by ECFP4 analysis. Two activity cliffs showing meaningful potency variation in the MAO-B chemical space were observed. The docking study revealed interactions with crucial residues TYR:435, TYR:326, CYS:172, and GLN:206 responsible for MAO-B activity. Molecular docking is in consensus with and complementary to pharmacophoric 3D QSAR, ECFP4, and MM-GBSA analysis. The computational scenario provided here will assist chemists in quickly designing and predicting new potent and selective candidates as MAO-B inhibitors for MAO-B-driven diseases. This approach can also be used to identify MAO-B inhibitors from other libraries or screen top molecules for other targets involved in suitable diseases.

Gut Microbiota Alterations in Trace Amine-Associated Receptor 9 (TAAR9) Knockout Rats

Trace amine-associated receptors (TAAR1-TAAR9) are a family of G-protein-coupled monoaminergic receptors which might have great pharmacological potential. It has now been well established that TAAR1 plays an important role in the central nervous system. Interestingly, deletion of TAAR9 in rats leads to alterations in the periphery. Previously, we found that knockout of TAAR9 in rats (TAAR9-KO rats) decreased low-density lipoprotein cholesterol levels in the blood. TAAR9 was also identified in intestinal tissues, and it is known that it responds to polyamines. To elucidate the role of TAAR9 in the intestinal epithelium, we analyzed TAAR9-co-expressed gene clusters in public data for cecum samples. As identified by gene ontology enrichment analysis, in the intestine, TAAR9 is co-expressed with genes involved in intestinal mucosa homeostasis and function, including cell organization, differentiation, and death. Additionally, TAAR9 was co-expressed with genes implicated in dopamine signaling, which may suggest a role for this receptor in the regulation of peripheral dopaminergic transmission. To further investigate how TAAR9 might be involved in colonic mucosal homeostasis, we analyzed the fecal microbiome composition in TAAR9-KO rats and their wild-type littermates. We identified a significant difference in the number of observed taxa between the microbiome of TAAR9-KO and wild-type rats. In TAAR9-KO rats, the gut microbial community became more variable compared with the wild-type rats. Furthermore, it was found that the family Saccharimonadaceae, which is one of the top 10 most abundant families in TAAR9-KO rat feces, is almost completely absent in wild-type animal fecal samples. Taken together, these data indicate a role of TAAR9 in intestinal function.

Modelling of p-tyramine transport across human intestinal epithelial cells predicts the presence of additional transporters

p-Tyramine (TYR) is an endogenous trace amine, which can also be synthesized by intestinal microbiota, and is present in commonly consumed diets. TYR is an agonist for the intracellular trace amine-associated receptor 1, which has been implicated in psychiatric, metabolic, and immune-related disorders. We have previously demonstrated TYR readily diffuses across lipid bilayers, while transport across Caco-2 cell membranes involves Organic Cation Transporter 2 (OCT2) and a Na⁺-dependent active transporter. Here we developed mathematical models to determine whether known kinetics for these processes are sufficient to explain observed transcellular TYR passage. Ordinary differential equations were developed for known TYR transport processes to predict concentration-time relationships. Michaelis-Menten kinetics were assumed for all transporter-mediated processes and a one phase exponential function used for simple diffusion. Modelled concentration-time plots were compared to published experimental results. Additional transporter functions were sequentially added to models to improve consistency, and a least squares error minimization approach utilized to determine added transporter kinetics. Finally, possible TYR compartmentalization was also modelled. Following apical loading, transport across the apical, but not the basolateral, membrane was modelled without additional transporters, suggesting a basolateral transporter was missing. Consistent with this, models of basolateral compartment loading did not match experimental observations, indicating missing basolateral transporters were bidirectional. Addition of a transporter with the kinetic characteristics of OCT2 did not improve models. Varying the kinetic parameters of the added transporter improved models of basolateral, but worsened apical, loading models, suggesting the need for either a directional preference in transporters, or intracellular TYR compartmentalization. Experimental parameters were recapitulated by introducing asymmetry into the apical OCT2 (K_{t_OCT2_apicaltocell} = 110.4 nM, K_{t_OCT2_celltoapical} = 1,227.9 nM), and a symmetric basolateral facilitated diffusion transporter (V_max = 6.0 nM/s, K_t = 628.3 nM). The apparent directionality of OCT2 may reflect altered TYR ionization due to known pH differences between compartments. Models for asymmetry and compartmentalization were compared by root mean square deviation from experimental data, and it was found that TYR compartmentalization could only partially replace the need for asymmetry of OCT2. In conclusion, modelling indicates that known TYR transport processes are insufficient to explain experimental concentration-time profiles and that asymmetry of the apical membrane OCT2 combined with additional, low affinity, basolateral membrane facilitated diffusion transporters are required.

Clinically Relevant Drug Interactions with Monoamine Oxidase Inhibitors

Monoamine oxidase inhibitors (MAOI) are a class of drugs that were originally developed for the treatment of depression but have since been expanded to be used in management of affective and neurological disorders, as well as stroke and aging-related neurocognitive changes. Ranging from irreversible to reversible and selective to non-selective, these drugs target the monoamine oxidase (MAO) enzyme and prevent the oxidative deamination of various monoamines and catecholamines such as serotonin and dopamine, respectively. Tyramine is a potent releaser of norepinephrine (NE) and is found in high concentrations in foods such as aged cheeses and meats. Under normal conditions, NE is unable to accumulate to toxic levels due to the presence of MAO-A, an enzyme that degrades neurotransmitters, including NE. When MAO-A is inhibited, the capacity to handle tyramine intake from the diet is significantly reduced causing the brain to be vulnerable to overstimulation of postsynaptic adrenergic receptors with as little as 8-10 mg of tyramine ingested and can result in life-threatening blood pressure elevations. In addition to adverse reactions with certain foods, both older and newer MAOIs can negatively interact with both sympathomimetic and serotonergic drugs. In general, patients on a MAOI want to avoid two types of medications: those that can elevate blood pressure via sympathomimetic actions (e.g., phenylephrine and oxymetazoline) and those that can increase serotonin levels via 5-HT reuptake inhibition (e.g., dextromethorphan, chlorpheniramine, and brompheniramine). Illicit drugs that stimulate the central nervous system such as ecstasy (MDMA, 3,4-methylenedioxymethamphetamine) act as serotonin releasers. Patient involvement is also crucial to ensure any interaction within the healthcare setting includes making other providers aware of a MAOI prescription as well as avoiding certain OTC medications that can interact adversely with MAOIs.

