The neuroprotective role of melatonin against amyloid beta peptide injected mice

The Vital Role of Melatonin and Its Metabolites in the Neuroprotection and Retardation of Brain Aging

While primarily produced in the pineal gland, melatonin's influence goes beyond its well-known role in regulating sleep, nighttime metabolism, and circadian rhythms, in the field of chronobiology. A plethora of new data demonstrates melatonin to be a very powerful molecule, being a potent ROS/RNS scavenger with anti-inflammatory, immunoregulatory, and oncostatic properties. Melatonin and its metabolites exert multiple beneficial effects in cutaneous and systemic aging. This review is focused on the neuroprotective role of melatonin during aging. Melatonin has an anti-aging capacity, retarding the rate of healthy brain aging and the development of age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, amyotrophic lateral sclerosis, etc. Melatonin, as well as its metabolites, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) and N1-acetyl-5-methoxykynuramine (AMK), can reduce oxidative brain damage by shielding mitochondria from dysfunction during the aging process. Melatonin could also be implicated in the treatment of neurodegenerative conditions, by modifying their characteristic low-grade neuroinflammation. It can either prevent the initiation of inflammatory responses or attenuate the ongoing inflammation. Drawing on the current knowledge, this review discusses the potential benefits of melatonin supplementation in preventing and managing cognitive impairment and neurodegenerative diseases.

Crosstalk between Oxidative Stress and Aging in Neurodegeneration Disorders

The world population is aging rapidly, and increasing lifespan exacerbates the burden of age-related health issues. On the other hand, premature aging has begun to be a problem, with increasing numbers of younger people suffering aging-related symptoms. Advanced aging is caused by a combination of factors: lifestyle, diet, external and internal factors, as well as oxidative stress (OS). Although OS is the most researched aging factor, it is also the least understood. OS is important not only in relation to aging but also due to its strong impact on neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease (AD), and Parkinson's disease (PD). In this review, we will discuss the aging process in relation to OS, the function of OS in neurodegenerative disorders, and prospective therapeutics capable of relieving neurodegenerative symptoms associated with the pro-oxidative condition.

Oxidative Stress and Aging as Risk Factors for Alzheimer's Disease and Parkinson's Disease: The Role of the Antioxidant Melatonin

Aging and neurodegenerative diseases share common hallmarks, including mitochondrial dysfunction and protein aggregation. Moreover, one of the major issues of the demographic crisis today is related to the progressive rise in costs for care and maintenance of the standard living condition of aged patients with neurodegenerative diseases. There is a divergence in the etiology of neurodegenerative diseases. Still, a disturbed endogenous pro-oxidants/antioxidants balance is considered the crucial detrimental factor that makes the brain vulnerable to aging and progressive neurodegeneration. The present review focuses on the complex relationships between oxidative stress, autophagy, and the two of the most frequent neurodegenerative diseases associated with aging, Alzheimer's disease (AD) and Parkinson's disease (PD). Most of the available data support the hypothesis that a disturbed antioxidant defense system is a prerequisite for developing pathogenesis and clinical symptoms of ADs and PD. Furthermore, the release of the endogenous hormone melatonin from the pineal gland progressively diminishes with aging, and people's susceptibility to these diseases increases with age. Elucidation of the underlying mechanisms involved in deleterious conditions predisposing to neurodegeneration in aging, including the diminished role of melatonin, is important for elaborating precise treatment strategies for the pathogenesis of AD and PD.

Multicomponent reactions as a privileged tool for multitarget-directed ligand strategies in Alzheimer's disease therapy

Among neurodegenerative pathologies affecting the older population, Alzheimer's disease is the most common type of dementia and leads to neurocognitive and behavioral disorders. It is a complex and progressive age-related multifactorial disease characterized by a series of highly interconnected pathophysiological processes. Within the last decade, the multitarget-directed ligand strategy has emerged as a viable approach to developing complex molecules that exhibit several pharmacophores which can target the different enzymes and receptors involved in the pathogenesis of the disease. Herein, we focus on using multicomponent reactions such as Hantzsch, Biginelli and Ugi to develop these biologically active multitopic ligands.

Novel melatonin-trientine conjugate as potential therapeutic agents for Alzheimer's disease

Researchers continue to explore drug targets to treat the characteristic pathologies of Alzheimer's disease (AD). Some drugs relieve the pathological processes of AD to some extent, but the failed clinical trials indicate that multifunctional agents seem more likely to achieve the therapy goals for this neurodegenerative disease. Herein, a novel compound named melatonin-trientine (TM) has been covalently synthesized with the natural antioxidant compounds melatonin and the metal ion chelator trientine. After toxicological and pharmacokinetic verification, we elucidated the effects of intraperitoneal administration of TM on AD-like pathology in 6-month-old mice that express both the β-amyloid (Aβ) precursor protein and presenilin-1 (APP/PS1). We found that TM significantly decreased Aβ deposition and neuronal degeneration in the brains of the APP/PS1 double transgenic mice. This result may be due to the upregulation of iron regulatory protein-2 (IRP2), insulin degrading enzyme (IDE), and low density lipoprotein receptor related protein 1 (LRP1), which leads to decreases in APP and Aβ levels. Additionally, TM may promote APP non-amyloidogenic processing by activating the melatonin receptor-2 (MT2)-dependent signaling pathways, but not MT1. In addition, TM plays an important role in blocking γ-secretase, tau hyperphosphorylation, neuroinflammation, oxidative stress, and metal ion dyshomeostasis. Our results suggest that TM may effectively maximize the therapeutic efficacy of targeting multiple mechanisms associated with AD pathology.

