Melatonin reduces amyloid beta-induced apoptosis in pheochromocytoma (PC12) cells

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.

Melatonin as a promising modulator of aging related neurodegenerative disorders: Role of microRNAs

One of the host risk factors involved in aging-related diseases is coupled with the reduction of endogenous melatonin (MLT) synthesis in the pineal gland. MLT is considered a well-known pleiotropic regulatory hormone to modulate a multitude of biological processes such as the regulation of circadian rhythm attended by potent anti-oxidant, anti-inflammatory, and anti-cancer properties. It has also been established that the microRNAs family, as non-coding mRNAs regulating post-transcriptional processes, also serve a crucial role to promote MLT-related advantageous effects in both experimental and clinical settings. Moreover, the anti-aging impact of MLT and miRNAs participation jointly are of particular interest, recently. In this review, we aimed to scrutinize recent advances concerning the therapeutic implications of MLT, particularly in the brain tissue in the face of aging. We also assessed the possible interplay between microRNAs and MLT, which could be considered a therapeutic strategy to slow down the aging process in the nervous system.

Melatonin alleviates intestinal injury, neuroinflammation and cognitive dysfunction caused by intestinal ischemia/reperfusion

Intestinal ischemia/reperfusion (I/R) can cause multiple organ damage with extremely high morbidity and mortality. Melatonin has anti-inflammatory, anti-oxidative and anti-apoptotic effects against various diseases. This study aimed to explore whether melatonin had a protective effect against intestinal I/R-induced neuroinflammation and cognitive dysfunction, and investigate its potential mechanisms. In this study, melatonin was administered to the rats with intestinal I/R, then histological changes in intestine and brain (frontal cortex and hippocampal CA1 area) tissues and cognitive function were detected, respectively. The encephaledema and blood-brain barrier (BBB) permeability were observed. Moreover, the alterations of proinflammatory factors (tumor necrosis factor-α, interleukin-6 and interleukin-1β), oxidative response (malondialdehyde, superoxide dismutase, and reactive oxygen species), apoptosis and proteins associated with inflammation,including Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (Myd88) and phosphorylated nuclear factor kappa beta (NF-κB), and apoptosis (cleaved caspase-3) in brain tissues were examined. Furthermore, the expressions of TLR4, Myd88, and microglial activity were observed by multiple immunofluorescence staining. The results showed that intestinal I/R-induced abnormal neurobehavior and cerebral damage were ameliorated after melatonin treatment, which were demonstrated by improved cognitive dysfunction and aggravated histology. Furthermore, melatonin decreased the levels of proinflammatory factors and oxidative stress in plasma, intestine and brain tissues, attenuated apoptotic cell, and inhibited the expressions of related proteins and the immunoreactivity of TLR4 or Myd88 in microglia in brain tissues. These findings showed that melatonin might relieve neuroinflammation and cognitive dysfunction caused by intestinal I/R, which could be, at least partially, related to the inhibition of the TLR4/Myd88 signaling in microglia.

Near-Infrared Responsive Dopamine/Melatonin-Derived Nanocomposites Abrogating in Situ Amyloid β Nucleation, Propagation, and Ameliorate Neuronal Functions

Alzheimer's disease (AD) is one of the common causes of dementia and mild cognitive impairments, which is progressively expanding among the elderly population worldwide. A short Amyloid-β (Aβ) peptide generated after amyloidogenic processing of amyloid precursor protein exist as intermolecular β-sheet rich oligomeric, protofibriler, and fibrillar structures and believe to be toxic species which instigate neuronal pathobiology in the brain and deposits as senile plaque. Enormous efforts are being made to develop an effective anti-AD therapy that can target Aβ processing, aggregation, and propagation and provide a synergistic neuroprotective effect. However, a nanodrug prepared from natural origin can confer a multimodal synergistic chemo/photothermal inhibition of Aβ pathobiology is not yet demonstrated. In the present work, we report a dopamine-melatonin nanocomposite (DM-NC), which possesses a synergistic near-infrared (NIR) responsive photothermal and pharmacological modality. The noncovalent interaction-mediated self-assembly of melatonin and dopamine oxidative intermediates leads to the evolution of DM-NCs that can withstand variable pH and peroxide environment. NIR-activated melatonin release and photothermal effect collectively inhibit Aβ nucleation, self-seeding, and propagation and can also disrupt the preformed Aβ fibers examined using in vitro Aβ aggregation and Aβ-misfolding cyclic amplification assays. The DM-NCs display a higher biocompatibility to neuroblastoma cells, suppress the AD-associated generation of intracellular reactive oxygen species, and are devoid of any negative impact on the axonal growth process. In okadaic acid-induced neuroblastoma and ex vivo midbrain slice culture-based AD model, DM-NCs exposure suppresses the intracellular Aβ production, aggregation, and accumulation. Therefore, this nature-derived nanocomposite demonstrates a multimodal NIR-responsive synergistic photothermal and pharmacological modality for effective AD therapy.

Novel Multitarget Directed Triazinoindole Derivatives as Anti-Alzheimer Agents

The multifaceted nature of Alzheimer's disease (AD) demands treatment with multitarget-directed ligands (MTDLs) to confront the key pathological aberrations. A novel series of triazinoindole derivatives were designed and synthesized. In vitro studies revealed that all the compounds showed moderate to good anticholinesterase activity; the most active compound 23e showed an IC₅₀ value of 0.56 ± 0.02 μM for AChE and an IC₅₀ value of 1.17 ± 0.09 μM for BuChE. These derivatives are also endowed with potent antioxidant activity. To understand the plausible binding mode of the compound 23e, molecular docking studies and molecular dynamics simulation studies were performed, and the results indicated significant interactions of 23e within the active sites of AChE as well as BuChE. Compound 23e successfully diminished H₂O₂-induced oxidative stress in SH-SY5Y cells and displayed excellent neuroprotective activity against H₂O₂ as well as Aβ-induced toxicity in SH-SY5Y cells in a concentration dependent manner. Furthermore, it did not show any significant toxicity in neuronal SH-SY5Y cells in the cytotoxicity assay. Compound 23e did not show any acute toxicity in rats at doses up to 2000 mg/kg, and it significantly reversed scopolamine-induced memory deficit in mice model. Additionally, compound 23e showed notable in silico ADMET properties. Taken collectively, these findings project compound 23e as a potential balanced MTDL in the evolution process of novel anti-AD drugs.

