Increased monoamine oxidase B activity in plaque-associated astrocytes of Alzheimer brains revealed by quantitative enzyme radioautography

In vitro Characterization of the Regional Binding Distribution of Amyloid PET Tracer Florbetaben and the Glia Tracers Deprenyl and PK11195 in Autopsy Alzheimer's Brain Tissue

BACKGROUND

Emerging evidence indicates a central role of gliosis in Alzheimer's disease (AD) pathophysiology. However, the regional distribution and interaction of astrogliosis and microgliosis in association with amyloid-β (Aβ) still remain uncertain.

OBJECTIVE

Here we studied the pathological profiles in autopsy AD brain by using specific imaging tracers.

METHODS

Autopsy brain tissues of AD (n = 15, age 70.4±8.5 years) and control cases (n = 12, age 76.6±10.9) were examined with homogenate binding assays, autoradiography for Aβ plaques (3H-florbetaben/3H-PIB), astrogliosis (3H-L-deprenyl), and microgliosis (3H-PK11195/3H-FEMPA), as well as immunoassays.

RESULTS

In vitro saturation analysis revealed high-affinity binding sites of 3H-florbetaben, 3H-L-deprenyl, and 3H-PK11195/3H-FEMPA in the frontal cortex of AD cases. In vitro3H-florbetaben binding increased across cortical and subcortical regions of AD compared to control with the highest binding in the frontal and parietal cortices. The in vitro3H-L-deprenyl binding showed highest binding in the hippocampus (dentate gyrus) followed by cortical and subcortical regions of AD while the GFAP expression was upregulated only in the hippocampus compared to control. The in vitro3H-PK11195 binding was solely increased in the parietal cortex and the hippocampus of AD compared to control. The 3H-florbetaben binding positively correlated with the 3H-L-deprenyl binding in the hippocampus and parietal cortex of AD and controls. Similarly, a positive correlation was observed between 3H-florbetaben binding and GFAP expression in hippocampus of AD and control.

CONCLUSION

The use of multi-imaging tracers revealed different regional pattern of changes in autopsy AD brain with respect to amyloid plaque pathology versus astrogliosis and microgliosis.

Overview of the Neuroprotective Effects of the MAO-Inhibiting Antidepressant Phenelzine

Phenelzine (PLZ) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. This multifaceted drug has a number of pharmacological and neurochemical effects in addition to inhibition of MAO, and findings on these effects have contributed to a body of evidence indicating that PLZ also has neuroprotective/neurorescue properties. These attributes are reviewed in this paper and include catabolism to the active metabolite β-phenylethylidenehydrazine (PEH) and effects of PLZ and PEH on the GABA-glutamate balance in brain, sequestration of reactive aldehydes, and inhibition of primary amine oxidase. Also discussed are the encouraging findings of the effects of PLZ in animal models of stroke, spinal cord injury, traumatic brain injury, and multiple sclerosis, as well other actions such as reduction of nitrative stress, reduction of the effects of a toxin on dopaminergic neurons, potential anticonvulsant actions, and effects on brain-derived neurotrophic factor, neural cell adhesion molecules, an anti-apoptotic factor, and brain levels of ornithine and N-acetylamino acids.

Gauging the role and impact of drug interactions and repurposing in neurodegenerative disorders

Neurodegenerative diseases (ND) are of vast origin which are characterized by gradual progressive loss of neurons in the brain region. ND can be classified according to the clinical symptoms present (e.g. Cognitive decline, hyperkinetic, and hypokinetic movements disorder) or by the pathological protein deposited (e.g., Amyloid, tau, Alpha-synuclein, TDP-43). Alzheimer's disease preceded by Parkinson's is the most prevalent form of ND world-wide. Multiple factors like aging, genetic mutations, environmental factors, gut microbiota, blood-brain barrier microvascular complication, etc. may increase the predisposition towards ND. Genetic mutation is a major contributor in increasing the susceptibility towards ND, the concept of one disease-one gene is obsolete and now multiple genes are considered to be involved in causing one particular disease. Also, the involvement of multiple pathological mechanisms like oxidative stress, neuroinflammation, mitochondrial dysfunction, etc. contributes to the complexity and makes them difficult to be treated by traditional mono-targeted ligands. In this aspect, the Poly-pharmacological drug approach which targets multiple pathological pathways at the same time provides the best way to treat such complex networked CNS diseases. In this review, we have provided an overview of ND and their pathological origin, along with a brief description of various genes associated with multiple diseases like Alzheimer's, Parkinson's, Multiple sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS), Huntington's and a comprehensive detail about the Poly-pharmacology approach (MTDLs and Fixed-dose combinations) along with their merits over the traditional single-targeted drug is provided. This review also provides insights into current repurposing strategies along with its regulatory considerations.

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).

Design, synthesis, and evaluation of 1, 4-benzodioxan-substituted chalcones as selective and reversible inhibitors of human monoamine oxidase B

The inhibition of monoamine oxidase B (MAO-B) could be an effective approach for the treatment of various neurological disorders. In this study, a series of 1, 4-benzodioxan-substituted chalcone derivatives were designed, synthesised and evaluated for their inhibitory activity against human MAO-B (hMAO-B). The majority of these compounds showed inhibitory activity and high selectivity. The most potent compound, (E)-1-(3-bromo-4-fluorophenyl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)prop-2-en-1-one (22), exhibited an IC₅₀ of 0.026 µM with a selectivity index greater than 1538. Kinetics and reversibility studies confirmed that the representative active compounds acted as competitive and reversible inhibitors of hMAO-B. The enzyme-inhibitor interactions were investigated by molecular docking studies and the rationale was provided. As these potent hMAO-B inhibitors exhibited low neurotoxicity and possessed promising drug-like properties, we believe that these active compounds could be further investigated as potential drug candidates for future in vivo studies.

Identification of Heterogeneous Subtypes of Mild Cognitive Impairment Using Cluster Analyses Based on PET Imaging of Tau and Astrogliosis

Background: Mild cognitive impairment (MCI) is a condition with diverse causes and clinical outcomes that can be categorized into subtypes. [¹⁸F]THK5351 has been known to detect reactive astrogliosis as well as tau which is accompanied by neurodegenerative changes. Here, we identified heterogeneous groups of MCI patients using THK retention patterns and a graph theory approach, allowing for the comparison of risk of progression to dementia in these MCI subgroups.

Methods: Ninety-seven participants including 60 MCI patients and individuals with normal cognition (NC, n = 37) were included and undertook 3T MRI, [¹⁸F]THK5351 PET, and detailed neuropsychological tests. [¹⁸F]Flutemetamol PET was also performed in 62 participants. We calculated similarities between MCI patients using their regional standardized uptake value ratio of THK retention in 75 ROIs, and clustered subjects with similar retention patterns using the Louvain method based on the modularity of the graph. The clusters of patients identified were compared with an age-matched control group using a general linear model. Dementia conversion was evaluated after a median follow-up duration of 34.6 months.

