Showing papers in "Journal of Pineal Research in 2014"
TL;DR: Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro‐oxidant.
Abstract: Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.
624 citations
TL;DR: The available evidence supports the suggestion that melatonin replacement therapy might contribute to restore a more healthy state of the organism.
Abstract: Melatonin is an old and ubiquitous molecule in nature showing multiple mechanisms of action and functions in practically every living organism. In mammals, pineal melatonin functions as a hormone and a chronobiotic, playing a major role in the regulation of the circadian temporal internal order. The anti-obesogen and the weight-reducing effects of melatonin depend on several mechanisms and actions. Experimental evidence demonstrates that melatonin is necessary for the proper synthesis, secretion, and action of insulin. Melatonin acts by regulating GLUT4 expression and/or triggering, via its G-protein-coupled membrane receptors, the phosphorylation of the insulin receptor and its intracellular substrates mobilizing the insulin-signaling pathway. Melatonin is a powerful chronobiotic being responsible, in part, by the daily distribution of metabolic processes so that the activity/feeding phase of the day is associated with high insulin sensitivity, and the rest/fasting is synchronized to the insulin-resistant metabolic phase of the day. Furthermore, melatonin is responsible for the establishment of an adequate energy balance mainly by regulating energy flow to and from the stores and directly regulating the energy expenditure through the activation of brown adipose tissue and participating in the browning process of white adipose tissue. The reduction in melatonin production, as during aging, shift-work or illuminated environments during the night, induces insulin resistance, glucose intolerance, sleep disturbance, and metabolic circadian disorganization characterizing a state of chronodisruption leading to obesity. The available evidence supports the suggestion that melatonin replacement therapy might contribute to restore a more healthy state of the organism.
446 citations
TL;DR: New evidence is provided suggesting that melatonin alleviates the inhibitory effects of NaCl stress on germination mainly by regulating the biosynthesis and catabolism of ABA and GA4.
Abstract: Although previous studies have found that melatonin can promote seed germination, the mechanisms involved in perceiving and signaling melatonin remain poorly understood. In this study, it was found that melatonin was synthesized during cucumber seed germination with a peak in melatonin levels occurring 14 hr into germination. This is indicative of a correlation between melatonin synthesis and seed germination. Meanwhile, seeds pretreated with exogenous melatonin (1 μM) showed enhanced germination rates under 150 mM NaCl stress compared to water-pretreated seeds under salinity stress. There are two apparent mechanisms by which melatonin alleviated salinity-induced inhibition of seed germination. Exogenous melatonin decreased oxidative damage induced by NaCl stress by enhancing gene expression of antioxidants. Under NaCl stress, compared to untreated control, the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly increased by approximately 1.3-5.0-fold, with a concomitant 1.4-2.0-fold increase of CsCu-ZnSOD, CsFe-ZnSOD, CsCAT, and CsPOD in melatonin-pretreated seeds. Melatonin also alleviated salinity stress by affecting abscisic acid (ABA) and gibberellin acid (GA) biosynthesis and catabolism during seed germination. Compared to NaCl treatment, melatonin significantly up-regulated ABA catabolism genes (e.g., CsCYP707A1 and CsCYP707A2, 3.5 and 105-fold higher than NaCl treatment at 16 hr, respectively) and down-regulated ABA biosynthesis genes (e.g., CsNECD2, 0.29-fold of CK2 at 16 hr), resulting in a rapid decrease of ABA content during the early stage of germination. At the same time, melatonin positively up-regulated GA biosynthesis genes (e.g., GA20ox and GA3ox, 2.3 and 3.9-fold higher than NaCl treatment at 0 and 12 hr, respectively), contributing to a significant increase of GA (especially GA4) content. In this study, we provide new evidence suggesting that melatonin alleviates the inhibitory effects of NaCl stress on germination mainly by regulating the biosynthesis and catabolism of ABA and GA4.
408 citations
TL;DR: The present work reviews the current information related to the beneficial effects of melatonin in maintaining the fluidity of biological membranes against free radical attack, and discusses its implications for ageing and disease.
Abstract: Free radicals generated within subcellular compartments damage macromolecules which lead to severe structural changes and functional alterations of cellular organelles. A manifestation of free radical injury to biological membranes is the process of lipid peroxidation, an autooxidative chain reaction in which polyunsaturated fatty acids in the membrane are the substrate. There is considerable evidence that damage to polyunsaturated fatty acids tends to reduce membrane fluidity. However, adequate levels of fluidity are essential for the proper functioning of biological membranes. Thus, there is considerable interest in antioxidant molecules which are able to stabilize membranes because of their protective effects against lipid peroxidation. Melatonin is an indoleamine that modulates a wide variety of endocrine, neural and immune functions. Over the last two decades, intensive research has proven this molecule, as well as its metabolites, to possess substantial antioxidant activity. In addition to their ability to scavenge several reactive oxygen and nitrogen species, melatonin increases the activity of the glutathione redox enzymes, that is, glutathione peroxidase and reductase, as well as other antioxidant enzymes. These beneficial effects of melatonin are more significant because of its small molecular size and its amphipathic behaviour, which facilitates ease of melatonin penetration into every subcellular compartment. In the present work, we review the current information related to the beneficial effects of melatonin in maintaining the fluidity of biological membranes against free radical attack, and further, we discuss its implications for ageing and disease.
368 citations
TL;DR: The up‐regulation of cold signaling genes by melatonin may stimulate the biosynthesis of cold‐protecting compounds and contribute to the increased growth of plants treated with exogenous melatonin under cold stress.
