Melatonin attenuates smoking-induced hyperglycemia via preserving insulin secretion and hepatic glycogen synthesis in rats

Melatonin Ameliorates Hepatic Ferroptosis in NAFLD by Inhibiting ER Stress via the MT2/cAMP/PKA/IRE1 Signaling Pathway

Ferroptosis, an iron-dependent cell death form, has recently been observed in the development of non-alcoholic fatty liver disease (NAFLD). Melatonin (Mel) shows potential benefits for preventing and treating liver diseases. Whether and how Mel ameliorates hepatic ferroptosis in NAFLD is not fully understood. Here we established a mouse model of NAFLD induced by long-term high-fat diet (HFD) feeding. We found that Mel treatment ameliorated global metabolic abnormalities and inhibited the progression of NAFLD in mice. Most importantly, Mel supplementation significantly improved HFD-induced iron homeostasis disorders in the liver, including iron overload and ferritin transport disorders. For another, Mel ameliorated HFD-induced hepatic lipid peroxidation. The recuperative role of exogenous Mel on hepatocyte ferroptosis was also observed in PA- or Erastin-treated HepG2 cells. Mechanistically, MT2, but not MT1, was involved in the effect of Mel. Furthermore, Mel treatment inhibited HFD or Erastin-activated ER stress and activated the PKA/IRE1 signaling pathway. Co-expression of p-PKA and p-IRE1 was enhanced by the MT2 antagonist. Inhibitions of PKA and IRE1 respectively improved hepatocyte ferroptosis, and activations of cAMP/PKA reversed Mel's effect on ferroptosis. Collectively, these findings suggest that exogenous Mel inhibits hepatic ferroptosis in NAFLD by ameliorating ER stress through the MT2/cAMP/PKA/IRE1 pathway, proving that Mel is a promising candidate drug for the treatment of hepatic ferroptosis in NAFLD.

Melatonin: Facts, Extrapolations and Clinical Trials

Melatonin is a fascinating molecule that has captured the imagination of many scientists since its discovery in 1958. In recent times, the focus has changed from investigating its natural role as a transducer of biological time for physiological systems to hypothesized roles in virtually all clinical conditions. This goes along with the appearance of extensive literature claiming the (generally) positive benefits of high doses of melatonin in animal models and various clinical situations that would not be receptor-mediated. Based on the assumption that melatonin is safe, high doses have been administered to patients, including the elderly and children, in clinical trials. In this review, we critically review the corresponding literature, including the hypotheses that melatonin acts as a scavenger molecule, in particular in mitochondria, by trying not only to contextualize these interests but also by attempting to separate the wheat from the chaff (or the wishful thinking from the facts). We conclude that most claims remain hypotheses and that the experimental evidence used to promote them is limited and sometimes flawed. Our review will hopefully encourage clinical researchers to reflect on what melatonin can and cannot do and help move the field forward on a solid basis.

Role of melatonin receptor 1B gene polymorphism and its effect on the regulation of glucose transport in gestational diabetes mellitus

Melatonin receptor 1B (MT2, encoded by the MTNR1B gene), a high-affinity receptor for melatonin, is associated with glucose homeostasis including glucose uptake and transport. The rs10830963 variant in the MTNR1B gene is linked to glucose metabolism disorders including gestational diabetes mellitus (GDM); however, the relationship between MT2-mediated melatonin signaling and a high birth weight of GDM infants from maternal glucose abnormality remains poorly understood. This article aims to investigate the relationship between rs10830963 variants and GDM development, as well as the effects of MT2 receptor on glucose uptake and transport in trophoblasts. TaqMan-MGB (minor groove binder) probe quantitative real-time polymerase chain reaction (qPCR) assays were used for rs10930963 genotyping. MT2 expression in the placenta of GDM and normal pregnant women was detected by immunofluorescence, western blot, and qPCR. The relationship between MT2 and glucose transporters (GLUTs) or peroxisome proliferator-activated receptor γ (PPARγ) was established by western blot, and glucose consumption of trophoblasts was measured by a glucose assay kit. The results showed that the genotype and allele frequencies of rs10830963 were significantly different between GDM and normal pregnant women (P<0.05). The fasting, 1-h and 2-h plasma glucose levels of G-allele carriers were significantly higher than those of C-allele carriers (P<0.05). Besides, the protein and messenger RNA (mRNA) expression of MT2 in the placenta of GDM was significantly higher than that of normal pregnant women (P<0.05). Melatonin could stimulate glucose uptake and GLUT4 and PPARγ protein expression in trophoblasts, which could be attenuated by MT2 receptor knockdown. In conclusion, the rs10830963 variant was associated with an increased risk of GDM. The MT2 receptor is essential for melatonin to raise glucose uptake and transport, which may be mediated by PPARγ.

