Metabolism of melatonin and biological activity of intermediates of melatoninergic pathway in human skin cells

Melatonin effects on oxidative stress and on TLR4/NF-kβ inflammatory pathway in the right ventricle of rats with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterised by an increase in mean pulmonary arterial pressure and a compromised the right ventricle (RV), together with progression to heart failure and premature death. Studies have evaluated the role of melatonin as a promising therapeutic strategy for PAH. The objective of this study was to evaluate melatonin's effects on oxidative stress and on the TLR4/NF-kβ inflammatory pathway in the RV of rats with PAH. Male Wistar rats were divided into the following groups: control, monocrotaline (MCT), and monocrotaline plus melatonin groups. These two last groups received one intraperitoneal injection of MCT (60 mg/kg) on the first day of experimental protocol. The monocrotaline plus melatonin group received 10 mg/kg/day of melatonin by gavage for 21 days. Echocardiographic analysis was performed, and the RV was collected for morphometric analysis oxidative stress and molecular evaluations. The main findings of the present study were that melatonin administration attenuated the reduction in RV function that was induced by monocrotaline, as assessed by TAPSE. In addition, melatonin prevented RV diastolic area reduction caused by PAH. Furthermore, animals treated with melatonin did not show an increase in ROS levels or in NF-kβ expression. In addition, the monocrotaline plus melatonin group showed a reduction in TLR4 expression when compared with control and monocrotaline groups. To our knowledge, this is the first study demonstrating a positive effect of melatonin on the TLR4/NF-kβ pathway in the RV of rats with PAH. In this sense, this study makes it possible to think of melatonin as a possible ally in mitigating RV alterations caused by PAH.

Melatonin for gastric cancer treatment: where do we stand?

Gastric cancer (GC) is the third leading reason of death in men and the fourth in women. Studies have documented an inhibitory function of melatonin on the proliferation, progression and invasion of GC cells. MicroRNAs (miRNAs) are small, non-coding RNAs that play an important function in regulation of biological processes and gene expression of the cells. Some studies reported that melatonin can suppress the progression of GC by regulating the exosomal miRNAs. Thus, melatonin represents a promising potential therapeutic agent for subjects with GC. Herein, we evaluate the existing data of both in vivo and in vitro studies to clarify the molecular processes involved in the therapeutic effects of melatonin in GC. The data emphasize the critical function of melatonin in several signaling ways by which it may inhibit cancer cell proliferation, decrease chemo-resistance, induce apoptosis as well as limit invasion, angiogenesis, and metastasis. This review provides a resource that identifies some of the mechanisms by which melatonin controls GC enlargement. In light of the findings, melatonin should be considered a novel and testable therapeutic mediator for GC treatment.

Melatonin improves nitric oxide bioavailability in isoproterenol induced myocardial injury

Isoproterenol administration is associated with cardiac inflammation and decreased NO availability. Melatonin has been reported to have cardioprotective effect. The aim of this study was to investigate the effect of melatonin on NO bioavailability and inflammation in myocardial injury induced by isoproterenol. Isoproterenol was administrated in male Wistar rats for 7 days to induce cardiac injury. The animals were divided into 3 groups: Control, Isoproterenol, Isoproterenol + Melatonin. Animals received melatonin for 7 days. Echocardiographic analysis was performed and the hearts were collected for molecular analysis. Animals that received isoproterenol demonstrated a reduction in left ventricle systolic and diastolic diameter, indicating the presence of concentric hypertrophy. Melatonin was able to attenuate this alteration. Melatonin also improved NO bioavailability and decreased NF-κβ, TNFα and IL-1β expression. In conclusion, melatonin exhibited a cardioprotective effect which was associated with improving NO bioavailability and decreasing the pro-inflammatory proteins.

Effect of melatonin as a therapeutic strategy against intrauterine growth restriction: a mini-review of current state

Intrauterine growth restriction (IUGR) or intrauterine growth retardation is a condition that the fetus does not grow as expected. And the biometric profile does not match with the age of fetus. This condition is associated with increased mortality and morbidity of the neonates along with increased risk of cardiovascular, lung, and central nervous system damage. Despite close monitoring of high-risk mothers and the development of new therapeutic approaches, the optimal outcome has not been achieved yet that it indicates the importance of investigations on new therapeutic approaches. Melatonin (MLT) is a neurohormone mainly produced by the pineal gland and has a wide range of effects on different organs due to the broad dispersion of its receptors. Moreover, melatonin is produced by the placenta and also its receptors have been found on the surface of this organ. Not only studies showed the importance of this neurohormone on growth and development of fetus but also they proved its highly anti-oxidant properties. As in IUGR the oxidative stress and inflammation increased melatonin could counteract these changes and improved organ's function. In this study, we found that use of MLT could be a good clinical approach for the treatment of IUGR as its high anti-oxidant activity and vasodilation could dampen the mechanisms lead to the IUGR development.

Partners in health and disease: pineal gland and purinergic signalling

In mammal's pineal glands, ATP interacts with the high-affinity P2Y1 and the low-affinity P2X7 receptors. ATP released from sympathetic nerve terminals potentiates noradrenaline-induced serotonin N-acetyltransferase (Snat) transcription, N-acetylserotonin (NAS), and melatonin (MLT) synthesis. Circulating melatonin impairs the expression of adhesion molecules in endothelial cells, blocking the migration of leukocytes. Acute defence response induced by pathogen- and danger/damage-associated molecular patterns (PAMPs and DAMPs) triggers the NF-κB pathway in pinealocytes and blocks the transcription of Snat. Therefore, the darkness hormone is not released, and neutrophils and monocytes migrate to the lesion sites. ATP released in high amounts from apoptotic and death cells was considered a DAMP, and the blockage of P2X7 receptors was tested as a new class of drugs for treating brain damage. However, this is not a simple equation. High ATP injected in a lateral ventricle blocked MLT, but not NAS, synthesis as it impairs the transcription of acetyl serotonin N-methyltransferase. NAS is released in the plasma and the cerebral spinal fluid. NAS also blocks the rolling and adhesion of leukocytes to endothelial cells. Otherwise, it is metabolised specifically in each brain area to provide the requested concentration of MLT as a neuroprotector. As observed in physiological conditions, high extracellular ATP, different from the other DAMPs, reports the environmental light/dark cycle rhythm because NAS substitutes MLT as the nocturnal chemical indicator, the darkness hormone. Thus, blocking the P2X7R should not be considered a universal therapy for improving acute strokes, as MLT and ATP are partners in health and disease.

The dual roles of serotonin in antitumor immunity

Research has shown that a significant portion of cancer patients experience depressive symptoms, often accompanied by neuroendocrine hormone imbalances. Depression is frequently associated with decreased levels of serotonin with the alternate name 5-hydroxytryptamine (5-HT), leading to the common use of selective serotonin reuptake inhibitors (SSRIs) as antidepressants. However, the role of serotonin in tumor regulation remains unclear, with its expression levels displaying varied effects across different types of tumors. Tumor initiation and progression are closely intertwined with the immune function of the human body. Neuroimmunity, as an interdisciplinary subject, has played a unique role in the study of the relationship between psychosocial factors and tumors and their mechanisms in recent years. This article offers a comprehensive review of serotonin's regulatory roles in tumor onset and progression, as well as its impacts on immune cells in the tumor microenvironment. The aim is to stimulate further interdisciplinary research and discover novel targets for tumor treatment.

