Design, synthesis and biological evaluation of rasagiline-clorgyline hybrids as novel dual inhibitors of monoamine oxidase-B and amyloid-ß aggregation against Alzheimer's disease.

A series of rasagiline-clorgyline hybrids was designed, synthesized and investigated in vitro for their inhibition of monoamine oxidase and amyloid-ß aggregation. Most of compounds were found to be selective and highly potent hMAO-B inhibitors showing IC50 values in the nanomolar, and exhibited a moderate inhibition of amyloid-ß aggregation. 7-((5-(methyl(prop-2-yn-1-yl)amino) pentyl)oxy)chroman-4-one (6j) was the most interesting compound identified in this research, endowed with higher hMAO-B potency (IC50 = 4 nM) and selectivity (SI > 25000) compared to the reference selective inhibitor rasagiline (IC50 = 141 nM, SI > 355), and exhibited good inhibitory activity against Aß1-42 aggregation (40.78%, 25 µM). Kinetic and molecular modeling studies revealed that 6j was a competitive reversible inhibitor for hMAO-B. Moreover, compound 6j displayed low toxicity and good neuroprotective effects in SH-SY5Y cell assay, and could penetrate the blood-brain barrier according to the parallel artificial membrane permeability assay. Pharmacokinetics assay revealed that compound 6j possessed good pharmacokinetic profiles after intravenous and oral administrations. Overall, these results highlighted that compound 6j was an effective and promising multitarget agent against Alzheimer's disease.

Discovery of novel 2,3-dihydro-1H-inden-1-amine derivatives as selective monoamine oxidase B inhibitors.

Inhibition of MAO-B has been an effective strategy for the treatment of Parkinson's disease. To find more potent and selective MAO-B inhibitors with novel chemical scaffold, we designed and synthesized a series of new 2,3-dihydro-1H-inden-1-amine derivatives on basis of our previous study. Furthermore, the corresponding structure-activity relationship (SAR) of these compounds is detailedly discussed. Compounds L4 (IC50 = 0.11 µM), L8 (IC50 = 0.18 µM), L16 (IC50 = 0.27 µM) and L17 (IC50 = 0.48 µM) showed similar MAO-B inhibitory activity as Selegiline. Moreover, L4, L16 and L17 also exhibited comparable selectivity with Selegiline, indicating that L4, L16 and L17 could be promising selective MAO-B inhibitors for further study.

Membrane Reconstitution of Monoamine Oxidase Enzymes on Supported Lipid Bilayers.

Monoamine oxidase A and B (MAO-A and B) are mitochondrial outer membrane enzymes that are implicated in a number of human diseases, and the pharmacological inhibition of these enzymes is a promising therapeutic strategy to alleviate disease symptoms. It has been suggested that optimal levels of enzymatic activity occur in the membrane-associated state, although details of the membrane association process remain to be understood. Herein, we have developed a supported lipid bilayer platform to study MAO-A and B binding and evaluate the effects of known pharmacological inhibitors on the membrane association process. By utilizing the quartz crystal microbalance-dissipation (QCM-D) technique, it was determined that both MAOs exhibit tight binding to negatively and positively charged bilayers with distinct concentration-dependent binding profiles while only transiently binding to neutral bilayers. Importantly, in the presence of known inhibitors, the MAOs showed increased binding to negatively charged bilayers, although there was no effect of inhibitor treatment on binding to positively charged bilayers. Taken together, our findings establish that the membrane association of MAOs is highly dependent on membrane surface charge, and we outline an experimental platform to support the in vitro reconstitution of monoamine oxidases on synthetic membranes, including the evaluation of pharmacological drug candidates.

Selective inhibition of monoamine oxidase A by hispidol.

Hispidol, an aurone, isolated from Glycine max Merrill, was found to potently and selectively inhibit an isoform of recombinant human monoamine oxidase-A (MAO-A), with an IC50 value of 0.26 µM, and to inhibit MAO-B, but with lower potency (IC50 = 2.45 µM). Hispidol reversibly and competitively inhibited MAO-A with a Ki value of 0.10 µM with a potency much greater than toloxatone (IC50 = 1.10 µM), a marketed drug. It also reversibly and competitively inhibited MAO-B (Ki = 0.51 µM). Sulfuretin, an analog of hispidol, effectively inhibited MAO-A (IC50 = 4.16 µM) but not MAO-B (IC50 > 80 µM). A comparison of their chemical structures showed that the 3'-hydroxyl group of sulfuretin might reduce its inhibitory activities against MAO-A and MAO-B. Flexible docking simulation revealed that the binding affinity of hispidol for MAO-A (-9.1 kcal/mol) was greater than its affinity for MAO-B (-8.7 kcal/mol). The docking simulation showed hispidol binds to the major pocket of MAO-A or MAO-B. The findings suggest hispidol is a potent, selective, reversible inhibitor of MAO-A, and that it be considered a novel lead compound for development of novel reversible inhibitors of MAO-A.

Kinetic and structural analysis of the irreversible inhibition of human monoamine oxidases by ASS234, a multi-target compound designed for use in Alzheimer's disease.

