Effects of Melatonin on Nervous System Aging: Neurogenesis and Neurodegeneration

Melatonin effects on animal behavior: circadian rhythm, stress response, and modulation of behavioral patterns

Melatonin plays a crucial role in various behavioral and physiological aspects of animals, including regulating their circadian rhythms. This review provides a comprehensive evaluation of the multifaceted effects of melatonin on animal behavior, such as temperament, stress, and aggression regulation. The focus is on the complex interactions between melatonin and the hormonal and neurotransmitter systems, highlighting how melatonin interacts with cortisol, serotonin, and dopamine to influence behavior. Additionally, it investigates the effects of melatonin on the hypothalamic-pituitary-gonada (HPG) axis and stress responses, emphasizing its potential to improve stress management and social interactions, thereby enhancing animal welfare. The review also examines the seasonal variations of melatonin and its impact on aggression and reproductive activities related to photoperiods, as well as its effects on learning and memory to suggest improvements in animal training methods and practices. Furthermore, it discusses the influence of melatonin on appetite and physical activity regulation, implying its involvement in metabolic processes. In conclusion, further research is needed to elucidate the complex mechanisms underlying the extensive influence of melatonin on animal behavior. Through this review, the aim is to integrate the overall knowledge about melatonin and animal behavioral temperament and to propose new research areas for animal management based on behavioral and hormonal regulation.

Melatonin Augments the Expression of Core Transcription Factors in Aged and Alzheimer's Patient Skin Fibroblasts

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Altered neurogenesis and the appearance of AD pathological hallmarks are fundamental to this disease. SRY-Box transcription factor 2 (Sox2), octamer-binding transcription factor 4 (Oct4), and Nanog are a set of core transcription factors that play a very decisive role in the preservation of pluripotency and the self-renewal capacity of embryonic and adult stem cells. These factors are critically involved in AD pathogenesis, senescence, and aging. Skin fibroblasts are emblematic of cellular damage in patients. We, therefore, in the present study, analyzed the basal expression of these factors in young, aged, and AD fibroblasts. AD fibroblasts displayed an altered expression of these factors, differing from aged and young fibroblasts. Since melatonin is well acknowledged for its anti-aging, anti-senescence and anti-AD therapeutic benefits, we further investigated the effects of melatonin treatment on the expression of these factors in fibroblasts, along with precise validation of the observed data in human neuroblastoma SH-SY5Y cells. Our findings reveal that melatonin administration augmented the expression levels of Sox2, Oct4, and Nanog significantly in both cells. Altogether, our study presents the neuroprotective potential and efficacy of melatonin, which might have significant therapeutic benefits for aging and AD patients.

The role of melatonergic system in intervertebral disc degeneration and its association with low back pain: a clinical study

Objective

The mechanisms of intervertebral disc degeneration (IVDD) in low back pain (LBP) patients are multiples. In this study, we attempt to investigate whether melatonergic system plays a potential role in IVDD patients with LBP by analyzing their clinical specimens. The fucus will be given to the correlation between the melatonin receptor expression and intervertebral disc tissue apoptosis.

Methods

In this clinical study, 107 lumbar intervertebral disc nucleus pulposus (NP) specimens from patients with LBP were collected with patients' consents. The disc height (DH) discrepancy ratio, range of motion and sagittal parameters of the pathological plane were measured and Pfirrmann grade was used to classified the grades of IVDD level. Discs at grades 1-3 were served as normal control and grades 4-5 were considered as IVDD. The expression levels of melatonin receptor 1A (MT1) and 1B (MT2) were measured by immunohistochemistry. The apoptosis of NP was assessed using TUNEL staining. Their potential associations among MT1/2, DH, apoptosis, sagittal parameters with IVDD and LBP were evaluated with statistical analysis.

Results

The incidence of IVDD was positively associated with age and negatively related to VAS scores for LBP (p < 0.001). Patients with higher degree of IVDD also have higher DH discrepancy ratio (p < 0.001), higher prevalence of lumbar instability (p = 0.003) and higher cell apoptosis compared to the control. Nevertheless, no statistically significant correlation was identified between Pfirrmann grade and lumbar sagittal parameters. MT1 and MT2 both were highly expressed in the NP tissues. Importantly, MT1 expression but not MT2 was significantly increased in the intervertebral disc tissue of patients with IVDD and its level correlated well with cell apoptosis level and the severity of IVDD as well as lower VAS scores for LBP.

Conclusion

The highly elevated MT1 expression was found in NP tissues of patients with IVDD and LBP compared to the control. This phenomenon probably reflects the compensating response of the body to the pathological alteration of the IVDD and LBP. Therefore, these findings provide the novel information to use selective agonists of MT1 to target IVDD and LBP clinically.

Modulation of neural circuits by melatonin in neurodegenerative and neuropsychiatric disorders

Neurodegenerative and neuropsychiatric disorders are two broad categories of neurological disorders characterized by progressive impairments in movement and cognitive functions within the central and peripheral nervous systems, and have emerged as a significant cause of mortality. Oxidative stress, neuroinflammation, and neurotransmitter imbalances are recognized as prominent pathogenic factors contributing to cognitive deficits and neurobehavioral anomalies. Consequently, preventing neurodegenerative and neuropsychiatric diseases has surfaced as a pivotal challenge in contemporary public health. This review explores the investigation of neurodegenerative and neuropsychiatric disorders using both synthetic and natural bioactive compounds. A central focus lies on melatonin, a neuroregulatory hormone secreted by the pineal gland in response to light-dark cycles. Melatonin, an amphiphilic molecule, assumes multifaceted roles, including scavenging free radicals, modulating energy metabolism, and synchronizing circadian rhythms. Noteworthy for its robust antioxidant and antiapoptotic properties, melatonin exhibits diverse neuroprotective effects. The inherent attributes of melatonin position it as a potential key player in the pathophysiology of neurological disorders. Preclinical and clinical studies have demonstrated melatonin's efficacy in alleviating neuropathological symptoms across neurodegenerative and neuropsychiatric conditions (depression, schizophrenia, bipolar disorder, and autism spectrum disorder). The documented neuroprotective prowess of melatonin introduces novel therapeutic avenues for addressing neurodegenerative and psychiatric disorders. This comprehensive review encompasses many of melatonin's applications in treating diverse brain disorders. Despite the strides made, realizing melatonin's full neuroprotective potential necessitates further rigorous clinical investigations. By unravelling the extended neuroprotective benefits of melatonin, future studies promise to deepen our understanding and augment the therapeutic implications against neurological deficits.

Melatonin secretion patterns are associated with cognitive vulnerability and brain structure in bipolar depression

Circadian rhythm disruption is a core symptom of bipolar disorder (BD), also reflected in altered patterns of melatonin release. Reductions of grey matter (GM) volumes are well documented in BD. We hypothesized that levels and timing of melatonin secretion in bipolar depression could be associated with depressive psychopathology and brain GM integrity. The onset of melatonin secretion under dim light conditions (DLMO) and the amount of time between DLMO and midsleep (i.e. phase angle difference; PAD) were used as circadian rhythm markers. To study the time course of melatonin secretion, an exponential curve fitting the melatonin values was calculated, and the slope coefficients (SLP) were obtained for each participant. Significant differences were found between HC and BD in PAD measures and melatonin profiles. Correlations between PAD and depressive psychopathology were identified. Melatonin secretion patterns were found to be associated with GM volumes in the Striatum and Supramarginal Gyrus in BD. Our findings emphasized the role of melatonin secretion role as a biological marker of circadian synchronization in bipolar depression and provided a novel insight for a link between melatonin release and brain structure.

