Melatonin Effects on Glucose Metabolism: Time To Unlock the Controversy

Fasting as an intervention to alter the impact of simulated night-shift work on glucose metabolism in healthy adults: a cluster randomised controlled trial

AIMS/HYPOTHESIS

Night-shift work causes circadian misalignment and impairs glucose metabolism. We hypothesise that food intake during night shifts may contribute to this phenomenon.

METHODS

This open-label, multi-arm, single-site, parallel-group controlled trial involved a 6 day stay at the University of South Australia's sleep laboratory (Adelaide, SA, Australia). Healthy, non-shift-working adults without obesity (N=55; age 24.5 ± 4.8 years; BMI 24.8 ± 2.8 kg/m2) were assigned to the next available run date and cluster randomised (1:1:1) to fasting-at-night (N=20), snack-at-night (N=17), or meal-at-night (N=18) conditions. One participant withdrew from each group, prior to starting the study. Due to study design, neither participants nor people collecting their measurements could be blinded. Statistical and laboratory staff were concealed to study allocation. Participants were fed at calculated energy balance, with the macronutrient composition of meals being similar across conditions. The primary outcomes were a linear mixed-effects model of glucose, insulin and NEFA AUC in response to a 75 g OGTT that was conducted prior to and after 4 consecutive nights of shift work plus 1 night of recovery sleep. Insulin sensitivity, insulinogenic and disposition indexes were also calculated.

RESULTS

Night-shift work impaired insulin sensitivity, as measured by insulin AUC (p=0.035) and the insulin sensitivity index (p=0.016) across all conditions. Insulin secretion, as measured by the insulinogenic index, was increased in the fasting-at-night condition only (p=0.030), resulting in a day×condition interaction in glucose AUC (p<0.001) such that glucose tolerance was impaired in the meal-at night (+2.00 [95% CI 1.45, 2.56], p<0.001) and snack at-night (+0.96 [0.36, 1.56], p=0.022) conditions vs the fasting-at-night (+0.34 [-0.21, 0.89]) condition. A day×condition interaction was also observed in NEFA AUC (p<0.001), being higher in the meal-at-night (+0.07 [0.03, 0.10]. p=0.001) and snack-at-night (0.01 [-0.03, 0.05], p=0.045) conditions vs the fasting-at-night condition (-0.02 [-0.06, 0.01]). No adverse events occurred.

CONCLUSIONS/INTERPRETATION

The timing of food intake has a critical effect on glucose metabolism during simulated night-shift work, which was readily amendable to a meal re-timing intervention.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR) ACTRN12616001556437 FUNDING: This work was funded by the National Health and Medical Research Council (NHMRC), APP1099077.

Circadian rhythms, metabolism, and nutrition support in critically ill adult patients: a narrative review

PURPOSE OF REVIEW

The human circadian system regulates several physiological processes, including metabolism, which becomes significantly disrupted during critical illness. The common use of 24-h continuous nutrition support feeding in the intensive care unit (ICU) may further exacerbate these disruptions; this review evaluates recent evidence comparing continuous and intermittent feeding schedules in critically ill adults.

RECENT FINDINGS

Research comparing different feeding schedules in critically ill adults remains limited. Recent meta-analyses suggest that continuous and intermittent feeding schedules in the ICU have comparable adverse event profiles, including gastrointestinal intolerance. A retrospective study found that continuous feeding did not impact the 24-h glucose variation in critically ill adults, and a randomized controlled trial reported no significant differences in amino acid, lipid-based, or small molecule metabolite profiles between the two feeding regimens. Potential benefits of intermittent feeding include stimulation of muscle protein synthesis, preservation of normal hormone secretion, and improved attainment of nutritional goals.

SUMMARY

Current evidence suggests comparable safety profiles for continuous and intermittent feeding schedules in critically ill adult patients. However, intermittent and daytime cyclic feeding are expected to align more closely with normal circadian physiology. Given the lack of existing supportive data, a dynamic approach - transitioning from continuous feeding in the early-acute metabolic phase to intermittent feeding or daytime cyclic feeding - may be appropriate.

The Detoxification Effects of Melatonin on Aflatoxin-Caused Toxic Effects and Underlying Molecular Mechanisms

Aflatoxins (AFTs) are a form of mycotoxins mainly produced by Aspergillus flavus and Aspergillus parasiticus, which are common contaminants in various agricultural sources such as feed, milk, food, and grain crops. Aflatoxin B1 (AFB1) is the most toxic one among all AFTs. AFB1 undergoes bioactivation into AFB1-8,9-epoxide, then leads to diverse harmful effects such as neurotoxicity, carcinogenicity, hepatotoxicity, reproductive toxicity, nephrotoxicity, and immunotoxicity, with specific molecular mechanisms varying in different pathologies. The detoxification of AFB1 is of great importance for safeguarding the health of animals and humans and has increasingly attracted global attention. Recent research has shown that melatonin supplementation can effectively mitigate AFB1-induced multiple toxic effects. The protection mechanisms of melatonin involve the inhibition of oxidative stress, the upregulation of antioxidant enzyme activity, the reduction of mitochondrial dysfunction, the inactivation of the mitochondrial apoptotic pathway, the blockade of inflammatory responses, and the attenuation of cytochrome P450 enzymes' expression and activities. In summary, this review sheds new light on the potential role of melatonin as a potential detoxifying agent against AFB1. Further exploration of the precise molecular mechanisms and clinical efficacy of this promising treatment is urgently needed.

Circadian Deregulation: Back Facing the Sun Toward Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) Development

Earth's rotation around its axis has pressured its inhabitants to adapt to 24 h cycles of day and night. Humans adapted their own circadian rhythms to the Earth's rhythms with a light-aligned awake-sleep cycle. As a consequence, metabolism undergoes drastic changes throughout the circadian cycle and needs plasticity to cope with opposing conditions in the day (when there is an increase in energy demands and food availability), and during the night (when prolonged fasting couples with cyclic changes in the energy demands across the sleep stages). In the last century, human behavior changed dramatically with a disregard for the natural circadian cycles. This misalignment in sleep and eating schedules strongly modulates the metabolism and energy homeostasis, favoring the development of obesity, metabolic syndrome, and metabolic dysfunction-associated steatotic liver disease (MASLD). This review summarizes the effects of circadian disruption, with a particular focus on the feeding and sleep cycles in the development of MASLD and hepatocellular carcinoma.

The real-world association between digital markers of circadian disruption and mental health risks

While circadian disruption is recognized as a potential driver of depression, its real-world impact is poorly understood. A critical step to addressing this is the noninvasive collection of physiological time-series data outside laboratory settings in large populations. Digital tools offer promise in this endeavor. Here, using wearable data, we first quantify the degrees of circadian disruption, both between different internal rhythms and between each internal rhythm and the sleep-wake cycle. Our analysis, based on over 50,000 days of data from over 800 first-year training physicians, reveals bidirectional links between digital markers of circadian disruption and mood both before and after they began shift work, while accounting for confounders such as demographic and geographic variables. We further validate this by finding clinically relevant changes in the 9-item Patient Health Questionnaire score. Our findings validate a scalable digital measure of circadian disruption that could serve as a marker for psychiatric intervention.

Practical application of melatonin for pancreas disorders: protective roles against inflammation, malignancy, and dysfunctions

Melatonin, a hormone primarily produced by the pineal gland, exhibits a range of physiological functions that extend beyond its well-known role in regulating circadian rhythms. This hormone influences energy metabolism, modulates insulin sensitivity, and plays a significant role in controlling sleep patterns and food intake. Notably, melatonin is also synthesized in various peripheral organs, including the gastrointestinal system and pancreas, suggesting its function as a local hormone. The presence of melatonin receptors in the pancreas underscores its relevance in pancreatic physiology. Pancreatic disorders, such as diabetes mellitus (DM), pancreatitis, and pancreatic cancer, often stem from inflammatory processes. The majority of these conditions are characterized by dysregulated immune responses and oxidative stress. Melatonin's anti-inflammatory properties are mediated through the inhibition of pro-inflammatory cytokines and the activation of antioxidant enzymes, which help to mitigate cellular damage. Furthermore, melatonin has demonstrated pro-apoptotic effects on cancer cells, promoting cell death in malignant tissues while preserving healthy cells. Thus, melatonin emerges as a multifaceted agent with significant therapeutic potential for pancreatic disorders. Its ability to reduce inflammation and oxidative stress positions it as a promising adjunct therapy for conditions such as diabetes mellitus, pancreatitis, and pancreatic cancer. By modulating immune responses and enhancing cellular resilience through antioxidant mechanisms, melatonin not only addresses the symptoms but also targets the underlying pathophysiological processes associated with these disorders. This review aims to categorize and summarize the impacts of melatonin on pancreatic functions and disorders, emphasizing its potential as a therapeutic agent for managing pancreatic dysfunctions. Future research should focus on elucidating the precise mechanisms by which melatonin exerts its protective effects on pancreatic tissues and exploring optimal dosing strategies for clinical applications. The integration of melatonin into treatment regimens may enhance existing therapies and offer new hope for individuals suffering from pancreatic dysfunctions.

Cross-sectional association of irregular dietary habits with glycemic control and body mass index among people with diabetes

AIMS/INTRODUCTION

To determine the association of irregular dietary habits with HbA1c and body mass index (BMI) in people with diabetes.