Melatonin/Sericin Wound Healing Patches: Implications for Melanoma Therapy

Melatonin and sericin exhibit antioxidant properties and may be useful in topical wound healing patches by maintaining redox balance, cell integrity, and regulating the inflammatory response. In human skin, melatonin suppresses damage caused by ultraviolet radiation (UVR) which involves numerous mechanisms associated with reactive oxygen species/reactive nitrogen species (ROS/RNS) generation and enhancing apoptosis. Sericin is a protein mainly composed of glycine, serine, aspartic acid, and threonine amino acids removed from the silkworm cocoon (particularly Bombyx mori and other species). It is of interest because of its biodegradability, anti-oxidative, and anti-bacterial properties. Sericin inhibits tyrosinase activity and promotes cell proliferation that can be supportive and useful in melanoma treatment. In recent years, wound healing patches containing sericin and melatonin individually have attracted significant attention by the scientific community. In this review, we summarize the state of innovation of such patches during 2021-2023. To date, melatonin/sericin-polymer patches for application in post-operational wound healing treatment has been only sparingly investigated and it is an imperative to consider these materials as a promising approach targeting for skin tissue engineering or regenerative dermatology.

Photo-neuro-immuno-endocrinology: How the ultraviolet radiation regulates the body, brain, and immune system

Ultraviolet radiation (UVR) is primarily recognized for its detrimental effects such as cancerogenesis, skin aging, eye damage, and autoimmune disorders. With exception of ultraviolet B (UVB) requirement in the production of vitamin D3, the positive role of UVR in modulation of homeostasis is underappreciated. Skin exposure to UVR triggers local responses secondary to the induction of chemical, hormonal, immune, and neural signals that are defined by the chromophores and extent of UVR penetration into skin compartments. These responses are not random and are coordinated by the cutaneous neuro-immuno-endocrine system, which counteracts the action of external stressors and accommodates local homeostasis to the changing environment. The UVR induces electrical, chemical, and biological signals to be sent to the brain, endocrine and immune systems, as well as other central organs, which in concert regulate body homeostasis. To achieve its central homeostatic goal, the UVR-induced signals are precisely computed locally with transmission through nerves or humoral signals release into the circulation to activate and/or modulate coordinating central centers or organs. Such modulatory effects will be dependent on UVA and UVB wavelengths. This leads to immunosuppression, the activation of brain and endocrine coordinating centers, and the modification of different organ functions. Therefore, it is imperative to understand the underlying mechanisms of UVR electromagnetic energy penetration deep into the body, with its impact on the brain and internal organs. Photo-neuro-immuno-endocrinology can offer novel therapeutic approaches in addiction and mood disorders; autoimmune, neurodegenerative, and chronic pain-generating disorders; or pathologies involving endocrine, cardiovascular, gastrointestinal, or reproductive systems.

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.

Melatonin and Its Metabolites Can Serve as Agonists on the Aryl Hydrocarbon Receptor and Peroxisome Proliferator-Activated Receptor Gamma

Melatonin is widely present in Nature. It has pleiotropic activities, in part mediated by interactions with high-affinity G-protein-coupled melatonin type 1 and 2 (MT1 and MT2) receptors or under extreme conditions, e.g., ischemia/reperfusion. In pharmacological concentrations, it is given to counteract the massive damage caused by MT1- and MT2-independent mechanisms. The aryl hydrocarbon receptor (AhR) is a perfect candidate for mediating the latter effects because melatonin has structural similarity to its natural ligands, including tryptophan metabolites and indolic compounds. Using a cell-based Human AhR Reporter Assay System, we demonstrated that melatonin and its indolic and kynuric metabolites act as agonists on the AhR with EC50's between 10-4 and 10-6 M. This was further validated via the stimulation of the transcriptional activation of the CYP1A1 promoter. Furthermore, melatonin and its metabolites stimulated AhR translocation from the cytoplasm to the nucleus in human keratinocytes, as demonstrated by ImageStream II cytometry and Western blot (WB) analyses of cytoplasmic and nuclear fractions of human keratinocytes. These functional analyses are supported by in silico analyses. We also investigated the peroxisome proliferator-activated receptor (PPAR)γ as a potential target for melatonin and metabolites bioregulation. The binding studies using a TR-TFRET kit to assay the interaction of the ligand with the ligand-binding domain (LBD) of the PPARγ showed agonistic activities of melatonin, 6-hydroxymelatonin and N-acetyl-N-formyl-5-methoxykynuramine with EC50's in the 10-4 M range showing significantly lower affinities that those of rosiglitazone, e.g., a 10-8 M range. These interactions were substantiated by stimulation of the luciferase activity of the construct containing PPARE by melatonin and its metabolites at 10-4 M. As confirmed by the functional assays, binding mode predictions using a homology model of the AhR and a crystal structure of the PPARγ suggest that melatonin and its metabolites, including 6-hydroxymelatonin, 5-methoxytryptamine and N-acetyl-N-formyl-5-methoxykynuramine, are excellent candidates to act on the AhR and PPARγ with docking scores comparable to their corresponding natural ligands. Melatonin and its metabolites were modeled into the same ligand-binding pockets (LBDs) as their natural ligands. Thus, functional assays supported by molecular modeling have shown that melatonin and its indolic and kynuric metabolites can act as agonists on the AhR and they can interact with the PPARγ at high concentrations. This provides a mechanistic explanation for previously reported cytoprotective actions of melatonin and its metabolites that require high local concentrations of the ligands to reduce cellular damage under elevated oxidative stress conditions. It also identifies these compounds as therapeutic agents to be used at pharmacological doses in the prevention or therapy of skin diseases.

Melanogenesis Is Directly Affected by Metabolites of Melatonin in Human Melanoma Cells

Melatonin (N-acetyl-5-methoxytryptamine, MEL), its kynurenic (N1-acetyl-N2-formyl-5-methoxykynurenine, AFMK) and indolic derivatives (6-hydroxymelatonin, 6(OH)MEL and 5-methoxytryptamine, 5-MT) are endogenously produced in human epidermis. Melatonin, produced by the pineal gland, brain and peripheral organs, displays a diversity of physiological functions including anti-inflammatory, immunomodulatory, and anti-tumor capacities. Herein, we assessed their regulatory effect on melanogenesis using amelanotic (A375, Sk-Mel-28) and highly pigmented (MNT-1, melanotic) human melanoma cell lines. We discovered that subjected compounds decrease the downstream pathway of melanin synthesis by causing a significant drop of cyclic adenosine monophosphate (cAMP) level, the microphthalmia-associated transcription factor (MITF) and resultant collapse of tyrosinase (TYR) activity, and melanin content comparatively to N-phenylthiourea (PTU, a positive control). We observed a reduction in pigment in melanosomes visualized by the transmission electron microscopy. Finally, we assessed the role of G-protein-coupled seven-transmembrane-domain receptors. Obtained results revealed that nonselective MT1 and MT2 receptor antagonist (luzindole) or selective MT2 receptor antagonist (4-P-PDOT) did not affect dysregulation of the melanin pathway indicating a receptor-independent mechanism. Our findings, together with the current state of the art, provide a convenient experimental model to study the complex relationship between metabolites of melatonin and the control of pigmentation serving as a future and rationale strategy for targeted therapies of melanoma-affected patients.

Melatonin as a Therapy for Preterm Brain Injury: What Is the Evidence?

Despite significant improvements in survival following preterm birth in recent years, the neurodevelopmental burden of prematurity, with its long-term cognitive and behavioral consequences, remains a significant challenge in neonatology. Neuroprotective treatment options to improve neurodevelopmental outcomes in preterm infants are therefore urgently needed. Alleviating inflammatory and oxidative stress (OS), melatonin might modify important triggers of preterm brain injury, a complex combination of destructive and developmental abnormalities termed encephalopathy of prematurity (EoP). Preliminary data also suggests that melatonin has a direct neurotrophic impact, emphasizing its therapeutic potential with a favorable safety profile in the preterm setting. The current review outlines the most important pathomechanisms underlying preterm brain injury and correlates them with melatonin's neuroprotective potential, while underlining significant pharmacokinetic/pharmacodynamic uncertainties that need to be addressed in future studies.