New Possibilities in the Therapeutic Approach to Alzheimer’s Disease

Despite the fact that Alzheimer’s disease (AD) is the most common cause of dementia, after many years of research regarding this disease, there is no casual treatment. Regardless of the serious public health threat it poses, only five medical treatments for Alzheimer’s disease have been authorized, and they only control symptoms rather than changing the course of the disease. Numerous clinical trials of single-agent therapy did not slow the development of disease or improve symptoms when compared to placebo. Evidence indicates that the pathological alterations linked to AD start many years earlier than a manifestation of the disease. In this pre-clinical period before the neurodegenerative process is established, pharmaceutical therapy might prove invaluable. Although recent findings from the testing of drugs such as aducanumab are encouraging, they should nevertheless be interpreted cautiously. Such medications may be able to delay the onset of dementia, significantly lowering the prevalence of the disease, but are still a long way from having a clinically effective disease-modifying therapy.

Amelioration of cognitive and biochemical impairment in Aβ-based rodent model of Alzheimer's disease following fractionated X-irradiation

Alzheimer's disease is characterized by deposition of amyloid-beta plaques in the brain. Available pharmaceuticals provide temporary symptomatic relief without affecting disease progression. Use of radiation was found effective in treating extra-cranial amyloidosis, therefore, the present study was designed to investigate the neuroprotective role of fractionated X-irradiation in Aβ_1-42-based rodent model of Alzheimer's disease. S.D. female rats were randomly divided into four groups: sham control (Group 1), Aβ_1-42 injected (Group 2), cranial X-irradiated (Group 3) and Aβ_1-42 injected followed by cranial X-irradiation (Group 4). A single dose of 5 µL Aβ_1-42 peptide was administered through intracerebroventricular (icv) injection in Group 2 and 4 animals, while Group 1 animals were administered 5 µL of bi-distilled water (icv). The group 4 animals were further subjected to 10 Gy X-irradiation (fractionated dose, 2 Gy × 5 days) after 4 weeks of Aβ_1-42 infusion of peptide. The animals in Group 3 were subjected to same dose of cranial fractionated X-irradiation (2 Gy × 5 days) only. Significant decrease in amyloid deposits were observed in the Aβ_1-42 + radiation-treated animals confirmed by histopathological analysis. These finding were in concordance with neurobehavioral tests that showed a significant improvement in Aβ_1-42-induced memory impairment in the animals subjected to fractionated cranial X-irradiation. Restoration of alterations in neurochemical and antioxidant defense indices further supported our results. The present study highlights the underexplored role of fractionated X-irradiation in curtailing the Aβ_1-42-induced neurotoxicity, suggesting a novel treatment option for Alzheimer's disease-associated pathologies.

Role of melatonin in Alzheimer's disease: From preclinical studies to novel melatonin-based therapies

Melatonin and novel melatonin-based therapies such as melatonin-containing hybrid molecules, melatonin analogues, and melatonin derivatives have been investigated as potential therapeutics against Alzheimer's disease (AD) pathogenesis. In this review, we examine the developmental trends of melatonin therapies for AD from 1997 to 2021. We then highlight the neuroprotective mechanisms of melatonin therapy derived from preclinical studies. These mechanisms include the alleviation of amyloid-related burden, neurofibrillary tangle accumulation, oxidative stress, neuroinflammation, apoptosis, mitochondrial dysfunction, and impaired neuroplasticity and neurotransmission. We further illustrate the beneficial effects of melatonin on behavior in animal models of AD. Next, we discuss the clinical effects of melatonin on sleep, cognition, behavior, psychiatric symptoms, electroencephalography findings, and molecular biomarkers in patients with mild cognitive impairment and AD. We then explore the effectiveness of novel melatonin-based therapies. Lastly, we discuss the limitations of current melatonin therapies for AD and suggest two emerging research themes for future study.

Neuroprotective role of Diosgenin, a NGF stimulator, against Aβ (1-42) induced neurotoxicity in animal model of Alzheimer's disease

Diosgenin is a neurosteroid derived from the plants and has been previously reported for its numerous health beneficial properties, such as anti-arrhythmic, hypolipidemic, and antiproliferative effects. Although several studies conducted earlier suggested cognition enhancement actions of diosgenin against neurodegenerative disorders, but the molecular mechanisms underlying are not clearly understood. In the present study, we investigated the neuroprotective effect of diosgenin in the Wistar rats that received an intracerebroventricular injection of Amyloid-β (1-42) peptides, representing a rodent model of Alzheimer's disease (AD). Animals were treated with 100 and 200 mg/kg/p.o of diosgenin for 28 days, followed by Amyloid-β (1-42) peptides infusion. Animals were assessed for the spatial learning and memory by using radial arm maze and passive avoidance task. Subsequently, animals were euthanized and brains were collected for biochemical estimations and histopathological studies. Our results revealed that, diosgenin administration dose dependently improved the spatial learning and memory and protected the animals from Amyloid-β (1-42) peptides induced disrupted cognitive functions. Further, biochemical analysis showed that diosgenin successfully attenuated Amyloid-β (1-42) mediated plaque load, oxidative stress, neuroinflammation and elevated acetylcholinesterase activity. In addition, histopathological evaluation also supported neuroprotective effects of diosgenin in hippocampus of rat brain when assessed using hematoxylin-eosin and Cresyl Violet staining. Thus, the aforementioned effects suggested protective action of diosgenin against Aβ (1-42) induced neuronal damage and thereby can serve as a potential therapeutic candidate for AD.

