The contribution of extrapineal sites of melatonin synthesis to circulating melatonin levels in higher vertebrates

Industrial and academic approaches to the search for alternative melatonin receptor ligands: An historical survey

The search for melatonin receptor agonists formed the main part of melatonin medicinal chemistry programs for the last three decades. In this short review, we summarize the two main aspects of these programs: the development of all the necessary tools to characterize the newly synthesized ligands at the two melatonin receptors MT1 and MT2, and the medicinal chemist's approaches to find chemically diverse ligands at these receptors. Both strategies are described. It turns out that the main source of tools were industrial laboratories, while the medicinal chemistry was mainly carried out in academia. Such complete accounts are interesting, as they delineate the spirits in which the teams were working demonstrating their strength and innovative character. Most of the programs were focused on nonselective agonists and few of them reached the market. In contrast, discovery of MT1-selective agonists and melatonergic antagonists with proven in vivo activity and MT1 or MT2-selectivity is still in its infancy, despite the considerable interest that subtype selective compounds may bring in the domain, as the physiological respective roles of the two subtypes of melatonin receptors, is still poorly understood. Poly-pharmacology applications and multitarget ligands have also been considered.

Advances in molecular mechanisms and therapeutic strategies for central nervous system diseases based on gut microbiota imbalance

BACKGROUD

Central nervous system (CNS) diseases pose a serious threat to human health, but the regulatory mechanisms and therapeutic strategies of CNS diseases need to be further explored. It has been demonstrated that the gut microbiota (GM) is closely related to CNS disease. GM structure disorders, abnormal microbial metabolites, intestinal barrier destruction and elevated inflammation exist in patients with CNS diseases and promote the development of CNS diseases. More importantly, GM remodeling alleviates CNS pathology to some extent.

AIM OF REVIEW

Here, we have summarized the regulatory mechanism of the GM in CNS diseases and the potential treatment strategies for CNS repair based on GM regulation, aiming to provide safer and more effective strategies for CNS repair from the perspective of GM regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The abundance and composition of GM is closely associated with the CNS diseases. On the basis of in-depth analysis of GM changes in mice with CNS disease, as well as the changes in its metabolites, therapeutic strategies, such as probiotics, prebiotics, and FMT, may be used to regulate GM balance and affect its microbial metabolites, thereby promoting the recovery of CNS diseases.

Intestinal melatonin levels and gut microbiota homeostasis are independent of the pineal gland in pigs

Introduction

Melatonin (MEL) is a crucial neuroendocrine hormone primarily produced by the pineal gland. Pinealectomy (PINX) has been performed on an endogenous MEL deficiency model to investigate the functions of pineal MEL and its relationship with various diseases. However, the effect of PINX on the gastrointestinal tract (GIT) MEL levels and gut microbiome in pigs has not been previously reported.

Methods

By using a newly established pig PINX model, we detected the levels of MEL in the GIT by liquid chromatography-tandem mass spectrometry. In addition, we examined the effects of PINX on the expression of MEL synthesis enzymes, intestinal histomorphology, and the intestinal barrier. Furthermore, 16S rRNA sequencing was performed to analyze the colonic microbiome.

Results

PINX reduced serum MEL levels but did not affect GIT MEL levels. Conversely, MEL supplementation increased MEL levels in the GIT and intestinal contents. Neither PINX nor MEL supplementation had any effect on weight gain, organ coefficient, serum biochemical indexes, or MEL synthetase arylalkylamine N-acetyltransferase (AANAT) expression in the duodenum, ileum, and colon. Furthermore, no significant differences were observed in the intestinal morphology or intestinal mucosal barrier function due to the treatments. Additionally, 16S rRNA sequencing revealed that PINX had no significant impact on the composition of the intestinal microbiota. Nevertheless, MEL supplementation decreased the abundance of Fibrobacterota and increased the abundance of Actinobacteriota, Desulfobacterota, and Chloroflexi.

Conclusion

We demonstrated that synthesis of MEL in the GIT is independent of the pineal gland. PINX had no influence on intestinal MEL level and microbiota composition in pigs, while exogenous MEL alters the structure of the gut microbiota.

The role of melatonin deficiency induced by pinealectomy on motor activity and anxiety responses in young adult, middle-aged and old rats

BACKGROUND

Aging affects anxiety levels in rats while the pineal gland, via its hormone melatonin, could modulate their inherited life "clock." The present study aimed to explore the impact of plasma melatonin deficiency on anxiety responses and the possible involvement of the hypothalamic-pituitary-adrenocortical (HPA) axis and heat shock proteins (Hsp) 70 and 90 in the frontal cortex (FC) and the hippocampus in young adult, middle-aged and elderly rats with pinealectomy.

RESULTS

Melatonin deficiency induced at different life stages did not affect the lifespan of rats. Pinealectomy abolished the circadian rhythm of motor activity, measured for 48 h in the actimeter, in young adult but not in middle-aged rats. Pinealectomy reduced the motor activity of the young adult rats during the dark phase and impaired the diurnal activity variations of old rats. The same generations (3- and 18 month-old rats with pinealectomy) had lower anxiety levels than the matched sham groups, measured in three tests: elevated-plus maze, light-dark test, and novelty-suppressed feeding test. While the activity of the HPA axis remained intact in young adult and middle-aged rats with melatonin deficiency, a high baseline corticosterone level and blunted stress-induced mechanism of its release were detected in the oldest rats. Age-associated reduced Hsp 70 and 90 levels in the FC but not in the hippocampus were detected. Pinealectomy diminished the expression of Hsp 70 in the FC of middle-aged rats compared to the matched sham rats.

CONCLUSIONS

Our results suggest that while melatonin hormonal dysfunction impaired the motor activity in the actimeter and emotional behavior in young adult and elderly rats, the underlying pathogenic mechanism in these generations might be different and needs further verification.

Melatonin as an Ameliorative Agent Against Cadmium- and Lead-Induced Toxicity in Fish: an Overview

Diverse anthropogenic activities and lack of knowledge on its consequences have promoted serious heavy metal contaminations in different aquatic systems throughout the globe. The non-biodegradable nature of most of these toxic heavy metals has increased the concern on their possible bioaccumulation in aquatic organisms as well as in other vertebrates. Among these aquatic species, fish are most sensitive to such contaminated water that not only decreases their chance of survivability in the nature but also increases the probability of biomagnifications of these heavy metals in higher order food chain. After entering the fish body, heavy metals induce detrimental changes in different vital organs by impairing multiple physiological and biochemical pathways that are essential for the species. Such alterations may include tissue damage, induction of oxidative stress, immune-suppression, endocrine disorders, uncontrolled cell proliferation, DNA damage, and even apoptosis. Although uncountable reports have explored the toxic effects of different heavy metals in diverse fish species, but surprisingly, only a few attempts have been made to ameliorate such toxic effects. Since, oxidative stress seems to be the underlying common factor in such heavy metal-induced toxicity, therefore, a potent and endogenous antioxidant with no side effect may be an appropriate therapeutic solution. Apart from summarizing the toxic effects of two important toxicants, i.e., cadmium and lead in fish, the novelty of the present treatise lies in its arguments in favor of using melatonin, an endogenous free radical scavenger and indirect antioxidant, in ameliorating the toxic effects of heavy metals in any fish species.

