Early and persistent alterations in prefrontal cortex MAO A and B in Alzheimer's disease

Indole-Based Compounds in the Development of Anti-Neurodegenerative Agents

Neurodegeneration is a gradual decay process leading to the depletion of neurons in both the central and peripheral nervous systems, ultimately resulting in cognitive dysfunctions and the deterioration of brain functions, alongside a decline in motor skills and behavioral capabilities. Neurodegenerative disorders (NDs) impose a substantial socio-economic strain on society, aggravated by the advancing age of the world population and the absence of effective remedies, predicting a negative future. In this context, the urgency of discovering viable therapies is critical and, despite significant efforts by medicinal chemists in developing potential drug candidates and exploring various small molecules as therapeutics, regrettably, a truly effective treatment is yet to be found. Nitrogen heterocyclic compounds, and particularly those containing the indole nucleus, which has emerged as privileged scaffold, have attracted particular attention for a variety of pharmacological applications. This review analyzes the rational design strategy adopted by different research groups for the development of anti-neurodegenerative indole-based compounds which have the potential to modulate various molecular targets involved in NDs, with reference to the most recent advances between 2018 and 2023.

Type-B monoamine oxidase inhibitors in neurological diseases: clinical applications based on preclinical findings

Type-B monoamine oxidase inhibitors, encompassing selegiline, rasagiline, and safinamide, are available to treat Parkinson's disease. These drugs ameliorate motor symptoms and improve motor fluctuation in the advanced stages of the disease. There is also evidence supporting the benefit of type-B monoamine oxidase inhibitors on non-motor symptoms of Parkinson's disease, such as mood deflection, cognitive impairment, sleep disturbances, and fatigue. Preclinical studies indicate that type-B monoamine oxidase inhibitors hold a strong neuroprotective potential in Parkinson's disease and other neurodegenerative diseases for reducing oxidative stress and stimulating the production and release of neurotrophic factors, particularly glial cell line-derived neurotrophic factor, which support dopaminergic neurons. Besides, safinamide may interfere with neurodegenerative mechanisms, counteracting excessive glutamate overdrive in basal ganglia motor circuit and reducing death from excitotoxicity. Due to the dual mechanism of action, the new generation of type-B monoamine oxidase inhibitors, including safinamide, is gaining interest in other neurological pathologies, and many supporting preclinical studies are now available. The potential fields of application concern epilepsy, Duchenne muscular dystrophy, multiple sclerosis, and above all, ischemic brain injury. The purpose of this review is to investigate the preclinical and clinical pharmacology of selegiline, rasagiline, and safinamide in Parkinson's disease and beyond, focusing on possible future therapeutic applications.

Mitochondrial Interaction with Serotonin in Neurobiology and Its Implication in Alzheimer's Disease

Alzheimer's disease (AD) is a lethal neurodegenerative disorder characterized by severe brain pathologies and progressive cognitive decline. While the exact cause of this disease remains unknown, emerging evidence suggests that dysregulation of neurotransmitters contributes to the development of AD pathology and symptoms. Serotonin, a critical neurotransmitter in the brain, plays a pivotal role in regulating various brain processes and is implicated in neurological and psychiatric disorders, including AD. Recent studies have shed light on the interplay between mitochondrial function and serotonin regulation in brain physiology. In AD, there is a deficiency of serotonin, along with impairments in mitochondrial function, particularly in serotoninergic neurons. Additionally, altered activity of mitochondrial enzymes, such as monoamine oxidase, may contribute to serotonin dysregulation in AD. Understanding the intricate relationship between mitochondria and serotonin provides valuable insights into the underlying mechanisms of AD and identifies potential therapeutic targets to restore serotonin homeostasis and alleviate AD symptoms. This review summarizes the recent advancements in unraveling the connection between brain mitochondria and serotonin, emphasizing their significance in AD pathogenesis and underscoring the importance of further research in this area. Elucidating the role of mitochondria in serotonin dysfunction will promote the development of therapeutic strategies for the treatment and prevention of this neurodegenerative disorder.

Comparison of Monoamine Oxidase-A, Aβ Plaques, Tau, and Translocator Protein Levels in Postmortem Human Alzheimer's Disease Brain

Increased monoamine oxidase-A (MAO-A) activity in Alzheimer's disease (AD) may be detrimental to the point of neurodegeneration. To assess MAO-A activity in AD, we compared four biomarkers, Aβ plaques, tau, translocator protein (TSPO), and MAO-A in postmortem AD. Radiotracers were [18F]FAZIN3 for MAO-A, [18F]flotaza and [125I]IBETA for Aβ plaques, [124/125I]IPPI for tau, and [18F]FEPPA for TSPO imaging. Brain sections of the anterior cingulate (AC; gray matter GM) and corpus callosum (CC; white matter WM) from cognitively normal control (CN, n = 6) and AD (n = 6) subjects were imaged using autoradiography and immunostaining. Using competition with clorgyline and (R)-deprenyl, the binding of [18F]FAZIN3 was confirmed to be selective to MAO-A levels in the AD brain sections. Increases in MAO-A, Aβ plaque, tau, and TSPO activity were found in the AD brains compared to the control brains. The [18F]FAZIN3 ratio in AD GM versus CN GM was 2.80, suggesting a 180% increase in MAO-A activity. Using GM-to-WM ratios of AD versus CN, a >50% increase in MAO-A activity was observed (AD/CN = 1.58). Linear positive correlations of [18F]FAZIN3 with [18F]flotaza, [125I]IBETA, and [125I]IPPI were measured and suggested an increase in MAO-A activity with increases in Aβ plaques and tau activity. Our results support the finding that MAO-A activity is elevated in the anterior cingulate cortex in AD and thus may provide a new biomarker for AD in this brain region.

Structure-Guided Design of N-Methylpropargylamino-Quinazoline Derivatives as Multipotent Agents for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complex disease with an unknown etiology. Available treatments, limited to cholinesterase inhibitors and N-methyl-d-aspartate receptor (NMDAR) antagonists, provide symptomatic relief only. As single-target therapies have not proven effective, rational specific-targeted combination into a single molecule represents a more promising approach for treating AD, and is expected to yield greater benefits in alleviating symptoms and slowing disease progression. In the present study, we designed, synthesized, and biologically evaluated 24 novel N-methylpropargylamino-quinazoline derivatives. Initially, compounds were thoroughly inspected by in silico techniques determining their oral and CNS availabilities. We tested, in vitro, the compounds' effects on cholinesterases and monoamine oxidase A/B (MAO-A/B), as well as their impacts on NMDAR antagonism, dehydrogenase activity, and glutathione levels. In addition, we inspected selected compounds for their cytotoxicity on undifferentiated and differentiated neuroblastoma SH-SY5Y cells. We collectively highlighted II-6h as the best candidate endowed with a selective MAO-B inhibition profile, NMDAR antagonism, an acceptable cytotoxicity profile, and the potential to permeate through BBB. The structure-guided drug design strategy applied in this study imposed a novel concept for rational drug discovery and enhances our understanding on the development of novel therapeutic agents for treating AD.

