Melatonin: Clinical Perspectives in Neurodegeneration

Melatonin and the nervous system: nanomedicine perspectives

The mechanism of action of melatonin on the nervous system, sleep, cognitive deficits, and aging is not fully understood. Neurodegenerative diseases (ND) are one of the leading causes of disability and mortality worldwide. Sleeping and cognitive impairments also represent common and serious public health problems, particularly deteriorating with the aging process. Melatonin, as a neuromodulatory hormone, regulates circadian rhythms and the sleep-wake cycle, with functions extending to antioxidant, anti-inflammatory, neuroprotective, and anti-aging properties. However, melatonin is a hydrophobic compound with relatively low water solubility and a short half-life. While melatonin can cross the blood-brain barrier, exogenous melatonin administered orally or intravenously has poor bioavailability, undergoes rapid metabolism in the circulation, and shows limited brain accumulation, ultimately compromising its therapeutic efficacy. In recent years, the convergence of melatonin research with nanomedicine ensures safe therapeutic uses, limited drug degradation, and perspectives for targeted drug delivery to the central nervous system. Here we outline the promising neurotherapeutic properties of nanomaterials as carriers loaded with melatonin drug alone or in combinations with other active molecules.

Melatonin ameliorates astrogliosis and microgliosis in a cuprizone demyelinating mouse model

Background and purpose

Several investigations have reported that melatonin is involved in the amelioration of the inflammatory process, improvement of myelin function, and regeneration in the central nervous system (CNS). The current study aimed to evaluate the protective effect of melatonin in cuprizone (CPZ)-induced myelin damage in the corpus callosum (CC) and explore the plausible underlying mechanisms of remyelination capacity and/or neuroprotection.

Method

We administered cuprizone in chow either alone daily for 6 weeks or combined with simultaneously applied melatonin intra-peritoneal injections. we studied demyelination by LFB staining, oligodendrocyte staining using anti-Olig2 or anti-APC antibodies. In addition, we visualized microgliosis and astrocytosis by staining with anti-Iba-1 and anti-GFAP antibodies. Furthermore, we study the effect of melatonin on mRNA expression of Musashi-1, Hes-1 and Notch-1 genes.

Results

Our data showed that cuprizone intoxication caused a significant oligodendrocyte loss, demyelination, and reactive gliosis in CC. Administration of melatonin prevented the demyelination in CC as determined by Luxol fast blue staining. Furthermore, we found that the melatonin significantly suppressed the cuprizone-induced microgliosis and astrocytosis. while the frequency of oligodendrocytes (Olig2+) was significantly enhanced in the CC after melatonin administration. In addition, melatonin significantly modulated Musashi1, Hes1, and Notch1 mRNA expression in the CC of mice.

Conclusion

These results provide evidence that melatonin abolishes destructive cuprizone effects in the mouse corpus callosum by restoring oligodendrocyte generation, remyelination, and decreasing astrogliosis and microgliosis.

Wearables in Chronomedicine and Interpretation of Circadian Health

Wearable devices have gained increasing attention for use in multifunctional applications related to health monitoring, particularly in research of the circadian rhythms of cognitive functions and metabolic processes. In this comprehensive review, we encompass how wearables can be used to study circadian rhythms in health and disease. We highlight the importance of these rhythms as markers of health and well-being and as potential predictors for health outcomes. We focus on the use of wearable technologies in sleep research, circadian medicine, and chronomedicine beyond the circadian domain and emphasize actigraphy as a validated tool for monitoring sleep, activity, and light exposure. We discuss various mathematical methods currently used to analyze actigraphic data, such as parametric and non-parametric approaches, linear, non-linear, and neural network-based methods applied to quantify circadian and non-circadian variability. We also introduce novel actigraphy-derived markers, which can be used as personalized proxies of health status, assisting in discriminating between health and disease, offering insights into neurobehavioral and metabolic status. We discuss how lifestyle factors such as physical activity and light exposure can modulate brain functions and metabolic health. We emphasize the importance of establishing reference standards for actigraphic measures to further refine data interpretation and improve clinical and research outcomes. The review calls for further research to refine existing tools and methods, deepen our understanding of circadian health, and develop personalized healthcare strategies.

Discovery of Effective Inhibitors Against Phosphodiesterase 9, a Potential Therapeutic Target of Alzheimer's Disease with Antioxidant Capacities

Alzheimer's disease (AD) is a widely recognized type of dementia that leads to progressive cognitive decline and memory loss, affecting a significant number of people and their families worldwide. Given the multifactorial nature of AD, multitarget-directed ligands (MTDLs) hold promise in developing effective drugs for AD. Phosphodiesterase-9 (PDE9) is emerging as a promising target for AD therapy. In this study, by combining a PDE9 inhibitor C33 with the antioxidant melatonin, we designed and discovered a series of pyrazolopyrimidinone derivatives that simultaneously inhibit PDE9 and possess antioxidant activities. Molecular docking, together with dynamics simulations, were applied to accelerate compound design and reduce synthetic work. Four out of the 14 compounds were validated as effective PDE9 inhibitors with comparable antioxidant activity. Notably, compounds 17b and 17d demonstrated IC50 values of 91 and 89 nM against PDE9, respectively, with good antioxidant activities (ORAC (Trolox) of 2.00 and 2.60). This work provides a new approach for designing MTDLs for the treatment of AD and offers insights for further structural modifications of PDE9 inhibitors with antioxidant capacities.

Molecular pathways and biological roles of melatonin and vitamin D; effects on immune system and oxidative stress

Melatonin and vitamin D are associated with the immune system and have important functions as antioxidants. Numerous attempts have been made to identify up to date activities of these molecules in various physiological conditions. The biosynthetic pathways of melatonin and vitamin D are correlated to sun exposure in an inverse manner. Vitamin D is biosynthesized when the skin is exposed to the sun's UV radiation, while melatonin synthesis occurs in the pineal gland principally during night. Additionally, vitamin D is particularly associated with intestinal absorption, metabolism, and homeostasis of ions including calcium, magnesium. However, melatonin has biological marks and impacts on the sleep-wake cycle. The roles of vitamin D and melatonin are opposed to each other individually, but either of them is implicated in the immune system. Recently studies have shown that melatonin and vitamin D have their specific set of aberrations in different cell signaling pathways, such as serine/threonine-specific protein kinase (Akt), phosphoinositide 3-kinase (PI3K), nuclear factor-κB (NF-κB), mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK), Wnt/β-catenin, and Notch. The aim of this review is to clarify the common biological functions and molecular mechanisms through which melatonin and vitamin D could deal with different signaling pathways.

Circadian Effects of Melatonin Receptor-Targeting Molecules In Vitro

Circadian rhythms are important for maintaining homeostasis, from regulating physiological activities (e.g., sleep-wake cycle and cognitive performance) to cellular processes (e.g., cell cycle and DNA damage repair). Melatonin is a key regulator of circadian rhythms and exerts control by binding to melatonin receptor 1 (MT1), decreasing neuronal firing in the suprachiasmatic nucleus (SCN). Previous work studying effects of melatonin on circadian rhythms utilized in vivo models. Since MT1 is also expressed outside of the brain, it is important to study impacts of melatonin on circadian gene oscillations in vitro. We evaluated the effects of melatonin and an MT1 inverse agonist, UCSF7447, in U2OS circadian reporter cell lines, which facilitate detailed assessments of oscillatory changes. We report that cellular circadian rhythms are responsive to treatment with MT1-targeting molecules; their activities are not dependent upon the SCN. Corroborating in vivo data, both melatonin and UCSF7447 lengthened the periods of BMAL1 and PER2, and while melatonin delayed circadian phases, UCSF7447 advanced them. Compounds were also dosed at two different times, however this did not yield changes. Our findings indicate the importance of utilizing in vitro models and that the direct effects of melatonin likely go beyond the SCN and should be explored further.

