Absence of melatonin induces night-time hepatic insulin resistance and increased gluconeogenesis due to stimulation of nocturnal unfolded protein response

Melatonin increases AKT and SOD gene and protein expressions in diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disease marked by hyperglycemia due to insulin deficiency or insulin resistance leading to many chronic complications. It is thus important to manage diabetes effectively in order to prevent and or delay these complications. Melatonin is produced by the pineal gland and regulates the wake-sleep circadian rhythm. Existing evidence suggests that melatonin may be effective in the management of DM. However, the evidence on the mechanism of the beneficial effect melatonin as a treatment for DM is limited. In this study, we investigated the effect of melatonin treatment on blood glucose, insulin (INS), AKT and superoxide dismutase (SOD) gene levels in diabetic rats. Non-diabetic and diabetic rats were treated orally for 4 weeks with either 25 mg or 50 mg/kg body weight of melatonin. At the end of the study, pancreatic and liver tissues morphology, glucose homeostasis, serum insulin and SOD levels, hepatic gene and protein expression of SOD as protecting antioxidant enzyme and AKT as central element involved in PI3K/AKT insulin signaling pathway were estimated. Melatonin treated diabetic rats showed reduced hyperglycemia, and increased serum insulin and SOD levels. In addition, melatonin induced an increased gene and protein expression of SOD and AKT. In conclusion, melatonin may play a role in treating diabetic rats via stimulation of insulin secretion, insulin signaling and reduction in oxidative stress.

Dim Light at Night Promotes Circadian Disruption in Female Rats, at the Metabolic, Reproductive, and Behavioral Level

Inhabitants of urban areas are constantly exposed to light at night, which is an important environmental factor leading to circadian disruption. Streetlights filtering light through the windows and night dim light lamps are common sources of dim light at night (DLAN). The female population is susceptible to circadian disruption. The present study is aimed to determine the impact of DLAN on female Wistar rats circadian rhythms, metabolism, reproductive physiology, and behavior. After 5 weeks of DLAN exposure daily, oscillations in activity and body temperature of female rats are abolished. DLAN also decreases nocturnal food ingestion, which results in a diminishment in total food consumption. These alterations in the temporal organization of the body are associated with a significant decrease in melatonin plasmatic levels, reproductive disruptions, decreased exploration times, and marked anhedonia. This study highlights the importance of avoiding exposure to light at night, even at low intensities, to maintain the circadian organization of physiology, and denotes the great necessity of increasing the studies in females since the sexual dimorphism within the effects of desynchronizing protocols has been poorly studied.

Enhancement of the SESN2-SHP cascade by melatonin ameliorates hepatic gluconeogenesis by inhibiting the CRBN-BTG2-CREBH signaling pathway

Melatonin is involved in the regulation of various biological functions. Here, we explored a novel molecular mechanism by which the melatonin-induced sestrin2 (SESN2)-small heterodimer partner (SHP) signaling pathway protects against fasting- and diabetes-mediated hepatic glucose metabolism. Various key gene expression analyses were performed and multiple metabolic changes were assessed in liver specimens and primary hepatocytes of mice and human participants. The expression of the hepatic cereblon (CRBN) and b-cell translocation gene 2 (BTG2) genes was significantly increased in fasting mice, diabetic mice, and patients with diabetes. Overexpression of Crbn and Btg2 increased hepatic gluconeogenesis by enhancing cyclic adenosine monophosphate (cAMP)-responsive element-binding protein H (CREBH), whereas this phenomenon was prominently ablated in Crbn null mice and Btg2-silenced mice. Interestingly, melatonin-induced SESN2 and SHP markedly reduced hepatic glucose metabolism in diabetic mice and primary hepatocytes, and this protective effect of melatonin was strikingly reversed by silencing Sesn2 and Shp. Finally, the melatonin-induced SESN2-SHP signaling pathway inhibited CRBN- and BTG2-mediated hepatic gluconeogenic gene transcription via the competition of BTG2 and the interaction of CREBH. Mitigation of the CRBN-BTG2-CREBH axis by the melatonin-SESN2-SHP signaling network may provide a novel therapeutic strategy to treat metabolic dysfunction due to diabetes.

A novel combination of sitagliptin and melatonin ameliorates T2D manifestations: studies on experimental diabetic models

INTRODUCTION

Type 2 diabetes (T2D) is an endocrine disorder characterized by hyperglycemia, insulin resistance, dysregulated glucose and lipid metabolism, reduced pancreatic β-cell function and mass, and a reduced incretin effect. Circadian rhythm disruption is associated with increased T2D risk. We have investigated the therapeutic potential of a combination of melatonin (M) and sitagliptin (S), a dipeptidyl peptidase IV (DPP-IV) inhibitor, in the amelioration of T2D manifestations in high-fat diet (HFD) induced T2D mouse model and also on β-cell proliferation under gluco-lipotoxicity stress in vitro.

METHODS

For in vivo study, mice were fed with HFD for 25 weeks to induce T2D and were treated with monotherapies and S + M for four weeks. For the in vitro study, primary mouse islets were exposed to normal glucose and high glucose + palmitate to induce gluco-lipotoxic stress.

RESULTS

Our results suggest that monotherapies and S + M improve metabolic parameters and glyco-lipid metabolism in the liver and adipose tissue, respectively, and improve mitochondrial function in the skeletal muscle. Moreover, it increases peripheral insulin sensitivity. Our in vitro and in vivo studies suggest that β-cell mass was preserved in all the drug-treated groups.

CONCLUSION

The combination treatment is superior to monotherapies in the management of T2D.

Melatonin and melatonin-agonists for metabolic syndrome components in patients treated with antipsychotics: A systematic review and meta-analysis

OBJECTIVE

Metabolic side effects are a limiting factor in the use of antipsychotics, which remain the cornerstone of long-term management of patients with severe mental illness. There is contrasting evidence on a possible role of melatonin and melatonin-agonists in attenuating antipsychotic-induced metabolic abnormalities.

DESIGN

We conducted a systematic review (PubMed, PsycInfo, Cochrane databases, up to August 2020) and a random-effect meta-analysis of double-blind, randomized placebo-controlled trials (RCTs) involving melatonin and melatonin-agonists in the treatment of antipsychotic-induced metabolic changes. The primary outcome was the standardized mean difference (SMD) of composite metabolic outcomes built with metabolic syndrome components. Secondary outcomes were individual metabolic syndrome components, and other anthropometric, glucose metabolism, lipid profile, and psychopathology measures.

RESULTS

Out of the initial 41 studies, six documented five separate RCTs randomizing 248 patients (126 to melatonin/ramelteon, 122 to placebo) affected by schizophrenia-spectrum disorders and bipolar disorder. Melatonin/ramelteon outperformed placebo on the primary outcome (SMD -0.28, 95% CI = -0.39 ÷ -0.168), as well as on all individual components of metabolic syndrome (systolic blood pressure MD -3.266, 95% CI = -6.020 ÷ -0.511; fasting glucose MD -3.766, 95% CI = -5.938 ÷ -1.593; triglycerides MD -9.800, 95% CI = -19.431 ÷ -0.169; HDL MD 2.995, 95% CI = 0.567 ÷ 5.423), except waist circumference.

CONCLUSIONS

Melatonin/ramelteon augmentation may be beneficial for non-anthropometric metabolic syndrome components in patients treated with antipsychotics.