Ultraviolet Radiation-Induced Mitochondrial Disturbances Are Attenuated by Metabolites of Melatonin in Human Epidermal Keratinocytes

Melatonin (N-acetyl-5-methoxytryptamine) is recognized as an effective antioxidant produced by the pineal gland, brain and peripheral organs, which also has anti-inflammatory, immunomodulatory, and anti-tumour capacities. Melatonin has been reported as a substance that counteracts ultraviolet radiation B (UVB)-induced intracellular disturbances. Nevertheless, the mechanistic actions of related molecules including its kynurenic derivatives (N1-acetyl-N2-formyl-5-methoxykynurenine (AFMK)), its indolic derivatives (6-hydroxymelatonin (6(OH)MEL) and 5-methoxytryptamine (5-MT)) and its precursor N-acetylserotonin (NAS) are only poorly understood. Herein, we treated human epidermal keratinocytes with UVB and assessed the protective effect of the studied substances in terms of the maintenance of mitochondrial function or their radical scavenging capacity. Our results show that UVB caused the significant elevation of catalase (CAT) and superoxide dismutase (Mn-SOD), the dissipation of mitochondrial transmembrane potential (mtΔΨ), a reduction in ATP synthesis, and the enhanced release of cytochrome c into cytosol, leading subsequently to UVB-mediated activation of the caspases and apoptosis (appearance of sub-G1 population). Our findings, combined with data reported so far, indicate the counteracting and beneficial actions of melatonin and its molecular derivatives against these deleterious changes within mitochondria. Therefore, they define a path to the development of novel strategies delaying mitochondrial aging and promoting the well-being of human skin.

The Melatonin-Mitochondrial Axis: Engaging the Repercussions of Ultraviolet Radiation Photoaging on the Skin's Circadian Rhythm

Sunlight is a vital element in modulating the central circadian rhythm, such as the regulation of the host's sleep-awake state. Sunlight is also considered to have a significant influence on the circadian rhythm of the skin. Over-exposure or prolonged exposure to sunlight can lead to skin photodamage, including hyperpigmentation, collagen degradation, fibrosis, and even skin cancer. Thus, this review will focus on the adverse effects of sunlight on the skin, not only in terms of photoaging but also its effect on the skin's circadian rhythm. Mitochondrial melatonin, regarded as a beneficial anti-aging substance for the skin, follows a circadian rhythm and exhibits a powerful anti-oxidative capacity, which has been shown to be associated with skin function. Thus, the review will focus on the influence of sunlight on skin status, not only in terms of ultraviolet radiation (UVR)-induced oxidative stress but also its mediation of circadian rhythms regulating skin homeostasis. In addition, this article will address issues regarding how best to unleash the biological potential of melatonin. These findings about the circadian rhythms of the skin have broadened the horizon of a whole new dimension in our comprehension of the molecular mechanisms of the skin and are likely to help pharmaceutical companies to develop more effective products that not only inhibit photoaging but keep valid and relevant throughout the day in future.

How cancer hijacks the body's homeostasis through the neuroendocrine system

During oncogenesis, cancer not only escapes the body's regulatory mechanisms, but also gains the ability to affect local and systemic homeostasis. Specifically, tumors produce cytokines, immune mediators, classical neurotransmitters, hypothalamic and pituitary hormones, biogenic amines, melatonin, and glucocorticoids, as demonstrated in human and animal models of cancer. The tumor, through the release of these neurohormonal and immune mediators, can control the main neuroendocrine centers such as the hypothalamus, pituitary, adrenals, and thyroid to modulate body homeostasis through central regulatory axes. We hypothesize that the tumor-derived catecholamines, serotonin, melatonin, neuropeptides, and other neurotransmitters can affect body and brain functions. Bidirectional communication between local autonomic and sensory nerves and the tumor, with putative effects on the brain, is also envisioned. Overall, we propose that cancers can take control of the central neuroendocrine and immune systems to reset the body homeostasis in a mode favoring its expansion at the expense of the host.

Concentration-dependent stimulation of melanin production as well as melanocyte and keratinocyte proliferation by melatonin in human eyelid epidermis

It remains unclear how the multifunctional indoleamine neurohormone, melatonin, alters melanin production and melanocytes within intact human epidermis under physiologically relevant conditions. In the current pilot study, we aimed to clarify this in long-term organ-cultured, full-thickness human eyelid skin, selected for its clinically recognized sensitivity to pigmentation-modulatory hormones. Warthin-Starry histochemistry showed that 100 μM melatonin significantly increased epidermal melanin content and melanocyte dendricity after 6 days of organ culture, even though tyrosinase activity in situ was inhibited, as assessed by quantitative immunohistomorphometry. While the higher melatonin dose tested here (200 μM) did not change epidermal melanization, but again inhibited tyrosinase activity, it increased the number and proliferation of both gp100⁺ epidermal melanocytes and keratinocytes as well as protein expression of the premelanosomal marker, gp100, ex vivo. Contrary to most previous studies, these eyelid skin organ culture results suggest that long-term melatonin application exerts overall stimulatory, dose-dependent effects on the epidermal pigmentary unit within intact human skin, which appear surprisingly tyrosinase-independent. While these provocative preliminary findings require further work-up and independent confirmation, they encourage one to systematically explore whether prolonged melatonin therapy can (re-)stimulate melanogenesis and increase the pool/activity of epidermal melanocytes in hypopigmented skin lesions.

N-Acetylserotonin is an oxidation-responsive activator of Nrf2 ameliorating colitis in rats

N-Acetylserotonin (NAS) is an intermediate in the melatonin biosynthetic pathway. We investigated the anti-inflammatory activity of NAS by focusing on its chemical feature oxidizable to an electrophile. NAS was readily oxidized by reaction with HOCl, an oxidant produced in the inflammatory state. HOCl-reacted NAS (Oxi-NAS), but not NAS, activated the anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2)-heme oxygenase (HO)-1 pathway in cells. Chromatographic and mass analyses demonstrated that Oxi-NAS was the iminoquinone form of NAS and could react with N-acetylcysteine possessing a nucleophilic thiol to form a covalent adduct. Oxi-NAS bound to Kelch-like ECH-associated protein 1, resulting in Nrf2 dissociation. Moreover, rectally administered NAS increased the levels of nuclear Nrf2 and HO-1 proteins in the inflamed colon of rats. Simultaneously, NAS was converted to Oxi-NAS in the inflamed colon. Rectal NAS mitigated colonic damage and inflammation. The anticolitic effects were significantly compromised by the coadministration of an HO-1 inhibitor.

The Role of Melatonin in Pregnancy and the Health Benefits for the Newborn

In the last few years, there have been significant evolutions in the understanding of the hormone melatonin in terms of its physiology, regulatory role, and potential utility in various domains of clinical medicine. Melatonin's properties include, among others, the regulation of mitochondrial function, anti-inflammatory, anti-oxidative and neuro-protective effects, sleep promotion and immune enhancement. As it is also bioavailable and has little or no toxicity, it has been proposed as safe and effective for the treatment of numerous diseases and to preserve human health. In this manuscript, we tried to evaluate the role of melatonin at the beginning of human life, in pregnancy, in the fetus and in newborns through newly published literature studies.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

Impact of Melatonin on RAW264.7 Macrophages during Mechanical Strain

The concentration of melatonin is elevated during the night when patients mainly wear removable orthodontic appliances. Next to periodontal ligament fibroblasts and osteoblasts, macrophages react to mechanical strain with an increased expression of inflammatory mediators. Here, we investigated the impact of melatonin on RAW264.7 macrophages exposed to tensile or compressive strain occurring during orthodontic tooth movement in the periodontal ligament. Before exposure to mechanical strain for 4 h, macrophages were pre-incubated with different melatonin concentrations for 24 h, to determine the dependence of melatonin concentration. Afterwards, we performed experiments with and without mechanical strain, the most effective melatonin concentration (25 µM), and the melatonin receptor 2 (MT2) specific antagonist 4P-PDOT. The expression of inflammatory genes and proteins was investigated by RT-qPCR, ELISAs, and immunoblot. Both tensile and compressive strain increased the expression of the investigated inflammatory factors interleukin-1-beta, interleukin-6, tumor necrosis factor alpha, and prostaglandin endoperoxide synthase-2. This effect was inhibited by the addition of melatonin. Incubation with 4P-PDOT blocked this anti-inflammatory effect of melatonin. Melatonin had an anti-inflammatory effect on macrophages exposed to mechanical strain, independent of the type of mechanical strain. As inhibition was possible with 4P-PDOT, the MT2 receptor might be involved in the regulation of the observed effects.