Melatonin Prevents Depression but Not Anxiety-like Behavior Produced by the Chemotherapeutic Agent Temozolomide: Implication of Doublecortin Cells and Hilar Oligodendrocytes

Melatonin is a hormone synthesized by the pineal gland with neuroprotective and neurodevelopmental effects. Also, melatonin acts as an antidepressant by modulating the generation of new neurons in the dentate gyrus of the hippocampus. The positive effects of melatonin on behavior and neural development may suggest it is used for reverting stress but also for the alterations produced by chemotherapeutic drugs influencing behavior and brain plasticity. In this sense, temozolomide, an alkylating/anti-proliferating agent used in treating brain cancer, is associated with decreased cognitive functions and depression. We hypothesized that melatonin might prevent the effects of temozolomide on depression- and anxiety-like behavior by modulating some aspects of the neurogenic process in adult Balb/C mice. Mice were treated with temozolomide (25 mg/kg) for three days of two weeks, followed by melatonin (8 mg/kg) for fourteen days. Temozolomide produced short- and long-term decrements in cell proliferation (Ki67-positive cells: 54.89% and 53.38%, respectively) and intermediate stages of the neurogenic process (doublecortin-positive cells: 68.23% and 50.08%, respectively). However, melatonin prevented the long-term effects of temozolomide with the increased number of doublecortin-positive cells (47.21%) and the immunoreactivity of 2' 3'-Cyclic-nucleotide-3 phosphodiesterase (CNPase: 82.66%), an enzyme expressed by mature oligodendrocytes, in the hilar portion of the dentate gyrus. The effects of melatonin in the temozolomide group occurred with decreased immobility in the forced swim test (45.55%) but not anxiety-like behavior. Thus, our results suggest that melatonin prevents the harmful effects of temozolomide by modulating doublecortin cells, hilar oligodendrocytes, and depression-like behavior tested in the forced swim test. Our study could point out melatonin's beneficial effects for counteracting temozolomide's side effects.

Reaction of different cell types of the brain on neurotoxin cuprizone and hormone melatonin treatment in young and aging mice

Introduction

The brain myelin and neurons destruction in multiple sclerosis may be associated with the production of neuroinflammatory cells (macrophages, astrocytes, T-lymphocytes) of pro-inflammatory cytokines and free radicals. The age-associated changes of the above cells can influence on the response of nervous system cells to toxic damaging and regulatory factors of humoral/endocrine nature, in particular pineal hormone melatonin. The study aim was (1) to evaluate changes of the brain macrophages, astrocytes, T-cells, neural stem cells, neurons, and central nervous system (CNS) functioning in the neurotoxin cuprizone-treated mice of different age; and (2) to assess in such mice the effects of exogenous melatonin and possible courses of its action.

Methods

A toxic demyelination and neurodegeneration model was induced in 129/Sv mice aged 3-5 and 13-15 months by adding cuprizone neurotoxin to their food for 3 weeks. From the 8th day of the cuprizone treatment, melatonin was injected intraperitoneally at 6 p.m. daily, at a dose of 1 mg/kg. The brain GFPA + -cells were evaluated by immunohistochemical method, the proportion of CD11b+, CD3+CD11b+, CD3+, CD3+CD4+, CD3+CD8+, Nestin+-cells was determined via flow cytometry. Macrophage activity was evaluated by their ability to phagocytose latex beads Morphometric analysis of the brain neurons and the behavioral reactions ("open field" and rotarod tests) were performed. To assess the involvement of the bone marrow and thymus in the action of melatonin, the amount of granulocyte/macrophage colony-forming cells (GM-CFC), and blood monocytes and thymic hormone thymulin were evaluated.

Results and discussion

The numbers of the GFAP+-, CD3+-, CD3+CD4+, CD3+CD8+, CD11b+, CD3+CD11b+, Nestin+-cells and macrophages phagocytic latex beads and malondialdehyde (MDA) content were increased in the brain of young and aging mice under cuprizone influence. The proportion of undamaged neurons within the brain, motor, affective, and exploratory activities, and muscle tone decreased in mice of both ages. Introducing melatonin to mice of any age reduced the number of GFAP+-, CD3+- cells and their subpopulations, macrophage activation, and MDA content. At the same time, the percentage of brain neurons that were unchanged increased as the number of Nestin+ cells decreased. The behavioral responses were also improved. Besides, the number of bone marrow GM-CFC and the blood level of monocytes and thymulin increased. The effects of both neurotoxin and melatonin on the brain astrocytes, macrophages T-cells, and immune system organs as well as the structure and functioning of neurons were more pronounced in the young mice.

Conclusion

We have observed the involvement of the astrocytes, macrophages, T-cells, neural stem cells, and neurons in the brain reaction of mice different age after administration of neurotoxin cuprizone and melatonin. The brain cell composition reaction has the age features. The neuroprotective effects of melatonin in cuprizone-treated mice have been realized through an improvement of the brain cell composition and oxidative stress factors and functioning of bone marrow and thymus.

Effect and Mechanism of Exogenous Melatonin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic review and Meta-analysis

Melatonin (MT) has been reported to control and prevent Alzheimer's disease (AD) in the clinic; however, the effect and mechanism of MT on AD have not been specifically described. Therefore, the main purpose of this meta-analysis was to explore the effect and mechanism of MT on AD models by studying behavioural indicators and pathological features. Seven databases were searched and 583 articles were retrieved. Finally, nine studies (13 analyses, 294 animals) were included according to pre-set criteria. Three authors independently judged the selected literature and the methodological quality. Meta-analysis showed that MT markedly ameliorated the learning ability by reducing the escape latency (EL), and the memory deficit was significantly corrected by increasing the dwell time in the target quadrant and crossings over the platform location in the Morris Water Maze (MWM). Among the pathological features, subgroup analysis found that MT may ease the symptoms of AD mainly by reducing the deposition of Aβ40 and Aβ42 in the cortex. In addition, MT exerted a superior effect on ameliorating the learning ability of senescence-related and metabolic AD models, and corrected the memory deficit of the toxin-induced AD model. The study was registered at PROSPERO (CRD42021226594).

Chronic Treatment with Melatonin Improves Hippocampal Neurogenesis in the Aged Brain and Under Neurodegeneration

Adult hippocampal neurogenesis is altered during aging and under different neuropsychiatric and neurodegenerative diseases. Melatonin shows neurogenic and neuroprotective properties during aging and neuropathological conditions. In this study, we evaluated the effects of chronic treatment with melatonin on different markers of neurodegeneration and hippocampal neurogenesis using immunohistochemistry in the aged and neurodegenerative brains of SAMP8 mice, which is an animal model of accelerated senescence that mimics aging-related Alzheimer’s pathology. Neurodegenerative processes observed in the brains of aged SAMP8 mice at 10 months of age include the presence of damaged neurons, disorganization in the layers of the brain cortex, alterations in neural processes and the length of neuronal prolongations and β-amyloid accumulation in the cortex and hippocampus. This neurodegeneration may be associated with neurogenic responses in the hippocampal dentate gyrus of these mice, since we observed a neurogenic niche of neural stem and progenitor/precursors cells in the hippocampus of SAMP8 mice. However, hippocampal neurogenesis seems to be compromised due to alterations in the cell survival, migration and/or neuronal maturation of neural precursor cells due to the neurodegeneration levels in these mice. Chronic treatment with melatonin for 9 months decreased these neurodegenerative processes and the neurodegeneration-induced neurogenic response. Noticeably, melatonin also induced recovery in the functionality of adult hippocampal neurogenesis in aged SAMP8 mice.