Membrane Melatonin Receptors Activated Cell Signaling in Physiology and Disease

The pineal hormone melatonin has attracted great scientific interest since its discovery in 1958. Despite the enormous number of basic and clinical studies the exact role of melatonin in respect to human physiology remains elusive. In humans, two high-affinity receptors for melatonin, MT1 and MT2, belonging to the family of G protein-coupled receptors (GPCRs) have been cloned and identified. The two receptor types activate Gi proteins and MT2 couples additionally to Gq proteins to modulate intracellular events. The individual effects of MT1 and MT2 receptor activation in a variety of cells are complemented by their ability to form homo- and heterodimers, the functional relevance of which is yet to be confirmed. Recently, several melatonin receptor genetic polymorphisms were discovered and implicated in pathology-for instance in type 2 diabetes, autoimmune disease, and cancer. The circadian patterns of melatonin secretion, its pleiotropic effects depending on cell type and condition, and the already demonstrated cross-talks of melatonin receptors with other signal transduction pathways further contribute to the perplexity of research on the role of the pineal hormone in humans. In this review we try to summarize the current knowledge on the membrane melatonin receptor activated cell signaling in physiology and pathology and their relevance to certain disease conditions including cancer.

Therapeutics for type-2 diabetes mellitus: a glance at the recent inclusions and novel agents under development for use in clinical practice

Diabetes mellitus (DM) is a chronic, progressive, and multifaceted illness resulting in significant physical and psychological detriment to patients. As of 2019, 463 million people are estimated to be living with DM worldwide, out of which 90% have type-2 diabetes mellitus (T2DM). Over the years, significant progress has been made in identifying the risk factors for developing T2DM, understanding its pathophysiology and uncovering various metabolic pathways implicated in the disease process. This has culminated in the implementation of robust prevention programmes and the development of effective pharmacological agents, which have had a favourable impact on the management of T2DM in recent times. Despite these advances, the incidence and prevalence of T2DM continue to rise. Continuing research in improving efficacy, potency, delivery and reducing the adverse effect profile of currently available formulations is required to keep pace with this growing health challenge. Moreover, new metabolic pathways need to be targeted to produce novel pharmacotherapy to restore glucose homeostasis and address metabolic sequelae in patients with T2DM. We searched PubMed, MEDLINE, and Google Scholar databases for recently included agents and novel medication under development for treatment of T2DM. We discuss the pathophysiology of T2DM and review how the emerging anti-diabetic agents target the metabolic pathways involved. We also look at some of the limiting factors to developing new medication and the introduction of unique methods, including facilitating drug delivery to bypass some of these obstacles. However, despite the advances in the therapeutic options for the treatment of T2DM in recent years, the industry still lacks a curative agent.

Melatonin ameliorates endocrine dysfunction and defective sperm integrity associated with high-fat diet-induced obesity in male Wistar rats

Obesity (OBS) has been established as a link to male hypogonadism with consequent infertility. Previous studies have shown that melatonin (MEL) modulates hypothalamic-pituitary-gonadal function. The present study therefore investigated the hypothesis that MEL supplementation would attenuate spermatogenic and steroidogenic dysfunctions associated with obesity induced by high-fat diet (HFD). Twenty-four adult male Wistar rats (n = 6/group) were used: control group received vehicle (normal saline), obese group received 40% high-fat diet and distilled water, MEL-treated group received MEL (4 mg/kg), and OBS + MEL group received MEL and 40% HFD and the treatment lasted for 12 weeks. HFD caused increased body weight, glucose intolerance, plasma triglyceride and low-density lipoprotein cholesterol/ very low-density lipoprotein cholesterol and malondialdehyde, as well as decreased antioxidant capacity, high-density lipoprotein cholesterol, gonadotrophin-releasing hormone, follicle-stimulating hormone and testosterone and altered sperm parameters. However, all these alterations were attenuated when supplemented with MEL. Taken together, these results indicate that HFD exposure causes endocrine dysfunction and disrupted sperm parameters in obese animals, which are accompanied by lipid peroxidation/defective antioxidant capacity. In addition, the present results suggest that melatonin supplementation restores endocrine function and sperm integrity in obese rat model by suppression of oxidative stress-dependent mechanism.

Agomelatine reduces circulating triacylglycerides and hepatic steatosis in fructose-treated rats

Agomelatine (AGO) is an antidepressant drug with agonistic activity at melatonin receptor 1 (MT1) and MT2 and with neutral antagonistic activity at serotonin receptor 5-HT2_C. Although experimental studies show that melatonin reduces hypertriglyceridemia and hepatic steatosis induced by excessive fructose intake, no studies have tested if AGO exerts similar actions. To address this issue we have treated male Wistar rats with fructose (15% in the drinking water) and/or AGO (40 mg/kg/day) for two weeks. AGO reduced body weight gain, feeding efficiency and hepatic lipid levels without affecting caloric intake in fructose-treated rats. AGO has also decreased very low-density lipoprotein (VLDL) production and circulating TAG levels after an oral load with olive oil. Accordingly, treatment with AGO reduced the hepatic expression of fatty acid synthase (Fasn), a limiting step for hepatic de novo lipogenesis (DNLG). The expression of apolipoprotein B (Apob) and microsomal triglyceride transfer protein (Mttp) in the ileum, two crucial proteins for intestinal lipoprotein production, were also downregulated by treatment with AGO. Altogether, the present data show that AGO mimics the metabolic benefits of melatonin when used in fructose-treated rats. This study also suggests that it is relevant to evaluate the potential of AGO to treat metabolic disorders in future clinical trials.

Agomelatine protects against obesity-induced renal injury by inhibiting endoplasmic reticulum stress/apoptosis pathway in rats

Obesity is recognized as a risk for the development of chronic kidney disease. Excessive fat accumulation in obesity is associated with the overproduction of reactive oxygen species with the underproduction of antioxidant mechanisms generating oxidative stress together with chronic low-grade inflammation which subsequently leads to the development of several obesity-related complications. It has been suggested that the abnormal lipid accumulation can induce endoplasmic reticulum (ER) stress and cellular apoptosis in several tissue types. Agomelatine is a relatively new antidepressant which is a synthetic agonist of melatonin. Previous study reported the antioxidant and anti-inflammatory effects of agomelatine. In this study, we investigated the therapeutic effects of agomelatine in obesity-related renal injury. Male Wistar rats were fed with normal diet or high-fat diet (HF) for 16 weeks. After that, vehicle or agomelatine or vildagliptin was orally administered to HF rats for 4 weeks. Our results indicated that HF rats demonstrated insulin resistance which was accompanied by an impairment of renal function and renal organic anion transporter 3 (Oat3) function as well as renal oxidative stress, ER stress, and apoptosis. Interestingly, agomelatine treatment not only improved the metabolic parameters, renal function and renal Oat3 function but also attenuated renal oxidative stress, ER stress and subsequent apoptosis. Therefore, agomelatine exerted renoprotective effects in obese insulin-resistant condition. These results suggested that agomelatine could be used as a drug to improve metabolic disturbance and prevent kidney dysfunction in obese condition.

Effects of melatonin supplementation on eating habits and appetite-regulating hormones: a systematic review of randomized controlled clinical and preclinical trials

Melatonin is a hormone involved in appetite regulation and food intake. Circadian chronorrupture caused by its absence has been associated with excessive food consumption, and there is evidence that exogenous melatonin supplementation can restore homeostasis. Therefore, the aim of this systematic review was to synthesize evidence from randomized controlled clinical and preclinical trials that evaluated the effects of exogenous melatonin supplementation on eating habits and appetite-regulating hormones. The protocol was registered in PROSPERO (number 42020175809). Medline, Scopus, Web of Science and Cochrane Library were systematically searched from January 2020 to February 2021. Of 3.695 articles identified, 2 clinical and 13 preclinical trials (n = 15) met the inclusion criteria. The outcomes were total food intake, calories, macronutrients, cholesterol intake, leptin and ghrelin levels. Interventions ranged from 28 to 336 days and dose of melatonin varied between 0.2 µg/mL of drinking water and 10 mg/day. Clinical trials were conducted with healthy adults, and preclinical trials with rodents and dogs. Of the 15 articles, five assessed food intake and leptin, four assessed food intake only, five assessed leptin only, and one assessed leptin and ghrelin serum levels. The majority of the articles were judged as having low risk of bias. Although findings are heterogeneous and do not allow a robust conclusion, this review adds to the growing body of evidence suggesting that exogenous melatonin may be a potential therapeutic agent against endocrine-metabolic disorders. This reversal is not necessarily associated with changes in food consumption, signaling that melatonin's metabolic effects may occur independently of energy intake. Further studies, especially with humans, are needed provide more evidences for melatonin supplementation in clinical practice, as well as to understand its role on eating habits and appetite-regulating hormones.