Abstract: Melatonin (N-acetyl-5-methoxytryptamine) has been implicated in abiotic and biotic stress tolerance in plants. However, information on the effects of melatonin in cold-stress tolerance in vivo is limited. In this study, the effect of melatonin was investigated in the model plant Arabidopsis thaliana challenged with a cold stress at 4⁰C for 72 and 120 hr. Melatonin-treated plants (10 and 30 μm) had significantly higher fresh weight, primary root length, and shoot height compared with the nontreated plants. To aid in the understanding of the role of melatonin in alleviating cold stress, we investigated the effects of melatonin treatment on the expression of cold-related genes. Melatonin up-regulated the expression of C-repeat-binding factors (CBFs)/Drought Response Element Binding factors (DREBs), a cold-responsive gene, COR15a, a transcription factor involved in freezing and drought-stress tolerance CAMTA1 and transcription activators of reactive oxygen species (ROS)-related antioxidant genes, ZAT10 and ZAT12, following cold stress. The up-regulation of cold signaling genes by melatonin may stimulate the biosynthesis of cold-protecting compounds and contribute to the increased growth of plants treated with exogenous melatonin under cold stress.
305 citations
TL;DR: RNA sequencing was employed to explore the mechanism of melatonin‐induced lateral root formation in cucumber under salt stress and will enable the scientific community to better define the molecular processes that affect lateralRoot formation in response to melatonin treatment.
Abstract: Cucumber is a model cucurbitaceous plant with a known genome sequence which is important for studying molecular mechanisms of root development. In this study, RNA sequencing was employed to explore the mechanism of melatonin-induced lateral root formation in cucumber under salt stress. Three groups of seeds were examined, that is, seeds primed without melatonin (CK), seeds primed in a solution containing 10 or 500 μmol/L melatonin (M10 and M500, respectively). These seeds were then germinated in NaCl solution. The RNA-seq analysis generated 16,866,670 sequence reads aligned with 17,920 genes, which provided abundant data for the analysis of lateral root formation. A total of 17,552, 17,450, and 17,393 genes were identified from roots of the three treatments (CK, M10 and M500, respectively). The expression of 121 genes was significantly up-regulated, and 196 genes were significantly down-regulated in M500 which showed an obvious increase on the number of lateral roots. These genes were significantly enriched in 57 KEGG pathways and 16 GO terms (M500 versus CK). Based on their expression pattern, peroxidase-related genes were selected as the candidates to be involved in the melatonin response. Several transcription factor families might play important roles in lateral root formation processes. A number of genes related to cell wall formation, carbohydrate metabolic processes, oxidation/reduction processes, and catalytic activity also showed different expression patterns as a result of melatonin treatments. This RNA-sequencing study will enable the scientific community to better define the molecular processes that affect lateral root formation in response to melatonin treatment.
237 citations
TL;DR: It is concluded that the application of melatonin to wine grapes is effective in reducing drought stress.
Abstract: Grapes are an important economic crop and are widely cultivated around the world. Most grapes are grown in arid or semi-arid regions, and droughts take a heavy toll in grape and wine production areas. Developing effective drought-resistant cultivation measures is a priority for viticulture. Melatonin, an indoleamine, mediates many physiological processes in plants. Herein, we examined whether exogenously applied melatonin could improve the resistance of wine grape seedlings grown from cuttings to polyethylene glycol-induced water-deficient stress. The application of 10% polyethylene glycol (PEG) markedly inhibited the growth of cuttings, caused oxidative stress and damage from H2 O2 and O2∙-, and reduced the potential efficiency of Photosystem II and the amount of chlorophyll. Application of melatonin partially alleviated the oxidative injury to cuttings, slowed the decline in the potential efficiency of Photosystem II, and limited the effects on leaf thickness, spongy tissue, and stoma size after application of PEG. Melatonin treatment also helped preserve the internal lamellar system of chloroplasts and alleviated the ultrastructural damage induced by drought stress. This ameliorating effect may be ascribed to the enhanced activity of antioxidant enzymes, increased levels of nonenzymatic antioxidants, and increased amount of osmoprotectants (free proline). We conclude that the application of melatonin to wine grapes is effective in reducing drought stress.
230 citations
TL;DR: The results elucidated the important role that membrane‐located melatonin synthase plays in drought tolerance and have significant implications in agriculture.
Abstract: Melatonin is a potent naturally occurring reactive oxygen species (ROS) and reactive nitrogen species (RNS) scavenger in plants. Melatonin protects plants from oxidative stress and, therefore, it improves their tolerance against a variety of environmental abiotic stressors. N-acetylserotonin-O-methyltransferase (ASMT) is a specific enzyme required for melatonin synthesis. In this report, an ASMT gene was cloned from apple rootstock (Malus zumi Mats) and designated as MzASMT1 (KJ123721). The MzASMT1 expression was induced by drought stress in apple leaves. The upregulation of MzASMT1 in the apple leaf positively relates to melatonin production over a 24-hr dark/light cycle. Purified MzASMT1 protein expressed in E. coli converted its substrates to melatonin with an activity of approximately 5.5 pmol/min/mg protein. The transient transformation in tobacco identified that MzASMT1 is located in cytoplasm of the cell. When MzASMT1 gene driven by 35S promoter was transferred to Arabidopsis, melatonin levels in transgenic Arabidopsis plants were 2-4 times higher than those in the wild type. The transgenic Arabidopsis plants had significantly lower intrinsic ROS than the wild type and therefore these plants exhibited greater tolerance to drought stress than that of wild type. This is, at least partially, attributed to the elevated melatonin levels resulting from the overexpression of MzASMT1. The results elucidated the important role that membrane-located melatonin synthase plays in drought tolerance. These findings have significant implications in agriculture.