Donepezil + chromone + melatonin hybrids as promising agents for Alzheimer's disease therapy

We describe herein the design, multicomponent synthesis and biological studies of new donepezil + chromone + melatonin hybrids as potential agents for Alzheimer's disease (AD) therapy. We have identified compound 14n as promising multitarget small molecule showing strong BuChE inhibition (IC50 = 11.90 ± 0.05 nM), moderate hAChE (IC50 = 1.73 ± 0.34 μM), hMAO A (IC50 = 2.78 ± 0.12 μM), and MAO B (IC50 = 21.29 ± 3.85 μM) inhibition, while keeping a strong antioxidant power (3.04 TE, ORAC test). Consequently, the results reported here support the development of new multitarget Donepezil + Chromone + Melatonin hybrids, such as compound 14n, as a potential drug for AD patients cure.

Critical evaluation of current Alzheimer's drug discovery (2018-19) & futuristic Alzheimer drug model approach

Alzheimer's disease (AD), a neurodegenerative disease responsible for death of millions of people worldwide is a progressive clinical disorder which causes neurons to degenerate and ultimately die. It is one of the common causes of dementia wherein a person's incapability to independently think, behave and decline in social skills can be quoted as major symptoms. However the early signs include the simple non-clinical symptoms such as forgetting recent events and conversations. Onset of these symptoms leads to worsened conditions wherein the AD patient suffers severe memory impairment and eventually becomes unable to work out everyday tasks. Even though there is no complete cure for AD, rigorous research has been going on to reduce the progress of AD. Currently, a very few clinical drugs are prevailing for AD treatment. So this is the need of hour to design, develop and discovery of novel anti-AD drugs. The main factors for the cause of AD according to scientific research reveals structural changes in brain proteins such as beta amyloid, tau proteins into plaques and tangles respectively. The abnormal proteins distort the neurons. Despite the high potencies of the synthesized molecules; they could not get on the clinical tests up to human usage. In this review article, the recent research carried out with respect to inhibition of AChE, BuChE, NO, BACE1, MAOs, Aβ, H3R, DAPK, CSF1R, 5-HT4R, PDE, σ₁R and GSK-3β is compiled and organized. The summary is focused mainly on cholinesterases, Aβ, BACE1 and MAOs classes of potential inhibitors. The review also covers structure activity relationship of most potent compounds of each class of inhibitors alongside redesign and remodeling of the most significant inhibitors in order to expect cutting edge inhibitory properties towards AD. Alongside the molecular docking studies of the some final compounds are discussed.

The Nutritional Components of Beer and Its Relationship with Neurodegeneration and Alzheimer's Disease

The prevalence of degenerative diseases has risen in western countries. Growing evidence suggests that demenia and other cognition affectations are associated with ambient factors including specific nutrients, food ingredients or specific dietary patterns. Mediterranean diet adherence has been associated with various health benefits and decreased risk of many diseases, including neurodegenerative disorders. Beer, as part of this protective diet, contains compounds such as silicon and hops that could play a major role in preventing brain disorders. In this review, different topics regarding Mediterranean diet, beer and the consumption of their main compounds and their relation to neurological health have been addressed. Taking into account published results from our group and other studies, the hypothesis linking aluminum intoxication with dementia and/or Alzheimer’s disease and the potential role of regular beer has also been considered. Beer, in spite of its alcohol content, may have some health benefits; nonetheless, its consumption is not adequate for all subjects. Thus, this review analyzed some promising results of non-alcoholic beer on several mechanisms engaged in neurodegeneration such as inflammation, oxidation, and cholinesterase activity, and their contribution to the behavioral modifications induced by aluminum intoxication. The review ends by giving conclusions and suggesting future topics of research related to moderate beer consumption and/or the consumption of its major compounds as a potential instrument for protecting against neurodegenerative disease progression and the need to develop nutrigenetic and nutrigenomic studies in aged people and animal models.

Acute and Chronic Sleep Deprivation-Related Changes in N-methyl-D-aspartate Receptor-Nitric Oxide Signalling in the Rat Cerebral Cortex with Reference to Aging and Brain Lateralization

Aging and chronic sleep deprivation (SD) are well-recognized risk factors for Alzheimer’s disease (AD), with N-methyl-D-aspartate receptor (NMDA) and downstream nitric oxide (NO) signalling implicated in the process. Herein, we investigate the impact of the age- and acute or chronic SD-dependent changes on the expression of NMDA receptor subunits (NR1, NR2A, and NR2B) and on the activities of NO synthase (NOS) isoforms in the cortex of Wistar rats, with reference to cerebral lateralization. In young adult controls, somewhat lateralized seasonal variations in neuronal and endothelial NOS have been observed. In aged rats, overall decreases in NR1, NR2A, and NR2B expression and reduction in neuronal and endothelial NOS activities were found. The age-dependent changes in NR1 and NR2B significantly correlated with neuronal NOS in both hemispheres. Changes evoked by chronic SD (dysfunction of endothelial NOS and the increasing role of NR2A) differed from those evoked by acute SD (increase in inducible NOS in the right side). Collectively, these results demonstrate age-dependent regulation of the level of NMDA receptor subunits and downstream NOS isoforms throughout the rat brain, which could be partly mimicked by SD. As described herein, age and SD alterations in the prevalence of NMDA receptors and NOS could contribute towards cognitive decline in the elderly, as well as in the pathobiology of AD and the neurodegenerative process.