Obese Neotomodon alstoni mice exhibit sexual dimorphism in the daily profile of circulating melatonin and clock proteins PER1 and BMAL1 in the hypothalamus and peripheral oscillators

Obesity is a global health threat and a risk factor for several metabolic conditions. Though circadian dysfunction has been considered among the multiple causes of obesity, little work has been done to explore the relationship between obesity, circadian dysfunction, and sexual dimorphism. The Neotomodon alstoni mouse is a suitable model for such research. This study employed N. alstoni mice in a chronobiological analysis to determine whether there is circadian desynchronization of relative PER1 and BMAL1 protein levels in the hypothalamus, liver, visceral white adipose tissue, kidney, and heart. It also compared differences between sexes and lean and obese N. alstoni adult mice, by recording behavior and daily circulating serum melatonin as markers of circadian output. We found that obese mice display reduced locomotor activity. Additionally, Cosinor analyses of the relative expression of PER1 and BMAL1 show differences between lean and obese mice in a sex-linked manner. The PER1 24 h rhythm was absent in all tissues of obese males and significant in the tissues of obese females. The BMAL1 24 h rhythm also was significant in most of the tissues tested in lean males, whereas it was significant and shifted the acrophase (peak time of rhythm) in most of the tissues in obese females. Both lean male and female mice showed a rhythmic 24 h pattern of circulating serum melatonin. This daily profile was not only absent in obese mice of both sexes but showed sexual dimorphism. Obese male mice showed lower circulating levels of melatonin compared to lean male mice, but they were higher in obese females compared to lean females. Our results suggest that obesity in N. alstoni is associated with an internal circadian desynchronization in a sex-dependent manner. Overall, this study reinforces the need for further research on the neuroendocrinology of obesity and circadian rhythms using this biological model.

Melatonin protects the heart and pancreas by improving glucose homeostasis, oxidative stress, inflammation and apoptosis in T2DM-induced rats

Cardiomyopathy and pancreatic injury are health issues associated with type 2 diabetes mellitus (T2DM) and are characterized by elevated oxidative stress, inflammation and apoptosis. Melatonin (MLT) is a hormone with multifunctional antioxidant activity. The protective effects of MLT on the heart and pancreas during the early development of diabetic cardiomyopathy and pancreatic injury were investigated in male Wistar rats with T2DM. MLT (10 mg/kg) was administered daily by gavage for 15 days after diabetic induction. Treatment of diabetic rats with MLT significantly normalized the levels of serum glucose, HbA1-c, and the lipid profile and improved the insulin levels and insulin resistance compared with diabetic rats, affirming its antidiabetic effect. MLT significantly prevented the development of oxidative stress and sustained the levels of glutathione and glutathione peroxidase activity in the heart and pancreas of diabetic animals, indicating its antioxidant capacity. Additionally, MLT prevented the increase in proinflammatory cytokines and expression of Bax, caspase-3 and P53. Furthermore, MLT enhanced the anti-inflammatory cytokine IL-10 and antiapoptotic protein Bcl-2. MLT controlled the levels of troponin T and creatine kinase-MB and lactate dehydrogenase activity, indicating its anti-inflammatory and antiapoptotic effects. Histological examinations confirmed the protective effects of MLT on T2DM-induced injury in the myocardium, pancreas and islets of Langerhans. In conclusion, the protective effects of melatonin on the heart and pancreas during the early development of T2DM are attributed to its antihyperglycemic, antilipidemic and antioxidant influences as well as its remarkable anti-inflammatory and antiapoptotic properties.

Maternal Melatonin Deficiency Leads to Endocrine Pathologies in Children in Early Ontogenesis

The review summarizes the results of experimental and clinical studies aimed at elucidating the causes and pathophysiological mechanisms of the development of endocrine pathology in children. The modern data on the role of epigenetic influences in the early ontogenesis of unfavorable factors that violate the patterns of the formation of regulatory mechanisms during periods of critical development of fetal organs and systems and contribute to the delayed development of pathological conditions are considered. The mechanisms of the participation of melatonin in the regulation of metabolic processes and the key role of maternal melatonin in the formation of the circadian system of regulation in the fetus and in the protection of the genetic program of its morphofunctional development during pregnancy complications are presented. Melatonin, by controlling DNA methylation and histone modification, prevents changes in gene expression that are directly related to the programming of endocrine pathology in offspring. Deficiency and absence of the circadian rhythm of maternal melatonin underlies violations of the genetic program for the development of hormonal and metabolic regulatory mechanisms of the functional systems of the child, which determines the programming and implementation of endocrine pathology in early ontogenesis, contributing to its development in later life. The significance of this factor in the pathophysiological mechanisms of endocrine disorders determines a new approach to risk assessment and timely prevention of offspring diseases even at the stage of family planning.

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

BACKGROUND

Obesity is an important clinical entity, causing many public health issues. Around two billion people in the world are overweight and obese. Almost 40% of American adults are obese and Brazil has about 18 million obese people. Nowadays, 415 million people have diabetes, around 1 in every 11 adults. These numbers will rise to 650 million people within 20 years. Melatonin shows a positive profile on the regulation of the metabolism of the human body.

OBJECTIVE

This study aimed to carry out a broad narrative review of the metabolic profile and associations between melatonin, diabetes and obesity.

METHODS

Article reviews, systematic reviews, prospective studies, retrospective studies, randomized, double-blind, and 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 content part of the paper, and 153 studies composed the narrative review.

RESULTS

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 the possible benefit of it. There is so far no consensus about the 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.

Maternal pineal melatonin in gestation and lactation physiology, and in fetal development and programming

Pregnancy and lactation are reproductive processes that rely on physiological adaptations that should be timely and adequately triggered to guarantee both maternal and fetal health. Pineal melatonin is a hormone that presents daily and seasonal variations that synchronizes the organism's physiology to the different demands across time through its specific mechanisms and ways of action. The reproductive system is a notable target for melatonin as it actively participates on reproductive physiology and regulates the hypothalamus-pituitary-gonads axis, influencing gonadotropins and sexual hormones synthesis and release. For its antioxidant properties, melatonin is also vital for the oocytes and spermatozoa quality and viability, and for blastocyst development. Maternal pineal melatonin blood levels increase during pregnancy and triggers the maternal physiological alterations in energy metabolism both during pregnancy and lactation to cope with the energy demands of both periods and to promote adequate mammary gland development. Moreover, maternal melatonin freely crosses the placenta and is the only source of this hormone to the fetus. It importantly times the conceptus physiology and influences its development and programing of several functions that depend on neural and brain development, ultimately priming adult behavior and energy and glucose metabolism. The present review aims to explain the above listed melatonin functions, including the potential alterations observed in the progeny gestated under maternal chronodisruption and/or hypomelatoninemia.