Secondary glaucoma: Toward interventions based on molecular underpinnings

Glaucoma is a heterogeneous group of progressive diseases that leads to irreversible blindness. Secondary glaucoma refers to glaucoma caused by a known underlying condition. Pseudoexfoliation and pigment dispersion syndromes are common causes of secondary glaucoma. Their respective deposits may obstruct the trabecular meshwork, leading to aqueous humor outflow resistance, ocular hypertension, and optic neuropathy. There are no disease-specific interventions available for either. Pseudoexfoliation syndrome is characterized by fibrillar deposits (pseudoexfoliative material) on anterior segment structures. Over a decade of multiomics analyses taken together with the current knowledge on pseudoexfoliative glaucoma warrant a re-think of mechanistic possibilities. We propose that the presence of nucleation centers (e.g., vitamin D binding protein), crosslinking enzymes (e.g., transglutaminase 2), aberrant extracellular matrix, flawed endocytosis, and abnormal aqueous-blood barrier contribute to the formation of proteolytically resistant pseudoexfoliative material. Pigment dispersion syndrome is characterized by abnormal iridolenticular contact that disrupts iris pigment epithelium and liberates melanin granules. Iris melanogenesis is aberrant in this condition. Cytotoxic melanogenesis intermediates leak out of melanosomes and cause iris melanocyte and pigment epithelium cell death. Targeting melanogenesis can likely decrease the risk of pigmentary glaucoma. Skin and melanoma research provides insights into potential therapeutics. We propose that specific prostanoid agonists and fenofibrates may reduce melanogenesis by inhibiting cholesterol internalization and de novo synthesis. Additionally, melatonin is a potent melanogenesis suppressor, antioxidant, and hypotensive agent, rendering it a valuable agent for pigmentary glaucoma. In pseudoexfoliative glaucoma, where environmental insults drive pseudoexfoliative material formation, melatonin's antioxidant and hypotensive properties may offer adjunct therapeutic benefits. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Age-related changes in the gut melatonin levels and its possible role in the regulation of feeding and digestibility, with the development of the gut from fingerling to adult stages of carp, Catla catla

The present study aims to understand the feeding-related age-bound changes in gut histoarchitecture and its response to gut melatonin (GM) titer regulating major digestive enzymes in carp, Catla catla. Therefore, gut samples were collected from different growth stages of carp, viz. (i) fingerling (FL), body weight (BW) ≥ 3 g to ≤ 20 g; (ii) advanced fingerling (AFL), BW > 20 g to ≤ 40 g; (iii) early juvenile (EJv), BW > 40 g to ≤ 70 g; (iv) juvenile (Jv), BW > 70 g to ≤ 200 g; (v) late juvenile (LJv), BW > 200 g to ≤ 300 g; (vi) preadult (PA), BW > 300 g to ≤ 500 g; (vii) subadult (SA), BW > 500 g to ≤ 1.00 kg; and (viii) adult (AD), BW > 1 kg to ≤ 2.5 kg. Data analysis revealed that the highest titer of GM was noted in FL, moderate in AFL, Jv, and PA, lower in EJv, SA, and AD, and lowest in LJv. Results depicted a negative correlation between the development of the gut and its melatonin content. Moreover, GM was positively associated with feeding intensity and gastro-somatic index (GaSI) and negatively related to ovarian onset and development. Following correlation and principal component analysis, several pieces of evidence were recorded on the role of gut melatonin in regulating digestive physiology. Finally, it indicates that gut melatonin has a progressively influential role in improving digestion, particularly protein and microbial digestion, with the development of an adult gut from the fingerling stage.

Circadian rhythms in colonic function

A rhythmic expression of clock genes occurs within the cells of multiple organs and tissues throughout the body, termed "peripheral clocks." Peripheral clocks are subject to entrainment by a multitude of factors, many of which are directly or indirectly controlled by the light-entrainable clock located in the suprachiasmatic nucleus of the hypothalamus. Peripheral clocks occur in the gastrointestinal tract, notably the epithelia whose functions include regulation of absorption, permeability, and secretion of hormones; and in the myenteric plexus, which is the intrinsic neural network principally responsible for the coordination of muscular activity in the gut. This review focuses on the physiological circadian variation of major colonic functions and their entraining mechanisms, including colonic motility, absorption, hormone secretion, permeability, and pain signalling. Pathophysiological states such as irritable bowel syndrome and ulcerative colitis and their interactions with circadian rhythmicity are also described. Finally, the classic circadian hormone melatonin is discussed, which is expressed in the gut in greater quantities than the pineal gland, and whose exogenous use has been of therapeutic interest in treating colonic pathophysiological states, including those exacerbated by chronic circadian disruption.

Influence of Different Light Spectra on Melatonin Synthesis by the Pineal Gland and Influence on the Immune System in Chickens

It is well known that the pineal gland in birds influences behavioural and physiological functions, including those of the immune system. The purpose of this research is to examine the endocrine-immune correlations between melatonin and immune system activity. Through a description of the immune-pineal axis, we formulated the objective to determine and describe: the development of the pineal gland; how light influences secretory activity; and how melatonin influences the activity of primary and secondary lymphoid organs. The pineal gland has the ability to turn light information into an endocrine signal suitable for the immune system via the membrane receptors Mel1a, Mel1b, and Mel1c, as well as the nuclear receptors RORα, RORβ, and RORγ. We can state the following findings: green monochromatic light (560 nm) increased serum melatonin levels and promoted a stronger humoral and cellular immune response by proliferating B and T lymphocytes; the combination of green and blue monochromatic light (560-480 nm) ameliorated the inflammatory response and protected lymphoid organs from oxidative stress; and red monochromatic light (660 nm) maintained the inflammatory response and promoted the growth of pathogenic bacteria. Melatonin can be considered a potent antioxidant and immunomodulator and is a critical element in the coordination between external light stimulation and the body's internal response.

Randomised controlled trial of melatonin for paediatric functional abdominal pain disorders

AIM

Melatonin seems to have a positive impact on the brain-gut axis and many direct and indirect effects on the gastrointestinal tract. This trial aimed at assessing the efficacy of melatonin combined with Lactobacillus Rhamnosus GG given in the treatment of paediatric patients with functional abdominal pain disorders.