Fe3O4 Nanozymes Improve Neuroblast Differentiation and Blood-Brain Barrier Integrity of the Hippocampal Dentate Gyrus in D-Galactose-Induced Aged Mice

Aging is a process associated with blood-brain barrier (BBB) damage and the reduction in neurogenesis, and is the greatest known risk factor for neurodegenerative disorders. However, the effects of Fe₃O₄ nanozymes on neurogenesis have rarely been studied. This study examined the effects of Fe₃O₄ nanozymes on neuronal differentiation in the dentate gyrus (DG) and BBB integrity of D-galactose-induced aged mice. Long-term treatment with Fe₃O₄ nanozymes (10 μg/mL diluted in ddH₂O daily) markedly increased the doublecortin (DCX) immunoreactivity and decreased BBB injury induced by D-galactose treatment. In addition, the decreases in the levels of antioxidant proteins including superoxide dismutase (SOD) and catalase as well as autophagy-related proteins such as Becin-1, LC3II/I, and Atg7 induced by D-galactose treatment were significantly ameliorated by Fe₃O₄ nanozymes in the DG of the mouse hippocampus. Furthermore, Fe₃O₄ nanozyme treatment showed an inhibitory effect against apoptosis in the hippocampus. In conclusion, Fe₃O₄ nanozymes can relieve neuroblast damage and promote neuroblast differentiation in the hippocampal DG by regulating oxidative stress, apoptosis, and autophagy.

Melatonin as an Anti-Aging Therapy for Age-Related Cardiovascular and Neurodegenerative Diseases

The concept of “aging” is defined as the set of gradual and progressive changes in an organism that leads to an increased risk of weakness, disease, and death. This process may occur at the cellular and organ level, as well as in the entire organism of any living being. During aging, there is a decrease in biological functions and in the ability to adapt to metabolic stress. General effects of aging include mitochondrial, cellular, and organic dysfunction, immune impairment or inflammaging, oxidative stress, cognitive and cardiovascular alterations, among others. Therefore, one of the main harmful consequences of aging is the development and progression of multiple diseases related to these processes, especially at the cardiovascular and central nervous system levels. Both cardiovascular and neurodegenerative pathologies are highly disabling and, in many cases, lethal. In this context, melatonin, an endogenous compound naturally synthesized not only by the pineal gland but also by many cell types, may have a key role in the modulation of multiple mechanisms associated with aging. Additionally, this indoleamine is also a therapeutic agent, which may be administered exogenously with a high degree of safety. For this reason, melatonin could become an attractive and low-cost alternative for slowing the processes of aging and its associated diseases, including cardiovascular and neurodegenerative disorders.

Early metabolic impairment as a contributor to neurodegenerative disease: Mechanisms and potential pharmacological intervention

The metabolic syndrome comprises a family of clinical and laboratory findings, including insulin resistance, hyperglycemia, hypertriglyceridemia, low high-density lipoprotein cholesterol levels, and hypertension, in addition to central obesity. The syndrome confers a high risk of cardiovascular mortality. Indeed, metabolic dysfunction has been shown to cause a direct insult to smooth muscle and endothelial components of the vasculature, which leads to vascular dysfunction and hyperreactivity. This, in turn, causes cerebral vasoconstriction and hypoperfusion, eventually contributing to cognitive deficits. Moreover, the metabolic syndrome disrupts key homeostatic processes in the brain, including apoptosis, autophagy, and neurogenesis. Impairment of such processes in the context of metabolic dysfunction has been implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer, Parkinson, and Huntington diseases. The aim of this review is to elucidate the role that the metabolic syndrome plays in the pathogenesis of the latter disorders, with a focus on the role of perivascular adipose inflammation in the peripheral-to-central transduction of the inflammatory insult. This review delineates common signaling pathways that contribute to these pathologies. Moreover, the role of therapeutic agents aimed at treating the metabolic syndrome, as well as their risk factors that interfere with the aforementioned pathways, are discussed as potential interventions for neurodegenerative diseases.

Targeting MicroRNA-144/451-AKT-GSK3β Axis Affects the Proliferation and Differentiation of Radial Glial Cells in the Mouse Hippocampal Dentate Gyrus

It is well known that aging induces a progressive decline in the proliferation and neural differentiation of radial glial cells (RGCs) in the hippocampal dentate gyrus (DG). The function of miR-144/451 is to activate stress-regulated molecular gene expression switches for cell proliferation and differentiation. We found that the miR-144/451 expression in the hippocampus was significantly reduced in aged mice compared to adult mice. Furthermore, the proliferation and neural differentiation of RGCs in the mouse hippocampal DG was decreased by miR-144/451 knockout (miR-144/451^-/-). Antioxidant agents, superoxide dismutases (SODs) and catalase, and the expression of melatonin's receptor in the hippocampus were decreased in the miR-144/451^-/- mice. In addition, the (protein kinase B) AKT/(glycogen synthase kinase 3β) GSK3β/(catenin beta-1) β-catenin signaling pathway was weakly activated in the hippocampus of miR-144/451^-/- mice, which was related to brain neurogenesis. Melatonin treatment improved the expression of miR-144/451 and antioxidant enzymes and activated the AKT/GSK3β/β-catenin pathway in the hippocampus of miR-144/451^-/- mice. When the AKT pathway was inhibited by LY294002, the neurogenerative and antioxidant effects of melatonin were significantly limited in the hippocampus of miR-144/451^-/- mice. In brief, our results indicated that miR-144/451 plays crucial roles in the proliferation and neural differentiation of RGCs via the regulation of the antioxidant and AKT/GSK3β/β-catenin pathways.

Chemotherapy-Induced Cognitive Impairment and Hippocampal Neurogenesis: A Review of Physiological Mechanisms and Interventions

A wide range of cognitive deficits, including memory loss associated with hippocampal dysfunction, have been widely reported in cancer survivors who received chemotherapy. Changes in both white matter and gray matter volume have been observed following chemotherapy treatment, with reduced volume in the medial temporal lobe thought to be due in part to reductions in hippocampal neurogenesis. Pre-clinical rodent models confirm that common chemotherapeutic agents used to treat various forms of non-CNS cancers reduce rates of hippocampal neurogenesis and impair performance on hippocampally-mediated learning and memory tasks. We review the pre-clinical rodent literature to identify how various chemotherapeutic drugs affect hippocampal neurogenesis and induce cognitive impairment. We also review factors such as physical exercise and environmental stimulation that may protect against chemotherapy-induced neurogenic suppression and hippocampal neurotoxicity. Finally, we review pharmacological interventions that target the hippocampus and are designed to prevent or reduce the cognitive and neurotoxic side effects of chemotherapy.

Melatonin: From Neurobiology to Treatment

Melatonin, the major regulator of the sleep/wake cycle, also plays important physiological and pharmacological roles in the control of neuronal plasticity and neuroprotection. Accordingly, the secretion of this hormone reaches the maximal extent during brain development (childhood-adolescence) while it is greatly reduced during aging, a condition associated to altered sleep pattern and reduced neuronal plasticity. Altogether, these properties of melatonin have allowed us to demonstrate in both experimental models and clinical studies the great chronobiotic efficacy and sleep promoting effects of exogenous melatonin. Thus, the prolonged release formulation of melatonin, present as a drug in the pharmaceutical market, has been recently recommended for the treatment of insomnia in over 55 years old subjects.

Neuronal apoptosis can be prevented by the combined therapy with melatonin and hypothermia in a neonatal rat model of hypoxic-ischemic encephalopathy

Introduction

Birth hypoxia is a leading cause of perinatal mortality and neurological morbidity, resulting in central nervous system injury. Cerebral hypoxia and ischemia can produce a severe brain damage following a typical pattern, defined by selective vulnerability of the brain regions. The neonates are most prone to hypoxic-ischemic injuries due to the lack of efficient antioxidant defense. Neonatal hypoxia-ischemia (HI) in a 7-day-old rat HI model can produce cell death by apoptotic or necrotic mechanisms. The degree of apoptotic or necrotic mechanisms responsible for cell death in neonatal hypoxia-ischemia are not very clear as yet. The form of neuronal death may also depend on the severity of ischemic injury. Necrosis predominates in more severe cases, whereas apoptosis occurs in areas with milder ischemic injury. A human study demonstrated apoptotic and necrotic forms of cell death after hypoxic injury, whereas in some brains from stillbirths, only apoptotic figures were observed. The expression of activated caspase-3 reflects the role of apoptosis in neonatal hypoxic ischemic brain injury.