191 citations
TL;DR: Melatonin may be a novel defense signaling molecule in plant–pathogen interactions, and N‐acetylserotonin also plays a role in inducing a series of defense genes, although serotonin does not.
Abstract: Melatonin plays pleiotropic roles in both animals and plants. The possible role of melatonin in plant innate immune responses was recently discovered. As an initial study, we employed Arabidopsis to determine whether melatonin is involved in defense against the virulent bacterial pathogen Pseudomonas syringae DC3000. The application of a 10 μM concentration of melatonin on Arabidopsis and tobacco leaves induced various pathogenesis-related (PR) genes, as well as a series of defense genes activated by salicylic acid (SA) and ethylene (ET), two key factors involved in plant defense response, compared to mock-treated leaves. The induction of these defense-related genes in melatonin-treated Arabidopsis matched an increase in resistance against the bacterium by suppressing its multiplication about ten-fold relative to the mock-treated Arabidopsis. Like melatonin, N-acetylserotonin also plays a role in inducing a series of defense genes, although serotonin does not. Furthermore, melatonin-induced PR genes were almost completely or partially suppressed in the npr1, ein2, and mpk6 Arabidopsis mutants, indicative of SA and ET dependency in melatonin-induced plant defense signaling. This suggests that melatonin may be a novel defense signaling molecule in plant-pathogen interactions.
188 citations
TL;DR: It is demonstrated that melatonin treatment attenuates MI/R injury by reducing oxidative stress damage via activation of SIRT1 signaling in a receptor‐dependent manner.
Abstract: Melatonin confers cardioprotective effect against myocardial ischemia/reperfusion (MI/R) injury by reducing oxidative stress. Activation of silent information regulator 1 (SIRT1) signaling also reduces MI/R injury. We hypothesize that melatonin may protect against MI/R injury by activating SIRT1 signaling. This study investigated the protective effect of melatonin treatment on MI/R heart and elucidated its potential mechanisms. Rats were exposed to melatonin treatment in the presence or the absence of the melatonin receptor antagonist luzindole or SIRT1 inhibitor EX527 and then subjected to MI/R operation. Melatonin conferred a cardioprotective effect by improving postischemic cardiac function, decreasing infarct size, reducing apoptotic index, diminishing serum creatine kinase and lactate dehydrogenase release, upregulating SIRT1, Bcl-2 expression and downregulating Bax, caspase-3 and cleaved caspase-3 expression. Melatonin treatment also resulted in reduced myocardium superoxide generation, gp91(phox) expression, malondialdehyde level, and increased myocardium superoxide dismutase (SOD) level, which indicate that the MI/R-induced oxidative stress was significantly attenuated. However, these protective effects were blocked by EX527 or luzindole, indicating that SIRT1 signaling and melatonin receptor may be specifically involved in these effects. In summary, our results demonstrate that melatonin treatment attenuates MI/R injury by reducing oxidative stress damage via activation of SIRT1 signaling in a receptor-dependent manner.
176 citations
TL;DR: Melatonin's role in bone physiology is described and how disruption of melatonin rhythms by light exposure at night, shift work, and disease can adversely impact on bone is discussed.
Abstract: An important role for melatonin in bone formation and restructuring has emerged, and studies demonstrate the multiple mechanisms for these beneficial actions. Statistical analysis shows that even with existing osteoporotic therapies, bone-related disease, and mortality are on the rise, creating a huge financial burden for societies worldwide. These findings suggest that novel alternatives need to be developed to either prevent or reverse bone loss to combat osteoporosis-related fractures. The focus of this review describes melatonin's role in bone physiology and discusses how disruption of melatonin rhythms by light exposure at night, shift work, and disease can adversely impact on bone. The signal transduction mechanisms underlying osteoblast and osteoclast differentiation and coupling with one another are discussed with a focus on how melatonin, through the regulation of RANKL and osteoprotegerin synthesis and release from osteoblasts, can induce osteoblastogenesis while inhibiting osteoclastogenesis. Also, melatonin's free-radical scavenging and antioxidant properties of this indoleamine are discussed as yet an additional mechanism by which melatonin can maintain one's bone health, especially oral health. The clinical use for melatonin in bone-grafting procedures, in reversing bone loss due to osteopenia and osteoporosis, and in managing periodontal disease is discussed.
TL;DR: The endogenous melatonin levels were significantly induced by cold stress (4°C) treatment and one cysteine2/histidine2‐type zinc finger transcription factor, ZAT6, was involved in melatonin‐mediated freezing stress response in Arabidopsis.
Abstract: Melatonin (N-acetyl-5-methoxytryptamine) is not only a widely known animal hormone, but also an important regulator in plant development and multiple abiotic stress responses. Recently, it has been revealed that melatonin alleviated cold stress through mediating several cold-related genes, including C-REPEAT-BINDING FACTORs (CBFs)/Drought Response Element Binding factors (DREBs), COR15a, and three transcription factors (CAMTA1, ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10), and ZAT12). In this study, we quantified the endogenous melatonin level in Arabidopsis plant leaves and found the endogenous melatonin levels were significantly induced by cold stress (4 °C) treatment. In addition, we found one cysteine2/histidine2-type zinc finger transcription factor, ZAT6, was involved in melatonin-mediated freezing stress response in Arabidopsis. Interestingly, exogenous melatonin enhanced freezing stress resistance was largely alleviated in AtZAT6 knockdown plants, but was enhanced in AtZAT6 overexpressing plants. Moreover, the expression levels of AtZAT6 and AtCBFs were commonly upregulated by cold stress (4 °C) and exogenous melatonin treatments, and modulation of AtZAT6 expression significantly affected the induction AtCBFs transcripts by cold stress (4 °C) and exogenous melatonin treatments. Taken together, AtZAT6-activated CBF pathway might be essential for melatonin-mediated freezing stress response in Arabidopsis.