The roles of the circadian hormone melatonin in drug addiction

Given the devastating social and health consequences of drug addiction and the limitations of current treatments, a new strategy is needed. Circadian system disruptions are frequently associated with drug addiction. Correcting abnormal circadian rhythms and improving sleep quality may thus be beneficial in the treatment of patients with drug addiction. Melatonin, an essential circadian hormone that modulates the biological clock, has anti-inflammatory, analgesic, anti-depressive, and neuroprotective effects via gut microbiota regulation and epigenetic modifications. It has attracted scientists' attention as a potential solution to drug abuse. This review summarized scientific evidence on the roles of melatonin in substance use disorders at the cellular, circuitry, and system levels, and discussed its potential applications as an intervention strategy for drug addiction.

The Prospective Application of Melatonin in Treating Epigenetic Dysfunctional Diseases

In the past, different human disorders were described by scientists from the perspective of either environmental factors or just by genetically related mechanisms. The rise in epigenetic studies and its modifications, i.e., heritable alterations in gene expression without changes in DNA sequences, have now been confirmed in diseases. Modifications namely, DNA methylation, posttranslational histone modifications, and non-coding RNAs have led to a better understanding of the coaction between epigenetic alterations and human pathologies. Melatonin is a widely-produced indoleamine regulator molecule that influences numerous biological functions within many cell types. Concerning its broad spectrum of actions, melatonin should be investigated much more for its contribution to the upstream and downstream mechanistic regulation of epigenetic modifications in diseases. It is, therefore, necessary to fill the existing gaps concerning corresponding processes associated with melatonin with the physiological abnormalities brought by epigenetic modifications. This review outlines the findings on melatonin’s action on epigenetic regulation in human diseases including neurodegenerative diseases, diabetes, cancer, and cardiovascular diseases. It summarizes the ability of melatonin to act on molecules such as proteins and RNAs which affect the development and progression of diseases.

Aloe vera and Streptozotocin-Induced Diabetes Mellitus

Diabetes mellitus is defined as prolonged hyperglycemia, which can harm the eyes, kidneys, and cardiovascular and neurological systems. Herbal agents and their derived supplements have been used for treatment of diabetes mellitus as a part of integrated complementary medicine for centuries. Numerous studies have considered Aloe vera (L.) Burm.f, Xanthorrhoeaceae, as an alternative medicine due to its abundant bioactive chemicals, such as alkaloids, anthraquinones, and enthrones, with therapeutical properties including antioxidant, anti-inflammatory, neuro-protective, and anti-diabetic effects. Aloe vera has received considerable attention in traditional medicine for the treatment of several diseases including diabetes mellitus. Numerous studies have investigated the effects of herbal agents on diabetes mellitus using a streptozotocin-induced diabetic model. Thereby, this article reviews the effects of Aloe vera prescription on streptozotocin-induced diabetes mellitus to provide a clear insight into the role of this medicinal plant in several biological functions, such as antioxidant, wound healing, anti-inflammatory, anti-hyperglycemic, and anti-hyperlipidemic in diabetic models.

Diabetes mellitus and melatonin: Where are we?