Circadian Disruption in Glaucoma: Causes, Consequences, and Countermeasures

This review explores the intricate relationship between glaucoma and circadian rhythm disturbances. As a principal organ for photic signal reception and transduction, the eye plays a pivotal role in coordinating the body's circadian rhythms through specialized retinal ganglion cells (RGCs), particularly intrinsically photosensitive RGCs (ipRGCs). These cells are critical in transmitting light signals to the suprachiasmatic nucleus (SCN), the central circadian clock that synchronizes physiological processes to the 24-hour light-dark cycle. The review delves into the central circadian body clock, highlighting the importance of the retino-hypothalamic tract in conveying light information from the eyes to the SCN. It underscores the role of melanopsin in ipRGCs in absorbing light and initiating biochemical reactions that culminate in the synchronization of the SCN's firing patterns with the external environment. Furthermore, the review discusses local circadian rhythms within the eye, such as those affecting photoreceptor sensitivity, corneal thickness, and intraocular fluid outflow. It emphasizes the potential of optical coherence tomography (OCT) in studying structural losses of RGCs in glaucoma and the associated circadian rhythm disruption. Glaucomatous retinal damage is identified as a cause of circadian disruption, with mechanisms including oxidative stress, neuroinflammation, and direct damage to RGCs. The consequences of such disruption are complex, affecting systemic and local circadian rhythms, sleep patterns, mood, and metabolism. Countermeasures, with implications for glaucoma management, are proposed that focus on strategies to improve circadian health through balanced melatonin timing, daylight exposure, and potential chronotherapeutic approaches. The review calls for further research to elucidate the mechanisms linking glaucoma and circadian disruption and to develop effective interventions to address this critical aspect of the disease.

Melatonin antagonizes oxidative stress-induced apoptosis in retinal ganglion cells through activating the thioredoxin-1 pathway

This study aimed to explore the role of melatonin in oxidative stress-induced injury on retinal ganglion cells and the underlying mechanisms. The immortalized RGC-5 cells were treated with H2O2 to induce oxidative injury. Cell viability was measured by Cell Counting Kit-8, and apoptosis was determined by flow cytometry and western blot assays. Reactive oxygen species (ROS), lactate dehydrogenase (LDH), and malondialdehyde (MDA) levels were examined to evaluate oxidative stress levels. In addition, Thioredoxin-1 (Trx1) was silenced in RGC-5 cells using small interfering RNA followed by signaling pathway examination to explore the underlying mechanisms of melatonin in alleviating oxidative injury. Melatonin pre-treatment significantly alleviated H2O2-induced apoptosis in RGC-5 cells. Melatonin also markedly reversed the upregulation of cleaved-caspase 3, cleaved-caspase 9, and Bax expression and downregulation of Bcl-2 expression induced by H2O2. Further analyses presented that melatonin significantly attenuated the increase of ROS, LDH, and MDA levels in RGC-5 cells after H2O2 treatment. Melatonin also abolished the downregulated expression of Superoxide dismutase type 1, Trx1, and Thioredoxin reductase 1, and the reduced activity of thioredoxin reductase in RGC-5 cells after H2O2 treatment. Notably, Trx1 knockdown significantly mitigated the protective effect of melatonin in alleviating H2O2-induced apoptosis and oxidative stress, while administration of compound C, a common inhibitor of c-Jun N-terminal kinase (JNK) signaling, partially reversed the effect of Trx1 silencing, thereby ameliorating the apoptosis and oxidative injury induced by H2O2 in RGC-5 cells. Melatonin could significantly alleviate oxidative stress-induced injury of retinal ganglion cells via modulating Trx1-mediated JNK signaling pathway.

Anti-Aging Tests for Middle Aged Women

The interest in aging and anti-aging research has increased significantly in recent years, leading to rapid expansion in the anti-aging market. Aging is associated with gradual physiological changes and an elevated risk of age-related ailments, and is divided into three categories: usual aging, successful aging, and pathological aging. Each category is associated with distinct implications for health and well-being. Middle-aged women who experience accelerated physiological changes that are intensified by hormonal changes during menopause are particularly vulnerable to chronic diseases. The importance of anti-aging tests is increasing since they enable early identification and intervention. Telomere length, oxidative stress markers, DNA repair markers, RNA profiles, inflammatory markers, hormone levels, and epigenetic changes are some molecular parameters studied to test for aging. In addition, a thorough review of middle-aged women's anti-aging profiles also includes monitoring the vitamin D levels and assessing the effects of endocrine-disrupting substances on ovarian aging. The application of personalized medicine paradigms, utilizing various diagnostic methods, will enable accurate risk prediction and the implementation of focused therapies, ultimately promoting the extension of health span and the improvement of quality of life in middle-aged women.

Protective Activity of Melatonin Combinations and Melatonin-Based Hybrid Molecules in Neurodegenerative Diseases

The identification of protective agents for the treatment of neurodegenerative diseases is the mainstay therapeutic goal to modify the disease course and arrest the irreversible disability progression. Pharmacological therapies synergistically targeting multiple pathogenic pathways, including oxidative stress, mitochondrial dysfunction, and inflammation, are prime candidates for neuroprotection. Combination or synergistic therapy with melatonin, whose decline correlates with altered sleep/wake cycle and impaired glymphatic "waste clearance" system in neurodegenerative diseases, has a great therapeutic potential to treat inflammatory neurodegenerative states. Despite the protective outcomes observed in preclinical studies, mild or poor outcomes were observed in clinical settings, suggesting that melatonin combinations promoting synergistic actions at appropriate doses might be more suitable to treat multifactorial neurodegenerative disorders. In this review, we first summarize the key melatonin actions and pathways contributing to cell protection and its therapeutic implication in Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). We remark the major controversies in the field, mostly generated by the lack of a common consensus for the optimal dosing, molecular targets, and toxicity. Then, we review the literature investigating the efficacy of melatonin combinations with approved or investigational neuroprotective agents and of melatonin-containing hybrid molecules, both in vitro and in animal models of AD, PD, and MS, as well as the efficacy of add-on melatonin in clinical settings. We highlight the rationale for such melatonin combinations with a focus on the comparison with single-agent treatment and on the assays in which an additive or a synergistic effect has been achieved. We conclude that a better characterization of the mechanisms underlying such melatonin synergistic actions under neuroinflammation at appropriate doses needs to be tackled to advance successful clinical translation of neuroprotective melatonin combination therapies or melatonin-based hybrid molecules.

Neuroprotective Effect of Melatonin in a Neonatal Hypoxia-Ischemia Rat Model Is Regulated by the AMPK/mTOR Pathway

BACKGROUND

Melatonin has been shown to be neuroprotective in different animal models of neonatal hypoxic-ischemic brain injury. However, its exact molecular mechanism of action remains unknown. Our aim was to prove melatonin's short- and long-term neuroprotection and investigate its role on the AMPK (AMP-activated protein kinase)/mTOR (mammalian target of rapamycin) pathway following neonatal hypoxic-ischemic brain injury.

METHODS AND RESULTS

Seven-day-old Wistar rat pups were exposed to hypoxia-ischemia, followed by melatonin or vehicle treatment. Detailed analysis of the AMPK/mTOR/autophagy pathway, short- and long-term neuroprotection, myelination, and oligodendrogenesis was performed at different time points. At 7 days after hypoxia-ischemia, melatonin-treated animals showed a significant decrease in tissue loss, increased oligodendrogenesis, and myelination. Long-term neurobehavioral results showed significant motor improvement following melatonin treatment. Molecular pathway analysis showed a decrease in the AMPK expression, with a significant increase at mTOR's downstream substrates, and a significant decrease at the autophagy marker levels in the melatonin group compared with the vehicle group.