Melatonin as a mitochondrial protector in neurodegenerative diseases

Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.

Melatonin: A pleiotropic molecule that modulates DNA damage response and repair pathways

DNA repair is responsible for maintaining the integrity of the genome. Perturbations in the DNA repair pathways have been identified in several human cancers. Thus, compounds targeting DNA damage response (DDR) hold great promise in cancer therapy. A great deal of effort, in pursuit of new anticancer drugs, has been devoted to understanding the basic mechanisms and functions of the cellular DNA repair machinery. Melatonin, a widely produced indoleamine in all organisms, is associated with a reduced risk of cancer and has multiple regulatory roles on the different aspects of the DDR and DNA repair. Herein, we have mainly discussed how defective components in different DNA repair machineries, including homologous recombination (HR), nonhomologous end-joining (NHEJ), base excision repair (BER), nucleotide excision repair (NER), and finally DNA mismatch repair (MMR), can contribute to the risk of cancer. Melatonin biosynthesis, mode of action, and antioxidant effects are reviewed along with the means by which the indoleamine regulates DDR at the transduction, mediation, and functional levels. Finally, we summarize recent studies that illustrate how melatonin can be combined with DNA-damaging agents to improve their efficacy in cancer therapy.

N-Adamantyl-4-methylthiazol-2-amine suppresses amyloid β-induced neuronal oxidative damage in cortical neurons

Recently, we have reported that N-adamantyl-4-methylthiazol-2-amine (KHG26693) successfully reduced the production of oxidative stress in streptozotocin-induced diabetic rats and lipopolysaccharide-induced BV-2 microglial cells by increasing their antioxidant capacity. However, antioxidative effects of KHG26693 against Aβ (Aβ)-induced oxidative stress have not yet been reported. In the present study, we further investigated the antioxidative function of KHG26693 in Aβ-mediated primary cultured cortical neurons. We showed here that KHG26693 attenuated Aβ-induced cytotoxicity, increase of Bax/Bcl-2 ratio, elevation of caspase-3 expression, and impairment of mitochondrial membrane potential in cultured primary cortical neurons. KHG26693 also decreases the Aβ-mediated formation of malondialdehyde, reactive oxygen species, and NO production by decreasing nitric oxide synthase (iNOS) and NADPH oxidase level. Moreover, KHG26693 suppress the Aβ-induced oxidative stress through a possible mechanism involving attenuation of GSH and antioxidant enzyme activities such as glutathione reductase and glutathione peroxidase (GPx). Finally, pretreatment of cortical neurons with KHG26693 significantly reduced the Aβ-induced protein oxidation and nitration. To our knowledge, this is the first report, showing that KHG26693 significantly attenuates Aβ-induced oxidative stress in primary cortical neurons, and may prove attractive strategies to reduce Aβ-induced neural cell death.

Melatonin: A Potential Anti-Oxidant Therapeutic Agent for Mitochondrial Dysfunctions and Related Disorders

Mitochondria play a central role in cellular physiology. Besides their classic function of energy metabolism, mitochondria are involved in multiple cell functions, including energy distribution through the cell, energy/heat modulation, regulation of reactive oxygen species (ROS), calcium homeostasis, and control of apoptosis. Simultaneously, mitochondria are the main producer and target of ROS with the result that multiple mitochondrial diseases are related to ROS-induced mitochondrial injuries. Increased free radical generation, enhanced mitochondrial inducible nitric oxide synthase (iNOS) activity, enhanced nitric oxide (NO) production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pores have all been suggested as factors responsible for impaired mitochondrial function. Because of these, neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and aging, are caused by ROS-induced mitochondrial dysfunctions. Melatonin, the major hormone of the pineal gland, also acts as an anti-oxidant and as a regulator of mitochondrial bioenergetic function. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other anti-oxidants, and thus has emerged as a major potential therapeutic tool for treating neurodegenerative disorders. Multiple in vitro and in vivo experiments have shown the protective role of melatonin for preventing oxidative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. With these functions in mind, this article reviews the protective role of melatonin with mechanistic insights against mitochondrial diseases and suggests new avenues for safe and effective treatment modalities against these devastating neurodegenerative diseases. Future insights are also discussed.

Neuroprotective Effect of Brassica oleracea Sprouts Crude Juice in a Cellular Model of Alzheimer's Disease

β-Amyloid peptide (Aβ) aberrant production and aggregation are major factors implicated in the pathogenesis of Alzheimer's disease (AD), causing neuronal death via oxidative stress. Several studies have highlighted the importance of polyphenolic antioxidant compounds in the treatment of AD, but complex food matrices, characterized by a different relative content of these phytochemicals, have been neglected. In the present study, we analyzed the protective effect on SH-SY5Y cells treated with the fragment Aβ 25-35 by two crude juices of broccoli sprouts containing different amounts of phenolic compounds as a result of different growth conditions. Both juices protected against Aβ-induced cytotoxicity and apoptotic cell death as evidenced by cell viability, nuclear chromatin condensation, and apoptotic body formation measurements. These effects were mediated by the modulation of the mitochondrial function and of the HSP70 gene transcription and expression. Furthermore, the juices upregulated the intracellular glutathione content and mRNA levels or activity of antioxidant enzymes such as heme oxygenase-1, thioredoxin, thioredoxin reductase, and

NAD(P)H

quinone oxidoreductase 1 via activation of NF-E2-related factor 2 (Nrf2). Although the effects of the two juices were similar, the juice enriched in phenolic compounds showed a greater efficacy in inducing the activation of the Nrf2 signalling pathway.