Diabetes mellitus (DM) and diabetes-related complications are amongst the leading causes of mortality worldwide. The international diabetes federation (IDF) has estimated 592 million people to suffer from DM by 2035. Hence, finding a novel biomolecule that can effectively aid diabetes management is vital, as other existing drugs have numerous side effects. Melatonin, a pineal hormone having antioxidative and anti-inflammatory properties, has been implicated in circadian dysrhythmia-linked DM. Reduced levels of melatonin and a functional link between melatonin and insulin are implicated in the pathogenesis of type 2 diabetes (T2D) Additionally, genomic studies revealed that rare variants in melatonin receptor 1b (MTNR1B) are also associated with impaired glucose tolerance and increased risk of T2D. Moreover, exogenous melatonin treatment in cell lines, rodent models, and diabetic patients has shown a potent effect in alleviating diabetes and other related complications. This highlights the role of melatonin in glucose homeostasis. However, there are also contradictory reports on the effects of melatonin supplementation. Thus, it is essential to explore if melatonin can be taken from bench to bedside for diabetes management. This review summarizes the therapeutic potential of melatonin in various diabetic models and whether it can be considered a safe drug for managing diabetic complications and diabetic manifestations like oxidative stress, inflammation, ER stress, mitochondrial dysfunction, metabolic dysregulation, etc.

Effect of melatonin on stress-induced hyperglycemia and insulin resistance in critically-ill patients: A randomized double-blind, placebo-controlled clinical trial

BACKGROUND

Hyperglycemia is a common finding which is associated with increased mortality and morbidity among critically ill patients. There is currently no evidence that melatonin could improve stress induced hyperglycemia (SIH). In this study, we evaluated the effect of melatonin on blood sugar and insulin resistance (IR) in critically-ill patients.

METHODS

104 critically-ill patients with SIH divided into two groups, receiving melatonin (6 mg BD for 3 days) or placebo. Changes of blood sugar, IR indices including homeostasis model assessment for insulin resistance and homeostasis model assessment adiponectin (HOMA-AD) ratios, Glasgow coma scale (GCS) were evaluated on the 4th day of melatonin prescription. On the 7Th day of study, changes of ventilator dependency and delirium were considered. Mortality and intensive care unit (ICU) stay were also compared between groups.

RESULTS

On day 4, patients in the melatonin group had significantly lower blood glucose and HMOA-IR level compared with the placebo group (P=0.04 and P=0.03, respectively) whereas HOMA-AD level did not differ significantly from placebo group (p>0.2). Also, we did not observe any significant difference in GCS level at this time between groups (p>0.2). On day 7, melatonin could not improve ventilator dependency and delirium significantly (p>0.2) and also could not reduce mortality and ICU stay in comparison with placebo (p>0.2, P=0.2, respectively).

CONCLUSION

Melatonin supplementation showed positive effect on blood sugar and somehow insulin resistance whereas it could not improve ICU complications.

Mechanisms of Melatonin in Obesity: A Review

Obesity and its complications have become a prominent global public health problem that severely threatens human health. Melatonin, originally known as an effective antioxidant, is an endogenous hormone found throughout the body that serves various physiological functions. In recent decades, increasing attention has been paid to its unique function in regulating energy metabolism, especially in glucose and lipid metabolism. Accumulating evidence has established the relationship between melatonin and obesity; nevertheless, not all preclinical and clinical evidence indicates the anti-obesity effect of melatonin, which makes it remain to conclude the clinical effect of melatonin in the fight against obesity. In this review, we have summarized the current knowledge of melatonin in regulating obesity-related symptoms, with emphasis on its underlying mechanisms. The role of melatonin in regulating the lipid profile, adipose tissue, oxidative stress, and inflammation, as well as the interactions of melatonin with the circadian rhythm, gut microbiota, sleep disorder, as well as the α7nAChR, the opioidergic system, and exosomes, make melatonin a promising agent to open new avenues in the intervention of obesity.

Melatonin attenuates smoking-induced atherosclerosis by activating the Nrf2 pathway via NLRP3 inflammasomes in endothelial cells

