Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

Melatonin suppresses hepatocellular carcinoma progression via lncRNA-CPS1-IT-mediated HIF-1α inactivation

Melatonin is the primary pineal hormone that relays light/dark cycle information to the circadian system. It was recently reported to exert intrinsic antitumor activity in various cancers. However, the regulatory mechanisms underlying the antitumor activity of melatonin are poorly understood. Moreover, a limited number of studies have addressed the role of melatonin in hepatocellular carcinoma (HCC), a major life-threatening malignancy in both sexes in Taiwan. In this study, we investigated the antitumor effects of melatonin in HCC and explored the regulatory mechanisms underlying these effects. We observed that melatonin significantly inhibited the proliferation, migration, and invasion of HCC cells and significantly induced the expression of the transcription factor FOXA2 in HCC cells. This increase in FOXA2 expression resulted in upregulation of lncRNA-CPS1 intronic transcript 1 (CPS1-IT1), which reduced HIF-1α activity and consequently resulted in the suppression of epithelial-mesenchymal transition (EMT) progression and HCC metastasis. Furthermore, the results of the in vivo experiments confirmed that melatonin exerts tumor suppressive effects by reducing tumor growth. In conclusion, our findings suggested that melatonin inhibited HCC progression by reducing lncRNA-CPS1-IT1-mediated EMT suppression and indicated that melatonin could be a promising treatment for HCC.

Endogenous melatonin promotes rhythmic recruitment of neutrophils toward an injury in zebrafish

Neutrophil recruitment to injured tissue appears to be an evolutionarily conserved strategy for organisms to fight against exogenous insults. Recent studies have shown rhythmic migration of neutrophils and several factors, including melatonin, have been implicated in regulating this rhythmic migration. The mechanisms underlying how endogenous melatonin regulates rhythmic neutrophils migration, however, are unclear. Here we generated a zebrafish annat2 mutant that lacks endogenous melatonin and, subsequently, a Tg(lyz:EGFP);aanat2^−/− transgenic line that allows for monitoring neutrophils migration visually in live zebrafish. We observed that migrating neutrophils are significantly reduced in aanat2^−/− mutant zebrafish under a light/dark condition, and the disrupted migrating rhythmicity of neutrophils in aanat2^−/− zebrafish is independent of the circadian clock. Further, we also found that endogenous melatonin enhances neutrophils migration likely by inducing the expression of cytokines such as interleukin-8 and interleukin-1β. Together, our findings provide evidence that endogenous melatonin promotes rhythmic migration of neutrophils through cytokines in zebrafish.

Beneficial Effects of Adjuvant Melatonin in Minimizing Oral Mucositis Complications in Head and Neck Cancer Patients Receiving Concurrent Chemoradiation

OBJECTIVES

Oral mucositis is a major cause of pain and delayed cancer treatment leading to poor survival in head and neck cancer patients receiving concurrent chemoradiation. The study evaluated the effect of adjuvant melatonin on minimizing oral mucositis complications to reduce these treatment delays and interruptions.

DESIGN

A randomized, double-blind, double dummy, placebo-controlled clinical trial.

SETTING

Ubon Ratchathani Cancer Hospital, Thailand.

PARTICIPANTS

Thirty-nine head and neck cancer patients receiving concurrent chemoradiation (5 days/week of radiation plus chemotherapy three or six cycles).

METHODS

Patients were randomized to receive 20 mg melatonin gargle (or matched placebo) before each irradiation, and 20 mg melatonin capsules (or matched placebo) taken nightly during 7 weeks of concurrent chemoradiation. Endpoints were oral mucositis events (incidence and time to grade 3 mucositis or grade 2 xerostomia), pain medication consumption and quality of life (QOL).

RESULTS

Melatonin group reported lower incidence of grade 3 oral mucositis (42% vs. 55%) and grade 2 xerostomia (20% vs. 21%); no statistical significance was detected. Melatonin regimen delayed onset of grade 3 mucositis (median 34 days vs. 50 days; p = 0.0318), allowing median time of 16 more patient visits before its onset and fewer interrupted treatments due to oral mucositis were reported (n = 1 vs. n = 5). There was no difference of grade 2 xerostomia (median 32 days vs. 50 days; p = 0.624). Morphine consumption was also reduced (median 57 mg vs. 0 mg; p = 0.0342), while QOL was comparable during the study period.

CONCLUSION

Adjuvant melatonin delayed the onset of oral mucositis, which enables uninterrupted cancer treatment and reduced the amount of morphine used for pain treatment.

High Concentration of Melatonin Regulates Leaf Development by Suppressing Cell Proliferation and Endoreduplication in Arabidopsis

N-acetyl-5-methoxytryptamine (Melatonin), as a crucial messenger in plants, functions in adjusting biological rhythms, stress tolerance, plant growth and development. Several studies have shown the retardation effect of exogenous melatonin treatment on plant growth and development. However, the in vivo role of melatonin in regulating plant leaf growth and the underlying mechanism are still unclear. In this study, we found that high concentration of melatonin suppressed leaf growth in Arabidopsis by reducing both cell size and cell number. Further kinetic analysis of the fifth leaves showed that melatonin remarkably inhibited cell division rate. Additionally, flow cytometic analysis indicated that melatonin negatively regulated endoreduplication during leaf development. Consistently, the expression analysis revealed that melatonin regulated the transcriptional levels of key genes of cell cycle and ribosome. Taken together, this study suggests that high concentration of melatonin negatively regulated the leaf growth and development in Arabidopsis, through modulation of endoreduplication and the transcripts of cell cycle and ribosomal key genes.

Melatonin promotes circadian rhythm-induced proliferation through Clock/histone deacetylase 3/c-Myc interaction in mouse adipose tissue

Melatonin is synthesized in the pineal gland and controls circadian rhythm of peripheral adipose tissue, resulting in changes in body weight. Although core regulatory components of clock rhythmicity have been defined, insight into the mechanisms of circadian rhythm-mediated proliferation in adipose tissue is still limited. Here, we showed that melatonin (20 mg/kg/d) promoted circadian and proliferation processes in white adipose tissue. The circadian amplitudes of brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (Bmal1, P<.05) and circadian locomotor output cycles kaput (Clock, P<.05), period 2 (Per2, P<.05), cyclin E (P<.05), and c-Myc (P<.05) were directly increased by melatonin in adipose tissue. Melatonin also promoted cell cycle and increased cell numbers (P<.05), which was correlated with the Clock expression (P<.05). Further analysis demonstrated that Clock bound to the E-box elements in the promoter region of c-Myc and then directly stimulated c-Myc transcription. Moreover, Clock physically interacted with histone deacetylase 3 (HDAC3) and formed a complex with c-Myc to promote adipocyte proliferation. Melatonin also attenuated circadian disruption and promoted adipocyte proliferation in chronic jet-lagged mice and obese mice. Thus, our study found that melatonin promoted adipocyte proliferation by forming a Clock/HDAC3/c-Myc complex and subsequently driving the circadian amplitudes of proliferation genes. Our data reveal a novel mechanism that links circadian rhythm to cell proliferation in adipose tissue. These findings also identify a new potential means for melatonin to prevent and treat sleep deprivation-caused obesity.