MATERIALS AND METHODS

We included 4,421 people with diabetes aged 20-74 years (type 1 diabetes (T1D), 19.1%) who answered a questionnaire at mealtime. Adjusted least square means in HbA1c and BMI in patients with irregular dietary habits: "irregular mealtimes (irregular)," "skipping breakfast (SB)," and "late dinner (LD)" were compared to those with "regular dietary habits (regular)." Multivariable logistic regression analyses were performed to examine the association of irregular dietary habits with HbA1c ≥ 7% and BMI ≥25 kg/m2.

RESULTS

HbA1c was significantly higher for "irregular" in both sexes and for "LD" in women than those of "regular" in people with T1D. HbA1c was significantly higher for "LD," and BMI was higher for almost all irregular dietary habits than those of "regular" in people with type 2 diabetes (T2D). Odds ratios (ORs) for HbA1c ≥7% were 3.20 (95% confidence interval (CI), 1.30-7.89) for T1D women with "irregular" and 1.73 (1.20-2.49) and 2.20 (1.14-3.65) for T2D men and women with "LD," respectively. ORs for BMI ≥25 kg/m2 were 1.60 (95% CI, 1.15-2.22) for T2D men with "irregular" and 1.43 (1.02-2.01) and 2.11 (1.21-3.65) for T2D women and men with "LD," respectively.

CONCLUSIONS

Irregular mealtimes are associated with poor glycemic control in T1D women and are associated with obesity in T2D men. Furthermore, a late dinner was associated with high HbA1c levels and BMI in people with T2D.

Investigation of the structural changes in the hippocampus and prefrontal cortex using FTIR spectroscopy in sleep deprived mice

Sleep is a basic, physiological requirement for living things to survive and is a process that covers one third of our lives. Melatonin is a hormone that plays an important role in the regulation of sleep. Sleep deprivation affect brain structures and functions. Sleep deprivation causes a decrease in brain activity, with particularly negative effects on the hippocampus and prefrontal cortex. Despite the essential role of protein and lipids vibrations, polysaccharides, fatty acid side chains functional groups, and ratios between amides in brain structures and functions, the brain chemical profile exposed to gentle handling sleep deprivation model versus Melatonin exposure remains unexplored. Therefore, the present study, aims to investigate a molecular profile of these regions using FTIR spectroscopy measurement's analysis based on lipidomic approach with chemometrics and multivariate analysis to evaluate changes in lipid composition in the hippocampus, prefrontal regions of the brain. In this study, C57BL/6J mice were randomly assigned to either the control or sleep deprivation group, resulting in four experimental groups: Control (C) (n = 6), Control + Melatonin (C + M) (n = 6), Sleep Deprivation (S) (n = 6), and Sleep Deprivation + Melatonin (S + M) (n = 6). Interventions were administered each morning via intraperitoneal injections of melatonin (10 mg/kg) or vehicle solution (%1 ethanol + saline), while the S and S + M groups underwent 6 h of daily sleep deprivation from using the Gentle Handling method. All mice were individually housed in cages with ad libitum access to food and water within a 12-hour light-dark cycle. Results presented that the brain regions affected by insomnia. The structure of phospholipids, changed. Yet, not only changes in lipids but also in amides were noticed in hippocampus and prefrontal cortex tissues. Additionally, FTIR results showed that melatonin affected the lipids as well as the amides fraction in cortex and hippocampus collected from both control and sleep deprivation groups.

Transcutaneous auricular vagal nerve stimulation modulates blood glucose in ZDF rats via intestinal melatonin receptors and melatonin secretion

Background

Melatonin (MLT) and its receptor deficiency have been shown to be associated with type 2 diabetes mellitus (T2DM). Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive alternative intervention for patients suffering from hyperglycemia. Here, we aimed to investigate the role of taVNS on blood glucose modulation via intestinal melatonin receptors (MRs) and MLT secretion in hyperglycemia.

Methods

Adult male Zucker diabetes fatty (ZDF) rats and Zucker lean (ZL) littermates were used. Forty ZDF rats were randomized into ZDF, taVNS, Px + taVNS and Lu + Px + taVNS groups (Px: pinealectomy, Lu: Luzindole). ZL rats served as a control group for comparison with ZDF rats without involvement in the taVNS intervention. Thirty min-taVNS interventions (2/15 Hz, 2 mA, 30 min/days) were administered once daily under anesthesia for 3 consecutive weeks in taVNS, Px + taVNS and Lu + Px + taVNS groups. Body weight and fasting blood glucose (FBG) were measured weekly in all rats, and real-time blood glucose was tested in the ZL and ZDF groups before, during and after the taVNS intervention. Plasma MLT concentration and the expression of MRs in the duodenum, jejunum and ileum were measured by the end of experiments.

Results

Compared with the ZL group, the level of FBG and body weight increased (all p < 0.01), plasma MLT secretion and the expression of MRs in duodenum, jejunum and ileum of ZDF rats decreased obviously (all p < 0.05), respectively. TaVNS can significantly reverse the hyperglycemia by regulating the non-pineal-derived MLT and MRs system in Px + taVNS group. Compared with the ZDF group, the expression of different intestinal MRs in the taVNS group was increased and more compactly arranged (both p < 0.05), the level of plasma MLT secretion was up-regulated (p < 0.01), and FBG and body weight were decreased (both p < 0.01). Meanwhile, after taVNS intervention in rats in the Px + taVNS group, we observed an increase in MLT secretion and the number of intestinal MRs compared with the taVNS group (all p > 0.05). In contrast, ZDF rats in which the pineal gland was excised by taVNS intervention and injected with the MRs antagonist Luzindole did not show these changes.

Conclusion

The glucose reduction effect of taVNS may be related to regulating MLT levels and expressing intestinal MRs.

Alzheimer's Disease, Obesity, and Type 2 Diabetes: Focus on Common Neuroglial Dysfunctions (Critical Review and New Data on Human Brain and Models)

BACKGROUND/OBJECTIVES

Obesity, type 2 diabetes (T2D), and Alzheimer's disease (AD) are pathologies that affect millions of people worldwide. They have no effective therapy and are difficult to prevent and control when they develop. It has been known for many years that these diseases have many pathogenic aspects in common. We highlight in this review that neuroglial cells (astroglia, oligodendroglia, and microglia) play a vital role in the origin, clinical-pathological development, and course of brain neurodegeneration. Moreover, we include the new results of a T2D-AD mouse model (APP+PS1 mice on a high-calorie diet) that we are investigating.

METHODS

Critical bibliographic revision and biochemical neuropathological study of neuroglia in a T2D-AD model.

RESULTS

T2D and AD are not only "connected" by producing complex pathologies in the same individual (obesity, T2D, and AD), but they also have many common pathogenic mechanisms. These include insulin resistance, hyperinsulinemia, hyperglycemia, oxidative stress, mitochondrial dysfunction, and inflammation (both peripheral and central-or neuroinflammation). Cognitive impairment and AD are the maximum exponents of brain neurodegeneration in these pathological processes. both due to the dysfunctions induced by metabolic changes in peripheral tissues and inadequate neurotoxic responses to changes in the brain. In this review, we first analyze the common pathogenic mechanisms of obesity, T2D, and AD (and/or cerebral vascular dementia) that induce transcendental changes and responses in neuroglia. The relationships between T2D and AD discussed mainly focus on neuroglial responses. Next, we present neuroglial changes within their neuropathological context in diverse scenarios: (a) aging involution and neurodegenerative disorders, (b) human obesity and diabetes and obesity/diabetes models, (c) human AD and in AD models, and (d) human AD-T2D and AD-T2D models. An important part of the data presented comes from our own studies on humans and experimental models over the past few years. In the T2D-AD section, we included the results of a T2D-AD mouse model (APP+PS1 mice on a high-calorie diet) that we investigated, which showed that neuroglial dysfunctions (astrocytosis and microgliosis) manifest before the appearance of amyloid neuropathology, and that the amyloid pathology is greater than that presented by mice fed a normal, non-high-caloric diet A broad review is finally included on pharmacological, cellular, genic, and non-pharmacological (especially diet and lifestyle) neuroglial-related treatments, as well as clinical trials in a comparative way between T2D and AD. These neuroglial treatments need to be included in the multimodal/integral treatments of T2D and AD to achieve greater therapeutic efficacy in many millions of patients.

CONCLUSIONS

Neuroglial alterations (especially in astroglia and microglia, cornerstones of neuroinflammation) are markedly defining brain neurodegeneration in T2D and A, although there are some not significant differences between each of the studied pathologies. Neuroglial therapies are a very important and p. promising tool that are being developed to prevent and/or treat brain dysfunction in T2D-AD. The need for further research in two very different directions is evident: (a) characterization of the phenotypic changes of astrocytes and microglial cells in each region of the brain and in each phase of development of each isolated and associated pathology (single-cell studies are mandatory) to better understand the pathologies and define new therapeutic targets; (b) studying new therapeutic avenues to normalize the function of neuroglial cells (preventing neurotoxic responses and/or reversing them) in these pathologies, as well as the phenotypic characteristics in each moment of the course and place of the neurodegenerative process.