METHODS

Forty-two patients aged 4-18 years old who fulfilled the Rome IV Diagnostic Criteria for functional abdominal pain disorders were enrolled. Melatonin 3 or 5 mg in combination with Lactobacillus Rhamnosus GG (group 1, n = 22) or a placebo in combination with Lactobacillus Rhamnosus GG (control group, n = 20) were taken in the evening for a period of 4 weeks. The study duration was 12 weeks. The primary study endpoint was represented by clinical improvement at week 12 - defined as at least a 50% reduction in mean abdominal pain index (API) from baseline to week 12.

RESULTS

The mean API was reduced by more than 50% between T0 and T2 in the group of children treated with melatonin. However, the difference in the distributions of the variations of the scores between the two groups was not significant between T0 and T2 (P = 0.082), while it was significant between T0 and T1 (P = 0.001). Similar results were obtained by analysing the API variables 'weekly frequency of pain' (item 1) and 'perceived intensity of pain' (item 4) individually.

CONCLUSIONS

This is the first study to investigate the role of the combination of melatonin and Lactobacillus Rhamnosus GG in the treatment of children with functional abdominal pain disorders. Melatonin combined with Lactobacillus Rhamnosus GG can be considered a therapeutic option for these conditions in children.

Function, structure, evolution, regulation of a potent drug target, arylalkylamine N-acetyltransferase

Arylalkylamine N-acetyltransferase (aaNAT) catalyzes the transacetylation of acetyl coenzyme A to arylamines and arylalkylamines. Based on three-dimensional structural information, aaNAT belongs to the GCN5-related N-acetyltransferases superfamily with a conserved acetyl-CoA binding domain (Dyda et al., 2000). By comparison of sequence similarity, aaNAT is usually divided into vertebrate aaNAT (VT-aaNAT) and non-vertebrate aaNAT (NV-aaNAT) (Cazaméa-Catalan et al., 2014). Insects have evolved multiple aaNATs in comparison to mammals, thus more diverse functions are also reflected in insects. This chapter will summarize previous studies on the function, regulation, structure and evolution of aaNAT, and provide insight into future pest management.

Melatonin inhibits ferroptosis and delays age-related cataract by regulating SIRT6/p-Nrf2/GPX4 and SIRT6/NCOA4/FTH1 pathways

BACKGROUND

Cataracts are the main cause of reversible blindness worldwide. The ageing of the lens caused by ultraviolet B (UVB) radiation is mostly related to oxidative stress (OS). Little is known about whether OS induced by UVB enhances the sensitivity of lens epithelial cells to ferroptotic stress, which may be a new mechanism leading to age-related cataracts (ARCs).

METHODS

Ferroptosis was detected by transmission electron microscopy (TEM), iron assay, lipid peroxidation (MDA) assay, real-time PCR, western blotting, and immunofluorescence. Genetic engineering technology was used to investigate the regulatory relationship among Sirtuin 6 (SIRT6), nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear receptor coactivator 4 (NCOA4), glutathione peroxidase 4 (GPX4) and ferritin heavy chain (FTH1). Knockdown and overexpression of SIRT6 locally in vivo in rats were performed to probe the regulatory mechanism of SIRT6 in ferroptosis in ARCs.

FINDINGS

Here, we observed that UVB can drastically induce ferroptosis in lens epithelial cells in vivo and in vitro. Surprisingly, inhibition of ferroptosis was the direct reason that melatonin rescued B-3, SRA01/04 and HEK-293 T cells survival; the pan-caspase inhibitor Z-Vad-FMK did not significantly reverse the death of UVB-irradiated cells compared with that in the UVB+DMSO group. SIRT6 was an upstream regulator of phosphorylated Nrf2 (p-Nrf2) and NCOA4 in B-3, SRA01/04 and HEK-293 T cells. Melatonin inhibited ferroptosis through the SIRT6/p-Nrf2/GPX4 and SIRT6/COA4/FTH1 pathways to neutralize lipid peroxidation toxicity, which protected cells against ferroptotic stress in vitro and delayed cataract formation caused by UVB exposure in rats.

INTERPRETATION

Our findings reveal a novel causal role of melatonin in the pathogenesis of ARCs, which raises the possibility of selectively targeting the activation of SIRT6 and ferroptotic resistance as a latent antioxidative therapeutic strategy for ARCs.

Intestinal microbiota and melatonin in the treatment of secondary injury and complications after spinal cord injury

Spinal cord injury (SCI) is a central nervous system (CNS) disease that can cause sensory and motor impairment below the level of injury. Currently, the treatment scheme for SCI mainly focuses on secondary injury and complications. Recent studies have shown that SCI leads to an imbalance of intestinal microbiota and the imbalance is also associated with complications after SCI, possibly through the microbial-brain-gut axis. Melatonin is secreted in many parts of the body including pineal gland and gut, effectively protecting the spinal cord from secondary damage. The secretion of melatonin is affected by circadian rhythms, known as the dark light cycle, and SCI would also cause dysregulation of melatonin secretion. In addition, melatonin is closely related to the intestinal microbiota, which protects the barrier function of the gut through its antioxidant and anti-inflammatory effects, and increases the abundance of intestinal microbiota by influencing the metabolism of the intestinal microbiota. Furthermore, the intestinal microbiota can influence melatonin formation by regulating tryptophan and serotonin metabolism. This paper summarizes and reviews the knowledge on the relationship among intestinal microbiota, melatonin, and SCI in recent years, to provide new theories and ideas for clinical research related to SCI treatment.

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.

A Review of the Potential Effects of Melatonin in Compromised Mitochondrial Redox Activities in Elderly Patients With COVID-19

Melatonin, an endogenous indoleamine, is an antioxidant and anti-inflammatory molecule widely distributed in the body. It efficiently regulates pro-inflammatory and anti-inflammatory cytokines under various pathophysiological conditions. The melatonin rhythm, which is strongly associated with oxidative lesions and mitochondrial dysfunction, is also observed during the biological process of aging. Melatonin levels decline considerably with age and are related to numerous age-related illnesses. The signs of aging, including immune aging, increased basal inflammation, mitochondrial dysfunction, significant telomeric abrasion, and disrupted autophagy, contribute to the increased severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. These characteristics can worsen the pathophysiological response of the elderly to SARS-CoV-2 and pose an additional risk of accelerating biological aging even after recovery. This review explains that the death rate of coronavirus disease (COVID-19) increases with chronic diseases and age, and the decline in melatonin levels, which is closely related to the mitochondrial dysfunction in the patient, affects the virus-related death rate. Further, melatonin can enhance mitochondrial function and limit virus-related diseases. Hence, melatonin supplementation in older people may be beneficial for the treatment of COVID-19.