Melatonin, a Full Service Anti-Cancer Agent: Inhibition of Initiation, Progression and Metastasis

There is highly credible evidence that melatonin mitigates cancer at the initiation, progression and metastasis phases. In many cases, the molecular mechanisms underpinning these inhibitory actions have been proposed. What is rather perplexing, however, is the large number of processes by which melatonin reportedly restrains cancer development and growth. These diverse actions suggest that what is being observed are merely epiphenomena of an underlying more fundamental action of melatonin that remains to be disclosed. Some of the arresting actions of melatonin on cancer are clearly membrane receptor-mediated while others are membrane receptor-independent and involve direct intracellular actions of this ubiquitously-distributed molecule. While the emphasis of melatonin/cancer research has been on the role of the indoleamine in restraining breast cancer, this is changing quickly with many cancer types having been shown to be susceptible to inhibition by melatonin. There are several facets of this research which could have immediate applications at the clinical level. Many studies have shown that melatonin's co-administration improves the sensitivity of cancers to inhibition by conventional drugs. Even more important are the findings that melatonin renders cancers previously totally resistant to treatment sensitive to these same therapies. Melatonin also inhibits molecular processes associated with metastasis by limiting the entrance of cancer cells into the vascular system and preventing them from establishing secondary growths at distant sites. This is of particular importance since cancer metastasis often significantly contributes to death of the patient. Another area that deserves additional consideration is related to the capacity of melatonin in reducing the toxic consequences of anti-cancer drugs while increasing their efficacy. Although this information has been available for more than a decade, it has not been adequately exploited at the clinical level. Even if the only beneficial actions of melatonin in cancer patients are its ability to attenuate acute and long-term drug toxicity, melatonin should be used to improve the physical wellbeing of the patients. The experimental findings, however, suggest that the advantages of using melatonin as a co-treatment with conventional cancer therapies would far exceed improvements in the wellbeing of the patients.

Circadian Rhythms in Adipose Tissue Physiology

The different types of adipose tissues fulfill a wide range of biological functions-from energy storage to hormone secretion and thermogenesis-many of which show pronounced variations over the course of the day. Such 24-h rhythms in physiology and behavior are coordinated by endogenous circadian clocks found in all tissues and cells, including adipocytes. At the molecular level, these clocks are based on interlocked transcriptional-translational feedback loops comprised of a set of clock genes/proteins. Tissue-specific clock-controlled transcriptional programs translate time-of-day information into physiologically relevant signals. In adipose tissues, clock gene control has been documented for adipocyte proliferation and differentiation, lipid metabolism as well as endocrine function and other adipose oscillations are under control of systemic signals tied to endocrine, neuronal, or behavioral rhythms. Circadian rhythm disruption, for example, by night shift work or through genetic alterations, is associated with changes in adipocyte metabolism and hormone secretion. At the same time, adipose metabolic state feeds back to central and peripheral clocks, adjusting behavioral and physiological rhythms. In this overview article, we summarize our current knowledge about the crosstalk between circadian clocks and energy metabolism with a focus on adipose physiology. © 2017 American Physiological Society. Compr Physiol 7:383-427, 2017.

2-Hydroxymelatonin, a Predominant Hydroxylated Melatonin Metabolite in Plants, Shows Antitumor Activity against Human Colorectal Cancer Cells

2-Hydroxymelatonin is a predominant hydroxylated melatonin metabolite in plants. To investigate whether it has potent cytotoxic effects on colorectal cancer cells, four colorectal cancer cell lines, Caco2, HCT116, DLD1, and CT26, were treated with 2-hydroxymelatonin and melatonin. 2-Hydroxymelatonin had a much lower IC₅₀ value than melatonin in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cytotoxic effect of 2-hydroxymelatonin was much stronger than that of melatonin at high concentrations (1000 or 2000 μM) in HCT116, DLD1, and CT26 cells, but only at intermediate concentrations (250 or 500 μM) in Caco2 cells. The cytotoxicity of 2-hydroxymelatonin was induced through activation of the apoptotic signaling pathway, as confirmed by Hoechst staining and Annexin V-FITC/propidium iodide double labeling of cells treated with a lethal dose (1 mM). However, sub-lethal doses of 2-hydroxymelatonin inhibited the invasive ability of Caco2 cells. Epithelial-mesenchymal transition (EMT) markers were significantly regulated by 2-hydroxymelatonin. Overall, the anti-cancer activity of 2-hydroxymelatonin is more potent than that of melatonin. Taken together, 2-hydroxymelatonin exhibits potent anti-cancer activity against human colorectal cancer cells via induction of apoptosis and inhibition of EMT.

Abnormal environmental light exposure in the intensive care environment

PURPOSE

We sought to characterize ambient light exposure in the intensive care unit (ICU) environment to identify patterns of light exposure relevant to circadian regulation.

METHODS

A light monitor was affixed to subjects' bed at eye level in a modern intensive care unit and continuously recorded illuminescence for at least 24h per subject. Blood was sampled hourly and measured for plasma melatonin. Subjects underwent hourly vital sign and bedside neurologic assessments. Care protocols and the ICU environment were not modified for the study.

RESULTS

A total of 67,324 30-second epochs of light data were collected from 17 subjects. Light intensity peaked in the late morning, median 64.1 (interquartile range 19.7-138.7) lux. The 75th percentile of light intensity exceeded 100lx only between 9AM and noon, and never exceeded 150lx. There was no correlation between melatonin amplitude and daytime, nighttime or total light exposure (Spearman's correlation coefficients all <0.2 and p>0.5).

CONCLUSIONS

Patients' environmental light exposure in the intensive care unit is consistently low and follows a diurnal pattern. No effect of nighttime light exposure was observed on melatonin secretion. Inadequate daytime light exposure in the ICU may contribute to abnormal circadian rhythms.

The acute exposure of tetrachloro-p-benzoquinone (a.k.a. chloranil) triggers inflammation and neurological dysfunction via Toll-like receptor 4 signaling: The protective role of melatonin preconditioning

This study is aimed to investigate the inflammation and neurological dysfunction induced by tetrachloro-p-benzoquinone (TCBQ) through Toll-like receptor 4 (TLR4) signaling. We also investigated the protective role of melatonin as an antioxidant and anti-inflammatory agent. In vitro model was established by rat pheochromocytoma PC12 cells, meanwhile, TLR4 wild-type (C57BL/6) and knockout mice (C57BL/10ScNJ TLR4^-/-) were used as in vivo model. In vitro study showed TCBQ exposure enhanced the expression of TLR4, myeloid differentiation factor 88 (MyD88) at both transcriptional and post-transcriptional levels. By contrast, melatonin decreased TLR4 and MyD88 expressions. Moreover, our result indicated that melatonin disrupted the formation of TLR4/MyD88/MD2/CD14 complex. In addition, melatonin terminated TCBQ-mediated phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular regulated protein kinase (ERK) signaling and hampered its downstream pro-inflammatory cytokine releases. In vivo result also indicated TLR4 deficiency partially protected against TCBQ-induced morphological and neuropathological changes in mice brain, suggested the role of TLR4. In conclusion, melatonin modulates TCBQ-mediated inflammatory genes through TLR4/MyD88-dependent signaling pathway. Our current study, to the best of our knowledge, is the first time show melatonin not only disrupt the binding of TLR4 and MyD88, but also restricted the formation of TLR4/MD2/CD14 complex, suggesting that melatonin supplementary may represent a valuable therapeutic strategy for inflammatory neurological dysfunction.

Melatonin Regulates Root Architecture by Modulating Auxin Response in Rice

It has been suggested that melatonin acts as an important regulator in controlling root growth and development, but the underlying molecular mechanism driving this relationship remains undetermined. In this study, we demonstrated that melatonin acts as a potent molecule to govern root architecture in rice. Treatments with melatonin significantly inhibited embryonic root growth, and promoted lateral root formation and development. Genome-wide expression profiling by RNA-sequencing revealed auxin-related genes were significantly activated under melatonin treatment. Moreover, several transcription factors and candidate cis-regulatory elements involved in root growth and developments, as well as auxin-related processes, were over-represented in both co-up and -down differentially expressed genes, suggesting that melatonin-mediated root growth occurs in an auxin signal pathway-dependent manner. Further, gravitropic response analysis determined that melatonin affects auxin-regulated processes in rice root. These data show that melatonin shapes root architecture by directly or indirectly activating the auxin signaling pathway.