Ortholog genes from cactophilic Drosophila provide insight into human adaptation to hallucinogenic cacti

Cultural transformations of lifestyles and dietary practices have been key drivers of human evolution. However, while most of the evidence of genomic adaptations is related to the hunter-gatherer transition to agricultural societies, little is known on the influence of other major cultural manifestations. Shamanism is considered the oldest religion that predominated throughout most of human prehistory and still prevails in many indigenous populations. Several lines of evidence from ethno-archeological studies have demonstrated the continuity and importance of psychoactive plants in South American cultures. However, despite the well-known importance of secondary metabolites in human health, little is known about its role in the evolution of ethnic differences. Herein, we identified candidate genes of adaptation to hallucinogenic cactus in Native Andean populations with a long history of shamanic practices. We used genome-wide expression data from the cactophilic fly Drosophila buzzatii exposed to a hallucinogenic columnar cactus, also consumed by humans, to identify ortholog genes exhibiting adaptive footprints of alkaloid tolerance. Genomic analyses in human populations revealed a suite of ortholog genes evolving under recent positive selection in indigenous populations of the Central Andes. Our results provide evidence of selection in genetic variants related to alkaloids toxicity, xenobiotic metabolism, and neuronal plasticity in Aymara and Quechua populations, suggesting a possible process of gene-culture coevolution driven by religious practices.

How to Optimize the Effectiveness and Safety of Parkinson's Disease Therapy? - A Systematic Review of Drugs Interactions with Food and Dietary Supplements

BACKGROUND

Despite increasing worldwide incidence of Parkinson's disease, the therapy is still suboptimal due to the diversified clinical manifestations, lack of sufficient treatment, the poor adherence in advanced patients, and varied response. Proper intake of medications regarding food and managing drug-food interactions may optimize Parkinson's disease treatment.

OBJECTIVES

We investigated potential effects that food, beverages, and dietary supplements may have on the pharmacokinetics and pharmacodynamics of drugs used by parkinsonian patients; identified the most probable interactions; and shaped recommendations for the optimal intake of drugs regarding food.

METHODS

We performed a systematic review in adherence to PRISMA guidelines, and included a total of 81 studies in the qualitative synthesis.

RESULTS AND CONCLUSION

We found evidence for levodopa positive interaction with coffee, fiber and vitamin C, as well as for the potential beneficial impact of low-fat and protein redistribution diet. Contrastingly, high-protein diet and ferrous sulfate supplements can negatively affect levodopa pharmacokinetics and effectiveness. For other drugs, the data of food impact are scarce. Based on the available limited evidence, all dopamine agonists (bromocriptine, cabergoline, ropinirole), tolcapone, rasagiline, selegiline in tablets, safinamide, amantadine and pimavanserin can be taken with or without a meal. Opicapone and orally disintegrating selegiline tablets should be administered on an empty stomach. Of monoamine oxidase B inhibitors, safinamide is the least susceptible for interaction with the tyramine-rich food, whereas selegiline and rasagiline may lose selectivity to monoamine oxidase B when administered in supratherapeutic doses. The level of presented evidence is low due to the poor studies design, their insufficient actuality, and missing data.

Revisiting the Role of Astrocytic MAOB in Parkinson's Disease

Monoamine oxidase-B (MAOB) has been believed to mediate the degradation of monoamine neurotransmitters such as dopamine. However, this traditional belief has been challenged by demonstrating that it is not MAOB but MAOA which mediates dopamine degradation. Instead, MAOB mediates the aberrant synthesis of GABA and hydrogen peroxide (H₂O₂) in reactive astrocytes of Parkinson’s disease (PD). Astrocytic GABA tonically suppresses the dopaminergic neuronal activity, whereas H₂O₂ aggravates astrocytic reactivity and dopaminergic neuronal death. Recently discovered reversible MAOB inhibitors reduce reactive astrogliosis and restore dopaminergic neuronal activity to alleviate PD symptoms in rodents. In this perspective, we redefine the role of MAOB for the aberrant suppression and deterioration of dopaminergic neurons through excessive GABA and H₂O₂ synthesis of reactive astrocytes in PD.

Antidepressant activity of Riparin A in murine model

Depression and anxiety are common neuropsychiatric disorders that usually appear as comorbidities. The development of new drugs is crucial for safer and more effective clinical management of both disorders. Riparin A is a synthetic chemical analog of riparins that naturally occur in several medicinal plants. Marked pharmacological effects such as anxiolytic and antidepressant properties characterize this class of compounds. However, little is known about the potential anxiolytic and antidepressant effects of Riparin A. In this work, we showed that, unlike other riparins, Riparin A exerts only a very mild anxiolytic-like effect as demonstrated by the results of classical behavioral tests such as the elevated plus-maze, light-dark box and open-field tests in rats. However, all doses of Riparin A (2.5; 5.0 and 10 mg/kg; intraperitoneal) have shown significant antidepressant activity in rats submitted to forced swimming test. In addition to this interesting pharmacological property, Riparin A did not promote any important alterations in the locomotor performance of the animals as specifically demonstrated by the rotarod test. Furthermore, Riparin A did not induce sedation in treated animals; instead, this compound appears to increase the animal's state of alertness as measured by the latency time to loss of reflexes and time to recovery from sleep in rats submitted to the pentobarbital-induced sleep time test. The present results point to an antidepressant effect of Riparin A and reinforce the pharmaceutical interest in the group of riparins, particularly their high potential for use in new studies investigating the structure-activity relationships between member compounds.