Long-term effects of melatonin and resveratrol on aging rats: A multi-biomarker approach

Aging-related impaired body structure and functions may be, at least partially, caused by elevated oxidative stress. Melatonin (MEL) and resveratrol (RSV) may act as antioxidant and anti-aging compounds, but these actions in experimental animals and humans are controversial. Herein, a rat model of aging was used to study the long-term sex-related effects of MEL and RSV treatment on body mass and blood/plasma parameters of DNA damage, oxidative status (glutathione and malondialdehyde levels), and concentrations of sex hormones. Starting from the age of 3mo, for the next 9mo or 21mo male and female Wistar rats (n = 4-7 per group) were given water to drink (controls) or 0.1 % ethanol in water (vehicle), or MEL or RSV (each 10 mg/L vehicle). DNA damage in whole blood cells was tested by comet assay, whereas in plasma, glutathione, malondialdehyde, and sex hormones were determined by established methods. Using statistical analysis of data by ANOVA/Scheffe post hoc, we observed a similar sex- and aging-dependent rise of body mass in both sexes and drop of plasma testosterone in control and vehicle-treated male rats, whose pattern remained unaffected by MEL and RSV treatment. Compared with controls, all other parameters remained largely unchanged in aging and differently treated male and female rats. We concluded that the sex- and aging-related pattern of growth and various blood parameters in rats were not affected by the long-term treatment with MEL and RSV at the estimated daily doses (300-400 μg/kg b.m.) that exceed usual moderate consumption in humans.

A Focus on Enterochromaffin Cells among the Enteroendocrine Cells: Localization, Morphology, and Role

The intestinal epithelium plays a key role in managing the relationship with the environment, the internal and external inputs, and their changes. One percent of the gut epithelium is represented by the enteroendocrine cells. Among the enteroendocrine cells, a group of specific cells characterized by the presence of yellow granules, the enterochromaffin cells, has been identified. These granules contain many secretion products. Studies showed that these cells are involved in gastrointestinal inflammatory conditions and hyperalgesia; their number increases in these conditions both in affected and not-affected zones of the gut. Moreover, they are involved in the preservation and modulation of the intestinal function and motility, and they sense metabolic-nutritional alterations. Sometimes, they are confused or mixed with other enteroendocrine cells, and it is difficult to define their activity. However, it is known that they change their functions during diseases; they increased in number, but their involvement is related mainly to some secretion products (serotonin, melatonin, substance P). The mechanisms linked to these alterations are not well investigated. Herein, we provide an up-to-date highlight of the main findings about these cells, from their discovery to today. We emphasized their origin, morphology, and their link with diet to better evaluate their role for preventing or treating metabolic disorders considering that these diseases are currently a public health burden.

Melatonin and the Programming of Stem Cells

Melatonin interacts with various types of stem cells, in multiple ways that comprise stimulation of proliferation, maintenance of stemness and self-renewal, protection of survival, and programming toward functionally different cell lineages. These various properties are frequently intertwined but may not be always jointly present. Melatonin typically stimulates proliferation and transition to the mature cell type. For all sufficiently studied stem or progenitor cells, melatonin’s signaling pathways leading to expression of respective morphogenetic factors are discussed. The focus of this article will be laid on the aspect of programming, particularly in pluripotent cells. This is especially but not exclusively the case in neural stem cells (NSCs) and mesenchymal stem cells (MSCs). Concerning developmental bifurcations, decisions are not exclusively made by melatonin alone. In MSCs, melatonin promotes adipogenesis in a Wnt (Wingless-Integration-1)-independent mode, but chondrogenesis and osteogenesis Wnt-dependently. Melatonin upregulates Wnt, but not in the adipogenic lineage. This decision seems to depend on microenvironment and epigenetic memory. The decision for chondrogenesis instead of osteogenesis, both being Wnt-dependent, seems to involve fibroblast growth factor receptor 3. Stem cell-specific differences in melatonin and Wnt receptors, and contributions of transcription factors and noncoding RNAs are outlined, as well as possibilities and the medical importance of re-programming for transdifferentiation.

Melatonin as the Cornerstone of Neuroimmunoendocrinology

Much attention has been recently drawn to studying melatonin – a hormone whose synthesis was first found in the epiphysis (pineal gland). This interest can be due to discovering the role of melatonin in numerous physiological processes. It was the discovery of melatonin synthesis in endocrine organs (pineal gland), neural structures (Purkinje cells in the cerebellum, retinal photoreceptors), and immunocompetent cells (T lymphocytes, NK cells, mast cells) that triggered the evolution of new approaches to the unifield signal regulation of homeostasis, which, at the turn of the 21st century, lead to the creation of a new integral biomedical discipline — neuroimmunoendocrinology. While numerous hormones have been verified over the last decade outside the “classical” locations of their formation, melatonin occupies an exclusive position with regard to the diversity of locations where it is synthesized and secreted. This review provides an overview and discussion of the major data regarding the role of melatonin in various physiological and pathological processes, which affords grounds for considering melatonin as the “cornerstone” on which neuroimmunoendocrinology has been built as an integral concept of homeostasis regulation.

The Role of Nutrient Supplementation in the Management of Chronic Pain in Fibromyalgia: A Narrative Review

INTRODUCTION

The multifaceted clinical presentation of fibromyalgia (FM) supports the modern understanding of the disorder as a more global condition than one simply affecting pain sensation. The main pharmacologic therapies used clinically include anti-epileptics and anti-depressants. Conservative treatment options include exercise, myofascial release, psychotherapy, and nutrient supplementation.

METHODS

Narrative review.

RESULTS

Nutrient supplementation is a broadly investigated treatment modality as numerous deficiencies have been linked to FM. Additionally, a proposed link between gut microbiome patterns and chronic pain syndromes has led to studies investigating probiotics as a possible treatment. Despite positive results, much of the current evidence regarding this topic is of poor quality, with variable study designs, limited sample sizes, and lack of control groups.

CONCLUSIONS

The etiology of FM is complex, and has shown to be multi-factorial with genetics and environmental exposures lending influence into its development. Preliminary results are promising, however, much of the existing evidence regarding diet supplementation is of poor quality. Further, more robust studies are needed to fully elucidate the potential of this alternative therapeutic option.

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

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

Divergent Importance of Chronobiological Considerations in High- and Low-dose Melatonin Therapies

Melatonin has been used preclinically and clinically for different purposes. Some applications are related to readjustment of circadian oscillators, others use doses that exceed the saturation of melatonin receptors MT1 and MT2 and are unsuitable for chronobiological purposes. Conditions are outlined for appropriately applying melatonin as a chronobiotic or for protective actions at elevated levels. Circadian readjustments require doses in the lower mg range, according to receptor affinities. However, this needs consideration of the phase response curve, which contains a silent zone, a delay part, a transition point and an advance part. Notably, the dim light melatonin onset (DLMO) is found in the silent zone. In this specific phase, melatonin can induce sleep onset, but does not shift the circadian master clock. Although sleep onset is also under circadian control, sleep and circadian susceptibility are dissociated at this point. Other limits of soporific effects concern dose, duration of action and poor individual responses. The use of high melatonin doses, up to several hundred mg, for purposes of antioxidative and anti-inflammatory protection, especially in sepsis and viral diseases, have to be seen in the context of melatonin's tissue levels, its formation in mitochondria, and detoxification of free radicals.