Melatonin and the pathologies of weakened or dysregulated circadian oscillators

Dynamic aspects of melatonin's actions merit increasing future attention. This concerns particularly entirely different effects in senescent, weakened oscillators and in dysregulated oscillators of cancer cells that may be epigenetically blocked. This is especially obvious in the case of sirtuin 1, which is upregulated by melatonin in aged tissues, but strongly downregulated in several cancer cells. These findings are not at all controversial, but are explained on the basis of divergent changes in weakened and dysregulated oscillators. Similar findings can be expected to occur in other accessory oscillator components that are modulated by melatonin, among them several transcription factors and metabolic sensors. Another cause of opposite effects concerns differences between nocturnally active laboratory rodents and the diurnally active human. This should be more thoroughly considered in the field of metabolic syndrome and related pathologies, especially with regard to type 2 diabetes and other aspects of insulin resistance. Melatonin was reported to impair glucose tolerance in humans, especially in carriers of the risk allele of the MT₂ receptor gene, MTNR1B, that contains the SNP rs10830963. These findings contrast with numerous reports on improvements of glucose tolerance in preclinical studies. However, the relationship between melatonin and insulin may be more complex, as indicated by loss-of-function mutants of the MT₂ receptor that are also prodiabetic, by the age-dependent time course of risk allele overexpression, by progressive reduction in circadian amplitudes and melatonin secretion, which are aggravated in diabetes. By supporting high-amplitude rhythms, melatonin may be beneficial in preventing or delaying diabetes.

Cancer metastasis: Mechanisms of inhibition by melatonin

Melatonin is a naturally occurring molecule secreted by the pineal gland and known as a gatekeeper of circadian clocks. Mounting evidence indicates that melatonin, employing multiple and interrelated mechanisms, exhibits a variety of oncostatic properties in a myriad of tumors during different stages of their progression. Tumor metastasis, which commonly occurs at the late stage, is responsible for the majority of cancer deaths; metastases lead to the development of secondary tumors distant from a primary site. In reference to melatonin, the vast majority of investigations have focused on tumor development and progression at the primary site. Recently, however, interest has shifted toward the role of melatonin on tumor metastases. In this review, we highlight current advances in understanding the molecular mechanisms by which melatonin counteracts tumor metastases, including experimental and clinical observations; emphasis is placed on the impact of both cancer and non-neoplastic cells within the tumor microenvironment. Due to the broad range of melatonin's actions, the mechanisms underlying its ability to interfere with metastases are numerous. These include modulation of cell-cell and cell-matrix interaction, extracellular matrix remodeling by matrix metalloproteinases, cytoskeleton reorganization, epithelial-mesenchymal transition, and angiogenesis. The evidence discussed herein will serve as a solid foundation for urging basic and clinical studies on the use of melatonin to understand and control metastatic diseases.

Effects of Melatonin on Anti-oxidative Systems and Photosystem II in Cold-Stressed Rice Seedlings

Melatonin (N-acetyl-5-methoxytryptamine) plays important role in multiple plant developmental processes and stress responses. We investigated the possible mediatory role of melatonin in growth, photosynthesis, and the response to cold stress in rice by using three different experiments: soaking seed; immersing roots, and spraying to leaves with 0, 20, or 100 μM melatonin. After 6 days of cold stress, the growth of rice seedlings was significantly inhibited, but this inhibition was alleviated by exogenous melatonin. Furthermore, exogenous melatonin pretreatment alleviated the accumulation of reactive oxygen species, malondialdehyde and cell death induced by cold stress. Melatonin pretreatment also relieved the stress-induced inhibitions to photosynthesis and photosystem II activities. Further investigations showed that, antioxidant enzyme activities and non-enzymatic antioxidant levels were increased by melatonin pretreatments. The treatment methods of seed soaking and root immersion were more effective in improving cold stress resistance than the spraying method. The results also indicated the dose-dependent response of melatonin on rice physiological, biochemical, and photosynthetic parameters.

Sleep, Melatonin, and the Menopausal Transition: What Are the Links?

The pineal hormone Melatonin plays an important role in the regulation of the circadian sleep/wake cycle, mood, and perhaps immune functions, carcinogensis and reproduction. The human circadian rhythm of melatonin release from the pineal gland is tightly synchronized with the habitual hours of sleep. Peri- and postmenopausal women often complain of difficulties initiating and/or maintaining sleep, with frequent nocturnal and early morning awakenings. In this review we discuss the pathophysiology of melatonin function as it relates to sleep disorders in menopausal women, highlighting the potential use of exogenous melatonin during the menopausal transition and beyond.

Timing of light exposure affects mood and brain circuits

Temporal organization of physiology is critical for human health. In the past, humans experienced predictable periods of daily light and dark driven by the solar day, which allowed for entrainment of intrinsic circadian rhythms to the environmental light-dark cycles. Since the adoption of electric light, however, pervasive exposure to nighttime lighting has blurred the boundaries of day and night, making it more difficult to synchronize biological processes. Many systems are under circadian control, including sleep-wake behavior, hormone secretion, cellular function and gene expression. Circadian disruption by nighttime light perturbs those processes and is associated with increasing incidence of certain cancers, metabolic dysfunction and mood disorders. This review focuses on the role of artificial light at night in mood regulation, including mechanisms through which aberrant light exposure affects the brain. Converging evidence suggests that circadian disruption alters the function of brain regions involved in emotion and mood regulation. This occurs through direct neural input from the clock or indirect effects, including altered neuroplasticity, neurotransmission and clock gene expression. Recently, the aberrant light exposure has been recognized for its health effects. This review summarizes the evidence linking aberrant light exposure to mood.

Comparison of melatonin with growth factors in promoting precursor cells proliferation in adult mouse subventricular zone

Melatonin, secreted mainly by the pineal gland, plays roles in various physiological functions including protecting cell death. We showed in previous study that the proliferation and differentiation of precursor cells from the adult mouse subventricular zone (SVZ) can be modulated by melatonin via the MT1 melatonin receptor. Since melatonin and epidermal growth factor receptor (EGFR) share some signaling pathway components, we investigated whether melatonin can promote the proliferation of precursor cells from the adult mouse SVZ via the extracellular signal-regulated protein kinase /mitogen-activated protein kinase (ERK/MAPK) pathways in comparison with epidermal growth factor (EGF). Melatonin-induced ERK/MAPK pathways compared with EGF were measured by using in vitro and vivo models. We used neurosphere proliferation assay, immunocytochemistry, and immuno-blotting to analyze significant differences between melatonin and growth factor treatment. We also used specific antagonist and inhibitors to confirm the exactly signaling pathway including luzindole and U0126. We found that significant increase in proliferation was observed when two growth factors (EGF+bFGF) and melatonin were used simultaneously compared with EGF + bFGF or compared with melatonin alone. In addition, the present result suggested the synergistic effect occurred of melatonin and growth factors on the activating the ERK/MAPK pathway. This study exhibited that melatonin could act as a trophic factor, increasing proliferation in precursor cells mediated through the melatonin receptor coupled to ERK/MAPK signaling pathways. Understanding the mechanism by which melatonin regulates precursor cells may conduct to the development of novel strategies for neurodegenerative disease therapy.

Melatonin: A Mitochondrial Targeting Molecule Involving Mitochondrial Protection and Dynamics

Melatonin has been speculated to be mainly synthesized by mitochondria. This speculation is supported by the recent discovery that aralkylamine N-acetyltransferase/serotonin N-acetyltransferase (AANAT/SNAT) is localized in mitochondria of oocytes and the isolated mitochondria generate melatonin. We have also speculated that melatonin is a mitochondria-targeted antioxidant. It accumulates in mitochondria with high concentration against a concentration gradient. This is probably achieved by an active transportation via mitochondrial melatonin transporter(s). Melatonin protects mitochondria by scavenging reactive oxygen species (ROS), inhibiting the mitochondrial permeability transition pore (MPTP), and activating uncoupling proteins (UCPs). Thus, melatonin maintains the optimal mitochondrial membrane potential and preserves mitochondrial functions. In addition, mitochondrial biogenesis and dynamics is also regulated by melatonin. In most cases, melatonin reduces mitochondrial fission and elevates their fusion. Mitochondrial dynamics exhibit an oscillatory pattern which matches the melatonin circadian secretory rhythm in pinealeocytes and probably in other cells. Recently, melatonin has been found to promote mitophagy and improve homeostasis of mitochondria.