Melatonin in Synaptic Impairments of Alzheimer's Disease

Alzheimer's disease (AD) underlies dementia for millions of people worldwide with no effective treatment. The dementia of AD is thought stem from the impairments of the synapses because of their critical roles in cognition. Melatonin is a neurohormone mainly released by the pineal gland in a circadian manner and it regulates brain functions in various manners. It is reported that both the melatonin deficit and synaptic impairments are present in the very early stage of AD and strongly contribute to the progress of AD. In the mammalian brains, the effects of melatonin are mainly relayed by two of its receptors, melatonin receptor type 1a (MT1) and 1b (MT2). To have a clear idea on the roles of melatonin in synaptic impairments of AD, this review discussed the actions of melatonin and its receptors in the stabilization of synapses, modulation of long-term potentiation, as well as their contributions in the transmissions of glutamatergic, GABAergic and dopaminergic synapses, which are the three main types of synapses relevant to the synaptic strength. The synaptic protective roles of melatonin in AD treatment were also summarized. Regarding its protective roles against amyloid-β neurotoxicity, tau hyperphosphorylation, oxygenation, inflammation as well as synaptic dysfunctions, melatonin may be an ideal therapeutic agent against AD at early stage.

Current advances of pharmacological properties of 7-chloro-4-(phenylselanyl) quinoline: Prevention of cognitive deficit and anxiety in Alzheimer's disease model

This study investigated the effect of 7-chloro-4-(phenylselanyl) quinoline (4-PSQ) at a dose of 1 mg/kg in memory impairment and anxiety in an Alzheimer's disease (AD) model induced by amyloid β-peptide (Aβ) (fragment 25-35) in mice. The involvement of acetylcholinesterase (AChE) activity and lipid peroxidation in hippocampus and cerebral cortex was evaluated. Male Swiss mice were pretreated with 4-PSQ (1 mg/kg, intragastrically (i.g.), daily) for fourteen days. Thirty minutes after the first treatment with 4-PSQ, the animals received a single injection of Aβ (3 nmol/3 μl/per site, intracerebroventricular (i.c.v.)). Mice were submitted to the behavioral tasks (open-field, elevated plus maze, Barnes maze, object recognition and location, and step-down inhibitory avoidance tests) from the fifth day onwards. On the fifteenth day, blood was removed for analysis of biochemical markers (glucose, triglycerides, urea, aspartate (AST) and alanine (ALT) aminotrasferases), and cerebral cortex and hippocampus for determination of AChE activity and thiobarbituric acid reactive species (TBARS) levels. Aβ caused memory impairment, anxiogenic behavior, increased AChE activity in the cerebral structures and TBARS levels in the cerebral cortex. 4-PSQ was effective to protect against behavioral changes, AChE activity and TBARS levels. In conclusion, 4-PSQ protected against learning and memory impairment and anxiety in a mouse model of AD induced by Aβ, and anticholinesterase and antioxidant actions are involved in the pharmacological effect of the compound.

In Vitro Effects of Serotonin, Melatonin, and Other Related Indole Compounds on Amyloid-β Kinetics and Neuroprotection

SCOPE

Amyloid-β peptide is the main component of senile plaques in Alzheimer's disease. The inhibition of amyloid-β peptide assembly, the destabilization of amyloid-β peptide aggregates, and the decrease of its cytotoxicity for the prevention of neuronal death are considered neuroprotective effects. In this work, the protective effects against amyloid-β peptide aggregation and cytotoxicity of eight indolic compounds are evaluated: tryptophan, tryptamine, serotonin, tryptophol, N-acetylserotonin, 3-indoleacetic acid, tryptophan ethyl ester, and melatonin.

METHODS AND RESULTS

Thioflavin T spectroscopic assay, transmission electron microscopy, western blotting, circular dichroism, NMR, cell viability (thiazolyl blue tetrazolium bromide assay), quantitative PCR, and heme oxygenase activity are used. Serotonin is the most effective compound for inhibiting amyloid-β peptide aggregation. Almost all the indolic compounds tested prevent amyloid-β peptide-induced and increase cell viability, being between 9 and 25%. Melatonin and serotonin are the most active. Moreover, serotonin increased the expression of SIRT-1 and 2, heat shock protein 70, and heme oxygenase activity, this being a possible mechanism underlying the observed neuroprotective effect.

CONCLUSION

Melatonin and other related indolic compounds, mainly serotonin, show an inhibitory and destabilizing effect on amyloid-β peptide fibril formation and they possess neuroprotective properties related to the vitagenes system.

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.