Melatonin controversies, an update

Melatonin was discovered more than 60 years ago. Since then, several seminal discoveries have allowed us to define its function as a neuroendocrine hormone and its molecular targets in mammals and many other species. However, many fundamental issues have not yet been solved such as the subcellular localization of melatonin synthesis and the full spectrum of its molecular targets. In addition, a considerable number of controversies persist in the field, mainly concerning how many functions melatonin has. Altogether, this illustrates how "immature" the field still is. The intention of this opinion article is to note the controversies and limitations in the field, to initiate a discussion and to make proposals/guidelines to overcome them and move the field forward.

Impact of light stimulation during incubation on hatching traits and post-hatch performance of commercial broilers

Light in terms of photo- and scoto-periods is the key ambient factor affecting the physiology of birds through establishing normal biological clock and circadian rhythms. In natural incubation light significantly influences embryonic development, however, at commercial setups eggs are incubated under a dark environment. Presently not a single commercial poultry hatchery is using light during incubation; hence, comprehensive studies are needed to address the industry for considering light as a potential embryonic growth stimulant. In the present study, white Light-emitting diodes (LEDs; 5000 K) were installed in the incubator and 250 lx light intensity was provided for 0, 12, and 24 h per day during the whole incubation period. A total of 900 broiler hatching eggs (Hubbard classic; from 58 weeks old parents) were randomly allocated to 3 treatment groups, having 5 replicates of 60 eggs each, a tray was considered as replicate during incubation and these eggs were incubated under standard incubation protocols. After hatching, a total of 300 chicks were picked and divided into 3 described treatments (0, 12, and 24 h of photo-stimulation to eggs during incubation) having 5 replicates of 20 birds each. The results indicated that incubation of eggs under 12 and 24 h of lighting significantly improved (P ≤ 0.05) hatch window, hatchability % (0.0002), a hatch of fertile % (0.001), and carcass yield % (0.0454). Embryonic mortality, dead germs, and dead in shell embryos were lower in eggs incubated under 12 h light. Significantly better FCR (0.0006), stress susceptibilities such as H/L ratio (0.0227), and physical asymmetry (0.0065) were observed among the birds incubated under 12 h light (P ≤ 0.05). In conclusion, an appropriate light stimuli (12 h) may help to improve hatching traits and post-hatch performance of commercial broiler.

Melatonin ameliorates microvessel abnormalities in the cerebral cortex and hippocampus in a rat model of Alzheimer's disease

Melatonin can attenuate cardiac microvascular ischemia/reperfusion injury, but it remains unclear whether melatonin can also ameliorate cerebral microvascular abnormalities. Rat models of Alzheimer’s disease were established by six intracerebroventricular injections of amyloid-beta 1–42, administered once every other day. Melatonin (30 mg/kg) was intraperitoneally administered for 13 successive days, with the first dose given 24 hours prior to the first administration of amyloid-beta 1–42. Melatonin ameliorated learning and memory impairments in the Morris water maze test, improved the morphology of microvessels in the cerebral cortex and hippocampus, increased microvessel density, alleviated pathological injuries of cerebral neurons, and decreased the expression of vascular endothelial growth factor and vascular endothelial growth factor receptors 1 and 2. These findings suggest that melatonin can improve microvessel abnormalities in the cerebral cortex and hippocampus by lowering the expression of vascular endothelial growth factor and its receptors, thereby improving the cognitive function of patients with Alzheimer’s disease. This study was approved by the Animal Care and Use Committee of Jinzhou Medical University, China (approval No. 2019015) on December 6, 2018.

Melatonin improves uterine-conceptus interaction via regulation of SIRT1 during early pregnancy

Melatonin has been shown to improve in vitro fertilization and offspring survival after bacterial infection, but its role in regulating maternal-fetal communication during early pregnancy has not been investigated. Results of this study demonstrated expression of abundant melatonin receptors in conceptus and endometrium during early pregnancy. In gilts, expression of melatonin receptor 1A (MTNR1A or MT1) and melatonin receptor 1B (MTNR1B or MT2) increased in trophectoderm (Tr) and uterine luminal epithelium (LE) with advancing days during early pregnancy in a different manner. Melatonin increased proliferation and migration of porcine trophectoderm (pTr) cell, the percent pTr cells in the G2 phase of the cell cycle, and the expression of implantation-related genes by pTr cells and endometrial luminal epithelium (pLE). Melatonin also attenuated the production of LPS-induced pro-inflammatory cytokines and tunicamycin-induced endoplasmic reticulum (ER) stress-sensing proteins. The expression of sirtuin 1 (SIRT1) as a potential target of melatonin increased between Days 9 and 14 of gestation. Co-treatment with SIRT1 inhibitor EX527 and melatonin restored cell-cell interactions through PI3K and MAPK signaling. Knockdown of SIRT1 decreased the expression of implantation-related genes, as well as migration of pTr and pLE cells. The expression of microRNAs regulated by SIRT1 was suppressed in response to melatonin. Furthermore, melatonin significantly increased lipopolysaccharide (LPS)-reduced fertilization and embryogenesis in zebrafish model. These results suggest that melatonin may improve the uterine-conceptus interactions via the regulation of SIRT1 during early pregnancy.

Gut Dysbiosis Dysregulates Central and Systemic Homeostasis via Suboptimal Mitochondrial Function: Assessment, Treatment and Classification Implications

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The gut and mitochondria have emerged as two important hubs at the cutting edge of research across a diverse array of medical conditions, including most psychiatric conditions. This article highlights the interaction of the gut and mitochondria over the course of development, with an emphasis on the consequences for transdiagnostic processes across psychiatry, but with relevance to wider medical conditions. As well as raised levels of circulating lipopolysaccharide (LPS) arising from increased gut permeability, the loss of the short-chain fatty acid, butyrate, is an important mediator of how gut dysbiosis modulates mitochondrial function. Reactive cells, central glia and systemic immune cells are also modulated by the gut, in part via impacts on mitochondrial function in these cells. Gut-driven alterations in the activity of reactive cells over the course of development are proposed to be an important determinant of the transdiagnostic influence of glia and the immune system. Stress, including prenatal stress, also acts via the gut. The suppression of butyrate, coupled to raised LPS, drives oxidative and nitrosative stress signalling that culminates in the activation of acidic sphingomyelinase-induced ceramide. Raised ceramide levels negatively regulate mitochondrial function, both directly and via its negative impact on daytime, arousal-promoting orexin and night-time sleep-promoting pineal gland-derived melatonin. Both orexin and melatonin positively regulate mitochondria oxidative phosphorylation. Consequently, gut-mediated increases in ceramide have impacts on the circadian rhythm and the circadian regulation of mitochondrial function. Butyrate, orexin and melatonin can positively regulate mitochondria via the disinhibition of the pyruvate dehydrogenase complex, leading to increased conversion of pyruvate to acetyl- CoA. Acetyl-CoA is a necessary co-substrate for the initiation of the melatonergic pathway in mitochondria and therefore the beneficial effects of mitochondria melatonin synthesis on mitochondrial function. This has a number of treatment implications across psychiatric and wider medical conditions, including the utilization of sodium butyrate and melatonin.

