ArticleLiterature Review

Melatonin and its Relationships with Diabetes and Obesity: A Literature Review

Authors:
  • IPEMED Medical School
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Abstract

Significance Obesity is a multifactorial disease with many risks to public health, affecting 39.6% of American adults and 18.5% of young people. Brazil ranks fifth in the world ranking, with about 18 million obese people. It is estimated that 415 million people live with diabetes in the world, which is roughly 1 in 11 of the world's adult population. This is expected to rise to 642 million people living with diabetes worldwide by 2040. In this scenario, Melatonin has evidenced an important function in the regulation of energy metabolism. Objective to carry out a broad narrative review of the literature on the main aspects of the influence of melatonin on Diabetes Mellitus and obesity. Methods Article reviews, systematic reviews, prospective studies, retrospective studies, randomized, double-blind, placebo-controlled trials in humans recently published were selected and analyzed. A total of 368 articles were collated and submitted to the eligibility analysis. Subsequently, 215 studies were selected to compose the textual part of the manuscript and 153 to compose the Narrative Review. Results and final considerations Studies suggest a possible role of melatonin in metabolic diseases such as obesity, T2DM and metabolic syndrome. Intervention studies using this hormone in metabolic diseases are still unclear regarding a possible benefit of it. There is so far no consensus about a possible role of melatonin as an adjuvant in the treatment of metabolic diseases. More studies are necessary to define possible risks and benefits of melatonin as a therapeutic agent.

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Circadian rhythms are ubiquitous in biological systems and control metabolic processes throughout the body. Misalignment of these circadian rhythms increases risk of developing metabolic diseases. Thus, disruption of the circadian system has been proven to affect onset of type 2 diabetes mellitus (T2DM). In this context, the pineal indoleamine melatonin is a signaling molecule able to entrain circadian rhythms. There is mounting evidence that suggests a link between disturbances in melatonin production and impaired insulin, glucose, lipid metabolism, and antioxidant capacity. Besides, several genetic association studies have causally associated various single nucleotide polymorphysms (SNPs) of human MT2 receptor with increased risk of developing T2DM. Taken together, these data suggest that endogenous as well as exogenous melatonin may influence diabetes and associated metabolic disturbances not only by regulating insulin secretion, but also by providing protection against reactive oxygen species (ROS), since pancreatic β-cells are very susceptible to oxidative stress due to their low antioxidant capacity.
Article
Circadian misalignment is hypothesized to contribute to increased diabetes and obesity among shift workers and individuals with late sleep timing. Accordingly, the goal of our study was to identify-among normal and overweight/obese adults-associations between circadian timing (dim light melatonin onset; DLMO) and circadian misalignment (the interval between DLMO and sleep onset) with metabolic disease risk. This was a secondary analysis of data from a larger study. Participants ages 18 to 50 years without depression, diabetes, or shift work, with sleep duration 6.5 h or more, completed the following evaluations: 7 days of wrist actigraphy, circadian timing assessment (DLMO), and a fasting blood draw to measure glucose and insulin and calculate the Homeostatic Model of Assessment-Insulin Resistance (HOMA-IR). Data were analyzed using correlation and regression analyses controlling for age, sex, DLMO, and sleep duration. Analyses were conducted for the entire sample ( n = 54) and stratified by normal weight ( n = 36) and overweight/obese groups ( n = 18). Mean age was 26.4 years (SD = 7.1 years). Average sleep duration was 436.2 min (SD = 55.1 min), DLMO was 2250h (SD = 01:31), and interval between DLMO and sleep onset was 2 h 18 min (SD = 53 min). Average BMI was 24.3 kg/m2 (SD = 4.5 kg/m2). Circadian timing and interval between DLMO and sleep onset were not associated with glucose, insulin, or HOMA-IR in the main analyses. Among overweight/obese participants, a shorter interval between DLMO and sleep onset was associated with higher insulin ( B[SE] = -5.12 [2.24], p = 0.04) and HOMA-IR ( B[SE] = -1.32 [0.57], p = 0.04). Results of our multivariable model indicated that among overweight/obese participants, insulin was 5.1 pmol/L higher and HOMA was 1.3 µU/mL higher for every hour closer that sleep onset was to DLMO. The strengths of this study include the use of objective measures of circadian timing, but results should be considered hypothesis generating due to the small sample size and use of subgroup analyses.