Objectives

The aim of this study was to evaluate the possible neuroprotective effect of melatonin and hypothermia in hypoxic-ischemic encephalopathy in newborn rats. Local damages induced by hypoxia and ischemia were assessed by evaluating the changes in terms of histology and apoptosis.

Methods

The experiment was conducted on 20 newborn Wistar rats premedicated for seven days with melatonin in a dose of 20 mg/kg/day. On the 7^th postnatal day (P7), the newborn rats were exposed to ischemia (by clamping the right carotid artery) and hypobaric hypoxia (8% O₂ for 90 minutes) and some groups to hypothermia.

Results

In this experimental model of neonatal encephalopathy, melatonin, in a dose of 20 mg/kg/day has neuroprotective effect by reducing the number of cells expressing apoptosis in Cornu Ammonis (CA) (Ammon's Horn) CA1, CA2, CA3 and dentate gyrus of the hippocampus when combined with hypothermia.

Conclusion

The results of this study prove that melatonin is protective in ischemic-hypoxic brain injuries, but the protection is conditioned in most of the brain regions (excepting cerebral cortex) by conjugation with post-injury hypothermia treatment.

Melatonin and its mechanism of action in the female reproductive system and related malignancies

Melatonin (N-acetyl-5-methoxytryptamine), the main product of pineal gland in vertebrates, is well known for its multifunctional role which has great influences on the reproductive system. Recent studies documented that melatonin is a powerful free radical scavenger that affects the reproductive system function and female infertility by MT1 and MT2 receptors. Furthermore, cancer researches indicate the influence of melatonin on the modulation of tumor cell signaling pathways resulting in growth inhibitor of the both in vivo/in vitro models. Cancer adjuvant therapy can also benefit from melatonin through therapeutic impact and decreasing the side effects of radiation and chemotherapy. This article reviews the scientific evidence about the influence of melatonin and its mechanism of action on the fertility potential, physiological alteration, and anticancer efficacy, during experimental and clinical studies.

Melatonin as an Oncostatic Molecule Based on Its Anti-Aromatase Role in Breast Cancer

Breast cancer is the most common type of cancer. In the developmental stages of breast cancer, estrogens are strongly involved. As estrogen synthesis is regulated by the enzyme aromatase, targeting the activity of this enzyme represents a therapeutic option. The pineal hormone melatonin may exert a suppressive role on aromatase activity, leading to reduced estrogen biosynthesis. A melatonin-mediated decrease in the expression of aromatase promoters and associated genes would provide suitable evidence of this molecule’s efficacy as an aromatase inhibitor. Furthermore, melatonin intensifies radiation-induced anti-aromatase effects and counteracts the unwanted disadvantages of chemotherapeutic agents. In this manner, this review summarizes the inhibitory role of melatonin in aromatase action, suggesting its role as a possible oncostatic molecule in breast cancer.

Protective Effects of Melatonin on Neurogenesis Impairment in Neurological Disorders and Its Relevant Molecular Mechanisms

Neurogenesis is the process by which functional new neurons are generated from the neural stem cells (NSCs) or neural progenitor cells (NPCs). Increasing lines of evidence show that neurogenesis impairment is involved in different neurological illnesses, including mood disorders, neurogenerative diseases, and central nervous system (CNS) injuries. Since reversing neurogenesis impairment was found to improve neurological outcomes in the pathological conditions, it is speculated that modulating neurogenesis is a potential therapeutic strategy for neurological diseases. Among different modulators of neurogenesis, melatonin is a particularly interesting one. In traditional understanding, melatonin controls the circadian rhythm and sleep-wake cycle, although it is not directly involved in the proliferation and survival of neurons. In the last decade, it was reported that melatonin plays an important role in the regulation of neurogenesis, and thus it may be a potential treatment for neurogenesis-related disorders. The present review aims to summarize and discuss the recent findings regarding the protective effects of melatonin on the neurogenesis impairment in different neurological conditions. We also address the molecular mechanisms involved in the actions of melatonin in neurogenesis modulation.

Daily and seasonal mitochondrial protection: Unraveling common possible mechanisms involving vitamin D and melatonin

From an evolutionary point of view, vitamin D and melatonin appeared very early and share functions related to defense mechanisms. In the current clinical setting, vitamin D is exclusively associated with phosphocalcic metabolism. Meanwhile, melatonin has chronobiological effects and influences the sleep-wake cycle. Scientific evidence, however, has identified new actions of both molecules in different physiological and pathological settings. The biosynthetic pathways of vitamin D and melatonin are inversely related relative to sun exposure. A deficiency of these molecules has been associated with the pathogenesis of cardiovascular diseases, including arterial hypertension, neurodegenerative diseases, sleep disorders, kidney diseases, cancer, psychiatric disorders, bone diseases, metabolic syndrome, and diabetes, among others. During aging, the intake and cutaneous synthesis of vitamin D, as well as the endogenous synthesis of melatonin are remarkably depleted, therefore, producing a state characterized by an increase of oxidative stress, inflammation, and mitochondrial dysfunction. Both molecules are involved in the homeostatic functioning of the mitochondria. Given the presence of specific receptors in the organelle, the antagonism of the renin-angiotensin-aldosterone system (RAAS), the decrease of reactive species of oxygen (ROS), in conjunction with modifications in autophagy and apoptosis, anti-inflammatory properties inter alia, mitochondria emerge as the final common target for melatonin and vitamin D. The primary purpose of this review is to elucidate the common molecular mechanisms by which vitamin D and melatonin might share a synergistic effect in the protection of proper mitochondrial functioning.

Functions of adiponectin signaling in regulating neural plasticity and its application as the therapeutic target to neurological and psychiatric diseases

Convergent lines of evidence indicate the critical roles of adiponectin in regulating neural functions on different levels. Because of the importance in maintaining neural plasticity including adult neurogenesis and synaptic plasticity, adiponectin has the potential to serve as the treatment targets in therapies of neurological and psychiatric disorders. Hence, systematic review is needed to summarize how adiponectin works in the brain, and how the adiponectin pathway is employed as the treatment method needs to be determined. Moreover, the benefits of adiponectin as the regulator for neural plasticity such as synaptic plasticity and neurogenesis have been supported by many literatures. In the current article, we reviewed the functions of adiponectin in different types of neural plasticity. We also demonstrated the potential value of adiponectin as the treatment target for different types of neurodegenerative and psychiatric disorders. Taken together, this review offers a new insight about adiponectin as the ideal target to develop the new treatment methods against neurodegeneration or psychiatric diseases.

Melatonin alleviates intervertebral disc degeneration by disrupting the IL-1β/NF-κB-NLRP3 inflammasome positive feedback loop

The inflammatory response is induced by the overexpression of inflammatory cytokines, mainly interleukin (IL)-1β, and is one of the main causes of intervertebral disc degeneration (IVDD). NLR pyrin domain containing 3 (NLRP3) inflammasome activation is an important source of IL-1β. As an anti-inflammatory neuroendocrine hormone, melatonin plays various roles in different pathophysiological conditions. However, its roles in IVDD are still not well understood and require more examination. First, we demonstrated that melatonin delayed the progression of IVDD and relieved IVDD-related low back pain in a rat needle puncture IVDD model; moreover, NLRP3 inflammasome activation (NLRP3, p20, and IL-1β levels) was significantly upregulated in severely degenerated human discs and a rat IVDD model. Subsequently, an IL-1β/NF-κB-NLRP3 inflammasome activation positive feedback loop was found in nucleus pulposus (NP) cells that were treated with IL-1β. In these cells, expression of NLRP3 and p20 was significantly increased, NF-κB signaling was involved in this regulation, and mitochondrial reactive oxygen species (mtROS) production increased. Furthermore, we found that melatonin disrupted the IL-1β/NF-κB-NLRP3 inflammasome activation positive feedback loop in vitro and in vivo. Melatonin treatment decreased NLRP3, p20, and IL-1β levels by inhibiting NF-κB signaling and downregulating mtROS production. Finally, we showed that melatonin mediated the disruption of the positive feedback loop of IL-1β in vivo. In this study, we showed for the first time that IL-1β promotes its own expression by upregulating NLRP3 inflammasome activation. Furthermore, melatonin disrupts the IL-1β positive feedback loop and may be a potential therapeutic agent for IVDD.

