Melatonin is an ubiquitous molecule with a variety of functions including potent antioxidative properties. Due to its lipophilic character, it easily crosses cellular and intracellular membranes and ...reaches all subcellular organelles. Because of its ability to scavenge free radicals, melatonin protects against oxidative stress, for example, induced by ultraviolet radiation (UVR). Here, we investigated, in a dose‐dependent (0, 10, 25, and 50 mJ/cm2) and time‐dependent (0, 4, 24, 48 hr post‐UVR) manner, whether melatonin prevents the UVR‐mediated alterations in ATP synthesis and the generation of reactive oxygen species (ROS) in normal human epidermal keratinocytes (NHEK). Additionally, we evaluated the molecular mechanism of action of melatonin with regard to activation of phase‐2 antioxidative enzymes via nuclear erythroid 2‐related factor (Nrf2). We found that (i) melatonin counteracted UVR‐induced alterations in the ATP synthesis and reduced free radical formation; (ii) melatonin induced the translocation of Nrf2 transcription factor from the cytosol into the nucleus resulting in, (iii) melatonin enhanced gene expression of phase‐2 antioxidative enzymes including γ‐glutamylcysteine synthetase (γ‐GCS), heme oxygenase‐1 (HO‐1), and NADPH: quinone dehydrogenase‐1 (NQO1) representing an elevated antioxidative response of keratinocytes. These results suggest that melatonin not only directly scavenges ROS, but also significantly induces the activation of phase‐2 antioxidative enzymes via the Nrf2 pathway uncovering a new action mechanism that supports the ability of keratinocytes to protect themselves from UVR‐mediated oxidative stress.
The recent pandemic of COVID-19 has already infected millions of individuals and has resulted in the death of hundreds of thousands worldwide. Based on clinical features, pathology, and the ...pathogenesis of respiratory disorders induced by this and other highly homogenous coronaviruses, the evidence suggests that excessive inflammation, oxidation, and an exaggerated immune response contribute to COVID-19 pathology; these are caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This leads to a cytokine storm and subsequent progression triggering acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), and often death. We and others have reported melatonin to be an anti-inflammatory and anti-oxidative molecule with a high safety profile. It is effective in critical care patients by reducing their vascular permeability and anxiety, inducing sedation, and improving their quality of sleep. As melatonin shows no harmful adverse effects in humans, it is imperative to introduce this indoleamine into clinical trials where it might be beneficial for better clinical outcomes as an adjuvant treatment of COVID-19-infected patients. Herein, we strongly encourage health care professionals to test the potential of melatonin for targeting the COVID-19 pandemic. This is urgent, since there is no reliable treatment for this devastating disease.
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.
UV radiation (UVR) induces serious structural and functional alterations in human skin leading to skin aging and carcinogenesis. Reactive oxygen species are key players in UVR‐mediated photodamage ...and induce the DNA‐base‐oxidized, intermediate 8‐hydroxy‐2'‐deoxyguanosine (8‐OHdG). Herein, we report the protective action of melatonin against UVR‐induced 8‐OHdG formation and depletion of antioxidative enzymes using ex vivo human full‐thickness skin exposed to UVR in a dose (0, 100, 300 mJ/cm2)‐ and time‐dependent manner (0, 24, 48 hr post‐UVR). Dynamics of depletion of antioxidative enzymes including catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), or 8‐OHdG formation were studied by real‐time PCR and immunofluorescence/immunohistochemical staining. UVR‐treated skin revealed significant and immediate (0 hr 300 mJ/cm2) reduction of gene expression, and this effect intensified within 24 hr post‐UVR. Simultaneous increase in 8‐OHdG‐positive keratinocytes occurred already after 0 hr post‐UVR reaching 71% and 99% up‐regulation at 100 and 300 mJ/cm2, respectively (P < 0.001). Preincubation with melatonin (10−3 m) led to 32% and 29% significant reductions in 8‐OHdG‐positive cells and the prevention of antioxidative enzyme gene and protein suppression. Thus, melatonin was shown to play a crucial role as a potent antioxidant and DNA protectant against UVR‐induced oxidative damage in human skin.