Antioxidative effects of ethyl 2-(3-(benzo[d]thiazol-2-yl)ureido)acetate against amyloid β-induced oxidative cell death via NF-κB, GSK-3β and β-catenin signaling pathways in cultured cortical neurons

We have previously shown that 2-(3-(benzo[d]thiazol-2-yl)ureido)acetate (KHG21834) attenuates amyloid beta(Aβ)25-35-induced apoptotic death and shows anti-inflammatory activity against Aβ25-35-induced microglial activation. However, antioxidative effects of KHG21834 against Aβ-induced oxidative stress have not yet been reported. In the present study, we investigated the antioxidative function of KHG21834 in primary cultured cortical neurons, to expand the potential therapeutic efficacy of KHG21834. Pretreatment with KHG21834 protected against Aβ-induced neuronal cell death and mitochondrial damage, and significantly restored GSH levels and the activities of catalase, superoxide dismutase, and glutathione peroxidase, and also suppressed the production of reactive oxygen species and protein oxidation. These results imply that KHG21834 may play a role in cellular defense mechanisms against Aβ-induced oxidative stress in cultured cortical neurons. Furthermore, KHG21834 significantly attenuated the effects of Aβ treatment on levels of NF-κB, β-catenin, and GSK-3β proteins in cortical neurons. Taken together, our results suggest that the antioxidant effects of KHG21834 may result at least in part from its ability to regulate the NF-κB, β-catenin, and GSK-3β signaling pathways. To our knowledge, this is the first report showing that KHG21834 significantly attenuates Aβ25-35-induced oxidative stress in primary cortical neurons, and provides novel insights into KHG21834 as a possible therapeutic agent for the treatment of Aβ-mediated neurotoxicity involving oxidative stress.

Protective effects of anthocyanins against amyloid beta-induced neurotoxicity in vivo and in vitro

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders in recent world, characterized by increased production of amyloid beta in the nervous system with an ultimate effect of apoptotic neurodegeneration. This study was aimed to investigate the neuroprotective effect of black soybean anthocyanins in a neurodegenerative model of amyloid beta 1-42 (Aβ1-42). Aβ1-42 was treated to HT22 cell lines or adult male rats via intra-cerebro-ventricular injection to induce neurotoxicity in these experimental models. Anthocyanins were treated 0.2 mg/kg in case of cell lines or 4 mg/kg intragastrically to adult rats to protect against Aβ-induced neurodegeneration. Assay for cell viability, mitochondrial membrane potential (Ψm), intracellular free Ca(2+) and apoptotic cells (fluoro-jade B and TUNEL) were performed in vitro while western blot analyses were performed to the hippocampal proteins of adult rats. Our results showed that Aβ1-42 treatment reduced cell viability, disturbed the Ψm and Ca(2+) homeostasis in and out of the cell, and increased neuronal apoptosis. Treatment with anthocyanins for 12 hr retained the cell viability, normalized Ψm and Ca(2+) level, and decreased the neuronal cell death. In accordance, anthocyanins reversed Aβ-induced effect on protein expression of mitochondrial apoptotic pathway (Bax, cytochrome C, caspase-9 and caspase-3) and major Alzheimer's markers i.e. Aβ, APP, P-tau and BACE-1. Overall, our results showed that anthocyanins are potential candidates to treat neurodegenerative disorders like AD.

Puerarin protects against β-amyloid-induced microglia apoptosis via a PI3K-dependent signaling pathway

Puerarin extracted from Radix puerariae is well-known for its anti-oxidative and neuroprotective activities. In this study, we investigated the protective effect of puerarin on amyloid-β protein (Aβ)-induced cytotoxicity and its potential mechanisms in BV-2 and primary microglial cells. We found that pretreatment with puerarin afforded protection against Aβ-induced cytotoxicity through inhibiting apoptosis in BV-2 and primary microglial cells. This result was also confirmed by the activated caspase-3 assay. Phospho-Akt and Bcl-2 expression increased after pretreatment with puerarin in BV-2 and primary microglial cells exposed to Aβ, whereas Bax expression and cytochrome c release decreased. In addition, puerarin treatment prevented the loss of mitochondrial membrane potential and reactive oxygen species production. Interestingly, these effects of puerarin against Aβ insult were abolished by LY294002, an inhibitor of PI3K phosphorylation. Taken together, these findings suggest that puerarin prevents Aβ-induced microglial apoptosis via the activation of PI3K/Akt signaling pathway, and might be a potential preventive or therapeutic agent for Alzheimer's disease.

Beta amyloid-induced upregulation of death receptor 6 accelerates the toxic effect of N-terminal fragment of amyloid precursor protein

Amyloid precursor protein (APP) plays essential roles in the development of the Alzheimer's disease. Although full-length APP has been thoroughly studied, the role of the cleavage fragments especially the N-terminal fragments (N-APPs) in Alzheimer's disease pathogenesis was still elusive. In this study, we demonstrated that application of recombinant APP₁₈₋₂₈₆ could enhance beta amyloid (Aβ)-induced neuronal injuries which were related to the activation of apoptosis proteins. Aβ treatment could induce a slight increase of N-APPs release. In addition, expression of death receptor 6 (DR6) was increased in Aβ-treated neurons and APP transgenic mice. Moreover, the effect of APP₁₈₋₂₈₆ on Aβ-induced injuries could be suppressed by the application of recombinant DR6₄₁₋₃₄₁ and DR6 antibody. Furthermore, pull-down assay revealed that APP₁₈₋₂₈₆ could bind both exogenous and endogenous DR6. Aβ promoted APP₁₈₋₂₈₆ targeting to neuron which was accompanied with the increase of DR6 expression, whereas downregulation of DR6 by interference RNA could alleviate the binding of N-APPs to neuron and also suppressed Aβ-dependent toxic effect with N-APPs. These results suggested that APP N-terminal fragments might play neurotoxic roles in Aβ-induced neuronal injuries through cell surface DR6.

A novel assay for high-throughput screening of anti-Alzheimer's disease drugs to determine their efficacy by real-time monitoring of changes in PC12 cell proliferation