Transcriptome Analysis of Pineal Glands in the Mouse Model of Alzheimer's Disease

The pineal gland maintains the circadian rhythm in the body by secreting the hormone melatonin. Alzheimer's disease (AD) is the most common neurodegenerative disease. Pineal gland impairment in AD is widely observed, but no study to date has analyzed the transcriptome in the pineal glands of AD. To establish resources for the study on pineal gland dysfunction in AD, we performed a transcriptome analysis of the pineal glands of AD model mice and compared them to those of wild type mice. We identified the global change of diverse protein-coding RNAs, which are implicated in the alteration in cellular transport, protein transport, protein folding, collagen expression, histone dosage, and the electron transfer system. We also discovered various dysregulated long noncoding RNAs and circular RNAs in the pineal glands of mice with AD. This study showed that the expression of diverse RNAs with important functional implications in AD was changed in the pineal gland of the AD mouse model. The analyzed data reported in this study will be an important resource for future studies to elucidate the altered physiology of the pineal gland in AD.

Melatonin protects against methotrexate-induced memory deficit and hippocampal neurogenesis impairment in a rat model

Methotrexate (MTX) is a chemotherapy agent linked to cognitive deficits in cancer patients received chemotherapy treatment. MTX decreases cell proliferation in the hippocampus, which is concomitant with cognitive deficits in animal models. The present study aimed to investigate the disadvantages of MTX on cognition associated with cell division, survival, and immature neurons involved in hippocampal neurogenesis, as well as the practical neuroprotective effects of melatonin. Male Sprague Dawley rats were given two injections of MTX (75 mg/kg) on days 8 and 15 followed by Leucovorin (LCV, 6 mg/kg) at hours 18, 26, 42, 50 via i.p. injection. Some rats received co-treatment with melatonin (8 mg/kg, i.p. injection) for 15 days before and during MTX administration (preventive), 15 days after MTX administration (recovery), or both (30 days total; throughout). Hippocampal-dependent memory was examined using novel objection location (NOL) and novel object recognition (NOR) tests. Cell division, survival and immature neurons in the subgranular zone (SGZ) in the hippocampus were evaluated using immunofluorescence staining. Rats given MTX/LCV were found to have cognitive memory deterioration based on the NOL and NOR tests. Moreover, reductions in cell division, cell survival, and the numbers of immature neurons were detected in the MTX/LCV group when compared to the controls. This damage was not observed in rats in the preventive, recovery, or throughout groups. These findings reveal that melatonin has the potential to diminish the negative effects of MTX on memory and neurogenesis. This also indicates the benefit of melatonin co-administration in patients who undergo chemotherapy treatment.

The role of melatonin, a multitasking molecule, in retarding the processes of ageing

Biological ageing is generally accompanied by a gradual loss of cellular functions and physiological integrity of organ systems, the consequential enhancement of vulnerability, senescence and finally death. Mechanisms which underlie ageing are primarily attributed to an array of diverse but related factors including free radical-induced damage, dysfunction of mitochondria, disruption of circadian rhythms, inflammaging, genomic instability, telomere attrition, loss of proteostasis, deregulated sensing of nutrients, epigenetic alterations, altered intercellular communication, and decreased capacity for tissue repair. Melatonin, a prime regulator of human chronobiological and endocrine physiology, is highly reputed as an antioxidant, immunomodulatory, antiproliferative, oncostatic, and endocrine-modulatory molecule. Interestingly, several recent reports support melatonin as an anti-ageing agent whose multifaceted functions may lessen the consequences of ageing. This review depicts four categories of melatonin's protective effects on ageing-induced molecular and structural alterations. We also summarize recent findings related to the function of melatonin during ageing in various tissues and organs.

Effects of Melatonin and Its Underlying Mechanism on Ethanol-Stimulated Senescence and Osteoclastic Differentiation in Human Periodontal Ligament Cells and Cementoblasts

The present study evaluated the protective effects of melatonin in ethanol (EtOH)-induced senescence and osteoclastic differentiation in human periodontal ligament cells (HPDLCs) and cementoblasts and the underlying mechanism. EtOH increased senescence activity, levels of reactive oxygen species (ROS) and the expression of cell cycle regulators (p53, p21 and p16) and senescence-associated secretory phenotype (SASP) genes (interleukin [IL]-1β, IL-6, IL-8 and tumor necrosis factor-α) in HPDLCs and cementoblasts. Melatonin inhibited EtOH-induced senescence and the production of ROS as well as the increased expression of cell cycle regulators and SASP genes. However, it recovered EtOH-suppressed osteoblastic/cementoblastic differentiation, as evidenced by alkaline phosphatase activity, alizarin staining and mRNA expression levels of Runt-related transcription factor 2 (Runx2) and osteoblastic and cementoblastic markers (glucose transporter 1 and cementum-derived protein-32) in HPDLCs and cementoblasts. Moreover, it inhibited EtOH-induced osteoclastic differentiation in mouse bone marrow⁻derived macrophages (BMMs). Inhibition of protein never in mitosis gene A interacting-1 (PIN1) by juglone or small interfering RNA reversed the effects of melatonin on EtOH-mediated senescence as well as osteoblastic and osteoclastic differentiation. Melatonin blocked EtOH-induced activation of mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK) and Nuclear factor of activated T-cells (NFAT) c-1 pathways, which was reversed by inhibition of PIN1. This is the first study to show the protective effects of melatonin on senescence-like phenotypes and osteoclastic differentiation induced by oxidative stress in HPDLCs and cementoblasts through the PIN1 pathway.

Cytoprotective Effect of Epigallocatechin Gallate (EGCG)-5'-O-α-Glucopyranoside, a Novel EGCG Derivative

Epigallocatechin gallate (EGCG) is a well-studied polyphenol with antioxidant effects. Since EGCG has low solubility and stability, many researchers have modified EGCG residues to ameliorate these problems. A novel EGCG derivative, EGCG-5′-O-α-glucopyranoside (EGCG-5′Glu), was synthesized, and its characteristics were investigated. EGCG-5′Glu showed antioxidant effects in cell and cell-free systems. Under SNP-derived radical exposure, EGCG-5′Glu decreased nitric oxide (NO) production, and recovered ROS-mediated cell viability. Moreover, EGCG-5′Glu regulated apoptotic pathways (caspases) and cell survival molecules (phosphoinositide 3-kinase (PI3K) and phosphoinositide-dependent kinase 1 (PDK1)). In another radical-induced condition, ultraviolet B (UVB) irradiation, EGCG-5′Glu protected cells from UVB and regulated the PI3K/PDK1/AKT pathway. Next, the proliferative effect of EGCG-5′Glu was examined. EGCG-5′Glu increased cell proliferation by modulating nuclear factor (NF)-κB activity. EGCG-5′Glu protects and repairs cells from external damage via its antioxidant effects. These results suggest that EGCG-5′Glu could be used as a cosmetics ingredient or dietary supplement.