Mechanisms of Melatonin in Alleviating Alzheimer's Disease

Alzheimer's disease (AD) is a chronic, progressive and prevalent neurodegenerative disease characterized by the loss of higher cognitive functions and an associated loss of memory. The thus far "incurable" stigma for AD prevails because of variations in the success rates of different treatment protocols in animal and human studies. Among the classical hypotheses explaining AD pathogenesis, the amyloid hypothesis is currently being targeted for drug development. The underlying concept is to prevent the formation of these neurotoxic peptides which play a central role in AD pathology and trigger a multispectral cascade of neurodegenerative processes post-aggregation. This could possibly be achieved by pharmacological inhibition of β- or γ-secretase or stimulating the nonamyloidogenic α-secretase. Melatonin the pineal hormone is a multifunctioning indoleamine. Production of this amphiphilic molecule diminishes with advancing age and this decrease runs parallel with the progression of AD which itself explains the potential benefits of melatonin in line of development and devastating consequences of the disease progression. Our recent studies have revealed a novel mechanism by which melatonin stimulates the nonamyloidogenic processing and inhibits the amyloidogenic processing of β-amyloid precursor protein (βAPP) by stimulating α -secretases and consequently down regulating both β- and γ-secretases at the transcriptional level. In this review, we discuss and evaluate the neuroprotective functions of melatonin in AD pathogenesis, including its role in the classical hypotheses in cellular and animal models and clinical interventions in AD patients, and suggest that with early detection, melatonin treatment is qualified to be an anti-AD therapy.

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.

Alzheimer's disease like pathology induced six weeks after aggregated amyloid-beta injection in rats: increased oxidative stress and impaired long-term memory with anxiety-like behavior

OBJECTIVES

Amyloid-beta (Aβ) peptide deposition into insoluble plaques is a pathological hallmark of Alzheimer's disease (AD), but soluble oligomeric Aβ is considered to be more potent and has been hypothesized to directly impair learning and memory. Also, evidences from some clinical studies indicated that Aβ oligomer formation is the major cause for early AD onset. However, the biochemical mechanism involved in the oligomer-induced toxicity is not very well addressed. So, thise present study was undertaken to study the effects of single intracerebroventricular (icv) injection of protofibrillar Aβ 1-42 on the behavioral and biochemical profile in rats.

METHODS

Rats were divided into two groups (n = 8 per group): (1) sham control group and (2) Aβ 1-42 injected group. A single dose of protofibrillar Aβ 1-42 (5 ul) through icv injection was bilaterally administered into the dorsal hippocampus, while sham control animals were administered with 5 µl of vehicle.

RESULTS

The results demonstrated that the protofibrillar Aβ significantly inhibited long-term memory retention and increased anxiety levels as shown by the behavioral studies. The amyloid deposits were present inside the brain even six weeks after injection as confirmed by thioflavin-T staining and the neurodegeneration induced by these deposits was confirmed by Nissl's staining in hippocampal and cortical regions. The amyloid aggregates induced reactive oxygen species (ROS) production, acetylcholinesterase activity, nitrite levels, lipid peroxidation, and inhibited antioxidant enzyme activity in hippocampus, cortex, and striatum regions of rat brain after six weeks.

DISCUSSION

The present study indicated that protofibrillar Aβ 1-42 injection altered long term memory, induced anxiety-like behavior and also developed Alzheimer's disease like pathology in rats.

Melatonin and Other Tryptophan Metabolites Produced by Yeasts: Implications in Cardiovascular and Neurodegenerative Diseases

Yeast metabolism produces compounds derived from tryptophan, which are found in fermented beverages, such as wine and beer. In particular, melatonin and serotonin, may be relevant due to their bioactivity in humans. Indeed, the former is a neurohormone related to circadian rhythms, which also has a putative protective effect against degenerative diseases. Moreover, serotonin is a neurotransmitter itself, in addition to being a precursor of melatonin synthesis. This paper summarizes data reported on fermented beverages, to evaluate dietary intake. Additionally, the article reviews observed effects of yeast amino acid metabolites on the prevention of neurodegenerative diseases (Alzheimer’s and Parkinson’s) and angiogenesis, focusing on evidence of the molecular mechanism involved and identification of molecular targets.

Emerging Role of the Cerebrospinal Fluid - Neuronal Interface in Neuropathology

The choroid plexus and cerebrospinal fluid have recently begun to emerge as essential regulators of neural function. Factors produced by the choroid plexus are released into the ventricular environment and thus provide a rich source of extracellular signaling molecules throughout the central nervous system. Identified factors in the cerebrospinal fluid include growth factors, hormones, proteins, peptides, lipids, glucose, microRNAs (miRNAs), messenger RNA (mRNA), and enzymes. In addition to mediating neural function, these factors have the potential to serve as biomarkers of disease states. In this review, we highlight recent advances demonstrating the importance of extracellular signaling mechanisms in mediating neural function and provide recent evidence for their role in neuropathology.