Article
Diabetic retinopathy (DR), a microvascular complication of diabetes mellitus (DM), remains as one of the major causes of vision loss worldwide. The release of pro-inflammatory cytokines and the adhesion of leukocytes to retinal capillaries are initial events in DR development. Inflammation, ER stress, oxidative stress and autophagy are major causative factors involved in the pathogenesis of DR. Diabetes associated hyperglycemia leads to mitochondrial electron transport chain dysfunction culminating in a rise in ROS generation. Since mitochondria are the major source of ROS production, oxidative stress induced by mitochondrial dysfunction also contributes to the development of diabetic retinopathy. Autophagy increases in the retina of diabetic patients and is regulated by ER stress, oxidative stress and inflammation-related pathways. Autophagy functions as a double-edged sword in DR. Under mild stress, autophagic activity can lead to cell survival while during severe stress, dysregulated autophagy results in massive cell death and may have a role in initiation and exacerbation of DR. Melatonin and its metabolites play protective roles against inflammation, ER stress and oxidative stress due to their direct free radical scavenger activities and indirect antioxidant activity via the stimulation antioxidant enzymes including glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase. Melatonin also acts as a cell survival agent by modulating autophagy in various cell types and under different conditions through amelioration of oxidative stress, ER stress and inflammation. Herein, we review the possible effects of melatonin on diabetic retinopathy, focusing on its ability to regulate autophagy processes.
Article
Background & aims: Melatonin supplementation may be associated with blood lipids improvement; however, the current evidence from randomized controlled trials (RCTs) is inconsistent. The present study aimed to systematically review and analyze RCTs assessing the effects of melatonin supplementation on blood lipids. Methods: A comprehensive literature search in several database was performed up to January 2017. Quantitative data synthesis was performed using a fixed or random-effects model, with weight mean difference (WMD) and 95% confidence intervals (CI). Standard methods were used for assessment of heterogeneity, meta-regression, sensitivity analysis and publication bias. Results: A total of 8 RCTs were eligible. Meta-analysis suggested a significant association between melatonin supplementation and a reduction in triglycerides (WMD: -31.54 mg/dL, 95% CI: -50.71, -12.38, p = 0.001), and total cholesterol levels (WMD: -18.48 mg/dL, 95% CI: -35.33, -1.63, p = 0.032), while no significant effect on LDL-C (WMD: -2.37 mg/dL, 95% CI: -11.61, -6.86, p = 0.615) and HDL-C (WMD: 1.28 mg/dL, 95% CI: -0.66, 3.23, p = 0.197) was found. In sub-group analysis, a significant decrease in triglycerides was found at doses ≥8 mg/d and when trials last ≥8 weeks. In addition, a significant decrease of total cholesterol was found at doses ≥8 mg/d and when total cholesterol baseline levels were ≥200 mg/dL. Conclusions: Melatonin supplementation has significant effects on triglycerides and total cholesterol levels, which was more evident in higher dose and longer duration and also in a higher concentration of cholesterol levels. Further studies are required to determine the benefits of melatonin on lipid profile.
Article
Aim: To investigate the effect of glucocorticoids on BAT function in humans MATERIALS & METHODS: In a randomised double-blind cross-over design, 13 healthy adults underwent 1 week of oral prednisolone (15mg/day) and placebo treatment with an intervening 2-week wash-out period. BAT function was assessed in response to cooling (19(0) C) and to a standardised meal, by measuring fluoro-deoxyglucose (FDG) uptake using Positron Emission Tomography-Computed Tomography and skin temperatures overlying the supraclavicular (SCL) BAT depots using infrared thermography. Postprandial energy and substrate metabolism was assessed by indirect calorimetry. Results: During cooling, prednisolone significantly reduced BAT FDG uptake (standardised uptake value, SUVmax, 6.1±2.2 vs 3.7±1.2; P<0.05) and SCL temperature (-0.45±0.1 vs -1.0±0.1(0) C; P<0.01) compared to placebo. Postprandially, prednisolone significantly blunted the rise in SCL temperature (+0.2±0.1 vs -0.3±0.1(0) C; P<0.05), enhanced energy production (+221±17 vs +283±27 kcal/day; P<0.01) and lipid synthesis (+16.3±3.2 vs +23.6±4.9 mg/min; P<0.05). The prednisolone-induced reduction in SCL temperature significantly correlated with the reduction in FDG uptake (r=0.65, P<0.05), while the increase in energy production significantly correlated with the increase in lipogenesis (r=0.6, P<0.05). Conclusion: Prolonged glucocorticoid suppresses the function of human BAT. The enhancement of energy production and lipogenesis in the face of reduced dissipation of energy as heat suggests that glucocorticoids channel energy towards fat storage after nutrient intake. This is a novel mechanism of glucocorticoid-induced obesity.