Substantial evidence suggests that the effects of smoking in atherosclerosis are associated with inflammation mediated by endothelial cells. However, the mechanisms and potential drug therapies for smoking-induced atherosclerosis remain to be clarified. Considering that melatonin exerts beneficial effects in cardiovascular diseases, we examined its effects on cigarette smoke-induced vascular injury. We found that cigarette smoke extract (CSE) treatment induced NLRP3-related pyroptosis in human aortic endothelial cells (HAECs). CSE also induced ROS generation and upregulated the Nrf2 pathway in HAECs. Furthermore, pretreatment of HAECs with Nrf2-specific siRNA and an Nrf2 activator revealed that Nrf2 can inhibit CSE-induced ROS/NLRP3 activation. Nrf2 also improved cell viability and the expression of VEGF and eNOS in CSE-treated HAECs. In balloon-induced carotid artery injury model rats exposed to cigarette smoke, melatonin treatment reduced intimal hyperplasia in the carotid artery. Mechanistic studies revealed that compared with the control group, Nrf2 activation was increased in the melatonin group, whereas ROS levels and the NLRP3 inflammasome pathway were inhibited. These results reveal that melatonin might effectively protect against smoking-induced vascular injury and atherosclerosis through the Nrf2/ROS/NLRP3 signaling pathway. Overall, these observations provide compelling evidence for the clinical use of melatonin to reduce smoking-related inflammatory vascular injury and atherosclerosis.

Potential Role of Melatonin as an Adjuvant for Atherosclerotic Carotid Arterial Stenosis

Carotid artery stenosis (CAS) is an atherosclerotic disease characterized by a narrowing of the artery lumen and a high risk of ischemic stroke. Risk factors of atherosclerosis, including smoking, hypertension, hyperglycemia, hyperlipidemia, aging, and disrupted circadian rhythm, may potentiate atherosclerosis in the carotid artery and further reduce the arterial lumen. Ischemic stroke due to severe CAS and cerebral ischemic/reperfusion (I/R) injury after the revascularization of CAS also adversely affect clinical outcomes. Melatonin is a pluripotent agent with potent anti-inflammatory, anti-oxidative, and neuroprotective properties. Although there is a shortage of direct clinical evidence demonstrating the benefits of melatonin in CAS patients, previous studies have shown that melatonin may be beneficial for patients with CAS in terms of reducing endothelial damage, stabilizing arterial plaque, mitigating the harm from CAS-related ischemic stroke and cerebral I/R injury, and alleviating the adverse effects of the related risk factors. Additional pre-clinical and clinical are required to confirm this speculation.

Abnormal expression of TRIAP1 and its role in gestational diabetes mellitus-related pancreatic β cells

Gestational diabetes mellitus (GDM) is a disease that is typically characterized by insulin resistance and pancreatic β cell dysfunction. Currently, the role of TP53-regulated inhibitor of apoptosis 1 (TRIAP1) in the process of GDM remains to be elucidated. Therefore, the present study investigated the effects of TRIAP1 on GDM-related pancreatic β cells. Reverse transcription-quantitative PCR and western blot assays were conducted to analyze the expression levels of TRIAP1 in the peripheral blood of patients with GDM and subjects with healthy pregnancies. Subsequently, TRIAP1 small interfering RNA (siRNA), control siRNA, TRIAP1 plasmid and control plasmid were transfected into INS-1 cells to assess the effects of TRIAP1 on pancreatic β cells. ELISA was used to assess the total insulin content and insulin secretion of pancreatic β cells. MTT and flow cytometry assays were performed to determine the viability and apoptosis of pancreatic β cells. The results demonstrated that TRIAP1 expression was downregulated in peripheral blood samples from patients with GDM. Transfection with TRIAP1 siRNA significantly decreased the levels of total insulin content and reduced insulin secretion in pancreatic β cells. In addition, downregulation of TRIAP1 in pancreatic β cells significantly induced cell apoptosis and reduced cell viability. Accordingly, transfection of INS1 cells with TRIAP1 siRNA increased the levels of the apoptosis-associated genes apoptotic protease-activating factor 1, caspase-3, caspase-7 and caspase-9. However, transfection of the cells with TRIAP1 plasmid resulted in the opposite effects. TRIAP1 increased the growth of pancreatic β cells and their ability to secrete insulin, thus playing a protective role in GDM. The findings verified the effects and the underlying mechanism of TRIAP1 in pancreatic β cells and may provide additional clinical applications for the therapy of GDM.