Monoamine oxidases (MAO) and cholinesterases are validated targets in the design of drugs for the treatment of Alzheimer's disease. The multi-target compound N-((5-(3-(1-benzylpiperidin-4-yl)propoxy)-1-methyl-1H-indol-2-yl)methyl)-N-methylprop-2-yn-1-amine (ASS234), bearing the MAO-inhibiting propargyl group attached to a donepezil moiety that inhibits cholinesterases, retained activity against human acetyl- and butyryl-cholinesterases. The inhibition of MAO A and MAO B by ASS234 was characterized and compared to other known MAO inhibitors. ASS234 was almost as effective as clorgyline (kinact/KI=3×10(6) min(-1)M(-1)) and was shown by structural studies to form the same N5 covalent adduct with the FAD cofactor.

Coupling of a high-resolution monoamine oxidase-A inhibitor assay and HPLC-SPE-NMR for advanced bioactivity profiling of plant extracts.

INTRODUCTION: Depression is a mental disease causing large personal and socio-economic problems, and new improved drugs are therefore needed. Selective monoamine oxidase A (MAO-A) inhibitors are potential anti-depressants, but discovering new MAO-A inhibitors from natural sources by bioassay-guided approaches are a lengthy and time-consuming process. New analytical technologies that allow simultaneously chemical and biological screening of extracts are therefore urgently needed. METHOD: In the present study we describe coupling of a photometric microplate-based high-resolution MAO-A inhibitor assay with a hyphenated system consisting of high-performance liquid chromatography, solid-phase extraction and tube transfer nuclear magnetic resonance (HPLC-SPE-ttNMR). The standard compound clorgyline, and an extract of black pepper (Piper nigrum L.), representing a complex plant matrix, were used for proof-of-concept. RESULTS: The work with clorgyline showed that the microplate-based high-resolution assay produced MAO-A inhibition profiles that easily allowed detection of submicrogram amounts of this selective MAO-A inhibitor. Furthermore, the HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform allowed identification of piperine and two piperine analogues as the main MAO-A inhibitors in the black pepper petroleum ether extract. CONCLUSION: The HPLC-SPE-ttNMR/high-resolution MAO-A inhibition assay platform is a powerful tool for fast and efficient identification of new MAO-A inhibitors from complex extracts, and promise future advancement in the search for new anti-depressants from natural sources.

Evaluation of the oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to toxic pyridinium cations by monoamine oxidase (MAO) enzymes and its use to search for new MAO inhibitors and protective agents.

Monoamine oxidase (MAO) enzymes catalyze the oxidative deamination of amines and neurotransmitters and inhibitors of MAO are useful as neuroprotectants. This work evaluates the human MAO-catalyzed oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a dopaminergic neurotoxin, to the directly-acting neurotoxic metabolites, 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP(+)) and 1-methyl-4-phenylpyridinium (MPP(+)) measured by High-Performance Liquid Chromatography (HPLC), and this approach is subsequently used as a new method for screening of MAO inhibitors and protective agents. Oxidation of MPTP by human MAO-B was more efficient than by MAO-A. R-Deprenyl, a known neuroprotectant, norharman (ß-carboline), 5-nitroindazole and menadione (vitamin K3) inhibited MAO-B and reduced the formation of toxic pyridinium cations. Clorgyline and the ß-carbolines, harman and norharman, inhibited the oxidation of MPTP by MAO-A. Cigarette smoke, as well as the naturally occurring ß-carbolines (norharman and harman) isolated from smoke and coffee inhibited the oxidation of MPTP by MAO-B and/or MAO-A, suggesting protective effects against MPTP. The results show the suitability of the approach used to search for new MAO inhibitors with eventual neuroprotective activity.

Eugenol and its structural analogs inhibit monoamine oxidase A and exhibit antidepressant-like activity.

Eugenol (1) is an active principle of Rhizoma acori graminei, a medicinal herb used in Asia for the treatment of symptoms reminiscent of Alzheimer's disease (AD). It has been shown to protect neuronal cells from the cytotoxic effect of amyloid beta peptides (Abetas) in cell cultures and exhibit antidepressant-like activity in mice. Results from this study show that eugenol inhibits monoamine oxidase A (MAOA) preferentially with a K(i)=26 microM. It also inhibits MAOB but at much higher concentrations (K(i)=211 microM). In both cases, inhibition is competitive with respect to the monoamine substrate. Survey of compounds structurally related to eugenol has identified a few that inhibit MAOs more potently. Structure activity relationship reveals structural features important for MAOA and MAOB inhibition. Molecular docking experiments were performed to help explain the SAR outcomes. Four of these compounds, two (1, 24) inhibiting MAOA selectively and the other two (19, 21) inhibiting neither MAOA nor MAOB, were tested for antidepressant-like activity using the forced swim test in mice. Results suggest a potential link between the antidepressant activity of eugenol and its MAOA inhibitory activity.

Sulfur-substituted alpha-alkyl phenethylamines as selective and reversible MAO-A inhibitors: biological activities, CoMFA analysis, and active site modeling.