Expression of Cyclin-D1 in Astrocytes Varies During Aging

D-Cyclins control progression through the G1 phase and the G1/S transition of the cell cycle. In the adult brain, they regulate neurogenesis which is limited to the sub-granular zone of the dentate gyrus (DG) and to the sub-ventricular zone (SVZ) of the lateral ventricles. Yet, D-cyclins have also been detected in other parts of the adult brain in differentiated neurons that do not proliferate and rather die by apoptosis in response to cell cycle reactivation. Expression of D-cyclins in astrocytes has also been reported but published results, such as those concerning neurons, appear conflictual. We carried out this study in order to clarify the general pattern of D-cyclin expression in the mouse brain. By performing GFAP/cyclin-D1 double labeling experiments, we detected hypertrophic astrocytes expressing cyclin-D1 in their cytoplasmic processes. Their number increased with age in the hippocampus area but decreased with age in the SVZ. Clusters of astrocytes expressing cyclin-D1 were also detected in the cortical areas of old mice and around blood vessels of neurogenic areas. Other non-asteroidal small cells, probably stem cells, expressed both GFAP and nuclear cyclin-D1 in the neurogenic area of the DG and in the SVZ at a higher density in young mice than in old mice. Finally, cells expressing cyclin-D1 but not GFAP were also found scattered in the striatum and the CA1 region of the hippocampus, and at a high percentage in cortical layers of young and old mice. Our results suggest that astrocytes may control neuronal functions and proliferation by modulating, in normal or altered conditions such as aging or degenerative diseases, cyclin-D1 expression.

Effects of Scopolamine and Melatonin Cotreatment on Cognition, Neuronal Damage, and Neurogenesis in the Mouse Dentate Gyrus

It has been demonstrated that melatonin plays important roles in memory improvement and promotes neurogenesis in experimental animals. We examined effects of melatonin on cognitive deficits, neuronal damage, cell proliferation, neuroblast differentiation and neuronal maturation in the mouse dentate gyrus after cotreatment of scopolamine (anticholinergic agent) and melatonin. Scopolamine (1 mg/kg) and melatonin (10 mg/kg) were intraperitoneally injected for 2 and/or 4 weeks to 8-week-old mice. Scopolamine treatment induced significant cognitive deficits 2 and 4 weeks after scopolamine treatment, however, cotreatment of scopolamine and melatonin significantly improved spatial learning and short-term memory impairments. Two and 4 weeks after scopolamine treatment, neurons were not damaged/dead in the dentate gyrus, in addition, no neuronal damage/death was shown after cotreatment of scopolamine and melatonin. Ki67 (a marker for cell proliferation)- and doublecortin (a marker for neuroblast differentiation)-positive cells were significantly decreased in the dentate gyrus 2 and 4 weeks after scopolamine treatment, however, cotreatment of scopolamine and melatonin significantly increased Ki67- and doublecortin-positive cells compared with scopolamine-treated group. However, double immunofluorescence for NeuN/BrdU, which indicates newly-generated mature neurons, did not show double-labeled cells (adult neurogenesis) in the dentate gyrus 2 and 4 weeks after cotreatment of scopolamine and melatonin. Our results suggest that melatonin treatment recovers scopolamine-induced spatial learning and short-term memory impairments and restores or increases scopolamine-induced decrease of cell proliferation and neuroblast differentiation, but does not lead to adult neurogenesis (maturation of neurons) in the mouse dentate gyrus following scopolamine treatment.

Melatonin antagonizes interleukin-18-mediated inhibition on neural stem cell proliferation and differentiation

Neural stem cells (NSCs) are self‐renewing, pluripotent and undifferentiated cells which have the potential to differentiate into neurons, oligodendrocytes and astrocytes. NSC therapy for tissue regeneration, thus, gains popularity. However, the low survivals rate of the transplanted cell impedes its utilities. In this study, we tested whether melatonin, a potent antioxidant, could promote the NSC proliferation and neuronal differentiation, especially, in the presence of the pro‐inflammatory cytokine interleukin‐18 (IL‐18). Our results showed that melatonin per se indeed exhibited beneficial effects on NSCs and IL‐18 inhibited NSC proliferation, neurosphere formation and their differentiation into neurons. All inhibitory effects of IL‐18 on NSCs were significantly reduced by melatonin treatment. Moreover, melatonin application increased the production of both brain‐derived and glial cell‐derived neurotrophic factors (BDNF, GDNF) in IL‐18‐stimulated NSCs. It was observed that inhibition of BDNF or GDNF hindered the protective effects of melatonin on NSCs. A potentially protective mechanism of melatonin on the inhibition of NSC's differentiation caused IL‐18 may attribute to the up‐regulation of these two major neurotrophic factors, BNDF and GNDF. The findings indicate that melatonin may play an important role promoting the survival of NSCs in neuroinflammatory diseases.

Activation of melatonin receptor (MT1/2) promotes P-gp transporter in methamphetamine-induced toxicity on primary rat brain microvascular endothelial cells

Melatonin has been known as a neuroprotective agent for the central nervous system (CNS) and the blood-brain barrier (BBB), which is the primary structure that comes into contact with several neurotoxins including methamphetamine (METH). Previous studies have reported that the activation of melatonin receptors (MT1/2) by melatonin could protect against METH-induced toxicity in brain endothelial cells via several mechanisms. However, its effects on the P-glycoprotein (P-gp) transporter, the active efflux pump involved in cell homeostasis, are still unclear. Thus, this study investigated the role of melatonin and its receptors on the METH-impaired P-gp transporter in primary rat brain microvascular endothelial cells (BMVECs). The results showed that METH impaired the function of the P-gp transporter, significantly decreasing the efflux of Rho123 and P-gp expression, which caused a significant increase in the intracellular accumulation of Rho123, and these responses were reversed by the interaction of melatonin with its receptors. Blockade of the P-gp transporter by verapamil caused oxidative stress, apoptosis, and cell integrity impairment after METH treatment, and these effects could be reversed by melatonin. Our results, together with previous findings, suggest that the interaction of melatonin with its receptors protects against the effects of the METH-impaired P-gp transporter and that the protective role in METH-induced toxicity was at least partially mediated by the regulation of the P-gp transporter. Thus, melatonin and its receptors (MT1/2) are essential for protecting against BBB impairment caused by METH.

Aging and Oxidative Stress Decrease Pineal Elongation Factor 2: In Vivo Protective Effect of Melatonin in Young Rats Treated With Cumene Hydroperoxide

We studied the alterations of Elongation Factor 2 (eEF2) in the pineal gland of aged rats as well as the possible protective role of exogenous melatonin on these changes in young rats treated with cumene hydroperoxide (CH), a compound that promotes lipid peroxidation and inhibits protein synthesis. The study was performed using male Wistar rats of 3 (control), 12, and 24 months and 3-month-old rats treated with CH, melatonin, and CH plus melatonin. We found that pineal eEF-2 is affected by aging and CH, these changes being prevented by exogenous melatonin in the case of CH-treated rats. The proteomic studies show that many other proteins are affected by aging and oxidative stress in the pineal gland. The results suggest that one of the possible mechanisms underlying pineal gland dysfunction during aging is the effect of lipid peroxidation on eEF-2, which is a key component of protein synthesis machinery. J. Cell. Biochem. 118: 182-190, 2017. © 2016 Wiley Periodicals, Inc.

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.

Does melatonin influence the apoptosis in rat uterus of animals exposed to continuous light?