Indolic and kynuric pathways of skin melatonin metabolism were monitored by liquid chromatography mass spectrometry in human keratinocytes, melanocytes, dermal fibroblasts, and melanoma cells. ...Production of 6‐hydroxymelatonin 6(OH)M, N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine (AFMK) and 5‐methoxy‐tryptamine (5‐MT) was detected in a cell type‐dependent fashion. The major metabolites, 6(OH)M and AFMK, were produced in all cells. Thus, in immortalized epidermal (HaCaT) keratinocytes, 6(OH)M was the major product with Vmax = 63.7 ng/106 cells and Km = 10.2 μM, with lower production of AFMK and 5‐MT. Melanocytes, keratinocytes, and fibroblasts transformed melatonin primarily into 6(OH)M and AFMK. In melanoma cells, 6(OH)M and AFMK were produced endogenously, a process accelerated by exogenous melatonin in the case of AFMK. In addition, N‐acetylserotonin was endogenously produced by normal and malignant melanocytes. Metabolites showed selective antiproliferative effects on human primary epidermal keratinocytes in vitro. In ex vivo human skin, both melatonin and AFMK‐stimulated expression of involucrin and keratins‐10 and keratins‐14 in the epidermis, indicating their stimulatory role in building and maintaining the epidermal barrier. In summary, the metabolism of melatonin and its endogenous production is cell type‐dependent and expressed in all three main cell populations of human skin. Furthermore, melatonin and its metabolite AFMK stimulate differentiation in human epidermis, indicating their key role in building the skin barrier.—Kim, T.‐K., Kleszczyński, K., Janjetovic, Z., Sweatman, T., Lin, Z., Li, W., Reiter, R. J., Fischer, T. W., Slominski, A. T. Metabolism of melatonin and biological activity of intermediates of melatoninergic pathway in human skin cells. FASEB J. 27, 2742‐2755 (2013). www.fasebj.org
Despite groundbreaking new treatments such as checkpoint inhibition and targeted therapy, the overall response and survival rates are limited in patients with metastatic melanoma. Here, we ...hypothesize that melatonin and its metabolites could be promising boosters of the efficacy of BRAF/MEK inhibitors in patients with advanced melanoma. Melatonin, a well‐known endogenous synchronizer of the circadian biorhythm has a variety of promising effects for melanoma biology. It regulates proliferation, apoptosis and oxidative phosphorylation via melatonin receptors, and receptor‐independent pathways due to its lipophilicity. By means of interfering with the above cellular pathways, melatonin and related compounds may alter the cAMP‐PKA‐MITF axis, modulate tumor cell metabolism, affect MAPK signalling pathway thereby enhancing the suppressive effect of BRAF/MEK inhibitors on melanoma cell growth, and survival. Such findings could fuel preclinical studies and clinical studies where melatonin or its metabolites are combined with targeted therapy to better treat patients with metastatic melanoma.
Antimicrobial peptides (AMPs) are important components of the innate immune system and are involved in skin protection against environmental insults and in wound healing. Herein, we assessed the gene ...expression of chemerin (Rarres2), cathelicidin CRAMP (Camp), and three β‐defensins (Defb1, Defb3, and Defb14) in mouse skin during light/dark cycle (LD 12:12) and constant darkness (DD). Next, we examined the survival of bacteria applied on the skin at specific times during the day. We found that the expression of Rarres2, Camp, and Defb1 was the highest at 4 h after the beginning of darkness, during high activity of mice. These rhythms, however, were not maintained under DD in the skin but were present in the liver. This indicated that in the case of skin, a circadian input was masked by daily changes of light in the environment. In contrast, Defb3 and Defb14 showed the highest mRNA levels when the mice slept, and these rhythmic mRNA oscillations were maintained under DD. This shows that Rarres2, Camp, and Defb1 levels in the skin are correlated with high locomotor activity in mice and they are controlled by daily changes of light and dark. Alternatively, oscillations in the mRNA levels of Defb3 and Defb14 seem to protect skin and heal wounds during sleep. These rhythms are maintained under DD, indicating that they are regulated by a circadian clock. Our study suggests that daily AMP expression affects the survival of bacteria on the surface of skin, which depends on the phase of AMP cycling.
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 EC
's between 10
and 10
M. This was further validated via the stimulation of the transcriptional activation of the
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
-acetyl-
-formyl-5-methoxykynuramine with EC
's in the 10
M range showing significantly lower affinities that those of rosiglitazone, e.g., a 10
M range. These interactions were substantiated by stimulation of the luciferase activity of the construct containing PPARE by melatonin and its metabolites at 10
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
-acetyl-
-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.
Extracellular vesicles (EVs) serve as central mediators in communication between tumor and non-tumor cells. These interactions are largely dependent on the function of the endothelial barrier and the ...set of receptors present on its surface, as endothelial cells (ECs) are a plenteous source of EVs. The molecular basis for EV secretion and action in the tumor microenvironment (TME) has not been fully elucidated to date. Emerging evidence suggests a prominent role of inflammatory pathways in promoting tumor progression and metastasis. Although transforming growth factor β (TGF-β) is a cytokine with strong immunomodulatory and protective activity in benign and early-stage cancer cells, it plays a pro-tumorigenic role in advanced cancer cells, which is known as the "TGF-β paradox". Thus, the aim of this review is to describe the correlation between EV release, TGF-β-dependent inflammation, and dysregulation of downstream TGF-β signaling in the context of cancer development.
Melatonin (Mel) is the major biologically active molecule secreted by the pineal gland. Mel and its metabolites, 6-hydroxymelatonin (6(OH)Mel) and 5-methoxytryptamine (5-MT), possess a variety of ...functions, including the scavenging of free radicals and the induction of protective or reparative mechanisms in the cell. Their amphiphilic character allows them to cross cellular membranes and reach subcellular organelles, including the mitochondria. Herein, the action of Mel, 6(OH)Mel, and 5-MT in human MNT-1 melanoma cells against ultraviolet B (UVB) radiation was investigated. The dose of 50 mJ/cm² caused a significant reduction of cell viability up to 48%, while investigated compounds counteracted this deleterious effect. UVB exposure increased catalase activity and led to a simultaneous Ca
influx (16%), while tested compounds prevented these disturbances. Additional analysis focused on mitochondrial respiration performed in isolated mitochondria from the liver of BALB/cJ mice where Mel, 6(OH)Mel, and 5-MT significantly enhanced the oxidative phosphorylation at the dose of 10
M with lower effects seen at 10
or 10
M. In conclusion, Mel, 6(OH)Mel and 5-MT protect MNT-1 cells, which express melatonin receptors (MT1 and MT2) against UVB-induced oxidative stress and mitochondrial dysfunction, including the uncoupling of oxidative phosphorylation.
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