Application of Melatonin with N-Acetylcysteine Exceeds Traditional Treatment for Acetaminophen-Induced Hepatotoxicity

Acetaminophen (APAP) overdose is one of the leading causes of acute liver damage. Given N-acetylcysteine (NAC) and melatonin (MLT) both have an attenuated value for APAP-induced liver toxification, where an optimized integrated treatment has not been well deciphered. Here, by giving a single dose of APAP (500 mg/kg) to wild-type male mice, combined with a single dose of 500 mg/kg NAC or 100 mg/kg MLT separately as the therapeutic method, this study aimed to investigate the effects of NAC and melatonin (MLT) alone or combined on acetaminophen (APAP)-induced liver injury. In this study, NAC and MLT both partially have an alleviated function in APAP-challenged liver injury. However, MLT's add-on role strengthens the hepatoprotective effect of NAC on APAP-induced liver damage and resolute the inflammatory infiltration. Meanwhile, the combination of two reagents attenuates the decreased glutathione (GSH) and activation of the p38/JNK pathway. The combination of MLT and NAC can further ameliorate APAP-induced liver injury, which provides a novel strategy for drug-induced liver injury (DILI).

Melatonin Improves Ischemia-Induced Circulation Recovery Impairment in Mice with Streptozotocin-Induced Diabetes by Improving the Endothelial Progenitor Cells Functioning

Patients with diabetes mellitus tend to develop ischemia-related complications and have compromised endothelial progenitor cell (EPC) function. Melatonin protects against ischemic injury, possibly via EPC modulation. We investigated whether melatonin pretreatment could restore EPC function impairment and improve circulation recovery in a diabetic critical limb ischemia mouse model. Under 25 mM high-glucose medium in vitro, EPC proliferation, nitric oxide production, tube formation, and endothelial nitric oxide synthase (eNOS) phosphorylation were significantly suppressed. Hyperglycemia promoted EPC senescence and apoptosis as well as increased reactive oxygen species (ROS) production. Melatonin treatment reversed the harmful effects of hyperglycemia on EPC through adenosine monophosphate–activated protein kinase-related mechanisms to increase eNOS phosphorylation and heme oxygenase-1 expression. In an in-vivo study, after a 4-week surgical induction of hindlimb ischemia, mice with streptozotocin (STZ)-induced diabetes showed significant reductions in new vessel formation, tissue reperfusion, and EPC mobilization in ischemic hindlimbs compared to non-diabetic mice. Mice with STZ-induced diabetes that received melatonin treatment (10 mg/kg/day, intraperitoneal) had significantly improved blood perfusion ratios of ischemic to non-ischemic limb, EPC mobilization, and densities of capillaries. In addition, a murine bone marrow transplantation model to support these findings demonstrated that melatonin stimulated bone marrow-originated EPCs to differentiate into vascular endothelial cells in femoral ligation-induced ischemic muscles. In summary, this study suggests that melatonin treatment augments EPC function along with neovascularization in response to ischemia in diabetic mice. We illustrated the protective effects of melatonin on EPC H2O2 production, senescence, and migration through melatonin receptors and modulating eNOS, AMPK, and HO-1 activities at the cellular level. Thus, melatonin might be used to treat the impairment of EPC mobilization and circulation recuperation in response to ischemic injury caused by chronic hyperglycemia. Additional studies are needed to elucidate the applicability of the results in humans.

Impact of Tea Processing on Tryptophan, Melatonin, Phenolic and Flavonoid Contents in Mulberry (Morus alba L.) Leaves: Quantitative Analysis by LC-MS/MS

Mulberry (Morus alba L.) leaves from two cultivars, Yai-Burirum (YB) and Khunphai (KP), were prepared into green tea (GT) and black tea (BT). Compared to fresh leaf (FL) extract, GT and BT extracts were evaluated for their total phenolic and total flavonoid contents. Total phenolic content (TPCs) in all samples ranged between 129.93 and 390.89 mg GAE/g extract. The processing of tea decreased the levels of TPC when compared to FL extracts in both cultivars. The total flavonoid content (TFCs) in all samples was found in the range of 10.15–39.09 mg QE/g extract and TFCs in GT and BT extracts were higher than FL extracts. The change in tryptophan, melatonin, phenolic and flavonoid contents was investigated by liquid chromatography–mass spectroscopy (LC-MS). The results exhibited that tryptophan contents in all samples were detected in the range 29.54–673.72 µg/g extract. Both GT and BT extracts increased tryptophan content compared to FL extracts. BT extracts presented the highest amounts of tryptophan among others in both cultivars. Phenolic compounds were found in mulberry leaf extracts, including gallic acid, caffeic acid, gentisic acid, protocatechuic acid and chlorogenic acid. Chlorogenic acid presented the highest amount in all samples. Almost all phenolic acids were increased in the processed tea extracts except chlorogenic acid. Rutin was the only flavonoid that was detected in all extracts in the range 109.48–1009.75 mg/g extract. The change in phenolic and flavonoid compounds during tea processing resulted in the change in antioxidant capacities of the GT and BT extracts. All extracts presented acetylcholinesterase enzyme (AChE) inhibitory activity with IC₅₀ in the range 146.53–165.24 µg/mL. The processing of tea slightly increased the AChE inhibitory effect of GT and BT extracts. In conclusion, processed tea from mulberry leaves could serve as a new alternative functional food for health-concerned consumers because it could be a promising source of tryptophan, phenolics and flavonoids. Moreover, the tea extracts also had antioxidative and anti-AChE activities.

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Melatonin and the Brain–Heart Crosstalk in Neurocritically Ill Patients—From Molecular Action to Clinical Practice

Brain injury, especially traumatic brain injury (TBI), may induce severe dysfunction of extracerebral organs. Cardiac dysfunction associated with TBI is common and well known as the brain–heart crosstalk, which broadly refers to different cardiac disorders such as cardiac arrhythmias, ischemia, hemodynamic insufficiency, and sudden cardiac death, which corresponds to acute disorders of brain function. TBI-related cardiac dysfunction can both worsen the brain damage and increase the risk of death. TBI-related cardiac disorders have been mainly treated symptomatically. However, the analysis of pathomechanisms of TBI-related cardiac dysfunction has highlighted an important role of melatonin in the prevention and treatment of such disorders. Melatonin is a neurohormone released by the pineal gland. It plays a crucial role in the coordination of the circadian rhythm. Additionally, melatonin possesses strong anti-inflammatory, antioxidative, and antiapoptotic properties and can modulate sympathetic and parasympathetic activities. Melatonin has a protective effect not only on the brain, by attenuating its injury, but on extracranial organs, including the heart. The aim of this study was to analyze the molecular activity of melatonin in terms of TBI-related cardiac disorders. Our article describes the benefits resulting from using melatonin as an adjuvant in protection and treatment of brain injury-induced cardiac dysfunction.