Results: MCI patients were categorized into four groups according to their THK retention patterns: (1) limbic type; (2) diffuse type; (3) sparse type; and (4) AD type (retention pattern as in AD). Subjects of the limbic type were characterized by older age, small hippocampal volumes, and reduced verbal memory and frontal/executive functions. Patients of the diffuse type had relatively large vascular burden, reduced memory capacity and some frontal/executive functions. Co-morbidity and mortality were more frequent in this subgroup. Subjects of the sparse type were younger and declined only in terms of visual memory and attention. No individuals in this subgroup converted to dementia. Patients in the AD type group exhibited the poorest cognitive function. They also had the smallest hippocampal volumes and the highest risk of progression to dementia (90.9%).

Conclusion: Using cluster analyses with [¹⁸F]THK5351 retention patterns, it is possible to identify clinically-distinct subgroups of MCI patients and those at greater risk of progression to dementia.

PET Agents in Dementia: An Overview

This article presents an overview of imaging agents for PET that have been applied for research and diagnostic purposes in patients affected by dementia. Classified by the target which the agents visualize, seven groups of tracers can be distinguished, namely radiopharmaceuticals for: (1) Misfolded proteins (ß-amyloid, tau, α-synuclein), (2) Neuroinflammation (overexpression of translocator protein), (3) Elements of the cholinergic system, (4) Elements of monoamine neurotransmitter systems, (5) Synaptic density, (6) Cerebral energy metabolism (glucose transport/ hexokinase), and (7) Various other proteins. This last category contains proteins involved in mechanisms underlying neuroinflammation or cognitive impairment, which may also be potential therapeutic targets. Many receptors belong to this category: AMPA, cannabinoid, colony stimulating factor 1, metabotropic glutamate receptor 1 and 5 (mGluR1, mGluR5), opioid (kappa, mu), purinergic (P2X7, P2Y12), sigma-1, sigma-2, receptor for advanced glycation endproducts, and triggering receptor expressed on myeloid cells-1, besides several enzymes: cyclooxygenase-1 and 2 (COX-1, COX-2), phosphodiesterase-5 and 10 (PDE5, PDE10), and tropomyosin receptor kinase. Significant advances in neuroimaging have been made in the last 15 years. The use of 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (FDG) for quantification of regional cerebral glucose metabolism is well-established. Three tracers for ß-amyloid plaques have been approved by the Food and Drug Administration and European Medicines Agency. Several tracers for tau neurofibrillary tangles are already applied in clinical research. Since many novel agents are in the preclinical or experimental stage of development, further advances in nuclear medicine imaging can be expected in the near future. PET studies with established tracers and tracers for novel targets may result in early diagnosis and better classification of neurodegenerative disorders and in accurate monitoring of therapy trials which involve these targets. PET data have prognostic value and may be used to assess the response of the human brain to interventions, or to select the appropriate treatment strategy for an individual patient.

Safinamide in neurological disorders and beyond: Evidence from preclinical and clinical studies

The discovery and development of safinamide, an alpha-aminoamide, has been a valuable addition to the existing clinical management of Parkinson's disease (PD). The journey of safinamide dates back to the year 1983, when an alpha-aminoamide called milacemide showed a weak anticonvulsant activity. Milacemide was then structurally modified to give rise to safinamide, which in turn produced robust anticonvulsant activity. The underlying mechanism behind this action of safinamide is attributed to the inhibition of voltage gated calcium and sodium channels. Moreover, owing to the importance of ion channels in maintaining neuronal circuitry and neurotransmitter release, numerous studies explored the potential of safinamide in neurological diseases including PD, stroke, multiple sclerosis and neuromuscular disorders such as Duchenne muscular dystrophy and non-dystrophic myotonias. Nevertheless, evidence from multiple preclinical studies suggested a potent, selective and reversible inhibitory activity of safinamide against monoamine oxidase (MAO)-B enzyme which is responsible for degrading dopamine, a neurotransmitter primarily implicated in the pathophysiology of PD. Therefore, clinical studies were conducted to assess safety and efficacy of safinamide in PD. Indeed, results from various Phase 3 clinical trials suggested strong evidence of safinamide as an add-on therapy in controlling the exacerbation of PD. This review presents a thorough developmental history of safinamide in PD and provides comprehensive insight into plausible mechanisms via which safinamide can be explored in other neurological and muscular diseases.

Neuroinflammation in psychiatric disorders: PET imaging and promising new targets

Neuroinflammation is a multifaceted physiological and pathophysiological response of the brain to injury and disease. Given imaging findings of 18 kDa translocator protein (TSPO) and the development of radioligands for other inflammatory targets, PET imaging of neuroinflammation is at a particularly promising stage. This Review critically evaluates PET imaging results of inflammation in psychiatric disorders, including major depressive disorder, schizophrenia and psychosis disorders, substance use, and obsessive-compulsive disorder. We also consider promising new targets that can be measured in the brain, such as monoamine oxidase B, cyclooxygenase-1 and cyclooxygenase-2, colony stimulating factor 1 receptor, and the purinergic P2X7 receptor. Thus far, the most compelling TSPO imaging results have arguably been found in major depressive disorder, for which consistent increases have been observed, and in schizophrenia and psychosis, for which patients show reduced TSPO levels. This pattern highlights the importance of validating brain biomarkers of neuroinflammation for each condition separately before moving on to patient stratification and treatment monitoring trials.

Neuroinflammation and Tau Colocalize in vivo in Progressive Supranuclear Palsy

OBJECTIVE

We examined the relationship between tau pathology and neuroinflammation using [11 C]PK11195 and [18 F]AV-1451 PET in 17 patients with progressive supranuclear palsy (PSP) Richardson's syndrome. We tested the hypothesis that neuroinflammation and tau protein aggregation colocalize macroscopically, and correlate with clinical severity.

METHODS

Nondisplaceable binding potential (BPND ) for each ligand was quantified in 83 regions of interest (ROIs). The [11 C]PK11195 and [18 F]AV-1451 BPND values were correlated across all regions. The spatial distributions of [11 C]PK11195 and [18 F]AV-1451 binding were determined by principal component analyses (PCAs), and the loading of each spatial component compared against the patients' clinical severity (using the PSP rating scale).

RESULTS

Regional [11 C]PK11195 and [18 F]AV-1451 binding were positively correlated (R = 0.577, p < 0.0001). The PCA identified 4 components for each ligand, reflecting the relative expression of tau pathology or neuroinflammation in distinct groups of brain regions. Positive associations between [11 C]PK11195 and [18 F]AV-1451 components' loadings were found in both subcortical (R = 0.769, p < 0.0001) and cortical regions (R = 0.836, p < 0.0001). There were positive correlations between clinical severity and both subcortical tau pathology (R = 0.667, p = 0.003) and neuroinflammation (R = 0.788, p < 0.001).