Associations of sleep duration with open angle glaucoma in the Korea national health and nutrition examination survey

The aim of this study is to investigate the relationship between sleep duration and glaucoma, stratified by obesity status.This study was conducted using data from the Korean National Health and Nutrition Examination Survey V 2010 to 2012. Open-angle glaucoma was diagnosed according to the International Society of Geographical and Epidemiological Ophthalmology criteria. Subjects were divided into subgroups based on those who were overweight (body mass index ≥25 kg/m or <25 kg/m) or with abdominal obesity (based on waist circumference). Multiple logistic regression analysis was done to estimate the magnitude of the association between sleep duration (<7 h, 7-<9, or ≥9 hours) and prevalence of glaucoma in the total population and in the subgroups.Individuals who slept <5 hours per night had the highest prevalence of glaucoma (5.55 ± 1.09%), followed by those who slept ≥9 hours per night (4.56 ± 0.10%), and then by those who slept 5 to <6 hours per night (4.15 ± 0.68%), which revealed a U-shaped pattern (P for trend = 0.072). Among overweight individuals, subjects who slept <7 hours and those who slept ≥9 hours were significantly more likely to have glaucoma compared with subjects who slept 7 to <9 hours after adjusting for survey year, age, sex, smoking, drinking, exercise, education level, household income, hypertension, intraocular pressure, stress, and depression (odds ratio, 2.41; 95% confidence interval, 1.14-5.03). Unlike for overweight individuals, sleep duration in nonoverweight individuals was not statistically significantly associated with glaucoma.Our results reveal a U-shaped association between sleep duration and the prevalence of glaucoma. An effect of sleep duration on glaucoma was present in the subgroup of overweight patients.

Daily NO rhythms in peripheral clocks in aging male Wistar rats: protective effects of exogenous melatonin

In mammals suprachiasmatic nucleus (SCN), acts as a light entrainable master clock and by generation of temporal oscillations regulates the peripheral organs acting as autonomous clocks resulting in overt behavioral and physiological rhythms. SCN also controls synthesis and release of melatonin (hormonal message for darkness) from pineal. Nitric Oxide (NO) acts as an important neurotransmitter in generating the phase shifts of circadian rhythms and participates in sleep-wake processes, maintenance of vascular tone as well as signalling and regulating inflammatory processes. Aging is associated with disruption of circadian timing system and decline in endogenous melatonin leading to several physiological disorders. Here we report the effect of aging on NO daily rhythms in various peripheral clocks such as kidney, intestine, liver, heart, lungs and testis. NO levels were measured at zeitgeber time (ZT) 0, 6, 12 and 18 in these tissues using Griess assay in male Wistar rats. Aging resulted in alteration of NO levels as well as phase of NO in both 12 and 24 months groups. Correlation analysis demonstrated loss of stoichiometric interaction between the various peripheral clocks with aging. Age induced alterations in NO daily rhythms were found to be most significant in liver and, interestingly least in lungs. Neurohormone melatonin, an endogenous synchroniser and an antiaging agent decreases with aging. We report further differential restoration with exogenous melatonin administration of age induced alterations in NO daily rhythms and mean levels in kidney, intestine and liver and the stoichiometric interactions between the various peripheral clocks.

Behavioral and molecular effects of prenatal continuous light exposure in the adult rat

Disruption of the maternal environment during pregnancy leads to behavioral changes and diseases in the adult offspring. To explore the influence of prenatal continuous light exposure (PCLE) on the adult offspring, we exposed pregnant Wistar rats to constant light during late gestation. Adult PCLE offspring showed an anxiety-like behavior and impairment of short-term memory in different tests. Measurements in the whole brain homogenates from newborn and adult offspring indicated decreased melatonin and serotonin levels and increased reactive oxygen species level in PCLE offspring. Further, we determined melatonin-, serotonin-, oxidative stress-, apoptosis-, and circadian system-related genes expression in different brain areas of adult offspring. The serotonin reuptaker Slc6a4 displayed a decreased expression in the prefrontal cortex of PCLE group. The circadian rhythm-related gene Rora was upregulated in the amygdala of PCLE offspring. Our results point to adverse behavioral effects of PCLE on adult offspring, involving serotonin and melatonin signaling dysregulation, increased chronic oxidative stress, and altered gene expression.

Potential pleiotropic beneficial effects of adjuvant melatonergic treatment in posttraumatic stress disorder

Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune, and autonomic system, similar to chronic stress and may play a central role in the development of stress-related disorders. Recent articles have focused on the role of sleep and circadian disruption in the pathophysiology of posttraumatic stress disorder (PTSD), suggesting that chronodisruption plays a causal role in PTSD development. Direct and indirect human and animal PTSD research suggests circadian system-linked neuroendocrine, immune, metabolic and autonomic dysregulation, linking circadian misalignment to PTSD pathophysiology. Recent experimental findings also support a specific role of the fundamental synchronizing pineal hormone melatonin in mechanisms of sleep, cognition and memory, metabolism, pain, neuroimmunomodulation, stress endocrinology and physiology, circadian gene expression, oxidative stress and epigenetics, all processes affected in PTSD. In the current paper, we review available literature underpinning a potentially beneficiary role of an add-on melatonergic treatment in PTSD pathophysiology and PTSD-related symptoms. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. We conclude that adjuvant melatonergic treatment could provide a potentially promising treatment strategy in the management of PTSD and especially PTSD-related syndromes and comorbidities. Rigorous preclinical and clinical studies are needed to validate this hypothesis.

Light and the City: Breast Cancer Risk Factors Differ Between Urban and Rural Women in Israel

Women are exposed to indoor and outdoor artificial light at night (ALAN) in urban and rural environments. Excessive exposure to hazardous ALAN containing short wavelength light may suppress pineal melatonin production and lead to an increased breast cancer (BC) risk. Our objective was to address the differences in BC risks related to light exposure in urban and rural communities. We examined indoor and outdoor light habits of BC patients and controls that had lived in urban and rural areas in a 5-year period, 10 to 15 years before the time of the study. Individual data, night time sleeping habits and individual exposure to ALAN habits were collected using a questionnaire. A total of 252 women (110 BC patients and 142 controls) participated in this study. The sample was divided to subgroups according to dwelling area and disease status. Age matching was completed between all subgroups. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated for urban and rural women separately, using binary logistic regression. OR results of urban population (92 BC patients and 72 control) revealed that BC risk increases with daily use of cellphone (OR = 2.13, 95% CI = 1.01-4.49, P < .05) and residence near strong ALAN sources (OR = 1.51, 95% CI = 0.99-2.30, P < .06). Nevertheless, BC risk decreases if a woman was born in Israel (OR = 0.44, 95% CI = 0.21-0.93, P < .03), longer sleep duration (OR = 0.75, 95% CI = 0.53-1.05, P < .1), and reading with bed light illumination before retiring to sleep (OR = 0.77, 95% CI = 0.61-0.96, P < .02). Furthermore, in the rural population (18 BC patients and 66 control) BC risk increases with the number of years past since the last menstruation (OR = 1.12, 95% CI = 1.03-1.22, P < .01). However, BC risk decreases with longer sleep duration (OR = 0.53, 95% CI = 0.24-1.14, P < .1), reading with room light illumination before retiring to sleep (OR = 0.55, 95% CI = 0.29-1.06, P < .07), and sleeping with closed shutters during the night (OR = 0.66, 95% CI = 0.41-1.04, P < .08). These data support the idea that indoor and outdoor nighttime light exposures differ between urban and rural women. Therefore, we suggest that women can influence BC risk and incidence by applying protective personal lighting habits. Further studies with larger sample sizes are needed to strengthen the results.

Pineal Gland Calcification in Kurdistan: A Cross-Sectional Study of 480 Roentgenograms

Objective

The goal of this study was to compare the incidence of Pineal Gland Calcification (PGC) by age group and gender among the populations living in the Kurdistan Region-Iraq.