Role of melatonin in mitigation of insulin resistance and ensuing diabetic cardiomyopathy

Addressing insulin resistance or hyperinsulinemia might offer a viable treatment approach to stop the onset of diabetic cardiomyopathy, as these conditions independently predispose to the development of the disease, which is initially characterized by diastolic abnormalities. The development of diabetic cardiomyopathy appears to be driven mainly by insulin resistance or impaired insulin signalling and/or hyperinsulinemia. Oxidative stress, hypertrophy, fibrosis, cardiac diastolic dysfunction, and, ultimately, systolic heart failure are the outcomes of these pathophysiological alterations. Melatonin is a ubiquitous indoleamine, a widely distributed compound secreted mainly by the pineal gland, and serves a variety of purposes in almost every living creature. Melatonin is found to play a leading role by improving myocardial cell metabolism, decreasing vascular endothelial cell death, reversing micro-circulation disorders, reducing myocardial fibrosis, decreasing oxidative and endoplasmic reticulum stress, regulating cell autophagy and apoptosis, and enhancing mitochondrial function. This review highlights a relationship between insulin resistance and associated cardiomyopathy. It explores the potential therapeutic strategies offered by the neurohormone melatonin, an important antioxidant that plays a leading role in maintaining glucose homeostasis by influencing the glucose transporters independently and through its receptors. The vast distribution of melatonin receptors in the body, including beta cells of pancreatic islets, asserts the role of this indole molecule in maintaining glucose homeostasis. Melatonin controls the production of GLUT4 and/or the phosphorylation process of the receptor for insulin and its intracellular substrates, activating the insulin-signalling pathway through its G-protein-coupled membrane receptors.

Exploring Australian Dietitians' knowledge, experience and perspectives of time-restricted eating in private practice: A qualitative study

Time-restricted eating is a novel nutrition intervention with evidence of beneficial effects on weight loss, blood glucose management, and other metabolic health outcomes. Adherence to time-restricted eating is higher than some traditional nutrition interventions to support individuals living with overweight/obesity and type 2 diabetes mellitus. However, there may be an evidence-practice gap of time-restricted eating in Australian dietetic practice. The present study aimed to explore dietitians' knowledge, experiences, and perspectives of time-restricted eating and timing of eating advice in practice. Semi-structured interviews with 10 private practice dietitians across Australia were conducted. Audio recordings were transcribed and analysed thematically. Six themes were identified: (i) distinction of time-restricted eating to other fasting protocols; (ii) knowledge of health benefits of time-restricted eating; (iii) patient-led advice frequently given: timing of breakfast and dinner; (iv) dietitian-led advice frequently given: eating cut-off time to avoid late night snacking; (v) barriers and facilitators to offering time-restricted eating or timing of eating advice; (vi) timing of eating advice within professional guidelines and resources. These findings suggest the need for development of professional resources and educational development tools for dietitians on time-restricted eating.

Hesperetin alleviates aflatoxin B1 induced liver toxicity in mice: Modulating lipid peroxidation and ferritin autophagy

One of the ways Aflatoxin B1 damages the liver is through ferroptosis. Ferroptosis is characterized by the build-up of lipid peroxides and reactive oxygen species (ROS) due to an excess of iron. Dietary supplements have emerged as a promising strategy for treating ferroptosis in the liver. The flavonoid component hesperetin, which is mostly present in citrus fruits, has a number of pharmacological actions, such as those against liver fibrosis, cancer, and hyperglycemia. However, hesperetin's effects and mechanisms against hepatic ferroptosis are still unknown. In this study, 24 male C57BL/6 J mice were randomly assigned to CON, AFB1 (0.45 mg/kg/day), and AFB1+ hesperetin treatment groups (40 mg/kg/day). The results showed that hesperetin improved the structural damage of the mouse liver, down-regulated inflammatory factors (Cxcl1, Cxcl2, CD80, and F4/80), and alleviated liver fibrosis induced by aflatoxin B1. Hesperetin reduced hepatic lipid peroxidation induced by iron accumulation by up-regulating the levels of antioxidant enzymes (GPX4, GSH-Px, CAT, and T-AOC). It is worth noting that hesperetin not only improved lipid peroxidation but also maintained the dynamic balance of iron ions by reducing ferritin autophagy. Mechanistically, hesperetin's ability to regulate ferritin autophagy mostly depends on the PI3K/AKT/mTOR/ULK1 pathway. In AFB1-induced HepG2 cells, the addition of PI3K inhibitor (LY294002) and AKT inhibitor (Miransertib) confirmed that hesperetin regulated the PI3K/AKT/mTOR/ULK1 pathway to inhibit ferritin autophagy and reduced the degradation of ferritin in lysosomes. In summary, our results suggest that hesperetin not only regulates the antioxidant system but also inhibits AFB1-induced ferritin hyperautophagy, thereby reducing the accumulation of iron ions to mitigate lipid peroxidation. This work provides a fresh perspective on the mechanism behind hesperetin and AFB1-induced liver damage in mice.

Energy Intake and Dietary Glycemic Load in Late Morning and Risk of Type 2 Diabetes: The Hispanic Community Health Study/Study of Latinos-A Multicenter Prospective Cohort Study

OBJECTIVE

To evaluate the association between meal timing and type 2 diabetes risk in U.S. Hispanic/Latino adults.

RESEARCH DESIGN AND METHODS

The Hispanic Community Health Study/Study of Latinos (HCHS/SOL) is a multicenter, community-based, prospective cohort study. This study included 8,868 HCHS/SOL adults without diabetes at baseline (2008-2011) and attending the visit 2 examination (2014-2017). Energy intake and glycemic load (GL) in each meal timing were assessed at baseline using two 24-h dietary recalls. Incident diabetes was identified through annual follow-up calls or at visit 2. Hazard ratios (HRs) for incident diabetes were estimated using Cox models, accounting for the complex survey design.

RESULTS

The study population (50.9% female) had a baseline mean age of 39.0 (95% CI, 38.4-39.5) years. Over a median (range) follow-up of 5.8 (0.8-9.6) years, 1,262 incident diabetes cases were documented. Greater energy intake and GL in late morning (9:00-11:59 a.m.) were associated with a lower diabetes risk, whereas greater energy intake and GL in other meal timings were not. After accounting for diet quantity and quality, sociodemographic characteristics, lifestyle factors, and chronic conditions, the HRs were 0.94 (95% CI, 0.91-0.97) per 100-kcal energy intake increment and 0.93 (0.89-0.97) per 10-unit GL increment in late morning. Replacing energy intake or GL from early morning (6:00-8:59 a.m.), afternoon (12:00-5:59 p.m.), or evening (6:00-11:59 p.m.) with late-morning equivalents was associated with a comparably lower diabetes risk.

CONCLUSIONS

This study identified late morning as a favorable meal timing in Hispanic/Latino adults, providing a novel perspective on type 2 diabetes prevention that warrants confirmation.

Glycemic response to meals with a high glycemic index differs between morning and evening: a randomized cross-over controlled trial among students with early or late chronotype

PURPOSE

Glycemic response to the same meal depends on daytime and alignment of consumption with the inner clock, which has not been examined by individual chronotype yet. This study examined whether the 2-h postprandial and 24-h glycemic response to a meal with high glycemic index (GI) differ when consumed early or late in the day among students with early or late chronotype.

METHODS

From a screening of 327 students aged 18-25 years, those with early (n = 22) or late (n = 23) chronotype participated in a 7-day randomized controlled cross-over intervention study. After a 3-day observational phase, standardized meals were provided on run-in/washout (days 4 and 6) and intervention (days 5 and 7), on which participants received a high GI meal (GI = 72) in the morning (7 a.m.) or in the evening (8 p.m.). All other meals had a medium GI. Continuous glucose monitoring was used to measure 2-h postprandial and 24-h glycemic responses and their variability.

RESULTS

Among students with early chronotype 2-h postprandial glucose responses to the high GI meal were higher in the evening than in the morning (iAUC: 234 (± 92) vs. 195 (± 91) (mmol/L) × min, p = 0.042). Likewise, mean and lowest 2-h postprandial glucose values were higher when the high GI meal was consumed in the evening (p < 0.001; p = 0.017). 24-h glycemic responses were similar irrespective of meal time. Participants with late chronotype consuming a high GI meal in the morning or evening showed similar 2-h postprandial (iAUC: 211 (± 110) vs. 207 (± 95) (mmol/L) × min, p = 0.9) and 24-h glycemic responses at both daytimes.

CONCLUSIONS

Diurnal differences in response to a high GI meal are confined to those young adults with early chronotype, whilst those with a late chronotype seem vulnerable to both very early and late high GI meals. Registered at clinicaltrials.gov (NCT04298645; 22/01/2020).

Melatonin decreases human adipose tissue insulin sensitivity

Melatonin is a pineal hormone that modulates the circadian system and exerts soporific and phase-shifting effects. It is also involved in many other physiological processes, such as those implicated in cardiovascular, endocrine, immune, and metabolic functions. However, the role of melatonin in glucose metabolism remains contradictory, and its action on human adipose tissue (AT) explants has not been demonstrated. We aimed to assess whether melatonin (a pharmacological dose) influences insulin sensitivity in human AT. This will help better understand melatonin administration's effect on glucose metabolism. Abdominal AT (subcutaneous and visceral) biopsies were obtained from 19 participants with severe obesity (age: 42.84 ± 12.48 years; body mass index: 43.14 ± 8.26 kg/m2) who underwent a laparoscopic gastric bypass. AT biopsies were exposed to four different treatments: control (C), insulin alone (I) (10 nM), melatonin alone (M) (5000 pg/mL), and insulin plus melatonin combined (I + M). All four conditions were repeated in both subcutaneous and visceral AT, and all were performed in the morning at 8 a.m. (n = 19) and the evening at 8 p.m. (in a subsample of n = 12). We used western blot analysis to determine insulin signaling (using the pAKT/tAKT ratio). Furthermore, RNAseq analyses were performed to better understand the metabolic pathways involved in the effect of melatonin on insulin signaling. As expected, insulin treatment (I) increased the pAKT/tAKT ratio compared with control (p < .0001). Furthermore, the addition of melatonin (I + M) resulted in a decrease in insulin signaling as compared with insulin alone (I); this effect was significant only during the evening time (not in the morning time). Further, RNAseq analyses in visceral AT during the evening condition (at 8 p.m.) showed that melatonin resulted in a prompt transcriptome response (around 1 h after melatonin addition), particularly by downregulating the insulin signaling pathway. Our results show that melatonin reduces insulin sensitivity in human AT during the evening. These results may partly explain the previous studies showing a decrease in glucose tolerance after oral melatonin administration in the evening or when eating late when endogenous melatonin is present.