INTERPRETATION

We show that tau pathology and neuroinflammation colocalize in PSP, and that individual differences in subcortical tau pathology and neuroinflammation are linked to clinical severity. Although longitudinal studies are needed to determine causal associations between these molecular pathologies, we suggest that the combination of tau- and immune-oriented strategies may be useful for effective disease-modifying treatments in PSP. ANN NEUROL 2020;88:1194-1204.

18F-THK5351 PET Can Identify Lesions of Acute Traumatic Brain Injury

A 67-year-old woman sustained a mild traumatic brain injury (TBI) in a traffic accident and had an initial Glasgow Coma Scale score of 13. She underwent F-THK5351 PET 18 days after TBI. Fused F-THK5351 PET/MRI showed that the location of F-THK5351 accumulations corresponded anatomically to intraparenchymal lesions of acute TBI on MRI. F-THK5351 reportedly binds to monoamine oxidase B highly expressed in astrocytes. Furthermore, TBI induces reactive astrogliosis or blood-brain barrier breakdown included in primary brain injury. Therefore, F-THK5351 uptake may represent primary brain injury in acute TBI lesions.

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.

A dual-acting 5-HT6 receptor inverse agonist/MAO-B inhibitor displays glioprotective and pro-cognitive properties

The complex etiology of Alzheimer's disease has initiated a quest for multi-target ligands to address the multifactorial causes of this neurodegenerative disorder. In this context, we designed dual-acting 5-HT₆ receptor (5-HT₆R) antagonists/MAO-B inhibitors using pharmacophore hybridization strategy. Our approach involved linking priviliged scaffolds of 5-HT₆R with aryloxy fragments derived from reversible and irreversible MAO-B inhibitors. The study identified compound 48 that acts as an inverse agonist of 5-HT₆R at G_s signaling and an irreversible MAO-B inhibitor. Compound 48 showed moderate metabolic stability in rat microsomal assay, artificial membrane permeability, no hepatotoxicity, and it was well distributed to the brain. Additionally, 48 showed glioprotective properties in a model of cultured astrocytes using 6-OHDA as the cytotoxic agent. Finally, compound 48 (MED = 1 mg/kg, p.o.) fully reversed memory deficits in the NOR task induced by scopolamine in rats. A better understanding of effects exerted by dual-acting 5-HT₆R/MAO-B modulators may impact the future development of neurodegenerative-directed treatment strategies.

18F-SMBT-1: A Selective and Reversible PET Tracer for Monoamine Oxidase-B Imaging

Reactive astrocytes play a key role in the pathogenesis of various neurodegenerative diseases. Monoamine oxidase-B (MAO-B) is one of the promising targets for the imaging of astrogliosis in the human brain. A novel selective and reversible MAO-B tracer, (S)-(2-methylpyrid-5-yl)-6-[(3-¹⁸F-fluoro-2-hydroxy)propoxy]quinoline (¹⁸F-SMBT-1), was successfully developed via lead optimization from the first-generation tau PET tracer ¹⁸F-THK-5351. Methods: SMBT-1 was radiolabeled with ¹⁸F using the corresponding precursor. The binding affinity of radiolabeled compounds to MAO-B was assessed using saturation and competitive binding assays. The binding selectivity of ¹⁸F-SMBT-1 to MAO-B was evaluated by autoradiography of frozen human brain tissues. The pharmacokinetics and metabolism were assessed in normal mice after intravenous administration of ¹⁸F-SMBT-1. A 14-d toxicity study after the intravenous administration of ¹⁸F-SMBT-1 was performed using rats and mice. Results: In vitro binding assays demonstrated a high binding affinity of ¹⁸F-SMBT-1 to MAO-B (dissociation constant, 3.7 nM). In contrast, it showed low binding affinity to MAO-A and protein aggregates such as amyloid-β and tau fibrils. Autoradiographic analysis showed higher amounts of ¹⁸F-SMBT-1 binding in the Alzheimer disease brain sections than in the control brain sections. ¹⁸F-SMBT-1 binding was completely displaced with the reversible MAO-B inhibitor lazabemide, demonstrating the high selectivity of ¹⁸F-SMBT-1 for MAO-B. Furthermore, ¹⁸F-SMBT-1 showed a high uptake by brain, rapid washout, and no radiolabeled metabolites in the brain of normal mice. ¹⁸F-SMBT-1 showed no significant binding to various receptors, ion channels, or transporters, and no toxic effects related to its administration were observed in mice and rats. Conclusion: ¹⁸F-SMBT-1 is a promising and selective MAO-B PET tracer candidate, which would be useful for quantitative monitoring of astrogliosis in the human brain.

Protective effects of chondroitin sulphate nano-selenium on a mouse model of Alzheimer's disease

In this study, the effect of chondroitin sulphate nano-selenium (CS@Se) on Alzheimer's disease (AD) in mice was investigated. CS@Se alleviated anxiety and improved the spatial learning and memory impairment in AD mice. CS@Se significantly reduced cell oedema and pyknosis, protected the mitochondria, and improved abnormal changes in the ultrastructure of hippocampal neuron synapses of AD mice. Moreover, CS@Se significantly increased the levels of superoxide dismutase(SOD), glutathione peroxidase (GSH-Px), Na⁺/K⁺-ATPase assay (Na⁺/K⁺-ATPase) and acetyltransferase (ChAT), and decreased the levels of malondialdehyde (MDA) and acetylcholinesterase (ChAE) in AD mice. Western blot results showed that CS@Se can attenuate excessive phosphorylation of tau (Ser396/Ser404) by regulating the expression of glycogen synthase kinase-3 beta (GSK-3β). In addition, CS@Se can activate the extracellular signal-regulated kinase 1/2 (ERK 1/2) and p38 mitogen-activated protein kinase (p38 MAPK) signalling pathways to inhibit nuclear transcription factor kappa B (NF-κB) nuclear translocation, thereby regulating the expression of pro-inflammatory cytokines. In summary, CS@Se can reduce oxidative stress damage, inhibit excessive tau phosphorylation, reduce inflammation to delay AD development, and increase the learning and memory capacities of AD mice.

Hepatic monoamine oxidase B is involved in endogenous geranylgeranoic acid synthesis in mammalian liver cells

Geranylgeranoic acid (GGA) originally was identified in some animals and has been developed as an agent for preventing second primary hepatoma. We previously have also identified GGA as an acyclic diterpenoid in some medicinal herbs. Recently, we reported that in human hepatoma-derived HuH-7 cells, GGA is metabolically labeled from ¹³C-mevalonate. Several cell-free experiments have demonstrated that GGA is synthesized through geranylgeranial by oxygen-dependent oxidation of geranylgeraniol (GGOH), but the exact biochemical events giving rise to GGA in hepatoma cells remain unclear. Monoamine oxidase B (MOAB) has been suggested to be involved in GGOH oxidation. Here, using two human hepatoma cell lines, we investigated whether MAOB contributes to GGA biosynthesis. Using either HuH-7 cell lysates or recombinant human MAOB, we found that: 1) the MAO inhibitor tranylcypromine dose-dependently downregulates endogenous GGA levels in HuH-7 cells; and 2) siRNA-mediated MAOB silencing reduces intracellular GGA levels in HuH-7 and Hep3B cells. Unexpectedly, however, CRISPR/Cas9-generated MAOB-KO human hepatoma Hep3B cells had GGA levels similar to those in MAOB-WT cells. A sensitivity of GGA levels to siRNA-mediated MAOB downregulation was recovered when the MAOB-KO cells were transfected with a MAOB-expression plasmid, suggesting that MAOB is the enzyme primarily responsible for GGOH oxidation and that some other latent metabolic pathways may maintain endogenous GGA levels in the MAOB-KO hepatoma cells. Along with the previous findings, these results provide critical insights into the biological roles of human MAOB and provide evidence that hepatic MAOB is involved in endogenous GGA biosynthesis via GGOH oxidation.