Methods

This prospective study examined skull X-rays of 480 patients between the ages of 3 and 89 years who sought care at a large teaching public hospital in Duhok, Iraq from June 2014 to November 2014. Descriptive statistics and a binary logistic regression were used for analysis.

Results

The overall incidence rate of PGC among the study population was 26.9% with the 51–60 age group and males having the highest incidence. PGC incidence increased after the first decade and remained steady until the age of 60. Thereafter the incidence began to decrease. Logistic regression analysis revealed that both age and gender significantly affected the risk of PGC. After adjusting for age, males were 1.94 (95% CI, 1.26–2.99) times more likely to have PGC compared to females. In addition, a one year increase in age increases the odds of developing PGC by 1.02 (95% CI, 1.01–1.03) units after controlling for the effects of gender.

Conclusion

Our analysis demonstrated a close relationship between PGC and age and gender, supporting a link between the development of PGC and these factors. This study provides a basis for future researchers to further investigate the nature and mechanisms underlying pineal gland calcification.

Endocrine regulation of circadian physiology

Endogenous circadian clocks regulate 24-h rhythms of behavior and physiology to align with external time. The endocrine system serves as a major clock output to regulate various biological processes. Recent findings suggest that some of the rhythmic hormones can also provide feedback to the circadian system at various levels, thus contributing to maintaining the robustness of endogenous rhythmicity. This delicate balance of clock-hormone interaction is vulnerable to modern lifestyle factors such as shiftwork or high-calorie diets, altering physiological set points. In this review, we summarize the current knowledge on the communication between the circadian timing and endocrine systems, with a focus on adrenal glucocorticoids and metabolic peptide hormones. We explore the potential role of hormones as systemic feedback signals to adjust clock function and their relevance for the maintenance of physiological and metabolic circadian homeostasis.

Circadian regulation of lipid metabolism

The circadian system temporally coordinates daily rhythms in feeding behaviour and energy metabolism. The objective of the present paper is to review the mechanisms that underlie circadian regulation of lipid metabolic pathways. Circadian rhythms in behaviour and physiology are generated by master clock neurons in the suprachiasmatic nucleus (SCN). The SCN and its efferent targets in the hypothalamus integrate light and feeding signals to entrain behavioural rhythms as well as clock cells located in peripheral tissues, including the liver, adipose tissue and muscle. Circadian rhythms in gene expression are regulated at the cellular level by a molecular clock comprising a core set of clock genes/proteins. In peripheral tissues, hundreds of genes involved in lipid biosynthesis and fatty acid oxidation are rhythmically activated and repressed by clock proteins, hence providing a direct mechanism for circadian regulation of lipids. Disruption of clock gene function results in abnormal metabolic phenotypes and impaired lipid absorption, demonstrating that the circadian system is essential for normal energy metabolism. The composition and timing of meals influence diurnal regulation of metabolic pathways, with food intake during the usual rest phase associated with dysregulation of lipid metabolism. Recent studies using metabolomics and lipidomics platforms have shown that hundreds of lipid species are circadian-regulated in human plasma, including but not limited to fatty acids, TAG, glycerophospholipids, sterol lipids and sphingolipids. In future work, these lipid profiling approaches can be used to understand better the interaction between diet, mealtimes and circadian rhythms on lipid metabolism and risk for obesity and metabolic diseases.

Decreased 6-Sulfatoxymelatonin Excretion in Male GH-Deficient Children and Adolescents

AIM

To evaluate melatonin secretion in a group of untreated and treated male growth hormone (GH)-deficient children and adolescents.

METHODS

We studied 44 male subjects: 8 untreated GH-deficient patients (GHDnt), 16 treated GH-deficient patients (GHDt) and 20 healthy children and adolescents as control group (CG). We measured urinary 6-sulfatoxymelatonin (6-SM) in total (24-hour samples), nocturnal (18.00-8.00 h) and diurnal samples (8.00-18.00 h). Levels of 6-SM were expressed as micrograms excreted per time interval and x0394; values (difference between nighttime and daytime values).

RESULTS

Significant differences were observed among the 3 groups of pediatric subjects studied for total 6-SM (p < 0.0001), nocturnal 6-SM (p < 0.0001) and x0394; values (p < 0.0001). Subsequent analysis showed significantly higher levels for total 6-SM, nocturnal 6-SM and nighttime-daytime x0394; in the CG versus the GHDnt (p < 0.01) and in the CG versus the GHDt group (p < 0.01). No significant correlations were found between 6-SM excretion and insulin-like growth factor-1 values in the children and adolescents studied.

CONCLUSIONS

GH-deficient patients showed lower levels of 6-SM. Our findings provide a different insight to a further understanding of some chronobiological disorders involved in GH deficiency in children.

Melatonin rhythms in renal transplant recipients with sleep-wake disturbances

We assessed salivary melatonin levels in renal transplant (RTx) recipients who participated in a randomised, multicentre wait-list controlled trial on the effect of bright light therapy on their sleep and circadian rhythms. A large proportion of RTx recipients in our cohort had unexpectedly low melatonin values, which precluded calculation of the dim-light melatonin onset (DLMO) as a circadian marker. Thus, the aim of this post hoc analysis was to describe the melatonin profile of home-dwelling RTx recipients diagnosed with sleep-wake disturbances (SWDs). The participants were characterised by means of sleep questionnaires, validated psychometric instruments [Pittsburgh sleep quality Index (PSQI), Epworth sleepiness scale (ESS), Morningness-Eveningness Questionnaire (MEQ) and Depression, Anxiety and Stress Scale (DASS)] in addition to melatonin assay in saliva. Data were analysed with descriptive statistics and group comparisons made with appropriate post hoc tests. RTx recipients [n = 29 (aged 54.83 ± 13.73, transplanted 10.62 ± 6.84 years ago)] were retrospectively grouped into two groups: RTx recipients whose dim light melatonin onset (DLMO) could be calculated (n = 11) and those whose DLMO could not be calculated (n = 18). RTx recipients having a measurable DLMO had a number of differences from those without DLMO: they were younger [46.4 ± 14.9 compared to 60.0 ± 10.3 (p = .007)], had higher haemoglobin values [135.36 ± 12.01 versus 122.82 ± 11.56 (p = .01)], less anxiety [4 (0;8) versus 12 (6.5;14) (p = .021)] and a better overall sense of coherence [SOC Score: 71.09 ± 12.78 versus 56.28 ± 15.48 (p = 0.013)]. These results suggest that RTx recipients whose DLMO could be calculated have less health impairments, underlying the relevance of a stable circadian system.

Melatonin relieves neuropathic allodynia through spinal MT2-enhanced PP2Ac and downstream HDAC4 shuttling-dependent epigenetic modification of hmgb1 transcription

Melatonin (MLT; N-acetyl-5-methoxytryptamine) exhibits analgesic properties in chronic pain conditions. While researches linking MLT to epigenetic mechanisms have grown exponentially over recent years, very few studies have investigated the contribution of MLT-associated epigenetic modification to pain states. Here, we report that together with behavioral allodynia, spinal nerve ligation (SNL) induced a decrease in the expression of catalytic subunit of phosphatase 2A (PP2Ac) and enhanced histone deacetylase 4 (HDAC4) phosphorylation and cytoplasmic accumulation, which epigenetically alleviated HDAC4-suppressed hmgb1 gene transcription, resulting in increased high-mobility group protein B1 (HMGB1) expression selectively in the ipsilateral dorsal horn of rats. Focal knock-down of spinal PP2Ac expression also resulted in behavioral allodynia in association with similar protein expression as observed with SNL. Notably, intrathecal administration with MLT increased PP2Ac expression, HDAC4 dephosphorylation and nuclear accumulation, restored HDAC4-mediated hmgb1 suppression and relieved SNL-sensitized behavioral pain; these effects were all inhibited by spinal injection of 4P-PDOT (a MT2 receptor antagonist, 30 minutes before MLT) and okadaic acid (OA, a PP2A inhibitor, 3 hr after MLT). Our findings demonstrate a novel mechanism by which MLT ameliorates neuropathic allodynia via epigenetic modification. This MLT-exhibited anti-allodynia is mediated by MT2-enhanced PP2Ac expression that couples PP2Ac with HDAC4 to induce HDAC4 dephosphorylation and nuclear import, herein increases HDAC4 binding to the promoter of hmgb1 gene and upregulates HMGB1 expression in dorsal horn neurons.