Molecular Insights into SARS-CoV2-Induced Alterations of the Gut/Brain Axis

For a yet unknown reason, a substantial share of patients suffering from COVID-19 develop long-lasting neuropsychiatric symptoms ranging from cognitive deficits to mood disorders and/or an extreme fatigue. We previously reported that in non-neural cells, angiotensin-1 converting enzyme 2 (ACE2), the gene coding for the SARS-CoV2 host receptor, harbors tight co-expression links with dopa-decarboxylase (DDC), an enzyme involved in the metabolism of dopamine. Here, we mined and integrated data from distinct human expression atlases and found that, among a wide range of tissues and cells, enterocytes of the small intestine express the highest expression levels of ACE2, DDC and several key genes supporting the metabolism of neurotransmitters. Based on these results, we performed co-expression analyses on a recently published set of RNA-seq data obtained from SARS-CoV2-infected human intestinal organoids. We observed that in SARS-CoV2-infected enterocytes, ACE2 co-regulates not only with DDC but also with a specific group of genes involved in (i) the dopamine/trace amines metabolic pathway, (ii) the absorption of microbiota-derived L-DOPA and (iii) the absorption of neutral amino acids serving as precursors to neurotransmitters. We conclude that in patients with long COVID, a chronic infection and inflammation of small intestine enterocytes might be indirectly responsible for prolonged brain alterations.

Differential Susceptibilities of Catecholamines to Metabolism by Monoamine Oxidases

The endogenous catecholamines dopamine (DA), norepinephrine (NE), and epinephrine (EPI) play key roles in neurobehavioral, cardiovascular, and metabolic processes; various clinical disorders; and effects of numerous drugs. Steps in intracellular catecholamine synthesis and metabolism were delineated long ago, but there remains a knowledge gap. Catecholamines are metabolized by two isoforms of monoamine oxidase (MAO), MAO-A and MAO-B, and although the anatomic localization of MAO-A and MAO-B and substrate specificities of enzyme inhibitors are well characterized, relative susceptibilities of the endogenous catecholamines to enzymatic oxidation by MAO-A and MAO-B have not been studied systematically. MAOs catalyze the conversion of catecholamines to catecholaldehydes-3,4-dihydroxyphenylacetaldehyde (DOPAL) from DA and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) from NE and EPI. In this study we exploited the technical ability to assay DOPAL and DOPEGAL simultaneously with the substrate catecholamines to compare DA, NE, and EPI in their metabolism by MAO-A and MAO-B. For both MAO isoforms, DA was the better substrate compared to NE or EPI, which were metabolized equally. Since catecholaminergic neurons express mainly MAO-A, the finding that MAO-A is more efficient than MAO-B in metabolizing endogenous catecholamines reinforces the view that the predominant route of intraneuronal enzymatic oxidation of catecholamines is via MAO-A. The results have implications for clinical neurochemistry, experimental therapeutics, and computational models of catecholaminergic neurodegeneration. For instance, the greater susceptibility of DA than the other catecholamines to both MAO isoforms can help explain relatively high concentrations of the deaminated DA metabolite 3,4-dihydroxyphenylacetic acid than of the NE metabolite 3,4-dihydroxyphenylglycol in human plasma and urine. SIGNIFICANCE STATEMENT: Endogenous catecholamines are metabolized by monoamine oxidase (MAO)-A and -B, yielding the catecholaldehydes 3,4-dihydroxyphenylacetaldehyde (DOPAL) from dopamine (DA) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) from norepinephrine (NE) and epinephrine (EPI). Based on measurements of DOPAL and DOPEGAL production, DA is a better substrate than NE or EPI for both MAO isoforms, and MAO-A is more efficient than MAO-B in metabolizing DA, NE, and EPI. MAO-A is the main route of intraneuronal metabolism of endogenous catecholamines.

The Alkaloids from Lophophora diffusa and Other "False Peyotes"

Commonly, false peyote refers to Lophophora diffusa. However, several other unrelated cacti go by this colloquial name. They either resemble "true" peyote, Lophophora williamsii, or are found in similar habitats. To date, over 40 different alkaloids have been isolated from the Lophophora genus. Of these, only the pharmacological actions of mescaline (1) have been extensively investigated. The major alkaloid in L. diffusa is pellotine (2), a tetrahydroisoquinoline (THIQ), which was briefly marketed as a sleeping aid around the beginning of the 20th century, following reports of its hypnotic properties in humans. Pharmacological experiments with the Lophophora THIQs were performed at the turn of the 20th century, whereas the chemical synthesis was not realized until several decades later. The biosynthetic pathways of the main Lophophora alkaloids were reported at the end of the 1960s. In this review, the relationship of the different "false peyotes" to L. williamsii, in regard to their alkaloid content, the bio- and chemical synthesis of the most relevant alkaloids, and their corresponding pharmacology will be outlined and discussed.