Naturally occurring melatonin: Sources and possible ways of its biosynthesis

According to recent reports, the global market for melatonin is worth 700 million USD in 2018 and would reach 2,790 million USD by 2025, growing at a CAGR of 18.9% during 2019 to 2025. Having regard to the prevalence of sleep and circadian rhythm disorders and a clear tendency to increase the demand for melatonin, and the current lack of alternative green and cost-efficient technologies of its synthesis, the supply of this remedy will not be enough to guarantee melatonin supply and affordability on a global scale. The emergence of naturally occurring melatonin and its isomers in fermented foods has opened an exciting new research area; there are still, however, some obscure points in the efficient microbiological biosynthesis of melatonin. This review summarizes the research progress and recent evidence related to melatonin and its isomers in various foodstuffs. Additionally, one possible way to synthesize melatonin is also discussed. The evidence pointed out that the presence of melatonin and its isomers is not exclusive for grapes and grape-derived products, because it can be also found in sweet and sour cherries. However, different species of both Saccharomyces and non-Saccharomyces yeasts could be used to obtain melatonin and melatonin isomers in the process of alcoholic fermentation biotechnologically. The availability of L-tryptophan has been a key factor in determining the concentration of indolic compounds produced, and the utilization of probiotic lactic acid bacteria could help in the formation of melatonin isomers during malolactic fermentation. These approaches are environmentally friendly alternatives with a safer profile than conventional ones and could represent the future for sustainable industrial-scale melatonin production.

Melatonin Alleviates Neuronal Damage After Intracerebral Hemorrhage in Hyperglycemic Rats

Background

This study sought to investigate a novel effect of melatonin in reducing brain injury in an in vivo hyperglycemic intracerebral hemorrhage (ICH) model and further explore the mechanisms of protection.

Methods

Hyperglycemia ICH was induced in Sprague-Dawley rats by streptozocin injection followed by autologous blood injection into the striatum. A combined approach including RNA-specific depletion, electron microscopy, magnetic resonance, Western blots, and immunohistological staining was applied to quantify the brain injuries after ICH.

Results

Hyperglycemia resulted in enlarged hematoma volume, deteriorated brain edema, and aggravated neuronal mitochondria damage 3 days after ICH. Post-treatment with melatonin 2 hours after ICH dose-dependently improved neurological behavioral performance lasting out to 14 days after ICH. This improved neurological function was associated with enhanced structural and functional integrity of mitochondria. Mechanistic studies revealed that melatonin alleviated mitochondria damage in neurons via activating the PPARδ/PGC-1α pathway. Promisingly, melatonin treatment delayed until 6 hours after ICH still reduced brain edema and improved neurological functions. Melatonin supplementation reduces neuronal damage after hyperglycemic ICH by alleviating mitochondria damage in a PPARδ/PGC-1α-dependent manner.

Conclusion

Melatonin may represent a therapeutic strategy with a wide therapeutic window to reduce brain damage and improve long-term recovery after ICH.

Cigarette smoke exposure impairs lipid metabolism by decreasing low-density lipoprotein receptor expression in hepatocytes

BACKGROUND

Cigarette smoke (CS) exposure impairs serum lipid profiles and the function of vascular endothelial cells, which accelerates the atherosclerosis. However, the precise mechanism and effect on the expression of low-density lipoprotein receptor (LDLR) in the liver by CS exposure is still unclear.

METHODS

In this study, adult male C57BL/6 J mice were divided into three groups, with one group being exposed to CS for 6 weeks. HepG2 cells were treated with CS extract at concentrations of 1, 2.5, 5, and 10%.

RESULTS

The serum levels of total cholesterol (TC), triglycerides (TGs), and low-density lipoprotein cholesterol (LDL-C) for the CS-exposure group were significantly higher than those in the control group (P < 0.05). Moreover, CS exposure decreased the LDLR expression in the hepatocytes and promoted inflammation in the blood vessel walls. Melatonin was intraperitoneally injected at 10 mg/kg/d for 6 weeks alongside CS exposure, and this significantly decreased the levels of TC, TGs, and LDL-C and decreased the expression of intercellular adhesion molecule-1 and the infiltration of cluster determinant 68-cells. In vitro, CS extract prepared by bubbling CS through phosphate-buffered saline decreased the LDLR expression in HepG2 cells in a time- and concentration-dependent manner, and this effect was prevented by pretreatment with 100 μM melatonin.