A series of phenethylamine derivatives with various ring substituents and with or without N-methyl and/or C-alpha methyl or ethyl groups was synthesized and assayed for their ability reversibly to inhibit monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). Several compounds showed potent and selective MAO-A inhibitory activity (IC(50) in the submicromolar range) but none showed appreciable activity toward MAO-B. A three-dimensional quantitative structure-activity relationship study for MAO-A inhibition was performed on the series using comparative molecular field analysis (CoMFA). The resulting model gave a cross-validated q(2) of 0.72 and showed that in this series of compounds steric properties of the substituents were more important than electrostatic effects. Molecular modeling based on the recently published crystal structure of inhibitor-bound MAO-A provided detailed evidence for specific interactions of the ligands with the enzyme, supported by previous references and consistent with results from the CoMFA. On the basis of these results, structural determinants for selectivity of substituted amphetamines for MAO-A are discussed.

Crystallization and preliminary crystallographic analysis of rat monoamine oxidase A complexed with clorgyline.

Monoamine oxidase (MAO) is an FAD-containing mitochondrial outer-membrane protein which catalyzes the degradation of several neurotransmitters in the central nervous system. The two subtypes of MAO, MAOA and MAOB, have similar primary sequences but different substrate and inhibitor specificities. The structure of human MAOB has recently been determined, but the structure of MAOA remains unknown. To clarify the mechanisms underlying their unique substrate and inhibitor recognition and thereby facilitate the development of new specific inhibitors to treat MAO-related neurological disorders, rat MAOA was crystallized in a complex with the specific inhibitor clorgyline. Diffraction data were collected to 3.2 A resolution. The crystal belongs to the space group P4(3)2(1)2, with unit-cell parameters a = b = 158.2, c = 258.4 A.

Strategy for the formation of parametric images under conditions of low injected radioactivity applied to PET studies with the irreversible monoamine oxidase A tracers [11C]clorgyline and deuterium-substituted [11C]clorgyline.

The construction of parametric positron emission tomography images of enzyme or receptor concentration obtained using irreversibly binding radiotracers presents problems not usually encountered with reversibly binding radiotracers. Difficulties are most apparent in brain regions having low blood flow and/or high enzyme or receptor concentration and are exacerbated with noisy data. This is especially true when minimal doses of radiotracer are administered. A comparison was recently reported of the irreversible monoamine oxidase A (MAO A) radiotracers [11C]clorgyline (CLG) and deuterium-substituted [11C]clorgyline (CLG-D) in the human brain using region of interest (ROI) analysis in which the authors observed an unexpected loss of image contrast with CLG-D compared with CLG. In order to more fully investigate patterns of binding of these irreversibly binding radiotracers, a strategy was devised to reduce noise in the generation of parametric images of the model term related to enzyme or receptor concentration. The generalized linear least squares (GLLS) method of Feng et al. (1995), a rapid linear method that is unbiased, was used for image-wide parameter estimation. Since GLLS can fail in the presence of large amounts of noise, local voxels were grouped within the image to increase the signal, and the GLLS method was combined with the standard nonlinear estimation methods when necessary. Voxels were grouped together depending on their proximity and whether they fell within a specified range of the time-integrated image. It was assumed that voxels meeting both criteria are functionally related. Simulations reflecting varying enzyme concentrations were performed to assess precision and accuracy of parameter estimates in the presence of varying amounts of noise. Using this approach, images were generated of the combination parameter lambdak3 (lambda = K1/k2, where K1 and k2 are plasma-to-tissue and tissue-to-plasma transport constants, respectively) that is related to enzyme concentration as well as images of the transport constant K1 for individual subjects. Reasonably high-quality images of both K1 and lambdak3 were obtained for CLG and CLG-D for individual subjects even with low injected doses averaging 6 mCi. While there were no differences in the K1 images, the lambdak3 images revealed the loss of contrast previously reported for CLG-D using the ROI analysis. This method should be generalizable to other tracers and should facilitate the analysis of group differences.

Synthesis and characterization of 11C-labeled fluoroclorgyline: a monoamine oxidase A specific inhibitor for positron emission tomography.

A new radioligand for monoamine oxidase type A (MAO-A), [11C]fluoroclorgyline, was synthesized from its desmethyl precursor by N-methylation reaction using [11C]methyl iodide with a radiochemical yield of 75-85%. The radiochemical purity of the product was more than 99% and the specific radioactivity was 7.4-18.5 GBq/micromol. The in vivo tissue distribution studies of [11C]fluoroclorgyline in mice demonstrated its high initial uptake and prolonged retention in the brain, comparable to those of [11C]clorgyline. A selective interaction with MAO-A in the accumulation of [11C]fluorclorgyline was confirmed by a competition experiment performed with the MAO-A specific inhibitor,clorgyline, and MAO-B specific inhibitor, l-deprenyl. These very desirable characteristics of [11C]fluoroclorgyline suggested that its 18F labeled counterpart, [18F]fluoroclorgyline, would have great potential as a longer-lived alternative to 11C labeled clorgyline for in vivo studies of MAO-A in the human brain with positron emission tomography (PET).