Article
Physiological levels of glucocorticoids are required for proper metabolic control, and excessive glucocorticoid action has been linked to a variety of pandemic metabolic diseases. microRNA (miRNA)-19b plays a critical role in the pathogenesis of glucocorticoid-induced metabolic diseases. This study sought to explore the potential of miRNA-based therapeutics targeting adipose tissue. Our results showed that overexpressed miR-19b in stromal vascular fraction cells derived from subcutaneous adipose tissue had the same effects as dexamethasone treatment on the inhibition of adipose browning and oxygen consumption rate. The inhibition of miR-19b blocked dexamethasone -mediated suppression of the expression of browning marker genes as well as the oxygen consumption rate in differentiated stromal vascular fraction cells derived from subcutaneous and brown adipose tissue. While overexpressed miR-19b in stromal vascular fraction cells derived from brown adipose tissue also had the same effects as dexamethasone treatment on the inhibition of brown adipose differentiation and energy expenditure. Glucocorticoids transcriptionally regulate the expression of miR-19b via a glucocorticoid receptor-mediated direct DNA binding mechanism. This study confirmed that miR-19b is an essential target for glucocorticoid-mediated control of adipose tissue browning. It is hoped that the plasticity of the adipose organ can be exploited in the next generation of therapeutic strategies to combat the increasing incidence of metabolic diseases, including obesity and diabetes.
Article
Introduction: The use of second-generation atypical antipsychotics has an increasing role in the development of metabolic syndrome. However, these medications due to metabolic disorders can lead to an increased risk of cardiovascular disease and subsequently mortality as well as reduced adherence to treatment. The main objective of current study was to determine the ability of melatonin to reduce the metabolic effects of second-generation antipsychotics. Methods: This double blind controlled clinical trial was conducted on 100 patients aged 18-64 years old were treated with the second-generation antipsychotics for the first time. The patients were divided randomly into two groups of 50. The case group received slow-release melatonin at a dose of 3mg and the control group was given oral placebo at 8 p.m. Results: The findings in melatonin group indicated significantly increase of HDL and decreased fasting blood sugar and systolic blood pressure, as well as had statistically significant increase in waist circumference, weight and BMI compared with placebo group. Conclusion: According to the findings, it can be claimed that the addition of melatonin to atypical antipsychotics has led to a reduction in some of the metabolic effects of these drugs. In this study, HDL level was increased, and the mean systolic blood pressure and FBS were decreased in the melatonin group. Considering that these factors are contributing to cardiovascular disease as a leading cause of mortality in psychiatric patients, so the use of melatonin can reduce some of the medical effects of long-term treatment of atypical antipsychotics.
Article
Changes in photoperiod length are transduced into neuroendocrine signals by melatonin (MEL) secreted by the pineal gland triggering seasonally adaptive responses in many animal species. Siberian hamsters, transferred from a long-day ‘summer-like’ photoperiod (LD) to a short-day ‘winter-like’ photoperiod (SD), exhibit a naturally-occurring reversal in obesity. Photoperiod-induced changes in adiposity are mediated by the duration of MEL secretion and can be mimicked by exogenously administered MEL into animals housed in LD. Evidence suggests that MEL increases the sympathetic nervous system (SNS) drive to white adipose tissue (WAT). Here, we investigated whether MEL-driven seasonally adaptive losses in body fat are associated with WAT lipolysis and browning. Hamsters were subcutaneously administered vehicle (LD + VEH) or 0.4 mg/kg MEL (LD + MEL) daily for 10 weeks while animals housed in SD served as a positive control. MEL and SD exposure significantly decreased the retroperitoneal (RWAT), inguinal (IWAT), epididymal (EWAT) WAT, food intake and caused testicular regression compared with the LD + VEH group. MEL/SD induced lipolysis in the IWAT and EWAT, browning of the RWAT, IWAT, and EWAT, and increased UCP1 expression in the IBAT. Additionally, MEL/SD significantly increased the number of shared MEL receptor 1a and dopamine beta-hydroxylase-immunoreactive neurons in discrete brain sites, notably the paraventricular hypothalamic nucleus, dorsomedial hypothalamic nucleus, arcuate nucleus, locus coeruleus and dorsal motor nucleus of vagus. Collectively, these findings support our hypothesis that SD-exposed Siberian hamsters undergo adaptive decreases in body adiposity due to SNS-stimulated lipid mobilization and generalized WAT browning.