Melatonin Prevents UVB-Induced Skin Photoaging by Inhibiting Oxidative Damage and MMP Expression through JNK/AP-1 Signaling Pathway in Human Dermal Fibroblasts

Exposure to ultraviolet (UV) irradiation causes damage to the skin and induces photoaging. UV irradiation stimulates production of reactive oxygen/nitrogen species, which results in activation of epidermal growth factor receptor (EGFR) and mitogen-activated protein kinases (MAPK) in fibroblasts. MAPKs are responsible for activation of activator protein-1 (AP-1), which subsequently upregulates expression of matrix metalloproteinases (MMPs). Melatonin is a potent free radical scavenger which is known to have photoprotective effects. The aim of this study is to investigate the underlying molecular mechanisms for the photoprotective effects of melatonin in UVB-irradiated primary human dermal fibroblasts (HDFs) in terms of EGFR activation, oxidative/nitrosative damage, JNK/AP-1 activation, MMP activities, and the levels of tissue inhibitors of metalloproteinase-1 (TIMP-1) and type I procollagen (PIP-C). In this study, HDFs were pretreated with 1 μM of melatonin and then irradiated with 0.1 J/cm² of UVB. Changes in the molecules were analyzed at different time points. Melatonin inhibited UVB-induced oxidative/nitrosative stress damage by reducing malondialdehyde, the ratio of oxidized/reduced glutathione, and nitrotyrosine. Melatonin downregulated UV-induced activation of EGFR and the JNK/AP-1 signaling pathway. UVB-induced activities of MMP-1 and MMP-3 were decreased and levels of TIMP-1 and PIP-C were increased by melatonin. These findings suggest that melatonin can protect against the adverse effects of UVB radiation by inhibiting MMP-1 and MMP-3 activity and increasing TIMP-1 and PIP-C levels, probably through the suppression of oxidative/nitrosative damage, EGFR, and JNK/AP-1 activation in HDFs.

Melatonin and cortisol as components of the cutaneous stress response system in fish: Response to oxidative stress

The skin being a passive biological barrier that defends the organism against harmful external factors is also a site of action of the system responding to stress. It appears that melatonin (Mel) and its biologically active metabolite AFMK (N1-acetyl-N2-formyl-5-methoxykynuramine), both known as effective antioxidants, together with cortisol, set up a local (cutaneous) stress response system (CSRS) of fish, similar to that of mammals. Herein we comment on recent studies on CSRS in fish and show the response of three-spined stickleback skin to oxidative stress induced by potassium dichromate. Our study indicates that exposure of the three-spined stickleback to K₂Cr₂O₇ affects Mel and cortisol levels and pigment dispersion in melanophores in the skin. In our opinion, an increased concentration of Mel and cortisol in the skin may be the strategy to cope with oxidative stress, where both components act locally to prevent damage caused by active oxygen molecules. Furthermore, the pigment dispersion may be a valuable, easy-to-observe mark of oxidative stress, useful in the evaluation of fish welfare.

Ex vivo permeation parameters and skin deposition of melatonin-loaded microemulsion for treatment of alopecia

Background

Melatonin (MEL) is a powerful antioxidant molecule with anti-androgenic property. A microemulsion (ME) system loaded with MEL was designed for treatment of androgenic alopecia. Pseudo-ternary phase diagram was constructed, and ME formulae were developed using coconut oil, Tween 80 and PEG 400. In the present study, MEL ME was characterized and evaluated for droplet size, polydispersity index, zeta potential, morphology using TEM imaging. MEL ex vivo permeation study through rat skin followed by tape stripping for stratum corneum (SC) was performed for different ME formulae, to determine skin permeation parameters and detect SC-MEL deposition.

Results

Spherical and uniform particles of MEL-loaded microemulsion were formulated with high stability. In ex vivo permeation study, MEL ME exhibited low steady-state skin flux along with pronounced SC deposition which prevailed a controlled release manner.

Conclusion

The results suggested that MEL ME could be a promising candidate for further permeation and in vivo studies for androgenic alopecia treatment.

Revisiting the role of melatonin in human melanocyte physiology: A skin context perspective

The evolutionarily ancient methoxyindoleamine, melatonin, has long perplexed investigators by its versatility of functions and mechanisms of action, which include the regulation of vertebrate pigmentation. Although first discovered through its potent skin-lightening effects in amphibians, melatonin's role in human skin and hair follicle pigmentation and its impact on melanocyte physiology remain unclear. Synthesizing our limited current understanding of this role, we specifically examine its impact on melanogenesis, oxidative biology, mitochondrial function, melanocyte senescence, and pigmentation-related clock gene activity, with emphasis on human skin, yet without ignoring instructive pointers from nonhuman species. Given the strict dependence of melanocyte functions on the epithelial microenvironment, we underscore that melanocyte responses to melatonin are best interrogated in a physiological tissue context. Current evidence suggests that melatonin and some of its metabolites inhibit both, melanogenesis (via reducing tyrosinase activity) and melanocyte proliferation by stimulating melatonin membrane receptors (MT1, MT2). We discuss whether putative melanogenesis-inhibitory effects of melatonin may occur via activation of Nrf2-mediated PI3K/AKT signaling, estrogen receptor-mediated and/or melanocortin-1 receptor- and cAMP-dependent signaling, and/or via melatonin-regulated changes in peripheral clock genes that regulate human melanogenesis, namely Bmal1 and Per1. Melatonin and its metabolites also accumulate in melanocytes where they exert net cyto- and senescence-protective as well as antioxidative effects by operating as free radical scavengers, stimulating the synthesis and activity of ROS scavenging enzymes and other antioxidants, promoting DNA repair, and enhancing mitochondrial function. We argue that it is clinically and biologically important to definitively clarify whether melanocyte cell culture-based observations translate into melatonin-induced pigmentary changes in a physiological tissue context, that is, in human epidermis and hair follicles ex vivo, and are confirmed by clinical trial results. After defining major open questions in this field, we close by suggesting how to begin answering them in clinically relevant, currently available preclinical in situ research models.

Effect of Melatonin on Psoriatic Phenotype in Human Reconstructed Skin Model

Psoriasis is an inflammatory and auto-immune skin-disease characterized by uncontrolled keratinocyte proliferation. Its pathogenesis is not still fully understood; however, an aberrant and excessive inflammatory and immune response can contribute to its progression. Recently, more attention has been given to the anti-inflammatory and immunomodulators effects of melatonin in inflammatory diseases. The aim of this paper was to investigate the effect of melatonin on psoriatic phenotype and also in S. aureus infection-associated psoriasis, with an in vitro model using Skinethic Reconstructed Human Epidermis (RHE). An in vitro model was constructed using the RHE, a three-dimensional-model obtained from human primary-keratinocytes. RHE-cells were exposed to a mix of pro-inflammatory cytokines, to induce a psoriatic phenotype; cells were also infected with S. aureus to aggravate psoriasis disease, and then were treated with melatonin at the concentrations of 1 nM, 10 nM, and 50 nM. Our results demonstrated that melatonin at higher concentrations significantly reduced histological damage, compared to the cytokine and S. aureus groups. Additionally, the treatment with melatonin restored tight-junction expression and reduced pro-inflammatory cytokine levels, such as interleukin-1β and interleukin-12. Our results suggest that melatonin could be considered a promising strategy for psoriasis-like skin inflammation, as well as complications of psoriasis, such as S. aureus infection.