Melatonin has been described as a protective agent against cell death and oxidative stress in different tissues, including in the reproductive system. However, the information on the action of this hormone in rat uterine apoptosis is low. Our objective was to evaluate the effects of melatonin on mechanisms of cell death in uterus of rats exposed to continuous light stress. Twenty adult Wistar rats were divided into two groups: GContr (vehicle control) and GExp which were treated with melatonin (0.4 mg/mL), both were exposed to continuous light for 90 days. The uterus was removed and processed for quantitative real time PCR (qRT-PCR), using PCR-array plates of the apoptosis pathway; for immunohistochemistry and TUNEL. The results of qRT-PCR of GEXP group showed up-regulation of 13 and 7, pro-apoptotic and anti-apoptotic genes, respectively, compared to GContr group. No difference in pro-apoptotic proteins (Bax, Fas and Faslg) expression was observed by immunohistochemistry, although the number of TUNEL-positive cells was lower in the group treated with melatonin compared to the group not treated with this hormone. Our data suggest that melatonin influences the mechanism and decreases the apoptosis in uterus of rats exposed to continuous light.

Recent Advances in Neurogenic Small Molecules as Innovative Treatments for Neurodegenerative Diseases

The central nervous system of adult mammals has long been considered as a complex static structure unable to undergo any regenerative process to refurbish its dead nodes. This dogma was challenged by Altman in the 1960s and neuron self-renewal has been demonstrated ever since in many species, including humans. Aging, neurodegenerative, and some mental diseases are associated with an exponential decrease in brain neurogenesis. Therefore, the controlled pharmacological stimulation of the endogenous neural stem cells (NSCs) niches might counteract the neuronal loss in Alzheimer’s disease (AD) and other pathologies, opening an exciting new therapeutic avenue. In the last years, druggable molecular targets and signalling pathways involved in neurogenic processes have been identified, and as a consequence, different drug types have been developed and tested in neuronal plasticity. This review focuses on recent advances in neurogenic agents acting at serotonin and/or melatonin systems, Wnt/β-catenin pathway, sigma receptors, nicotinamide phosphoribosyltransferase (NAMPT) and nuclear erythroid 2-related factor (Nrf2).

Melatonin decreases brain apoptosis, oxidative stress, and CD200 expression and increased survival rate in mice infected by Venezuelan equine encephalitis virus

BACKGROUND

Pro-inflammatory and oxidative events during brain Venezuelan equine encephalitis virus infection could lead to apoptosis and induce anti-inflammatory responses (increased expression of CD200). The aim of this study was to determine the effect of melatonin on brain apoptosis, oxidative stress, and CD200 molecule in mice and neuroblastoma cultures infected by Venezuelan equine encephalitis virus.

METHODS

Mice were infected with 10 median lethal doses (LD50) of Venezuelan equine encephalitis virus, treated with melatonin (500 µg/kg bw; three days before infection and during all experimental time) and sacrificed on days 1, 3, and 5 postinfection. Brain samples were obtained at those periods of time. In addition, infected neuroblastoma cell cultures (multiplicity of infection [MOI]: 1) were treated with 0, 0.1, 0.5, and 1 mM of melatonin and analyzed at 2, 4, and 6 h. CD200 and apoptosis expressions were analyzed by immunohistochemistry and TUNEL assay, respectively. Nitrites and malondialdehyde were determined by appropriate biochemical methods.

RESULTS

Increased brain expression of apoptosis, nitrite, and malondialdehyde productions and CD200 of infected mice were found. Melatonin diminished those expressions. Similarly, high apoptosis expression and nitrite and malondialdehyde productions on infected neuroblastoma cultures were diminished by melatonin. Melatonin increased the survival rate (25%) in Venezuelan equine encephalitis virus-infected animals compared with untreated infected mice (0%).

CONCLUSIONS

Neurological damage during brain Venezuelan equine encephalitis virus infection could be mediated by apoptosis and oxidative stress and CD200 molecule could be an important anti-inflammatory response. Melatonin could be beneficial reducing apoptosis and oxidative stress.

Physiological melatonin levels in healthy older people: A systematic review

OBJECTIVE

Melatonin plays a major role in maintaining circadian rhythm. Previous studies showed that its secretion pattern and levels could be disturbed in persons with dementia, psychiatric disorders, sleep disorders or with cancer. Also ageing is a factor that could alter melatonin levels, although previous research provides contradicting results. As melatonin supplementation is increasingly applied in older persons as sleep medication, it is important to know if melatonin levels decrease in healthy ageing and/or secretion patterns change. The objective of this study is to determine physiological levels and secretion patterns of melatonin in healthy older people.

METHODS

We performed a systematic review and searched PubMed and Embase for studies published between January 1st 1980 and October 5th 2015 that measured melatonin in healthy persons aged ≥65years.

RESULTS

Nineteen studies were retrieved. The number of participants ranged from 5 to 60 per study. Melatonin was mostly measured by radioimmunoassay (RIA) and the number of measurements per 24hours varied from 1 to 96. Sixteen studies showed a secretion pattern with a clear peak concentration, mostly at 0200h or 0300h. Maximum concentrations varied greatly from 11.2 to 91.3pgml(-1). Maximum melatonin level in studies with participants mean aged 65-70years was 49.3pgml(-1) and in studies with participants mean aged ≥75years 27.8pgml(-1), p-value <0.001.

CONCLUSION

Total melatonin production in 24hours seems not to change in healthy ageing, but the maximal nocturnal peak concentration of melatonin might decline. It is important to take this into account when prescribing melatonin supplementation to older people.

Mammalian Target of Rapamycin: Its Role in Early Neural Development and in Adult and Aged Brain Function

The kinase mammalian target of rapamycin (mTOR) integrates signals triggered by energy, stress, oxygen levels, and growth factors. It regulates ribosome biogenesis, mRNA translation, nutrient metabolism, and autophagy. mTOR participates in various functions of the brain, such as synaptic plasticity, adult neurogenesis, memory, and learning. mTOR is present during early neural development and participates in axon and dendrite development, neuron differentiation, and gliogenesis, among other processes. Furthermore, mTOR has been shown to modulate lifespan in multiple organisms. This protein is an important energy sensor that is present throughout our lifetime its role must be precisely described in order to develop therapeutic strategies and prevent diseases of the central nervous system. The aim of this review is to present our current understanding of the functions of mTOR in neural development, the adult brain and aging.

Melatonin administration reverses the alteration of amyloid precursor protein-cleaving secretases expression in aged mouse hippocampus

Beta-amyloid (Aβ) peptide is the pathological hallmark of Alzheimer's disease (AD). Interestingly, Aβ is normally synthesized in the brain of healthy people; however, during advanced aging, the level of Aβ peptides increases. As a result, the aggregation of Aβ peptides leads to trafficking problems, synaptic loss, inflammation, and cell death. Melatonin, the hormone primarily synthesized and secreted from the pineal gland, is decreased with progressing age, particularly in Alzheimer's disease patients. The loss of melatonin levels and the abnormal accumulation of some proteins, such as Aβ peptides in the brains of AD patients are considered important factors in the initiation of the cognitive symptoms of dementia. A previous study in mice reported that increased brain melatonin levels remarkably diminished the potentially toxic Aβ peptide levels. The present study showed that aged mice significantly impaired spatial memory in the Morris Water Maze task. We also showed that α-, β-, and γ-secretases, which are type-I membrane protein proteases responsible for Aβ production, showed alterations in both mRNA and protein expression in the hippocampus of aged mice. The long-term administration of melatonin, mice had shorter escape latencies and remained in the target quadrant longer compared to the aged group. Melatonin attenuated the reduction of α-secretase and inhibited the increase of β- and γ-secretases. Moreover, melatonin attenuated the upregulation of pNFkB and the reduction of sirtuin1 in the hippocampus of aged mice. These results suggested that melatonin protected against Aβ peptide production in aged mice. Hence, melatonin loss in aging could be recompensed through dietary supplementation as a beneficial therapeutic strategy for AD prevention and progression.