Article
Objective: Melatonin has been widely studied in the treatment of sleep disorders and evidence is accumulating on a possible role for melatonin influencing mood. Our aim was to determine the efficacy and acceptability of melatonin for mood disorders. Method: We conducted a comprehensive systematic review of randomized clinical trials on patients with mood disorders, comparing melatonin to placebo. Results: Eight clinical trials were included; one study in bipolar, three in unipolar depression and four in seasonal affective disorder. We have only a small study on patients with bipolar disorder, while we have more studies testing melatonin as an augmentation strategy for depressive episodes in major depressive disorder and seasonal affective disorder. The acceptability and tolerability were good. We analyzed data from three trials on depressive episodes and found that the evidence for an effect of melatonin in improving mood symptoms is not significant (SMD = 0.37; 95% CI [-0.05, 0.37]; P = 0.09). The small sample size and the differences in methodology of the trials suggest that our results are based on data deriving from investigations occurring early in this field of study. Conclusion: There is no evidence for an effect of melatonin on mood disorders, but the results are not conclusive and justify further research.
Article
DNA repair is responsible for maintaining the integrity of the genome. Perturbations in the DNA repair pathways have been identified in several human cancers. Thus, compounds targeting DNA damage response (DDR) hold great promise in cancer therapy. A great deal of effort, in pursuit of new anticancer drugs, has been devoted to understanding the basic mechanisms and functions of the cellular DNA repair machinery. Melatonin, a widely-produced indoleamine in all organisms is associated with a reduced risk of cancer and has multiple regulatory roles on the different aspects of the DDR and DNA repair. Herein, we have mainly discussed how defective components in different DNA repair machineries, including homologous recombination (HR), non-homologous end joining (NHEJ), base excision repair (BER), nucleotide excision repair (NER) and finally DNA mismatch repair (MMR) can contribute to the risk of cancer. Melatonin biosynthesis, mode of action and antioxidant effects are reviewed along with the means by which the indoleamine regulates DDR at the transduction, mediation and functional levels. Finally, we summarize recent studies which illustrate how melatonin can be combined with DNA damaging agents to improve their efficacy in cancer therapy. This article is protected by copyright. All rights reserved.
Article
Objectives: We aimed to evaluate melatonin effectiveness in weight gain reduction following olanzapine use for 11-17-year-old bipolar disorder patients. Experimental design: Seventy-seven adolescent outpatients, subsequent to their initial diagnosis of bipolar I disorder by a psychiatrist, entered this study. After assessing inclusion and exclusion criteria, 48 patients consented to participate. Twenty-four patients were allocated to receive olanzapine, lithium carbonate, and melatonin, and 24 patients were allocated to receive olanzapine, lithium carbonate, and placebo by simple randomization. The Young Mania Rating Scale (YMRS) was performed at baseline. Before treatment and after 6 and 12 weeks of treatment, weight, height, and body mass index (BMI) were measured. Analysis of variance (ANOVA) with repeated measure and t-test were used to analyze data. Principal observations: Nineteen patients in each group finished the study and their data were entered for analysis. Mean rise in BMI in the melatonin group compared with placebo (2.45 vs. 3.25 respectively) was marginally significant (t = 1.936; df = 36; p = 0.061). ANOVA with repeated measure also showed a marginally significant difference (F = 3.74; df = 1; p = 0.061) between groups and across time in regard to BMI. Mean body weight rise in the melatonin group compared with the placebo group (5.8 kg vs. 8.2 kg respectively) was marginally significant (t = 1.923; df = 28; p = 0.065). ANOVA with repeated measure also showed a marginally significant difference (F = 3.73; df = 1.1; p = 0.056) between groups and across time for body weight. Conclusions: Coadministration of melatonin with olanzapine and lithium carbonate in adolescents with bipolar disorder could reduce the sharp weight gain side effect of these drugs to near significance.