CONCLUSIONS

Melatonin treatment reduced brain area loss and promoted oligodendrogenesis with a clear improvement of motor function. We found that melatonin associated neuroprotection is regulated via the AMPK/mTOR/autophagy pathway. Considering the beneficial effects of melatonin and the results of our study, melatonin seems to be an optimal candidate for the treatment of newborns with hypoxic-ischemic brain injury in high- as well as in low- and middle-income countries.

Natural Compounds for Preventing Age-Related Diseases and Cancers

Aging is a multifaceted process influenced by hereditary factors, lifestyle, and environmental elements. As time progresses, the human body experiences degenerative changes in major functions. The external and internal signs of aging manifest in various ways, including skin dryness, wrinkles, musculoskeletal disorders, cardiovascular diseases, diabetes, neurodegenerative disorders, and cancer. Additionally, cancer, like aging, is a complex disease that arises from the accumulation of various genetic and epigenetic alterations. Circadian clock dysregulation has recently been identified as an important risk factor for aging and cancer development. Natural compounds and herbal medicines have gained significant attention for their potential in preventing age-related diseases and inhibiting cancer progression. These compounds demonstrate antioxidant, anti-inflammatory, anti-proliferative, pro-apoptotic, anti-metastatic, and anti-angiogenic effects as well as circadian clock regulation. This review explores age-related diseases, cancers, and the potential of specific natural compounds in targeting the key features of these conditions.

The mechanisms of mitochondrial abnormalities that contribute to sleep disorders and related neurodegenerative diseases

Sleep is a highly intricate biological phenomenon, and its disorders play a pivotal role in numerous diseases. However, the specific regulatory mechanisms remain elusive. In recent years, the role of mitochondria in sleep disorders has gained considerable attention. Sleep deprivation not only impairs mitochondrial morphology but also decreases the number of mitochondria and triggers mitochondrial dysfunction. Furthermore, mitochondrial dysfunction has been implicated in the onset and progression of various sleep disorder-related neurological diseases, especially neurodegenerative conditions. Therefore, a greater understanding of the impact of sleep disorders on mitochondrial dysfunction may reveal new therapeutic targets for neurodegenerative diseases. In this review, we comprehensively summarize the recent key findings on the mechanisms underlying mitochondrial dysfunction caused by sleep disorders and their role in initiating or exacerbating common neurodegenerative diseases. In addition, we provide fresh insights into the diagnosis and treatment of sleep disorder-related diseases.

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

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

Astrocyte response to melatonin treatment in rats under high-carbohydrate high-fat diet

The involvement of consumption of high-carbohydrate high-fat (HCHF) diet in cognitive impairment is attributed, at least in part, to the activation of astrocytes, which contributes to the development of neuroinflammation, oxidative stress, and subsequent cognitive deficits. This study aimed to assess the influence of melatonin on cognitive impairment and astrogliosis induced by the HCHF diet in rats. Male Wistar rats were fed an HCHF diet for eight weeks to induce obesity and metabolic syndrome. Subsequently, they received oral melatonin treatment for four weeks at doses of 5 mg/kg, 10 mg/kg, and 30 mg/kg, alongside the HCHF diet. Cognitive function was evaluated using the Y-maze test, while the levels of proinflammatory cytokines, oxidative stress, and the number glial fibrillary acidic protein (GFAP) positive cells were assessed in the hippocampi and hypothalamus. The consumption of the HCHF diet resulted in weight gain, hyperlipidemia, impaired glucose tolerance, cognitive decline, neuroinflammation, oxidative stress damage, and astrogliosis in rats. Although melatonin treatment did not demonstrate beneficial effects on blood glucose and lipid metabolism, it improved the impaired working memory caused by the HCHF diet. Melatonin exhibited a dose-dependent reduction of astrogliosis, neuroinflammation, and lipid peroxidation while restored superoxide dismutase in the hippocampus and hypothalamus of HCHF diet-treated rats. These findings provide evidence that melatonin inhibits astrocyte activation, thereby attenuating inflammation and minimizing oxidative stress damage induced by the HCHF diet.

Chronotherapeutic Approaches

The chapter provides a comprehensive review of current approaches to personalized chronodiagnosis and chronotherapy. We discuss circadian clock drug targets that aim to affect cellular clock machinery, circadian mechanisms of pharmacokinetics/pharmacodynamics, and chronotherapeutic approaches aimed at increasing treatment efficacy and minimizing its side effects. We explore how chronotherapy can combat acquired and compensatory drug resistance. Non-pharmacological interventions for clock preservation and enhancement are also overviewed, including light treatment, melatonin, sleep scheduling, time-restricted feeding, physical activity, and exercise.

Melatonin in cancer biology: pathways, derivatives, and the promise of targeted delivery

Melatonin, historically recognized for its primary role in regulating circadian rhythms, has expanded its influence particularly due to its wide range of biological activities. It has firmly established itself in cancer research. To highlight its versatility, we delved into how melatonin interacts with key signaling pathways, such as the Wnt/β-Catenin, PI3K, and NF-κB pathways, which play foundational roles in tumor development and progression. Notably, melatonin can intricately modulate these pathways, potentially affecting various cellular functions such as apoptosis, metastasis, and immunity. Additionally, a comprehensive review of current clinical studies provides a dual perspective. These studies confirm melatonin's potential in cancer management but also underscore its inherent limitations, particularly its limited bioavailability, which often relegates it to a supplementary role in treatments. Despite this limitation, there is an ongoing quest for innovative solutions and current advancements include the development of melatonin derivatives and cutting-edge delivery systems. By synthesizing the past, present, and future, this review provides a detailed overview of melatonin's evolving role in oncology, positioning it as a potential cornerstone in future cancer therapeutics.

Melatonin affects the expression of microRNA-21: A mini-review of current evidence

Melatonin (MLT) is an endogenous hormone produced by pineal gland which possess promising anti-tumor effects. Anti-inflammatory and anti-oxidant properties of MLT, along with its immunomodulatory, proapoptotic, and anti-angiogenic properties, are often referred to the main mechanisms of its anti-tumor effects. Recent evidence has suggested that epigenetic alterations are also involved in the anti-tumor properties of MLT. Among these MLT-induced epigenetic alterations is modulation of the expression of several oncogenic and tumor suppressor microRNAs(miRNAs). MiRNAs are among the most promising and potential therapeutic and diagnostic tools in different diseases and enhanced the development of better therapeutic drugs. Suppression of oncomicroRNAs such as microRNA-21, - 20a, and - 27a as well as, up-regulation of microRNA-34 a/c are among the most important effects of MLT on microRNAs homeostasis. Recently, miR-21 has attracted the attention of scientists due to the its wide range of effects on different cancers and diseases. Regulation of this RNA may be a key to the development of better therapeutic targets. The present review will summarize the findings of in vitro and experimental studies of MLT-induced impacts on the expression of microRNAs which are involved in different models and numerous stages of tumor initiation, growth, metastasis, and chemo-resistance.

Potential of Tryptamine Derivatives as Multi-Target Directed Ligands for Alzheimer's Disease: AChE, MAO-B, and COX-2 as Molecular Targets

Extensive research has been dedicated to develop compounds that can target multiple aspects of Alzheimer's disease (AD) treatment due to a growing understanding of AD's complex multifaceted nature and various interconnected pathological pathways. In the present study, a series of biological assays were performed to evaluate the potential of the tryptamine analogues synthesized earlier in our lab as multi-target-directed ligands (MTDLs) for AD. To assess the inhibitory effects of the compounds, various in vitro assays were employed. Three compounds, SR42, SR25, and SR10, displayed significant AChE inhibitory activity, with IC50 values of 0.70 µM, 0.17 µM, and 1.00 µM, respectively. These values superseded the standard drug donepezil (1.96 µM). In the MAO-B inhibition assay, SR42 (IC50 = 43.21 µM) demonstrated superior inhibitory effects as compared to tryptamine and other derivatives. Moreover, SR22 (84.08%), SR24 (79.30%), and SR42 (75.16%) exhibited notable percent inhibition against the COX-2 enzyme at a tested concentration of 100 µM. To gain insights into their binding mode and to validate the biological results, molecular docking studies were conducted. Overall, the results suggest that SR42, a 4,5 nitro-benzoyl derivative of tryptamine, exhibited significant potential as a MTDL and warrants further investigation for the development of anti-Alzheimer agents.