In Vitro Anti-Venom Potentials of Aqueous Extract and Oils of Toona ciliata M. Roem against Cobra Venom and Chemical Constituents of Oils

There are high mortality and morbidity rates from poisonous snakebites globally. Many medicinal plants are locally used for snakebite treatment in Uganda. This study aimed to determine the in vitro anti-venom activities of aqueous extract and oils of Toona ciliata against Naja melanoleuca venom. A mixture of venom and extract was administered intramuscularly in rats. Anticoagulant, antiphospholipase A2 (PLA2) inhibition assay, and gel electrophoresis for anti-venom activities of oils were done. The chemical constituents of the oils of ciliata were identified using Gas chromatography-tandem mass spectroscopy (GC-MS/MS). The LD50 of the venom was 0.168 ± 0.21 µg/g. The venom and aqueous extract mixture (1.25 µg/g and 3.5 mg/g) did not cause any rat mortality, while the control with venom only (1.25 µg/g) caused death in 1 h. The aqueous extract of T. ciliata inhibited the anticoagulation activity of N. melanoleuca venom from 18.58 min. to 4.83 min and reduced the hemolytic halo diameter from 24 to 22 mm. SDS-PAGE gel electrophoresis showed that oils completely cleared venom proteins. GC-MS/MS analysis showed that the oils had sesquiterpene hydrocarbons (60%) in the volatile oil (VO) and oxygenated sesquiterpenes (48.89%) in the non-volatile oils (NVO). Some major compounds reported for the first time in T. ciliata NVOs were: Rutamarin (52.55%), β-Himachalol (9.53%), Girinimbine (6.68%) and Oprea1 (6.24%). Most compounds in the VO were reported for the first time in T. ciliata, including the major ones Santalene (8.55%) and Himachal-7-ol (6.69%). The result showed that aqueous extract and oils of T. ciliata have anti-venom/procoagulant activities and completely neutralized the venom. We recommend a study on isolation and testing the pure compounds against the same venom.

Mushroom Natural Products in Neurodegenerative Disease Drug Discovery

The variety of drugs available to treat neurodegenerative diseases is limited. Most of these drug's efficacy is restricted by individual genetics and disease stages and usually do not prevent neurodegeneration acting long after irreversible damage has already occurred. Thus, drugs targeting the molecular mechanisms underlying subsequent neurodegeneration have the potential to negate symptom manifestation and subsequent neurodegeneration. Neuroinflammation is a common feature of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis, and is associated with the activation of the NLRP3 inflammasome, which in turn leads to neurodegeneration. Inflammasome activation and oligomerisation is suggested to be a major driver of disease progression occurring in microglia. With several natural products and natural product derivatives currently in clinical trials, mushrooms have been highlighted as a rich and largely untapped source of biologically active compounds in both in vitro and in vivo neurodegenerative disease models, partially supported by successful clinical trial evaluations. Additionally, novel high-throughput methods for the screening of natural product compound libraries are being developed to help accelerate the neurodegenerative disease drug discovery process, targeting neuroinflammation. However, the breadth of research relating to mushroom natural product high-throughput screening is limited, providing an exciting opportunity for further detailed investigations.

Integrated analyses of brain and platelet omics reveal their common altered and driven molecules in Alzheimer's disease

Platelets may serve as a perfect peripheral source for exploring diagnostic biomarkers for Alzheimer's disease (AD); however, the molecular linkage between platelet and the brain is missing. To find the common altered and driving molecules in both brain and the platelet, we performed an integrated analysis of our platelet omics and brain omics reported in the literature, and analyzed their correlations with AD-specific pathology and cognitive impairment. By integrating the gene and protein expression profiles from 269 AD patients, we deduced 239 differentially expressed proteins (DEPs) appeared in both brain and the platelet, and 70.3% of them had consistent changes. Further analysis demonstrated that the altered brain and peripheral regulations were pinpointed into 10 imbalanced pathways. We also found that 117 DEPs, including ADAM10, were closely associated to the AD-specific β-amyloid and tau pathologies; and the changes of IDH3B and RTN1 had a potential diagnostic value for cognitive impairment analyzed by machine learning. Finally, we identified that HMOX2 and SERPINA3 could serve as driving molecules in neurodegeneration, and they were increased and decreased in AD patients, respectively. Together, this integrated brain and platelet omics provides a valuable resource for establishing efficient peripheral diagnostic biomarkers and potential therapeutic targets for AD.

Monoamine oxidase inhibitors: A concise review with special emphasis on structure activity relationship studies

Monoamine oxidase enzyme is necessary for the management of brain functions. It oxidatively metabolizes monoamines and produces ammonia, aldehyde and hydrogen peroxide as by-products. Excessive production of by-products of monoamine metabolism generates free radicals which cause cellular apoptosis and several neurodegenerative disorders for example Alzheimer's disease, Parkinson's disease, depression and autism. The inhibition of MAOs is an attractive target for the treatment of neurological disorders. Clinically approved MAO inhibitors for example selegiline, rasagiline, clorgyline, pargyline etc. are irreversible in nature and cause some adverse effects while recently studied reversible MAO inhibitors are devoid of harmful effects of old monoamine oxidase inhibitors. In this review article we have listed various synthesized molecules containing different moieties like coumarin, chalcone, thiazole, thiourea, caffeine, pyrazole, chromone etc. along with their activity, mode of action, structure activity relationship and molecular docking studies.

Almond intake during pregnancy in rats improved the cognitive performance of adult male offspring

Background: Based on evidence there are accepted links among early nutrition, epigenetic processes, and cognitive performance. Almond as a nutritious food could exert neuroprotective effects and improve anxiety, learning, and memory.Methods: In the current study, female rats were fed with a diet containing 5% (w/w) almonds during the mating period (two days) and gestation period (21 consecutive days). Then, the effect of the almond diet on short-term memory (Y maze), anxiety (elevated plus maze), and stress adaptation (forced swimming test) were investigated in the adult male offspring. The hippocampus (HIP), prefrontal cortex (PFC), and amygdala (AMY) of offspring were collected, and the level of cyclic AMP response element-binding proteins (CREB), brain-derived neurotrophic factor (BDNF) was assessed by western blotting. Also, Monoamine oxidases (MAO)-A and B activity were evaluated via enzymatic assays.Results: Our results indicated that prenatal almond consumption improved memory, made a modest reduction in anxiety-like behavior, and increased stress adaptation in adult male offspring. Also, molecular assessments showed an increased level of CREB phosphorylation and BDNF in the HIP and PFC of the almond group, while the activity of MAO-A and MAO-B was inhibited by almond consumption in mentioned areas.Discussion: These findings introduce almonds as a beneficial diet during pregnancy, for improving short-term memory, stress adaptation, and cognitive performance in adult offspring.

