Is Phytomelatonin Complex Better Than Synthetic Melatonin? The Assessment of the Antiradical and Anti-Inflammatory Properties.

This work aims to assess the recently established anti-inflammatory and antioxidant potential of melatonin of plant origin extracted from the plant matrix as a phytomelatonin complex (PHT-MLT), and compare its activity with synthetic melatonin (SNT-MLT) when used on its own or with vitamin C. For this purpose, a COX-2 enzyme inhibitory activity test, an antiradical activity in vitro and on cell lines assays, was performed on both PHT-MLT and SNT-MLT products. COX-2 inhibitory activity of PHT-MLT was found to be ca. 6.5 times stronger than that of SNT-MLT (43.3% and 6.7% enzyme inhibition, equivalent to the activity of acetylsalicylic acid in conc. 30.3 ± 0.2 and 12.0 ± 0.3 mg/mL, respectively). Higher antiradical potential and COX-2 inhibitory properties of PHT-MLT could be explained by the presence of additional naturally occurring constituents in alfalfa, chlorella, and rice, which were clearly visible on the HPLC-ESI-QTOF-MS fingerprint. The antiradical properties of PHT-MLT determined in the DPPH test (IC50 of 21.6 ± 1 mg of powder/mL) were found to originate from the presence of other metabolites in the 50% EtOH extract while SNT-MLT was found to be inactive under the applied testing conditions. However, the antioxidant studies on HaCaT keratinocytes stimulated with H2O2 revealed a noticeable activity in all samples. The presence of PHT-MLT (12.5, 25 and 50 µg/mL) and vitamin C (12.5, 25 and 50 µg/mL) in the H2O2-pretreated HaCaT keratinocytes protected the cells from generating reactive oxygen species. This observation confirms that MLT-containing samples affect the intracellular production of enzymes and neutralize the free radicals. Presented results indicated that MLT-containing products in combination with Vitamin C dosage are worth to be considered as a preventive alternative in the therapy of various diseases in the etiopathogenesis, of which radical and inflammatory mechanisms play an important role.

Selective Pseudo-irreversible Butyrylcholinesterase Inhibitors Transferring Antioxidant Moieties to the Enzyme Show Pronounced Neuroprotective Efficacy In Vitro and In Vivo in an Alzheimer's Disease Mouse Model.

A series of multitarget-directed ligands (MTDLs) was designed by functionalizing a pseudo-irreversible butyrylcholinesterase (BChE) inhibitor. The obtained hybrids were investigated in vitro regarding their hBChE and hAChE inhibition, their enzyme kinetics, and their antioxidant physicochemical properties (DPPH, ORAC, metal chelating). In addition, in vitro assays were applied to investigate antioxidant effects using murine hippocampal HT22 cells and immunomodulatory effects on the murine microglial N9 cell line. The MTDLs retained their antioxidative properties compared to the parent antioxidant-moieties in vitro and the inhibition of hBChE was maintained in the submicromolar range. Representative compounds were tested in a pharmacological Alzheimer's disease (AD) mouse model and demonstrated very high efficacy at doses as low as 0.1 mg/kg. The most promising compound was also tested in BChE-/- mice and showed reduced efficacy. In vivo neuroprotection by BChE inhibition can be effectively enhanced by incorporation of structurally diverse antioxidant moieties.

N-Nitrosomelatonin, an efficient nitric oxide donor and transporter in Arabidopsis seedlings.

Nitric oxide (NO) produced in plant cells has the unique ability to interact with various other biomolecules, thereby facilitating its own as well as their signaling and associated actions at their sites of biosynthesis and at other sites via transcellular long distance transport of the molecular complexes. Melatonin (Mel) is one such biomolecule produced in plant cells which has fascinated plant biologists with regard to its molecular crosstalk with other molecules to serve its roles as a growth regulator. Present work reports the synthesis of N-nitrosomelatonin (NOMela) and its preferential uptake by Arabidopsis seedlings roots and long distance transport to the leaves through vascular strands. Equimolar (250 µM) concentrations of NOMela and S-nitrosoglutathione (GSNO) in aqueous solutions bring about 52.8% more release of NO from NOMela than from GSNO. Following confocal laser scanning microscopic (CLSM) imaging, Pearson's correlation coefficient analysis of the Scatter gram of endogenously taken up NOMela demonstrates significant NO signal in roots emanating from mitochondria. NOMela (250 µM) taken up by Arabidopsis seedling roots also proved more efficient as a NO transporter from primary root to leaves than 250 µM of GSNO. These novel observations on NOMela thus hold promise to decipher its crucial role as a NO carrier and reservoir in plant cells, and also as a facilitator of melatonin action in plant development.