TL;DR: Melatonin improved the neurological outcome in rats by protecting against neural apoptosis after the induction of filament perforation SAH; moreover, the mechanism of these antiapoptosis effects was related to the enhancement of autophagy, which ameliorated cell apoptosis via a mitochondrial pathway.
Abstract: Melatonin is a strong antioxidant that has beneficial effects against early brain injury (EBI) following a subarachnoid hemorrhage (SAH) in rats; protection includes reduced mortality and brain water content. The molecular mechanisms underlying these clinical effects in the SAH model, however, have not been clearly identified. This study was undertaken to determine the influence of melatonin on neural apoptosis and the potential mechanism of these effects in EBI following SAH using the filament perforation model of SAH in male Sprague Dawley rats. Melatonin (150 mg/kg) or vehicle was given via an intraperitoneal injection 2 hr after SAH induction. Brain samples were extracted 24 hr after SAH. The results show that melatonin treatment markedly reduced caspase-3 activity and the number of TUNEL-positive cells, while the treatment increased the LC3-II/LC3-I, an autophagy marker, which indicated that melatonin-enhanced autophagy ameliorated apoptotic cell death in rats subjected to SAH. To further identify the mechanism of autophagy protection, we demonstrated that melatonin administration reduced Bax translocation to the mitochondria and the release of cytochrome c into the cytosol. Taken together, this report demonstrates that melatonin improved the neurological outcome in rats by protecting against neural apoptosis after the induction of filament perforation SAH; moreover, the mechanism of these antiapoptosis effects was related to the enhancement of autophagy, which ameliorated cell apoptosis via a mitochondrial pathway.
TL;DR: The significantly higher melatonin content in oHIOMT lines than oAANAT lines provides new proof for the important role of ASMT in plant melatonin synthesis, and the enhanced drought tolerance of oHIomT lines will also be an important contribution for plant engineering.
Abstract: In animals, the melatonin biosynthesis pathway has been well defined after the isolation and identification of the four key genes that are involved in the conversion of tryptophan to melatonin. In plants, there are special alternative catalyzing steps, and plant genes share very low homology with the animal genes. It was of interest to examine the phenotype of transgenic Micro-Tom tomato plants overexpressing the homologous sheep oAANAT and oHIOMT genes responsible for the last two steps of melatonin synthesis. The oAANAT transgenic plants have higher melatonin levels and lower indoleacetic acid (IAA) contents than control due to the competition for tryptophan, the same precursor for both melatonin and IAA. Therefore, the oAANAT lines lose the 'apical dominance' inferring that melatonin likely lacks auxin activity. The significantly higher melatonin content in oHIOMT lines than oAANAT lines provides new proof for the important role of ASMT in plant melatonin synthesis. In addition, the enhanced drought tolerance of oHIOMT lines will also be an important contribution for plant engineering.
TL;DR: The information summarized in this review should serve as a comprehensive reference for the action of melatonin in cardioprotection and hopefully will contribute to the design of future experimental research.
Abstract: Cardiac tissue loss is one of the most important factors leading to the unsatisfactory recovery even after treatment of ischemic heart disease. Melatonin, a circadian molecule with marked antioxidant properties, protects against ischemia-reperfusion (IR) injury. In particular, the myocardial protection of melatonin is substantial. We initially focus on the cardioprotective effects of melatonin in myocardial IR. These studies showed how melatonin preserves the microstructure of the cardiomyocyte and reduces myocardial IR injury. Thereafter, downstream signaling pathways of melatonin were summarized including Janus kinase 2/signal transducers and activators of transcription 3, nitric oxide-synthase, and nuclear factor erythroid 2 related factor 2. Herein, we propose the clinical applications of melatonin in several ischemic heart diseases. Collectively, the information summarized in this review (based on in vitro, animal, and human studies) should serve as a comprehensive reference for the action of melatonin in cardioprotection and hopefully will contribute to the design of future experimental research.
TL;DR: Melatonin emerges a novel and potential modulator of MSC lineage commitment and adipogenic differentiation and other aspects of the physiological and pharmacological effects of melatonin as regulator of M SC are discussed in this review.
Abstract: Among the numerous functions of melatonin, the control of survival and differentiation of mesenchymal stem cells (MSCs) has been recently proposed. MSCs are a heterogeneous population of multipotent elements resident in tissues such as bone marrow, muscle, and adipose tissue, which are primarily involved in developmental and regeneration processes, gaining thus increasing interest for tissue repair and restoration therapeutic protocols. Receptor-dependent and receptor-independent responses to melatonin are suggested to occur in these cells. These involve antioxidant or redox-dependent functions of this indolamine as well as secondary effects resulting from autocrine and paracrine responses. Inflammatory cytokines and adipokines, proangiogenic/mitogenic stimuli, and other mediators that influence the differentiation processes may affect the survival and functional integrity of these mesenchymal precursor cells. In this scenario, melatonin seems to regulate signaling pathways that drive commitment and differentiation of MSC into osteogenic, chondrogenic, adipogenic, or myogenic lineages. Common pathways suggested to be involved as master regulators of these processes are the Wnt/β-catenin pathway, the MAPKs and the, TGF-β signaling. In this respect melatonin emerges a novel and potential modulator of MSC lineage commitment and adipogenic differentiation. These and other aspects of the physiological and pharmacological effects of melatonin as regulator of MSC are discussed in this review.