An updated patent review on monoamine oxidase (MAO) inhibitors

INTRODUCTION

: Monoamine oxidase (MAO) inhibitors are currently used as antidepressants (selective MAO-A inhibitors) or as co-adjuvants for neurodegenerative diseases (selective MAO-B inhibitors). The research within this field is attracting attention due to their crucial role in the modulation of brain functions, mood and cognitive activity, and monoamine catabolism.

AREAS COVERED

MAO inhibitors (2018-2021) are discussed according to their chemotypes. Structure-activity relationships are derived for each chemical scaffold (propargylamines, chalcones, indoles, benzimidazoles, (iso)coumarins, (iso)benzofurans, xanthones, and tetralones), while the chemical entities were divided into newly synthesized molecules and natural metabolites. The mechanism of action and type of inhibition are also considered. Lastly, new therapeutic applications are reported, which demonstrates the clinical potential of these inhibitors as well as the possibility of repurposing existing drugs for a variety of diseases.

EXPERT OPINION

MAO inhibitors here reported exhibit different potencies (from the micro- to nanomolar range) and isoform selectivity. These compounds are clinically licensed for multi-faceted neurodegenerative pathologies due to their ability to also act against other relevant targets (cholinesterases, inflammation, and oxidative stress). Moreover, the drug repurposing approach is an attractive strategy by which MAO inhibitors may be applied for the treatment of prostate cancer, inflammation, vertigo, and type 1 diabetes.

Noradrenaline in Alzheimer's Disease: A New Potential Therapeutic Target

A growing body of evidence demonstrates the important role of the noradrenergic system in the pathogenesis of many neurodegenerative processes, especially Alzheimer’s disease, due to its ability to control glial activation and chemokine production resulting in anti-inflammatory and neuroprotective effects. Noradrenaline involvement in this disease was first proposed after finding deficits of noradrenergic neurons in the locus coeruleus from Alzheimer’s disease patients. Based on this, it has been hypothesized that the early loss of noradrenergic projections and the subsequent reduction of noradrenaline brain levels contribute to cognitive dysfunctions and the progression of neurodegeneration. Several studies have focused on analyzing the role of noradrenaline in the development and progression of Alzheimer’s disease. In this review we summarize some of the most relevant data describing the alterations of the noradrenergic system normally occurring in Alzheimer’s disease as well as experimental studies in which noradrenaline concentration was modified in order to further analyze how these alterations affect the behavior and viability of different nervous cells. The combination of the different studies here presented suggests that the maintenance of adequate noradrenaline levels in the central nervous system constitutes a key factor of the endogenous defense systems that help prevent or delay the development of Alzheimer’s disease. For this reason, the use of noradrenaline modulating drugs is proposed as an interesting alternative therapeutic option for Alzheimer’s disease.

Coexpression of Gene Transcripts with Monoamine Oxidase A Quantified by Human In Vivo Positron Emission Tomography

The monoamine oxidase A (MAO-A) is integral to monoamine metabolism and is thus relevant to the pathophysiology of various neuropsychiatric disorders; however, associated gene-enzyme relations are not well understood. This study aimed to unveil genes coexpressed with MAO-A. Therefore, 18 179 mRNA expression maps (based on the Allen Human Brain Atlas) were correlated with the cerebral distribution volume (VT) of MAO-A assessed in 36 healthy subjects (mean age ± standard deviation: 32.9 ± 8.8 years, 18 female) using [11C]harmine positron emission tomography scans. Coexpression analysis was based on Spearman's ρ, over-representation tests on Fisher's exact test with false discovery rate (FDR) correction. The analysis revealed 35 genes in cortex (including B-cell translocation gene family, member 3, implicated in neuroinflammation) and 247 genes in subcortex (including kallikrein-related peptidase 10, implicated in Alzheimer's disease). Significantly over-represented Gene Ontology terms included "neuron development", "neuron differentiation", and "cell-cell signaling" as well as "axon" and "neuron projection". In vivo MAO-A enzyme distribution and MAOA expression did not correlate in cortical areas (ρ = 0.08) while correlation was found in subcortical areas (ρ = 0.52), suggesting influences of region-specific post-transcriptional and -translational modifications. The herein reported information could contribute to guide future genetic studies, deepen the understanding of associated pathomechanisms and assist in the pursuit of novel therapeutic targets.

The molecular mechanism, targets, and novel molecules in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological illness that causes dementia mainly in the elderly. The challenging obstacles related to AD has freaked global healthcare system to encourage scientists in developing novel therapeutic startegies to overcome with the fatal disease. The current treatment therapy of AD provides only symptomatic relief and to some extent disease-modifying effects. The current approach for AD treatment involves designing of cholinergic inhibitors, Aβ disaggregation inducing agents, tau inhibitors and several antioxidants. Hence, extensive research on AD therapy urgently requires a deep understanding of its pathophysiology and exploration of various chemical scaffolds to design and develop a potential drug candidate for the treatment. Various issues linked between disease and therapy need to be considered such as BBB penetration capability, clinical failure and multifaceted pathophisiology requires a proper attention to develop a lead candidate. This review article covers all probable mechanisms including one of the recent areas for investigation i.e., lipid dyshomeostasis, pathogenic involvement of P. gingivalis and neurovascular dysfunction, recently reported molecules and drugs under clinical investigations and approved by FDA for AD treatment. Our summarized information on AD will attract the researchers to understand and explore current status and structural modifications of the recently reported heterocyclic derivatives in drug development for AD therapy.

Association of the MAOB rs1799836 Single Nucleotide Polymorphism and APOE ɛ4 Allele in Alzheimer's Disease

BACKGROUND

The dopaminergic system is functionally compromised in Alzheimer's dis-ease (AD). The activity of monoamine oxidase B (MAOB), the enzyme involved in the degradation of dopamine, is increased during AD. Also, increased expression of MAOB occurs in the post-mortem hippocampus and neocortex of patients with AD. The MAOB rs1799836 polymorphism modulates MAOB transcription, consequently influencing protein translation and MAOB activity. We recently showed that cerebrospinal fluid levels of amyloid β1-42 are decreased in patients carry- ing the A allele in MAOB rs1799836 polymorphism.

OBJECTIVE

The present study compares MAOB rs1799836 polymorphism and APOE, the only con- firmed genetic risk factor for sporadic AD.

METHOD

We included 253 participants, 127 of whom had AD, 57 had mild cognitive impairment, 11 were healthy controls, and 58 suffered from other primary causes of dementia. MAOB and APOE polymorphisms were determined using TaqMan SNP Genotyping Assays.