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Overall, gut dysbiosis and increased gut permeability have significant impacts on central and systemic homeostasis via the regulation of mitochondrial function, especially in central glia and systemic immune cells.

Neuromodulation of the Pineal Gland via Electrical Stimulation of Its Sympathetic Innervation Pathway

Stimulation of the pineal gland via its sympathetic innervation pathway results in the production of N-acetylserotonin and melatonin. Melatonin has many therapeutic roles and is heavily implicated in the regulation of the sleep-wake cycle. In addition, N-acetylserotonin has recently been reported to promote neurogenesis in the brain. Upregulation of these indoleamines is possible via neuromodulation of the pineal gland. This is achieved by electrical stimulation of structures or fibres in the pineal gland sympathetic innervation pathway. Many studies have performed such pineal neuromodulation using both invasive and non-invasive methods. However, the effects of various experimental variables and stimulation paradigms has not yet been reviewed and evaluated. This review summarises these studies and presents the optimal experimental protocols and stimulation parameters necessary for maximal upregulation of melatonin metabolic output.

Effect of acute total sleep deprivation on plasma melatonin, cortisol and metabolite rhythms in females

Disruption to sleep and circadian rhythms can impact on metabolism. The study aimed to investigate the effect of acute sleep deprivation on plasma melatonin, cortisol and metabolites, to increase understanding of the metabolic pathways involved in sleep/wake regulation processes. Twelve healthy young female participants remained in controlled laboratory conditions for ~92 hr with respect to posture, meals and environmental light (18:00-23:00 hr and 07:00-09:00 hr <8 lux; 23:00-07:00 hr 0 lux (sleep opportunity) or <8 lux (continuous wakefulness); 09:00-18:00 hr ~90 lux). Regular blood samples were collected for 70 hr for plasma melatonin and cortisol, and targeted liquid chromatography-mass spectrometry metabolomics. Timepoints between 00:00 and 06:00 hr for day 1 (baseline sleep), day 2 (sleep deprivation) and day 3 (recovery sleep) were analysed. Cosinor analysis and MetaCycle analysis were performed for detection of rhythmicity. Night-time melatonin levels were significantly increased during sleep deprivation and returned to baseline levels during recovery sleep. No significant differences were observed in cortisol levels. Of 130 plasma metabolites quantified, 41 metabolites were significantly altered across the study nights, with the majority decreasing during sleep deprivation, most notably phosphatidylcholines. In cosinor analysis, 58 metabolites maintained their rhythmicity across the study days, with the majority showing a phase advance during acute sleep deprivation. This observation differs to that previously reported for males. Our study is the first of metabolic profiling in females during sleep deprivation and recovery sleep, and offers a novel view of human sleep/wake regulation and sex differences.

Hydroxyindole-O-methyltransferase (HIOMT) activity in the retina of melatonin-proficient mice

Numerous pieces of evidence support the expression by the mammalian retina of Hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4), the enzyme directly responsible for the biosynthesis of the pineal chronobiotic hormone melatonin (MLT). However, conflicting results obtained so far by enzyme-kinetic and immune-detection techniques still make HIOMT presence and relevance in the eye a matter of debate. This work aimed at evaluating unambiguously HIOMT activity in the mouse retina, a valuable model for studying the effects of MLT variations on ocular pathophysiology. Since laboratory mouse strains can bear genetic polymorphisms yielding defective enzymes of MLT biosynthesis, retinas and control pineal glands used in this study were obtained in a MLT-proficient crossing of A/J mice, the A/J/C57BL/10 strain. To improve the radiochemical reference assay, we tested different homogenization procedures coupled with HPLC detection. Concomitantly, we quantified MLT, and its precursor N-acetyl-serotonin (NAS) by HPLC coupled to electrochemical detection in retinas isolated from either light- or dark-adapted mice. Results showed that the standard radio-chemical assay was successful for pineal HIOMT only, whereas specific homogenization buffers and HPLC were required to detect retinal activity, presumably due to interfering methyl-transferases inhibited by NAS. Under present conditions, retinal HIOMT V_max accounted for by ≈ 40 fmol/h/mg protein, 2.6-hundreds-fold lower than the pineal counterpart, displaying equivalent K_Ms (≈10 μM). Moreover, NAS and MLT rapidly decreased in light-exposed isolated retinas, corroborating light-sensitive in-situ MLT formation. Conclusively, we measured mouse retinal HIOMT kinetics under basal conditions, a useful result to elucidate the regulatory patterns, the possible impact on eye health, and therapeutic approaches related to this enzyme.

Deciphering the melatonin metabolism in Saccharomyces cerevisiae by the bioconversion of related metabolites

Melatonin (Mel), originally considered a neurohormone, has been detected in beverages and food-fermented products in which yeast metabolism is highly important. This indolamine is synthesized from serotonin, with L-tryptophan being the initial substrate of both. Regarding Mel metabolism, the biosynthetic pathway in mammals consists in four-step reactions. However, six genes are implicated in the synthesis of Mel in plants, which suggest the presence of many pathways. The aim of this study was to provide new empirical data on the production of Mel and other indole-related compounds in the yeast Saccharomyces cerevisiae (S. cerevisiae). To this end, we performed the addition of the pathway intermediates in S. cerevisiae cells in different growth stages (exponential and arrested cells) to follow the bioconversion and new indolic compound production from them. The different bioconverted indolic compounds tested (L-tryptophan, 5-hydroxytryptophan, tryptamine, serotonin, N-acetylserotonin, 5-methoxytryptamine, and Mel) were analyzed by UHPLC-MS/MS from the extra- and intracellular contents. Our results showed that serotonin, in yeast, was prevalently formed via tryptophan decarboxylation, followed by tryptamine hydroxylation as in plants. Mel production from serotonin can be achieved by either N-acetylation, followed by O-methylation or O-methylation, in turn followed by N-acetylation. Accordingly, the classic pathway of Mel synthesis in vertebrates does not seems prevalent in yeast.

The roles of radio-functional natural chemicals for the development of cancer radiation therapy

Ionizing radiation (IR) targeted at killing cancer cells also damages normal human cells and tissues through oxidative stress. Thus, the practical treatment of cancer using radiation therapy (RT) is sometimes limited because of the acute side effects in individual patients. In addition, some radioresistant cancers are difficult to treat with limited doses of IR, which leads to treatment failure. Natural chemicals that have unique physiological functions and low toxicity offer significant advantages for the development of new radiation therapies. Natural chemicals can counteract the oxidative damage caused by IR during RT because of their strong antioxidant ability. Certain natural chemicals can also serve as radiosensitizers that can enhance the cancer-killing effects. This review article discusses the main roles of radio-functional natural chemicals in the development of cancer RT.