Chromone and donepezil hybrids as new multipotent cholinesterase and monoamine oxidase inhibitors for the potential treatment of Alzheimer's disease

A series of chromone and donepezil hybrids were designed, synthesized, and evaluated as multipotent cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors for the potential therapy of Alzheimer's disease (AD). In vitro studies showed that the great majority of these compounds exhibited potent inhibitory activity toward BuChE and AChE and clearly selective inhibition for hMAO-B. In particular, compound 5c presented the most balanced potential for ChE inhibition (BuChE: IC₅₀ = 5.24 μM; AChE: IC₅₀ = 0.37 μM) and hMAO-B selectivity (IC₅₀ = 0.272 μM, SI = 247). Molecular modeling and kinetic studies suggested that 5c was a mixed-type inhibitor, binding simultaneously to peripheral and active sites of AChE. It was also a competitive inhibitor, which occupied the substrate and entrance cavities of MAO-B. Moreover, compound 5c could penetrate the blood-brain barrier (BBB) and showed low toxicity to rat pheochromocytoma (PC12) cells. Altogether, these results indicated that compound 5c might be a hopeful multitarget drug candidate with possible impact on Alzheimer's disease therapy.

Dysregulation of multiple metabolic networks related to brain transmethylation and polyamine pathways in Alzheimer disease: A targeted metabolomic and transcriptomic study

BACKGROUND

There is growing evidence that Alzheimer disease (AD) is a pervasive metabolic disorder with dysregulation in multiple biochemical pathways underlying its pathogenesis. Understanding how perturbations in metabolism are related to AD is critical to identifying novel targets for disease-modifying therapies. In this study, we test whether AD pathogenesis is associated with dysregulation in brain transmethylation and polyamine pathways.

METHODS AND FINDINGS

We first performed targeted and quantitative metabolomics assays using capillary electrophoresis-mass spectrometry (CE-MS) on brain samples from three groups in the Baltimore Longitudinal Study of Aging (BLSA) (AD: n = 17; Asymptomatic AD [ASY]: n = 13; Control [CN]: n = 13) (overall 37.2% female; mean age at death 86.118 ± 9.842 years) in regions both vulnerable and resistant to AD pathology. Using linear mixed-effects models within two primary brain regions (inferior temporal gyrus [ITG] and middle frontal gyrus [MFG]), we tested associations between brain tissue concentrations of 26 metabolites and the following primary outcomes: group differences, Consortium to Establish a Registry for Alzheimer's Disease (CERAD) (neuritic plaque burden), and Braak (neurofibrillary pathology) scores. We found significant alterations in concentrations of metabolites in AD relative to CN samples, as well as associations with severity of both CERAD and Braak, mainly in the ITG. These metabolites represented biochemical reactions in the (1) methionine cycle (choline: lower in AD, p = 0.003; S-adenosyl methionine: higher in AD, p = 0.005); (2) transsulfuration and glutathione synthesis (cysteine: higher in AD, p < 0.001; reduced glutathione [GSH]: higher in AD, p < 0.001); (3) polyamine synthesis/catabolism (spermidine: higher in AD, p = 0.004); (4) urea cycle (N-acetyl glutamate: lower in AD, p < 0.001); (5) glutamate-aspartate metabolism (N-acetyl aspartate: lower in AD, p = 0.002); and (6) neurotransmitter metabolism (gamma-amino-butyric acid: lower in AD, p < 0.001). Utilizing three Gene Expression Omnibus (GEO) datasets, we then examined mRNA expression levels of 71 genes encoding enzymes regulating key reactions within these pathways in the entorhinal cortex (ERC; AD: n = 25; CN: n = 52) and hippocampus (AD: n = 29; CN: n = 56). Complementing our metabolomics results, our transcriptomics analyses also revealed significant alterations in gene expression levels of key enzymatic regulators of biochemical reactions linked to transmethylation and polyamine metabolism. Our study has limitations: our metabolomics assays measured only a small proportion of all metabolites participating in the pathways we examined. Our study is also cross-sectional, limiting our ability to directly test how AD progression may impact changes in metabolite concentrations or differential-gene expression. Additionally, the relatively small number of brain tissue samples may have limited our power to detect alterations in all pathway-specific metabolites and their genetic regulators.

CONCLUSIONS

In this study, we observed broad dysregulation of transmethylation and polyamine synthesis/catabolism, including abnormalities in neurotransmitter signaling, urea cycle, aspartate-glutamate metabolism, and glutathione synthesis. Our results implicate alterations in cellular methylation potential and increased flux in the transmethylation pathways, increased demand on antioxidant defense mechanisms, perturbations in intermediate metabolism in the urea cycle and aspartate-glutamate pathways disrupting mitochondrial bioenergetics, increased polyamine biosynthesis and breakdown, as well as abnormalities in neurotransmitter metabolism that are related to AD.

Binding of [18F]AV1451 in post mortem brain slices of semantic variant primary progressive aphasia patients

Purpose

In vivo tau-PET tracer retention in the anterior temporal lobe of patients with semantic variant primary progressive aphasia (SV PPA) has consistently been reported. This is unexpected as the majority of these patients have frontotemporal lobar degeneration TDP (FTLD-TDP).

Methods

We conducted an in vitro [¹⁸F]AV1451 autoradiography binding study in five cases with a clinical diagnosis of SV PPA constituting the range of pathologies (i.e., three FTLD-TDP, one Alzheimer’s disease (AD), and one Pick’s disease (PiD)). Binding was compared with two controls without neurodegeneration, two typical AD, one corticobasal syndrome with underlying AD, and one frontotemporal dementia behavioral variant with FTLD-TDP. The effect of blocking with the authentic reference material and with the MAO-B inhibitor deprenyl was assessed. Immunohistochemistry was performed on adjacent cryosections.

Results

Absence of specific [¹⁸F]AV1451 binding was observed for all three SV PPA FTLD-TDP cases. The absence of binding in controls as well as the successful blocking with authentic AV1451 in cases with tauopathy demonstrated specificity of the [¹⁸F]AV1451 signal for tau. The specific [¹⁸F]AV1451 binding was highest in AD, followed by PiD. This binding colocalized with the respective tau lesions and could not be blocked by deprenyl. Similar pilot findings were obtained with [¹⁸F]THK5351.