Insight into the cardioprotective effects of melatonin: shining a spotlight on intercellular Sirt signaling communication

Cardiovascular diseases (CVDs) are the leading causes of death and illness worldwide. While there have been advancements in the treatment of CVDs using medication and medical procedures, these conventional methods have limited effectiveness in halting the progression of heart diseases to complete heart failure. However, in recent years, the hormone melatonin has shown promise as a protective agent for the heart. Melatonin, which is secreted by the pineal gland and regulates our sleep-wake cycle, plays a role in various biological processes including oxidative stress, mitochondrial function, and cell death. The Sirtuin (Sirt) family of proteins has gained attention for their involvement in many cellular functions related to heart health. It has been well established that melatonin activates the Sirt signaling pathways, leading to several beneficial effects on the heart. These include preserving mitochondrial function, reducing oxidative stress, decreasing inflammation, preventing cell death, and regulating autophagy in cardiac cells. Therefore, melatonin could play crucial roles in ameliorating various cardiovascular pathologies, such as sepsis, drug toxicity-induced myocardial injury, myocardial ischemia-reperfusion injury, hypertension, heart failure, and diabetic cardiomyopathy. These effects may be partly attributed to the modulation of different Sirt family members by melatonin. This review summarizes the existing body of literature highlighting the cardioprotective effects of melatonin, specifically the ones including modulation of Sirt signaling pathways. Also, we discuss the potential use of melatonin-Sirt interactions as a forthcoming therapeutic target for managing and preventing CVDs.

Diabetes-associated Genetic Variation in MTNR1B and Its Effect on Islet Function

Context

Multiple common genetic variants have been associated with type 2 diabetes, but the mechanism by which they predispose to diabetes is incompletely understood. One such example is variation in MTNR1B, which implicates melatonin and its receptor in the pathogenesis of type 2 diabetes.

Objective

To characterize the effect of diabetes-associated genetic variation at rs10830963 in the MTNR1B locus on islet function in people without type 2 diabetes.

Design

The association of genetic variation at rs10830963 with glucose, insulin, C-peptide, glucagon, and indices of insulin secretion and action were tested in a cohort of 294 individuals who had previously undergone an oral glucose tolerance test (OGTT). Insulin sensitivity, β-cell responsivity to glucose, and Disposition Indices were measured using the oral minimal model.

Setting

The Clinical Research and Translation Unit at Mayo Clinic, Rochester, MN.

Participants

Two cohorts were utilized for this analysis: 1 cohort was recruited on the basis of prior participation in a population-based study in Olmsted County. The other cohort was recruited on the basis of TCF7L2 genotype at rs7903146 from the Mayo Biobank.

Intervention

Two-hour, 7-sample OGTT.

Main Outcome Measures

Fasting, nadir, and integrated glucagon concentrations.

Results

One or 2 copies of the G-allele at rs10830963 were associated with increased postchallenge glucose and glucagon concentrations compared to subjects with the CC genotype.

Conclusion

The effects of rs10830963 on glucose homeostasis and predisposition to type 2 diabetes are likely to be partially mediated through changes in α-cell function.

Circadian-independent light regulation of mammalian metabolism

The daily light-dark cycle is a key zeitgeber (time cue) for entraining an organism's biological clock, whereby light sensing by retinal photoreceptors, particularly intrinsically photosensitive retinal ganglion cells, stimulates the suprachiasmatic nucleus of the hypothalamus, a central pacemaker that in turn orchestrates the rhythm of peripheral metabolic activities. Non-rhythmic effects of light on metabolism have also been long known, and their transduction mechanisms are only beginning to unfold. Here, we summarize emerging evidence that, in mammals, light exposure or deprivation profoundly affects glucose homeostasis, thermogenesis and other metabolic activities in a clock-independent manner. Such light regulation could involve melanopsin-based, intrinsically photosensitive retinal ganglion cell-initiated brain circuits via the suprachiasmatic nucleus of the hypothalamus and other nuclei, or direct stimulation of opsins expressed in the hypothalamus, adipose tissue, blood vessels and skin to regulate sympathetic tone, lipolysis, glucose uptake, mitochondrial activation, thermogenesis, food intake, blood pressure and melanogenesis. These photic signalling events may coordinate with circadian-based mechanisms to maintain metabolic homeostasis, with dysregulation of this system underlying metabolic diseases caused by aberrant light exposure, such as environmental night light and shift work.

Dysregulated 24 h melatonin secretion associated with intrinsically photosensitive retinal ganglion cell function in diabetic retinopathy: a cross-sectional study

AIMS/HYPOTHESIS

The aim of this study was to explore whether diabetic retinopathy is associated with alterations of the circadian system, and to examine the role of reduced intrinsically photosensitive retinal ganglion cell (ipRGC) function.

METHODS

Participants with type 2 diabetes, with diabetic retinopathy (n=14) and without diabetic retinopathy (n=9) underwent 24 h blood sampling for melatonin and cortisol under controlled laboratory conditions. ipRGC function was inferred from the post-illumination pupil response (PIPR). Habitual sleep duration, efficiency and variability were assessed by actigraphy.

RESULTS

Participants with diabetic retinopathy compared to participants without diabetic retinopathy had smaller PIPR (p=0.007), lower 24 h serum melatonin output (p=0.042) and greater day-to-day sleep variability (p=0.012). By contrast, 24 h cortisol profiles, sleep duration and efficiency were similar in both groups. Six individuals with diabetic retinopathy had no detectable dim-light melatonin onset. PIPR correlated with 24 h mean melatonin levels (r=0.555, p=0.007).

CONCLUSIONS/INTERPRETATION

ipRCG dysfunction in diabetic retinopathy is associated with disruptions of the 24 h melatonin rhythm, suggesting circadian dysregulation in diabetic retinopathy.

Assessment of melatonin's therapeutic effectiveness against hepatic steatosis induced by a high-carbohydrate high-fat diet in rats

Several studies have demonstrated the protective effects of melatonin against metabolic diseases, such as liver steatosis. However, its therapeutic effects have received less scrutiny. The present study aimed to explore melatonin's therapeutic effectiveness in treating non-alcoholic fatty liver disease (NAFLD) induced by a high-carbohydrate high-fat (HCHF) diet in rats. The NAFLD was developed in male Wistar rats using an HCHF diet for 8 weeks. Afterward, they were given melatonin orally for four weeks at doses of 5 mg/kg, 10 mg/kg, and 30 mg/kg, along with the HCHF diet. In addition, six age-matched healthy rats received the highest dose of melatonin (30 mg/kg) for the same duration. Rats on the HCHF diet exhibited obesity, dyslipidemia, hyperglycemia, glucose intolerance, insulin resistance, inflammation, oxidative stress, and liver injury (steatosis). Melatonin treatment at 10 mg/kg and 30 mg/kg reduced body weight, adiposity index, oxidative damage, and inflammation but did not affect impaired glucose metabolism induced by the HCHF diet. Meanwhile, the highest dose of melatonin (30 mg/kg) reduced the liver steatosis index in HCHF rats but caused mild liver damage in healthy rats. In conclusion, using melatonin demonstrated positive outcomes in treating NAFLD induced by the HCHF diet in rats, with no noteworthy effects observed in healthy rats. A moderate dosage of 10 mg/kg of melatonin proved to be a safer and more efficient method for reducing HCHF diet-induced NAFLD in rats. Higher melatonin doses should be cautiously administered due to potential disruptions in lipid metabolism and the risk of liver complications.

Circadian desynchrony and glucose metabolism

The circadian timing system controls glucose metabolism in a time-of-day dependent manner. In mammals, the circadian timing system consists of the main central clock in the bilateral suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks in peripheral tissues. The oscillations produced by these different clocks with a period of approximately 24-h are generated by the transcriptional-translational feedback loops of a set of core clock genes. Glucose homeostasis is one of the daily rhythms controlled by this circadian timing system. The central pacemaker in the SCN controls glucose homeostasis through its neural projections to hypothalamic hubs that are in control of feeding behavior and energy metabolism. Using hormones such as adrenal glucocorticoids and melatonin and the autonomic nervous system, the SCN modulates critical processes such as glucose production and insulin sensitivity. Peripheral clocks in tissues, such as the liver, muscle, and adipose tissue serve to enhance and sustain these SCN signals. In the optimal situation all these clocks are synchronized and aligned with behavior and the environmental light/dark cycle. A negative impact on glucose metabolism becomes apparent when the internal timing system becomes disturbed, also known as circadian desynchrony or circadian misalignment. Circadian desynchrony may occur at several levels, as the mistiming of light exposure or sleep will especially affect the central clock, whereas mistiming of food intake or physical activity will especially involve the peripheral clocks. In this review, we will summarize the literature investigating the impact of circadian desynchrony on glucose metabolism and how it may result in the development of insulin resistance. In addition, we will discuss potential strategies aimed at reinstating circadian synchrony to improve insulin sensitivity and contribute to the prevention of type 2 diabetes.