Melatonin in Alzheimer's Disease: Literature Review and Therapeutic Trials

There are currently no effective treatments to prevent, halt, or reverse Alzheimer's disease (AD), the most common cause of dementia in older adults. Melatonin, a relatively harmless over-the-counter supplement, may offer some benefits to patients with AD. Melatonin is known for its sleep-enhancing properties, but research shows that it may provide other advantages as well, such as antioxidant and anti-amyloidogenic properties. Clinical trials for melatonin use in AD have mixed results but, overall, show modest benefits. However, it is difficult to interpret clinical research in this area as there is little standardization to guide the administration and study of melatonin. This review covers basic biology and clinical research on melatonin in AD focusing on prominent hypotheses of pathophysiology of neurodegeneration and cognitive decline in AD (i.e., amyloid and tau hypotheses, antioxidant and anti-inflammation, insulin resistance and glucose homeostasis, the cholinergic hypothesis, sleep regulation, and the hypothalamic-pituitary-adrenal axis and cortisol). This is followed by a discussion on pending clinical trials, considerations for future research protocols, and open questions in the field.

The Effect of Melatonin on Increasing the Health Related Quality of Life in Non-Metastatic Breast Cancer Patients: Three-Year Follow up a Clinical Trial

INTRODUCTION

Although breast cancer is common worldwide, if diagnosed early and treated on time, the probability of recovery is high and patients often experience a long life. Reducing the quality of life is a common side effect in patients. Melatonin may have an important role in fatigue, sleep disorders and, as a result, the health-related quality of life (HRQoL) in people. About 184 patients with breast cancer were enrolled in 2 groups: intervention with daily melatonin intake of 18 mg for 3 years (93 patients) and the control group with placebo intake (91 patients). Health-related quality of life and the effect of melatonin on increasing that were evaluated with the EORTC QLQ-C30 questionnaire, third edition at the beginning, 2 months later and 3 years after the beginning of the study.

RESULTS

The general score of the HRQoL was significantly different both in the passage of time and in the comparative study of the 2 groups, and it was better in the melatonin group (P < .05).

CONCLUSION

Long-term use of 18 mg of melatonin for 3 years in patients with non-metastatic breast cancer can lead to an increase in the patients' quality of life.

Melatonin as a Chronobiotic and Cytoprotector in Non-communicable Diseases: More than an Antioxidant

A circadian disruption, manifested by disturbed sleep and low-grade inflammation, is commonly seen in noncommunicable diseases (NCDs). Cardiovascular, respiratory and renal disorders, diabetes and the metabolic syndrome, cancer, and neurodegenerative diseases are among the most common NCDs prevalent in today's 24-h/7 days Society. The decline in plasma melatonin, which is a conserved phylogenetic molecule across all known aerobic creatures, is a constant feature in NCDs. The daily evening melatonin surge synchronizes both the central pacemaker located in the hypothalamic suprachiasmatic nuclei (SCN) and myriads of cellular clocks in the periphery ("chronobiotic effect"). Melatonin is the prototypical endogenous chronobiotic agent. Several meta-analyses and consensus studies support the use of melatonin to treat sleep/wake cycle disturbances associated with NCDs. Melatonin also has cytoprotective properties, acting primarily not only as an antioxidant by buffering free radicals, but also by regulating inflammation, down-regulating pro-inflammatory cytokines, suppressing low-grade inflammation, and preventing insulin resistance, among other effects. Melatonin's phylogenetic conservation is explained by its versatility of effects. In animal models of NCDs, melatonin treatment prevents a wide range of low-inflammation-linked alterations. As a result, the therapeutic efficacy of melatonin as a chronobiotic/cytoprotective drug has been proposed. Sirtuins 1 and 3 are at the heart of melatonin's chronobiotic and cytoprotective function, acting as accessory components or downstream elements of circadian oscillators and exhibiting properties such as mitochondrial protection. Allometric calculations based on animal research show that melatonin's cytoprotective benefits may require high doses in humans (in the 100 mg/day range). If melatonin is expected to improve health in NCDs, the low doses currently used in clinical trials (i.e., 2-10 mg) are unlikely to be beneficial. Multicentre double-blind studies are required to determine the potential utility of melatonin in health promotion. Moreover, melatonin dosage and levels used should be re-evaluated based on preclinical research information.

Oxidative Stress in Alzheimer's Disease: The Shortcomings of Antioxidant Therapies

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by gradual and progressive cognitive decline leading to dementia. At its core, the neuropathological features of AD include hallmark accumulations of amyloid-β and hyperphosphorylated tau proteins. Other harmful processes, such as oxidative stress and inflammation, contribute to the disease's neuropathological progression. This review evaluates the role of oxidative stress in AD, placing a spotlight on the disappointing outcomes of various antioxidant clinical trials. Several hypotheses are discussed that might elucidate the failures of these therapies in AD. Specifically: 1) The paradoxical and overlooked harmful implications of prooxidant intermediates, particularly stemming from conventional antioxidants like vitamins E and C; 2) The challenges and failure to appreciate the issue of bioavailability-epitomized by the dictum "no on-site protection, no protection"-and the preeminent, yet often ignored, role played by endogenous antioxidant enzymes in combating oxidative stress; 3) The influence of unrecognized etiologies, such as latent infectious agents and others, as foundational drivers of oxidative stress in AD; 4) The underestimation of the complexity of oxidative mechanisms and the necessity of multi-targeted therapeutic approaches, such as those provided by various diets; and 5) The limitations of clinical trial designs in fully capturing the effects of antioxidants on AD progression. This article also examines the outcomes of select clinical trials while highlighting the challenges and barriers these therapies pose, offering insights into potential mechanisms to overcome their marginal success.

Modulating Stress Proteins in Response to Therapeutic Interventions for Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative illness characterized by the degeneration of dopaminergic neurons in the substantia nigra, resulting in motor symptoms and without debilitating motors. A hallmark of this condition is the accumulation of misfolded proteins, a phenomenon that drives disease progression. In this regard, heat shock proteins (HSPs) play a central role in the cellular response to stress, shielding cells from damage induced by protein aggregates and oxidative stress. As a result, researchers have become increasingly interested in modulating these proteins through pharmacological and non-pharmacological therapeutic interventions. This review aims to provide an overview of the preclinical experiments performed over the last decade in this research field. Specifically, it focuses on preclinical studies that center on the modulation of stress proteins for the treatment potential of PD. The findings display promise in targeting HSPs to ameliorate PD outcomes. Despite the complexity of HSPs and their co-chaperones, proteins such as HSP70, HSP27, HSP90, and glucose-regulated protein-78 (GRP78) may be efficacious in slowing or preventing disease progression. Nevertheless, clinical validation is essential to confirm the safety and effectiveness of these preclinical approaches.