Maternal Chronodisruption Throughout Pregnancy Impairs Glucose Homeostasis and Adipose Tissue Physiology in the Male Rat Offspring

Compelling evidence in rats support the idea that gestational chronodisruption induces major changes in maternal circadian rhythms and fetal development and that these changes impact adult life at many physiological levels. Using a model of chronic photoperiod shifting throughout gestation (CPS), in which pregnant female rats (Sprague-Dawley strain; n = 16 per group) were exposed to lighting schedule manipulation every 3-4 days reversing the photoperiod completely or light/dark photoperiod (12/12; LD), we explored in the adult rat male offspring body weight gain, glucose homeostasis, adipose tissue content, adipose tissue response to norepinephrine (NE), and adipose tissue proteomic in the basal condition with standard diet (SD) and in response to high-fat diet (HFD). In adult CPS male (100-200 days old; n = 8 per group), we found increasing body weight, under SD and adiposity. Also, we found an increased response to intraperitoneal glucose (IGTT). After 12 weeks of HFD, white adipose tissue depots in CPS offspring were increased further, and higher IGTT and lower intraperitoneal insulin tolerance response were found, despite the lack of changes in food intake. In in vitro experiments, we observed that adipose tissue (WAT and BAT) glycerol response to NE from CPS offspring was decreased, and it was completely abolished by HFD. At the proteomic level, in CPS adipose tissue, 275 proteins displayed differential expression, compared with LD animals fed with a standard diet. Interestingly, CPS offspring and LD fed with HFD showed 20 proteins in common (2 upregulated and 18 downregulated). Based on these common proteins, the IPA analysis found that two functional pathways were significantly altered by CPS: network 1 (AKT/ERK) and network 2 (TNF/IL4; data are available via ProteomeXchange with identifier PXD026315). The present data show that gestational chronodisruption induced deleterious effects in adipose tissue recruitment and function, supporting the idea that adipose tissue function was programmed in utero by gestational chronodisruption, inducing deficient metabolic responses that persist into adulthood.

Melatonin stimulates transcription of the rat phosphoenolpyruvate carboxykinase gene in hepatic cells

Melatonin plays physiological roles in various critical processes, including circadian rhythms, oxidative stress defenses, anti-inflammation responses, and immunity; however, the current understanding of the role of melatonin in hepatic glucose metabolism is limited. In this study, we examined whether melatonin affects gene expression of the key gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK). We found that melatonin treatment increased PEPCK mRNA levels in rat highly differentiated hepatoma (H4IIE) cells and primary cultured hepatocytes. In addition, we found that melatonin induction was synergistically enhanced by dexamethasone, whereas it was dominantly inhibited by insulin. We also report that the effect of melatonin was blocked by inhibitors of mitogen-activated protein kinase/extracellular signal-regulated protein kinase (MAPK/ERK), RNA polymerase II, and protein synthesis. Furthermore, the phosphorylated (active) forms of ERK1 and ERK2 (ERK1/2) increased 15 min after melatonin treatment. We performed luciferase reporter assays to show that melatonin specifically stimulated promoter activity of the PEPCK gene. Additional reporter analysis using 5'-deleted constructs revealed that the regulatory regions responsive to melatonin mapped to two nucleotide regions, one between -467 and -398 nucleotides and the other between -128 and +69 nucleotides, of the rat PEPCK gene. Thus, we conclude that melatonin induces PEPCK gene expression via the ERK1/2 pathway at the transcriptional level, and that induction requires de novo protein synthesis.

Chronological Age Interacts with the Circadian Melatonin Receptor 1B Gene Variation, Determining Fasting Glucose Concentrations in Mediterranean Populations. Additional Analyses on Type-2 Diabetes Risk

Gene-age interactions have not been systematically investigated on metabolic phenotypes and this modulation will be key for a better understanding of the temporal regulation in nutrigenomics. Taking into account that aging is typically associated with both impairment of the circadian system and a decrease in melatonin secretion, we focused on the melatonin receptor 1B (MTNR1B)-rs10830963 C>G variant that has been associated with fasting glucose concentrations, gestational diabetes, and type-2 diabetes. Therefore, our main aim was to investigate whether the association between the MTNR1B-rs10830963 polymorphism and fasting glucose is age dependent. Our secondary aims were to analyze the polymorphism association with type-2 diabetes and explore the gene-pregnancies interactions on the later type-2 diabetes risk. Three Mediterranean cohorts (n = 2823) were analyzed. First, a cross-sectional study in the discovery cohort consisting of 1378 participants (aged 18 to 80 years; mean age 41 years) from the general population was carried out. To validate and extend the results, two replication cohorts consisting of elderly individuals were studied. In the discovery cohort, we observed a strong gene-age interaction (p = 0.001), determining fasting glucose in such a way that the increasing effect of the risk G-allele was much greater in young (p = 5.9 × 10^-10) than in elderly participants (p = 0.805). Consistently, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose concentrations in the two replication cohorts (mean age over 65 years) did not reach statistical significance (p > 0.05 for both). However, in the elderly cohorts, significant associations between the polymorphism and type-2 diabetes at baseline were found. Moreover, in one of the cohorts, we obtained a statistically significant interaction between the MTNR1B polymorphism and the number of pregnancies, retrospectively assessed, on the type-2 diabetes risk. In conclusion, the association of the MTNR1B-rs10830963 polymorphism with fasting glucose is age-dependent, having a greater effect in younger people. However, in elderly subjects, associations of the polymorphism with type-2 diabetes were observed and our exploratory analysis suggested a modulatory effect of the number of past pregnancies on the future type-2 diabetes genetic risk.

Effects of altered photoperiod due to COVID-19 lockdown on pregnant women and their fetuses

Maternal circadian rhythms provide highly important input into the entrainment and programming of fetal and newborn circadian rhythms. The light-dark cycle is an important regulator of the internal biological clock. Even though pregnant women spend a greater part of the day at home during the latter stages of pregnancy, natural light exposure is crucial for the fetus. The current recommended COVID-19 lockdown might dramatically alter normal environmental lighting conditions of pregnant women, resulting in exposure to extremely low levels of natural daylight and high-intensity artificial light sources during both day and night. This article summarizes the potential effects on pregnant woman and their fetuses due to prolonged exposure to altered photoperiod and as consequence altered circadian system, known as chronodisruption, that may result from the COVID-19 lockdown.

Cardioprotective effects of melatonin: Focusing on its roles against diabetic cardiomyopathy

Melatonin is a pineal-produced indole known for its anti-aging, antiapoptotic and antioxidant properties. In past decades, the protective potentials of melatonin for cardiovascular diseases, such as atherosclerosis and myocardial infarction, have been widely revealed, triggering more investigations focused on other cardioprotective effects of melatonin. Recently, the roles of melatonin in diabetic cardiomyopathy (DCM) have attracted increased attention. In this regard, researchers found that melatonin attenuated cardiac fibrosis and hypertrophy, thus interrupting the development of DCM. Retinoid-related orphan receptor α is a key melatonin receptor that contributed to the cardioprotective effect of melatonin in hearts with DCM. For the downstream mechanisms, the inhibition of mammalian STE20-like kinase 1 plays a pivotal role, which exerts antiapoptotic and proautophagic effects, thus enhancing cardiac tolerance in high-glucose conditions. In addition, other signalling mechanisms, such as sirtuin-1/peroxisome proliferator-activated receptor gamma-coactivator alpha and endoplasmic reticulum-related signalling, are also involved in the protective effects of melatonin on cardiomyocytes under diabetic conditions. This review will focus on the protective signalling mechanisms regulated by melatonin and provide a better understanding of the therapeutic applications of melatonin signalling in DCM.