Melatonin in energy control: Circadian time-giver and homeostatic monitor

Melatonin is a neurohormone synthesized from dietary tryptophan in various organs, including the pineal gland and the retina. In the pineal gland, melatonin is produced at night under the control of the master clock located in the suprachiasmatic nuclei of the hypothalamus. Under physiological conditions, the pineal gland seems to constitute the unique source of circulating melatonin. Melatonin is involved in cellular metabolism in different ways. First, the circadian rhythm of melatonin helps the maintenance of proper internal timing, the disruption of which has deleterious effects on metabolic health. Second, melatonin modulates lipid metabolism, notably through diminished lipogenesis, and it has an antidiabetic effect, at least in several animal models. Third, pharmacological doses of melatonin have antioxidative, free radical-scavenging, and anti-inflammatory properties in various in vitro cellular models. As a result, melatonin can be considered both a circadian time-giver and a homeostatic monitor of cellular metabolism, via multiple mechanisms of action that are not all fully characterized. Aging, circadian disruption, and artificial light at night are conditions combining increased metabolic risks with diminished circulating levels of melatonin. Accordingly, melatonin supplementation could be of potential therapeutic value in the treatment or prevention of metabolic disorders. More clinical trials in controlled conditions are needed, notably taking greater account of circadian rhythmicity.

Circadian dysfunction and cardio-metabolic disorders in humans

The topic of human circadian rhythms is not only attracting the attention of clinical researchers from various fields but also sparking a growing public interest. The circadian system comprises the central clock, located in the suprachiasmatic nucleus of the hypothalamus, and the peripheral clocks in various tissues that are interconnected; together they coordinate many daily activities, including sleep and wakefulness, physical activity, food intake, glucose sensitivity and cardiovascular functions. Disruption of circadian regulation seems to be associated with metabolic disorders (particularly impaired glucose tolerance) and cardiovascular disease. Previous clinical trials revealed that disturbance of the circadian system, specifically due to shift work, is associated with an increased risk of type 2 diabetes mellitus. This review is intended to provide clinicians who wish to implement knowledge of circadian disruption in diagnosis and strategies to avoid cardio-metabolic disease with a general overview of this topic.

Melatonin-mediated corrective changes in gut microbiota of experimentally chronodisrupted C57BL/6J mice

Chronic consumption of a high-calorie diet coupled with an altered sleep-wake cycle causes disruption of circadian clock that can impact the gut microbiome leading to metabolic syndrome and associated diseases. Herein, we investigate the effects of a high fat high fructose diet (H) alone or in combination with photoperiodic shifts induced chronodisruption (CD) on gut microbiota of C57BL/6J male mice. Further, the merits of daily evening intraperitoneal administration of melatonin in restoring gut microbiota are studied herein. Experimental groups viz. H, CD and HCD mice recorded higher levels of serum pro-inflammatory cytokines (TNF-α and IL-6) and lower levels of the anti-inflammatory cytokine, IL-10. These findings correlate with a concomitant increase in the transcripts of TLR4, TNF-α, and IL-6 in small intestine of the said groups. A decrement in mRNA levels of Ocln, ZO-1 and Vdr in these groups implied towards an altered gut permeability. These results were in agreement with the observed decrement in percentage abundance of total gut microflora and Firmicutes: Bacteroidetes (F/B) ratio. Melatonin administration accounted for lower-level inflammation (serum and gut) along with an improvement in gut permeability markers. The total abundance of gut microflora and F/B ratio showed an improvement in all the melatonin-treated groups and the same is the highlight of this study. Taken together, our study is the first to report perturbations in gut microbiota resulting due to a combination of photoperiodic shifts induced CD and a high fat high calorie diet-induced lifestyle disorder. Further, melatonin-mediated rejuvenation of gut microbiome provides prima facie evidence of its role in improving gut dysbiosis that needs a detailed scrutiny.

Melatonin Improves Glucose Homeostasis and Insulin Sensitivity by Mitigating Inflammation and Activating AMPK Signaling in a Mouse Model of Sleep Fragmentation

Sleep fragmentation (SF) can increase inflammation and production of reactive oxygen species (ROS), leading to metabolic dysfunction. SF is associated with inflammation of adipose tissue and insulin resistance. Several studies have suggested that melatonin may have beneficial metabolic effects due to activating AMP-activated protein kinase (AMPK). However, it is unclear whether melatonin affects the AMPK signaling pathway in SF-induced metabolic dysfunction. Therefore, we hypothesize that SF induces metabolic impairment and inflammation in white adipose tissue (WAT), as well as altered intracellular homeostasis. We further hypothesize that these conditions could be improved by melatonin treatment. We conducted an experiment using adult male C57BL/6 mice, which were divided into three groups: control, SF, and SF with melatonin treatment (SF+Mel). The SF mice were housed in SF chambers, while the SF+Mel mice received daily oral melatonin. After 12 weeks, glucose tolerance tests, insulin tolerance tests, adipose tissue inflammation tests, and AMPK assessments were performed. The SF mice showed increased weight gain, impaired glucose regulation, inflammation, and decreased AMPK in WAT compared to the controls. Melatonin significantly improved these outcomes by mitigating SF-induced metabolic dysfunction, inflammation, and AMPK downregulation in adipose tissue. The therapeutic efficacy of melatonin against cardiometabolic impairments in SF may be due to its ability to restore adipose tissue homeostatic pathways.

MTNR1B genotype and effects of carbohydrate quantity and dietary glycaemic index on glycaemic response to an oral glucose load: the OmniCarb trial

AIMS/HYPOTHESIS

A type 2 diabetes-risk-increasing variant, MTNR1B (melatonin receptor 1B) rs10830963, regulates the circadian function and may influence the variability in metabolic responses to dietary carbohydrates. We investigated whether the effects of carbohydrate quantity and dietary glycaemic index (GI) on glycaemic response during OGTTs varied by the risk G allele of MTNR1B-rs10830963.

METHODS

This study included participants (n=150) of a randomised crossover-controlled feeding trial of four diets with high/low GI levels and high/low carbohydrate content for 5 weeks. The MTNR1B-rs10830963 (C/G) variant was genotyped. Glucose response during 2 h OGTT was measured at baseline and the end of each diet intervention.

RESULTS

Among the four study diets, carrying the risk G allele (CG/GG vs CC genotype) of MTNR1B-rs10830963 was associated with the largest AUC of glucose during 2 h OGTT after consuming a high-carbohydrate/high-GI diet (β 134.32 [SE 45.69] mmol/l × min; p=0.004). The risk G-allele carriers showed greater increment of glucose during 0-60 min (β 1.26 [0.47] mmol/l; p=0.008) or 0-90 min (β 1.10 [0.50] mmol/l; p=0.028) after the high-carbohydrate/high-GI diet intervention, but not after consuming the other three diets. At high carbohydrate content, reducing GI levels decreased 60 min post-OGTT glucose (mean -0.67 [95% CI: -1.18, -0.17] mmol/l) and the increment of glucose during 0-60 min (mean -1.00 [95% CI: -1.67, -0.33] mmol/l) and 0-90 min, particularly in the risk G-allele carriers (pinteraction <0.05 for all).

CONCLUSIONS/INTERPRETATION

Our study shows that carrying the risk G allele of MTNR1B-rs10830963 is associated with greater glycaemic responses after consuming a diet with high carbohydrates and high GI levels. Reducing GI in a high-carbohydrate diet may decrease post-OGTT glucose concentrations among the risk G-allele carriers.

Chrononutrition in the context of Ramadan: Potential implications

Every year, healthy adult Muslims practice dawn to sunset fasting for a whole lunar month. No food or fluid is allowed for the fasting time window. After sunset, eating is allowed. The dramatic change in the timing of meals is accompanied by changes in sleeping hours and thus alterations in circadian rhythms. Hormonal mechanisms mainly determined by the latter also change. These include shifts in cortisol and melatonin. Food-dependent hormones such as Ghrelin and leptin also show changes. A well-established principle of chrononutrition is that the timing of eating may be as or more important than the content of food. Ramadan fasting (RF) is distinct from other forms of intermittent fasting, although there are also some similarities with time restricted eating (TRE). Both have been shown to have health benefits. Here, we examine existing literature to understand and learn from this very commonly practiced form of fasting and its relationships to circadian rhythms and homoeostatic mechanisms.

Glycemic and sleep effects of daytime compared with those of overnight infusions of home parenteral nutrition in adults with short bowel syndrome: A quasi-experimental pilot trial

BACKGROUND

Patients with short bowel syndrome (SBS) dependent on home parenteral nutrition (HPN) commonly cycle infusions overnight, likely contributing to circadian misalignment and sleep disruption.