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the accumulation of senile plaque and neurofibrilary tangle formation in the brain, including the cerebral cortex and hippocampus. Nowadays, the first-line treatment for AD is the application of acetylcholinesterase inhibitors. However, acetylcholinesterase inhibitors are basically anti-symptomatic for a limited aspect of AD pathology and are associated with serious side-effects. With the advantage of multiple targets, pathways and systems, Chinese herbal compounds hold promising potential for the development of drugs for the treatment of AD. Over the past few years, with the development of Chinese herbal compounds and in vitro pharmacological studies, cell-based disease models are one of the main methods used to screen Chinese herbal compounds for potential efficacy. Testing the efficacy of possible anti-Alzheimer’s disease drugs and the development of new drugs are hindered by the lack of objective high-throughput screening methods. Currently, the assessment of the effects of drugs is usually made by MTT assays, involving laborious, subjective, low-throughput methods. Herein, we suggest a novel application for a real-time cell monitoring device (xCELLigence) that can simply and objectively assess the effective composition of Chinese herbal compounds by assessing amyloid-β peptide Aβ1-42-induced apoptosis in PC12 cells. We detected the proliferation and motility of the cells using a fully automated high-throughput and real-time system. We quantitatively assessed cell motility and determined the real-time IC₅₀ values of various anti-AD drugs that intervene in several developmental stages of Aβ1-42-induced apoptosis in PC12 cells, Then, we identified the optimal time phase by curative efficacy. Our data indicate that this technique may aid in the discovery and development of novel anti-Alzheimer’s disease drugs. It is possible to utilize a similar technique to measure changes in electrical impedance as cells attach and spread in a culture dish covered with a gold microelectrode array that covers approximately 80% of the area on the bottom of a well. As cells attach and spread on the electrode surface, it leads to an increase in electrical impedance of 9–12. The impedance is displayed as a dimensionless parameter termed the cell index, which is directly proportional to the total area of tissue culture well that is covered by the cells. Hence, the cell index can be used to monitor cell adhesion, spreading, morphological variation and cell density.

Reciprocal interactions between sleep, circadian rhythms and Alzheimer's disease: focus on the role of hypocretin and melatonin

AD, sleep and circadian rhythm physiology display an intricate relationship. On the one hand, AD pathology leads to sleep and circadian disturbances, with a clear negative influence on quality of life. On the other hand, there is increasing evidence that both sleep and circadian regulating systems exert an influence on AD pathology. In this review we describe the impairments of both sleep regulating systems and circadian rhythms in AD and their link to clinical symptoms, as this may increase knowledge on appropriate diagnosis and adequate treatment of sleep problems in AD. Furthermore we discuss how sleep regulating systems, and especially neurotransmitters such as melatonin and hypocretin, may affect AD pathophysiology, as this may provide a role for lack of sleep and circadian rhythm deterioration in the onset of AD.

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.

Melatonin alleviates cadmium-induced cellular stress and germ cell apoptosis in testes

Increasing evidence demonstrates that melatonin has an anti-apoptotic effect in somatic cells. However, whether melatonin can protect against germ cell apoptosis remains obscure. Cadmium (Cd) is a testicular toxicant and induces germ cell apoptosis. In this study, we investigated the effects of melatonin on Cd-evoked germ cell apoptosis in testes. Male ICR mice were intraperitoneally (i.p.) injected with melatonin (5 mg/kg) every 8 hr, beginning at 8 hr before CdCl(2) (2.0 mg/kg, i.p.). As expected, acute Cd exposure resulted in germ cell apoptosis in testes, as determined by terminal dUTP nick-end labeling (TUNEL) staining. Melatonin significantly alleviated Cd-induced testicular germ cell apoptosis. An additional experiment showed that spliced form of XBP-1, the target of the IRE-1 pathway, was significantly increased in testes of mice injected with CdCl(2). GRP78, an endoplasmic reticulum (ER) chaperone, and CHOP, a downstream target of the PERK pathway, were upregulated in testes of Cd-treated mice. In addition, acute Cd exposure significantly increased testicular eIF2α and JNK phosphorylation, indicating that the unfolded protein response (UPR) pathway was activated by CdCl(2). Interestingly, melatonin almost completely inhibited Cd-induced ER stress and the UPR in testes. In addition, melatonin obviously attenuated Cd-induced heme oxygenase (HO)-1 expression and protein nitration in testes. Taken together, these results suggest that melatonin alleviates Cd-induced cellular stress and germ cell apoptosis in testes. Melatonin may be useful as pharmacological agents to protect against Cd-induced testicular toxicity.

Anti-amyloidogenic and anti-apoptotic role of melatonin in Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative disorder characterized by the presence of senile plaques, neurofibrillary tangles and neuronal loss. Amyloid-β protein (Aβ) deposition plays a critical role in the development of AD. It is now generally accepted that massive neuronal death due to apoptosis is a common characteristic in the brains of patients suffering from neurodegenerative diseases, and apoptotic cell death has been found in neurons and glial cells in AD. Melatonin is a secretory product of the pineal gland; melatonin is a potent antioxidant and free radical scavenger and may play an important role in aging and AD. Melatonin decreases during aging and patients with AD have a more profound reduction of this indoleamine. Additionally, the antioxidant properties, the anti-amyloidogenic properties and anti-apoptotic properties of melatonin in AD models have been studied. In this article, we review the anti-amyloidogenic and anti-apoptotic role of melatonin in AD

Structurally distinct toxicity inhibitors bind at common loci on β-amyloid fibril

The accumulation of aggregated β-Amyloid (Aβ) in the brain is a hallmark of Alzheimer's disease and is thought to play a role in the neurotoxicity associated with the disease. The mechanism by which Aβ aggregates induce toxicity is uncertain. Nonetheless, several small molecules have been found to interact with Aβ fibrils and to prevent their toxicity. In this paper we studied the binding of these known toxicity inhibitors to Aβ fibrils, as a means to explore surfaces or loci on Aβ aggregates that may be significant in the mechanism of action of these inhibitors. We believe knowledge of these binding loci will provide insight into surfaces on the Aβ fibrils important in Aβ biological activity. The program DOCK was used to computationally dock the inhibitors to an Aβ fibril. The inhibitors docked at two shared binding loci, near Lys28 and at the C-termini near Asn27 and Val39. The docking predictions were experimentally verified using lysine specific chemical modifications and Aβ fibrils mutated at Asn27. We found that both Congo red and Myricetin, despite being structurally different, bound at the same two sites. Additionally, our data suggests that three additional Aβ toxicity inhibitors may also bind in one of the sites. Identification of these common binding loci provides targets on the Aβ fibril surface that can be tested in the future for their role in Aβ biological activity.

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.

The failure of mitochondria leads to neurodegeneration: Do mitochondria need a jump start?

Mitochondria are the power engine generating biochemical energy in the cell. Mitochondrial dysfunction and bioenergy deficiency is closely linked to the pathogenesis of neurodegenerative disorders. Mitochondria play a variety of roles by integrating extracellular signals and executing important intracellular events in neuronal survival and death. In this context, the regulation of mitochondrial function via therapeutic approaches may exert some salutary and neuroprotective mechanisms. Understanding the relationship of mitochondria-dependent pathogenesis may provide important pharmacological utility in the treatment of neurodegenerative conditions such as Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease and Parkinson's disease. Indeed, the modulation of mitochondrial pathways is rapidly emerging as a novel therapeutic target. This review focuses on how mitochondria are involved in neurodegeneration and what therapeutics are available to target mitochondrial pathways.