Melatonin prevents cisplatin-induced primordial follicle loss via suppression of PTEN/AKT/FOXO3a pathway activation in the mouse ovary

Premature ovarian failure (POF) is a major side effect of chemotherapy in young cancer patients. To develop pharmaceutical agents for preserving fertility, it is necessary to understand the mechanisms responsible for chemotherapy-induced follicle loss. Here, we show that treatment with cisplatin, a widely used anticancer drug, depleted the dormant follicle pool in mouse ovaries by excessive activation of the primordial follicles, without inducing follicular apoptosis. Moreover, we show that co-treatment with the antioxidant melatonin prevented cisplatin-induced disruption of the follicle reserve. We quantified the various stages of growing follicles, including primordial, primary, secondary, and antral, to demonstrate that cisplatin treatment alone significantly decreased, whereas melatonin co-treatment preserved, the number of primordial follicles in the ovary. Importantly, analysis of the PTEN/AKT/FOXO3a pathway demonstrated that melatonin significantly decreased the cisplatin-mediated inhibitory phosphorylation of PTEN, a key negative regulator of dormant follicle activation. Moreover, melatonin prevented the cisplatin-induced activating phosphorylation of AKT, GSK3β, and FOXO3a, all of which trigger follicle activation. Additionally, we show that melatonin inhibited the cisplatin-induced inhibitory phosphorylation and nuclear export of FOXO3a, which is required in the nucleus to maintain dormancy of the primordial follicles. These findings demonstrate that melatonin attenuates cisplatin-induced follicle loss by preventing the phosphorylation of PTEN/AKT/FOXO3a pathway members; thus, melatonin is a potential therapeutic agent for ovarian protection and fertility preservation during chemotherapy in female cancer patients.

Neuroprotective effect of acute melatonin treatment on hippocampal neurons against irradiation by inhibition of caspase-3

Neuronal cell apoptosis is associated with various factors that induce neurological damage, including radiation exposure. When administered prior to exposure to radiation, a protective agent may prevent cellular and molecular injury. The present study aimed to investigate whether melatonin exerts a neuroprotective effect by inhibiting the caspase cell death pathway. Male Sprague-Dawley rats were administered melatonin (100 mg/kg body weight) 30 min prior to radiation exposure in red light during the evening. In order to elucidate whether melatonin has a neuroprotective role, immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick-end labeling, Nissl staining, reverse transcription-quantitative polymerase chain reaction, reactive oxygen species analysis and western blotting were performed. At 24 h post-melatonin treatment, caspase-3 mRNA and protein expression levels were significantly decreased. These results demonstrated that melatonin may protect hippocampal neurons via the inhibition of caspase-3 when exposed to irradiation. Therefore, caspase-3 inhibition serves a neuroprotective and antioxidant role in the interventional treatment of melatonin. The results of the present study suggested that melatonin may have a potential therapeutic effect against irradiation; however, further studies are required in order to elucidate the underlying antioxidant mechanisms.

Male-female differences in 6-sulfatoxymelatonin excretion in hypopituitary patients

OBJECTIVE

To evaluate melatonin secretion in adult hypopituitary patients with Growth Hormone deficiency (AGHD) on and off replacement therapy.

SUBJECTS AND METHODS

We studied 48 subjects: 12 (6 males) untreated AGHD (AGHDnt), 20 (10 males) treated AGHD (AGHDt) and 16 healthy subjects (8 males) as control group (CG). We measured urinary 6-sulfatoxymelatonin (6-SM) in total (24 h samples), nocturnal (6-SMn): 1800-0800 and diurnal samples (6-SMd): 0800-1800.

RESULTS

Significant differences were observed among the 3 groups of male subjects, in total 6-SM (p < 0.05), nocturnal 6-SM (p < 0.02) and nighttime-daytime delta values (p < 0.003). CG had significantly higher values than the AGHDnt in total 6-SM (p < 0.01), nocturnal 6-SM (p < 0.05) and nighttime-daytime delta values (p < 0.01). AGHDt patients showed significantly higher levels in nighttime-daytime delta values than AGHDnt patients (p < 0.05). In females, no significant differences were found among the 3 groups studied in total, nocturnal, diurnal or nighttime-daytime delta values. In males, significant correlations were found among total 6-SM (r = 0.58; p = 0.029), nocturnal 6-SM (r = 0.70; p = 0.006) and nighttime-daytime delta values (r = 0.71; p = 0.004) vs. serum IGF-1 levels in subjects evaluated. In females, significant correlations were found among total 6-SM (r = 0.57; p = 0.02) vs. serum IGF-1 levels in subjects evaluated. A tendency towards a significant correlation was found in diurnal 6-SM (r = 0.48; p = 0.07).

CONCLUSIONS

Our findings show a sexual dimorphism in 6-SM excretion in AGHD patients and provide an interesting approach to a further understanding of some chronobiological disorders involved in GH deficiency.

Stable isotope dilution ultra-high performance liquid chromatography-tandem mass spectrometry quantitative profiling of tryptophan-related neuroactive substances in human serum and cerebrospinal fluid

Many compounds related to L-tryptophan (L-TRP) have interesting biological or pharmacological activity, and their abnormal neurotransmission seems to be linked to a wide range of neurodegenerative and psychiatric diseases. A high-throughput method based on ultra-high performance liquid chromatography connected to electrospray tandem mass spectrometry (UHPLC-ESI-MS/MS) was developed for the quantitative analysis of L-TRP and 16 of its metabolites in human serum and cerebrospinal fluid (CSF), representing both major and minor routes of L-TRP catabolism. The combination of a fast LC gradient with selective tandem mass spectrometry enabled accurate analysis of almost 100 samples in 24h. The standard isotope dilution method was used for quantitative determination. The method's lower limits of quantification for serum and cerebrospinal fluid ranged from 0.05 to 15nmol/L and 0.3 to 45nmol/L, respectively. Analytical recoveries ranged from 10.4 to 218.1% for serum and 22.1 to 370.0% for CSF. The method's accuracy ranged from 82.4 to 128.5% for serum matrix and 90.7 to 127.7% for CSF matrix. All intra- and inter-day coefficients of variation were below 15%. These results demonstrate that the new method is capable of quantifying endogenous serum and CSF levels of a heterogeneous group of compounds spanning a wide range of concentrations. The method was used to determine the physiological levels of target analytes in serum and CSF samples from 18 individuals, demonstrating its reliability and potential usefulness in large-scale epidemiological studies.

Melatonin: Current Status and Future Perspectives in Plant Science

Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous molecule with pleiotropic actions in different organisms. It performs many important functions in human, animals, and plants; these range from regulating circadian rhythms in animals to controlling senescence in plants. In this review, we summarize the available information regarding the presence of melatonin in different plant species, along with highlighting its biosynthesis and mechanisms of action. We also collected the available information on the effects of melatonin application on commercially important crops to improve their growth and development. Additionally, we have identified many new aspects where melatonin may have possible roles in plants, for example, its function in improving the storage life and quality of fruits and vegetables, its role in vascular reconnection during the grafting process and nutrient uptake from roots by modifying root architecture. Another potentially important aspect is the production of melatonin-rich food crops (cereals, fruits, and vegetables) through combination of conventional and modern breeding approaches, to increase plant resistance against biotic and abiotic stress, leading to improved crop yields, and the nutraceutical value of produce to solve food security issues.