RESULTS

We observed that the frequency of APOE ɛ4/ɛ4 homozygotes and APOE ɛ4 carriers is sig- nificantly increased among patients carrying the AA MAOB rs1799836 genotype.

CONCLUSION

These results indicate that the MAOB rs1799836 polymorphism is a potential genetic biomarker of AD and a potential target for the treatment of decreased dopaminergic transmission and cognitive deterioration in AD.

Sources and triggers of oxidative damage in neurodegeneration

Neurodegeneration describes a group of more than 300 neurological diseases, characterised by neuronal loss and intra- or extracellular protein depositions, as key neuropathological features. Multiple factors play role in the pathogenesis of these group of disorders: mitochondrial dysfunction, membrane damage, calcium dyshomeostasis, metallostasis, defect clearance and renewal mechanisms, to name a few. All these factors, without exceptions, have in common the involvement of immensely increased generation of free radicals and occurrence of oxidative stress, and as a result - exhaustion of the scavenging potency of the cellular redox defence mechanisms. Besides genetic predisposition and environmental exposure to toxins, the main risk factor for developing neurodegeneration is age. And although the "Free radical theory of ageing" was declared dead, it is undisputable that accumulation of damage occurs with age, especially in systems that are regulated by free radical messengers and those that oppose oxidative stress, protein oxidation and the accuracy in protein synthesis and degradation machinery has difficulties to be maintained. This brief review provides a comprehensive summary on the main sources of free radical damage, occurring in the setting of neurodegeneration.

Xenobiotic transport and metabolism in the human brain

Organisms have metabolic pathways responsible for eliminating endogenous and exogenous toxicants. Generally, we associate the liver par excellence as the organ in charge of detoxifying the body; however, this process occurs in all tissues, including the brain. Due to the presence of the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB), the Central Nervous System (CNS) is considered a partially isolated organ, but similar to other organs, the CNS possess xenobiotic transporters and metabolic pathways associated with the elimination of xenobiotic agents. In this review, we describe the different systems related to the detoxification of xenobiotics in the CNS, providing examples in which their association with neurodegenerative processes is suspected. The CNS detoxifying systems include carrier-mediated, active efflux and receptor-mediated transport, and detoxifying systems that include phase I and phase II enzymes, as well as those enzymes in charge of neutralizing compounds such as electrophilic agents, reactive oxygen species (ROS), and free radicals, which are products of the bioactivation of xenobiotics. Moreover, we discuss the differential expression of these systems in different regions of the CNS, showing the different detoxifying needs and the composition of each region in terms of the cell type, neurotransmitter content, and the accumulation of xenobiotics and/or reactive compounds.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Exploring the Role of Monoamine Oxidase Activity in Aging and Alzheimer's Disease

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that exert a crucial role in the metabolism of neurotransmitters of the central nervous system. The impaired function of MAOs is associated with copious brain diseases. The alteration of monoamine metabolism is a characteristics feature of aging. MAO plays a crucial role in the pathogenesis of Alzheimer's disease (AD) - a progressive neurodegenerative disorder associated with an excessive accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles (NFTs). Activated MAO has played a critical role in the development of amyloid plaques from Aβ, as well as the formation of the NFTs. In the brain, MAO mediated metabolism of monoamines is the foremost source of reactive oxygen species formation. The elevated level of MAO-B expression in astroglia has been reported in the AD brains adjacent to amyloid plaques. Increased MAO-B activity in the cortical and hippocampal regions is associated with AD. This review describes the pathogenic mechanism of MAOs in aging as well as the development and propagation of Alzheimer's pathology.

N-Propargylamine-hydroxypyridinone hybrids as multitarget agents for the treatment of Alzheimer's disease

AD is a progressive brain disorder. Because of the lack of remarkable single-target drugs against neurodegenerative disorders, the multitarget-directed ligand strategy has received attention as a promising therapeutic approach. Herein, we rationally designed twenty-nine hybrids of N-propargylamine-hydroxypyridinone. The designed hybrids possessed excellent iron-chelating activity (pFe³⁺ = 17.09-22.02) and potent monoamine oxidase B inhibitory effects. Various biological evaluations of the optimal compound 6b were performed step by step, including inhibition screening of monoamine oxidase (hMAO-B IC₅₀ = 0.083 ± 0.001 µM, hMAO-A IC₅₀ = 6.11 ± 0.08 µM; SI = 73.5), prediction of blood-brain barrier permeability and mouse behavioral research. All of these favorable results proved that the N-propargylamine-hydroxypyridinone scaffold is a promising structure for the discovery of multitargeted ligands for AD therapy.

Multi-Target-Directed Ligands as an Effective Strategy for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurological disorder, and multiple pathological factors are believed to be involved in the genesis and progression of the disease. A number of hypotheses, including Acetylcholinesterase, Monoamine oxidase, β-Amyloid, Tau protein, etc., have been proposed for the initiation and progression of the disease. At present, acetylcholine esterase inhibitors and memantine (NMDAR antagonist) are the only approved therapies for the symptomatic management of AD. Most of these single-target drugs have miserably failed in the treatment or halting the progression of the disease. Multi-factorial diseases like AD require complex treatment strategies that involve simultaneous modulation of a network of interacting targets. Since the last few years, Multi-Target-Directed Ligands (MTDLs) strategy, drugs that can simultaneously hit multiple targets, is being explored as an effective therapeutic approach for the treatment of AD. In the current review article, the authors have briefly described various pathogenic pathways associated with AD. The importance of Multi-Target-Directed Ligands and their design strategies in recently reported articles have been discussed in detail. Potent leads are identified through various structure-activity relationship studies, and their drug-like characteristics are described. Recently developed promising compounds have been summarized in the article. Some of these MTDLs with balanced activity profiles against different targets have the potential to be developed as drug candidates for the treatment of AD.