Protective effect of pyrroloquinoline quinone against Abeta-induced neurotoxicity in human neuroblastoma SH-SY5Y cells

The neurotoxicity of aggregated beta-amyloid (Abeta) has been implicated as a critical cause in the pathogenesis of Alzheimer's disease (AD). It can cause neurotoxicity in AD by evoking a cascade of oxidative damage-dependent apoptosis to neurons. In the present study, we for the first time investigated the protective effect of pyrroloquinoline quinone (PQQ), an anionic, water soluble compound that acts as a redox cofactor of bacterial dehydrogenases, on Abeta-induced SH-SY5Y cytotoxicity. Abeta(25-35) significantly reduced cell viability, increased the number of apoptotic-like cells, and increased ROS production. All of these phenotypes induced by Abeta(25-35) were markedly reversed by PQQ. PQQ pretreatment recovered cells from Abeta(25-35)-induced cell death, prevented Abeta(25-35)-induced apoptosis, and decreased ROS production. PQQ strikingly decreased Bax/Bcl-2 ratio, and suppressed the cleavage of caspase-3. These results indicated that PQQ could protect SH-SY5Y cells against beta-amyloid induced neurotoxicity.

Characterization of the endocannabinoid system in human neuronal cells and proteomic analysis of anandamide-induced apoptosis

Anandamide (AEA) is an endogenous agonist of type 1 cannabinoid receptors (CB1R) that, along with metabolic enzymes of AEA and congeners, compose the "endocannabinoid system." Here we report the biochemical, morphological, and functional characterization of the endocannabinoid system in human neuroblastoma SH-SY5Y cells that are an experimental model for neuronal cell damage and death, as well as for major human neurodegenerative disorders. We also show that AEA dose-dependently induced apoptosis of SH-SY5Y cells. Through proteomic analysis, we further demonstrate that AEA-induced apoptosis was paralleled by an approximately 3 to approximately 5-fold up-regulation or down-regulation of five genes; IgG heavy chain-binding protein, stress-induced phosphoprotein-1, and triose-phosphate isomerase-1, which were up-regulated, are known to act as anti-apoptotic agents; actin-related protein 2/3 complex subunit 5 and peptidylprolyl isomerase-like protein 3 isoform PPIL3b were down-regulated, and the first is required for actin network formation whereas the second is still function-orphan. Interestingly, only the effect of AEA on BiP was reversed by the CB1R antagonist SR141716, in SH-SY5Y cells as well as in human neuroblastoma LAN-5 cells (that express a functional CB1R) but not in SK-NBE cells (which do not express CB1R). Silencing or overexpression of BiP increased or reduced, respectively, AEA-induced apoptosis of SH-SY5Y cells. In addition, the expression of BiP and of the BiP-related apoptotic markers p53 and PUMA was increased by AEA through a CB1R-dependent pathway that engages p38 and p42/44 mitogen-activated protein kinases. Consistently, this effect of AEA was minimized by SR141716. In conclusion, we identified BiP as a key protein in neuronal apoptosis induced by AEA.

Antioxidant neuroprotection against ethanol-induced apoptosis in HN2-5 cells

Earlier studies from this and other laboratories show that ethanol induces apoptotic death of fetal and neonatal neurons. One mechanism that underlies these effects is the ethanol-associated reduction in the phosphatidylinositol 3' kinase pro-survival pathway. Another mechanism involves the oxidative stress caused by the ethanol-associated increase in reactive oxygen species (ROS). In the present study, we used the murine HN2-5 hippocampal-derived cell line to investigate the effects of ethanol on ROS levels and apoptosis. We also investigated the potential neuroprotective effects of two structurally unrelated antioxidants: N-acetylcysteine (NAC) and melatonin. The results demonstrate that NAC blocked an ethanol-associated increase in ROS. In addition, NAC and melatonin prevented the augmentation of apoptosis in ethanol-treated neurons. Both antioxidants significantly elevated the expression of the anti-apoptotic gene XIAP in ethanol-treated and/or control neurons and melatonin increased Bcl-2 expression in ethanol-treated neurons. Thus, it is possible that the neuroprotective effects of NAC and melatonin involve their ability to augment the expression of one or more anti-apoptotic gene as well as their classical antioxidant actions. Additional studies are needed to establish the effectiveness of these antioxidants to prevent the loss of neurons which accompanies in utero exposure to ethanol.

Microtubules modulate melatonin receptors involved in phase-shifting circadian activity rhythms: in vitro and in vivo evidence

MT1 melatonin receptors expressed in Chinese hamster ovary (CHO) cells remain sensitive to a melatonin re-challenge even following chronic melatonin exposure when microtubules are depolymerized in the cell, an exposure that normally results in MT1 receptor desensitization. We extended our findings to MT2 melatonin receptors using both in vitro and in vivo approaches. Using CHO cells expressing human MT2 melatonin receptors, microtubule depolymerization prevents the loss in the number of high potency states of the receptor when compared to melatonin-treated cells. In addition, microtubule depolymerization increases melatonin-induced PKC activity but not PI hydrolysis via Gi proteins similar to that shown for MT1Rs. Furthermore, microtubule depolymerization in MT2-CHO cells enhances the exchange of GTP on Gi-proteins using a photoaffinity analog of GTP. To test whether microtubules are capable of modulating melatonin-induced phase-shifts, microtubules are depolymerized specifically within the suprachiasmatic nucleus of the hypothalamus (SCN) of the Long Evans rat and the efficacy of melatonin to phase shift their circadian activity rhythms was assessed and compared to animals with intact SCN microtubules. We find that microtubule depolymerization in the SCN using either Colcemid or nocodazole enhances the efficacy of 10 pm melatonin to phase-shift the activity rhythms of the Long Evans rat. No enhancement occurs in the presence of beta-lumicolchicine, the inactive analog of Colcemid. Taken together, these data suggest that microtubule dynamics can modulate melatonin-induced phase shifts of circadian activity rhythms which may explain, in part, why circadian disturbances occur in individuals afflicted with diseases associated with microtubule disturbances.