CONCLUSIONS

In conclusion, CS exposure impaired lipid metabolism and decreased LDLR expression in hepatocytes, and these effects could be prevented by melatonin supplementation. These findings implied that melatonin has the potential therapeutic applicability in the prevention of lipid metabolic disorder in smokers.

Physiological factors contributing to HbA1c in the normal and pre-diabetic range: a cross-sectional analysis

PURPOSE

Little is known about the underlying physiology that contributes to Haemoglobin A1c (HbA_1c) in the normal and pre-diabetic range. We determined the contribution of fasting plasma glucose (FPG), 2-h plasma glucose (2hPG), insulin secretion, insulin sensitivity and endogenous glucose production to HbA_1c levels in the normal and pre-diabetic range.

METHODS

A total of 62 Danish men and women with normal or impaired glucose regulation were studied. HbA_1c levels were measured and participants underwent an oral glucose tolerance test with measurements of FPG and 2hPG, an intravenous glucose tolerance test for determination of first-phase insulin release, and a hyperinsulinaemic euglycaemic clamp for estimation of peripheral and hepatic insulin sensitivity. Associations of HbA_1c with the different measures of glucose metabolism were analysed by linear regression analysis.

RESULTS

HbA_1c levels ranged from 28 to 45 mmol/mol (4.7-6.3%) in the study population. 1 SD higher (log) FPG concentration (~1 mmol/L) was associated with 2 mmol/mol higher HbA_1c concentration (P < 0.001). In comparison, 1 SD higher levels of (log) first-phase insulin secretion or (log) disposition index were associated with 1.5 mmol/mol lower HbA_1c levels (P < 0.05). HbA_1c was not associated with peripheral or hepatic insulin sensitivity, endogenous glucose production or 2hPG levels.

CONCLUSION

HbA_1c levels within the normal and pre-diabetic range seem to reflect decreased insulin secretion to a higher extent than insulin resistance. Therefore, early prevention strategies for high-risk individuals identified by HbA_1c are not straightforward. More research on how to improve the health of beta cells either directly or indirectly in high-risk individuals is needed.

Melatonin alleviates progression of uterine endometrial cancer by suppressing estrogen/ubiquitin C/SDHB-mediated succinate accumulation

Succinate is an important intermediate of the tricarboxylic acid cycle. Recently discovered roles of succinate demonstrate its involvement in immunity and cancer biology; however, the precise underlying mechanisms of its involvement in these additional roles remain to be determined. In the present study, succinate dehydrogenase (SDH) B was decreased in uterine endometrial cancer cells (UECC) under negative regulation of estrogen. This decrease was the result of lower expression levels of ubiquitin C (UBC), which was associated with the activation of peroxisome proliferator-activated receptor gamma and specificity protein 1. The decreased levels of SDHB resulted in the accumulation of succinate in UECC, and thus, a decrease in the production of fumaric acid. Succinate downregulated voltage-gated potassium channel subfamily Q member 1 (KCNQ1) levels by activating serum/glucocorticoid regulated kinase 1 and promoted the growth of UECC in vitro and in vivo. Treatment with melatonin restricted estrogen/UBC/SDHB-induced succinate accumulation and upregulated expression of KCNQ1 and reduced the succinate-mediated growth of UECC in vitro and in vivo. Furthermore, overexpression of melatonin receptor 1B amplified the inhibitory effects of melatonin on succinate-mediated UECC growth. Together, the data in the present study suggest that melatonin suppresses UECC progression by inhibiting estrogen/UBC/SDHB-induced succinate accumulation. The present study provides a scientific basis for potential therapeutic strategies and targets in UEC, particularly for patients with abnormally low levels of SDHB.