Relationships of Cerebrospinal Fluid Alzheimer's Disease Biomarkers and COMT, DBH, and MAOB Single Nucleotide Polymorphisms

The noradrenergic and dopaminergic systems are affected in Alzheimer’s disease (AD). Polymorphisms in genes encoding enzymes and proteins that are components of these systems can affect products of transcription and translation and lead to altered enzymatic activity and alterations in overall dopamine and noradrenaline levels. Catechol-O-methyltransferase (COMT) and monoamine oxidase B (MAOB) are the enzymes that regulate degradation of dopamine, while dopamine β-hydroxylase (DBH) is involved in synthesis of noradrenaline. COMT Val158Met (rs4680), DBH rs1611115 (also called –1021C/T or –970C/T), and MAOB rs1799836 (also called A644G) polymorphisms have been previously associated with AD. We assessed whether these polymorphisms are associated with cerebrospinal fluid (CSF) AD biomarkers including total tau (t-tau), phosphorylated tau proteins (p-tau₁₈₁, p-tau₁₉₉, and p-tau₂₃₁), amyloid-β₄₂ (Aβ₄₂), and visinin-like protein 1 (VILIP-1) to test possible relationships of specific genotypes and pathological levels of CSF AD biomarkers. The study included 233 subjects: 115 AD, 53 mild cognitive impairment, 54 subjects with other primary causes of dementia, and 11 healthy controls. Significant decrease in Aβ₄₂ levels was found in patients with GG compared to AG COMT Val158Met genotype, while t-tau and p-tau₁₈₁ levels were increased in patients with AA compared to AG COMT Val158Met genotype. Aβ₄₂ levels were also decreased in carriers of A allele in MAO-B rs1799836 polymorphism, while p-tau₁₈₁ levels were increased in carriers of T allele in DBH rs1611115 polymorphism. These results indicate that COMT Val158Met, DBH rs1611115, and MAOB rs1799836 polymorphisms deserve further investigation as genetic markers of AD.

The role of monoamine oxidase enzymes in the pathophysiology of neurological disorders

Monoamine oxidase enzymes are responsible for the degredation of serotonin, dopamine, and norepinephrine in the central neurvous system. Although it has been nearly 100 years since they were first described, we are still learning about their role in the healthy brain and how they are altered in various disease states. The present review provides a survey of our current understanding of monoamine oxidases, with a focus on their contributions to neuropsychiatric, neurodevelopmental, and neurodegenerative disease. Important species differences in monoamine oxidase function and development in the brain are highlighted. Sex-specific monoamine oxidase regulatory mechanisms and their implications for various neurological disorders are also discussed. While our understanding of these critical enzymes has expanded over the last century, gaps exist in our understanding of sex and species differences and the roles monoamine oxidases may play in conditions often comorbid with neurological disorders.

Monoamine oxidases in age-associated diseases: New perspectives for old enzymes

Population aging is one of the most significant social changes of the twenty-first century. This increase in longevity is associated with a higher prevalence of chronic diseases, further rising healthcare costs. At the molecular level, cellular senescence has been identified as a major process in age-associated diseases, as accumulation of senescent cells with aging leads to progressive organ dysfunction. Of particular importance, mitochondrial oxidative stress and consequent organelle alterations have been pointed out as key players in the aging process, by both inducing and maintaining cellular senescence. Monoamine oxidases (MAOs), a class of enzymes that catalyze the degradation of catecholamines and biogenic amines, have been increasingly recognized as major producers of mitochondrial ROS. Although well-known in the brain, evidence showing that MAOs are also expressed in a variety of peripheral organs stimulated a growing interest in the extra-cerebral roles of these enzymes. Besides, the fact that MAO-A and/or MAO-B are frequently upregulated in aged or dysfunctional organs has uncovered new perspectives on their roles in pathological aging. In this review, we will give an overview of the major results on the regulation and function of MAOs in aging and age-related diseases, paying a special attention to the mechanisms linked to the increased degradation of MAO substrates or related to MAO-dependent ROS formation.

Pyrazole Scaffold Synthesis, Functionalization, and Applications in Alzheimer's Disease and Parkinson's Disease Treatment (2011-2020)

The remarkable prevalence of pyrazole scaffolds in a versatile array of bioactive molecules ranging from apixaban, an anticoagulant used to treat and prevent blood clots and stroke, to bixafen, a pyrazole-carboxamide fungicide used to control diseases of rapeseed and cereal plants, has encouraged both medicinal and organic chemists to explore new methods in developing pyrazole-containing compounds for different applications. Although numerous synthetic strategies have been developed in the last 10 years, there has not been a comprehensive overview of synthesis and the implication of recent advances for treating neurodegenerative disease. This review first presents the advances in pyrazole scaffold synthesis and their functionalization that have been published during the last decade (2011-2020). We then narrow the focus to the application of these strategies in the development of therapeutics for neurodegenerative diseases, particularly for Alzheimer's disease (AD) and Parkinson's disease (PD).

Monoamine Oxidase Inhibitors: From Classic to New Clinical Approaches

Monoamine oxidases (MAOs) are involved in the oxidative deamination of different amines and neurotransmitters. This pointed them as potential targets for several disorders and along the last 70 years a wide variety of MAO inhibitors have been developed as successful drugs for the treatment of complex diseases, being the first drugs approved for depression in the late 1950s. The discovery of two MAO isozymes (MAO-A and B) with different substrate selectivity and tissue expression patterns led to novel therapeutic approaches and to the development of new classes of inhibitors, such as selective irreversible and reversible MAO-B inhibitors and reversible MAO-A inhibitors. Significantly, MAO-B inhibitors constitute a widely studied group of compounds, some of them approved for the treatment of Parkinson's disease. Further applications are under development for the treatment of Alzheimer's disease, amyotrophic lateral sclerosis, and cardiovascular diseases, among others. This review summarizes the most important aspects regarding the development and clinical use of MAO inhibitors, going through mechanistic and structural details, new indications, and future perspectives. Monoamine oxidases (MAOs) catalyze the oxidative deamination of different amines and neurotransmitters. The two different isozymes, MAO-A and MAO-B, are located at the outer mitochondrial membrane in different tissues. The enzymatic reaction involves formation of the corresponding aldehyde and releasing hydrogen peroxide (H₂O₂) and ammonia or a substituted amine depending on the substrate. MAO's role in neurotransmitter metabolism made them targets for major depression and Parkinson's disease, among other neurodegenerative diseases. Currently, these compounds are being studied for other diseases such as cardiovascular ones.

2-Propargylamino-naphthoquinone derivatives as multipotent agents for the treatment of Alzheimer's disease

Alzheimer's disease is a progressive brain disorder with characteristic symptoms and several pathological hallmarks. The concept of "one drug, one target" has not generated any new drugs since 2004. The new era of drug development in the field of AD builds upon rationally designed multi-target directed ligands that can better address the complexity of AD. Herewith, we designed ten novel derivatives of 2-propargylamino-naphthoquinone. The biological evaluation of these compounds includes inhibition of monoamine oxidase A/B, inhibition of amyloid-beta aggregation, radical-scavenging, and metal-chelating properties. Some of the compounds possess low cytotoxicity profile with an anti-inflammatory ability in the lipopolysaccharide-stimulated cellular model. All these features warrant their further testing in the field of AD.