Circadian Rhythm Changes in Healthy Aging and Mild Cognitive Impairment

Disruptions in circadian rhythms can occur in healthy aging; however, these changes are more severe and pervasive in individuals with age-related and neurodegenerative diseases, such as dementia. Circadian rhythm alterations are also present in preclinical stages of dementia, for example, in patients with mild cognitive impairments (MCI); thus, providing a unique window of opportunity for early intervention in neurodegenerative disorders. Nonetheless, there is a lack of studies examining the association between relevant changes in circadian rhythms and their relationship with cognitive dysfunctions in MCI individuals. In this review, circadian system alterations occurring in MCI patients are examined compared to healthy aging individuals while also considering their association with MCI neurocognitive alterations. The main findings are that abnormal circadian changes in rest-activity, core body temperature, melatonin, and cortisol rhythms appear in the MCI stage and that these circadian rhythm disruptions are associated with some of the neurocognitive deficits observed in MCI patients. In addition, preliminary evidence indicates that interventions aimed at restoring regular circadian rhythms may prevent or halt the progress of neurodegenerative diseases and mitigate their related cognitive impairments. Future longitudinal studies with repeated follow-up assessments are needed to establish the translational potential of these findings in clinical practice.

Melatonin: a promising neuroprotective agent for cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion (CIR) injury is initiated by the generation of reactive oxygen species (ROS), which leads to the oxidation of cellular proteins, DNA, and lipids as an initial event. The reperfusion process impairs critical cascades that support cell survival, including mitochondrial biogenesis and antioxidant enzyme activity. Failure to activate prosurvival signals may result in increased neuronal cell death and exacerbation of CIR damage. Melatonin, a hormone produced naturally in the body, has high concentrations in both the cerebrospinal fluid and the brain. However, melatonin production declines significantly with age, which may contribute to the development of age-related neurological disorders due to reduced levels. By activating various signaling pathways, melatonin can affect multiple aspects of human health due to its diverse range of activities. Therefore, understanding the underlying intracellular and molecular mechanisms is crucial before investigating the neuroprotective effects of melatonin in cerebral ischemia-reperfusion injury.

Mitochondria in Huntington's disease: implications in pathogenesis and mitochondrial-targeted therapeutic strategies

Huntington's disease is a genetic disease caused by expanded CAG repeats on exon 1 of the huntingtin gene located on chromosome 4. Compelling evidence implicates impaired mitochondrial energetics, altered mitochondrial biogenesis and quality control, disturbed mitochondrial trafficking, oxidative stress and mitochondrial calcium dyshomeostasis in the pathogenesis of the disorder. Unfortunately, conventional mitochondrial-targeted molecules, such as cysteamine, creatine, coenzyme Q10, or triheptanoin, yielded negative or inconclusive results. However, future therapeutic strategies, aiming to restore mitochondrial biogenesis, improving the fission/fusion balance, and improving mitochondrial trafficking, could prove useful tools in improving the phenotype of Huntington's disease and, used in combination with genome-editing methods, could lead to a cure for the disease.

Changes in the Secretion of Melatonin and Selected Adipokines during the Progression of Parkinson's Disease-Preliminary Studies

Parkinson's disease (PD) is one of the most common neurodegenerative diseases affecting elderly people. Considering the gap in the literature on melatonin and adipokine levels in PD patients at various stages of the disease, we conducted a study to investigate the levels of selected parameters in PD patients at the disease's early (ES) and advanced (AS) stages. Melatonin, leptin, adiponectin, and resistin concentrations were measured in the blood serum of 20 PD patients without dyskinesia (ES), 24 PD patients with dyskinesia (AS), and 20 healthy volunteers as a control group (CG). The data were analyzed using ANOVA. Melatonin was significantly lower in ES (p < 0.05) and higher in AS patients (p < 0.05) compared to CG. The level of leptin was increased both in ES (p < 0.001) and AS (p < 0.001) versus CG, while resistin was increased only in patients with dyskinesia (p < 0.05). Higher melatonin (p < 0.001) and resistin (p < 0.05) and lower leptin (p < 0.05) levels were found in AS versus ES. The main findings of the study include the changes in inflammatory markers' levels during PD and a surprising increase in melatonin level in dyskinesia patients. Further research is necessary, which will be aimed at modulating the secretion of melatonin and adipokines as a treatment target for PD.

Melatonin as mitochondria-targeted drug

Oxidative damage is associated to numerous diseases as well as aging development. Mitochondria found in most eukaryotic organisms to create the energy of the cell, generate free radicals during its action and they are chief targets of the oxidants. Mitochondrial activities outspread outside the borders of the cell and effect human physiology by modulating interactions among cells and tissues. Therefore, it has been implicated in several human disorders and conditions. Melatonin (MLT) is an endogenously created indole derivative that modifies several tasks, involving mitochondria-associated activities. These possessions make MLT a powerful defender against a selection of free radical-linked disorders. MLT lessens mitochondrial anomalies causing from extreme oxidative stress and may improve mitochondrial physiology. It is a potent and inducible antioxidant for mitochondria. MLT is produced in mitochondria of conceivably of all cells and it also appears to be a mitochondria directed antioxidant which has related defensive properties as the synthesized antioxidant molecules. This chapter summarizes the suggestion that MLT is produced in mitochondria as well as disorders of mitochondrial MLT production that may associate to a number of mitochondria-linked diseases. MLT as a mitochondria-targeted drug is also discussed.

Therapeutic potential of melatonin and its derivatives in aging and neurodegenerative diseases

Aging is associated with increasing impairments in brain homeostasis and represents the main risk factor across most neurodegenerative disorders. Melatonin, a neuroendocrine hormone that regulates mammalian chronobiology and endocrine functions is well known for its antioxidant potential, exhibiting both cytoprotective and chronobiotic abilities. Age-related decline of melatonin disrupting mitochondrial homeostasis and cytosolic DNA-mediated inflammatory reactions in neurons is a major contributory factor in the emergence of neurological abnormalities. There is scattered literature on the possible use of melatonin against neurodegenerative mechanisms in the aging process and its associated diseases. We have searched PUBMED with many combinations of key words for available literature spanning two decades. Based on the vast number of experimental papers, we hereby review recent advancements concerning the potential impact of melatonin on cellular redox balance and mitochondrial dynamics in the context of neurodegeneration. Next, we discuss a broader explanation of the involvement of disrupted redox homeostasis in the pathophysiology of age-related diseases and its connection to circadian mechanisms. Our effort may result in the discovery of novel therapeutic approaches. Finally, we summarize the current knowledge on molecular and circadian regulatory mechanisms of melatonin to overcome neurodegenerative diseases (NDDs) such as Alzheimer's, Parkinson's, Huntington's disease, and amyotrophic lateral sclerosis, however, these findings need to be confirmed by larger, well-designed clinical trials. This review is also expected to uncover the associated molecular alterations in the aging brain and explain how melatonin-mediated circadian restoration of neuronal homeodynamics may increase healthy lifespan in age-related NDDs.

Nano-melatonin and-histidine modulate adipokines and neurotransmitters to improve cognition in HFD-fed rats: A formula to study

The established correlation between obesity and cognitive impairment portrays pharmacological products aimed at both disorders as an important therapeutic advance. Modulation of dysregulated adipokines and neurotransmitters is hence a critical aspect of the assessment of in-use drugs. At the cellular level, repairments in brain barrier integrity and cognitive flexibility are the main checkpoints. The aim of this study was to investigate whether melatonin and histidine, alone or in combination, could produce weight loss, meanwhile improve the cognitive processes. In this study, obese rat model was established by feeding high fat diet (HFD) composed of 25% fats (soybean oil) for 8 weeks, accompanied by melatonin (10 mg/kg), histidine (780 mg/kg), and combination of both in conventional form and nanoform. At the end of the study, adiposity hormones, neuronal monoamines and amino acids, brain derived neurotrophic factor (BDNF) and zonula occluden-1 (ZO-1) were assessed. HFD feeding resulted in significant weight gain and poor performance on cognitive test. Coadministration of histidine in the nanoform increased the level of ZO-1; an indicator of improving the brain barrier integrity, along with adjusting the adipokines and neurotransmitters levels, which had a positive impact on learning tasks. Cotreatment with melatonin resulted in an increase in the level of BDNF, marking ameliorated synaptic anomalies and learning disabilities, while reducing weight gain. On the other hand, the combination of melatonin and histidine reinstated the synaptic plasticity as well as brain barrier junctions, as demonstrated by increased levels of BDNF and ZO-1, positively affecting weight loss and the intellectual function.