The trace amine theory of spontaneous hypertension as induced by classic monoamine oxidase inhibitors

The classic monoamine oxidase inhibitors (MAOIs) tranylcypromine (TCP) and phenelzine (PLZ) are powerful antidepressants that come with an equally powerful stigma, and are thus rarely prescribed-despite their well-established effectiveness. Some of these preconceptions appear to stem from unclarity, as the etiology of a rare but important side effect, 'spontaneous hypertension' (SH)-a significant increase in blood pressure absent dietary tyramine ingestion-remains improperly elucidated. This paper aims at uprooting some of the stigma surrounding MAOIs by advancing the trace amine (TA) theory as the causative underpinning of SH. This theory posits that SH results from the considerable influx of TAs observed following TCP- or PLZ-administration. TAs are known, albeit at greatly supraphysiological levels, to raise blood pressure on account of their propensity to exert potent indirect sympathomimetic effects; additionally, some research posits that TAs may induce vasoconstrictive effects partly or wholly separate therefrom, which would then constitute a second hypertensive mechanism. TAs are endogenous to the human body in low quantities. Both TCP and PLZ cause marked elevations of 2-phenylethylamine (PEA), meta- and para-tyramine (m-/p-TYR), octopamine (OA), and tryptamine (TRYP), following both acute and (sub)chronic administration. This paper holds that TYR plays a pivotal role in causing SH, due to its strong pressor effect. Cautious treatment of SH is advised, given its typically self-limiting nature. The risk of hypotensive overshoots must be taken into account. For severe cases, this paper urges reconsideration, following suitable confirmation trials, of antipsychotics (notably risperidone) as these agents may reduce striatal p-TYR levels.

In vitro and in vivo evaluation of fluorinated indanone derivatives as potential positron emission tomography agents for the imaging of monoamine oxidase B in the brain

Monoamine oxidases (MAOs) play a key role in the metabolism of major monoamine neurotransmitters. In particular, the upregulation of MAO-B in Parkinson's disease, Alzheimer's disease and cancer augmented the development of selective MAO-B inhibitors for diagnostic and therapeutic purposes, such as the anti-parkinsonian MAO-B irreversible binder l-deprenyl (Selegiline®). Herein we report on the synthesis of novel fluorinated indanone derivatives for PET imaging of MAO-B in the brain. Out of our series, the derivatives 6, 8, 9 and 13 are amongst the most affine and selective ligands for MAO-B reported so far. For the derivative 6-((3-fluorobenzyl)oxy)-2,3-dihydro-1H-inden-1-one (6) exhibiting an outstanding affinity (K_iMAO-B = 6 nM), an automated copper-mediated radiofluorination starting from the pinacol boronic ester 17 is described. An in vitro screening in different species revealed a MAO-B region-specific accumulation of [¹⁸F]6 in rats and piglets in comparison to L-[³H]deprenyl. The pre-clinical in vivo assessment of [¹⁸F]6 in mice demonstrated the potential of indanones to readily cross the blood-brain barrier. Nonetheless, parallel in vivo metabolism studies indicated the presence of blood-brain barrier metabolites, thus arguing for further structural modifications. With the matching analytical profiles of the radiometabolite analysis from the in vitro liver microsome studies and the in vivo evaluation, the structure's elucidation of the blood-brain barrier penetrant radiometabolites is possible and will serve as basis for the development of new indanone derivatives suitable for the PET imaging of MAO-B.

Hydroxytyrosol as anti-parkinsonian molecule: Assessment using in-silico and MPTP-induced Parkinson's disease model

3-Hydroxytyrosol (HXT) is a natural polyphenol present in extra virgin olive oil. It is a key component of Mediterranean diet and is known for its strong antioxidant activity. The present study evaluated the potential of HXT as an anti-parkinsonian molecule in terms of its ability to inhibit MAO-B and thereby maintaining dopamine (DA) levels in Parkinson's disease (PD). In-silico molecular docking study followed by MMGBSA binding free energy calculation revealed that HXT has a strong binding affinity for MAO-B in comparison to MAO-A. Moreover, rasagiline and HXT interacted with the similar binding sites and modes of interactions. Additionally, molecular dynamics simulation studies revealed stable nature of HXT-MAO-B interaction and also provided information about the amino acid residues involved in binding. Moreover, in vitro studies revealed that HXT inhibited MAO-B in human platelets with IC₅₀ value of 7.78 μM. In vivo studies using MPTP-induced mouse model of PD revealed increase in DA levels with concomitant decrease in DA metabolites (DOPAC and HVA) on HXT treatment. Furthermore, MAO-B activity was also inhibited on HXT administration to PD mice. In addition, HXT treatment prevented MPTP-induced loss of DA neurons in substantia nigra and their nerve terminals in the striatum. HXT also attenuated motor impairments in PD mice assessed by catalepsy bar, narrow beam walk and open field tests. Thus, the present findings reveal HXT as a potential inhibitor of MAO-B, which may be used as a lead molecule for the development of therapeutics for PD.

Involvement of Organic Cation Transporter 2 and a Na+-dependent active transporter in p-tyramine transport across Caco-2 intestinal cells

AIMS

We have previously demonstrated that p-tyramine (TYR), an endogenous trace amine-associated receptor 1 agonist, passage across neuronal membranes involves a transporter exhibiting the pharmacological profile of Organic Cation Transporter 2 (OCT2). Since TYR is also a constituent of foodstuffs and produced by the intestinal microbiota, here we have investigated whether similar processes are involved in the passage of 100 nM TYR across apical and basolateral membranes of the Caco-2 human intestinal epithelial cell line.

MATERIALS AND METHODS

[³H]TYR transport across apical and basolateral membranes of Caco-2 cell monolayers was measured in the presence of inhibitors of TYR metabolizing enzymes. Cellular, apical, and basolateral compartments were collected at various timepoints, TYR concentrations calculated, and transport properties pharmacologically characterized.

KEY FINDINGS

Apical transport resulted in equimolar accumulation of TYR within cells. Pentamidine (OCT1/OCT2 inhibitor) decreased apical transport (P = 0.001) while atropine (OCT1 inhibitor) had no effect, suggesting apical transport involved OCT2. In contrast, basolateral transport resulted in 500-1000 nM cellular concentrations (P < 0.0001) indicating the presence of an active transporter. Replacement of Na⁺ on an equimolar basis with choline resulted in loss of TYR transport (P = 0.017). Unexpectedly, this active transport was also atropine-sensitive (P = 0.020). Kinetic analysis of the active transporter revealed V_max = 43.0 nM/s with a K_t = 33.1 nM.