Synthesis and biological evaluation of 3-arylbenzofuranone derivatives as potential anti-Alzheimer's disease agents

Multi-target drugs can better address the cascade of events involved in oxidative stress and the reduction in cholinergic transmission that occur in Alzheimer’s disease than cholinesterase inhibitors alone. We synthesised a series of 3-arylbenzofuranone derivatives and evaluated their antioxidant activity, cholinesterase inhibitory activity, and monoamine oxidase inhibitory activity. 3-Arylbenzofuranone compounds exhibit good antioxidant activity as well as selective acetylcholinesterase inhibitory activity. The IC₅₀ value of anti-acetylcholinesterase inhibition of Compound 20 (0.089 ± 0.01 μM) is similar to the positive drug donepezil (0.059 ± 0.003 μM). According to the experimental results, Compounds 7, 13 show a certain effect in the in vitro evaluation performed and have the potential as drug candidates for the treatment of Alzheimer’s disease.

A comprehensive review of monoamine oxidase inhibitors as Anti-Alzheimer's disease agents: A review

Monoamine oxidases (MAO-A and MAO-B) are mammalian flavoenzyme, which catalyze the oxidative deamination of several neurotransmitters like norepinephrine, dopamine, tyramine, serotonin, and some other amines. The oxidative deamination produces several harmful side products like ammonia, peroxides, and aldehydes during the biochemical reaction. The concentration of biochemical neurotransmitter alteration in the brain by MAO is directly related with several neurological disorders like Alzheimer's disease and Parkinson's disease (PD). Activated MAO also contributes to the amyloid beta (Aβ) aggregation by two successive cleft β-secretase and γ-secretase of amyloid precursor protein (APP). Additionally, activated MAO is also involved in aggregation of neurofibrillary tangles and cognitive destruction through the cholinergic neuronal damage and disorder of the cholinergic system. MAO inhibition has general anti-Alzheimer's disease effect as a consequence of oxidative stress reduction prompted by MAO enzymes. In this review, we outlined and addressed recent understanding on MAO enzymes such as their structure, physiological function, catalytic mechanism, and possible therapeutic goals in AD. In addition, it also highlights the current development and discovery of potential MAO inhibitors (MAOIs) from various chemical scaffolds.

Rutamarin: Efficient Liquid-Liquid Chromatographic Isolation from Ruta graveolens L. and Evaluation of Its In Vitro and In Silico MAO-B Inhibitory Activity

Naturally occurring coumarins are a group of compounds with many documented central nervous system (CNS) activities. However, dihydrofuranocoumarins have been infrequently investigated for their bioactivities at CNS level. Within the frame of this study, an efficient liquid–liquid chromatography method was developed to rapidly isolate rutamarin from Ruta graveolens L. (Rutaceae) dichloromethane extract (DCM). The crude DCM (9.78 mg/mL) and rutamarin (6.17 µM) were found to be effective inhibitors of human monoamine oxidase B (hMAO-B) with inhibition percentages of 89.98% and 95.26%, respectively. The inhibitory activity against human monoamine oxidase A (hMAO-A) for the DCM extract was almost the same (88.22%). However, for rutamarin, it significantly dropped to 25.15%. To examine the molecular interaction of rutamarin with hMAO- B, an in silico evaluation was implemented. A docking study was performed for the two enantiomers (R)-rutamarin and (S)-rutamarin. The (S)-rutamarin was found to bind stronger to the hMAO-B binging cavity.

Potential Enzymatic Targets in Alzheimer's: A Comprehensive Review

Alzheimer's, a degenerative cause of the brain cells, is called as a progressive neurodegenerative disease and appears to have a heterogeneous etiology with main emphasis on amyloid-cascade and hyperphosphorylated tau-cascade hypotheses, that are directly linked with macromolecules called enzymes such as β- & γ-secretases, colinesterases, transglutaminases, and glycogen synthase kinase (GSK-3), cyclin-dependent kinase (cdk-5), microtubule affinity-regulating kinase (MARK). The catalytic activity of the above enzymes is the result of cognitive deficits, memory impairment and synaptic dysfunction and loss, and ultimately neuronal death. However, some other enzymes also lead to these dysfunctional events when reduced to their normal activities and levels in the brain, such as α- secretase, protein kinase C, phosphatases etc; metabolized to neurotransmitters, enzymes like monoamine oxidase (MAO), catechol-O-methyltransferase (COMT) etc. or these abnormalities can occur when enzymes act by other mechanisms such as phosphodiesterase reduces brain nucleotides (cGMP and cAMP) levels, phospholipase A2: PLA2 is associated with reactive oxygen species (ROS) production etc. On therapeutic fronts, several significant clinical trials are underway by targeting different enzymes for development of new therapeutics to treat Alzheimer's, such as inhibitors for β-secretase, GSK-3, MAO, phosphodiesterase, PLA2, cholinesterases etc, modulators of α- & γ-secretase activities and activators for protein kinase C, sirtuins etc. The last decades have perceived an increasing focus on findings and search for new putative and novel enzymatic targets for Alzheimer's. Here, we review the functions, pathological roles, and worth of almost all the Alzheimer's associated enzymes that address to therapeutic strategies and preventive approaches for treatment of Alzheimer's.

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.

Structure-Based Specific Detection and Inhibition of Monoamine Oxidases and Their Applications in Central Nervous System Diseases

Monoamine oxidases (MAOs) are the enzymes that catalyze the oxidation of monoamines, such as dopamine, norepinephrine, and serotonin, which serve as key neurotransmitters in the central nervous system (CNS). MAOs play important roles in maintaining the homeostasis of monoamines, and the aberrant expression or activation of MAOs underlies the pathogenesis of monoamine neurotransmitter disorders, including neuropsychiatric and neurodegenerative diseases. Clearly, detecting and inhibiting the activities of MAOs is of great value for the diagnosis and therapeutics of these diseases. Accordingly, many specific detection probes and inhibitors have been developed and substantially contributed to basic and clinical studies of these diseases. In this review, progress in the detecting and inhibiting of MAOs and their applications in mechanism exploration and treatment of neurotransmitter-related disorders is summarized. Notably, how the detection probes and inhibitors of MAOs were developed has been specifically addressed. It is hoped that this review will benefit the design of more effective and sensitive probes and inhibitors for MAOs, and eventually the treatment of monoamine neurotransmitter disorders.