Assessment of Melatonin-Cultured Collagen/Chitosan Scaffolds Cross-Linked by a Glyoxal Solution as Biomaterials for Wound Healing

Chitosan (CTS) and collagen (Coll) are natural biomaterials that have been extensively used in tissue engineering or wound healing applications, either separately or as composite materials. Most methods to fabricate CTS/Coll matrices employ chemical crosslinking to obtain solid and stable scaffolds with the necessary porosity and mechanical properties to facilitate regeneration. In this study, we comparatively assessed the physicochemical properties of 3D scaffolds loaded with a cross-linker, glyoxal. Using a scanning electron microscope, we evaluated the microstructure of resultant matrices and their mechanistic testing by the determination of the compressive modulus (E_mod), the maximum force (F_max), thermogravimetric analysis (TG), Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR-ATR), and proliferation rate in vitro using human epidermal keratinocytes and dermal fibroblasts cultured in presence of melatonin solution (10⁻⁵ M). We observed that enhanced content of collagen (50CTS/50Coll or 20CTS/80Coll compared to 80CTS/20Coll) significantly elevated the physicochemical capacities of resultant materials. Besides, presence of 5% glyoxal increased porosity, E_mod and F_max, compared to scaffolds without glyoxal. Finally, keratinocytes and dermal fibroblasts cultured on subjected matrices in presence of melatonin revealed a prominently enhanced growth rate. This indicates that the combination of glyoxal and melatonin make it imperative to consider these materials as a promising approach for targeting skin tissue engineering or regenerative dermatology.

Considerations on the Controlled Delivery of Bioactive Compounds through Hyaluronic Acid Membrane

(1) Background: The standard treatment for periodontal disease, a chronic inflammatory state caused by the interaction between biofilms generated by organized oral bacteria and the local host defense response, consists of calculus and biofilm removal through mechanical debridement, associated with antimicrobial therapy that could be delivered either systemically or locally. The present study aimed to determine the effectiveness of a hyaluronic acid membrane matrix as a carrier for the controlled release of the active compounds of a formulation proposed as a topical treatment for periodontal disease, and the influence of pH on the complex system’s stability. (2) Methods: The obtained hyaluronic acid (HA) hydrogel membrane with dispersed melatonin (MEL), metronidazole (MZ), and tetracycline (T) was completely characterized through FTIR, XRD, thermal analysis, UV-Vis and fluorescence spectroscopy, fluorescence microscopy, zeta potential and dielectric analysis. The MTT viability test was applied to check the cytotoxicity of the obtained membranes, while the microbiological assessment was performed against strains of Staphylococcus spp. and Streptococcus spp. The spectrophotometric investigations allowed to follow up the release profile from the HA matrix for MEL, MZ, and T present in the topical treatment considered. We studied the behavior of the active compounds against the pH of the generated environment, and the release profile of the bioactive formulation based on the specific comportment towards pH variation. The controlled delivery of the bioactive compounds using HA as a supportive matrix was modeled applying Korsmeyer–Peppas, Higuchi, first-order kinetic models, and a newly proposed pseudo-first-order kinetic model. (3) Results: It was observed that MZ and T were released at higher active concentrations than MEL when the pH was increased from 6.75, specific for patients with periodontitis, to a pH of 7.10, characterizing the healthy patients. Additionally, it was shown that for MZ, there is a burst delivery up to 2.40 × 10⁻⁵ mol/L followed by a release decrease, while for MEL and T a short release plateau was recorded up to a concentration of 1.80 × 10⁻⁵ mol/L for MEL and 0.90 × 10⁻⁵ mol/L for T, followed by a continuous release; (4) Conclusions: The results are encouraging for the usage of the HA membrane matrix as releasing vehicle for the active components of the proposed topical treatment at a physiological pH.

Cosmeceutical Therapy: Engaging the Repercussions of UVR Photoaging on the Skin's Circadian Rhythm

Sunlight is an important factor in regulating the central circadian rhythm, including the modulation of our sleep/wake cycles. Sunlight had also been discovered to have a prominent influence on our skin's circadian rhythm. Overexposure or prolonged exposure to the sun can cause skin photodamage, such as the formation of irregular pigmentation, collagen degradation, DNA damage, and even skin cancer. Hence, this review will be looking into the detrimental effects of sunlight on our skin, not only at the aspect of photoaging but also at its impact on the skin's circadian rhythm. The growing market trend of natural-product-based cosmeceuticals as also caused us to question their potential to modulate the skin's circadian rhythm. Questions about how the skin's circadian rhythm could counteract photodamage and how best to maximize its biopotential will be discussed in this article. These discoveries regarding the skin's circadian rhythm have opened up a completely new level of understanding of our skin's molecular mechanism and may very well aid cosmeceutical companies, in the near future, to develop better products that not only suppress photoaging but remain effective and relevant throughout the day.

Further Evidence of the Melatonin Calmodulin Interaction: Effect on CaMKII Activity

Melatonin (MEL) is a pleiotropic indolamine that reaches multiple intracellular targets. Among these, MEL binds to calmodulin (CaM) with high affinity. In presence of Ca²⁺, CaM binds to CaM-dependent kinase II (CaMKII). The Ca²⁺-CaM/CaMKII pathway regulates a myriad of brain functions in different cellular compartments. Evidence showing the regulation of this cellular pathway by MEL is scarce. Thus, our main objective was to study the interaction of MEL with CaM and its effects on CaMKII activity in two microenvironments (aqueous and lipidic) naturally occurring within the cell. In addition, colocalization of MEL with CaM in vivo was explored in mice brain hippocampus. In vitro CaM-MEL interaction and the structural conformations of CaM in the presence of this indoleamine were assessed through electrophoretic mobility and isoelectric point. The functional consequence of this interaction was evaluated by measuring CaMKII activity. Ca²⁺-CaM-MEL increased the activity of CaMKII in aqueous buffer but reduced the kinase activity in lipid buffer. Importantly, MEL colocalizes in vivo with Ca²⁺-CaM in the hippocampus. Our evidence suggests that MEL regulates the key cellular Ca²⁺-CaM/CaMKII pathway and might explain why physiological MEL concentrations reduce CaMKII activity in some experimental conditions, while in others it drives biological processes through activation of this kinase.

Phytomelatonin: a potential phytotherapeutic intervention on COVID-19-exposed individuals

Phytomelatonin is a pleiotropic molecule that originated in higher plants with many diverse actions and is primarily an antioxidant. The recent identification and advancement of phytomelatonin unraveled the potential of this modulatory molecule being considered a new plant hormone, suggesting its relevance in treating respiratory infections, including COVID-19. Besides, this molecule is also involved in multiple hormonal, physiological, and biological processes at different levels of cell organization and has been marked for its ability to cross the blood-brain barrier and prominent antioxidant effects, reducing mitochondrial electron leakage, up-regulating antioxidant enzymes, acting as a free radical scavenger, and interfering with pro-inflammatory signaling pathways as seen in mood swings, body temperature, sleep, cancer, cardiac rhythms, and immunological regulation modulators. However, due to its diversity, availability, affordability, convenience, and high safety profile, phytomelatonin has also been suggested as a natural adjuvant. This review discussed the origin, content in various plant species, processes of extraction, and detection and therapeutic potentials of phytomelatonin in treating COVID-19-exposed individuals.