The antiproliferative activity of melatonin in B65 rat dopaminergic neuroblastoma cells is related to the downregulation of cell cycle-related genes

A potential application of melatonin is its ability to rescue many cell types from cell death, because of its antioxidant properties. Likewise, recent studies suggest that melatonin may also be used as an anti-tumor drug, due to its anti-proliferative properties in tumor cells when administered at physiologic or pharmacologic doses. In the present study, we investigated the mechanisms involved in the apoptosis induced by acute exposure to melatonin and roscovitine in the rat dopaminergic neuroblastoma B65 cell line. Cell growth studies revealed that, at 24 hr of treatment, roscovitine blocked cell growth and induced apoptosis whereas melatonin delayed cell growth and induced a slight increase in the number of apoptotic nuclei. Melatonin also increased the percentage of cells in the G1-phase of the cell cycle, whereas roscovitine blocked cells in the G2/M-phase. Both compounds significantly downregulated the transcriptional activity of cdk4, while melatonin also downregulated cdk2 and cyclin D1. Taken together, our data show that melatonin at millimolar concentrations inhibits dopaminergic B65 proliferation, induces cell apoptosis, and modulates cell cycle progression by inhibiting the transcriptional activity of cyclins and cdks related to the progression of the G1-phase.

Novel squamosamide derivative (compound FLZ) attenuates Abeta25-35-induced toxicity in SH-SY5Y cells

AIM

The aim of the present study was to investigate the protective effect of compound N-[2-(4-hydroxy-phenyl)-ethyl]-2-(2,5-dimethoxy-phenyl)-3-(3-methoxy-4-hydroxy-phenyl)-acrylamide (compound FLZ), a novel synthetic analogue of nature squamosamide, on Abeta25-35-induced toxicity and its active mechanism in human neuroblastoma SH-SY5Y cells.

METHODS

SH-SY5Y cells were pre-incubated with various concentrations of compound FLZ for 30 min and then cultivated with Abeta25-35 (25 micromol/L) for 48 h to induce neurotoxicity. Cell viability, lactate dehydrogenase (LDH) release, and the glutathione (GSH) level were determined by a biochemical analysis. The cell apoptotic ratio and intracellular reactive oxygen species (ROS) level were measured by a flow cytometry analysis. The expression of apoptosis protein (Bcl-2 and Bax) and cytochrome c release were assayed by the Western blot method.

RESULTS

The pretreatment of SH-SY5Y cells with FLZ (1 and 10 micromol/L) markedly increased cell viability and decreased LDH release and morphological injury. Also, FLZ attenuated the Abeta25-35-induced apoptotic cell ratio, regulated the apoptosis protein (Bcl-2 and Bax) expression, and decreased the cytochrome c release from mitochondria. FLZ also significantly inhibited the generation of ROS and the depletion of GSH induced by Abeta25-35 in SH-SY5Y cells.

CONCLUSION

FLZ has protective action against Abeta25-35-induced toxicity in SH-SY5Y cells, which might be mediated through its antioxidant property.

Melatonin Regulates the Viability and Differentiation of Rat Midbrain Neural Stem Cells

(1) Neurogenesis driven by neural stem cells (NSCs) is regulated by physiological and pathological factors. Melatonin (MT) has profound neurotrophic and neuroprotective effects. Hence, we studied the role of MT in regulating the viability and differentiation of NSCs derived from rat ventral midbrain. (2) NSCs were isolated from the rat ventral midbrain. The viability of NSCs was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-ulfophenyl)-2H-tetrazolium assay. The differentiation of NSCs was examined by analyzing the expression of the neural markers, MT receptors, brain derived neurotropic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) with semi-quantitative RT-PCR, immunofluorescence cytochemistry, and Western blot. (3) Our results showed that MT could promote the viability of NSCs. In addition, MT could significantly elevate the mRNA and protein levels of tyroxine hydroxylase (TH), a marker of dopaminergic neurons, and decrease the expression of the astrocytes maker glial fibrillary acidic protein (GFAP). MT also increased the production of BDNF and GDNF in the cultured NSCs. Meanwhile, we first found that two subtypes of MT receptors, MT1 and MT2, were expressed in the ventral midbrain NSCs. (4) These results demonstrated that MT could induce NSCs to differentiate into dopaminergic neurons and decrease astrocyte production. These findings also suggest that MT could offer a beneficial tool in guiding directional differentiation of NSCs.

Protective effect of benzothiazole derivative KHG21834 on amyloid β-induced neurotoxicity in PC12 cells and cortical and mesencephalic neurons

We have investigated the effect of KHG21834, a benzothiazole derivative, on the amyloid beta protein (Abeta)-induced cell death in rat pheochromocytoma (PC12) cells and rat cortical and mesencephalic neuron-glia cultures. KHG21834 attenuated the Abeta(25-35)-induced apoptotic death in PC12 cells determined by characteristic morphological alterations and positive in situ terminal end-labeling (TUNEL). In the cortical neuron-glia cultures, KHG21834 reduced the Abeta(25-35)-induced apoptosis determined by TUNEL staining. Immunocytochemical analysis and Western blot analysis of Abeta(25-35)-induced neurotoxicity in mesencephalic neuron-glia cultures with anti-tyrosine hydroxylase (TH) antibody showed that Abeta(25-35) decreased the expression of TH protein by 60% and KHG21834 significantly attenuated the Abeta(25-35)-induced reduction in the expression of TH. Moreover, KHG21834 attenuates Abeta(25-35)-induced toxicity concomitant with the reduction of activation of extracellular signal-regulated kinase (ERK)1/2 to a lesser extent. ERK1 was more sensitively affected than ERK2 in attenuation of Abeta(25-35)-induced phosphorylation by KHG21834. These results demonstrated that KHG21834 was capable of protecting neuronal cells from Abeta(25-35)-induced degeneration.