Gut Dysbiosis Dysregulates Central and Systemic Homeostasis via Suboptimal Mitochondrial Function: Assessment, Treatment and Classification Implications

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The gut and mitochondria have emerged as two important hubs at the cutting edge of research across a diverse array of medical conditions, including most psychiatric conditions. This article highlights the interaction of the gut and mitochondria over the course of development, with an emphasis on the consequences for transdiagnostic processes across psychiatry, but with relevance to wider medical conditions. As well as raised levels of circulating lipopolysaccharide (LPS) arising from increased gut permeability, the loss of the short-chain fatty acid, butyrate, is an important mediator of how gut dysbiosis modulates mitochondrial function. Reactive cells, central glia and systemic immune cells are also modulated by the gut, in part via impacts on mitochondrial function in these cells. Gut-driven alterations in the activity of reactive cells over the course of development are proposed to be an important determinant of the transdiagnostic influence of glia and the immune system. Stress, including prenatal stress, also acts via the gut. The suppression of butyrate, coupled to raised LPS, drives oxidative and nitrosative stress signalling that culminates in the activation of acidic sphingomyelinase-induced ceramide. Raised ceramide levels negatively regulate mitochondrial function, both directly and via its negative impact on daytime, arousal-promoting orexin and night-time sleep-promoting pineal gland-derived melatonin. Both orexin and melatonin positively regulate mitochondria oxidative phosphorylation. Consequently, gut-mediated increases in ceramide have impacts on the circadian rhythm and the circadian regulation of mitochondrial function. Butyrate, orexin and melatonin can positively regulate mitochondria via the disinhibition of the pyruvate dehydrogenase complex, leading to increased conversion of pyruvate to acetyl- CoA. Acetyl-CoA is a necessary co-substrate for the initiation of the melatonergic pathway in mitochondria and therefore the beneficial effects of mitochondria melatonin synthesis on mitochondrial function. This has a number of treatment implications across psychiatric and wider medical conditions, including the utilization of sodium butyrate and melatonin.

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Overall, gut dysbiosis and increased gut permeability have significant impacts on central and systemic homeostasis via the regulation of mitochondrial function, especially in central glia and systemic immune cells.

Dysregulation of Circadian Rhythms in Autism Spectrum Disorders

Background:

The alterations in neurological and neuroendocrine functions observed in the autism spectrum disorder (ASD) involves environmentally dependent dysregulation of neurodevelopment, in interaction with multiple coding gene defects. Disturbed sleep-wake patterns, as well as abnormal melatonin and glucocorticoid secretion, show the relevance of an underlying impairment of the circadian timing system to the behavioral phenotype of ASD. Thus, understanding the mechanisms involved in the circadian dysregulation in ASD could help to identify early biomarkers to improve the diagnosis and therapeutics as well as providing a significant impact on the lifelong prognosis.

Objective:

In this review, we discuss the organization of the circadian timing system and explore the connection between neuroanatomic, molecular, and neuroendocrine responses of ASD and its clinical manifestations. Here we propose interconnections between circadian dysregulation, inflammatory baseline and behavioral changes in ASD. Taking into account, the high relevancy of melatonin in orchestrating both circadian timing and the maintenance of physiological immune quiescence, we raise the hypothesis that melatonin or analogs should be considered as a pharmacological approach to suppress inflammation and circadian misalignment in ASD patients.

Strategy:

This review provides a comprehensive update on the state-of-art of studies related to inflammatory states and ASD with a special focus on the relationship with melatonin and clock genes. The hypothesis raised above was analyzed according to the published data.

Conclusion:

Current evidence supports the existence of associations between ASD to circadian dysregulation, behavior problems, increased inflammatory levels of cytokines, sleep disorders, as well as reduced circadian neuroendocrine responses. Indeed, major effects may be related to a low melatonin rhythm. We propose that maintaining the proper rhythm of the circadian timing system may be helpful to improve the health and to cope with several behavioral changes observed in ASD subjects.

Melatonin Supplementation Attenuates the Pro-Inflammatory Adipokines Expression in Visceral Fat from Obese Mice Induced by A High-Fat Diet

Obesity is defined as a condition of abnormal or excessive fat accumulation in white adipose tissue that results from the exacerbated consumption of calories associated with low energy expenditure. Fat accumulation in both adipose tissue and other organs contributes to a systemic inflammation leading to the development of metabolic disorders such as type 2 diabetes, hypertension, and dyslipidemia. Melatonin is a potent antioxidant and improves inflammatory processes and energy metabolism. Using male mice fed a high-fat diet (HFD—59% fat from lard and soybean oil; 9:1) as an obesity model, we investigated the effects of melatonin supplementation on the prevention of obesity-associated complications through an analysis of plasma biochemical profile, body and fat depots mass, adipocytes size and inflammatory cytokines expression in epididymal (EPI) adipose depot. Melatonin prevented a gain of body weight and fat depot mass as well as adipocyte hypertrophy. Melatonin also reversed the increase of total cholesterol, triglycerides and LDL-cholesterol. In addition, this neurohormone was effective in completely decreasing the inflammatory cytokines leptin and resistin in plasma. In the EPI depot, melatonin reversed the increase of leptin, Il-6, Mcp-1 and Tnf-α triggered by obesity. These data allow us to infer that melatonin presents an anti-obesity effect since it acts to prevent the progression of pro-inflammatory markers in the epididymal adipose tissue together with a reduction in adiposity.

New insights into the function of melatonin and its role in metabolic disturbances

INTRODUCTION

Melatonin is a pineal hormone that has acquired several unique modes of regulating the physiological effects in mammals due to its characteristic phylogenetic history. While melatonin exhibits immediate nocturnal effects, it also has next-day prospective effects that take place in the absence of this hormone. Besides that, the daily repetition and the annual variation in the duration of its synthesis determine its circadian and seasonal effects that characterize melatonin as a chronobiotic, a molecule that encodes time to the internal environment. Additionally, it presents transgenerational effects that are important for fetal programming, leading to a balanced energy metabolism in the adult life.

AREAS COVERED

Physiology, pathophysiology and therapeutic value of melatonin in metabolism and metabolic disorders.

EXPERT OPINION

The typical mechanisms of action of melatonin (immediate, prospective, chronobiotic and transgenerational) should be considered to adequately understand its physiological effects on the regulation of metabolism in humans and, as a result, to understand the metabolic pathophysiological consequences caused by its synthesis and/or signaling disturbances. That points to the importance of a broader understanding of melatonin actions, besides the classical endocrinological point of view, that would allow the clinician/research to proper interpret its role in health maintenance.

Melatonin Improves Fatty Liver Syndrome by Inhibiting the Lipogenesis Pathway in Hamsters with High-Fat Diet-Induced Hyperlipidemia

The aim of this study was to investigate the effect of melatonin on hepatic lipid metabolism in hamsters with high-fat diet (HFD)-induced dyslipidemia. Male Syrian hamsters were kept on either a chow control (C) or HFD for four weeks. After four weeks, animals fed the HFD were further randomly assigned to four groups: high-fat only (P), melatonin low-dosage (L), medium-dosage (M), and high-dosage (H) groups. The L, M, and H groups, respectively, received 10, 20, and 50 mg/kg/day of a melatonin solution, while the P and C groups received the ethanol vehicle. After eight weeks of the intervention, results showed that a low dose of melatonin significantly reduced HFD-induced hepatic cholesterol and triglycerides; decreased plasma cholesterol, triglycerides, and low-density lipoprotein cholesterol; and increased plasma high-density lipoprotein cholesterol (p < 0.05). In addition, melatonin markedly decreased activities of the hepatic lipogenic enzymes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) (p < 0.05), and elevated the relative hepatic carnitine palmitoyltransferase-1α expression in hamsters with HFD-induced hyperlipidemia. Consequently, melatonin reduced activities of the hepatic lipogenic enzymes, ACC and FAS. In summary, chronic melatonin administration improved HFD-induced dyslipidemia and hepatic lipid accumulation in Syrian hamsters with HFD-induced dyslipidemia, which might have occurred through inhibiting the lipogenesis pathway.