Comment on Minich et al. Is Melatonin the "Next Vitamin D"?: A Review of Emerging Science, Clinical Uses, Safety, and Dietary Supplements. Nutrients 2022, 14, 3934

I read an article by Minich D.M. et al. [...].

Light, Water, and Melatonin: The Synergistic Regulation of Phase Separation in Dementia

The swift rise in acceptance of molecular principles defining phase separation by a broad array of scientific disciplines is shadowed by increasing discoveries linking phase separation to pathological aggregations associated with numerous neurodegenerative disorders, including Alzheimer’s disease, that contribute to dementia. Phase separation is powered by multivalent macromolecular interactions. Importantly, the release of water molecules from protein hydration shells into bulk creates entropic gains that promote phase separation and the subsequent generation of insoluble cytotoxic aggregates that drive healthy brain cells into diseased states. Higher viscosity in interfacial waters and limited hydration in interiors of biomolecular condensates facilitate phase separation. Light, water, and melatonin constitute an ancient synergy that ensures adequate protein hydration to prevent aberrant phase separation. The 670 nm visible red wavelength found in sunlight and employed in photobiomodulation reduces interfacial and mitochondrial matrix viscosity to enhance ATP production via increasing ATP synthase motor efficiency. Melatonin is a potent antioxidant that lowers viscosity to increase ATP by scavenging excess reactive oxygen species and free radicals. Reduced viscosity by light and melatonin elevates the availability of free water molecules that allow melatonin to adopt favorable conformations that enhance intrinsic features, including binding interactions with adenosine that reinforces the adenosine moiety effect of ATP responsible for preventing water removal that causes hydrophobic collapse and aggregation in phase separation. Precise recalibration of interspecies melatonin dosages that account for differences in metabolic rates and bioavailability will ensure the efficacious reinstatement of the once-powerful ancient synergy between light, water, and melatonin in a modern world.

Chronic Administration of Melatonin: Physiological and Clinical Considerations

Background: Exogenous melatonin is commonly used to treat insomnia, other sleep problems, and numerous medical illnesses, including Alzheimer’s disease, autism spectrum disorder, and mild cognitive impairment in adults and children. There is evolving information regarding issues with the use of chronic melatonin. Methods: The present investigation was a narrative review. Results: Melatonin usage has risen dramatically in recent years. Many countries only allow melatonin prescriptions. In the United States (U.S.), it is classified as a dietary supplement accessible over the counter and can be derived from animals, microorganisms, or, most commonly, made synthetically. No regulatory agency oversees its manufacturing or sale in the U.S. melatonin concentration of marketed preparations varies widely between product labels and manufacturers. Melatonin’s ability to induce sleep is detectable. However, it is modest for most people. Sleep length appears to be less important in sustained-release preparations. The optimal dosage is unknown, and routinely used amounts vary substantially. Melatonin’s short-term negative effects are minimal, resolve at medicine cessation, and do not usually prevent usage overall. Much research on long-term melatonin administration has found no difference between exogenous melatonin and placebo in terms of long-term negative effects. Conclusion: Melatonin at low to moderate dosages (approximately 5–6 mg daily or less) appears safe. Long-term usage appears to benefit certain patient populations, such as those with autism spectrum disorder. Studies investigating potential benefits in reducing cognitive decline and increased longevity are ongoing. However, it is widely agreed that the long-term effects of taking exogenous melatonin have been insufficiently studied and warrant additional investigation.

Benefits of the Neurogenic Potential of Melatonin for Treating Neurological and Neuropsychiatric Disorders

There are several neurological diseases under which processes related to adult brain neurogenesis, such cell proliferation, neural differentiation and neuronal maturation, are affected. Melatonin can exert a relevant benefit for treating neurological disorders, given its well-known antioxidant and anti-inflammatory properties as well as its pro-survival effects. In addition, melatonin is able to modulate cell proliferation and neural differentiation processes in neural stem/progenitor cells while improving neuronal maturation of neural precursor cells and newly created postmitotic neurons. Thus, melatonin shows relevant pro-neurogenic properties that may have benefits for neurological conditions associated with impairments in adult brain neurogenesis. For instance, the anti-aging properties of melatonin seem to be linked to its neurogenic properties. Modulation of neurogenesis by melatonin is beneficial under conditions of stress, anxiety and depression as well as for the ischemic brain or after a brain stroke. Pro-neurogenic actions of melatonin may also be beneficial for treating dementias, after a traumatic brain injury, and under conditions of epilepsy, schizophrenia and amyotrophic lateral sclerosis. Melatonin may represent a pro-neurogenic treatment effective for retarding the progression of neuropathology associated with Down syndrome. Finally, more studies are necessary to elucidate the benefits of melatonin treatments under brain disorders related to impairments in glucose and insulin homeostasis.

Cross-sectional analysis of potential risk factors of the pineal gland calcification

The Pineal gland (PG) is the site of production of melatonin as an important central hormone in the body. It is not known yet whether PG calcification (PGC) is an age-associated physiological process or a pathologic condition caused by lifestyle-factors and metabolic-dysregulations.Here, we performed a cross-sectional analysis on 586 patients referred to have Computed Tomographic (CT) scans (above 15 years old), in the Ali Ebne Abi Taleb hospital radiology center in 2017-2018. Based on the CT-scans of the brain, the presence of PGC was recorded and a score of scale 0 to 6 (PGC_score) was calculated for its intensity based on the volume and the Hounsfield units of the calcified pineal. Logistic and ordered logistic regression tests were employed to determine potential risk factor of PGC and higher PGC_score, respectively, testing the factors age, sex, history of cardiovascular and metabolic diseases, smoking and opioid use. We found male sex (OR: 2.30 (95% CI:1.39-3.82) and smoking cigarettes (OR: 4.47 (95% CI:1.01-19.78)) as the main potential risk factors for the pineal gland calcification. For PGC_score, we found age to be dose-dependently associated with PGC_score only in patients aged below 63 (p-trend < 0.001). Stratifying for age, in patients < 63 years old, we found age, male sex (positive association) and dyslipidemia (negative association) as the main significantly associated factors of PGC_score. On the contrary, in patients aged >  = 63, cigarette smoking was the only significantly associated factor of higher PGC_score.In conclusion, our results indicate that at ages below 63, age, male sex and blood lipid are the main associated factors of higher PGC, but at ages above that, the lifestyle factor smoking is significantly associated with higher pineal gland calcification.

Aging, circadian disruption and neurodegeneration: Interesting interplay

The circadian system is an intricate molecular network of coordinating circadian clocks that organize the internal synchrony of the organism in response to the environment. These rhythms are maintained by genetically programmed positive and negative auto-regulated transcriptional and translational feedback loops that sustain 24-hour oscillations in mRNA and protein components of the endogenous circadian clock. Since inter and intracellular activity of the central pacemaker appears to reduce with aging, the interaction between the circadian clock and aging continues to elude our understanding. In this review article, we discuss circadian clock components at the molecular level and how aging adversely affects circadian clock functioning in rodents and humans. The natural decline in melatonin levels with aging strongly contributes to circadian dysregulation resulting in the development of neurological anomalies. Additionally, inappropriate environmental conditions such as Artificial Light at Night (ALAN) can cause circadian disruption or chronodisruption (CD) which can result in a variety of pathological diseases, including premature aging. Furthermore, we summarize recent evidence suggesting that CD may also be a predisposing factor for the development of age-related neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), although more investigation is required to prove this link. Finally, certain chrono-enhancement approaches have been offered as intervention strategies to prevent, alleviate, or mitigate the impacts of CD. This review thus aims to bring together recent advancements in the chronobiology of the aging process, as well as its role in NDDs.