Melatonin derivatives combat with inflammation-related cancer by targeting the Main Culprit STAT3.

The combination between two well-studied bioactive compounds melatonin and salicylic acid with proper modifications unexpectedly creates a sharp pair of "scissors" cutting off the vicious connection between inflammation and cancer by targeting a key contributor Signal Transducers and Activators of Transcription 3 (STAT3) in the two pathological processes. A representative compound P-3 with IC50 values on each tested cell line ranging from 7.37 to 18.62 µM among the designed melatonin derivatives is equipped with the ability of curbing inflammation-promoting cancer by down-regulating the expression, activation and nuclear translocation of STAT3, breaking the feedforward loop of STAT3 activation by decreasing the expression of pro-tumorigenic cytokines, and inducing cell apoptosis through ROS triggered Cyto-c/Caspase-3 pathway. This study suggests that the melatonin derivative P-3 is likely to become a promising chemical structure for developing the novel anti-cancer agents taking effect through hindering the mutual-promoting processes between inflammation and cancer.

New indole-7-aldehyde derivatives as melatonin analogues; synthesis and screening their antioxidant and anticancer potential.

Over the last decade, there has been substantial interest in the use of melatonin (MLT) and MLT-like compounds in the treatment of several diseases. MLT can scavenge different reactive oxygen species and can also stimulate the synthesis of antioxidant enzymes. Our ongoing study relies on changing the groups in the different modifiable sites of the indole ring to increase the antioxidant activity. In this study a new approach for substitution of indole ring as indole based MLT analogue was proposed. We report the synthesis and characterization of a series of new indole-7-aldehyde hydrazide/hydrazone derivatives as indole-based MLT analogues. Anticancer potential of the compounds were evaluated both by their antioxidant and CYP1 inhibitory activities. In vitro antioxidant capacity of the compounds was investigated both in a cell-based (DCFH assay) and a cell-free (DPPH assay) assay. Potential inhibitory effects of the compounds on CYP1 catalytic activity were investigated via EROD assay. Cytotoxic activity of the compounds was further evaluated by the MTT assay in CHO-K1 cells. MLT analogues having an o-halogenated aromatic moiety exhibited effective antioxidant properties without having any cytotoxic effect. In conclusion, MLT derivatives represent promising scaffolds for discovery of effective antioxidant agents.

Design, Synthesis, and Biological Activity of Hydrogen Peroxide Responsive Arylboronate Melatonin Hybrids.

Stimulus-responsive cleavage reactions have found broad use to direct drug release at a particular target disease area. Increased levels of reactive oxygen species (ROS) have been associated with the development and progression of cancer and several other disease states, motivating the development of drug conjugates that can undergo a chemoselective ROS-triggered release. Melatonin (MLT) and the reactive electrophile p-benzoquinone methide ( p-QM) have evidenced either cytoprotective or cytotoxic effects in biological systems, depending on the dose, cellular targets, and time of exposure. In this study, we report the synthesis and biological activity of two MLT derivatives linked to ROS-responsive arylboronate triggers (P1 and P2), which can be activated by endogenously generated hydrogen peroxide (H2O2) to release MLT, or 5-methoxytryptamine (5-MeOT), and p-QM-intermediates. Their H2O2-induced activation mechanism was studied by HPLC-DAD-MS. P1, which rapidly releases MLT and p-QM, was able to strongly induce the Nrf2 antioxidant signaling pathway, but was ineffective to provide protection against H2O2-mediated oxidative damage. By contrast, P1 exhibited strong toxic effects in HeLa cancer cells, without causing significant toxicity to normal NCTC-2544 cells. Similar, although more limited, effects were exerted by P2. In both cases, cytotoxicity was accompanied by depletion of cellular glutathione (GSH), probably as a consequence of p-QM release, and increased ROS levels. A role for MLT in toxicity was also observed, suggesting that the P1 released products, MLT and p-QM, contributed additively to promote cell death.