Conclusion

In vitro autoradiography showed no [¹⁸F]AV1451 binding in SV PPA due to FTLD-TDP, while specific binding was present in SV PPA due to AD and PiD. The discrepancy between in vitro and in vivo findings remains to be explained. The discordance is not related to [¹⁸F]AV1451 idiosyncrasies as [¹⁸F]THK5351 findings were similar.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04631-x) contains supplementary material, which is available to authorized users.

Etoposide Induces Mitochondrial Dysfunction and Cellular Senescence in Primary Cultured Rat Astrocytes

Brain aging is an inevitable process characterized by structural and functional changes and is a major risk factor for neurodegenerative diseases. Most brain aging studies are focused on neurons and less on astrocytes which are the most abundant cells in the brain known to be in charge of various functions including the maintenance of brain physical formation, ion homeostasis, and secretion of various extracellular matrix proteins. Altered mitochondrial dynamics, defective mitophagy or mitochondrial damages are causative factors of mitochondrial dysfunction, which is linked to age-related disorders. Etoposide is an anti-cancer reagent which can induce DNA stress and cellular senescence of cancer cell lines. In this study, we investigated whether etoposide induces senescence and functional alterations in cultured rat astrocytes. Senescence-associated β-galactosidase (SA-β-gal) activity was used as a cellular senescence marker. The results indicated that etoposide-treated astrocytes showed cellular senescence phenotypes including increased SA-β-gal-positive cells number, increased nuclear size and increased senescence-associated secretory phenotypes (SASP) such as IL-6. We also observed a decreased expression of cell cycle markers, including Phospho- Histone H3/Histone H3 and CDK2, and dysregulation of cellular functions based on wound-healing, neuronal protection, and phagocytosis assays. Finally, mitochondrial dysfunction was noted through the determination of mitochondrial membrane potential using tetramethylrhodamine methyl ester (TMRM) and the measurement of mitochondrial oxygen consumption rate (OCR). These data suggest that etoposide can induce cellular senescence and mitochondrial dysfunction in astrocytes which may have implications in brain aging and neurodegenerative conditions.

Astrocytes: Role and Functions in Brain Pathologies

Astrocytes are a population of cells with distinctive morphological and functional characteristics that differ within specific areas of the brain. Postnatally, astrocyte progenitors migrate to reach their brain area and related properties. They have a regulatory role of brain functions that are implicated in neurogenesis and synaptogenesis, controlling blood-brain barrier permeability and maintaining extracellular homeostasis. Mature astrocytes also express some genes enriched in cell progenitors, suggesting they can retain proliferative potential. Considering heterogeneity of cell population, it is not surprising that their disorders are related to a wide range of different neuro-pathologies. Brain diseases are characterized by the active inflammatory state of the astrocytes, which is usually described as up-regulation of glial fibrillary acidic protein (GFAP). In particular, the loss of astrocytes function as a result of cellular senescence could have implications for the neurodegenerative disorders, such as Alzheimer disease and Huntington disease, and for the aging brain. Astrocytes can also drive the induction and the progression of the inflammatory state due to their Ca²⁺ signals and that it is strongly related to the disease severity/state. Moreover, they contribute to the altered neuronal activity in several frontal cortex pathologies such as ischemic stroke and epilepsy. There, we describe the current knowledge pertaining to astrocytes' role in brain pathologies and discuss the possibilities to target them as approach toward pharmacological therapies for neuro-pathologies.

Identification of AV-1451 as a Weak, Nonselective Inhibitor of Monoamine Oxidase

[¹⁸F]AV-1451 is one of the most widely used radiotracers for positron emission tomography (PET) imaging of tau protein aggregates in neurodegenerative disorders. While the radiotracer binds with high affinity to tau neurofibrillary tangles, extensive clinical studies have simultaneously revealed off-target tracer accumulation in areas of low tau burden such as the basal ganglia and choroid plexus. Though there are a number of possible reasons for this accumulation, it is often attributed to off-target binding to monoamine oxidase (MAO). In this paper, we investigate the association between [¹⁸F]AV-1451 and MAO through (i) enzyme inhibition assays, (ii) autoradiography with postmortem tissue samples, and (iii) nonhuman primate PET imaging. We confirm that [¹⁸F]AV-1451 is a weak inhibitor of MAO-A and -B and that MAO inhibitors can alter binding of [¹⁸F]AV-1451 in autoradiography and in vivo PET imaging.

Modulation of dopamine metabolizing enzymes and antioxidant status by Capsicum annuum Lin in rotenone-intoxicated rat brain

Rotenone is a natural pesticide and environmental neurotoxin which mimics key aspects of Parkinson's disease. This study evaluated the effect of ethyl acetate extract of Capsicum annuum L. (C. annuum) in rotenone-intoxicated rats. Oral doses of C. annuum extract (50, 100 & 200 mg kg-1) and rotenone (2 mg kg-1 i.p.) were co-administered for 25 days during which rearing behavior was monitored. Biochemical alterations in the levels of tyrosine hydroxylase (TH), monoamine oxidase (MAO), superoxide dismutase (SOD) as well as reduced and oxidized glutathione (GSH) were estimated. Decrease in rearing behavior resulting from rotenone exposure was ameliorated by 200 mg kg-1 of C. annuum. Furthermore, rotenone exposure significantly (P < 0.05) decreased TH and increased MAO levels respectively. Impaired brain antioxidant capacity, typified by significantly (P < 0.05) decreased GSH redox status and SOD levels were also observed in rotenone-treated rats. However, co-administration of C. annuum ameliorated rotenone-induced derangements and potentiated the effect of levodopa. These results taken together suggests that C. annuum protects against rotenone-induced neurotoxicity by modulating dopamine metabolism and GSH redox status in rat brain.

Monoamine Oxidase B Total Distribution Volume in the Prefrontal Cortex of Major Depressive Disorder: An [11C]SL25.1188 Positron Emission Tomography Study

IMPORTANCE

Monoamine oxidase B (MAO-B) is an important, high-density enzyme in the brain that generates oxidative stress by hydrogen peroxide production, alters mitochondrial function, and metabolizes nonserotonergic monoamines. Recent advances in positron emission tomography radioligand development for MAO-B in humans enable highly quantitative measurement of MAO-B distribution volume (MAO-B VT), an index of MAO-B density. To date, this is the first investigation of MAO-B in the brain of major depressive disorder that evaluates regions beyond the raphe and amygdala.

OBJECTIVE

To investigate whether MAO-B VT is elevated in the prefrontal cortex in major depressive episodes (MDEs) of major depressive disorder.

DESIGN, SETTING, AND PARTICIPANTS

This case-control study was performed at a tertiary care psychiatric hospital from April 1, 2014, to August 30, 2018. Twenty patients with MDEs without current psychiatric comorbidities and 20 age-matched controls underwent carbon 11-labeled [11C]SL25.1188 positron emission tomography scanning to measure MAO-B VT. All participants were drug and medication free, nonsmoking, and otherwise healthy.