Melatonin: A Potential Candidate for the Treatment of Experimental and Clinical Perinatal Asphyxia

Perinatal asphyxia is considered to be one of the major causes of brain neurodegeneration in full-term newborns. The worst consequence of perinatal asphyxia is neurodegenerative brain damage, also known as hypoxic-ischemic encephalopathy. Hypoxic-ischemic encephalopathy is the leading cause of mortality in term newborns. To date, due to the complex mechanisms of brain damage, no effective or causal treatment has been developed that would ensure complete neuroprotection. Although hypothermia is the standard of care for hypoxic-ischemic encephalopathy, it does not affect all changes associated with encephalopathy. Therefore, there is a need to develop effective treatment strategies, namely research into new agents and therapies. In recent years, it has been pointed out that natural compounds with neuroprotective properties, such as melatonin, can be used in the treatment of hypoxic-ischemic encephalopathy. This natural substance with anti-inflammatory, antioxidant, anti-apoptotic and neurofunctional properties has been shown to have pleiotropic prophylactic or therapeutic effects, mainly against experimental brain neurodegeneration in hypoxic-ischemic neonates. Melatonin is a natural neuroprotective hormone, which makes it promising for the treatment of neurodegeneration after asphyxia. It is supposed that melatonin alone or in combination with hypothermia may improve neurological outcomes in infants with hypoxic-ischemic encephalopathy. Melatonin has been shown to be effective in the last 20 years of research, mainly in animals with perinatal asphyxia but, so far, no clinical trials have been performed on a sufficient number of newborns. In this review, we summarize the advantages and limitations of melatonin research in the treatment of experimental and clinical perinatal asphyxia.

Current Insights into the Risks of Using Melatonin as a Treatment for Sleep Disorders in Older Adults

Exogenous melatonin is commonly used for sleep disorders in older adults, and its use is increasing over time. It appears to have modest efficacy in treating insomnia and circadian rhythm sleep-wake disorders. Melatonin is commonly perceived to be a safe alternative to other hypnotics and is available without prescription in some jurisdictions. New evidence suggests that endogenous melatonin has pleomorphic effects on multiple organ systems, many of which are poorly understood. This narrative review summarizes the current evidence regarding the safety of melatonin in older adults (defined by age over 65 years). Melatonin appears to have a favorable safety profile in this population, however there is a dearth of evidence regarding the safety of prolonged use. There are several factors which increase the risk of adverse effects of melatonin in older adults, and these should be taken into consideration when prescribing to this population.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

The Lymphatic System In The Brain Clearance Mechanisms - New Therapeutic Perspectives For Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Pathological deposits of neurotoxic proteins within the brain, such as amyloid-ß and hyperphosphorylated tau tangles, are the prominent features in AD. According to recent studies, the newly discovered brain lymphatic system was demonstrated to be crucial in the clearance of metabolic macromolecules from the brain. Meningeal lymphatic vessels located in the dura mater drain the fluid, macromolecules, and immune cells from cerebrospinal fluid (CSF) and transport them, as lymph, to the deep cervical lymph nodes. The lymphatic system provides the perivascular exchange of CSF with interstitial fluid (ISF) and ensures the homeostasis of neuronal interstitial space. In this review, we aim to summarize recent findings on the role of the lymphatic system in AD pathophysiology and discuss possible therapeutic perspectives, targeting the lymphatic clearance mechanisms within the brain.

Melatonin and MitoEbselen-2 Are Radioprotective Agents to Mitochondria

Mitochondria are responsible for controlling cell death during the early stages of radiation exposure, but their perturbations are associated with late effects of radiation-related carcinogenesis. Therefore, it is important to protect mitochondria to mitigate the harmful effects of radiation throughout life. The glutathione peroxidase (GPx) enzyme is essential for the maintenance of mitochondrial-derived reactive oxygen species (ROS) levels. However, radiation inactivates the GPx, resulting in metabolic oxidative stress and prolonged cell injury in irradiated normal human fibroblasts. Here, we used the GPx activator N-acetyl-5-methoxy-tryptamine (melatonin) and a mitochondria-targeted mimic of GPx MitoEbselen-2 to stimulate the GPx. A commercial GPx activity assay kit was used to measure the GPx activity. ROS levels were determined by using some ROS indicators. Protein expression associated with the response of mitochondria to radiation was assessed using immunostaining. Concurrent pre-administration or post-administration of melatonin or MitoEbselen-2 with radiation maintained GPx activity and ROS levels and suppressed mitochondrial radiation responses associated with cellular damage and radiation-related carcinogenesis. In conclusion, melatonin and MitoEbselen-2 prevented radiation-induced mitochondrial injury and metabolic oxidative stress by targeting mitochondria. These drugs have the potential to protect against acute radiation injury and late effects of carcinogenesis in a variety of radiation scenarios assuming pre-administration or post-administration.

Research Evidence of the Role of the Glymphatic System and Its Potential Pharmacological Modulation in Neurodegenerative Diseases

The glymphatic system is a unique pathway that utilises end-feet Aquaporin 4 (AQP4) channels within perivascular astrocytes, which is believed to cause cerebrospinal fluid (CSF) inflow into perivascular space (PVS), providing nutrients and waste disposal of the brain parenchyma. It is theorised that the bulk flow of CSF within the PVS removes waste products, soluble proteins, and products of metabolic activity, such as amyloid-β (Aβ). In the experimental model, the glymphatic system is selectively active during slow-wave sleep, and its activity is affected by both sleep dysfunction and deprivation. Dysfunction of the glymphatic system has been proposed as a potential key driver of neurodegeneration. This hypothesis is indirectly supported by the close relationship between neurodegenerative diseases and sleep alterations, frequently occurring years before the clinical diagnosis. Therefore, a detailed characterisation of the function of the glymphatic system in human physiology and disease would shed light on its early stage pathophysiology. The study of the glymphatic system is also critical to identifying means for its pharmacological modulation, which may have the potential for disease modification. This review will critically outline the primary evidence from literature about the dysfunction of the glymphatic system in neurodegeneration and discuss the rationale and current knowledge about pharmacological modulation of the glymphatic system in the animal model and its potential clinical applications in human clinical trials.

Possible Application of Melatonin in Long COVID

Clinical sequelae and symptoms for a considerable number of COVID-19 patients can linger for months beyond the acute stage of SARS-CoV-2 infection, "long COVID". Among the long-term consequences of SARS-CoV-2 infection, cognitive issues (especially memory loss or "brain fog"), chronic fatigue, myalgia, and muscular weakness resembling myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are of importance. Melatonin may be particularly effective at reducing the signs and symptoms of SARS-CoV-2 infection due to its functions as an antioxidant, anti-inflammatory, and immuno-modulatory agent. Melatonin is also a chronobiotic medication effective in treating delirium and restoring the circadian imbalance seen in COVID patients in the intensive care unit. Additionally, as a cytoprotector, melatonin aids in the prevention of several COVID-19 comorbidities, including diabetes, metabolic syndrome, and ischemic and non-ischemic cardiovascular diseases. This narrative review discusses the application of melatonin as a neuroprotective agent to control cognitive deterioration ("brain fog") and pain in the ME/CFS syndrome-like documented in long COVID. Further studies on the therapeutic use of melatonin in the neurological sequelae of SARS-CoV-2 infection are warranted.