Protective Role of Melatonin and Its Metabolites in Skin Aging

The skin, being the largest organ in the human body, is exposed to the environment and suffers from both intrinsic and extrinsic aging factors. The skin aging process is characterized by several clinical features such as wrinkling, loss of elasticity, and rough-textured appearance. This complex process is accompanied with phenotypic and functional changes in cutaneous and immune cells, as well as structural and functional disturbances in extracellular matrix components such as collagens and elastin. Because skin health is considered one of the principal factors representing overall “well-being” and the perception of “health” in humans, several anti-aging strategies have recently been developed. Thus, while the fundamental mechanisms regarding skin aging are known, new substances should be considered for introduction into dermatological treatments. Herein, we describe melatonin and its metabolites as potential “aging neutralizers”. Melatonin, an evolutionarily ancient derivative of serotonin with hormonal properties, is the main neuroendocrine secretory product of the pineal gland. It regulates circadian rhythmicity and also exerts anti-oxidative, anti-inflammatory, immunomodulatory, and anti-tumor capacities. The intention of this review is to summarize changes within skin aging, research advances on the molecular mechanisms leading to these changes, and the impact of the melatoninergic anti-oxidative system controlled by melatonin and its metabolites, targeting the prevention or reversal of skin aging.

Skin senescence: mechanisms and impact on whole-body aging

The skin is the largest organ and has a key protective role. Similar to any other tissue, the skin is influenced not only by intrinsic/chronological aging, but also by extrinsic aging, triggered by environmental factors that contribute to accelerating the skin aging process. Aged skin shows structural, cellular, and molecular changes and accumulation of senescent cells. These senescent cells can induce or accelerate the age-related dysfunction of other nearby cells from the skin, or from different origins. However, the extent and underlying mechanisms remain unknown. In this opinion, we discuss the possible relevant role of skin senescence in the induction of aging phenotypes to other organs/tissues, contributing to whole-body aging. Moreover, we suggest that topical administration of senolytics/senotherapeutics could counteract the overall whole-body aging phenotype.

Possible Role of Pineal and Extra-Pineal Melatonin in Surveillance, Immunity, and First-Line Defense

Melatonin is a highly conserved molecule found in prokaryotes and eukaryotes that acts as the darkness hormone, translating environmental lighting to the whole body, and as a moderator of innate and acquired defense, migration, and cell proliferation processes. This review evaluates the importance of pineal activity in monitoring PAMPs and DAMPs and in mounting an inflammatory response or innate immune response. Activation of the immune-pineal axis, which coordinates the pro-and anti-inflammatory phases of an innate immune response, is described. PAMPs and DAMPs promote the immediate suppression of melatonin production by the pineal gland, which allows leukocyte migration. Monocyte-derived macrophages, important phagocytes of microbes, and cellular debris produce melatonin locally and thereby initiate the anti-inflammatory phase of the acute inflammatory response. The role of locally produced melatonin in organs that directly contact the external environment, such as the skin and the gastrointestinal and respiratory tracts, is also discussed. In this context, as resident macrophages are self-renewing cells, we explore evidence indicating that, besides avoiding overreaction of the immune system, extra-pineal melatonin has a fundamental role in the homeostasis of organs and tissues.

The Involvement of PDE4 in the Protective Effects of Melatonin on Cigarette-Smoke-Induced Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a significant disease threatening human health. Currently, roflumilast, a phosphodiesterase (PDE)4 inhibitor, is recommended as a therapeutic agent for COPD. In this study, we investigated the therapeutic effects of melatonin against COPD, focusing on determining whether it is a PDE4 inhibitor via in vivo and in vitro experiment using cigarette smoke (CS) and cigarette smoke condensate (CSC), respectively. In the in vivo experiments, melatonin treatment reduced inflammatory responses, including inflammatory cell counts. Melatonin treatment also suppressed the CS-exposure-induced upregulation of cytokine and matrix metalloproteinase (MMP)-9, reduced the PDE4B expression, and elevated cAMP levels. In addition, these effects were synergistic, as melatonin and roflumilast cotreatment eventually ameliorated the CS-exposure-induced worsening of lung function. In the CSC-stimulated NCI-H292 cells, melatonin inhibited elevation in the levels of inflammatory cytokines, MMP-9, and PDE4, and elevated cAMP levels. Furthermore, melatonin and roflumilast cotreatment was more effective on inflammatory responses than only melatonin or roflumilast treatment. Our results indicate that melatonin relieves inflammatory response and loss of lung function in COPD, which is associated with decreased PDE4 expression. Therefore, we suggest that melatonin is a putative candidate for the treatment of COPD.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Melatonin: A smart molecule in the DNA repair system

DNA repair is an important pathway for the protection of DNA molecules from destruction. DNA damage can be produced by oxidative reactive nitrogen or oxygen species, irritation, alkylating agents, depurination and depyrimidination; in this regard, DNA repair pathways can neutralize the negative effects of these factors. Melatonin is a hormone secreted from the pineal gland with an antioxidant effect by binding to oxidative factors. In addition, the effect of melatonin on DNA repair pathways has been proven by the literature. DNA repair is carried out by several mechanisms, of which homologous recombination repair (HRR) and non-homologous end-joining (NHEJ) are of great importance. Because of the importance of DNA repair in DNA integrity and the anticancer effect of this pathway, we presented the effect of melatonin on DNA repair factors regarding previous studies conducted in this area.

Melatonin Ameliorates Thermotolerance in Soybean Seedling through Balancing Redox Homeostasis and Modulating Antioxidant Defense, Phytohormones and Polyamines Biosynthesis

Global warming is impacting the growth and development of economically important but sensitive crops, such as soybean (Glycine max L.). Using pleiotropic signaling molecules, melatonin can relieve the negative effects of high temperature by enhancing plant growth and development as well as modulating the defense system against abiotic stresses. However, less is known about how melatonin regulates the phytohormones and polyamines during heat stress. Our results showed that high temperature significantly increased ROS and decreased photosynthesis efficiency in soybean plants. Conversely, pretreatment with melatonin increased plant growth and photosynthetic pigments (chl a and chl b) and reduced oxidative stress via scavenging hydrogen peroxide and superoxide and reducing the MDA and electrolyte leakage contents. The inherent stress defense responses were further strengthened by the enhanced activities of antioxidants and upregulation of the expression of ascorbate-glutathione cycle genes. Melatonin mitigates heat stress by increasing several biochemicals (phenolics, flavonoids, and proline), as well as the endogenous melatonin and polyamines (spermine, spermidine, and putrescine). Furthermore, the positive effects of melatonin treatment also correlated with a reduced abscisic acid content, down-regulation of the gmNCED3, and up-regulation of catabolic genes (CYP707A1 and CYP707A2) during heat stress. Contrarily, an increase in salicylic acid and up-regulated expression of the defense-related gene PAL2 were revealed. In addition, melatonin induced the expression of heat shock protein 90 (gmHsp90) and heat shock transcription factor (gmHsfA2), suggesting promotion of ROS detoxification via the hydrogen peroxide-mediated signaling pathway. In conclusion, exogenous melatonin improves the thermotolerance of soybean plants and enhances plant growth and development by activating antioxidant defense mechanisms, interacting with plant hormones, and reprogramming the biochemical metabolism.

The effect of narrow-band ultraviolet B radiation on sleep, happiness, and appetite: A prospective cohort study

BACKGROUND

The health benefits of sunlight are well documented, including the effects on happiness and sleep. However, only a few studies have investigated the benefits of artificial narrow-band ultraviolet B (NB-UVB) radiation.

OBJECTIVES

To investigate the effect of NB-UVB on sleep quality, happiness, and appetite.

METHODS

Patients from a single phototherapy unit were selected, and their epidemiological characteristics were documented. Subjects were asked to complete questionnaires including the Pittsburg Sleep Quality Index (PSQI), Subjective Happiness Scale (SHS), and the Simplified Nutritional Appetite Questionnaire (SNAQ) 4 weeks before and after the initiation of the NB-UVB therapy. The sample consisted of 52 patients.

RESULTS

Four weeks after the initiation of NB-UVB sessions, sleep quality was significantly improved (the PSQI decreased from 6.5 to 5.23 (t = -3.52, P < .01). In contrast, subjective happiness did not improve (the SHS decreased from baseline 5.5 to 5.2, P > .05). Similarly, appetite did not change (the SNAQ score increased from baseline 14.75 to 15.05, P > .05) and body mass index was not affected by phototherapy. In general, men were found to have better sleep quality before and after UV light therapy.