TL;DR: Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms, which may contribute in reducing metal‐induced toxicity as postulate here.
Abstract: Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.
TL;DR: Both melatonin and 6‐hydroxymelatonin had beneficial effects on sepsis‐induced mitochondrial dysfunction, oxidative stress, and cytokine responses at concentrations similar to those achieved in vivo.
Abstract: Sepsis is a massive inflammatory response mediated by infection, characterized by oxidative stress, release of cytokines, and mitochondrial dysfunction. Melatonin accumulates in mitochondria, and both it and its metabolites have potent antioxidant and anti-inflammatory activities and may be useful in sepsis. We undertook a phase I dose escalation study in healthy volunteers to assess the tolerability and pharmacokinetics of 20, 30, 50, and 100 mg oral doses of melatonin. In addition, we developed an ex vivo whole blood model under conditions mimicking sepsis to determine the bioactivity of melatonin and the major metabolite 6-hydroxymelatonin at relevant concentrations. For the phase I trial, oral melatonin was given to five subjects in each dose cohort (n = 20). Blood and urine were collected for measurement of melatonin and 6-hydroxymelatonin, and symptoms and physiological measures were assessed. Validated sleep scales were completed. No adverse effects after oral melatonin, other than mild transient drowsiness with no effects on sleeping patterns, were seen, and no symptoms were reported. Melatonin was rapidly cleared at all doses with a median [range] elimination half-life of 51.7 [29.5–63.2] min across all doses. There was considerable variability in maximum melatonin levels within each dose cohort, but 6-hydoxymelatonin sulfate levels were less variable and remained stable for several hours. For the ex vivo study, blood from 20 volunteers was treated with lipopolysaccharide and peptidoglycan plus a range of concentrations of melatonin/6-hydroxymelatonin. Both melatonin and 6-hydroxymelatonin had beneficial effects on sepsis-induced mitochondrial dysfunction, oxidative stress, and cytokine responses at concentrations similar to those achieved in vivo.
TL;DR: Maternal antenatal melatonin administration ameliorated oxidative stress, normalized myelination and rescued axonopathy within IUGR lamb brains, and IUBR + MLT lambs demonstrated significant functional improvements including a reduced time taken to attach to and suckle at the udder after birth.
Abstract: Fetal intrauterine growth restriction (IUGR) is a serious pregnancy complication associated with increased rates of perinatal morbidity and mortality, and ultimately with long-term neurodevelopmental impairments. No intervention currently exists that can improve the structure and function of the IUGR brain before birth. Here, we investigated whether maternal antenatal melatonin administration reduced brain injury in ovine IUGR. IUGR was induced in pregnant sheep at 0.7 gestation and a subset of ewes received melatonin via intravenous infusion until term. IUGR, IUGR + melatonin (IUGR + MLT) and control lambs were born naturally, neonatal behavioral assessment was used to examine neurological function and at 24 hr after birth the brain was collected for the examination of neuropathology. Compared to control lambs, IUGR lambs took significantly longer to achieve normal neonatal lamb behaviors, such as standing and suckling. IUGR brains showed widespread cellular and axonal lipid peroxidation, and white matter hypomyelination and axonal damage. Maternal melatonin administration ameliorated oxidative stress, normalized myelination and rescued axonopathy within IUGR lamb brains, and IUGR + MLT lambs demonstrated significant functional improvements including a reduced time taken to attach to and suckle at the udder after birth. Based on these observations, we began a pilot clinical trial of oral melatonin administration to women with an IUGR fetus. Maternal melatonin was not associated with adverse maternal or fetal effects and it significantly reduced oxidative stress, as evidenced by reduced malondialdehyde levels, in the IUGR + MLT placenta compared to IUGR alone. Melatonin should be considered for antenatal neuroprotective therapy in human IUGR.
TL;DR: It is demonstrated that melatonin levels increased as temperature increased when rice seedlings were exposed to various temperatures for 1 hr, and the relativeMelatonin levels were higher in the dark than under light conditions.
Abstract: Temperature and light are important environmental factors for plant growth and development. The final two enzymes in the melatonin synthesis pathway in plants are serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), which have thermophilic characteristics. Thus, the effects of temperature and light on melatonin synthesis in rice seedlings were investigated. Here, we demonstrated that melatonin levels increased as temperature increased when rice seedlings were exposed to various temperatures for 1 hr. Moreover, the relative melatonin levels were higher in the dark. For example, exposure of rice seedlings to 1-hr darkness at 55°C resulted in a melatonin yield of 4.9 ng/g fresh weight (fw), compared with 2.95 ng/g fw under light conditions. Temperature-dependent melatonin synthesis was closely associated with an increase in both SNAT and ASMT activities, but not with transcript levels of melatonin biosynthetic genes. The daily melatonin levels in field-grown rice plants were unaffected as the positive effect of the relatively high temperature during the day was counteracted by the negative effect of the high light. The opposite effect occurred during the night, in which the positive effect of darkness on melatonin synthesis was counteracted by the negative effect of a low temperature.
TL;DR: It is demonstrated that an alteration of endogenous melatonin levels leads to pleiotropic effects such as height, biomass, panicle number, flowering time, and grain yield, indicating that melatonin behaves as a signaling molecule in plant growth and reproduction.