Melatonin safeguards against fatty liver by antagonizing TRAFs-mediated ASK1 deubiquitination and stabilization in a β-arrestin-1 dependent manner

Melatonin has been previously shown to prevent nonalcoholic fatty liver disease (NAFLD), yet the underlying mechanisms are poorly understood. Here, we identified a previously unknown regulatory action of melatonin on apoptosis signal-regulating kinase 1 (ASK1) signaling pathway in the pathogenesis and development of NAFLD. Although melatonin administration did not alter food intake, it significantly alleviated fatty liver phenotypes, including the body weight gain, insulin resistance, hepatic lipid accumulation, steatohepatitis, and fibrosis in a high-fat diet (HFD)-induced NAFLD mouse model (in vivo). The protection of melatonin against NAFLD was not affected by inactivation of Kupffer cell in this model. In NAFLD mice liver, ASK1 signal cascade was substantially activated, evidence by the enhancement of total ASK1, phospho-ASK1, phospho-MKK3/6, phospho-p38, phospho-MKK4/7, and phospho-JNK. Melatonin treatment significantly suppressed the ASK1 upregulation and the phosphorylation of ASK1, MKK3/6, MKK4/7, p38, and JNK. Mechanistically, we found that lipid stress triggered the interaction between ASK1 and TNF receptor-associated factors (TRAFs), including TRAF1, TRAF2, and TRAF6, which resulted in ASK1 deubiquitination and thereby increased ASK1 protein stability. Melatonin did not alter ASK1 mRNA level; however, it activated a scaffold protein β-arrestin-1 and enabled it to bind to ASK1, which antagonized the TRAFs-mediated ASK1 deubiquitination, and thus reduced ASK1 protein stability. Consistent with these findings, knockout of β-arrestin-1 in mice partly abolished the protection of melatonin against NAFLD. Taken together, our results for the first time demonstrate that melatonin safeguards against NAFLD by eliminating ASK1 activation via inhibiting TRAFs-mediated ASK1 deubiquitination and stabilization in a β-arrestin-1 dependent manner.

Effects of melatonin implantation on carcass characteristics, meat quality and tissue levels of melatonin and prolactin in Inner Mongolian cashmere goats

Background

Implantation of goats with melatonin can induce cashmere growth and significantly increase cashmere production performance. However, the impact of melatonin implantation on the carcass characteristics, meat quality and related hormone levels in muscle and viscera of cashmere goats has not been studied. This experiment was conducted to determine the effects of melatonin implantation of cashmere goats during the non-growing period on meat quality and related hormone levels in the tissues. It aimed to provide a theoretical basis for the practical application of melatonin in cashmere goat production systems.

Results

Melatonin implantation (2 mg/kg live weight) had no influence (P > 0.05) on daily weight gain, carcass weight, dressing percentage, loin muscle area, or the pH, moisture level, crude fat (except for Gluteus muscle) and amino acid content of muscles of cashmere goats. After implantation for 1 month, shear force of Longissimus dorsi and water loss rate of Longissimus dorsi and Biceps femoris of cashmere goats were increased (P < 0.05), whereas the cooking yield of Gluteus muscle was reduced (P < 0.05). The melatonin treatment decreased (P < 0.05) muscle crude protein, Gluteus muscle crude fat and ∑n-3PUFA content and decreased (P < 0.05) ∑n-6PUFA content. However, after 2 months of implantation most of these effects had resolved. Melatonin implantation had no effect (P > 0.05) on the melatonin or prolactin contents of kidney, heart, spleen, liver, Longissimus dorsi, Biceps femoris and Gluteus muscles. Melatonin content of lung tissue was lowered (P < 0.05) and that of prolactin was elevated (P < 0.05) by the melatonin implantation.

Conclusion

This study has shown little impact of melatonin implantation of cashmere goats on carcass quality. A few meat quality indices i.e., shear force, water loss rate, ∑n-3PUFA, ∑n-6PUFA, and crude protein content of Longissimus dorsi; water loss rate, cooking yield and crude protein content of Biceps femoris; ether extract, crude protein content of Gluteus; were affected briefly (at 1 month of implantation) but these effects were not evident after 2 months of implantation. There was little effect of the melatonin treatments on tissue levels of melatonin or prolactin except in lung.