Osteogenesis from Dental Pulp Derived Stem Cells: A Novel Conditioned Medium Including Melatonin within a Mixture of Hyaluronic, Butyric, and Retinoic Acids

Human dental pulp stem cells (hDPSCs) have shown relevant potential for cell therapy in the orthopedic and odontoiatric fields. The optimization of their osteogenic potential is currently a major challenge. Vascular endothelial growth factor A (VEGF A) has been recently reported to act as a major conductor of osteogenesis in vitro and in vivo. Here, we attempted to prime endogenous VEGF A expression without the need for viral vector mediated gene transfer technologies. We show that hDPSCs exposure to a mixture of hyaluronic, butyric, and retinoic acids (HA + BU + RA) induced the transcription of a gene program of osteogenesis and the acquirement of an osteogenic lineage. Such response was also elicited by cell exposure to melatonin, a pleiotropic agent that recently emerged as a remarkable osteogenic inducer. Interestingly, the commitment to the osteogenic fate was synergistically enhanced by the combinatorial exposure to a conditioned medium containing both melatonin and HA + BU + RA. These in vitro results suggest that in vivo osteogenesis might be improved and further studies are needed.

Melatonin Regulates Root Meristem by Repressing Auxin Synthesis and Polar Auxin Transport in Arabidopsis

Melatonin (N-acetyl-5-methoxytryptamine) plays important roles in regulating both biotic and abiotic stress tolerance, biological rhythms, plant growth and development. Sharing the same substrate (tryptophan) for the biosynthesis, melatonin and auxin also have similar effects in plant development. However, the specific function of melatonin in modulating plant root growth and the relationship between melatonin and auxin as well as underlying mechanisms are still unclear. In this study, we found high concentration of melatonin remarkably inhibited root growth in Arabidopsis by reducing root meristem size. Further studies showed that melatonin negatively regulated auxin biosynthesis, the expression of PINFORMED (PIN) proteins as well as auxin response in Arabidopsis. Moreover, the root growth of the triple mutant pin1pin3pin7 was more tolerant than that of wild-type in response to melatonin treatment, suggesting the essential role of PIN1/3/7 in melatonin-mediated root growth. Combination treatment of melatonin and 5-Triiodobenzoic acid (TIBA) did not enhance melatonin-mediated reduction of root meristem size, indicating that polar auxin transport (PAT) may be necessary for the regulation of root meristem size by melatonin treatment. Taken together, this study indicates that melatonin regulates root growth in Arabidopsis, through auxin synthesis and polar auxin transport, at least partially.

Melatonergic system-based two-gene index is prognostic in human gliomas

Gliomas, the most common primary brain tumors in adults, are classified into four malignancy grades according to morphological features. Recent studies have shown that melatonin treatment induces cytotoxicity in glioma-initiating cells and reduces the invasion and migration of glioma cell lines, inhibiting the nuclear factor κB (NFκB) oncopathway. Given that C6 rat glioma cells produce melatonin, we investigated the correlation between the capacity of gliomas to synthesize/metabolize melatonin and their overall malignancy. We first characterized the melatonergic system of human gliomas cell lines with different grades of aggressiveness (HOG, T98G, and U87MG) and demonstrated that glioma-synthesized melatonin exerts an autocrine antiproliferative effect. Accordingly, the sensitivity to exogenous melatonin was higher for the most aggressive cell line, U87MG, which synthesized/accumulated less melatonin. Using The Cancer Genome Atlas RNAseq data of 351 glioma patients, we designed a predictive model of the content of melatonin in the tumor microenvironment, the ASMT:CYP1B1 index, combining the gene expression levels of melatonin synthesis and metabolism enzymes. The ASMT:CYP1B1 index negatively correlated with tumor grade, as well as with the expression of pro-proliferation and anti-apoptotic NFκB target genes. More importantly, the index was a grade- and histological type-independent prognostic factor. Even when considering only high-grade glioma patients, a low ASMT:CYP1B1 value, which suggests decreased melatonin and enhanced aggressiveness, was strongly associated with poor survival. Overall, our data reveal the prognostic value of the melatonergic system of gliomas and provide insights into the therapeutic role of melatonin.

Melatonin Regulates Root Meristem by Repressing Auxin Synthesis and Polar Auxin Transport in Arabidopsis

Melatonin (N-acetyl-5-methoxytryptamine) plays important roles in regulating both biotic and abiotic stress tolerance, biological rhythms, plant growth and development. Sharing the same substrate (tryptophan) for the biosynthesis, melatonin and auxin also have similar effects in plant development. However, the specific function of melatonin in modulating plant root growth and the relationship between melatonin and auxin as well as underlying mechanisms are still unclear. In this study, we found high concentration of melatonin remarkably inhibited root growth in Arabidopsis by reducing root meristem size. Further studies showed that melatonin negatively regulated auxin biosynthesis, the expression of PINFORMED (PIN) proteins as well as auxin response in Arabidopsis. Moreover, the root growth of the triple mutant pin1pin3pin7 was more tolerant than that of wild-type in response to melatonin treatment, suggesting the essential role of PIN1/3/7 in melatonin-mediated root growth. Combination treatment of melatonin and 5-Triiodobenzoic acid (TIBA) did not enhance melatonin-mediated reduction of root meristem size, indicating that polar auxin transport (PAT) may be necessary for the regulation of root meristem size by melatonin treatment. Taken together, this study indicates that melatonin regulates root growth in Arabidopsis, through auxin synthesis and polar auxin transport, at least partially.

Melatonin reduces excitotoxic blood-brain barrier breakdown in neonatal rats

The blood-brain barrier (BBB) is a complex structure that protects the central nervous system from peripheral insults. Understanding the molecular basis of BBB function and dysfunction holds significant potential for future strategies to prevent and treat neurological damage. The aim of our study was (1) to investigate BBB alterations following excitotoxicity and (2) to test the protective properties of melatonin. Ibotenate, a glutamate analog, was injected intracerebrally in postnatal day 5 (P5) rat pups to mimic excitotoxic injury. Animals were than randomly divided into two groups, one receiving intraperitoneal (i.p.) melatonin injections (5mg/kg), and the other phosphate buffer saline (PBS) injections. Pups were sacrificed 2, 4 and 18 h after ibotenate injection. We determined lesion size at 5 days by histology, the location and organization of tight junction (TJ) proteins by immunohistochemical studies, and BBB leakage by dextran extravasation. Expression levels of BBB genes (TJs, efflux transporters and detoxification enzymes) were determined in the cortex and choroid plexus by quantitative PCR. Dextran extravasation was seen 2h after the insult, suggesting a rapid BBB breakdown that was resolved by 4h. Extravasation was significantly reduced in melatonin-treated pups. Gene expression and immunohistochemical assays showed dynamic BBB modifications during the first 4h, partially prevented by melatonin. Lesion-size measurements confirmed white matter neuroprotection by melatonin. Our study is the first to evaluate BBB structure and function at a very early time point following excitotoxicity in neonates. Melatonin neuroprotects by preventing TJ modifications and BBB disruption at this early phase, before its previously demonstrated anti-inflammatory, antioxidant and axonal regrowth-promoting effects.

Heterogeneous ribonucleoprotein R regulates arylalkylamine N-acetyltransferase synthesis via internal ribosomal entry site-mediated translation in a circadian manner

Rhythmic arylalkylamine N-acetyltransferase (AANAT) synthesis is a prominent circadian-controlled response that occurs in most mammals. AANAT is the core enzyme in melatonin production; because melatonin participates in many physiological processes, the regulation of AANAT is an important research topic. In this study, we focused on the role of heterogeneous ribonucleoprotein R (hnRNP R) in the translation of AANAT. A novel RNA-binding protein hnRNP R widely interacted with the 5' untranslated region (UTR) of AANAT mRNA and contributed to translation through an internal ribosomal entry site (IRES). Fine-tuning of AANAT protein synthesis occurred in response to knockdown and overexpression of hnRNP R. Nocturnal elevation of AANAT protein was dependent on the rhythmic changes of hnRNP R, whose levels are elevated in the pineal gland during nighttime. Increases in hnRNP R additionally improved AANAT production in rat pinealocytes under norepinephrine (NE) treatment. These results suggest that cap-independent translation of AANAT mRNA plays a role in the rhythmic synthesis of melatonin through the recruitment of translational machinery to hnRNP R-bound AANAT mRNA.