Assessment of Tryptophan, Tryptophan Ethylester, and Melatonin Derivatives in Red Wine by SPE-HPLC-FL and SPE-HPLC-MS Methods

Melatonin (MEL) is an indoleamine produced mainly by the pineal gland in vertebrates. It plays a significant role in the regulation of circadian rhythms, mitigation of sleeping disorders, and jet lag. This compound is synthetized from tryptophan (TRP) and it has been found in seeds, fruits, and fermented beverages, including wine. Wine is also a source of other tryptophan derivatives, the tryptophan ethylester (TEE) and MEL isomers (MISs), for which the biological properties need to be elucidated. An analytical method for the simultaneous quantification of TRP, TEE, and MEL was developed by a Solid Phase Extraction (SPE) of a preconcentration of wine followed by high performance liquid chromatography (HPLC) analysis either with fluorescence or mass spectrometer detectors. The analytical method showed a relative standard deviation (RSD) lower than 8%, except for TRP (RSD 10.5% in wine). The recovery was higher than 76%. The versatility of SPE preconcentrations allowed for the adequate preconcentration of wine sample as well as detection of low concentrations, an important aspect especially for MEL (detection limit 0.0023 µg/L). The proposed method proved to be suitable for assessing the investigated compounds in some red wine samples, where 74.4⁻256.2 µg/L and 0.038⁻0.063 µg/L of TEE and MEL were detected, respectively. Five MISs were also found in wine samples in concentrations up to 1.97 µg/L.

Choroid plexus is an additional source of melatonin in the brain

The cerebrospinal fluid melatonin is released from the pineal gland, directly into the third ventricle, or produced de novo in the brain from extrapineal melatonin sources leading to a melatonin concentration gradient in the cerebrospinal fluid. Despite the interest on this topic, the brain areas capable of producing melatonin are not yet clear. Bearing this in mind, we hypothesized that the choroid plexus (CP) could be one of these melatonin sources. We analyzed and confirmed the presence of the four enzymes required for melatonin synthesis in rat CP and demonstrated that arylalkylamine N-acetyltransferase shows a circadian expression in female and male rat CP. Specifically, this enzyme colocalizes with mitochondria in rat CP epithelial cells, an organelle known to be involved in melatonin function and synthesis. Then, we demonstrated that melatonin is synthesized by porcine CP explants, although without a circadian pattern. In conclusion, our data show that the CP is a local source of melatonin to the central nervous system, probably contributing to its high levels in the cerebrospinal fluid. We believe that in the CP, melatonin might be regulated by its endogenous clock machinery and by the hormonal background.

THE EFFECT OF MELATONIN AGAINST GASTRIC OXIDATIVE STRESS AND DYSLIPIDEMIA IN STREPTOZOTOCIN-INDUCED DIABETIC RATS

OBJECTIVE

The aim of this study was to evaluate the possible protective effects of MT against gastric oxidative stress and dyslipidemia in streptozotocin (STZ) - induced diabetic rats.

METHODS

Forty male Wistar rats were randomly divided into five groups: control, diabetic, MT 5 mg/kg+ STZ, MT 10 mg/kg+ STZ and MT 20 mg/kg+ STZ. STZ (60 mg/kg) was intraperitoneally (ip) injected as a single dose for diabetes induction. One week after STZ administration, MT was injected daily as ip for 14 days. The levels of malondialdehyde (MDA), total thiol and glutathione, as well as superoxide dismutase (SOD) and catalase activities were measured in gastric tissue. Serum concentrations of triglycerides (TG), total cholesterol (TC), high density lipoprotein (HDL) and low density lipoprotein (LDL) were also determined.

RESULTS

Serum glucose significantly increased in diabetic group compared to control group. STZ induced a significant decrease in gastric tissue levels of total thiol, glutathione, catalase and SOD activities and a significant increase in MDA concentration. In diabetic rats, serum TG, LDL and TC were significantly higher and HDL was significantly lower than in the control group. Treatment of diabetic rats with MT caused a significant increase in gastric total thiol content and glutathione concentration as well as SOD and catalase activities. Gastric MDA concentration and serum LDL, TG and TC were significantly lower in MT-treated groups when compared with diabetic group.

CONCLUSION

These data suggested that MT has a therapeutic effect on gastric oxidative damage and dyslipidemia induced by diabetes that possibly may be due to its antioxidant effects.

Melatonin Administration Methods for Research in Mammals and Birds

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Aging of lymphoid organs: Can photobiomodulation reverse age-associated thymic involution via stimulation of extrapineal melatonin synthesis and bone marrow stem cells?

Thymic atrophy and the subsequent reduction in T-cell production are the most noticeable age-related changes affecting lymphoid organs in the immune system. In fact, thymic involution has been described as "programmed aging." New therapeutic approaches, such as photobiomodulation (PBM), may reduce or reverse these changes. PBM (also known as low-level laser therapy) involves the delivery of non-thermal levels of red or near-infrared light that are absorbed by mitochondrial chromophores, in order to prevent tissue death and stimulate healing and regeneration. PBM may reverse or prevent thymic involution due to its ability to induce extrapineal melatonin biosynthesis via cyclic adenosine monophosphate (AMP) or NF-kB activation, or alternatively by stimulating bone marrow stem cells that can regenerate the thymus. This perspective puts forward a hypothesis that PBM can alter thymic involution, improve immune functioning in aged people and even extend lifespan.

Chemotaxis of Escherichia coli to major hormones and polyamines present in human gut

The microorganisms in the gastrointestinal (GI) tract can influence the metabolism, immunity, and behavior of animal hosts. Increasing evidence suggests that communication between the host and the microbiome also occurs in the opposite direction, with hormones and other host-secreted compounds being sensed by microorganisms. Here, we addressed one key aspect of the host–microbe communication by studying chemotaxis of a model commensal bacterium, Escherichia coli, to several compounds present abundantly in the GI tract, namely catecholamines, thyroid hormones, and polyamines. Our results show that E. coli reacts to five out of ten analyzed chemicals, sensing melatonin, and spermidine as chemorepellents and showing mixed responses to dopamine, norepinephrine and 3,4-dihydroxymandelic acid. The strongest repellent response was observed for the polyamine spermidine, and we demonstrate that this response involves the low-abundance chemoreceptor Trg and the periplasmic binding protein PotD of the spermidine uptake system. The chemotactic effects of the tested compounds apparently correlate with their influence on growth and their stability in the GI tract, pointing to the specificity of the observed behavior. We hypothesize that the repellent responses observed at high concentrations of chemoeffective compounds might enable bacteria to avoid harmful levels of hormones and polyamines in the gut and, more generally, antimicrobial activities of the mucous layer.