The melatonin-N,N-dibenzyl(N-methyl)amine hybrid ITH91/IQM157 affords neuroprotection in an in vitro Alzheimer's model via hemo-oxygenase-1 induction

We have investigated the protective effects of ITH91/IQM157, a hybrid of melatonin and N,N-dibenzyl(N-methyl)amine, in an in vitro model of Alzheimer's disease (AD)-like pathology that combines amyloid beta (Aβ) and tau hyperphosphorylation induced by okadaic acid (OA), in the human neuroblastoma cell line SH-SY5Y. Combination of subtoxic concentrations of Aβ and OA caused a significant toxicity of 40% cell death, which mainly was apoptotic; this effect was accompanied by retraction of the cells' prolongations and accumulation of thioflavin-S stained protein aggregates. In this toxicity model, ITH91/IQM157 (1-1000 nM) reduced cell death measured as MTT reduction; at 100 nM, it prevented apoptosis, retraction of prolongations, and Aβ aggregates. The protective actions of ITH91/IQM157 were blocked by mecamylamine, luzindol, chelerythrine, PD98059, LY294002, and SnPP. We show that the combination of melatonin with a fragment endowed with AChE inhibition in a unique chemical structure, ITH91/IQM157, can reduce neuronal cell death induced by Aβ and OA by a signaling pathway that implicates both nicotinic and melatonin receptors, PKC, Akt, ERK1/2, and induction of hemoxygenase-1.

Melatonin: a "Higgs boson" in human reproduction

As the Higgs boson could be a key to unlocking mysteries regarding our Universe, melatonin, a somewhat mysterious substance secreted by the pineal gland primarily at night, might be a crucial factor in regulating numerous processes in human reproduction. Melatonin is a powerful antioxidant which has an essential role in controlling several physiological reactions, as well as biological rhythms throughout human reproductive life. Melatonin, which is referred to as a hormone, but also as an autocoid, a chronobiotic, a hypnotic, an immunomodulator and a biological modifier, plays a crucial part in establishing homeostatic, neurohumoral balance and circadian rhythm in the body through synergic actions with other hormones and neuropeptides. This paper aims to analyze the effects of melatonin on the reproductive function, as well as to shed light on immunological and oncostatic properties of one of the most powerful hormones.

Coffee and caffeine potentiate the antiamyloidogenic activity of melatonin via inhibition of Aβ oligomerization and modulation of the Tau-mediated pathway in N2a/APP cells

There is an increasing prevalence of Alzheimer's disease (AD), which has become a public health issue. However, the underlying mechanisms for the pathogenesis of AD are not fully understood, and the current therapeutic drugs cannot produce acceptable efficacy in AD patients. Previous animal studies have shown that coffee (Coff), caffeine (Caff), and melatonin (Mel) have beneficial effects on AD. Disturbed circadian rhythms are observed in AD, and chronotherapy has shown promising effects on AD. In this study, we examined whether a combination of Coff or Caff plus Mel produced a synergistic/additive effect on amyloid-β (Aβ) generation in Neuro-2a (N2a)/amyloid precursor protein (APP) cells and the possible mechanisms involved. Cells were treated with Coff or Caff, with or without combined Mel, with three different chronological regimens. In regimen 1, cells were treated with Coff or Caff for 12 hours in the day, followed by Mel for 12 hours in the night. For regimen 2, cells were treated with Coff or Caff plus Mel for 24 hours, from 7 am to 7 am the next day. In regimen 3, cells were treated with Coff or Caff plus Mel with regimen 1 or 2 for 5 consecutive days. The extracellular Aβ40/42 and Aβ oligomer levels were determined using enzyme-linked immunosorbent assay (ELISA) kits. The expression and/or phosphorylation levels of glycogen synthase kinase 3β (GSK3β), Erk1/2, PI3K, Akt, Tau, Wnt3α, β-catenin, and Nrf2 were detected by Western blot assay. The results showed that regimen 1 produced an additive antiamyloidogenic effect with significantly reduced extracellular levels of Aβ40/42 and Aβ42 oligomers. Regimen 2 did not result in remarkable effects, and regimen 3 showed a less antiamyloidogenic effect compared to regimen 1. Coff or Caff, plus Mel reduced oxidative stress in N2a/APP cells via the Nrf2 pathway. Coff or Caff, plus Mel inhibited GSK3β, Akt, PI3K p55, and Tau phosphorylation but enhanced PI3K p85 and Erk1/2 phosphorylation in N2a/APP cells. Coff or Caff, plus Mel downregulated Wnt3α expression but upregulated β-catenin. However, Coff or Caff plus Mel did not significantly alter the production of T helper cell (Th)1-related interleukin (IL)-12 and interferon (IFN)-γ and Th2-related IL-4 and IL-10 in N2a/APP cells. The autophagy of cells was not affected by the combinations. Taken together, combination of Caff or Coff, before treatment with Mel elicits an additive antiamyloidogenic effects in N2a/APP cells, probably through inhibition of Aβ oligomerization and modulation of the Akt/GSK3β/Tau signaling pathway.

ITH12410/SC058: a new neuroprotective compound with potential in the treatment of Alzheimer's disease

The neuroprotective profile of the dibenzothiadiazepine ITH12410/SC058 (2-chloro-5,6-dihydro-5,6-diacetyldibenzo[b,f][1,4,5]thiadiazepine) against several neurotoxicity models related to neurodegenerative diseases is herein described. ITH12410/SC058 protected SH-SY5Y cells against the loss of cell viability elicited by amyloid beta peptide and okadaic acid, a selective inhibitor of phosphoprotein phosphatase 2A that induces neurofibrillary tangle formation. Furthermore, ITH12410/SC058 is neuroprotective against several in vitro models of oxidative stress, that is, H2O2 exposure or incubation with rotenone plus oligomycin A in SH-SY5Y cells, and oxygen and glucose deprivation followed by reoxygenation in rat hippocampal slices. By contrast, ITH12410/SC058 was unable to significantly protect SH-SY5Y neuroblastoma cells against the toxicity elicited by Ca(2+) overload. Our results confirm the hypothesis that the dibenzothiadiazepine ITH12410/SC058 features its neuroprotective actions in a multitarget fashion, and is a promising drug for the treatment of neurodegenerative diseases.