Melatonin multiple effects on brown adipose tissue molecular machinery

Brown adipose tissue (BAT) influences energy balance through nonshivering thermogenesis, and its metabolism daily and seasonal variations are regulated by melatonin through partially known mechanisms. We evaluated the role of melatonin in BAT molecular machinery of male Control, pinealectomized (PINX), and melatonin-treated pinealectomized (PINX/Mel) adult rats. BAT was collected either every 3 hours over 24 hours or after cold or high-fat diet (HFD) acute exposure. HFD PINX animals presented decreased Dio2 expression, while HFD PINX/Mel animals showed increased Dio2, Ucp1, and Cidea expression. Cold-exposed PINX rats showed decreased Dio2 and Lhs expression, and melatonin treatment augmented Adrβ3, Dio2, Ucp1, and Cidea expression. Daily profiles analyses showed altered Dio2, Lhs, Ucp1, Pgc1α, and Cidea gene and UCP1 protein expression in PINX animals, leading to altered rhythmicity under sub-thermoneutral conditions, which was partially restored by melatonin treatment. The same was observed for mitochondrial complexes I, II, and IV protein expression and enzyme activity. Melatonin absence seems to impair BAT responses to metabolic challenges, and melatonin replacement reverses this effect, with additional increase in the expression of crucial genes, suggesting that melatonin plays an important role in several key points of the thermogenic activation pathway, influencing both the rhythmic profile of the tissue and its ability to respond to metabolic challenges, which is crucial for the organism homeostasis.

Melatonin in type 2 diabetes mellitus and obesity

Despite considerable advances in the past few years, obesity and type 2 diabetes mellitus (T2DM) remain two major challenges for public health systems globally. In the past 9 years, genome-wide association studies (GWAS) have established a major role for genetic variation within the MTNR1B locus in regulating fasting plasma levels of glucose and in affecting the risk of T2DM. This discovery generated a major interest in the melatonergic system, in particular the melatonin MT₂ receptor (which is encoded by MTNR1B). In this Review, we discuss the effect of melatonin and its receptors on glucose homeostasis, obesity and T2DM. Preclinical and clinical post-GWAS evidence of frequent and rare variants of the MTNR1B locus confirmed its importance in regulating glucose homeostasis and T2DM risk with minor effects on obesity. However, these studies did not solve the question of whether melatonin is beneficial or detrimental, an issue that will be discussed in the context of the peculiarities of the melatonergic system. Melatonin receptors might have therapeutic potential as they belong to the highly druggable G protein-coupled receptor superfamily. Clarifying the precise role of melatonin and its receptors on glucose homeostasis is urgent, as melatonin is widely used for other indications, either as a prescribed medication or as a supplement without medical prescription, in many countries in Europe and in the USA.

Circadian Etiology of Type 2 Diabetes Mellitus

The epidemic of Type 2 diabetes mellitus necessitates development of novel therapeutic and preventative strategies to attenuate expansion of this debilitating disease. Evidence links the circadian system to various aspects of diabetes pathophysiology and treatment. The aim of this review will be to outline the rationale for therapeutic targeting of the circadian system in the treatment and prevention of Type 2 diabetes mellitus and consequent metabolic comorbidities.

Melatonin Signaling a Key Regulator of Glucose Homeostasis and Energy Metabolism

Melatonin, a hormone synthesized by both the pineal gland and retina, functions as an important modulator of a number of physiological functions. In addition to its rather well-established roles in the regulation of circadian rhythms, sleep, and reproduction, melatonin has also been identified as an important regulator of glucose metabolism. Recent genomic studies have also shown that disruption of melatonin receptors signaling may contribute to the pathogenesis of type 2 diabetes, although the exact mechanisms underlying its action remain unclear. Additionally, a large number of animal studies have highlighted a role for melatonin in the regulation of both glucose metabolism and energy balance. This review summarizes the current knowledge on the role that melatonin and its associated receptors play in the regulation of metabolism.

Melatonin as a Hormone: New Physiological and Clinical Insights

Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans. In vertebrates, besides being produced in peripheral tissues and acting as an autocrine and paracrine signal, melatonin is centrally synthetized by a neuroendocrine organ, the pineal gland. Independently of the considered species, pineal hormone melatonin is always produced during the night and its production and secretory episode duration are directly dependent on the length of the night. As its production is tightly linked to the light/dark cycle, melatonin main hormonal systemic integrative action is to coordinate behavioral and physiological adaptations to the environmental geophysical day and season. The circadian signal is dependent on its daily production regularity, on the contrast between day and night concentrations, and on specially developed ways of action. During its daily secretory episode, melatonin coordinates the night adaptive physiology through immediate effects and primes the day adaptive responses through prospective effects that will only appear at daytime, when melatonin is absent. Similarly, the annual history of the daily melatonin secretory episode duration primes the central nervous/endocrine system to the seasons to come. Remarkably, maternal melatonin programs the fetuses' behavior and physiology to cope with the environmental light/dark cycle and season after birth. These unique ways of action turn melatonin into a biological time-domain-acting molecule. The present review focuses on the above considerations, proposes a putative classification of clinical melatonin dysfunctions, and discusses general guidelines to the therapeutic use of melatonin.

Integration of Circadian and Metabolic Control of Reproductive Function

Optimal fertility in humans and animals relies on the availability of sufficient metabolic fuels, information about which is communicated to the brain via levels of the hormones leptin and insulin. The circadian clock system is also critical; this input is especially evident in the precise timing of the female-specific surge of GnRH and LH secretion that triggers ovulation the next day. Chronodisruption and metabolic imbalance can both impair reproductive activity, and these two disruptions exacerbate each other, such that they often occur simultaneously. Kisspeptin neurons located in the anteroventral periventricular nucleus of the hypothalamus are able to integrate both circadian and metabolic afferent inputs and use this information to modulate the timing and magnitude of the preovulatory GnRH/LH surge. In an environment in which exposure to high caloric diets and chronodisruptors such as artificial night lighting, shift work, and transmeridian travel have become the norm, the implications of these factors for couples struggling to conceive deserve closer attention and more public education.

Melatonin treatment in fetal and neonatal diseases

This literature review aims to address the main scientific findings on oxidative stress activity in different gestational disorders, as well as the function and application of melatonin in the treatment of fetal and neonatal changes. Oxidative stress has been associated with the etiopathogenesis of recurrent miscarriages, preeclampsia, intrauterine growth restriction, and stillbirth. Both, the exacerbated consumption of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, and the increased synthesis of reactive oxygen species, such as superoxide, peroxynitrite, and hydrogen peroxide, induce phospholipid peroxidation and endothelial dysfunction, impaired invasion and death of trophoblast cells, impaired decidualization, and remodeling of maternal spiral arteries. It has been postulated that melatonin induces specific biochemical responses that regulate cell proliferation in fetuses, and that its antioxidant action promotes bioavailability of nitric oxide and, thus, placental perfusion and also fetal nutrition and oxygenation. Therefore, the therapeutic action of melatonin has been the subject of major studies that aim to minimize or prevent different injuries affecting this pediatric age group, such as intrauterine growth restriction, encephalopathy, chronic lung diseases, retinopathy of prematurity Conclusion: the results antioxidant and indicate that melatonin is an important therapy for the clinical treatment of these diseases.

Melatonin promotes reduction in TNF levels and improves the lipid profile and insulin sensitivity in pinealectomized rats with periodontal disease

AIM

This study aimed to investigate the effects of melatonin (ME) on insulin resistance (IR) and signaling (IS), proinflammatory cytokine levels, and lipid profiles in pinealectomyzed (PNX) rats with periodontal disease (PD).

MAIN METHODS

One hundred and forty-four rats (age = 40 days) were distributed into 8 groups: 1) control (CN); 2) PD only; 3) PNX only; 4) PNX and PD (PNXPD); 5) CN treated with ME (CNM); 6) PD treated with ME (PDM); 7) PNX treated with ME(PNXM); 8) PNX and PD treated with ME(PNXPDM). The PNX groups were subjected to pinealectomy at 40 and at 60 days of age. The animals were then subjected to PD induction in the mandibular first molars. After PD induction, the ME replacement therapy (MERT-5 mg/kg body weight) was performed using water for 28 days. After this period, the plasma concentration of glucose, insulin, TNF, IL-6, triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, and VLDL-cholesterol and the HOMA-IR index were determined. Akt serine phosphorylation status in the white adipose tissue, gastrocnemius muscle, and rat liver were also evaluated.