Melatonin as a versatile molecule to design novel multitarget hybrids against neurodegeneration.

Melatonin is an indoleamine produced mainly in the pineal gland. The natural decline of melatonin levels with aging strongly contributes to the development of neurodegenerative disorders. Pleiotropic actions displayed by melatonin prevent several processes involved in neurodegeneration such as neuroinflammation, oxidative stress, excitotoxicity and/or apoptosis. This review focuses on a number of melatonin hybrids resulting from the juxtaposition of tacrine, berberine, tamoxifen, curcumin, N,N-dibenzyl(N-methyl)amine, among others, with potential therapeutic effects for the treatment of neurodegenerative diseases.

[Novel agonists of melatonin receptors as promising hypotensive and neuroprotective agents for therapy of glaucoma]. / Novye agonisty melatoninovykh retseptorov kak perspektivnye gipotenzivnye i neiroprotektornye sredstva dlia terapii glaukomy.

Melatonin is a pineal hormone that has a capacity to lower intraocular pressure; it exhibits neuroprotective and antioxidant properties that make it possible to use melatonin in the therapy of glaucoma. Analogs of melatonin having affinity to melatonin receptors are promising candidates for application as antiglaucomatous drugs. Chemical modification of the melatonin structure can in-crease efficiency, bioavailability and selectivity of these analogs. We have designed and synthe-sized a number of new 2-oxindole derivatives - ligands of melatonin MT3 subtype receptors that displayed ability to lower intraocular pressure in normotensive rabbits and high antioxidant activity against hydroxyl radical and superoxide anion-radical. The antioxidant activity of new ligands was several times higher than one of melatonin that makes them prospective therapeutic tools for the diseases that include oxidative stress. The maximal hypotensive effect of analogs was comparable to that of melatonin itself but prolonged. Combination of these properties gives an opportunity of using the presented melatonin analogs in complex therapy of glaucoma.

The Antioxidant Additive Approach for Alzheimer's Disease Therapy: New Ferulic (Lipoic) Acid Plus Melatonin Modified Tacrines as Cholinesterases Inhibitors, Direct Antioxidants, and Nuclear Factor (Erythroid-Derived 2)-Like 2 Activators.

Novel multifunctional tacrines for Alzheimer's disease were obtained by Ugi-reaction between ferulic (or lipoic acid), a melatonin-like isocyanide, formaldehyde, and tacrine derivatives, according to the antioxidant additive approach in order to modulate the oxidative stress as therapeutic strategy. Compound 5c has been identified as a promising permeable agent showing excellent antioxidant properties, strong cholinesterase inhibitory activity, less hepatotoxicity than tacrine, and the best neuroprotective capacity, being able to significantly activate the Nrf2 transcriptional pathway.

Synthesis and evaluation of multi-target-directed ligands for the treatment of Alzheimer's disease based on the fusion of donepezil and melatonin.

A novel series of compounds obtained by fusing the acetylcholinesterase (AChE) inhibitor donepezil and the antioxidant melatonin were designed as multi-target-directed ligands for the treatment of Alzheimer's disease (AD). In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (eqBuChE and hBuChE), and ß-amyloid (Aß) aggregation, and to act as potential antioxidants and biometal chelators. Especially, 4u displayed a good inhibition of AChE (IC50 value of 193nM for eeAChE and 273nM for hAChE), strong inhibition of BuChE (IC50 value of 73nM for eqBuChE and 56nM for hBuChE), moderate inhibition of Aß aggregation (56.3% at 20µM) and good antioxidant activity (3.28trolox equivalent by ORAC assay). Molecular modeling studies in combination with kinetic analysis revealed that 4u was a mixed-type inhibitor, binding simultaneously to catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 4u could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Taken together, these results strongly indicated the hybridization approach is an efficient strategy to identify novel scaffolds with desired bioactivities, and further optimization of 4u may be helpful to develop more potent lead compound for AD treatment.