Melatonin attenuates lipopolysaccharide (LPS)-induced apoptotic liver damage in d-galactosamine-sensitized mice

D-Galactosamine (GalN) depletes UTP primarily in liver, resulting in decreased RNA synthesis in hepatocytes. When given together with a sublethal dose of lipopolysaccharide (LPS), GalN highly sensitizes animals to produce apoptotic liver injury with severe hepatic congestion, resulting in rapid death. Melatonin is a cytokine modulator, antioxidant and anti-apoptotic agent. In the present study, we investigated the effect of melatonin on LPS-induced apoptotic liver damage in GalN-sensitized mice. Female CD-1 mice were intraperitoneally (i.p.) injected with melatonin (5.0mg/kg) 30min before GalN/LPS (700mg10microg/kg, i.p.), another two doses of melatonin (2.5mg/kg, i.p.) being administered 1 and 2h after GalN/LPS. Results showed that serum alanine aminotransferase (ALT) activities were markedly increased 8h after GalN/LPS treatment, massive hemorrhage being observed in histological sections of liver from GalN/LPS-treated mice. Melatonin significantly attenuated GalN/LPS-induced elevation of serum ALT. In parallel, melatonin distinctly improved GalN/LPS-induced congestion. Additional experiment showed that melatonin significantly attenuated GalN/LPS-induced hepatic apoptosis, measured by inhibition of caspase-3 activities and attenuation of DNA laddering. Furthermore, melatonin markedly increased hepatic Se-dependent glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Rd) activities and attenuated hepatic glutathione (GSH) depletion in GalN/LPS-treated mice. Increases in serum tumor necrosis factor alpha (TNF-alpha), which were observed in GalN/LPS-treated mice, were significantly reduced by melatonin. However, melatonin had no effect on LPS-evoked nitric oxide production in GalN-sensitized mice. Taken together, these results indicate that melatonin protected against LPS-induced liver damage in GalN-sensitized mice through its strong ROS-scavenging, antiinflammatory and antiapoptotic effects.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

Disturbance and strategies for reactivation of the circadian rhythm system in aging and Alzheimer's disease

Circadian rhythm disturbances, such as sleep disorders, are frequently seen in aging and are even more pronounced in Alzheimer's disease (AD). Alterations in the biological clock, the suprachiasmatic nucleus (SCN), and the pineal gland during aging and AD are considered to be the biological basis for these circadian rhythm disturbances. Recently, our group found that pineal melatonin secretion and pineal clock gene oscillation were disrupted in AD patients, and surprisingly even in non-demented controls with the earliest signs of AD neuropathology (neuropathological Braak stages I-II), in contrast to non-demented controls without AD neuropathology. Furthermore, a functional disruption of the SCN was observed from the earliest AD stages onwards, as shown by decreased vasopressin mRNA, a clock-controlled major output of the SCN. The observed functional disconnection between the SCN and the pineal from the earliest AD stage onwards seems to account for the pineal clock gene and melatonin changes and underlies circadian rhythm disturbances in AD. This paper further discusses potential therapeutic strategies for reactivation of the circadian timing system, including melatonin and bright light therapy. As the presence of melatonin MT1 receptor in the SCN is extremely decreased in late AD patients, supplementary melatonin in the late AD stages may not lead to clear effects on circadian rhythm disorders.

Melatonin protection against lead-induced changes in human neuroblastoma cell cultures

The nervous system is the primary target for low-levels of lead (Pb) exposure and the developing brain appears to be especially vulnerable to Pb neurotoxicity. Chronic low-level Pb exposure causes growth retardation and intellectual impairment. In the present study the protective effect of melatonin during exposure to low-levels of Pb in human SH-SY5Y neuroblastoma cell cultures was assessed. The cells were exposed to Pb (0.01 to 10 microM) for 48 h. Pb inhibited the proliferation of neuroblastoma cells significantly in a concentration-dependent manner. A 50% inhibition (IC50) of cell proliferation was observed at about 5 microM Pb. Pb decreased (16% to 62%) the levels of total cellular glutathione (GSH) in a concentration (0.1 to 10 microM)-dependent manner. Exposure of cells to Pb (5 microM) for 48 h resulted in an eightfold increase in caspase-3 activity and prostaglandin E2 (PGE2) level. Pretreatment with melatonin (10 microM) blocked the effects of Pb on GSH content and caspase-3 activity, and showed significant improvement in reducing the level of PGE2. The results suggest that some of the neurotoxic effects of Pb may be partly mediated by apoptosis and pretreatment with melatonin can prevent these effects. The present study asserts the neuroprotective effect of melatonin in conditions of Pb-induced toxicity in neuroblastoma cell cultures.

Inhibition of the cdk5/p25 fragment formation may explain the antiapoptotic effects of melatonin in an experimental model of Parkinson's disease

In this study, the effects of melatonin on MPP+ -treated cerebellar granule neurons (CGNs) in culture were investigated. Results showed that MPP+ treatment significantly decreased cell viability and increased the apoptotic cell population at 24 and 48 hr. Calpain and caspase-3 activation was also determined, with results showing a strong increase in calpain (74%) and caspase 3 activity (70%), as measured by alpha-spectrin cleavage and fluorometric and colorimetric analysis, respectively. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in neuronal cell death in neurodegenerative diseases. Moreover, these studies indicate that this cleavage is mediated by calpains, and that MPP+ prompted an increase in cdk5 expression, as well as the cleavage of p35-p25, in a time-dependent manner. 1 mm Melatonin not only reduced the neurotoxic effects of MPP+ on cell viability, but also prevented apoptosis mediated by this Parkinsonian toxin in CGNs. 1 mm Melatonin reduced cdk5 expression, as well as the cleavage of p35-p25. These data indicate that melatonin possesses some neuro-protective properties against MPP+ -induced apoptosis. Moreover, these data suggest that the calpain/cdk5 signaling cascade has a potential role in the MPP+ -mediated apoptotic process in CGNs.

Beneficial effects of melatonin in experimental models of Alzheimer disease

Alzheimer's disease (AD), a progressive degenerative disorder, is characterized by the presence of amyloid deposits, neurofibrillary tangles and neuron loss. Emerging evidence indicates that antioxidants could be useful either for the prevention or treatment of AD. It has been shown that melatonin is a potent antioxidant and free radical scavenger. Additionally, melatonin stimulates several antioxidative enzymes and improves mitochondrial energy metabolism. These findings led us to study amyloid precursor protein transgenic mice, ovariectomized rats, and pheochromocytoma and astroglioma cell lines, to observe whether melatonin had any effect on Alzheimer's symptoms or pathological changes. We found that melatonin had many beneficial effects in experimental models of AD, including improvement of cognitive function, anti-oxidative injury, anti-apoptosis, inhibition of beta-amyloid (Abeta) deposition and Abeta fiber formation. Several groups have shown that melatonin has an inhibitory effect on tau protein hyperphosphorylation. These actions may potentially slow down or stop the progression of dementia.