KEY FINDINGS

PD, PNX, and PNXPD groups showed an increase in IR with elevated plasma levels of insulin and TNF compared to CN group. PNX and PNXPD groups presented alteration in lipid profile compared to CN group. MERT improved all of the analyzed parameters. No difference was observed in the IS among different groups.

SIGNIFICANCE

The results suggest that MERT efficiently prevents IR, improves lipid profile, and increases plasma levels of insulin and TNF in PD and PNX rats.

Constant light during lactation programs circadian and metabolic systems

Exposure to light at night is a disruptive condition for the adult circadian system, leading to arrhythmicity in nocturnal rodents. Circadian disruption is a risk factor for developing physiological and behavioral alterations, including weight gain and metabolic disease. During early stages of development, the circadian system undergoes a critical period of adjustment, and it is especially vulnerable to altered lighting conditions that may program its function, leading to long-term effects. We hypothesized that during lactation a disrupted light-dark cycle due to light at night may disrupt the circadian system and in the long term induce metabolic disorders. Here we explored in pups, short- and long-term effects of constant light (LL) during lactation. In the short term, LL caused a loss of rhythmicity and a reduction in the immunopositive cells of VIP, AVP, and PER1 in the suprachiasmatic nucleus (SCN). In the short term, the affection on the circadian clock in the pups resulted in body weight gain, loss of daily rhythms in general activity, plasma glucose and triglycerides (TG). Importantly, the DD conditions during development also induced altered daily rhythms in general activity and in the SCN. Exposure to LD conditions after lactation did not restore rhythmicity in the SCN, and the number of immunopositve cells to VIP, AVP, and PER1 remained reduced. In the long term, daily rhythmicity in general activity was restored; however, daily rhythms in glucose and TG remained disrupted, and daily mean levels of TG were significantly increased. Present results point out the programming role played by the LD cycle during early development in the function of the circadian system and on metabolism. This study points out the risk represented by exposure to an altered light-dark cycle during early stages of development.

ABBREVIATIONS

AVP: arginine vasopressin peptide; CRY: cryptochrome; DD: constant darkness; DM: dorsomedial; LD: light-dark cycle; LL: constant light; NICUs: neonatal intensive care units; P: postnatal days; PER: period; S.E.M.: standard error of the mean; SCN: suprachiasmatic nucleus; TG: triglycerides; VIP: vasointestinal peptide; VL: ventrolateral; ZT: zeitgeber time.

Angiogenic and antiangiogenic factors in preeclampsia

BACKGROUND

Pre-eclampsia is a multifactorial hypertensive disorder that is triggered by placental insufficiency and that accounts for up to 15% of maternal deaths. In normal pregnancies, this process depends on the balance between the expression of angiogenic factors and antiangiogenic factors, which are responsible for remodeling the spiral arteries, as well as for neoangiogenesis and fetal development.

PURPOSE

The aim of this review is to discuss the main scientific findings regarding the role of angiogenic and antiangiogenic factors in the etiopathogenesis of preeclampsia.

METHODS

An extensive research was conducted in the Pubmed database in search of scientific manuscripts discussing potential associations between angiogenic and antiangiogenic factors and preeclampsia. Ninety-one papers were included in this review.

RESULTS

There is an increased expression of soluble fms-like tyrosine kinase receptor and soluble endoglin in pre-eclampsia, as well as reduced placental expression of vascular endothelial growth factor and placental growth factor. Systemic hypertension, proteinuria and kidney injury - such as enlargement and glomerular fibrin deposit, capillary occlusion due to edema, and hypertrophy of endocapillary cells - are some of these changes. The complex etiopathogenesis of preeclampsia instigates research of different biomarkers that allow for the early diagnosis of this entity, such as vascular endothelial growth factor, placental growth factor, soluble fms-like tyrosine kinase receptor, soluble endoglin, placental glycoprotein pregnancy-associated plasma protein-A and protein 13.

CONCLUSION

Even though it is possible to establish an efficient and effective diagnostic tool, three key principles must be observed in the management of preeclampsia: prevention, early screening and treatment.

Effects of Melatonin on Glucose Homeostasis, Antioxidant Ability, and Adipokine Secretion in ICR Mice with NA/STZ-Induced Hyperglycemia

Diabetes is often associated with decreased melatonin level. The aim was to investigate the effects of different dosage of melatonin on glucose hemostasis, antioxidant ability and adipokines secretion in diabetic institute for cancer research (ICR) mice. Forty animals were randomly divided into five groups including control (C), diabetic (D), low-dosage (L), medium-dosage (M), and high-dosage (H) groups. Groups L, M, and H, respectively, received oral melatonin at 10, 20, and 50 mg/kg of BW (body weight) daily after inducing hyperglycemia by nicotinamide (NA)/ streptozotocin (STZ). After the six-week intervention, results showed that melatonin administration increased insulin level and performed lower area under the curve (AUC) in H group (p < 0.05). Melatonin could lower hepatic Malondialdehyde (MDA) level in all melatonin-treated groups and increase superoxide dismutase activity in H group (p < 0.05). Melatonin-treated groups revealed significant higher adiponectin in L group, and lower leptin/adiponectin ratio and leptin in M and H groups (p < 0.05). Melatonin could lower cholesterol and triglyceride in liver and decrease plasma cholesterol and low-density lipoprotein-cholesterol (LDL-C) in L group, and increase plasma high-density lipoprotein-cholesterol (HDL-C) in H group (p < 0.05). Above all, melatonin could decrease oxidative stress, increase the adiponectin level and improve dyslipidemia, especially in H group. These data support melatonin possibly being a helpful aid for treating hyperglycemia-related symptoms.

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

Daily interactions between the hypothalamic circadian clock at the suprachiasmatic nucleus (SCN) and peripheral circadian oscillators regulate physiology and metabolism to set temporal variations in homeostatic regulation. Phase coherence of these circadian oscillators is achieved by the entrainment of the SCN to the environmental 24-h light:dark (LD) cycle, coupled through downstream neural, neuroendocrine, and autonomic outputs. The SCN coordinate activity and feeding rhythms, thus setting the timing of food intake, energy expenditure, thermogenesis, and active and basal metabolism. In this work, we will discuss evidences exploring the impact of different photic entrainment conditions on energy metabolism. The steady-state interaction between the LD cycle and the SCN is essential for health and wellbeing, as its chronic misalignment disrupts the circadian organization at different levels. For instance, in nocturnal rodents, non-24 h protocols (i.e., LD cycles of different durations, or chronic jet-lag simulations) might generate forced desynchronization of oscillators from the behavioral to the metabolic level. Even seemingly subtle photic manipulations, as the exposure to a “dim light” scotophase, might lead to similar alterations. The daily amount of light integrated by the clock (i.e., the photophase duration) strongly regulates energy metabolism in photoperiodic species. Removing LD cycles under either constant light or darkness, which are routine protocols in chronobiology, can also affect metabolism, and the same happens with disrupted LD cycles (like shiftwork of jetlag) and artificial light at night in humans. A profound knowledge of the photic and metabolic inputs to the clock, as well as its endocrine and autonomic outputs to peripheral oscillators driving energy metabolism, will help us to understand and alleviate circadian health alterations including cardiometabolic diseases, diabetes, and obesity.