SIGNIFICANCE

We have demonstrated for the first time that TYR is transported across Caco-2 apical membranes via facilitated diffusion by OCT2, whereas transport across basolateral membranes is by a Na⁺-dependent, atropine-sensitive, active transporter.

The biogenic amine tryptamine, unlike β-phenylethylamine, shows in vitro cytotoxicity at concentrations that have been found in foods

β-phenylethylamine and tryptamine are biogenic amines (BA) often found in foods. In general, BA are assumed to be toxic and their accumulation in food is not recommended. However, present knowledge regarding the toxicity of β-phenylethylamine and tryptamine is limited; more information is needed if qualitative and quantitative risk assessments of foods are to be successfully conducted. This study describes a real-time analysis of β-phenylethylamine and tryptamine toxicity on a human intestinal epithelial cell line. Both BA caused cell necrosis and apoptosis, although the former was the main mode of action of β-phenylethylamine, and the latter the main mode of action of tryptamine. Only tryptamine was cytotoxic at concentrations found in BA-rich foods. The results presented in this work may contribute to establish legal limits for β-phenylethylamine and tryptamine in food.

Food sources and biomolecular targets of tyramine

Tyramine is a biogenic trace amine that is generated via the decarboxylation of the amino acid tyrosine. At pico- to nanomolar concentrations, it can influence a multitude of physiological mechanisms, exhibiting neuromodulatory properties as well as cardiovascular and immunological effects. In humans, the diet is the primary source of physiologically relevant tyramine concentrations, which are influenced by a large number of intrinsic and extrinsic factors. Among these factors are the availability of tyrosine in food, the presence of tyramine-producing bacteria, the environmental pH, and the salt content of food. The process of fermentation provides a particularly good source of tyramine in human nutrition. Here, the potential impact of dietary tyramine on human health was assessed by compiling quantitative data on the tyramine content in a variety of foods and then conducting a brief review of the literature on the physiological, cellular, and systemic effects of tyramine. Together, the data sets presented here may allow both the assessment of tyramine concentrations in food and the extrapolation of these concentrations to gauge the physiological and systemic effects in the context of human nutrition.

Review on Preclinical and Clinical Evidence of Food (Beverages, Fruits and Vegetables) and Drug Interactions: Mechanism and Safety

Background:

The therapeutic potency and efficacy of drugs can be affected by a patient’s dietary habit. The food composition and their nutritional value interact with drugs that lead to alteration of the therapeutic response of drugs in patients.

Objective:

This present review is an attempt to illustrate clinical reports of food-drug interaction. Further, it also highlights specific interaction mechanism(s) and the safety thereof.

Methods:

Through the search engine “Scopus”; literature on recent advances in food and drug interactions includes almost all therapeutic categories such as antimicrobials, antiviral, antifungal, antihistamines, anticoagulants, non-steroidal anti-inflammatory drugs, and drugs acting on the central nervous system and cardiovascular system.

Results:

Preclinical and clinical studies that have been conducted by various researchers affirm significant drug-food interactions across the various therapeutic categories of drugs. Preclinical studies have documented the effects of food, milk products, alcohols, fruit and vegetables on the drug absorption, metabolizing enzymes and drug transporters. The clinical studies on fruits/vegetables and drugs interactions report significant alteration in therapeutic response.

Conclusion:

Based on the preclinical and clinical reports, it can be concluded that the interaction of food with drug(s) significantly alters their therapeutic potential. The inputs from clinical practitioners to elucidate potential risk of food-drug interaction need to be intensified in order to prevent adverse clinical consequences.

Propargylamine-derived multi-target directed ligands for Alzheimer's disease therapy

Current options for the treatment of Alzheimeŕs disease have been restricted to prescription of acetylcholinesterase inhibitors or N-methyl-d-aspartate receptor antagonist, memantine. Propargylamine-derived multi-target directed ligands, such as ladostigil, M30, ASS234 and contilisant, involve different pathways. Apart from acting as inhibitors of both cholinesterases and monoamine oxidases, they show improvement of cognitive impairment, antioxidant activities, enhancement of iron-chelating activities, protect against tau hyperphosphorylation, block metal-associated oxidative stress, regulate APP and Aβ expression processing by the non-amyloidogenic α-secretase pathway, suppress mitochondrial permeability transition pore opening, and coordinate protein kinase C signaling and Bcl-2 family proteins. Other hybrid propargylamine derivatives are also reported.

Contemporary Options for the Management of Motor Complications in Parkinson's Disease: Updated Clinical Review

Parkinson's disease (PD) is a chronic, progressive condition affecting around 1% of the population older than 60 years. Upon long-term treatment with levodopa, the mainstay of treatment in PD, most patients, especially younger ones exposed to higher doses, will experience symptoms related to end-of-dose deterioration, peak-dose dyskinesias, and other motor fluctuations. Therapeutic strategies are grounded on modification of oral levodopa pharmacokinetics to extend levodopa benefit and development of new routes of drug delivery (e.g., levodopa/carbidopa intestinal gel infusion) or long-acting formulations of existing dopaminergic drugs to prolong the duration of striatal dopamine receptors stimulation. As our understanding of the pathophysiology of motor complications evolves, our therapeutic armamentarium is actively expanding and the focus of research is now actively pointing to the new non-dopaminergic agents acting both within the basal ganglia and in other brain regions (e.g., drugs acting on glutamate, GABA, serotonin, and calcium channels). Despite the fact that trials comparing the different therapeutic strategies are lacking, we aimed at devising practical evidence- and experience-guided suggestions for the clinical management of motor complications, emphasizing that this should always be an individualized endeavor. This review summarizes the pharmacological management of motor complications in PD, including new formulations and routes of delivery, and the newer released drugs such as istradefylline, opicapone, safinamide, and zonisamide. Advanced therapeutic strategies for selected cases such as treatment with apomorphine and surgical techniques (deep brain stimulation) are also discussed. A comprehensive knowledge of the available options and evidence is fundamental for the successful management of these challenging complications.