Melatonin mediated Foxp3-downregulation decreases cytokines production via the TLR2 and TLR4 pathways in H. pylori infected mice

Melatonin has important immuno-regulatory effects in inflammatory disorders but its specific role in Helicobacter pylori induced gastritis remains unclear. The aim of our study was to analyze the activity of melatonin against H. pylori induced gastritis in vivo, and explore the underlying mechanisms. The H. pylori infected mice showed extensive inflammatory cell infiltration in the gastric mucosa and submucosa, along with significantly reduced spleen and thymus weight. However, 2 and 6 weeks of treatment with 25 and 50 mg/kg melatonin restored the thymus weights relative to that of the untreated mice. TLR2 was upregulated in the gastric mucosa of the infected mice, which was restored to normal levels after 2 and 6 weeks of melatonin treatment. In contrast, TLR4 levels were similar between the treated and untreated mice. Furthermore, melatonin treatment restored spleen Foxp3 and serum TGF-β1 levels that were respectively increased and decreased in the infected mice. H. pylori infected mice also showed a decrease in the serum levels of IL-2, IL-6, IL-10, IL-17, IFN-γ and TFN-α following 2 and 6 weeks of melatonin treatment compared to the untreated mice. Melatonin treatment also resulted in decreased CD4+CD25+Foxp3+ Treg cell count in the spleen. The expression of TLR2, MyD88, p-ERK, p-p38, p65, p50 and Foxp3 in the gastric tissues were lower in the untreated mice compared to mice treated with melatonin for 2 weeks. However, the expression levels evened out after 6 weeks of treatment. Taken together, melatonin alleviates H. pylori induced gastritis by regulating TGF-β1 and Foxp3 expression via the TLR2 and TLR4 pathways.

Melatonin Uptake by Cells: An Answer to Its Relationship with Glucose?

Melatonin, N-acetyl-5-methoxytryptamine, is an indole mainly synthesized from tryptophan in the pineal gland and secreted exclusively during the night in all the animals reported to date. While the pineal gland is the major source responsible for this night rise, it is not at all the exclusive production site and many other tissues and organs produce melatonin as well. Likewise, melatonin is not restricted to vertebrates, as its presence has been reported in almost all the phyla from protozoa to mammals. Melatonin displays a large set of functions including adaptation to light: dark cycles, free radical scavenging ability, antioxidant enzyme modulation, immunomodulatory actions or differentiation–proliferation regulatory effects, among others. However, in addition to those important functions, this evolutionary ‘ancient’ molecule still hides further tools with important cellular implications. The major goal of the present review is to discuss the data and experiments that have addressed the relationship between the indole and glucose. Classically, the pineal gland and a pinealectomy were associated with glucose homeostasis even before melatonin was chemically isolated. Numerous reports have provided the molecular components underlying the regulatory actions of melatonin on insulin secretion in pancreatic beta-cells, mainly involving membrane receptors MTNR1A/B, which would be partially responsible for the circadian rhythmicity of insulin in the organism. More recently, a new line of evidence has shown that glucose transporters GLUT/SLC2A are linked to melatonin uptake and its cellular internalization. Beside its binding to membrane receptors, melatonin transportation into the cytoplasm, required for its free radical scavenging abilities, still generates a great deal of debate. Thus, GLUT transporters might constitute at least one of the keys to explain the relationship between glucose and melatonin. These and other potential mechanisms responsible for such interaction are also discussed here.

Melatonin attenuates smoking-induced hyperglycemia via preserving insulin secretion and hepatic glycogen synthesis in rats

Epidemiology survey indicated that cigarette smoking is a risk factor of diabetes. However, the precise mechanisms remain to be clarified. In this study, we found that smoking caused metabolic malfunctions on pancreas and liver in experimental animal model. These were indicated by hyperglycemia, increased serum hemoglobin A1c level and decreased insulin secretion, inhibition of liver glycogen synthase (LGS), and hepatic glycogen synthesis. Mechanistic studies revealed that all these alterations were caused by the inflammatory reaction and reactive oxygen species (ROS) induced by the smoking. Melatonin treatment significantly preserved the functions of both pancreas and liver by reducing β cell apoptosis, CD68-cell infiltration, ROS production, and caspase-3 expression. The siRNA-knockdown model identified that the protective effects of melatonin were mediated by melatonin receptor-2 (MT2). This study uncovered potentially underlying mechanisms related to the association between smoking and diabetes. In addition, it is, for first time, to report that melatonin effectively protects against smoking-induced glucose metabolic alterations and the signal transduction pathway of melatonin is mainly mediated by its MT2 receptor. These observations provide solid evidence for the clinically use of melatonin to reduce smoking-related diabetes, and the therapeutic regimens are absent currently.