Abstract: No previous reports have described the effects of an increase in endogenous melatonin levels on plant yield and reproduction. Here, the phenotypes of melatonin-rich transgenic rice plants overexpressing sheep serotonin N-acetyltransferase were investigated under field conditions. Early seedling growth of melatonin-rich transgenic rice was greatly accelerated, with enhanced biomass relative to the wild type (WT). However, flowering was delayed by 1 wk in the transgenic lines compared with the WT. Grain yields of the melatonin-rich transgenic lines were reduced by 33% on average. Other phenotypes also varied among the transgenic lines. For example, the transgenic line S1 exhibited greater height and biomass than the WT, while the S10 transgenic line showed diminished height and an increase in panicle numbers per plant. The expression levels of Oryza sativa homeobox1 (OSH1) and TEOSINTE BRANCHED1 (TB1) genes, two key regulators of meristem initiation and maintenance, were not altered in the transgenic lines. These data demonstrate that an alteration of endogenous melatonin levels leads to pleiotropic effects such as height, biomass, panicle number, flowering time, and grain yield, indicating that melatonin behaves as a signaling molecule in plant growth and reproduction.
TL;DR: The role of melatonin on doxorubicin‐induced bioenergetic failure, free radical generation, and cell death is reviewed to highlight other mitochondrial parameters which lack evidence to support the role ofmelatonin in the context of cardiotoxicity.
Abstract: Anthracyclines, such as doxorubicin, are among the most valuable treatments for various cancers, but their clinical use is limited due to detrimental side effects such as cardiotoxicity. Doxorubicin-induced cardiotoxicity is emerging as a critical issue among cancer survivors and is an area of much significance to the field of cardio-oncology. Abnormalities in mitochondrial functions such as defects in the respiratory chain, decreased adenosine triphosphate production, mitochondrial DNA damage, modulation of mitochondrial sirtuin activity and free radical formation have all been suggested as the primary causative factors in the pathogenesis of doxorubicin-induced cardiotoxicity. Melatonin is a potent antioxidant, is nontoxic, and has been shown to influence mitochondrial homeostasis and function. Although a number of studies support the mitochondrial protective role of melatonin, the exact mechanisms by which melatonin confers mitochondrial protection in the context of doxorubicin-induced cardiotoxicity remain to be elucidated. This review focuses on the role of melatonin on doxorubicin-induced bioenergetic failure, free radical generation, and cell death. A further aim is to highlight other mitochondrial parameters such as mitophagy, autophagy, mitochondrial fission and fusion, and mitochondrial sirtuin activity, which lack evidence to support the role of melatonin in the context of cardiotoxicity.
TL;DR: Using confocal microscopy, it is shown that SNAT protein is localized in chloroplasts, whereas ASMT is expressed in the cytoplasm, and catalytic efficiency values of SNAT and ASMT were higher at 55°C than at 30°C suggestive of increased melatonin production at high temperature in plants.
Abstract: Serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT) are the final two enzymes in the melatonin synthesis pathway in plants. Although their corresponding genes have been cloned, their cellular localization and enzymatic characteristics are unknown. Using confocal microscopy, we showed that SNAT protein is localized in chloroplasts, whereas ASMT is expressed in the cytoplasm. In vitro measurement of ASMT enzyme activity revealed a peak of activity in roots, but SNAT enzyme activity was not detected in any plant tissues. This may be attributed in part to an effect of chlorophyll because SNAT enzyme activity was greatly inhibited by chlorophyll in a dose-dependent manner. Because the SNAT protein of cyanobacteria is thermophilic, we examined the effect of temperature on the activity of the rice SNAT and ASMT enzymes. Purified recombinant rice SNAT and ASMT enzymes had an optimum temperature for activity of 55°C. The Km and Vmax values for SNAT at 55°C were 270 μm and 3.3 nmol/min/mg protein, whereas the Km and Vmax for ASMT were 222 μm and 9 nmol/min/mg protein, respectively. The catalytic efficiency (Vmax/Km) values of SNAT and ASMT were 16-fold and 4054-fold higher at 55°C than at 30°C suggestive of increased melatonin production at high temperature in plants.
TL;DR: Mechanistic explorations revealed that melatonin supplementation during bovine oocytes maturation significantly up‐regulated the expressions of oocyte maturation‐associated genes and that LHR1/2, EGFR are involved in signal transduction and epigenetic reprogramming.
Abstract: This study was performed to investigate the effect of melatonin on bovine oocyte maturation and subsequent embryonic development in vitro. The endogenous melatonin concentration in bovine follicular fluid is approximately 10(-11) M. To examine the potential beneficial effects of melatonin on bovine oocyte maturation in vitro, germinal vesicle (GV) oocytes were incubated with different concentrations of melatonin (10(-11), 10(-9), 10(-7), 10(-5), 10(-3) M). Melatonin supplementation at suitable concentrations significantly promoted oocyte maturation. The development of embryos and the mean cell number/blastocyst produced after in vitro fertilization were remarkably improved. The most effective melatonin concentrations obtained from the studies ranged from 10(-9) to 10(-7) M. The expression of melatonin receptor MT1 and MT2 genes was identified in cumulus cells, granulosa cells, and oocytes using reverse transcription PCR, immunofluorescence, and Western blot. The mechanistic studies show that the beneficial effects of melatonin on bovine oocyte maturation are mediated via melatonin membrane receptors as the melatonin receptor agonist (IIK7) promotes this effect while the melatonin receptor antagonist (luzindole) blocks this action. Mechanistic explorations revealed that melatonin supplementation during bovine oocyte maturation significantly up-regulated the expressions of oocyte maturation-associated genes (GDF9, MARF1, and DNMT1a) and cumulus cells expansion-related gene (PTX3, HAS1/2) and that LHR1/2, EGFR are involved in signal transduction and epigenetic reprogramming. The results obtained from the studies provide new information regarding the mechanisms by which melatonin promotes bovine oocyte maturation in vitro and provide an important reference for in vitro embryo production of bovine and the human-assisted reproductive technology.