Effect of miRs-17/20 on Vasospasm in Subarachnoid Hemorrhage Model of Rats

Aim: To investigate the effects of melatonin and miRNA-17/20 administration on vasospasm and vascular damage on the bacillary artery in the Subarachnoid hemorrhage (SAH) model of rats. Methods: Rats were divided into 6 groups: Sham,SAH,SAH+NegmiRNA,SAH+MEL,SAH-miRs-17/20 group,SAH+MEL+miRs-17/20.For creating the SAH model the skin was cut with a vertical incision in the anterior region of the head.120 µL of fresh non-heparinized autologous arterial blood collected from the tail artery was injected into the prechiasmatic cistern under aseptic conditions. All steps in the Sham were the same as in the SAH group, except for blood injection. In the SAH+NegmiRs-17/20, miRs-17/20 miRNA Mimic-Negative Control#1 was administered 1 hour after SAH operation. In the SAH+MEL,10 mg/kg melatonin was administered intraperitoneally 1 hour after the SAH operation. In the SAH-miRs-17/20,mimic-miR-17 and mimic-miR-20 were given intranasally 1 hour after the SAH operation.In the SAH+MEL+miRs-17/20,intranasal mimic-miR-17 and intraperitoneal melatonin were administered 1 hour after the SAH operation. Brain samples, including the bacillary artery, were taken and subjected to routine tissue processing procedures. Vessel samples were evaluated and graded in histological sections stained with the H-E method in terms of vasospasm, edema in the tunica media, and folding of the lamina elastica interna. Results: The co-administration of melatonin and miRs-17/20 reduced the vasospasm and edema formation in the vessel wall. It has also been demonstrated that the application of miRs-17/20 after SAH alone reduces the development of edema in the vessel wall and folding of the internasal lamina elastica due to vasospasm. Conclusion:It has been shown that miRs-17/20 can reduce vasospasm in the vessel wall and prevent vessel damage by reducing edema.

Redox Biology of Melatonin: Discriminating Between Circadian and Noncircadian Functions

Melatonin has not only to be seen as a regulator of circadian clocks. In addition to its chronobiotic functions, it displays other actions, especially in cell protection. This includes antioxidant, anti-inflammatory, and mitochondria-protecting effects. Although protection is also modulated by the circadian system, the respective actions of melatonin can be distinguished and differ with regard to dose requirements in therapeutic settings. It is the aim of this article to outline these differences in terms of function, signaling, and dosage. Focus has been placed on both the nexus and the dissecting properties between circadian and noncircadian mechanisms. This has to consider details beyond the classic view of melatonin's role, such as widespread synthesis in extrapineal tissues, formation in mitochondria, effects on the mitochondrial permeability transition pore, and secondary signaling, for example, via upregulation of sirtuins and by regulating noncoding RNAs, especially microRNAs. The relevance of these findings, the differences and connections between circadian and noncircadian functions of melatonin shed light on the regulation of inflammation, including macrophage/microglia polarization, damage-associated molecular patterns, avoidance of cytokine storms, and mitochondrial functions, with numerous consequences to antioxidative protection, that is, aspects of high actuality with regard to deadly viral and bacterial diseases. Antioxid. Redox Signal. 37, 704-725.

Targeting mitochondria in the regulation of neurodegenerative diseases: A comprehensive review

Mitochondria are one of the essential cellular organelles. Apart from being considered as the powerhouse of the cell, mitochondria have been widely known to regulate redox reaction, inflammation, cell survival, cell death, metabolism, etc., and are implicated in the progression of numerous disease conditions including neurodegenerative diseases. Since brain is an energy-demanding organ, mitochondria and their functions are important for maintaining normal brain homeostasis. Alterations in mitochondrial gene expression, mutations, and epigenetic modification contribute to inflammation and neurodegeneration. Dysregulation of reactive oxygen species production by mitochondria and aggregation of proteins in neurons leads to alteration in mitochondria functions which further causes neuronal death and progression of neurodegeneration. Pharmacological studies have prioritized mitochondria as a possible drug target in the regulation of neurodegenerative diseases. Therefore, the present review article has been intended to provide a comprehensive understanding of mitochondrial role in the development and progression of neurodegenerative diseases mainly Alzheimer's, Parkinson's, multiple sclerosis, and amyotrophic lateral sclerosis followed by possible intervention and future treatment strategies to combat mitochondrial-mediated neurodegeneration.

Melatonin Alters the miRNA Transcriptome of Inflammasome Activation in Murine Microglial Cells

Systemic inflammation can have devastating effects on the central nervous system via its resident immune cells, the microglia. One of the primary mediators of this inflammation is inflammasomes, multiprotein complexes that trigger a release of inflammatory proteins when activated. Melatonin, a hormone with anti-inflammatory effects, is an attractive candidate for suppressing such inflammation. In this study, we have investigated how melatonin alters the microRNA (miRNA) transcriptome of microglial cells. For that purpose, we have performed RNA sequencing on a lipopolysaccharide and adenosine triphosphate (LPS + ATP) induced NLR family pyrin domain containing 3 (NLRP3) inflammasome activation model in the N9 mouse microglial cell line, with and without melatonin pre-treatment. We have identified 136 differentially expressed miRNAs in cells exposed to LPS + ATP compared to controls and 10 differentially expressed miRNAs in melatonin pre-treated cells compared to the inflammasome group. We have identified miR-155-3p as a miRNA that is upregulated with inflammasome activation and downregulated with melatonin treatment. We further confirmed this pattern of miR-155-3p expression in the brains of mice injected intraperitoneally with LPS. Moreover, an overexpression study with miRNA-155-3p mimic supported the idea that the protective effects of melatonin in NLRP3 inflammasome activation are partly associated with miRNA-155-3p inhibition.

Melatonin drugs inhibit SARS-CoV-2 entry into the brain and virus-induced damage of cerebral small vessels

COVID-19 is a complex disease with short- and long-term respiratory, inflammatory and neurological symptoms that are triggered by the infection with SARS-CoV-2. Invasion of the brain by SARS-CoV-2 has been observed in humans and is postulated to be involved in post-COVID state. Brain infection is particularly pronounced in the K18-hACE2 mouse model of COVID-19. Prevention of brain infection in the acute phase of the disease might thus be of therapeutic relevance to prevent long-lasting symptoms of COVID-19. We previously showed that melatonin or two prescribed structural analogs, agomelatine and ramelteon delay the onset of severe clinical symptoms and improve survival of SARS-CoV-2-infected K18-hACE2 mice. Here, we show that treatment of K18-hACE2 mice with melatonin and two melatonin-derived marketed drugs, agomelatine and ramelteon, prevents SARS-CoV-2 entry in the brain, thereby reducing virus-induced damage of small cerebral vessels, immune cell infiltration and brain inflammation. Molecular modeling analyses complemented by experimental studies in cells showed that SARS-CoV-2 entry in endothelial cells is prevented by melatonin binding to an allosteric-binding site on human angiotensin-converting enzyme 2 (ACE2), thus interfering with ACE2 function as an entry receptor for SARS-CoV-2. Our findings open new perspectives for the repurposing of melatonergic drugs and its clinically used analogs in the prevention of brain infection by SARS-CoV-2 and COVID-19-related long-term neurological symptoms.

Potential role of tryptophan catabolism in cancer-related cognitive impairment

Oncology may be the most rapidly expanding field in medicine, with several innovative diagnostic and therapeutic procedures appearing daily. Advances in oncology have improved the survival rate for patients with cancer and promoting quality of life is now one of the goals in the care of these patients. Patients face a variety of disease- and treatment-related side effects, including anorexia, nausea, vomiting, recurring infections, and sleep difficulties. Cancer-related cognitive impairment (CRCI) is an overlooked clinical condition found in oncologic practice, particularly in patients with breast cancer. Although several potential mechanisms for CRCI have been hypothesized, to our knowledge, the exact mechanism is still unknown. Alterations in the tryptophan kynurenine pathway have been shown to impair cognitive skills in several mental illnesses. However, its possible function in CRCI has yet to be investigated. The aim of this was to examine the possible interactions between tryptophan catabolism and CRCI.