Modular Approach to 9-Monosubstituted Fluorene Derivatives Using Mo(V) Reagents.

Oxidative coupling using molybdenum(V) reagents provides fast access to highly functionalized 9-monosubstituted fluorenes. This synthetic approach is highly modular, is high yielding, and tolerates a variety of labile moieties, e.g. amides or iodo groups. The established protocol leads to promising precursors for pharmacologically important analogues of melatonin.

Neurogenic Potential Assessment and Pharmacological Characterization of 6-Methoxy-1,2,3,4-tetrahydro-ß-carboline (Pinoline) and Melatonin-Pinoline Hybrids.

6-Methoxy-1,2,3,4-tetrahydro-ß-carboline (pinoline) and N-acetyl-5-methoxytryptamine (melatonin) are both structurally related to 5-hydroxytryptamine (serotonin). Here we describe the design, synthesis, and characterization of a series of melatonin rigid analogues resulting from the hybridization of both pinoline and melatonin structures. The pharmacological evaluation of melatonin-pinoline hybrids comprises serotonergic and melatonergic receptors, metabolic enzymes (monoamine oxidases), antioxidant potential, the in vitro blood-brain barrier permeability, and neurogenic studies. Pinoline at trace concentrations and 2-acetyl-6-methoxy-1,2,3,4-tetrahydro-ß-carboline (2) were able to stimulate early neurogenesis and neuronal maturation in an in vitro model of neural stem cells isolated from the adult rat subventricular zone. Such effects are presumably mediated via serotonergic and melatonergic stimulation, respectively.

Anti-inflammatory activities of melatonin derivatives in lipopolysaccharide-stimulated RAW 264.7 cells and antinociceptive effects in mice.

Preclinical Research This study describes the anti-inflammatory activities of two semisynthesized melatonin (MT) derivatives, benzoyl-melatonin (BMT) and acetyl-melatonin (AMT), on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated macrophage cells (RAW 264.7) and their antinociceptive effects in mice. The MT derivatives inhibited production of nitric oxide NO and prostaglandin E2 in LPS-stimulated RAW264.7 cells in a dose-dependent manner with IC50 values lower than those of MT. BMT produced increased tail flick latency time, decreased number of writhes, and reduced nociceptive response in mice when compared with AMT and MT. BMT and AMT had enhanced anti-inflammatory effects in LPS-stimulated RAW264.7 compared with MT. However, in mouse studies BMT exhibited the highest potency as an anti-inflammatory agent and was longer-acting as an antinociceptive compound compared with AMT or MT, suggesting that BMT has potential as an anti-inflammatory and analgesic compound.

Synthetic indole and melatonin derivatives exhibit antimalarial activity on the cell cycle of the human malaria parasite Plasmodium falciparum.

Discovering the mechanisms by which cell signaling controls the cell cycle of the human malaria parasite Plasmodium falciparum is fundamental to designing more effective antimalarials. To better understand the impacts of melatonin structure and function on the cell cycle of P. falciparum, we have synthesized two families of structurally-related melatonin compounds (7-11 and 12-16). All synthesized melatonin analogs were assayed in P. falciparum culture and their antimalarial activities were measured by flow cytometry. We have found that the chemical modification of the carboxamide group attached at C-3 position of the indole ring of melatonin (6) was crucial for the action of the indole-related compounds on the P. falciparum cell cycle. Among the melatonin derivatives, only the compounds 12, 13 and 14 were capable of inhibiting the P. falciparum growth in low micromolar IC50. These results open good perspectives for the development of new drugs with novel mechanisms of action.

Antioxidant activity of indole-based melatonin analogues in erythrocytes and their voltammetric characterization.

Melatonin (MLT) is a strong free-radical scavenger, which protects the body from the effects of oxidants. In recent years, MLT have been described resulting in much attention in the development of synthetic compounds possessing. As a part of our ongoing study a series of indole-based MLT analogue hydrazide/hydrazone derivatives were synthesized, characterized and in vitro antioxidant activity was investigated by evaluating their reducing effect against oxidation of a redox sensitive fluorescent probe. Membrane stabilizing effect of all compounds was also investigated by lactate dehydrogenase leakage assay. Furthermore voltammetric methods have been applied to the synthesized compounds to characterize oxidation potentials to get insight into their metabolism owing to the oxidation mechanisms taking place at the electrode and in the body share similar principles.