Alzheimer Disease and Selected Risk Factors Disrupt a Co-regulation of Monoamine Oxidase-A/B in the Hippocampus, but Not in the Cortex

Monoamine oxidase-A (MAO-A) and MAO-B have both been implicated in the pathology of Alzheimer disease (AD). We examined 60 autopsied control and AD donor brain samples to determine how well MAO function aligned with two major risk factors for AD, namely sex and APOE ε4 status. MAO-A activity was increased in AD cortical, but not hippocampal, samples. In contrast, MAO-B activity was increased in both regions (with a strong input from female donors) whether sample means were compared based on: (a) diagnosis alone; (b) diagnosis-by-APOE ε4 status (i.e., carriers vs. non-carriers of the ε4 allele); or (c) APOE ε4 status alone (i.e., ignoring ‘diagnosis’ as a variable). Sample means strictly based on the donor’s sex did not reveal any difference in either MAO-A or MAO-B activity. Unexpectedly, we found that cortical MAO-A and MAO-B activities were highly correlated in both males and females (if focussing strictly on the donor’s sex), while in the hippocampus, any correlation was lost in female samples. Stratifying for sex-by-APOE ε4 status revealed a strong correlation between cortical MAO-A and MAO-B activities in both non-carriers and carriers of the allele, but any correlation in hippocampal samples was lost in carriers of the allele. A diagnosis of AD disrupted the correlation between MAO-A and MAO-B activities in the hippocampus, but not the cortex. We observed a novel region-dependent co-regulation of MAO-A and MAO-B mRNAs (but not proteins), while a lack of correlation between MAO activities and the respective proteins corroborated previous reports. Overexpression of human APOE4 increased MAO activity (but not mRNA/protein) in C6 and in HT-22 cell cultures. We identified a novel co-regulation of MAO-A and MAO-B activities that is spared from any influence of risk factors for AD or AD itself in the cortex, but vulnerable to these same factors in the hippocampus. Sex- and region-dependent abilities to buffer influences on brain MAO activities could have significant bearing on ambiguous outcomes when monoaminergic systems are targeted in clinical populations.

Loss of Trem2 in microglia leads to widespread disruption of cell coexpression networks in mouse brain

Rare heterozygous coding variants in the triggering receptor expressed in myeloid cells 2 (TREM2) gene, conferring increased risk of developing late-onset Alzheimer's disease, have been identified. We examined the transcriptional consequences of the loss of Trem2 in mouse brain to better understand its role in disease using differential expression and coexpression network analysis of Trem2 knockout and wild-type mice. We generated RNA-Seq data from cortex and hippocampus sampled at 4 and 8 months. Using brain cell-type markers and ontology enrichment, we found subnetworks with cell type and/or functional identity. We primarily discovered changes in an endothelial gene-enriched subnetwork at 4 months, including a shift toward a more central role for the amyloid precursor protein gene, coupled with widespread disruption of other cell-type subnetworks, including a subnetwork with neuronal identity. We reveal an unexpected potential role of Trem2 in the homeostasis of endothelial cells that goes beyond its known functions as a microglial receptor and signaling hub, suggesting an underlying link between immune response and vascular disease in dementia.

Pharmacological Effects of Scutellarin, An Active Component of Genus Scutellaria and Erigeron: A Systematic Review

Flavonoid compound scutellarin (Scu) is quite frequently met in the plant kingdom, particularly in the genus Scutellaria (Lamiaceae) and Erigeron (Asteraceae). The extract of the herb of Erigeron breviscapus, containing this component in high amount, has been used for many years in traditional Chinese medicine. In recent years, studies have made great progress on the usefulness of Scu for treating various diseases by testing its mechanism of action. They support the traditional use of Scu rich plant in heart and cerebral ischemia. Scu can potentially be applied in Alzheimer's disease, Helicobacter pylori infection, vascular complications of diabetes and as an inhibitor of certain carcinomas. Various methods were designed to improve its isolation from plant material, solubility, absorption and bioavailability. On the basis of recent studies, it is suggested that Scu could be a promising candidate for new natural drug and deserves particular attention in further research and development.

Dual/multitargeted xanthone derivatives for Alzheimer's disease: where do we stand?

To date, the current therapy for Alzheimer's disease (AD) based on acetylcholinesterase inhibitors is only symptomatic, being its efficacy limited. Hence, the recent research has been focused in the development of different pharmacological approaches. Here we discuss the potential of xanthone derivatives as new anti-Alzheimer agents. The interference of xanthone derivatives with acetylcholinesterase and other molecular targets and cellular mechanisms associated with AD have been recently systematically reported. Therefore, we report xanthones with anticholinesterase, monoamine oxidase and amyloid β aggregation inhibitory activities as well as antioxidant properties, emphasizing xanthone derivatives with dual/multitarget activity as potential agents to treat AD. We also propose the structural features for these activities that may guide the design of new, more effective xanthone derivatives. [Formula: see text].

Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease

Monoamine oxidase B (MAO-B) has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased MAO-B expression in astroglia has been observed adjacent to amyloid plaques in AD patient brains. This phenomenon is hypothesized to lead to increased production of hydrogen peroxide and reactive oxygen species (ROS), thereby contributing to AD pathology. Therefore, reduction of ROS-induced oxidative stress via inhibition of MAO-B activity may delay the progression of the disease. In the present study we report the pharmacological properties of sembragiline, a novel selective MAO-B inhibitor specifically developed for the treatment of AD, and on its effect on ROS-mediated neuronal injury and astrogliosis in MAO-B transgenic animals. Sembragiline showed potent and long-lasting MAO-B-selective inhibition and did not inhibit MAO-A at doses where full inhibition of MAO-B was observed. Such selectivity should translate into a favorable clinical safety profile. Indeed, sembragiline neither induced the serotonin syndrome when administered together with the serotonin precursor l-5-hydroxytryptophan in combination with antidepressants such as fluoxetine, nor potentiated the pressor effect of tyramine. Additionally, in experiments using a transgenic animal model conditionally overexpressing MAO-B in astroglia, sembragiline protected against neuronal loss and reduced both ROS formation and reactive astrogliosis. Taken together, these findings warrant further investigation of the potential therapeutic benefit of MAO-B inhibitors in patients with AD and other neurologic disorders.

Dual inhibitors of cholinesterases and monoamine oxidases for Alzheimer’s disease

Accumulating evidence indicates a solid relationship between several enzymes and Alzheimer’s disease. Cholinesterases and monoamine oxidases are closely associated with the disease symptomatology and progression and have been tackled simultaneously using several multifunctional ligands. This design strategy offers great chances to alter the course of Alzheimer’s disease, in addition to alleviation of the symptoms. More than 15 years of research has led to the identification of various dual cholinesterase/monoamine oxidase inhibitors, while some showing positive outcomes in clinical trials, thus giving rise to additional research efforts in the field. The aim of this review is to provide an update on the novel dual inhibitors identified recently and to shed light on their therapeutic potential.

Positron emission tomography measurement of brain MAO-B inhibition in patients with Alzheimer's disease and elderly controls after oral administration of sembragiline

PURPOSE

In Alzheimer's disease (AD), increased metabolism of monoamines by monoamine oxidase type B (MAO-B) leads to the production of toxic reactive oxygen species (ROS), which are thought to contribute to disease pathogenesis. Inhibition of the MAO-B enzyme may restore brain levels of monoaminergic neurotransmitters, reduce the formation of toxic ROS and reduce neuroinflammation (reactive astrocytosis), potentially leading to neuroprotection. Sembragiline (also referred as RO4602522, RG1577 and EVT 302 in previous communications) is a potent, selective and reversible inhibitor of MAO-B developed as a potential treatment for AD.