MAIN OUTCOMES AND MEASURES

The MAO-B VT in the prefrontal cortex (PFC). The second main outcome was to evaluate the association between MAO-B VT in the PFC and duration of major depressive disorder illness.

RESULTS

Twenty patients with MDEs (mean [SD] age, 34.2 [13.2] years; 11 women) and 20 healthy controls (mean [SD] age, 33.7 [13.1] years; 10 women) were recruited. Patients with MDEs had significantly greater MAO-B VT in the PFC (mean, 26%; analysis of variance, F1,38 = 19.6, P < .001). In individuals with MDEs, duration of illness covaried positively with MAO-B VT in the PFC (analysis of covariance, F1,18 = 15.2, P = .001), as well as most other cortex regions and the thalamus.

CONCLUSIONS AND RELEVANCE

Fifty percent (10 of 20) of patients with MDEs had MAO-B VT values in the PFC exceeding those of healthy controls. Greater MAO-B VT is an index of MAO-B overexpression, which may contribute to pathologies of mitochondrial dysfunction, elevated synthesis of neurotoxic products, and increased metabolism of nonserotonergic monoamines. Hence, this study identifies a common pathological marker associated with downstream consequences poorly targeted by the common selective serotonin reuptake inhibitor treatments. It is also recommended that the highly selective MAO-B inhibitor medications that are compatible for use with other antidepressants and have low risk for hypertensive crisis should be developed or repurposed as adjunctive treatment for MDEs.

Monoamine Oxidases (MAOs) as Privileged Molecular Targets in Neuroscience: Research Literature Analysis

Background: Monoamine oxidases (MAOs) were discovered nearly a century ago. This article aims to analyze the research literature landscape associated with MAOs as privileged class of neuronal enzymes (neuroenzymes) with key functions in the processes of neurodegeneration, serving as important biological targets in neuroscience. With the accumulating publications on this topic, we aimed to evaluate the publication and citation performance of the contributors, reveal the popular research themes, and identify its historical roots. Methods: The electronic database of Web of Science (WoS) Core Collection was searched to identify publications related to MAOs, which were analyzed according to their publication year, authorship, institutions, countries/regions, journal title, WoS category, total citation count, and publication type. VOSviewer was utilized to visualize the citation patterns of the words appearing in the titles and abstracts, and author keywords. CRExplorer was utilized to identify seminal references cited by the MAO publications. Results: The literature analysis was based on 19,854 publications. Most of them were original articles (n = 15,148, 76.3%) and reviews (n = 2,039, 10.3%). The top five WoS categories of the analyzed MAO publications were Pharmacology/Pharmacy (n = 4,664, 23.5%), Neurosciences (n = 4,416, 22.2%), Psychiatry (n = 2,906, 14.6%), Biochemistry/Molecular Biology (n = 2,691, 13.6%), and Clinical Neurology (n = 1,754, 8.8%). The top 10 institutions are scattered in the United States, UK, France, Sweden, Canada, Israel, and Russia, while the top 10 countries/regions with the most intensive research on the field of MAOs are the United States, followed by European and Asian countries. More highly cited publications generally involved neurotransmitters, such as dopamine (DA), serotonin, and norepinephrine (NE), as well as the MAO-A inhibitors moclobemide and clorgyline, and the irreversible MAO-B inhibitors selegiline and rasagiline. Conclusion: Through decades of research, the literature has accumulated many publications investigating the therapeutic effects of MAO inhibitors (MAOIs) on various neurological conditions, such as Alzheimer's disease (AD), Parkinson's disease (PD), and depression. We envision that MAO literature will continue to grow steadily, with more new therapeutic candidates being tested for better management of neurological conditions, in particular, with the development of multi-target acting drugs against neurodegenerative diseases.

Attenuation of the effects of oxidative stress by the MAO-inhibiting antidepressant and carbonyl scavenger phenelzine

Phenelzine (β-phenylethylhydrazine) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. It possesses a number of important pharmacological properties which may alter the effects of oxidative stress. After conducting a comprehensive literature search, the authors of this review paper aim to provide an overview and discussion of the mechanisms by which phenelzine may attenuate oxidative stress. It inhibits γ-aminobutyric acid (GABA) transaminase, resulting in elevated brain GABA levels, inhibits both MAO and primary amine oxidase and, due to its hydrazine-containing structure, reacts chemically to sequester a number of reactive aldehydes (e.g. acrolein and 4-hydroxy-2-nonenal) proposed to be implicated in oxidative stress in a number of neurodegenerative disorders. Phenelzine is unusual in that it is both an inhibitor of and a substrate for MAO, the latter action producing at least one active metabolite, β-phenylethylidenehydrazine (PEH). This metabolite inhibits GABA transaminase, is a very weak inhibitor of MAO but a strong inhibitor of primary amine oxidase, and sequesters aldehydes. Phenelzine may ameliorate the effects of oxidative stress by reducing formation of reactive metabolites (aldehydes, hydrogen peroxide, ammonia/ammonia derivatives) produced by the interaction of MAO with biogenic amines, by sequestering various other reactive aldehydes and by inhibiting primary amine oxidase. In PC12 cells treated with the neurotoxin MPP⁺, phenelzine has been reported to reduce several adverse effects of MPP⁺. It has also been reported to reduce lipid peroxidative damage induced in plasma and platelet proteins by peroxynitrite. In animal models, phenelzine has a neuroprotective effect in global ischemia and in cortical impact traumatic brain injury. Recent studies reported in the literature on the possible involvement of acrolein in spinal cord injury and multiple sclerosis indicate that phenelzine can attenuate adverse effects of acrolein in these models. Results from studies in our laboratories on effects of phenelzine and PEH on primary amine oxidase (which catalyzes formation of toxic aldehydes and is overexpressed in Alzheimer's disease), on sequestration of the toxic aldehyde acrolein, and on reduction of acrolein-induced toxicity in mouse cortical neurons are also reported.

Ligand fishing of anti-neurodegenerative components from Lonicera japonica using magnetic nanoparticles immobilised with monoamine oxidase B

In this work, monoamine oxidase B was immobilised onto magnetic nanoparticles to prepare a new type of affinity solid-phase extraction adsorbent, which was used to extract the possible anti-neurodegenerative components from the Lonicera japonica flower extracts. Coupled with high-performance liquid chromatography with mass spectrometry, two monoamine oxidase B ligands were fished-out and identified as isochlorogenic acid A and isochlorogenic acid C, which were found to be inhibitors of the enzyme for the first time, with similar half maximal inhibitory concentration values of 29.05 ± 0.49 and 29.77 ± 1.03 μM, respectively. Furthermore, equilibrium-dialysis dissociation assay of enzyme-inhibitor complex showed that both compounds have reversible binding patterns to monoamine oxidase B, and kinetic analysis demonstrated that they were mixed-type inhibitors for monoamine oxidase B, with K_i and K_is values of 9.55 and 37.24 μM for isochlorogenic acid A, 9.53 and 35.50 μM for isochlorogenic acid C, respectively. The results indicated that isochlorogenic acid A and isochlorogenic acid C were the major active components responsible for the anti-degenerative activity of the flowers of L. japonica, while magnetic nanoparticles immobilised monoamine oxidase B could serve as an efficient solid-phase extraction adsorbent to specifically extract monoamine oxidase B inhibitors from complex herbal extracts.