Article
Exposure to Artificial Light At Night (ALAN) results in a disruption of the circadian system, which is deleterious to health. In industrialized countries, 75% of the total workforce is estimated to have been involved in shift work and night work. Epidemiologic studies, mainly of nurses, have revealed an association between sustained night work and a 50–100% higher incidence of breast cancer. The potential and multifactorial mechanisms of the effects include the suppression of melatonin secretion by ALAN, sleep deprivation, and circadian disruption.
Article
Epigenetic modifications, including methylation or acetylation as well as posttranscriptional modifications are mechanisms used by eukaryotic cells to increase the genome diversity in terms of differential gene expression and protein diversity. Among these modifying enzymes, sirtuins, a class III histone deacetylase (HDAC) enzymes are of particular importance. Sirtuins regulate the cell cycle, DNA repair, cell survival and apoptosis, thus having important roles in normal and cancer cells. Sirtuins can also regulate metabolic pathways by changing preference for glycolysis under aerobic conditions as well as glutaminolysis. These actions make sirtuins a major target in numerous physiological processes as well as in other contexts such as calorie restriction-induced antiaging, cancer or neurodegenerative disease. Interestingly melatonin, a nighttime-produced indole synthesized by pineal gland and many other organs, have important cytoprotective effects in many tissues including aging, neurodegerative diseases, immunomodulation and cancer. The pleiotropic actions of melatonin in different physiological and pathological conditions indicate that may be basic cellular targetd for the indole. Thus, much research has focused attention on the potential mechanisms of the indole in modulating expression and/or activity of sirtuins. Numerous findings report a rise in activity, especially on SIRT1, in a diversity of cells and animal models after melatonin treatment. This contrasts, however, with data reporting an inhibitory effect of melatonin on this sirtuin in some tumor cells. This review tabulates and discusses the recent findings relating melatonin with sirtuins, particularly SIRT1 and mitochondrial SIRT3, showing the apparent dichotomy with the differential actions documented in normal and in cancer cells. This article is protected by copyright. All rights reserved.
Article
Gestational diabetes mellitus (GDM) is glucose intolerance detected during pregnancy. The MTNR1B gene is the genetic locus associated with type 2 diabetes, that may affect insulin secretion and pancreatic glucose sensing. In this study, we examined the association between MTNR1A (rs2119882) and MTNR1B (rs10830963, rs4753426) gene polymorphisms and the risk of GDM. According to the results of their oral glucose tolerance test (OGTT), the women were divided into two groups: 204 pregnant women with GDM and 207 pregnant women with normal glucose tolerance (NGT). There were no statistically significant differences in the distribution of MTNR1A rs2119882 and MTNR1B rs4753426 genotypes and alleles between women with GDM and healthy pregnant women. With regard to the MTNR1B rs10830963 polymorphism, we observed a statistically significant prevalence of GG and CG genotypes and the G allele among pregnant women with GDM (GG + CG vs CC, OR 1.50, 95% CI 1.02-2.22, p = 0.04; G vs C, OR 1.43, 95% CI 1.07-1.90, p = 0.016). In a multivariate logistic regression analysis, a higher number of MTNR1B rs10830963 G alleles was an independent significant predictor of a higher risk of GDM. The results of our study indicate that MTNR1B rs10830963 polymorphism is associated with GDM susceptibility, and women with a higher number of G alleles have an increased risk of GDM development.