Alzheimer disease: An interactome of many diseases

Alzheimer Disease (AD) is an outcome as well as source of many diseases. Alzheimer is linked with many other diseases like Diabetes type 2, cholesterolemia, hypertension and many more. But how each of these diseases affecting other is still unknown to scientific community. Signaling Pathways of one disease is interlinked with other disease. But to what extent healthy brain is affected when any signaling in human body is disturbed is the question that matters. There is a need of Pathway analysis, Protein-Protein interaction (PPI) and the conserved interactome study in AD and linked diseases. It will be helpful in finding the potent drug or vaccine target in conscious manner. In the present research the Protein-Protein interaction of all the proteins involved in Alzheimer Disease is analyzed using ViSANT and osprey tools and pathway analysis further reveals the significant genes/proteins linking AD with other diseases.

Melatonin in Alzheimer's disease

Alzheimer’s disease (AD), an age-related neurodegenerative disorder with progressive cognition deficit, is characterized by extracellular senile plaques (SP) of aggregated β-amyloid (Aβ) and intracellular neurofibrillary tangles, mainly containing the hyperphosphorylated microtubule-associated protein tau. Multiple factors contribute to the etiology of AD in terms of initiation and progression. Melatonin is an endogenously produced hormone in the brain and decreases during aging and in patients with AD. Data from clinical trials indicate that melatonin supplementation improves sleep, ameliorates sundowning and slows down the progression of cognitive impairment in AD patients. Melatonin efficiently protects neuronal cells from Aβ-mediated toxicity via antioxidant and anti-amyloid properties. It not only inhibits Aβ generation, but also arrests the formation of amyloid fibrils by a structure-dependent interaction with Aβ. Our studies have demonstrated that melatonin efficiently attenuates Alzheimer-like tau hyperphosphorylation. Although the exact mechanism is still not fully understood, a direct regulatory influence of melatonin on the activities of protein kinases and protein phosphatases is proposed. Additionally, melatonin also plays a role in protecting the cholinergic system and in anti-inflammation. The aim of this review is to stimulate interest in melatonin as a potentially useful agent in the prevention and treatment of AD.

Melatonin attenuates scopolamine-induced memory/synaptic disorder by rescuing EPACs/miR-124/Egr1 pathway

Alzheimer's disease (AD) is the most prevalent type of dementia in elderly people. There are decreased melatonin levels in the serum of AD patients, and melatonin supplements are able to reverse AD pathology and memory deficits in many animal experiments and clinical trials. However, the underlying mechanism regarding how melatonin rescues the AD-like memory/synaptic disorder remains unknown. Here, we use the Morris water maze, step-down inhibitory avoidance task, in vivo long-term potentiation recording, and Golgi staining and report that intraperitoneal injection of melatonin (1 mg/kg/day) for 14 days in rats effectively reverses the memory and synaptic impairment in scopolamine-induced amnesia, a well-recognized dementia animal model. Using real-time polymerase chain reaction and western blotting experiments, we further determined that melatonin rescues the EPACs/miR-124/Egr1 signal pathway, which is important in learning and memory, as reported recently. Our studies provide a novel underlying epigenetic mechanism for melatonin to attenuate the synaptic disorder and could benefit drug discovery in neurodegenerative diseases.

Melatonin increases dendritogenesis in the hilus of hippocampal organotypic cultures

Neuropsychiatric disorders are characterized by hippocampus decreased volume and loss of dendrite arborizations in the subiculum and prefrontal cortex. These structural changes are associated with diminished memory performance. Hilar neurons of the hippocampus integrate spatial memory and are lost in dementia. They receive information from dentate gyrus neurons through dendrites, while they send axonal tracts to the CA3 region. Dendrites are complex structures of neurons that receive chemical information from presynaptic and postsynaptic terminals. Melatonin, the main product of the pineal gland, has neuroprotective actions through its free radical-scavenging properties and decreases neuronal apoptosis. Recently, we found that melatonin increases dendrite maturation and complexity in new neurons formed in the dentate gyrus of mice. In addition, in N1E-115 cultured cells, the indole stimulates early stages of neurite formation, a process that is known to antecede dendrite formation and maturation. Thus, in this study, we explored whether melatonin stimulates dendrite formation and complexity in the adult rat hippocampus in organotypic slice cultures, which is a model that preserves the hippocampal circuitry and their tridimensional organizations of connectivity. The effects of melatonin were studied in nonpathological conditions and in the absence of harmful agents. The results showed that the indole at nocturnal concentrations reached in the cerebrospinal fluid stimulates dendritogenesis at formation, growth, and maturation stages. Also, data showed that dendrites formed became competent to form presynaptic specializations. Evidence strongly suggests that melatonin may be useful in the treatment of neuropsychiatric diseases to repair the loss of dendrites and re-establish lost synaptic connections.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Mitochondria and antioxidant targeted therapeutic strategies for Alzheimer's disease