Selegiline: a molecule with innovative potential

Monoamine oxidase B (MAO-B) inhibitors have an established role in the treatment of Parkinson's disease as monotherapy or adjuvant to levodopa. Two major recognitions were required for their introduction into this therapeutic field. The first was the elucidation of the novel pharmacological properties of selegiline as a selective MAO-B inhibitor by Knoll and Magyar and the original idea of Riederer and Youdim, supported by Birkmayer, to explore its effect in parkinsonian patients with on-off phases. In the 1960s, MAO inhibitors were mainly studied as potential antidepressants, but Birkmayer found that combined use of levodopa and various MAO inhibitors improved akinesia in Parkinson's disease. However, the serious side effects of the first non-selective MAO inhibitors prevented their further use. Later studies demonstrated that MAO-B, mainly located in glial cells, is important for dopamine metabolism in the brain. Recently, cell and molecular studies revealed interesting properties of selegiline opening new possibilities for neuroprotective mechanisms and a disease-modifying effect of MAO-B inhibitors.

Dynamic Changes in Biogenic Amine Content in the Traditional Brewing Process of Soy Sauce

A high concentration of biogenic amines have been reported to be hazardous for human health. This article is an analytical report on one lot to identify the changes of biogenic amines in each period of soy sauce brewing and clarify the key control point for biogenic amine production. The content of putrescine, cadaverine, spermidine, spermine, tryptamine, phenylethylamine, histamine, serotonin, tyramine, and agmatine was detected in the koji-making and fermenting process. The content of putrescine increased from 27.11 ± 1.05 to 185.86 ± 1.18 mg/kg in the koji-making process, indicating that putrescine is the main biogenic amine produced by microbes in this period. The content of tryptamine increased to the highest value of 581.77 ± 36.38 mg/L on day 24 of the fermenting process and then decreased rapidly to 81.98 ± 0.20 mg/L at the end (day 122). In addition, histamine and tyramine reached the highest values (486.91 ± 24.67 and 180.84 ± 2.32 mg/L, respectively) after 52 days of fermentation, followed by a decrease to 287.24 ± 15.00 and 144.67 ± 3.61 mg/L, respectively, at the end of the fermenting process. The samples were further characterized by the analysis of other indices, including the content of water, salt, soluble saltless solids, crude fat, total acid, amino acid nitrogen, total nitrogen, and ammonium salt. The content of soluble saltless solids decreased from 9.28 ± 0.16 to 5.30 ± 1.40 g/100 g during the first 38 days of fermentation, followed by an increase to 14.68 ± 1.12 g/100 g during the last 84 days. The content of total acid, crude fat, amino acid nitrogen, total nitrogen, and ammonium salt all increased rapidly in the early stage of the fermenting process and then slowed down.

Cerebral MAO Activity Is Not Altered by a Novel Herbal Antidepressant Treatment

Inhibition of monoamine oxidase (MAO)-A/B can ameliorate depressive- and anxiety-related symptoms via increase of monoamine extracellular levels. However, such inhibition can also instigate hypertensive response following exposure to dietary tyramine (i.e., "the cheese effect"). Novel herbal treatment (NHT) is an herbal formula that has been demonstrated to reduce depressive- and anxiety-like symptoms in pre-clinical studies. The aim of the current study was to examine whether the therapeutic potential of NHT is underlain by inhibition of MAO-A/B and whether NHT poses a risk for tyramine hyper-potentiation. Unpredictable chronic mild stress (UCMS)-exposed mice and naïve mice were treated for 3 weeks with NHT (30 mg/kg; i.p.), the selective serotonin reuptake inhibitor (SSRI) escitalopram (15 mg/kg; i.p.), or saline. Subsequently, MAO-A/B activities in the hypothalamus, striatum, and prefrontal cortex (PFC) were assessed. Exposure to UCMS led to significant increases in both MAO-A and MAO-B activities in the hypothalamus (p < 0.001) and in the PFC (p < 0.01 for MAO-A; p < 0.001 for MAO-B). Neither NHT nor escitalopram had any notable effects. Treatment with NHT was supported as safe in terms of risk for inducing a hypertensive response. The antidepressant- and anxiolytic-like effects of NHT are mediated via pathways other than MAO-A/B inhibition.

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.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

Inhibitors of MAO-B and COMT: their effects on brain dopamine levels and uses in Parkinson's disease

MAO-B and COMT are both enzymes involved in dopamine breakdown and metabolism. Inhibitors of these enzymes are used in the treatment of Parkinson's disease. This review article describes the scientific background to the localization and function of the enzymes, the physiological changes resulting from their inhibition, and the basic and clinical pharmacology of the various inhibitors and their role in treatment of Parkinson's disease.

Metabolic Effects of Oral Phenelzine Treatment on High-Sucrose-Drinking Mice

Phenelzine has been suggested to have an antiobesity effect by inhibiting de novo lipogenesis, which led us to investigate the metabolic effects of oral chronic phenelzine treatment in high-sucrose-drinking mice. Sucrose-drinking mice presented higher body weight gain and adiposity versus controls. Phenelzine addition did not decrease such parameters, even though fat pad lipid content and weights were not different from controls. In visceral adipocytes, phenelzine did not impair insulin-stimulated de novo lipogenesis and had no effect on lipolysis. However, phenelzine reduced the mRNA levels of glucose transporters 1 and 4 and phosphoenolpyruvate carboxykinase in inguinal white adipose tissue (iWAT), and altered circulating levels of free fatty acids (FFA) and glycerol. Interestingly, glycemia was restored in phenelzine-treated mice, which also had higher insulinaemia. Phenelzine-treated mice presented higher rectal temperature, which was associated to reduced mRNA levels of uncoupling protein 1 in brown adipose tissue. Furthermore, unlike sucrose-drinking mice, hepatic malondialdehyde levels were not altered. In conclusion, although de novo lipogenesis was not inhibited by phenelzine, the data suggest that the ability to re-esterify FFA is impaired in iWAT. Moreover, the effects on glucose homeostasis and oxidative stress suggest that phenelzine could alleviate obesity-related alterations and deserves further investigation in obesity models.