Synthesis of novel МТ3 receptor ligands via an unusual Knoevenagel condensation.

New 5-acetamido-substituted melatonin derivatives were efficiently synthesized in excellent yields via Knoevenagel condensation. The relative binding affinity of new synthesized compounds to MT3 receptor was tested via enzymatic assays and the X-ray structures of the most potent compounds were determined in complex with MT3.

Melatonin synthetic analogs as nitric oxide synthase inhibitors.

Nitric oxide (NO), which is produced by oxidation of L-arginine to L-citrulline in a process catalyzed by different isoforms of nitric oxide synthase (NOS), exhibits diverse roles in several physiological processes, including neurotransmission, blood pressure regulation and immunological defense mechanisms. On the other hand, an overproduction of NO is related with several disorders as Alzheimer's disease, Huntington's disease and the amyotrophic lateral sclerosis. Taking melatonin as a model, our research group has designed and synthesized several families of compounds that act as NOS inhibitors, and their effects on the excitability of N-methyl-D-aspartate (NMDA)-dependent neurons in rat striatum, and on the activity on both nNOS and iNOS were evaluated. Structural comparison between the three most representative families of compounds (kynurenines, kynurenamines and 4,5-dihydro-1H-pyrazole derivatives) allows the establishment of structure-activity relationships for the inhibition of nNOS, and a pharmacophore model that fulfills all of the observed SARs were developed. This model could serve as a template for the design of other potential nNOS inhibitors. The last family of compounds, pyrrole derivatives, shows moderate in vitro NOS inhibition, but some of these compounds show good iNOS/nNOS selectivity. Two of these compounds, 5-(2-aminophenyl)-1H-pyrrole-2-carboxylic acid methylamide and cyclopentylamide, have been tested as regulators of the in vivo nNOS and iNOS activity. Both compounds prevented the increment of the inducible NOS activity in both cytosol (iNOS) and mitochondria (i-mtNOS) observed in a MPTP model of Parkinson's disease.

Synthesis and comparison of antioxidant properties of indole-based melatonin analogue indole amino Acid derivatives.

Increased levels of reactive oxygen species attributed to oxidative stress have been found to be responsible for the development of some vital diseases such as cardiovascular, neurodegenerative and autoimmune diseases. Recently, it was observed that melatonin is a highly important antioxidant, and melatonin analogues are under investigation to find out improved antioxidant activity. In this study, 14 melatonin -based analogue indole amino acid and N-protected amino acid derivatives were synthesized and elucidated spectrometrically. To investigate the antioxidant activity of the synthesized compounds and to compare with melatonin, butylhydroxytoluene and vitamin E, lipid peroxidation inhibition and 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activities were tested. The results indicated that the synthesized new indole amino acid derivatives have similar activities to melatonin in 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity assay but more potent activities in lipid peroxidation inhibition assay.

N-Acetyl-5-arylalkoxytryptamine analogs: probing the melatonin receptors for MT(1) -selectivity.

A series of melatonin analogs obtained by the replacement of the ether methyl group with larger arylalkyl and aryloxyalkyl substituents was prepared in order to probe the melatonin receptors for MT(1) -selectivity. The most MT(1) -selective agents 11 and 15 were substituted with a Ph(CH(2) )(3) or a PhO(CH(2) )(3) group. Compounds 11 and 15 displayed 11.5-fold and 11-fold higher affinity for the MT(1) receptors than for the MT(2) subtype. Interestingly, in our binding assay 11 and 15 have shown considerably higher MT(1) -affinity and selectivity than the reference ligand, the dimeric agomelatine 1a.

Application of the bridgehead fragments for the design of conformationally restricted melatonin analogues.

Conformationally constrained analogues of the hormone melatonin with a side chain incorporated into the bicyclic bridgehead core were synthesized based on the homology modeling and molecular docking studies performed for the MT(2) melatonin receptor. The methoxy-indole derivative fused with exo-N-acetamino-substituted bicyclo[2.2.2]octane was found to possess nanomolar MT(2) receptor affinity.