Effects of melatonin and its analogues on neural stem cells

Neural stem cells (NSCs) are multipotent cells which are capable of self-replication and differentiation into neurons, astrocytes or oligodendrocytes in the central nervous system (CNS). NSCs are found in two main regions in the adult brain: the subgranular zone (SGZ) in the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ). The recent discovery of NSCs in the adult mammalian brain has fostered a plethora of translational and preclinical studies to investigate novel approaches for the therapy of neurodegenerative diseases. Melatonin is the major secretory product synthesized and secreted by the pineal gland and shows both a wide distribution within phylogenetically distant organisms from bacteria to humans and a great functional versatility. Recently, accumulated experimental evidence showed that melatonin plays an important role in NSCs, including its proliferation, differentiation and survival, which are modulated by many factors including MAPK/ERK signaling pathway, histone acetylation, neurotrophic factors, transcription factors, and apoptotic genes. The purpose of this review is to summarize the beneficial effects of melatonin on NSCs and further to discuss the potential usage of melatonin and its derivatives or analogues in the treatment of CNS neurodegenerative diseases.

Melatonin and cortisol profiles in late midlife and their association with age-related changes in cognition

Previous studies have reported an association between circadian disturbances and age-related cognitive impairment. The aim was to study the 24-hour profiles of melatonin and cortisol in relation to cognitive function in middle-aged male subjects. Fifty healthy middle-aged males born in 1953 were recruited from a population-based cohort based on previous cognitive assessments in young adulthood and late midlife. The sample included 24 cognitively high-functioning and 26 cognitively impaired participants. Saliva samples were collected every 4 hours over a 24-hour period and analyzed for cortisol and melatonin levels by immunoassay. All participants exhibited clear circadian rhythms of salivary melatonin and cortisol. Salivary melatonin concentrations had a nocturnal peak at approximately 4 am. The median nocturnal melatonin response at 4 am was significantly lower in the cognitively impaired group than in the high-functioning group (-4.6 pg/mL, 95% CI: -7.84, -1.36, P=0.006). The 24-hour mean melatonin concentration (high-functioning group: 4.80±0.70 pg/mL, vs cognitively impaired group: 4.81±0.76 pg/mL; P>0.05) (or the area under the curve, AUC) was not significantly different between the two groups. Cortisol levels were low during the night, and peaked at approximately 8 am. Median cortisol concentrations were similar at all times, as were the 24-hour mean cortisol concentrations and AUC. To the best of our knowledge, ours is the first study to assess circadian measures (ie, melatonin and cortisol) in healthy middle-aged men with different cognitive trajectories in midlife. We found evidence of altered circadian rhythms with a reduced nocturnal melatonin response at 4 am in men with cognitive impairment. The 24-hour concentration and AUC of melatonin and cortisol were similar in the cognitively high-functioning group and in the cognitively impaired.

CSF generation by pineal gland results in a robust melatonin circadian rhythm in the third ventricle as an unique light/dark signal

Pineal gland is an important organ for the regulation of the bio-clock in all vertebrate species. Its major secretory product is melatonin which is considered as the chemical expression of darkness due to its circadian peak exclusively at night. Pineal melatonin can be either released into the blood stream or directly enter into the CSF of the third ventricle via the pineal recess. We have hypothesized that rather than the peripheral circulatory melatonin circadian rhythm serving as the light/dark signal, it is the melatonin rhythm in CSF of the third ventricle that serves this purpose. This is due to the fact that melatonin circadian rhythm in the CSF is more robust in terms of its extremely high concentration and its precise on/off peaks. Thus, extrapineal-generated melatonin or diet-derived melatonin which enters blood would not interfere with the bio-clock function of vertebrates. In addition, based on the relationship of the pineal gland to the CSF and the vascular structure of this gland, we also hypothesize that pineal gland is an essential player for CSF production. We feel it participates in both the formation and reabsorption of CSF. The mechanisms associated with these processes are reviewed and discussed in this brief review.

Melatonin Counteracts at a Transcriptional Level the Inflammatory and Apoptotic Response Secondary to Ischemic Brain Injury Induced by Middle Cerebral Artery Blockade in Aging Rats

Aging increases oxidative stress and inflammation. Melatonin counteracts inflammation and apoptosis. This study investigated the possible protective effect of melatonin on the inflammatory and apoptotic response secondary to ischemia induced by blockade of the right middle cerebral artery (MCA) in aging male Wistar rats. Animals were subjected to MCA obstruction. After 24 h or 7 days of procedure, 14-month-old nontreated and treated rats with a daily dose of 10 mg/kg melatonin were sacrificed and right and left hippocampus and cortex were collected. Rats aged 2 and 6 months, respectively, were subjected to the same brain injury protocol, but they were not treated with melatonin. mRNA expression of interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), Bcl-2-associated death promoter (BAD), Bcl-2-associated X protein (BAX), glial fibrillary acidic protein (GFAP), B-cell lymphoma 2 (Bcl-2), and sirtuin 1 was measured by reverse transcription–polymerase chain reaction. In nontreated animals, a significant time-dependent increase in IL-1β, TNF-α, BAD, and BAX was observed in the ischemic area of both hippocampus and cortex, and to a lesser extent in the contralateral hemisphere. Hippocampal GFAP was also significantly elevated, while Bcl-2 and sirtuin 1 decreased significantly in response to ischemia. Aging aggravated these changes. Melatonin administration was able to reverse significantly these alterations. In conclusion, melatonin may ameliorate the age-dependent inflammatory and apoptotic response secondary to ischemic cerebral injury.

Melatonin and Ischemic Stroke: Mechanistic Roles and Action

Stroke is one of the most devastating neurological disabilities and brain's vulnerability towards it proves to be fatal and socio-economic loss of millions of people worldwide. Ischemic stroke remains at the center stage of it, because of its prevalence amongst the several other types attacking the brain. The various cascades of events that have been associated with stroke involve oxidative stress, excitotoxicity, mitochondrial dysfunction, upregulation of Ca(2+) level, and so forth. Melatonin is a neurohormone secreted by pineal and extra pineal tissues responsible for various physiological processes like sleep and mood behaviour. Melatonin has been implicated in various neurological diseases because of its antioxidative, antiapoptotic, and anti-inflammatory properties. We have previously reviewed the neuroprotective effect of melatonin in various models of brain injury like traumatic brain injury and spinal cord injury. In this review, we have put together the various causes and consequence of stroke and protective role of melatonin in ischemic stroke.

Melatonin attenuates impairments of structural hippocampal neuroplasticity in OXYS rats during active progression of Alzheimer's disease-like pathology

Translational research on Alzheimer's disease (AD) has often focused on reducing the high cerebral levels of amyloid-β (Aβ) as a key characteristic of AD pathogenesis. There is, however, a growing body of evidence that synaptic dysfunction may be crucial for the development of the most common (sporadic) form of AD. The applicability of melatonin (mainly produced by the pineal gland) to the treatment of AD is actively evaluated, but usually, such studies are based on animal models of early-onset AD, which is responsible for only ~5% of AD cases. We have shown previously that in OXYS rats (an established model of sporadic AD), accumulation of toxic forms of Aβ in the brain occurs later than does the development of signs of neurodegenerative changes and synaptic failure. In this regard, recently, we uncovered beneficial neuroprotective effects of melatonin (prophylactic dietary supplementation) in OXYS rats. Our aim here was to evaluate, starting at the age of active progression of AD-like pathology in OXYS rats, the effects of long-term oral administration of melatonin on the structure of synapses and on neuronal and glial cells of the hippocampus. Melatonin significantly increased hippocampal synaptic density and the number of excitatory synapses, decreased the number of inhibitory synapses, and upregulated pre- and postsynaptic proteins (synapsin I and PSD-95, respectively). Furthermore, melatonin improved the ultrastructure of neuronal and glial cells and reduced glial density. Based on our past and present results, the repair of neuroplasticity by melatonin is a promising strategy against AD.