The neuroprotective role of melatonin in neurological disorders

Melatonin is a neurohormone secreted from the pineal gland and has a wide-ranging regulatory and neuroprotective role. It has been reported that melatonin level is disturbed in some neurological conditions such as stroke, Alzheimer's disease, and Parkinson's disease, which indicates its involvement in the pathophysiology of these diseases. Its properties qualify it to be a promising potential therapeutic neuroprotective agent, with no side effects, for some neurological disorders. This review discusses and localizes the effect of melatonin in the pathophysiology of some diseases.

Melatonin as a Therapy for Traumatic Brain Injury: A Review of Published Evidence

Melatonin (MEL) is a hormone that is produced in the brain and is known to bind to MEL-specific receptors on neuronal membranes in several brain regions. MEL’s documented neuroprotective properties, low toxicity, and ability to cross the blood-brain-barrier have led to its evaluation for patients with traumatic brain injury (TBI), a condition for which there are currently no Food and Drug Administration (FDA)-approved therapies. The purpose of this manuscript is to summarize the evidence surrounding the use of melatonin after TBI, as well as identify existing gaps and future directions. To address this aim, a search of the literature was conducted using Pubmed, Google Scholar, and the Cochrane Database. In total, 239 unique articles were screened, and the 22 preclinical studies that met the a priori inclusion/exclusion criteria were summarized, including the study aims, sample (size, groups, species, strain, sex, age/weight), TBI model, therapeutic details (preparation, dose, route, duration), key findings, and conclusions. The evidence from these 22 studies was analyzed to draw comparisons across studies, identify remaining gaps, and suggest future directions. Taken together, the published evidence suggests that MEL has neuroprotective properties via a number of mechanisms with few toxic effects reported. Notably, available evidence is largely based on data from adult male rats and, to a lesser extent, mice. Few studies collected data beyond a few days of the initial injury, necessitating additional longer-term studies. Other future directions include diversification of samples to include female animals, pediatric and geriatric animals, and transgenic strains.

Domestic light at night and breast cancer risk: a prospective analysis of 105 000 UK women in the Generations Study

Background:

Circadian disruption caused by exposure to light at night (LAN) has been proposed as a risk factor for breast cancer and a reason for secular increases in incidence. Studies to date have largely been ecological or case-control in design and findings have been mixed.

Methods:

We investigated the relationship between LAN and breast cancer risk in the UK Generations Study. Bedroom light levels and sleeping patterns at age 20 and at study recruitment were obtained by questionnaire. Analyses were conducted on 105 866 participants with no prior history of breast cancer. During an average of 6.1 years of follow-up, 1775 cases of breast cancer were diagnosed. Cox proportional hazard models were used to calculate hazard ratios (HRs), adjusting for potential confounding factors.

Results:

There was no association between LAN level and breast cancer risk overall (highest compared with lowest LAN level at recruitment: HR=1.01, 95% confidence interval (CI): 0.88–1.15), or for invasive (HR=0.98, 95% CI: 0.85–1.13) or in situ (HR=0.96, 95% CI: 0.83–1.11) breast cancer, or oestrogen-receptor (ER) positive (HR=0.98, 95% CI: 0.84–1.14); or negative (HR=1.16, 95% CI: 0.82–1.65) tumours separately. The findings did not differ by menopausal status. Adjusting for sleep duration, sleeping at unusual times (non-peak sleep) and history of night work did not affect the results. Night waking with exposure to light, occurring around age 20, was associated with a reduced risk of premenopausal breast cancer (HR for breast cancer overall=0.74, 95% CI: 0.55–0.99; HR for ER-positive breast cancer=0.69, 95% CI: 0.49–0.97).

Conclusions:

In this prospective cohort analysis of LAN, there was no evidence that LAN exposure increased the risk of subsequent breast cancer, although the suggestion of a lower breast cancer risk in pre-menopausal women with a history of night waking in their twenties may warrant further investigation.

A Short-Day Photoperiod Delays the Timing of Puberty in Female Mice via Changes in the Kisspeptin System

The reproduction of seasonal breeders is modulated by exposure to light in an interval of 24 h defined as photoperiod. The interruption of reproductive functions in seasonally breeding rodents is accompanied by the suppression of the Kiss1 gene expression, which is known to be essential for reproduction. In non-seasonal male rodents, such as rats and mice, short-day photoperiod (SP) conditions or exogenous melatonin treatment also have anti-gonadotropic effects; however, whether photoperiod is able to modulate the puberty onset or Kiss1 gene expression in mice is unknown. In the present study, we investigated whether photoperiodism influences the sexual maturation of female mice via changes in the kisspeptin system. We observed that SP condition delayed the timing of puberty in female mice, decreased the hypothalamic expression of genes related to the reproductive axis and reduced the number of Kiss1-expressing neurons in the rostral hypothalamus. However, SP also reduced the body weight gain during development and affected the expression of neuropeptides involved in the energy balance regulation. When body weight was recovered via a reduction in litter size, the timing of puberty in mice born and raised in SP was advanced and the effects in hypothalamic mRNA expression were reverted. These results suggest that the SP delays the timing of puberty in female mice via changes in the kisspeptin system, although the effects on hypothalamic-pituitary-gonadal axis are likely secondary to changes in body weight gain.

Breastfeeding and the gut-brain axis: is there a role for melatonin?

The benefits of breastfeeding over formula feed are widely appreciated. However, for many mothers breastfeeding is not possible, highlighting the need for a significant improvement in the contents of formula feed. In this article, the overlooked role of melatonin and the melatonergic pathways in breast milk and in the regulation of wider breast milk components are reviewed. There is a growing appreciation that the benefits of breastfeeding are mediated by its effects in the infant gut, with consequences for the development of the gut-brain axis and the immune system. The melatonergic pathways are intimately associated with highly researched processes in the gut, gut microbiome and gut-brain axis. As the melatonergic pathways are dependent on the levels of serotonin availability as a necessary precursor, decreased melatonin is linked to depression and depression-associated disorders. The association of breastfeeding and the gut-brain axis with a host of medical conditions may be mediated by their regulation of processes that modulate depression susceptibility. The biological underpinnings of depression include increased levels of pro-inflammatory cytokines, oxidative stress, kynurenine pathway activity and dysregulation of the hypothalamic-pituitary adrenal axis, all of which can decrease melatonergic pathway activity. The inclusion of the melatonergic pathways in the biological interactions of breast milk and gut development has significant theoretical and treatment implications, as well as being important to the prevention of a host of infant-, child- and adult-onset medical conditions.

[Melatonin - known problems and perspectives of clinical usage]

The article discusses well-known and ongoing studies of mechanisms of action of melatonin. The main clinical effects of melatonin are discussed. The emphasis on the chronobiological effect of melatonin, its adaptogenic and anti-carcinogenic properties has been done in the article. The most frequent manifestations of epiphyseal melatonin deficiency are various functional disorders in the form of insomnia, anxiety or depressive disorders. Recommendations on the effective use of melatonin in its deficiency due to pathology are given.