Interleukin-17, oxidative stress, and inflammation: role of melatonin during Trypanosoma cruzi infection

Although the exact etiology of Chagas' disease remains unknown, the inflammatory process and oxidative stress are believed to be the main contributors to the dysfunction and pathogenesis during chronic Trypanosoma cruzi infection. Our hypothesis is that melatonin administered for 2 months daily could modulate the oxidative stress and the inflammatory response during the chronic infection. Flow cytometric analysis of macrophages and antigen-presenting cells (APC), expression of RT1B as well as LFA-1 and MCP-1 in CD4(+) and CD8(+) T cells and levels of interleukin-17A were assessed. The oxidative stress was evaluated through lipid peroxidation (LPO) analysis on the plasma of thiobarbituric acid-reactive substances (TBARS) and nitric oxide production. Decreased concentrations of nitrite and TBARS were found in infected and melatonin-treated animals, as well as a rising trend in the production of IL-17A as compared to infected and untreated counterparts. A significant decrease was found in the percentages of CD4(+) and CD8(+) T lymphocytes MCP-1 producers for infected and melatonin-treated rats. Reduced percentage of CD8(+) T cells producing LFA-1 was observed in control and melatonin-treated animals as compared to untreated rats. The cellular response of peritoneal APC cells and macrophages significantly dropped in infected and treated animals. As an endpoint, the use of antioxidant compounds such as melatonin emerges as a new and promising approach to control the oxidative stress during the chronic Chagas' disease partially mediated through the abrogation of LPO and the prevention of the inflammatory response and can be used for further investigation on treatment trials for other infectious diseases.

Inter-relationships of the chronobiotic, melatonin, with leptin and adiponectin: implications for obesity

Obesity and its medical complications represent a significant problem throughout the world. In recent decades, mechanisms underlying the progression of obesity have been intensively examined. The involvement of both the behavioral aspects, such as calorie-rich diet, low physical activity and sleep deprivation, and the intrinsic factors, including adipose tissue deregulation, chronic inflammation, oxidative stress, and chronodisruption, has been identified. The circadian disturbances of the adipose tissue endocrine function have been correlated with obesity. Leptin and adiponectin are adipokines strongly associated with glucose and lipid metabolism and with energy balance. Their synthesis and secretion display circadian rhythms that are disturbed in the obese state. Hyperleptinemia resulting in leptin resistance, and hypo-adiponectinemia have been linked to the pathophysiology of the obesity-related disorders. A deficiency of melatonin, one of the consequences of sleep deprivation, has also been demonstrated to correlate with obesity. Melatonin is a pineal secretory product involved in numerous actions, such as regulation of internal biological clocks and energy metabolism, and it functions as an antioxidant and as an anti-inflammatory agent. There exists a substantial amount of evidence supporting the beneficial effects of melatonin supplementation on obesity and its complications. In the current review, the results of studies related to the interactions between melatonin, and both leptin and adiponectin are discussed. Despite the existence of some inconsistencies, melatonin has been found to normalize the expression and secretion patterns of both adipokines. These results support the concept of melatonin as a potential therapeutic agent for obesity and related disorders.

Functions of melatonin in plants: a review

The number of studies on melatonin in plants has increased significantly in recent years. This molecule, with a large set of functions in animals, has also shown great potential in plant physiology. This review outlines the main functions of melatonin in the physiology of higher plants. Its role as antistress agent against abiotic stressors, such as drought, salinity, low and high ambient temperatures, UV radiation and toxic chemicals, is analyzed. The latest data on their role in plant-pathogen interactions are also discussed. Both abiotic and biotic stresses produce a significant increase in endogenous melatonin levels, indicating its possible role as effector in these situations. The existence of endogenous circadian rhythms in melatonin levels has been demonstrated in some species, and the data, although limited, suggest a central role of this molecule in the day/night cycles in plants. Finally, another aspect that has led to a large volume of research is the involvement of melatonin in aspects of plant development regulation. Although its role as a plant hormone is still far of from being fully established, its involvement in processes such as growth, rhizogenesis, and photosynthesis seems evident. The multiple changes in gene expression caused by melatonin point to its role as a multiregulatory molecule capable of coordinating many aspects of plant development. This last aspect, together with its role as an alleviating-stressor agent, suggests that melatonin is an excellent prospect for crop improvement.

Oxidative stress-induced methemoglobinemia is the silent killer during snakebite: a novel and strategic neutralization by melatonin

Oxidative stress-induced methemoglobinemia remained an untouched area in venom pharmacology till date. This study for the first time explored the potential of animal venoms to oxidize hemoglobin to methemoglobin. In in vitro whole-blood assay, methemoglobin forming ability of venoms varied as Naja naja > Ophiophagus hannah > Echis carinatus > Daboia russellii > Apis mellifera > Mesobuthus tamulus > Hippasa partita. Being highly potential, N. naja venom was further studied to observe methemoglobin formation in RBCs and in combinations with PMNs and PBMCs, where maximum effect was observed in RBCs + PMNs combination. Naja naja venom/externally added methemoglobin-induced methemoglobin formation was in parallel with ROS generation in whole blood/RBCs/RBCs + PMNs/RBCs + PBMCs. In in vivo studies, the lethal dose (1 mg/kg body weight, i.p.) of N. naja venom readily induced methemoglobin formation, ROS generation, expression of inflammatory markers, and hypoxia-inducible factor-3α. Although the mice administered with three effective doses of antivenom recorded zero mortality; the methemoglobin and ROS levels remained high. However, one effective dose of antivenom when administered along with melatonin (1:50; venom/melatonin, w/w), not only offered 100% survival of experimental mice, but also significantly reduced methemoglobin level, and oxidative stress markers including hypoxia-inducible factor-3α. This study provides strong drive that, complementing melatonin would not only reduce the antivenom load, but for sure greatly increase the success rate of antivenom therapy and drastically minimize the global incidence of snakebite deaths. However, further detailed investigations are needed before translating the combined therapy towards the bed side.

Melatonin attenuates carbon tetrachloride-induced liver fibrosis via inhibition of necroptosis

We investigated the protective mechanisms of melatonin (MLT) associated with necroptosis signaling and damage-associated molecular patterns, which are mediated by the activation of pattern recognition receptors in liver fibrosis. Rats were given an intraperitoneal injection of carbon tetrachloride (CCl4) dissolved in olive oil (1:3, vol/vol) twice a week (0.5 mL/kg) for 8 weeks. During this period, MLT was administered orally at 2.5, 5, and 10 mg/kg once a day. Chronic CCl4 administration increased hepatic hydroxyproline content and hepatocellular damage. MLT attenuated these increases. The expression levels of transforming growth factor β1 and α-smooth muscle actin that were increased by chronic CCl4 exposure were attenuated by MLT. CCl4 significantly increased receptor-interacting protein 1 (RIP1) expression, the formation of the RIP1 and RIP3 necrosome complex, and the level of mixed lineage kinase domain-like protein in liver tissue, which were attenuated by MLT. MLT also attenuated CCl4-induced increases in serum high-mobility group box 1 (HMGB1) and interleukin 1α, as well as the interaction between HMGB1 receptors for advanced glycation end products (RAGE). The increases in toll-like receptor 4 expression, p38, c-Jun N-terminal kinases phosphorylation, and nuclear factor κB translocation were suppressed by MLT. MLT attenuated the overexpression of RAGE, increased level of early growth response protein 1, and increased messenger RNA level of macrophage inflammatory protein 2. Our findings suggest MLT may prevent liver fibrosis by inhibiting necroptosis-associated inflammatory signaling.