Article
Background Disturbance of the circadian rhythm has been associated with disease states, such as metabolic disorders, depression and cancer. Quantification of the circadian markers such as melatonin and cortisol critically depend on reliable and reproducible analytical methods. Previously, melatonin and cortisol were primarily analyzed separately, mainly using immunoassays. Methods Here we describe the validation and application of a high-throughput liquid chromatography in combination with mass spectrometry (LC-MS/MS) method for the combined analysis of melatonin and cortisol in plasma and saliva. The LC-MS/MS method was validated according to international validation guidelines. We used this method to analyze total plasma, free plasma (as obtained by equilibrium dialysis) and saliva melatonin and cortisol in healthy adults. Results Validation results for plasma and saliva melatonin and cortisol were well within the international validation criteria. We observed no difference between saliva collected by passive drooling or Salivette. Moreover, we noted a significant difference in saliva vs. free plasma melatonin. We observed on average 36% (95% CI: 4%–60%) higher salivary melatonin levels in comparison to free plasma melatonin, suggestive of local production of melatonin in the salivary glands. Conclusions The novel outcome of this study is probably due to the high precision of our LC-MS/MS assay. These outcomes illustrate the added value of accurate and sensitive mass spectrometry based methods for the quantification of neuroendocrine biomarkers.
Article
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Article
Type 2 diabetes (T2D) is a global pandemic. Genome-wide association studies (GWASs) have identified >100 genetic variants associated with the disease, including a common variant in the melatonin receptor 1 b gene (MTNR1B). Here, we demonstrate increased MTNR1B expression in human islets from risk G-allele carriers, which likely leads to a reduction in insulin release, increasing T2D risk. Accordingly, in insulin-secreting cells, melatonin reduced cAMP levels, and MTNR1B overexpression exaggerated the inhibition of insulin release exerted by melatonin. Conversely, mice with a disruption of the receptor secreted more insulin. Melatonin treatment in a human recall-by-genotype study reduced insulin secretion and raised glucose levels more extensively in risk G-allele carriers. Thus, our data support a model where enhanced melatonin signaling in islets reduces insulin secretion, leading to hyperglycemia and greater future risk of T2D. The findings also imply that melatonin physiologically serves to inhibit nocturnal insulin release.
Article
The metabolic syndrome (MS) is a collection of risk factors for cardiovascular disease, including obesity, hypertension, hyperinsulinemia, glucose intolerance and dyslipidemia. MS is associated with low-grade inflammation of the white adipose tissue, which can subsequently lead to insulin resistance, impaired glucose tolerance and diabetes. Adipocytes secrete proinflammatory cytokines as well as leptin and trigger a vicious circle which leads to additional weight gain largely as fat. The imbalance between inflammatory and anti-inflammatory signals is crucial to aging. Healthy aging can benefit from melatonin, a compound known to possess direct and indirect antioxidant properties, to have a significant protective effect on mitochondrial function, to enhance circadian rhythm amplitudes, to modulate the immune system and to exhibit neuroprotective actions. Melatonin levels decrease in the course of senescence and are more strongly reduced in diseases related to insulin resistance. This short review article analyzes the multiple protective actions of melatonin that are relevant to the attenuation of inflammatory responses and progression of inflammaging and how melatonin is effective to curtail MS in animal models of hyperadiposity. The clinical data supporting the possible therapeutical use of melatonin in human MS are also reviewed. Since attention has been focused on the development of potent melatonin analogs with prolonged effects (ramelteon, agomelatine, tasimelteon, piromelatine) and in clinical trials these analogs were administered in doses considerably higher than those usually employed for melatonin, clinical trials on melatonin in the range of 50-100 mg/day are needed to further assess its therapeutic value in MS.
Book
The book aims to cover basic physiologic functions of melatonin, and its therapeutic applications in humans for a variety of clinically relevant disorders. This book contains chapters on the recent aspects of melatonin physiology, its receptors and their role in mitochondrial function, its immunomodulatory role and importance in seasonal dependent diseases, role in human reproduction, role in sleep, circadian rhythm and sleep disorders, role in neurologic disorders such as Parkinson?s disease, Alzheimer?s disease. Additionally, melatonin?s therapeutic use in neurobehavioral disorders in children, migraine and tension headache is also covered in this book. Melatonin?s antioxidant role in Duchenne?s muscular dystrophy and in glaucoma have also been discussed in short chapters. Two major melatonin agonists, ramelteon and agomelatine are discussed extensively on their current clinical application and ongoing research. Two chapters on agomelatonin and its role in mood disorders, particularly depressive disorders, are an important feature of this book. The chapters are written by experts from the global academia recognized for their original research and published work in the field of melatonin science.