METHODS

This study assessed the relationship between plasma concentration of sembragiline and brain MAO-B inhibition in patients with AD and in healthy elderly control (EC) subjects. Positron emission tomography (PET) scans using [11C]-L-deprenyl-D2 radiotracer were performed in ten patients with AD and six EC subjects, who received sembragiline each day for 6-15 days.

RESULTS

At steady state, the relationship between sembragiline plasma concentration and MAO-B inhibition resulted in an Emax of ∼80-90 % across brain regions of interest and in an EC50 of 1-2 ng/mL. Data in patients with AD and EC subjects showed that near-maximal inhibition of brain MAO-B was achieved with 1 mg sembragiline daily, regardless of the population, whereas lower doses resulted in lower and variable brain MAO-B inhibition.

CONCLUSIONS

This PET study confirmed that daily treatment of at least 1 mg sembragiline resulted in near-maximal inhibition of brain MAO-B enzyme in patients with AD.

Key Targets for Multi-Target Ligands Designed to Combat Neurodegeneration

HIGHLIGHTS Compounds that interact with multiple targets but minimally with the cytochrome P450 system (CYP) address the many factors leading to neurodegeneration.Acetyl- and Butyryl-cholineEsterases (AChE, BChE) and Monoamine Oxidases A/B (MAO A, MAO B) are targets for Multi-Target Designed Ligands (MTDL).ASS234 is an irreversible inhibitor of MAO A >MAO B and has micromolar potency against the cholinesterases.ASS234 is a poor CYP substrate in human liver, yielding the depropargylated metabolite.SMe1EC2, a stobadine derivative, showed high radical scavenging property, in vitro and in vivo giving protection in head trauma and diabetic damage of endothelium.Control of mitochondrial function and morphology by manipulating fission and fusion is emerging as a target area for therapeutic strategies to decrease the pathological outcome of neurodegenerative diseases. Growing evidence supports the view that neurodegenerative diseases have multiple and common mechanisms in their aetiologies. These multifactorial aspects have changed the broadly common assumption that selective drugs are superior to "dirty drugs" for use in therapy. This drives the research in studies of novel compounds that might have multiple action mechanisms. In neurodegeneration, loss of neuronal signaling is a major cause of the symptoms, so preservation of neurotransmitters by inhibiting the breakdown enzymes is a first approach. Acetylcholinesterase (AChE) inhibitors are the drugs preferentially used in AD and that one of these, rivastigmine, is licensed also for PD. Several studies have shown that monoamine oxidase (MAO) B, located mainly in glial cells, increases with age and is elevated in Alzheimer (AD) and Parkinson's Disease's (PD). Deprenyl, a MAO B inhibitor, significantly delays the initiation of levodopa treatment in PD patients. These indications underline that AChE and MAO are considered a necessary part of multi-target designed ligands (MTDL). However, both of these targets are simply symptomatic treatment so if new drugs are to prevent degeneration rather than compensate for loss of neurotransmitters, then oxidative stress and mitochondrial events must also be targeted. MAO inhibitors can protect neurons from apoptosis by mechanisms unrelated to enzyme inhibition. Understanding the involvement of MAO and other proteins in the induction and regulation of the apoptosis in mitochondria will aid progress toward strategies to prevent the loss of neurons. In general, the oxidative stress observed both in PD and AD indicate that antioxidant properties are a desirable part of MTDL molecules. After two or more properties are incorporated into one molecule, the passage from a lead compound to a therapeutic tool is strictly linked to its pharmacokinetic and toxicity. In this context the interaction of any new molecules with cytochrome P450 and other xenobiotic metabolic processes is a crucial point. The present review covers the biochemistry of enzymes targeted in the design of drugs against neurodegeneration and the cytochrome P450-dependent metabolism of MTDLs.

Molecular aspects of monoamine oxidase B

Monoamine oxidases (MAO) influence the monoamine levels in brain by virtue of their role in neurotransmitter breakdown. MAO B is the predominant form in glial cells and in platelets. MAO B structure, function and kinetics are described as a background for the effect of alterations in its activity on behavior. The need to inhibit MAO B to combat decreased brain amines continues to drive the search for new drugs. Reversible and irreversible inhibitors are now designed using data-mining, computational screening, docking and molecular dynamics. Multi-target ligands designed to combat the elevated activity of MAO B in Alzheimer's and Parkinson's Diseases incorporate MAO inhibition (usually irreversible) as well as iron chelation, antioxidant or neuroprotective properties. The main focus of drug design is the catalytic activity of MAO, but the imidazoline I2 site in the entrance cavity of MAO B is also a pharmacological target. Endogenous regulation of MAO B expression is discussed briefly in light of new studies measuring mRNA, protein, or activity in healthy and degenerative samples, including the effect of DNA methylation on the expression. Overall, this review focuses on examples of recent research on the molecular aspects of the expression, activity, and inhibition of MAO B.

Combining in vitro and in silico approaches to evaluate the multifunctional profile of rosmarinic acid from Blechnum brasiliense on targets related to neurodegeneration

Natural products are important sources of chemical diversity leading to unique scaffolds that can be exploited in the discovery of new drug candidates or chemical probes. In this context, chemical and biological investigation of ferns and lycophytes occurring in Brazil is an approach adopted by our research group aiming at discovering bioactive molecules acting on neurodegeneration targets. In the present study, rosmarinic acid (RA) isolated from Blechnum brasiliense showed an in vitro multifunctional profile characterized by antioxidant effects, and monoamine oxidases (MAO-A and MAO-B) and catechol-O-methyl transferase (COMT) inhibition. RA showed antioxidant effects against hydroxyl (HO(•)) and nitric oxide (NO) radicals (IC50 of 29.4 and 140 μM, respectively), and inhibition of lipid peroxidation (IC50 of 19.6 μM). In addition, RA inhibited MAO-A, MAO-B and COMT enzymes with IC50 values of 50.1, 184.6 and 26.7 μM, respectively. The MAO-A modulation showed a non-time-dependent profile, suggesting a reversible mechanism of inhibition. Structural insights on RA interactions with MAO-A and COMT were investigated by molecular docking. Finally, RA (up to 5 mM) demonstrated no cytotoxicity on polymorphonuclear rat cells. Taken together, our results suggest that RA may be exploited as a template for the development of new antioxidant molecules possessing additional MAO and COMT inhibition effects to be further investigated on in vitro and in vivo models of neurodegenerative diseases.

Recent developments on the structure–activity relationship studies of MAO inhibitors and their role in different neurological disorders

Development of MAO inhibitors as effective drug candidates for the management and/or treatment of different neurological disorders.