METHODS

The objective of this quasi-experimental, single-arm, controlled, pilot trial was to examine the feasibility, safety, and efficacy of daytime infusions of HPN in adults with SBS without diabetes. Enrolled patients were fitted with a continuous glucose monitor and wrist actigraph and were instructed to cycle their infusions overnight for 1 wk, followed by daytime for another week. The 24-h average blood glucose, the time spent >140 mg/dL or <70 mg/dL, and sleep fragmentation were derived for each week and compared using Wilcoxon signed-rank test. Patient-reported quality-of-life outcomes were also compared between the weeks.

RESULTS

Twenty patients (mean age, 51.7 y; 75% female; mean body mass index, 21.5 kg/m2) completed the trial. Overnight infusions started at 21:00 and daytime infusions at 09:00. No serious adverse events were noted. There were no differences in 24-h glycemia (daytime-median: 93.00 mg/dL; 95% CI: 87.7-99.9 mg/dL, compared with overnight-median: 91.1 mg/dL; 95% CI: 89.6-99.0 mg/dL; P = 0.922). During the day hours (09:00-21:00), the mean glucose concentrations were 13.5 (5.7-22.0) mg/dL higher, and the time spent <70 mg/dL was 15.0 (-170.0, 22.5) min lower with daytime than with overnight HPN. Conversely, during the night hours (21:00-09:00), the glucose concentrations were 16.6 (-23.1, -2.2) mg/dL lower with daytime than with overnight HPN. There were no differences in actigraphy-derived measures of sleep and activity rhythms; however, sleep timing was later, and light at night exposure was lower with daytime than with overnight HPN. Patients reported less sleep disruptions due to urination and fewer episodes of uncontrollable diarrhea or ostomy output with daytime HPN.

CONCLUSIONS

Daytime HPN was feasible and safe in adults with SBS and, compared with overnight HPN, improved subjective sleep without increasing 24-h glucose concentrations. This trial was registered at clinicaltrials.gov as NCT04743960 (https://classic.

CLINICALTRIALS

gov/ct2/show/NCT04743960).

Delayed dinnertime impairs glucose tolerance in healthy young adults

To explore the relationship between mealtime delays of up to 3 h and subsequent glucose fluctuations, healthy young adults were allocated to three delayed dinnertimes in randomized order. Participants consumed test meals for lunch and dinner. After assessing the glucose responses using intermittently scanned continuous glucose monitoring devices (isCGM), the peak glucose elevation, and incremental area under the curve (iAUC) of postprandial glucose during certain intervals increased significantly when the time between lunch and dinner was delayed by 1 h or more. Our results support the importance of improving irregular mealtime habits, such as late eating.

The melatonin receptor genes are linked and associated with the risk of polycystic ovary syndrome

Polycystic ovarian syndrome (PCOS) is a genetically complex disorder that involves the interplay of multiple genes and environmental factors. It is characterized by anovulation and irregular menses and is associated with type 2 diabetes. Neuroendocrine pathways and ovarian and adrenal dysfunctions are possibly implicated in the disorder pathogenesis. The melatonin system plays a role in PCOS. Melatonin receptors are expressed on the surface of ovarian granulosa cells, and variations in the melatonin receptor genes have been associated with increased risk of PCOS in both familial and sporadic cases. We have recently reported the association of variants in MTNR1A and MTNR1B genes with familial type 2 diabetes. In this study, we aimed to investigate whether MTNR1A and MTNR1B contribute to PCOS risk in peninsular families. In 212 Italian families phenotyped for PCOS, we amplified by microarray 14 variants in the MTNR1A gene and 6 variants in the MTNR1B gene and tested them for linkage and linkage disequilibrium with PCOS. We detected 4 variants in the MTNR1A gene and 2 variants in the MTNR1B gene significantly linked and/or in linkage disequilibrium with the risk of PCOS (P < 0.05). All variants are novel and have not been reported before with PCOS or any of its related phenotypes, except for 3 variants previously reported by us to confer risk for type 2 diabetes and 1 variant for type 2 diabetes-depression comorbidity. These findings implicate novel melatonin receptor genes' variants in the risk of PCOS with potential functional roles.

Melatonin attenuates diabetic cardiomyopathy by increasing autophagy of cardiomyocytes via regulation of VEGF-B/GRP78/PERK signaling pathway

AIMS

Diabetic cardiomyopathy (DCM) is a major cause of mortality in patients with diabetes, and the potential strategies for treating DCM are insufficient. Melatonin (Mel) has been shown to attenuate DCM, however, the underlying mechanism remains unclear. The role of vascular endothelial growth factor-B (VEGF-B) in DCM is little known. In present study, we aimed to investigate whether Mel alleviated DCM via regulation of VEGF-B and explored its underlying mechanisms.

METHODS AND RESULTS

We found that Mel significantly alleviated cardiac dysfunction and improved autophagy of cardiomyocytes in type 1 diabetes mellitus (T1DM) induced cardiomyopathy mice. VEGF-B was highly expressed in DCM mice in comparison with normal mice, and its expression was markedly reduced after Mel treatment. Mel treatment diminished the interaction of VEGF-B and Glucose-regulated protein 78 (GRP78) and reduced the interaction of GRP78 and protein kinase RNA -like ER kinase (PERK). Furthermore, Mel increased phosphorylation of PERK and eIF2α, then up-regulated the expression of ATF4. VEGF-B-/- mice imitated the effect of Mel on wild type diabetic mice. Interestingly, injection with Recombinant adeno-associated virus serotype 9 (AAV9)-VEGF-B or administration of GSK2656157 (GSK), an inhibitor of phosphorylated PERK abolished the protective effect of Mel on DCM. Furthermore, rapamycin, an autophagy agonist displayed similar effect with Mel treatment; while 3-Methyladenine (3-MA), an autophagy inhibitor neutralized the effect of Mel on high glucose-treated neonatal rat ventricular myocytes.

CONCLUSIONS

These results demonstrated that Mel attenuated DCM via increasing autophagy of cardiomyocytes, and this cardio-protective effect of Mel was dependent on VEGF-B/GRP78/PERK signaling pathway.

Melatonin in Alzheimer's Disease: Literature Review and Therapeutic Trials

There are currently no effective treatments to prevent, halt, or reverse Alzheimer's disease (AD), the most common cause of dementia in older adults. Melatonin, a relatively harmless over-the-counter supplement, may offer some benefits to patients with AD. Melatonin is known for its sleep-enhancing properties, but research shows that it may provide other advantages as well, such as antioxidant and anti-amyloidogenic properties. Clinical trials for melatonin use in AD have mixed results but, overall, show modest benefits. However, it is difficult to interpret clinical research in this area as there is little standardization to guide the administration and study of melatonin. This review covers basic biology and clinical research on melatonin in AD focusing on prominent hypotheses of pathophysiology of neurodegeneration and cognitive decline in AD (i.e., amyloid and tau hypotheses, antioxidant and anti-inflammation, insulin resistance and glucose homeostasis, the cholinergic hypothesis, sleep regulation, and the hypothalamic-pituitary-adrenal axis and cortisol). This is followed by a discussion on pending clinical trials, considerations for future research protocols, and open questions in the field.

Melatonin as a Mediator of the Gut Microbiota-Host Interaction: Implications for Health and Disease

In recent years, the role played by melatonin on the gut microbiota has gained increasingly greater attention. Additionally, the gut microbiota has been proposed as an alternative source of melatonin, suggesting that this antioxidant indoleamine could act as a sort of messenger between the gut microbiota and the host. This review analyses the available scientific literature about possible mechanisms involved in this mediating role, highlighting its antioxidant effects and influence on this interaction. In addition, we also review the available knowledge on the effects of melatonin on gut microbiota composition, as well as its ability to alleviate dysbiosis related to sleep deprivation or chronodisruptive conditions. The melatonin-gut microbiota relationship has also been discussed in terms of its role in the development of different disorders, from inflammatory or metabolic disorders to psychiatric and neurological conditions, also considering oxidative stress and the reactive oxygen species-scavenging properties of melatonin as the main factors mediating this relationship.

Monoamines' role in islet cell function and type 2 diabetes risk

The two monoamines serotonin and melatonin have recently been highlighted as potent regulators of islet hormone secretion and overall glucose homeostasis in the body. In fact, dysregulated signaling of both amines are implicated in β-cell dysfunction and development of type 2 diabetes mellitus (T2DM). Serotonin is a key player in β-cell physiology and plays a role in expansion of β-cell mass. Melatonin regulates circadian rhythm and nutrient metabolism and reduces insulin release in human and rodent islets in vitro. Herein, we focus on the role of serotonin and melatonin in islet physiology and the pathophysiology of T2DM. This includes effects on hormone secretion, receptor expression, genetic variants influencing β-cell function, melatonin treatment, and compounds that alter serotonin availability and signaling.

Association between dinner timing and glucose metabolism in rural China: A large-scale cross-sectional study

OBJECTIVES

Meal timing is a major risk factor for metabolic disease. The aim of this study was to assess the relationship between dinner timing and glucose metabolism in the rural Chinese population.

METHODS

This cross-sectional study included 7701 participants from a Henan rural cohort study. Basic information was collected by in-person questionnaires. Multiple linear regression analysis was used to evaluate the relationship between dinner timing and fasting insulin (FINS), fasting plasma glucose (FPG), and homeostatic model assessment for insulin resistance (HOMA-IR). Restricted cubic spline was employed to investigate the dose-response relationship between dinner timing and FINS, FPG, and HOMA-IR. A generalized linear model was used to explore the interaction effect of age and dinner timing on FINS, FPG, and HOMA-IR.