Mechanisms of the antilipolytic response of human adipocytes to tyramine, a trace amine present in food

Tyramine is found in foodstuffs, the richest being cheeses, sausages, and wines. Tyramine has been recognized to release catecholamines from nerve endings and to trigger hypertensive reaction. Thereby, tyramine-free diet is recommended for depressed patients treated with irreversible inhibitors of monoamine oxidases (MAO) to limit the risk of hypertension. Tyramine is a substrate of amine oxidases and also an agonist at trace amine-associated receptors. Our aim was to characterize the dose-dependent effects of tyramine on human adipocyte metabolic functions. Lipolytic activity was determined in adipocytes from human subcutaneous abdominal adipose tissue. Glycerol release was increased by a fourfold factor with classical lipolytic agents (1 μM isoprenaline, 1 mM isobutylmethylxanthine) while the amine was ineffective from 0.01 to 100 μM and hardly stimulatory at 1 mM. Tyramine exhibited a partial antilipolytic effect at 100 μM and 1 mM, which was similar to that of insulin but weaker than that obtained with agonists at purinergic A1 receptors, α₂-adrenoceptors, or nicotinic acid receptors. Gi-protein blockade by Pertussis toxin abolished all these antilipolytic responses save that of tyramine. Indeed, tyramine antilipolytic effect was impaired by MAO-A inhibition. Tyramine inhibited protein tyrosine phosphatase activities in a manner sensitive to ascorbic acid and amine oxidase inhibitors. Thus, millimolar tyramine restrained lipolysis via the hydrogen peroxide it generates when oxidized by MAO. Since tyramine plasma levels have been reported to reach 0.2 μM after ingestion of 200 mg tyramine in healthy individuals, the direct effects we observed in vitro on adipocytes could be nutritionally relevant only when the MAO-dependent hepato-intestinal detoxifying system is overpassed.

Body fat reduction without cardiovascular changes in mice after oral treatment with the MAO inhibitor phenelzine

BACKGROUND AND PURPOSE

Phenelzine is an antidepressant drug known to increase the risk of hypertensive crisis when dietary tyramine is not restricted. However, this MAO inhibitor inhibits other enzymes not limited to the nervous system. Here we investigated if its antiadipogenic and antilipogenic effects in cultured adipocytes could contribute to decreased body fat in vivo, without unwanted hypertensive or cardiovascular effects.

EXPERIMENTAL APPROACH

Mice were fed a standard chow and given 0.028% phenelzine in drinking water for 12 weeks. Body composition was determined by NMR. Cardiovascular dysfunction was assessed by heart rate variability analyses and by evaluation of cardiac oxidative stress markers. MAO activity, hydrogen peroxide release and triacylglycerol turnover were assayed in white adipose tissue (WAT), alongside determination of glucose and lipid circulating levels.

KEY RESULTS

Phenelzine-treated mice exhibited lower body fat content, subcutaneous WAT mass and lipid content in skeletal muscles than control, without decreased body weight gain or food consumption. A modest alteration of cardiac sympathovagal balance occurred without depressed aconitase activity. In WAT, phenelzine impaired the lipogenic but not the antilipolytic actions of insulin, MAO activity and hydrogen peroxide release. Phenelzine treatment lowered non-fasting blood glucose and phosphoenolpyruvate carboxykinase expression. In vitro, high doses of phenelzine decreased both lipolytic and lipogenic responses in mouse adipocytes.

CONCLUSION AND IMPLICATIONS

As phenelzine reduced body fat content without affecting cardiovascular function in mice, it may be of benefit in the treatment of obesity-associated complications, with the precautions of use recommended for antidepressant therapy.

Methylene blue and its analogues as antidepressant compounds

Methylene Blue (MB) is considered to have diverse medical applications and is a well-described treatment for methemoglobinemias and ifosfamide-induced encephalopathy. In recent years the focus has shifted to MB as an antimalarial agent and as a potential treatment for neurodegenerative disorders such as Alzheimer's disease. Of interest are reports that MB possesses antidepressant and anxiolytic activity in pre-clinical models and has shown promise in clinical trials for schizophrenia and bipolar disorder. MB is a noteworthy inhibitor of monoamine oxidase A (MAO-A), which is a well-established target for antidepressant action. MB is also recognized as a non-selective inhibitor of nitric oxide synthase (NOS) and guanylate cyclase. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) cascade is strongly linked to the neurobiology of mood, anxiety and psychosis, while the inhibition of NOS and/or guanylate cyclase has been associated with an antidepressant response. This action of MB may contribute significantly to its psychotropic activity. However, these disorders are also characterised by mitochondrial dysfunction and redox imbalance. By acting as an alternative electron acceptor/donor MB restores mitochondrial function, improves neuronal energy production and inhibits the formation of superoxide, effects that also may contribute to its therapeutic activity. Using MB in depression co-morbid with neurodegenerative disorders, like Alzheimer's and Parkinson's disease, also represents a particularly relevant strategy. By considering their physicochemical and pharmacokinetic properties, analogues of MB may provide therapeutic potential as novel multi-target strategies in the treatment of depression. In addition, low MAO-A active analogues may provide equal or improved response with a lower risk of adverse effects.