Oxidative stress and mitochondrial dysfunction are important features present in Alzheimer's disease (AD). They appear early and contribute to disease progression, both in human postmortem AD brains as well as in transgenic AD mouse brains. For this reason, targeting oxidative stress and mitochondria in AD may lead to the development of promising therapeutic strategies. Several exogenous antioxidant compounds have been tested and found beneficial in transgenic AD mice, such as vitamins and spices. However, their efficacy was much more modest in human trials. More recently, new strategies have been elaborated to promote endogenous antioxidant systems. Different pathways involved in oxidative stress response have been identified. Compounds able to upregulate these pathways are being generated and tested in animal models of AD and in human patients. Upregulation of antioxidant gene expression was beneficial in mice, giving hope for future avenues in the treatment of AD and other neurodegenerative disorders.

Synthesis, inhibitory activity of cholinesterases, and neuroprotective profile of novel 1,8-naphthyridine derivatives

1,8-Naphthyridine derivatives related to 17 (ITH4012), a neuroprotective compound reported by our research group, have been synthesized. In general, they have shown better inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) than most tacrine derivatives previously synthesized in our laboratory. The compounds presented an interesting neuroprotective profile in SH-SY5Y neuroblastoma cells stressed with rotenone/oligomycin A. Moreover, compound 14 (ethyl 5-amino-2-methyl-6,7,8,9-tetrahydrobenzo[b][1,8]naphthyridine-3-carboxylate) also caused protection in cells stressed with okadaic acid (OA) or amyloid beta 1-42 peptide (Abeta(1-42)). Interestingly, compound 14 prevented the OA-induced PP2A inhibition, one of the enzymes implicated in tau dephosphorylation. This compound also exhibited neuroprotection against neurotoxicity elicited by oxygen and glucose deprivation in hippocampal slices. Because these stressors caused neuronal damage related to physiopathological hallmarks found in the brain of Alzheimer's disease (AD) patients, we conclude that compound 14 deserves further in vivo studies in AD models to test its therapeutic potential in this disease.

Is modulation of nicotinic acetylcholine receptors by melatonin relevant for therapy with cholinergic drugs?

Melatonin, the darkness hormone, synchronizes several physiological functions to light/dark cycle. Besides the awake/sleep cycle that is intuitively linked to day/night, daily variations in memory acquisition and innate or acquired immune responses are some of the major activities linked to melatonin rhythm. The daily variation of these complex processes is due to changes in specific mechanisms. In the last years we focused on the influence of melatonin on the expression and function of nicotinic acetylcholine receptors (nAChRs). Melatonin, either "in vivo" or "in vitro", increases, in a selective manner, the efficiency of alpha-bungarotoxin (alpha-BTX)-sensitive nAChRs. Melatonin's effect on receptors located in rat sympathetic nerve terminals, cerebellum, skeletal muscle and chick retina, was tested. We observed that melatonin is essential for the development of alpha-BTX-sensitive nAChRs, and important for receptor maintenance in aging models. Taking into account that both melatonin and alpha-7 nAChRs (one of the subtypes sensitive to alpha-BTX) are involved in the development of Alzheimer's disease, here we discuss the possibility of a therapeutic strategy focused on both melatonin replacement and its potential association with cholinergic drugs.

Protection against cognitive deficits and markers of neurodegeneration by long-term oral administration of melatonin in a transgenic model of Alzheimer disease

The neurohormone melatonin has been reported to exert anti-beta-amyloid aggregation, antioxidant, and anti-inflammatory actions in various in vitro and animal models. To comprehensively determine the potential for long-term melatonin treatment to protect Alzheimer's transgenic mice against cognitive impairment and development of beta-amyloid (Abeta) neuropathology, we administered melatonin (100 mg/L drinking water) to APP + PS1 double transgenic (Tg) mice from 2-2.5 months of age to their killing at age 7.5 months. A comprehensive behavioral battery administered during the final 6 weeks of treatment revealed that Tg mice given melatonin were protected from cognitive impairment in a variety of tasks of working memory, spatial reference learning/memory, and basic mnemonic function; Tg control mice remained impaired in all of these cognitive tasks/domains. Immunoreactive Abeta deposition was significantly reduced in hippocampus (43%) and entorhinal cortex (37%) of melatonin-treated Tg mice. Although soluble and oligomeric forms of Abeta1-40 and 1-42 were unchanged in the hippocampus and cortex of the same melatonin-treated Tg mice, their plasma Abeta levels were elevated. These Abeta results, together with our concurrent demonstration that melatonin suppresses Abeta aggregation in brain homogenates, are consistent with a melatonin-facilitated removal of Abeta from the brain. Inflammatory cytokines such as tumor necrosis factor (TNF)-alpha were decreased in hippocampus (but not plasma) of Tg+ melatonin mice. Finally, the cortical mRNA expression of three antioxidant enzymes (SOD-1, glutathione peroxidase, and catalase) was significantly reduced to non-Tg levels by long-term melatonin treatment in Tg mice. Thus, melatonin's cognitive benefits could involve its anti-Abeta aggregation, anti-inflammatory, and/or antioxidant properties. Our findings provide support for long-term melatonin therapy as a primary or complementary strategy for abating the progression of Alzheimer disease.