Article
We report the relationship between patterns of post-awakening salivary melatonin and cortisol secretion in healthy participants (n=51; mean age 21.6 ± 5.0 years). Saliva samples were collected within the domestic setting, at 0, 15, 30 and 45 min post-awakening on 2 consecutive typical weekdays. Analyses were undertaken on data with electronically verified sample timing accuracy (< 5 min delay between awakening and the start of saliva sampling). Melatonin secretion declined linearly by an average of 29% within the first 45 minutes post-awakening. In contrast there was a marked 112% surge in cortisol, characteristic of the cortisol awakening response. No day-differences in melatonin or cortisol secretion were observed but melatonin concentrations were lower with later awakening. Despite contrasting post-awakening changes in these hormones there was a lack of relationship between overall levels or patterns of melatonin and cortisol during this period.
Article
Melatonin is a powerful antioxidant. Decreased melatonin excretion has been reported to be associated with several oxidative stress-related diseases. The urinary metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s), has proved to be a very reliable index of melatonin production. The present study aims to evaluate the level of urinary aMT6s in patients with type 2 diabetes mellitus and diabetic retinopathy. Urine samples were collected from 10 patients with diabetes and no diabetic retinopathy (NDR), 19 patients with nonproliferative diabetic retinopathy (NPDR), 38 patients with proliferative diabetic retinopathy (PDR), and 16 subjects without diabetes mellitus, who served as controls. The level of aMT6s in specimens was assayed by a commercial aMT6s ELISA kit, creatinine levels were also measured for each sample to get urinary aMT6s/creatinine ratio. Creatinine-adjusted urinary aMT6s values were compared among four groups. The urinary aMT6s (mean ± SD) levels were 9.95 ± 2.42, 9.90 ± 2.28, 8.40 ± 1.84 and 5.58 ± 1.33 ng/mg creatinine in the controls and in patients with NDR, NPDR, or PDR, respectively. The urinary aMT6s level of the PDR group was significantly lower than that of the control, NDR and DR groups. No significant difference was found among the control, NDR and DR groups. After adjustment for various factors (age, smoking, cancer, and coronary heart disease) that may influence the aMT6s level, the odds-ratio of urinary aMT6s comparing PDR patients to controls was 0.246 (95% confidence interval = 0.108-0.558, P = 0.001). Therefore, the urinary aMT6s level is significantly decreased in diabetic patients with PDR but not in diabetic patients without PDR, which indicates that decreased urinary aMT6s level may be associated with the pathogenesis of PDR.
Article
Objective: Apart from regulating the circadian rhythm, melatonin exerts a variety of actions in the living organism. Among these functions, melatonin is believed to have a positive effect on body weight and energy metabolism. So far, the evidence for this relies mainly on animal models. In this study we aimed to determine the effects of melatonin on body composition, lipid and glucose metabolism in humans. Design/methods: In a double blind, placebo controlled study we randomised 81 post-menopausal women to one year of treatment with melatonin (1 or 3mg nightly) or placebo. Body composition was measured by DXA. Measures were obtained at baseline and after one year of treatment along with leptin, adiponectin and insulin. Markers of glucose homeostasis were measured at the end of the study. Results: In response to treatment, fat mass decreased in the melatonin group by 6.9% (95%CI: 1.4%; 12.4%, p=0.02) compared to placebo. A borderline significant increase in lean mass of 5.2% was found in the melatonin group compared to placebo (3.3%, (IQR:-1.7; 6.2) vs. -1.9%, (IQR:-5.7; 5.8), p=0.08). After adjusting for BMI, lean mass increased by 2.6% (95%CI: 0.1; 5.0, p=0.04) in the melatonin group. Changes in body weight and BMI did not differ between groups. Adiponectin increased borderline significantly by 21% in the melatonin group compared to placebo (p=0.08). No significant changes were observed for leptin, insulin, or markers of glucose homeostasis. Conclusion: Our results suggest a possibly beneficial effect of melatonin on body composition and lipid metabolism as one year of treatment reduces fat mass, increases lean mass and is associated with a trend towards an increase in adiponectin. This article is protected by copyright. All rights reserved.