Assessment of Enzyme Inhibition: A Review with Examples from the Development of Monoamine Oxidase and Cholinesterase Inhibitory Drugs

The actions of many drugs involve enzyme inhibition. This is exemplified by the inhibitors of monoamine oxidases (MAO) and the cholinsterases (ChE) that have been used for several pharmacological purposes. This review describes key principles and approaches for the reliable determination of enzyme activities and inhibition as well as some of the methods that are in current use for such studies with these two enzymes. Their applicability and potential pitfalls arising from their inappropriate use are discussed. Since inhibitor potency is frequently assessed in terms of the quantity necessary to give 50% inhibition (the IC50 value), the relationships between this and the mode of inhibition is also considered, in terms of the misleading information that it may provide. Incorporation of more than one functionality into the same molecule to give a multi-target-directed ligands (MTDLs) requires careful assessment to ensure that the specific target effects are not significantly altered and that the kinetic behavior remains as favourable with the MTDL as it does with the individual components. Such factors will be considered in terms of recently developed MTDLs that combine MAO and ChE inhibitory functions.

Evaluation of the inhibitory effects of eckol and dieckol isolated from edible brown alga Eisenia bicyclis on human monoamine oxidases A and B

Eckol and dieckol are important phlorotannins found in edible brown algae including Eisenia bicyclis, Ecklonia stolonifera, and others. Inhibition of monoamine oxidase (MAO) play an important role in the early management of Parkinson's disease (PD). The aim of this study was to determine the effectiveness of eckol and dieckol isolated from the methanolic extract of E. bicyclis against PD by the inhibition of human MAO-A and MAO-B (hMAO-A and hMAO-B). A sensitive enzyme-based chemiluminescent assay and kinetics methods were used to investigate enzyme inhibition and mode of inhibition. A molecular docking simulation was performed to clarify the binding characteristics of eckol and dieckol to hMAO-A and hMAO-B. The results suggested that methanolic extract of E. bicyclis and its isolated phlorotannins, eckol and dieckol, have potent inhibitory activity against hMAO-A and hMAO-B. The enzyme-based kinetics results demonstrated eckol mixed and non-competitive inhibition of hMAO-A and hMAO-B, respectively, while dieckol non-competitively inhibited both hMAOs. Molecular docking simulation predicted that eckol and dieckol exhibit higher binding affinity towards hMAO-A and hMAO-B through hydrogen bonding and hydrophobic interactions. These findings implicate eckol and dieckol as inhibitors of hMAOs that might be of potential value in the management of PD.

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

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

Inhibitors of MAO-A and MAO-B in Psychiatry and Neurology

Inhibitors of MAO-A and MAO-B are in clinical use for the treatment of psychiatric and neurological disorders respectively. Elucidation of the molecular structure of the active sites of the enzymes has enabled a precise determination of the way in which substrates and inhibitor molecules are metabolized, or inhibit metabolism of substrates, respectively. Despite the knowledge of the strong antidepressant efficacy of irreversible MAO inhibitors, their clinical use has been limited by their side effect of potentiation of the cardiovascular effects of dietary amines (“cheese effect”). A number of reversible MAO-A inhibitors which are devoid of cheese effect have been described in the literature, but only one, moclobemide, is currently in clinical use. The irreversible inhibitors of MAO-B, selegiline and rasagiline, are used clinically in treatment of Parkinson's disease, and a recently introduced reversible MAO-B inhibitor, safinamide, has also been found efficacious. Modification of the pharmacokinetic characteristics of selegiline by transdermal administration has led to the development of a new drug form for treatment of depression. The clinical potential of MAO inhibitors together with detailed knowledge of the enzyme's binding site structure should lead to future developments with these drugs.

Monoamine oxidase inhibition improves vascular function in mammary arteries from nondiabetic and diabetic patients with coronary heart disease

Monoamine oxidases (MAOs) are mitochondrial enzymes with 2 isoforms that have emerged as important contributors to cardiovascular oxidative stress via the constant generation of hydrogen peroxide. The present study was purported to assess whether MAO-derived H2O2 contributes to the endothelial dysfunction in mammary arteries harvested from coronary heart disease patients with and without diabetes mellitus subjected to coronary artery bypass grafting. To this aim, the effects of MAO inhibition on vascular contractility to phenylephrine and endothelial-dependent relaxation (EDR) in response to acetylcholine were studied in vascular segments. Clorgyline (irreversible MAO-A inhibitor), selegiline (irreversible MAO-B inhibitor), and moclobemide (reversible MAO-A inhibitor) were applied in the organ bath (10 μmol/L). MAO expression was assessed by immunohistochemistry. We found a constant impairment of EDR that has been significantly attenuated in the presence of the MAO-A and MAO-B inhibitors in both groups of coronary heart disease patients. MAO-B was the dominant isoform in all human diseased vessels. In conclusion, in vitro inhibition of MAO significantly improved EDR in human mammary arteries, regardless of the presence of diabetes. These data suggest that MAO inhibitors might be useful in restoring endothelial response in clinical conditions associated with increased oxidative stress, such as coronary artery disease and diabetes.

Familial dysautonomia: History, genotype, phenotype and translational research

Familial dysautonomia (FD) is a rare neurological disorder caused by a splice mutation in the IKBKAP gene. The mutation arose in the 1500s within the small Jewish founder population in Eastern Europe and became prevalent during the period of rapid population expansion within the Pale of Settlement. The carrier rate is 1:32 in Jews descending from this region. The mutation results in a tissue-specific deficiency in IKAP, a protein involved in the development and survival of neurons. Patients homozygous for the mutations are born with multiple lesions affecting mostly sensory (afferent) fibers, which leads to widespread organ dysfunction and increased mortality. Neurodegenerative features of the disease include progressive optic atrophy and worsening gait ataxia. Here we review the progress made in the last decade to better understand the genotype and phenotype. We also discuss the challenges of conducting controlled clinical trials in this rare medically fragile population. Meanwhile, the search for better treatments as well as a neuroprotective agent is ongoing.