CONCLUSION

Our data suggest that NB-UVB exposure over 4 weeks improves sleep quality; however, it does not influence happiness or appetite.

Potential Therapeutic Effects of Melatonin Mediate via miRNAs in Cancer

miRNAs are evolutionarily conserved non-coding ribonucleic acids with a length of between 19 and 25 nucleotides. Because of their ability to regulate gene expression, miRNAs have an important function in the controlling of various biological processes, such as cell cycle, differentiation, proliferation, and apoptosis. Owing to the long-standing regulative potential of miRNAs in tumor-suppressive pathways, scholars have recently paid closer attention to the expression profile of miRNAs in various types of cancer. Melatonin, an indolic compound secreted from pineal gland and some peripheral tissues, has been considered as an effective anti-tumor hormone in a wide spectrum of cancers. Furthermore, it induces apoptosis, inhibits tumor metastasis and invasion, and also angiogenesis. A growing body of evidence indicates the effects of melatonin on miRNAs expression in broad spectrum of diseases, including cancer. Due to the long-term effects of the regulation of miRNAs expression, melatonin could be a promising therapeutic factor in the treatment of cancers via the regulation of miRNAs. Therefore, in this review, we will discuss the effects of melatonin on miRNAs expression in various types of cancers.

Evaluation of Polymeric Matrix Loaded with Melatonin for Wound Dressing

The development of scaffolds mimicking the extracellular matrix containing bioactive substances has great potential in tissue engineering and wound healing applications. This study investigates melatonin-a methoxyindole present in almost all biological systems. Melatonin is a bioregulator in terms of its potential clinical importance for future therapies of cutaneous diseases. Mammalian skin is not only a prominent melatonin target, but also produces and rapidly metabolizes the multifunctional methoxyindole to biologically active metabolites. In our methodology, chitosan/collagen (CTS/Coll)-contained biomaterials are blended with melatonin at different doses to fabricate biomimetic hybrid scaffolds. We use rat tail tendon- and Salmo salar fish skin-derived collagens to assess biophysical and cellular properties by (i) Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), (ii) thermogravimetric analysis (TG), (iii) scanning electron microscope (SEM), and (iv) proliferation ratio of cutaneous cells in vitro. Our results indicate that melatonin itself does not negatively affect biophysical properties of melatonin-immobilized hybrid scaffolds, but it induces a pronounced elevation of cell viability within human epidermal keratinocytes (NHEK), dermal fibroblasts (NHDF), and reference melanoma cells. These results demonstrate that this indoleamine accelerates re-epithelialization. This delivery is a promising technique for additional explorations in future dermatotherapy and protective skin medicine.

Differential and Overlapping Effects of Melatonin and Its Metabolites on Keratinocyte Function: Bioinformatics and Metabolic Analyses

We investigated the effects of melatonin and its selected metabolites, i.e., N¹-Acetyl-N²-formyl-5-methoxykynurenamine (AFMK) and 6-hydroxymelatonin (6(OH)Mel), on cultured human epidermal keratinocytes (HEKs) to assess their homeostatic activities with potential therapeutic implications. RNAseq analysis revealed a significant number of genes with distinct and overlapping patterns, resulting in common regulation of top diseases and disorders. Gene Set Enrichment Analysis (GSEA), Reactome FIViZ, and Ingenuity Pathway Analysis (IPA) showed overrepresentation of the p53-dependent G1 DNA damage response gene set, activation of p53 signaling, and NRF2-mediated antioxidative pathways. Additionally, GSEA exhibited an overrepresentation of circadian clock and antiaging signaling gene sets by melatonin derivatives and upregulation of extension of telomere signaling in HEKs, which was subsequently confirmed by increased telomerase activity in keratinocytes, indicating possible antiaging properties of metabolites of melatonin. Furthermore, Gene Ontology (GO) showed the activation of a keratinocyte differentiation program by melatonin, and GSEA indicated antitumor and antilipidemic potential of melatonin and its metabolites. IPA also indicated the role of Protein Kinase R (PKR) in interferon induction and antiviral response. In addition, the test compounds decreased lactate dehydrogenase A (LDHA) and lactate dehydrogenase C (LDHC) gene expression. These results were validated by qPCR and by Seahorse metabolic assay with significantly decreased glycolysis and lactate production under influence of AFMK or 6(OH)Mel in cells with a low oxygen consumption rate. In summary, melatonin and its metabolites affect keratinocytes’ functions via signaling pathways that overlap for each tested molecule with some distinctions.

Mitochondrial function is controlled by melatonin and its metabolites in vitro in human melanoma cells

Melanoma is a leading cause of cancer deaths worldwide. Although immunotherapy has revolutionized the treatment for some patients, resistance towards therapy and unwanted side effects remain a problem for numerous individuals. Broad anti-cancer activities of melatonin are recognized; however, additional investigations still need to be elucidated. Herein, using various human melanoma cell models, we explore in vitro the new insights into the regulation of melanoma by melatonin and its metabolites which possess, on the other side, high safety profiles and biological meaningful. In this study, using melanotic (MNT-1) and amelanotic (A375, G361, Sk-Mel-28) melanoma cell lines, the comparative oncostatic responses, the impact on melanin content (for melanotic MNT-1 melanoma cells) as well as the mitochondrial function controlled by melatonin, its precursor (serotonin), a kynuric (N¹ -acetyl-N² -formyl-5-methoxykynuramine, AFMK) and indolic pathway (6-hydroxymelatonin, 6(OH)MEL and 5-methoxytryptamine, 5-MT) metabolites were assessed. Namely, significant disturbances were observed in bioenergetics as follows: (i) uncoupling of oxidative phosphorylation (OXPHOS), (ii) attenuation of glycolysis, (iii) dissipation of mitochondrial transmembrane potential (mtΔΨ) accompanied by (iv) massive generation of reactive oxygen species (ROS), and (v) decrease of glucose uptake. Collectively, these results together with previously published reports provide a new biological potential and make an imperative to consider using melatonin or its metabolites for complementary future treatments of melanoma-affected patients; however, these associations should be additionally investigated in clinical setting.

The Potentials of Melatonin in the Prevention and Treatment of Bacterial Meningitis Disease

Bacterial meningitis (BM) is an acute infectious central nervous system (CNS) disease worldwide, occurring with 50% of the survivors left with a long-term serious sequela. Acute bacterial meningitis is more prevalent in resource-poor than resource-rich areas. The pathogenesis of BM involves complex mechanisms that are related to bacterial survival and multiplication in the bloodstream, increased permeability of blood-brain barrier (BBB), oxidative stress, and excessive inflammatory response in CNS. Considering drug-resistant bacteria increases the difficulty of meningitis treatment and the vaccine also has been limited to several serotypes, and the morbidity rate of BM still is very high. With recent development in neurology, there is promising progress for drug supplements of effectively preventing and treating BM. Several in vivo and in vitro studies have elaborated on understanding the significant mechanism of melatonin on BM. Melatonin is mainly secreted in the pineal gland and can cross the BBB. Melatonin and its metabolite have been reported as effective antioxidants and anti-inflammation, which are potentially useful as prevention and treatment therapy of BM. In bacterial meningitis, melatonin can play multiple protection effects in BM through various mechanisms, including immune response, antibacterial ability, the protection of BBB integrity, free radical scavenging, anti-inflammation, signaling pathways, and gut microbiome. This manuscript summarizes the major neuroprotective mechanisms of melatonin and explores the potential prevention and treatment approaches aimed at reducing morbidity and alleviating nerve injury of BM.