TL;DR: Combined treatment with melatonin and A‐adMSC was superior to A‐ADMSC alone in protecting the kidneys from sepsis‐induced injury.
Abstract: This study tested whether combined therapy with melatonin and apoptotic adipose-derived mesenchymal stem cells (A-ADMSCs) offered additional benefit in ameliorating sepsis-induced acute kidney injury. Adult male Sprague-Dawley rats (n = 65) were randomized equally into five groups: Sham controls (SC), sepsis induced by cecal-ligation and puncture (CLP), CLP-melatonin, CLP-A-ADMSC, and CLP-melatonin-A-ADMSC. Circulating TNF-α level at post-CLP 6 hr was highest in CLP and lowest in SC groups, higher in CLP-melatonin than in CLP-A-ADMSC and CLP-melatonin-A-ADMSC groups (all P < 0.001). Immune reactivity as reflected in the number of splenic helper-, cytoxic-, and regulatory-T cells at post-CLP 72 hr exhibited the same pattern as that of circulating TNF-α among all groups (P < 0.001). The histological scoring of kidney injury and the number of F4/80+ and CD14+ cells in kidney were highest in CLP and lowest in SC groups, higher in CLP-melatonin than in CLP-A-ADMSC and CLP-melatonin-A-ADMSC groups, and higher in CLP-A-ADMSC than in CLP-melatonin-A-ADMSC groups (all P < 0.001). Changes in protein expressions of inflammatory (RANTES, TNF-1α, NF-κB, MMP-9, MIP-1, IL-1β), apoptotic (cleaved caspase 3 and PARP, mitochondrial Bax), fibrotic (Smad3, TGF-β) markers, reactive-oxygen-species (NOX-1, NOX-2), and oxidative stress displayed a pattern identical to that of kidney injury score among the five groups (all P < 0.001). Expressions of antioxidants (GR+, GPx+, HO-1, NQO-1+) were lowest in SC group and highest in CLP-melatonin-A-ADMSC group, lower in CLP than in CLP-melatonin and CLP-A-ADMSC groups, and lower in CLP-melatonin- than in CLP-A-ADMSC-tretaed animals (all P < 0.001). In conclusion, combined treatment with melatonin and A-ADMSC was superior to A-ADMSC alone in protecting the kidneys from sepsis-induced injury.
TL;DR: TheArabidopsis comt knockout mutant exhibited less production of melatonin than the wild type when Arabidopsis leaves were infiltrated with 1 mm NAS, suggestive of in vivo role of COMT in melatonin biosynthesis in plants.
Abstract: Although a plant N-acetylserotonin methyltransferase (ASMT) was recently cloned from rice, homologous genes appear to be absent in dicotyledonous plants. To clone an ASMT de novo from a dicotyledonous plant, we expressed eight Arabidopsis thaliana O-methyltransferase (OMT) cDNAs in Escherichia coli and screened for ASMT activity by measuring melatonin production after the application of 1 mm N-acetylserotonin (NAS). Among the eight strains harboring the full-length cDNAs, the OMT3 strain produced high levels of melatonin, suggesting that OMT3 encodes an active ASMT. OMT3 is already known as caffeic acid OMT (COMT), suggesting multiple functions for this enzyme. The purified recombinant A. thaliana COMT (AtCOMT) showed high ASMT activity, catalyzing the conversion of NAS to melatonin. The Km and Vmax values for ASMT activity were 233 μm and 1800 pmol/min/mg protein, while the Km and Vmax values for COMT activity were 103 μm and 564,000 pmol/min/mg protein, respectively. The catalytic efficiency (Vmax /Km ) for ASMT activity was 709-fold lower than for COMT. In vitro, ASMT activity was dramatically decreased by the addition of caffeic acid in a dose-dependent manner, but the activity of COMT was not altered by NAS. Lastly, the Arabidopsis comt knockout mutant exhibited less production of melatonin than the wild type when Arabidopsis leaves were infiltrated with 1 mm NAS, suggestive of in vivo role of COMT in melatonin biosynthesis in plants.
TL;DR: It is suggested that melatonin is a potential chemotherapeutic agent for treatment of colon cancer, the effects of which are mediated by regulation of both cell death and senescence in cancerous cells with minimized cardiotoxicity.
Abstract: In Asia, the incidence of colorectal cancer has been increasing gradually due to a more Westernized lifestyle. The aim of study is to determine the interaction between melatonin-induced cell death and cellular senescence. We treated HCT116 human colorectal adenocarcinoma cells with 10 μm melatonin and determined the levels of cell death-related proteins and evaluated cell cycle kinetics. The plasma membrane melatonin receptor, MT1, was significantly decreased by melatonin in a time-dependent manner, whereas the nuclear receptor, RORα, was increased only after 12 hr treatment. HCT116 cells, which upregulated both pro-apoptotic Bax and anti-apoptotic Bcl-xL in the early response to melatonin treatment, activated autophagic as well as apoptotic machinery within 18 hr. Melatonin decreased the S-phase population of the cells to 57% of the control at 48 hr, which was concomitant with a reduction in BrdU-positive cells in the melatonin-treated cell population. We found not only marked attenuation of E- and A-type cyclins, but also increased expression of p16 and p-p21. Compared to the cardiotoxicity of Trichostatin A in vitro, single or cumulative melatonin treatment induced insignificant detrimental effects on neonatal cardiomyocytes. We found that 10 μm melatonin activated cell death programs early and induced G1-phase arrest at the advanced phase. Therefore, we suggest that melatonin is a potential chemotherapeutic agent for treatment of colon cancer, the effects of which are mediated by regulation of both cell death and senescence in cancerous cells with minimized cardiotoxicity.