Astrocyte activation and altered metabolism in normal aging, age-related CNS diseases, and HAND

Astrocytes regulate local cerebral blood flow, maintain ion and neurotransmitter homeostasis, provide metabolic support, regulate synaptic activity, and respond to brain injury, insults, and infection. Because of their abundance, extensive connectivity, and multiple roles in the brain, astrocytes are intimately involved in normal functioning of the CNS and their dysregulation can lead to neuronal dysfunction. In normal aging, decreased biological functioning and reduced cognitive abilities are commonly experienced in individuals free of overt neurological disease. Moreover, in several age-related CNS diseases, chronic inflammation and altered metabolism have been reported. Since people with HIV (PWH) are reported to experience rapid aging with chronic inflammation, altered brain metabolism is likely to be exacerbated. In fact, many studies report altered metabolism in astrocytes in diseases such as Alzheimer's, Parkinson's, and HIV. This review will address the roles of astrocyte activation and altered metabolism in normal aging, in age-related CNS disease, and in HIV-associated neurocognitive disorders.

Rational Design of Novel Selective Dual-Target Inhibitors of Acetylcholinesterase and Monoamine Oxidase B as Potential Anti-Alzheimer's Disease Agents

Multifunctional agents aiming at cholinesterases (ChEs) and monoamine oxidases (MAOs) are promising therapy for Alzheimer's disease (AD). Herein, a series of novel propargylamine-modified pyrimidinylthiourea derivatives (1-4) were designed and synthesized as dual inhibitors of ChEs and MAOs with other functions against AD. Most of these derivatives inhibited ChEs and MAOs with IC₅₀ values in the micro- or nanomolar ranges. Compound 1c displayed the dual functional profile of targeting the AChE (IC₅₀ = 0.032 ± 0.007 μM) and MAO-B (IC₅₀ = 2.117 ± 0.061 μM), along with the improved blood-brain barrier (BBB) permeability, antioxidant ability, and good copper chelating property in vitro. Animal studies showed that compound 1c·HCl could inhibit the cerebral AChE/MAO-B activities and alleviate scopolamine-induced cognitive impairment in mice. Combined with good oral bioavailability ( F = 45.55%), these findings demonstrated that compound 1c may be a potent brain permeable multifunctional candidate for the treatment of AD.

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.

Discovery of monoamine oxidase inhibitors by medicinal chemistry approaches

Neuropsychiatric disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD) and depression, have seriously inconvenienced the lives of patients. Growing evidence indicates that these diseases are closely related to the monoamine oxidase (MAO) enzyme, making it an attractive target for the exploitation of potent MAO inhibitors (MAOIs) with high selectivity and low side effects. Although various MAOIs have been discovered, the discovery of an ideal MAOI is not an easy task. In this review, we discuss the currently available rational design strategies for obtaining ideal MAOIs, including ligand-based and receptor-based design strategies, and these strategies were further illustrated with the aid of specific examples from the recent literature. To better understanding the biological activity of MAO, we also highlight the binding modes of typical inhibitors against MAO. Besides, advanced strategies for finding upcoming potent MAOIs were prospected.

3D-QSAR and in-silico Studies of Natural Products and Related Derivatives as Monoamine Oxidase Inhibitors

BACKGROUND

The computational development of human monoamine oxidase (MAO) inhibitors led to advancement in drug design and the treatment of many neurodegenerative diseases and neuropsychiatric disorders. The computational development of human monoamine oxidase (MAO) inhibitors led to advancement in drug design and the treatment of many neurodegenerative diseases and neuropsychiatric disorders. Different natural heterocyclic structures are reported to display selective MAO inhibitory activity by preclinical and in-silico modeling.

OBJECTIVE

Currently, the major interest is devoted to the study of natural based therapeutic agents from the different categories. Therefore, we presenting the review to critically discuss and outline the recent advances in our knowledge on the importance of natural and natural based ligand-MAO insilico methods for novel MAO inhibitors.

DISCUSSION

Several natural and related synthetic heterocyclic compounds such as coumarins, β- carboline, piperine, naphthoquinone, morpholine, caffeine, amphetamine moreover flavonoids, chalcones, xanthones, curcumin are discussed for their MAO inhibitory profile along with molecular docking and quantitative structure-activity relationship studies.

CONCLUSION

It is clear that, by this computational drug design approach, more particular, reversible and potent compounds can be proposed as MAO inhibitors by exact changes on the fundamental framework.

Chlorogenic Acid from Hawthorn Berry (Crataegus pinnatifida Fruit) Prevents Stress Hormone-Induced Depressive Behavior, through Monoamine Oxidase B-Reactive Oxygen Species Signaling in Hippocampal Astrocytes of Mice

SCOPE

Oxidative stress has been implicated in mental disorders, including depression. Chlorogenic acid (CGA), one of the abundant phenolic compounds in herbs and fruits, has the properties of a natural antioxidant and free-radical scavenger. Therfore, we investigated the antidepressant-like effects and active mechanisms of CGA from the extract of Crataegus pinnatifida (CP) fruit.

METHODS AND RESULTS

Depression-like phenotypes were induced in mice by daily injection of stress hormone for 1-2 weeks. The brains of these animals exhibited reduced brain-derived neurotrophic factor expression and increased astrocytic hypertrophy, which are typical markers of depression in animal models. Stress hormone injection 1) upregulated monoamine oxidase B (MAOB) expression and 2) reduced spine numbers along neuronal dendrites, which indicates synaptic depression. The oral administration of CGA (30 mg kg^-1 ) or CP (300 mg kg^-1 ) prevented MAOB activation following reactive oxygen species (ROS) production and had an ameliorative effect on depressive behavioral tests (e.g., tail suspension and forced swim tests). In vitro assays performed on cultured C8-D1A cells revealed that CGA and CP inhibited MAOB activity and ROS production.

CONCLUSION

Our study indicates that CGA and CP extracts prevented depressive behavior and thereby have potential as natural antidepressants.

Single-word comprehension deficits in the nonfluent variant of primary progressive aphasia

BACKGROUND

A subset of patients with the nonfluent variant of primary progressive aphasia (PPA) exhibit concomitant single-word comprehension problems, constituting a 'mixed variant' phenotype. This phenotype is rare and currently not fully characterized. The aim of this study was twofold: to assess the prevalence and nature of single-word comprehension problems in the nonfluent variant and to study multimodal imaging characteristics of atrophy, tau, and amyloid burden associated with this mixed phenotype.