RESULTS

After adjusting for confounding factors, FINS concentration was reduced by 0.482 mmol/L (P < 0.001) for each hour delay in dinner timing. Furthermore, the HOMA-IR index decreased by 0.122 mmol/L for each hour delay. The results indicated a noticeable trend of decreasing values associated with later dinner timing (FINS: Poverall association < 0.001, Pnonlinear association = 0.144; HOMA-IR: Poverall association = 0.001, Pnonlinear association = 0.186). The interaction between age and dinner time significantly correlated with FINS and HOMA-IR (P < 0.05). This relationship was statistically significant before 69 y (P < 0.05).

CONCLUSION

A significant association between dinner timing and glucose metabolism was observed in the rural Chinese population. Delayed dinner timing may be associated with lower fasting insulin. The negative effect of dinner timing on FINS and HOMA-IR was diminished with age.

Role of Melatonin in the Onset of Metabolic Syndrome in Women

Metabolic syndrome (MetS) is a constellation of several associated cardiometabolic risk factors that increase the risk of developing type 2 diabetes mellitus (T2DM), cardiovascular diseases, and mortality. The role of hormonal factors in the development of MetS is assumed. In women, an insulin-resistant state that is associated with polycystic ovarian syndrome and increased deposition of intra-abdominal adipose tissue promotes the development of MetS and increases cardiovascular risk. The neuroendocrine hormone melatonin is secreted mainly at night under the regulatory action of the suprachiasmatic nucleus in the hypothalamus. Melatonin secretion is influenced by exogenous factors such as light and seasons and endogenous factors such as age, sex, and body weight. At present, the role of melatonin in metabolic disorders in humans is not fully understood. In this review, we set out to analyze the relationship of melatonin with the main features of MetS in women. Data from experimental and clinical studies on the role of melatonin in glucose metabolism and on the involvement of melatonin in lipid disturbances in MetS are reviewed. The complex influence of melatonin on hypertension is discussed. The changes in melatonin, leptin, and ghrelin and their relation to various metabolic processes and vascular dysfunction are discussed.

G Protein-Coupled Receptors and the Rise of Type 2 Diabetes in Children

The human genome counts hundreds of GPCRs specialized to sense thousands of different extracellular cues, including light, odorants and nutrients in addition to hormones. Primordial GPCRs were likely glucose transporters that became sensors to monitor the abundance of nutrients and direct the cell to switch from aerobic metabolism to fermentation. Human β cells express multiple GPCRs that contribute to regulate glucose homeostasis, cooperating with many others expressed by a variety of cell types and tissues. These GPCRs are intensely studied as pharmacological targets to treat type 2 diabetes in adults. The dramatic rise of type 2 diabetes incidence in pediatric age is likely correlated to the rapidly evolving lifestyle of children and adolescents of the new century. Current pharmacological treatments are based on therapies designed for adults, while youth and puberty are characterized by a different hormonal balance related to glucose metabolism. This review focuses on GPCRs functional traits that are relevant for β cells function, with an emphasis on aspects that could help to differentiate new treatments specifically addressed to young type 2 diabetes patients.

Effects of exogenous melatonin on body mass and thermogenesis in red-backed vole (Eothenomys miletus) between Kunming and Dali regions

Melatonin (MEL) is an indole hormone synthesized and secreted by the pineal gland at night, which is involved in the regulation of body mass and thermogenesis in small mammals. To test the effects of exogenous MEL on body mass and thermogenic ability in two different red-backed vole (Eothenomys miletus) populations from two different regions (Kunming [KM] and Dali [DL]) with different annual variation in climatic variables, such as temperature, sunshine and rainfall. we traced the changes of energy balance in E. miletus from KM and DL, which were placed at 25 ± 1°C with photoperiod of 12 L:12 D, intraperitoneal injection of MEL was performed daily for 28 days. The results showed that body mass and food intake were significantly decreased, while resting metabolic rate (RMR) and nonshivering thermogenesis (NST) were significantly increased after MEL injection; Contents of total protein, mitochondrial protein, the activities of cytochrome C oxidase (COX) and α-glycerophosphate oxidase (α-PGO) in liver and brown adipose tissue (BAT) were enhanced; the activity of thyroxin 5'-deiodinase (T₄ 5'-DII) and uncoupling protein 1 (UCP1) in BAT were also increased. Serum leptin, triiodothyronine (T₃ ) levels and T₃ /T₄ ratio were significantly increased, thyroxine (T₄ ) levels was significantly decreased. Moreover, body mass and food intake in E. miletus from KM were higher than those from DL, but RMR and NST were lower than those from DL. Changes of body mass, food intake and thermogenic activity of KM were higher than those of DL when exposed to injection of MEL, indicating that E. miletus in KM were more sensitive to MEL. Furthermore, MEL was involved in the regulation of body mass and thermogenesis in E. miletus between KM and DL.

Melatonin increases susceptibility to atrial fibrillation in obesity via Akt signaling impairment in response to lipid overload

Melatonin has been proven to have antiarrhythmic potential; however, several studies have recently challenged this view. Herein, using a mouse model of obesity-induced atrial fibrillation (AF), we tentatively explored whether exogenous melatonin supplementation could increase AF susceptibility in the context of obesity. We observed that an 8-week drinking administration of melatonin (60 µg/ml in water) induced a greater susceptibility to AF in obese mice, although obesity-induced structural remodeling was alleviated. An investigation of systemic insulin sensitivity showed that melatonin treatment improved insulin sensitivity in obese mice, whereas it inhibited glucose-stimulated insulin secretion. Notably, melatonin treatment inhibited protein kinase B (Akt) signaling in the atria of obese mice and palmitate-treated neonatal rat cardiomyocytes, thereby providing an AF substrate. Melatonin increased lipid stress in obesity, as evidenced by elevated lipid accumulation and lipolysis-related gene expression, thus contributing to the impairment in atrial Akt signaling. Taken together, our results demonstrated that melatonin could increase AF susceptibility in obesity, probably due to increased lipid stress and resultant impairment of atrial Akt signaling. Our findings suggest that special precautions should be taken when administering melatonin to obese subjects.

Melatonin Treatment in Kidney Diseases

Melatonin is a neurohormone that is mainly secreted by the pineal gland. It coordinates the work of the superior biological clock and consequently affects many processes in the human body. Disorders of the waking and sleeping period result in nervous system imbalance and generate metabolic and endocrine derangements. The purpose of this review is to provide information regarding the potential benefits of melatonin use, particularly in kidney diseases. The impact on the cardiovascular system, diabetes, and homeostasis causes melatonin to be indirectly connected to kidney function and quality of life in people with chronic kidney disease. Moreover, there are numerous reports showing that melatonin plays a role as an antioxidant, free radical scavenger, and cytoprotective agent. This means that the supplementation of melatonin can be helpful in almost every type of kidney injury because inflammation, apoptosis, and oxidative stress occur, regardless of the mechanism. The administration of melatonin has a renoprotective effect and inhibits the progression of complications connected to renal failure. It is very important that exogenous melatonin supplementation is well tolerated and that the number of side effects caused by this type of treatment is low.

Benefits of the Neurogenic Potential of Melatonin for Treating Neurological and Neuropsychiatric Disorders

There are several neurological diseases under which processes related to adult brain neurogenesis, such cell proliferation, neural differentiation and neuronal maturation, are affected. Melatonin can exert a relevant benefit for treating neurological disorders, given its well-known antioxidant and anti-inflammatory properties as well as its pro-survival effects. In addition, melatonin is able to modulate cell proliferation and neural differentiation processes in neural stem/progenitor cells while improving neuronal maturation of neural precursor cells and newly created postmitotic neurons. Thus, melatonin shows relevant pro-neurogenic properties that may have benefits for neurological conditions associated with impairments in adult brain neurogenesis. For instance, the anti-aging properties of melatonin seem to be linked to its neurogenic properties. Modulation of neurogenesis by melatonin is beneficial under conditions of stress, anxiety and depression as well as for the ischemic brain or after a brain stroke. Pro-neurogenic actions of melatonin may also be beneficial for treating dementias, after a traumatic brain injury, and under conditions of epilepsy, schizophrenia and amyotrophic lateral sclerosis. Melatonin may represent a pro-neurogenic treatment effective for retarding the progression of neuropathology associated with Down syndrome. Finally, more studies are necessary to elucidate the benefits of melatonin treatments under brain disorders related to impairments in glucose and insulin homeostasis.

Molecular basis of ligand selectivity for melatonin receptors

Sleep disorders in adults are related to adverse health effects such as reduced quality of life and increased mortality. About 30-40% of adults are suffering from different sleep disorders. The human melatonin receptors (MT1 and MT2) are family A G protein-coupled receptors that respond to the neurohormone melatonin MEL which regulates circadian rhythm and sleep. Many efforts have been made to develop drugs targeting melatonin receptors to treat insomnia, circadian rhythm disorders, and even cancer. However, designing subtype-selective melatonergic drugs remains challenging due to their high similarities in both sequences and structures. MEL (a function-selective compound with a bulky β-naphthyl group) behaves as an MT2-selective antagonist, whereas it is an agonist of MT1. Here, molecular dynamics simulations were used to investigate the ligand selectivity of MT receptors at the atomic level. We found that the binding conformation of MEL differs in different melatonin receptors. In MT1, the naphthalene ring of MEL forms a structure perpendicular to the membrane surface. In contrast, there is a 130° angle between the naphthalene ring of MEL and the membrane surface in MT2. Because of this conformational difference, the MEL leads to a constant water channel in MT1 which activates the receptor. However, MEL hinders the formation of continuous water channels, resulting in an inactive state of MT2. Furthermore, we found that A117^3.29 in MT2 is a crucial amino acid capable of hindering the conformational flip of the MEL molecule. These results, coupled with previous functional data, reveal that although MT1 and MT2 share highly similar orthosteric ligand-binding pockets, they also display distinctive features that could be used to design selective compounds. Our findings provide new insights into functionally selective melatonergic drug development for sleep disorders.