TL;DR: The results provide biochemical evidence for the presence of a serotonin O‐methylation pathway in plant melatonin biosynthesis and suggest that serotonin can be converted into either N‐acetylserotonin by SNAT or into 5‐MT byCOMT, after which it is metabolized into melatonin by COMT or SNAT, respectively.
Abstract: Serotonin N-acetyltransferase (SNAT) is the penultimate enzyme in melatonin biosynthesis. We cloned SNAT from Arabidopsis thaliana (AtSNAT) and functionally characterized this enzyme for the first time from dicotyledonous plants. Similar to rice SNAT, AtSNAT was found to localize to chloroplasts with peak enzyme activity at 45 °C (Km , 309 μm; Vmax , 1400 pmol/min/mg protein). AtSNAT also catalyzed 5-methoxytryptamine (5-MT) into melatonin with high catalytic activity (Km , 51 μm; Vmax , 5300 pmol/min/mg protein). In contrast, Arabidopsis caffeic acid O-methyltransferase (AtCOMT) localized to the cytoplasm. Interestingly, AtCOMT can methylate serotonin into 5-MT with low catalytic activity (Km , 3.396 mm; Vmax , 528 pmol/min/mg protein). These data suggest that serotonin can be converted into either N-acetylserotonin by SNAT or into 5-MT by COMT, after which it is metabolized into melatonin by COMT or SNAT, respectively. To support this hypothesis, serotonin was incubated in the presence of both AtSNAT and AtCOMT enzymes. In addition to melatonin production, the production of major intermediates depended on incubation temperatures; N-acetylserotonin was predominantly produced at high temperatures (45 °C), while low temperatures (37 °C) favored the production of 5-MT. Our results provide biochemical evidence for the presence of a serotonin O-methylation pathway in plant melatonin biosynthesis.
TL;DR: It is demonstrated that melatonin modulates motility and invasiveness of HepG2 cell in vitro through a molecular mechanism that involves TIMP‐1 upregulation and attenuation of MMP‐9 expression and activity via NF‐κB signal pathway inhibition.
Abstract: Hepatocellular carcinoma (HCC) is one of the most lethal human cancers worldwide because of its high incidence and its metastatic potential. Extracellular matrix degradation by matrix metalloproteinases (MMPs) has been connected with cancer cell invasion, and it has been suggested that inhibition of MMPs by synthetic and natural inhibitors may be of great importance in the HCC therapies. Melatonin, the main product of the pineal gland, exerts antiproliferative, proapoptotic, and antiangiogenic properties in HepG2 human hepatocellular cells, and exhibits anti-invasive and antimetastatic activities by suppressing the enzymatic activity of MMP-9 in different tumor types. However, the underlying mechanism of anti-invasive activity in HCC models has not been fully elucidated. Here, we demonstrate that 1 mm melatonin dosage reduced in IL-1β-induced HepG2 cells MMP-9 gelatinase activity and inhibited cell invasion and motility through downregulation of MMP-9 gene expression and upregulation of the MMP-9-specific inhibitor tissue inhibitor of metalloproteinases (TIMP)-1. No significant changes were observed in the expression and activity of MMP-2, the other proteinase implicated in matrix collagen degradation, and its tissue inhibitor, TIMP-2. Also, melatonin significantly suppressed IL-1β-induced nuclear factor-kappaB (NF-κB) translocation and transcriptional activity. In summary, we demonstrate that melatonin modulates motility and invasiveness of HepG2 cell in vitro through a molecular mechanism that involves TIMP-1 upregulation and attenuation of MMP-9 expression and activity via NF-κB signal pathway inhibition.
TL;DR: To generate melatonin‐rich rice plants, three tryptophan decarboxylase isogenes in the rice genome were overexpressed through overexpression of TDC1, TDC2, and TDC3, resulting in increased melatonin content and enhanced levels of melatonin intermediates.
Abstract: A major goal of plant biotechnology is to improve the nutritional qualities of crop plants through metabolic engineering. Melatonin is a well-known bioactive molecule with an array of health-promoting properties, including potent antioxidant capability. To generate melatonin-rich rice plants, we first independently overexpressed three tryptophan decarboxylase isogenes in the rice genome. Melatonin levels were altered in the transgenic lines through overexpression of TDC1, TDC2, and TDC3; TDC3 transgenic seed (TDC3-1) had melatonin concentrations 31-fold higher than those of wild-type seeds. In TDC3 transgenic seedlings, however, only a doubling of melatonin content occurred over wild-type levels. Thus, a seed-specific accumulation of melatonin appears to occur in TDC3 transgenic lines. In addition to increased melatonin content, TDC3 transgenic lines also had enhanced levels of melatonin intermediates including 5-hydroxytryptophan, tryptamine, serotonin, and N-acetylserotonin. In contrast, expression levels of melatonin biosynthetic mRNA did not increase in TDC3 transgenic lines, indicating that increases in melatonin and its intermediates in these lines are attributable exclusively to overexpression of the TDC3 gene.