METHODS

A consecutive memory-clinic recruited series of 20 PPA patients (12 nonfluent, five semantic, and three logopenic variants) were studied on neurolinguistic and neuropsychological domains relative to 64 cognitively intact healthy older control subjects. The neuroimaging battery included high-resolution volumetric magnetic resonance imaging processed with voxel-based morphometry, and positron emission tomography with the tau-tracer [18F]-THK5351 and amyloid-tracer [11C]-Pittsburgh Compound B.

RESULTS

Seven out of 12 subjects who had been classified a priori with nonfluent variant PPA showed deficits on conventional single-word comprehension tasks along with speech apraxia and agrammatism, corresponding to a mixed variant phenotype. These mixed variant cases included three females and four males, with a mean age at onset of 65 years (range 44-77 years). Object knowledge and object recognition were additionally affected, although less severely compared with the semantic variant. The mixed variant was characterized by a distributed atrophy pattern in frontal and temporoparietal regions. A more focal pattern of elevated [18F]-THK5351 binding was present in the supplementary motor area, the left premotor cortex, midbrain, and basal ganglia. This pattern was closely similar to that seen in pure nonfluent variant PPA. At the individual patient level, elevated [18F]-THK5351 binding in the supplementary motor area and premotor cortex was present in six out of seven mixed variant cases and in five and four of these cases, respectively, in the thalamus and midbrain. Amyloid biomarker positivity was present in two out of seven mixed variant cases, compared with none of the five pure nonfluent cases.

CONCLUSIONS

A substantial proportion of PPA patients with speech apraxia and agrammatism also have single-word comprehension deficits. At the neurobiological level, the mixed variant shows a high degree of similarity with the pure nonfluent variant of PPA.

TRIAL REGISTRATION

EudraCT, 2014-002976-10 . Registered on 13-01-2015.

Quantitative evaluation of tau PET tracers 18F-THK5351 and 18F-AV-1451 in Alzheimer's disease with standardized uptake value peak-alignment (SUVP) normalization

PURPOSE

Off-target binding in the reference region is a challenge for recent tau tracers 18F-AV-1451 and 18F-THK5351. The conventional standardized uptake value ratio (SUVR) method relies on the average uptake from an unaffected tissue sample, and therefore is susceptible to biases from off-target binding as well as variability among individuals in the reference region. We propose a new method, standardized uptake value peak-alignment (SUVP), to reduce the bias of the SUVR, and improve the quantitative assessment of tau deposition.

METHODS

The SUVP normalizes uptake values by their mode and standard deviation. Instead of using a reference region, the SUVP derives the contrast from unaffected voxels over the whole brain. Using SUVP and SUVR methods, we evaluated the global and regional tau binding of 18F-THK5351 and 18F-AV-1451 on two independent cohorts (N = 18 and 32, respectively), each with cognitively normal (NL) subjects and Alzheimer's disease (AD) subjects.

RESULTS

Both tracers showed significantly increased binding for AD in the targeted cortical areas. In the temporal cortex, SUVP had a higher classification success rate (CSR) than SUVR (0.96 vs 0.89 for 18F-THK5351; 0.86 vs 0.75 for 18F-AV-1451), as well as higher specificity under fixed sensitivity around 0.80 (0.70 vs 0.45 specificity for 18F-THK5351; 1.00 vs 0.78 for 18F-AV-1451). In the cerebellar cortex, an AD-NL group difference with effect size (Cohen's d) of 0.62 was observed for AV-1451, confirming the limitation of the SUVR approach using this region as a reference. A smaller cerebellar effect size (0.09) was observed for THK5351.

CONCLUSION

The SUVP method reduces the bias of the reference region and improves the NL-AD classification compared to the SUVR approach.

Neuroimaging-pathological correlations of [18F]THK5351 PET in progressive supranuclear palsy

Recent positron emission tomography (PET) studies have demonstrated the accumulation of tau PET tracer in the affected region of progressive supranuclear palsy (PSP) cases. To confirm the binding target of radiotracer in PSP, we performed an imaging-pathology correlation study in two autopsy-confirmed PSP patients who underwent [¹⁸F]THK5351 PET before death. One patient with PSP Richardson syndrome showed elevated tracer retention in the globus pallidus and midbrain. In a patient with PSP-progressive nonfluent aphasia, [¹⁸F]THK5351 retention also was observed in the cortical areas, particularly the temporal cortex. Neuropathological examination confirmed PSP in both patients. Regional [¹⁸F]THK5351 standardized uptake value ratio (SUVR) in antemortem PET was significantly correlated with monoamine oxidase-B (MAO-B) level, reactive astrocytes density, and tau pathology at postmortem examination. In in vitro autoradiography, specific THK5351 binding was detected in the area of antemortem [¹⁸F]THK5351 retention, and binding was blocked completely by a reversible selective MAO-B inhibitor, lazabemide, in brain samples from these patients. In conclusion, [¹⁸F]THK5351 PET signals reflect MAO-B expressing reactive astrocytes, which may be associated with tau accumulation in PSP.

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.

Sembragiline in Moderate Alzheimer's Disease: Results of a Randomized, Double-Blind, Placebo-Controlled Phase II Trial (MAyflOwer RoAD)

Background: Sembragiline is a potent, selective, long-acting, and reversible MAO-B inhibitor developed as a potential treatment for Alzheimer’s disease (AD).

Objective: To evaluate the safety, tolerability, and efficacy of sembragiline in patients with moderate AD.

Methods: In this Phase II study (NCT01677754), 542 patients with moderate dementia (MMSE 13–20) on background acetylcholinesterase inhibitors with/without memantine were randomized (1:1:1) to sembragiline 1 mg, 5 mg, or placebo once daily orally for 52 weeks.

Results: No differences between treated groups and placebo in adverse events or in study completion. The primary endpoint, change from baseline in ADAS-Cog11, was not met. At Week 52, the difference between sembragiline and placebo in ADAS-Cog11 change from baseline was – 0.15 (p = 0.865) and 0.90 (p = 0.312) for 1 and 5 mg groups, respectively. Relative to placebo at Week 52 (but not at prior assessment times), the 1 mg and 5 mg sembragiline groups showed differences in ADCS-ADL of 2.64 (p = 0.051) and 1.89 (p = 0.160), respectively. A treatment effect in neuropsychiatric symptoms (as assessed by the difference between sembragiline and placebo on BEHAVE-AD-FW) was also seen at Week 52 only: – 2.80 (p = 0.014; 1 mg) and – 2.64 (p = 0.019; 5 mg), respectively. A post hoc subgroup analysis revealed greater treatment effects on behavior and functioning in patients with more severe baseline behavioral symptoms (above the median).

Conclusions: This study showed that sembragiline was well-tolerated in patients with moderate AD. The study missed its primary and secondary endpoints. Post hoc analyses suggested potential effect on neuropsychiatric symptoms and functioning in more behaviorally impaired study population at baseline.