Maternal high-fat diet induces metabolic stress response disorders in offspring hypothalamus

Maternal obesity has been shown to increase the risk of obesity and related disorders in the offspring, which has been partially attributed to changes of appetite regulators in the offspring hypothalamus. On the other hand, endoplasmic reticulum (ER) stress and autophagy have been implicated in hypothalamic neuropeptide dysregulation, thus may also play important roles in such transgenerational effect. In this study, we show that offspring born to high-fat diet-fed dams showed significantly increased body weight and glucose intolerance, adiposity and plasma triglyceride level at weaning. Hypothalamic mRNA level of the orexigenic neuropeptide Y (NPY) was increased, while the levels of the anorexigenic pro-opiomelanocortin (POMC), NPY1 receptor (NPY1R) and melanocortin-4 receptor (MC4R) were significantly downregulated. In association, the expression of unfolded protein response (UPR) markers including glucose-regulated protein (GRP)94 and endoplasmic reticulum DNA J domain-containing protein (Erdj)4 was reduced. By contrast, protein levels of autophagy-related genes Atg5 and Atg7, as well as mitophagy marker Parkin, were slightly increased. The administration of 4-phenyl butyrate (PBA), a chemical chaperone of protein folding and UPR activator, in the offspring from postnatal day 4 significantly reduced their body weight, fat deposition, which were in association with increased activating transcription factor (ATF)4, immunoglobulin-binding protein (BiP) and Erdj4 mRNA as well as reduced Parkin, PTEN-induced putative kinase (PINK)1 and dynamin-related protein (Drp)1 protein expression levels. These results suggest that hypothalamic ER stress and mitophagy are among the regulatory factors of offspring metabolic changes due to maternal obesity.

Chronomedicine and type 2 diabetes: shining some light on melatonin

In mammals, the circadian timing system drives rhythms of physiology and behaviour, including the daily rhythms of feeding and activity. The timing system coordinates temporal variation in the biochemical landscape with changes in nutrient intake in order to optimise energy balance and maintain metabolic homeostasis. Circadian disruption (e.g. as a result of shift work or jet lag) can disturb this continuity and increase the risk of cardiometabolic disease. Obesity and metabolic disease can also disturb the timing and amplitude of the clock in multiple organ systems, further exacerbating disease progression. As our understanding of the synergy between the timing system and metabolism has grown, an interest has emerged in the development of novel clock-targeting pharmaceuticals or nutraceuticals for the treatment of metabolic dysfunction. Recently, the pineal hormone melatonin has received some attention as a potential chronotherapeutic drug for metabolic disease. Melatonin is well known for its sleep-promoting effects and putative activity as a chronobiotic drug, stimulating coordination of biochemical oscillations through targeting the internal timing system. Melatonin affects the insulin secretory activity of the pancreatic beta cell, hepatic glucose metabolism and insulin sensitivity. Individuals with type 2 diabetes mellitus have lower night-time serum melatonin levels and increased risk of comorbid sleep disturbances compared with healthy individuals. Further, reduced melatonin levels, and mutations and/or genetic polymorphisms of the melatonin receptors are associated with an increased risk of developing type 2 diabetes. Herein we review our understanding of molecular clock control of glucose homeostasis, detail the influence of circadian disruption on glucose metabolism in critical peripheral tissues, explore the contribution of melatonin signalling to the aetiology of type 2 diabetes, and discuss the pros and cons of melatonin chronopharmacotherapy in disease management.

Factors involved in white-to-brown adipose tissue conversion and in thermogenesis: a review

Obesity is the result of energy intake chronically exceeding energy expenditure. Classical treatments against obesity do not provide a satisfactory long-term outcome for the majority of patients. After the demonstration of functional brown adipose tissue in human adults, great effort is being devoted to develop therapies based on the adipose tissue itself, through the conversion of fat-accumulating white adipose tissue into energy-dissipating brown adipose tissue. Anti-obesity treatments that exploit endogenous, pharmacological and nutritional factors to drive such conversion are especially in demand. In the present review, we summarize the current knowledge about the various molecules that can be applied in promoting white-to-brown adipose tissue conversion and energy expenditure and the cellular mechanisms involved.

Metabolic Impact of Light Phase-Restricted Fructose Consumption Is Linked to Changes in Hypothalamic AMPK Phosphorylation and Melatonin Production in Rats

Recent studies show that the metabolic effects of fructose may vary depending on the phase of its consumption along with the light/dark cycle. Here, we investigated the metabolic outcomes of fructose consumption by rats during either the light (LPF) or the dark (DPF) phases of the light/dark cycle. This experimental approach was combined with other interventions, including restriction of chow availability to the dark phase, melatonin administration or intracerebroventricular inhibition of adenosine monophosphate-activated protein kinase (AMPK) with Compound C. LPF, but not DPF rats, exhibited increased hypothalamic AMPK phosphorylation, glucose intolerance, reduced urinary 6-sulfatoxymelatonin (6-S-Mel) (a metabolite of melatonin) and increased corticosterone levels. LPF, but not DPF rats, also exhibited increased chow ingestion during the light phase. The mentioned changes were blunted by Compound C. LPF rats subjected to dark phase-restricted feeding still exhibited increased hypothalamic AMPK phosphorylation but failed to develop the endocrine and metabolic changes. Moreover, melatonin administration to LPF rats reduced corticosterone and prevented glucose intolerance. Altogether, the present data suggests that consumption of fructose during the light phase results in out-of-phase feeding due to increased hypothalamic AMPK phosphorylation. This shift in spontaneous chow ingestion is responsible for the reduction of 6-S-Mel and glucose intolerance.

Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase

Melatonin is a hormone synthesized in the pineal gland, which modulates several functions within the organism, including the synchronization of glucose metabolism and glucose-stimulated insulin secretion (GSIS). Melatonin can mediate different signaling pathways in pancreatic islets through two membrane receptors and via antioxidant or pro-oxidant enzymes modulation. NADPH oxidase (NOX) is a pro-oxidant enzyme responsible for the production of the reactive oxygen specie (ROS) superoxide, generated from molecular oxygen. In pancreatic islets, NOX-derived ROS can modulate glucose metabolism and regulate insulin secretion. Considering the roles of both melatonin and NOX in islets, the aim of this study was to evaluate the association of NOX and ROS production on glucose metabolism, basal and GSIS in pinealectomized rats (PINX) and in melatonin-treated isolated pancreatic islets. Our results showed that ROS content derived from NOX activity was increased in PINX at baseline (2.8 mM glucose), which was followed by a reduction in glucose metabolism and basal insulin secretion in this group. Under 16.7 mM glucose, an increase in both glucose metabolism and GSIS was observed in PINX islets, without changes in ROS content. In isolated pancreatic islets from control animals incubated with 2.8 mM glucose, melatonin treatment reduced ROS content, whereas in 16.7 mM glucose, melatonin reduced ROS and GSIS. In conclusion, our results demonstrate that both basal and stimulated insulin secretion can be regulated by melatonin through the maintenance of ROS homeostasis in pancreatic islets.

When to eat? The influence of circadian rhythms on metabolic health: are animal studies providing the evidence?

As obesity and metabolic diseases rise, there is need to investigate physiological and behavioural aspects associated with their development. Circadian rhythms have a profound influence on metabolic processes, as they prepare the body to optimise energy use and storage. Moreover, food-related signals confer temporal order to organs involved in metabolic regulation. Therefore food intake should be synchronised with the suprachiasmatic nucleus (SCN) to elaborate efficient responses to environmental challenges. Human studies suggest that a loss of synchrony between mealtime and the SCN promotes obesity and metabolic disturbances. Animal research using different paradigms has been performed to characterise the effects of timing of food intake on metabolic profiles. Therefore the purpose of the present review is to critically examine the evidence of animal studies, to provide a state of the art on metabolic findings and to assess whether the paradigms used in rodent models give the evidence to support a 'best time' for food intake. First we analyse and compare the current findings of studies where mealtime has been shifted out of phase from the light-dark cycle. Then, we analyse studies restricting meal times to different moments within the active period. So far animal studies correlate well with human studies, demonstrating that restricting food intake to the active phase limits metabolic disturbances produced by high-energy diets and that eating during the inactive/sleep phase leads to a worse metabolic outcome. Based on the latter we discuss the missing elements and possible mechanisms leading to the metabolic consequences, as these are still lacking.