Role of Melatonin in Daily Variations of Plasma Insulin Level and Pancreatic Clock Gene Expression in Chick Exposed to Monochromatic Light

To clarify the effect of monochromatic light on circadian rhythms of plasma insulin level and pancreatic clock gene expression and its mechanism, 216 newly hatched chicks were divided into three groups (intact, sham operation and pinealectomy) and were raised under white (WL), red (RL), green (GL) or blue (BL) light for 21 days. Their plasma and pancreas were sampled at six four-hour intervals. For circadian rhythm analysis, measurements of plasma melatonin, insulin, and clock gene expression (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2, and cPer3) were made. Plasma melatonin, insulin, and the pancreatic clock gene all expressed rhythmically in the presence of monochromatic light. Red light reduced the mesor and amplitude of plasma melatonin in comparison to green light. The mesor and amplitude of the pancreatic clock gene in chickens exposed to red light were dramatically reduced, which is consistent with the drop in plasma melatonin levels. Red light, on the other hand, clearly raised the level of plasma insulin via raising the expression of cVamp2, but not cInsulin. After the pineal gland was removed, the circadian expressions of plasma melatonin and pancreatic clock gene were significantly reduced, but the plasma insulin level and the pancreatic cVamp2 expression were obviously increased, resulting in the disappearance of differences in insulin level and cVamp2 expression in the monochromatic light groups. Therefore, we hypothesize that melatonin may be crucial in the effect of monochromatic light on the circadian rhythm of plasma insulin level by influencing the expression of clock gene in chicken pancreas.

Melatonin supplementation promotes muscle fiber hypertrophy and regulates lipid metabolism of skeletal muscle in weaned piglets

Melatonin has been reported to play crucial roles in regulating meat quality, improving reproductive properties, and maintaining intestinal health in animal production, but whether it regulates skeletal muscle development in weaned piglet is rarely studied. This study was conducted to investigate the effects of melatonin on growth performance, skeletal muscle development, and lipid metabolism in animals by intragastric administration of melatonin solution. Twelve 28-d-old DLY (Duroc × Landrace × Yorkshire) weaned piglets with similar body weight were randomly divided into two groups: control group and melatonin group. The results showed that melatonin supplementation for 23 d had no effect on growth performance, but significantly reduced serum glucose content (P < 0.05). Remarkably, melatonin increased longissimus dorsi muscle (LDM) weight, eye muscle area and decreased the liver weight in weaned piglets (P < 0.05). In addition, the cross-sectional area of muscle fibers was increased (P < 0.05), while triglyceride levels were decreased in LDM and psoas major muscle by melatonin treatment (P < 0.05). Transcriptome sequencing showed melatonin induced the expression of genes related to skeletal muscle hypertrophy and fatty acid oxidation. Enrichment analysis indicated that melatonin regulated cholesterol metabolism, protein digestion and absorption, and mitophagy signaling pathways in muscle. Gene set enrichment analysis also confirmed the effects of melatonin on skeletal muscle development and mitochondrial structure and function. Moreover, quantitative real-time polymerase chain reaction analysis revealed that melatonin supplementation elevated the gene expression of cell differentiation and muscle fiber development, including paired box 7 (PAX7), myogenin (MYOG), myosin heavy chain (MYHC) IIA and MYHC IIB (P < 0.05), which was accompanied by increased insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein 5 (IGFBP5) expression in LDM (P < 0.05). Additionally, melatonin regulated lipid metabolism and activated mitochondrial function in muscle by increasing the mRNA abundance of cytochrome c oxidase subunit 6A (COX6A), COX5B, and carnitine palmitoyltransferase 2 (CPT2) and decreasing the mRNA expression of peroxisome proliferator-activated receptor gamma (PPARG), acetyl-CoA carboxylase (ACC) and fatty acid-binding protein 4 (FABP4) (P < 0.05). Together, our results suggest that melatonin could promote skeletal muscle growth and muscle fiber hypertrophy, improve mitochondrial function and decrease fat deposition in muscle.

Melatonin and Aging

The health problems associated with the aging process are becoming increasingly widespread due to the increase in mean life expectancy taking place globally. While decline of many organ functions is an unavoidable concomitant of senescence, these can be delayed or moderated by a range of factors. Among these are dietary changes and weight control, taking sufficient exercise, and the utilization of various micronutrients. The utility of incurring appropriate changes in lifestyle is generally not confined to a single organ system but has a broadly positive systemic effect.Among one of the most potent means of slowing down age-related changes is the use of melatonin, a widely distributed biological indole. While melatonin is well known as a treatment for insomnia, it has a wide range of beneficial qualities many of which are relevant. This overview describes how several of the properties of melatonin are especially relevant to many of the changes associated with senescence. Changes in functioning of the immune system are particularly marked in the aged, combining diminishing effectiveness with increasing ineffective and harmful activity. Melatonin treatment appears able to moderate and partially reverse this detrimental drift toward immune incompetence.

Genetics of circadian rhythms and sleep in human health and disease

Circadian rhythms and sleep are fundamental biological processes integral to human health. Their disruption is associated with detrimental physiological consequences, including cognitive, metabolic, cardiovascular and immunological dysfunctions. Yet many of the molecular underpinnings of sleep regulation in health and disease have remained elusive. Given the moderate heritability of circadian and sleep traits, genetics offers an opportunity that complements insights from model organism studies to advance our fundamental molecular understanding of human circadian and sleep physiology and linked chronic disease biology. Here, we review recent discoveries of the genetics of circadian and sleep physiology and disorders with a focus on those that reveal causal contributions to complex diseases.

Infusion timing and sleep habits of adults receiving home parenteral and enteral nutrition: A patient-oriented survey study

BACKGROUND

The emerging field of chrononutrition investigates the effects of the timing of nutritional intake on human physiology and disease pathology. It remains largely unknown when patients receiving home nutrition support routinely administer home parenteral nutrition (HPN) and/or home enteral nutrition (HEN).

METHODS

The present descriptive study included data collected from a patient-oriented survey designed to assess the timing of infusions and sleep habits of patients receiving HPN and HEN in the United States.

RESULTS

A total of 100 patients were included. Patients had a mean age of 44.1 years and 81% were female. Among 73 patients supported with HPN and 27 patients supported with HEN, 86% and 44% reported overnight infusions, respectively. The median start and end times of overnight infusions were 2100 (interquartile range [IQR] = 1900-2200) and 0800 (IQR = 0700-1000), respectively, for HPN and 2000 (IQR = 1845-2137) and 0845 (IQR = 0723-1000), respectively, for HEN. Overnight infusions started 2.0 h (IQR = 1.1-3.0) and 2.0 h (IQR = 0.6-3.3) before bedtime for HPN and HEN, respectively, and stopped 12.9 min (IQR = -21.3 to 29.1) and 30.0 min (IQR = -17.1 to 79.3) after wake time for HPN and HEN, respectively. Sleep disruption because of nutrition support or urination was most common among patients receiving infusions overnight compared with those receiving infusions continuously or during the daytime.

CONCLUSIONS

Our survey study focusing on a novel and medically relevant dimension of nutrition found that most HPN-dependent and HEN-dependent patients receive infusions overnight while asleep. Our findings suggest that overnight infusions coinciding with sleep may result in sleep and circadian disruption.

Research gaps and opportunities in precision nutrition: an NIH workshop report

Precision nutrition is an emerging concept that aims to develop nutrition recommendations tailored to different people's circumstances and biological characteristics. Responses to dietary change and the resulting health outcomes from consuming different diets may vary significantly between people based on interactions between their genetic backgrounds, physiology, microbiome, underlying health status, behaviors, social influences, and environmental exposures. On 11-12 January 2021, the National Institutes of Health convened a workshop entitled "Precision Nutrition: Research Gaps and Opportunities" to bring together experts to discuss the issues involved in better understanding and addressing precision nutrition. The workshop proceeded in 3 parts: part I covered many aspects of genetics and physiology that mediate the links between nutrient intake and health conditions such as cardiovascular disease, Alzheimer disease, and cancer; part II reviewed potential contributors to interindividual variability in dietary exposures and responses such as baseline nutritional status, circadian rhythm/sleep, environmental exposures, sensory properties of food, stress, inflammation, and the social determinants of health; part III presented the need for systems approaches, with new methods and technologies that can facilitate the study and implementation of precision nutrition, and workforce development needed to create a new generation of researchers. The workshop concluded that much research will be needed before more precise nutrition recommendations can be achieved. This includes better understanding and accounting for variables such as age, sex, ethnicity, medical history, genetics, and social and environmental factors. The advent of new methods and technologies and the availability of considerably more data bring tremendous opportunity. However, the field must proceed with appropriate levels of caution and make sure the factors listed above are all considered, and systems approaches and methods are incorporated. It will be important to develop and train an expanded workforce with the goal of reducing health disparities and improving precision nutritional advice for all Americans.