1800 MHz electromagnetic field effects on melatonin release from isolated pineal glands

Isolated pineal glands of Djungarian hamsters (Phodopus sungorus) were continuously perifused by Krebs-Ringer buffer, stimulated with the beta-adrenergic receptor agonist isoproterenol to induce melatonin synthesis, and exposed for 7 hr to a 1800 MHz continuous wave (CW) or pulsed GSM (Global System for Mobile Communications)-modulated electromagnetic signal at specific absorption rate (SAR) rates of 8, 80, 800, and 2700 mW/kg. Experiments were performed in a blind fashion. Perifusate samples were collected every hour, and melatonin concentrations were measured by a specific radioimmunoassay. Both types of signal significantly enhanced melatonin release at 800 mW/kg SAR, while at 2700 mW/kg SAR, melatonin levels were elevated in the CW, but suppressed in the GSM-exposed pineal glands. As a temperature rise of approximately 1.2 degrees C was measured at 2700 mW/kg SAR, effects at this level are thermal. With regard to radiofrequency electromagnetic fields, the data do not support the 'melatonin hypothesis,' according to which nonthermal exposure suppresses melatonin synthesis.

Early melatonin supplementation alleviates oxidative stress in a transgenic mouse model of Alzheimer's disease

Multiple lines of evidence demonstrated that increased brain oxidative stress is a key feature of Alzheimer's disease (AD). Melatonin is a potent endogenous antioxidant and free radical scavenger. A transgenic mouse model for AD mimics the accumulation of senile plaques, neuronal loss, and memory impairment. Four-month-old transgenic mice were administrated melatonin at 10 mg/kg for 4 months. We investigated the long-term influence of melatonin on these mice before amyloid plaques were deposited. We found an increase in the levels of brain thiobarbituric acid-reactive substances (TBARS) and a decrease in glutathione (GSH) content, as well as accelerated upregulation of the apoptotic-related factors, such as Bax, caspase-3, and prostate apoptosis response-4 (Par-4) in transgenic mice, but not in wild-type (WT) littermates. Significantly, the increase in TBARS levels, reduction in superoxide dismutase activity, and GSH content were reinstated by melatonin. In addition, transgenic mice administered melatonin (10 mg/kg) showed a significant reduction in upregulated expression of Bax, caspase-3 and Par-4, indicating inhibited triggering of neuronal apoptosis. These results supported the hypothesis that oxidative stress was an early event in AD pathogenesis and that antioxidant therapy may be beneficial only if given at this stage of the disease process. In sharp contrast to conventional antioxidants, melatonin crosses the blood-brain barrier, is relatively devoid of toxicity, and constitutes a potential therapeutic candidate in AD treatment.

Anti-inflammatory actions of melatonin and its metabolites, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) and N1-acetyl-5-methoxykynuramine (AMK), in macrophages

Inflammation is a complex phenomenon involving multiple cellular and molecular interactions which must be tightly regulated. Cyclooxygenase-2 (COX) is the key enzyme that catalyzes the two sequential steps in the biosynthesis of PGs from arachidonic acid. The inducible isoform of COX, namely COX-2, plays a critical role in the inflammatory response and its over-expression has been associated with several pathologies including neurodegenerative diseases and cancer. Melatonin is the main product of the pineal gland with well documented antioxidant and immuno-modulatory effects. Since the action of the indole on COX-2 has not been previously described, the goal of the present report was to test the effect of melatonin on the activities of COX-2 and inducible nitric oxide synthase (iNOS), using lipopolysaccharide (LPS)-activated RAW 264.7 macrophages as a model. Melatonin and its metabolites, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) and N1-acetyl-5-methoxykynuramine (AMK), prevented COX-2 activation induced by LPS, without affecting COX-1 protein levels. The structurally related compound 6-methoxy-melatonin only partially prevented the increase in COX-2 protein levels induced by the toxin. Likewise melatonin prevented iNOS activation and reduced the concentration of products from both enzymes, PGE(2) and nitric oxide. Another endogenous antioxidant like N-acetyl-cysteine (NAC) did not reduced COX-2 significantly. The current finding corroborates a role of melatonin as an anti-inflammatory agent and, for the first time, COX-2 and iNOS as molecular targets for either melatonin or its metabolites AFMK and AMK. These anti-inflammatory actions seem not to be exclusively mediated by the free radical scavenging properties of melatonin. As a consequence, the present work suggests these substances as a new class of potential anti-inflammatory agents without the classical side effects due to COX-1 inhibition.

Long-term melatonin or 17beta-estradiol supplementation alleviates oxidative stress in ovariectomized adult rats

Melatonin is an endogenously generated potent antioxidant. Our previous results indicated that melatonin improved learning and memory deficits in the transgenic mouse model of Alzheimer's disease (AD) and ovariectomized (OVX) rats by improving cholinergic nerve system dysfunction, preventing apoptosis. In this study we aim to investigate the antioxidative effects of melatonin or estradiol in the brains of ovariectomized rats. OVX Sprague-Dawley rats received daily injections of melatonin (5, 10, or 20 mg/kg), 17beta-estradiol (80 microg/kg), or sesame oil for 16 weeks. We found an increase in brain mitochondrial thiobarbituric acid-reactive substances (TBARS) levels, a decrease in mitochondrial glutathione (GSH) content as well as mitochondrial superoxide dismutase (SOD) activity and upregulation of the apoptotic-related factors, such as Bax, Caspase-3, and Prostate apoptosis response-4 (Par-4) in the frontal cortex of OVX rats. In addition to oxidative stress, OVX also caused decreased activities of mitochondrial respiration complex I and complex IV, which implicated mitochondrial dysfunction. Melatonin or 17beta-estradiol antagonized the detrimental effects induced by OVX. Furthermore, immunohistochemistry results revealed that the abnormal upregulation of the apoptotic related factor such as Bax, Caspase-3, and (Par-4) greatly reduced expression after melatonin or 17beta-estradiol supplement action. These findings demonstrate the important effects of melatonin or 17beta-estradiol on postmenopausal neuropathy and support the potential application of melatonin in the treatment of dementia in postmenopausal women. Early, long-term melatonin application is a promising strategy which could potentially be applied in a clinical setting.