Article
We investigated the association between rs4753426 single nucleotide polymorphisms in the melatonin receptor 1B (MTNR1B) gene and the risk of developing gestational diabetes mellitus (GDM). A total of 516 gravidas (186 with GDM and 330 non-diabetic controls) were enrolled in the study. Genotype and allele frequencies of rs4753426 in the MTNR1B gene were detected by DNA sequencing. Fasting plasma glucose and fasting insulin levels were measured to calculate the homeostasis model assessment for insulin resistance (HOMA-IR) and for β-cell function. Three genotypes (CC, CT, and TT) were found in both groups. The frequencies of CC, CT, and TT genotypes for the GDM group were 70.97, 22.58, and 6.45% vs 53.03, 39.70, and 7.27% in the control group, respectively. Significant differences were observed in genotype frequencies between groups (P < 0.05). T and C allele frequencies in the GDM group were 17.74 and 82.26%, respectively, and in the control group were 27.12 and 72.88%, respectively. Significant differences in T and C allele frequencies were found between groups (P < 0.05). In the GDM group, the C allele was associated with increased fasting plasma glucose level and reduced pancreatic β-cell function (P < 0.05). There were no significant differences in total cholesterol, triglyceride, low-density lipoprotein, high-density lipoprotein concentration, or HOMA-IR between groups (P > 0.05). The single nucleotide polymorphism rs4753426 in MTNR1B may be a susceptibility gene locus for GDM, and the C allele may contribute to the increased fasting plasma glucose level and reduced pancreatic β-cell function.
Article
Daily variations of metabolism, physiology and behaviour are controlled by a network of coupled circadian clocks, comprising a master clock in the suprachiasmatic nuclei of the hypothalamus and a multitude of secondary clocks in the brain and peripheral organs. Light cues synchronize the master clock that conveys temporal cues to other body clocks via neuronal and hormonal signals. Feeding at unusual times can reset the phase of most peripheral clocks. While the neuroendocrine aspect of circadian regulation has been underappreciated, this review aims at showing that the role of hormonal rhythms as internal time-givers is the rule rather than the exception. Adrenal glucocorticoids, pineal melatonin and adipocyte-derived leptin participate in internal synchronization (coupling) within the multi-oscillatory network. Furthermore, pancreatic insulin is involved in food synchronization of peripheral clocks, while stomach ghrelin provides temporal signals modulating behavioural anticipation of mealtime. Circadian desynchronization induced by shift work or chronic jet lag has harmful effects on metabolic regulation, thus favouring diabetes and obesity. Circadian deregulation of hormonal rhythms may participate in internal desynchronization and associated increase in metabolic risks. Conversely, adequate timing of endocrine therapies can promote phase-adjustment of the master clock (e.g. via melatonin agonists) and peripheral clocks (e.g. via glucocorticoid agonists). © 2015 John Wiley & Sons Ltd.
Article
Temporal organization plays a key role in humans, and presumably all species on Earth. A core building block of the chronobiological architecture is the master clock, located in the suprachi asmatic nuclei [SCN], which organizes "when" things happen in sub-cellular biochemistry, cells, organs and organisms, including humans. Conceptually, time messenging should follow a 5 step-cascade. While abundant evidence suggests how steps 1 through 4 work, step 5 of "how is central time information transmitted througout the body?" awaits elucidation. Step 1: Light provides information on environmental (external) time; Step 2: Ocular interfaces between light and biological (internal) time are intrinsically photosensitive retinal ganglion cells [ipRGS] and rods and cones; Step 3: Via the retinohypothalamic tract external time information reaches the light-dependent master clock in the brain, viz the SCN; Step 4: The SCN translate environmental time information into biological time and distribute this information to numerous brain structures via a melanopsin-based network. Step 5: Melatonin, we propose, transmits, or is a messenger of, internal time information to all parts of the body to allow temporal organization which is orchestrated by the SCN. Key reasons why we expect melatonin to have such role include: First, melatonin, as the chemical expression of darkness, is centrally involved in time- and timing-related processes such as encoding clock and calendar information in the brain; Second, melatonin travels throughout the body without limits and is thus a ubiquitous molecule. The chemial conservation of melatonin in all tested species could make this molecule a candidate for a universal time messenger, possibly constituting a legacy of an all-embracing evolutionary history.
Article
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