Melatonin Supplementation Decreases Hypertrophic Obesity and Inflammation Induced by High-Fat Diet in Mice

Meta-analysis and machine learning reveal the antiobesity effects of melatonin on obese rodents

Melatonin appears to be a promising supplement for obesity treatment. The antiobesity effects of melatonin on obese rodents are influenced by various factors, including the species, sex, the dosage of melatonin, treatment duration, administration via, daily treatment time, and initial body weight (IBW). Therefore, we conducted a meta-analysis and machine learning study to evaluate the antiobesity effect of melatonin on obese mice or rats from 31 publications. The results showed that melatonin significantly reduced body weight, serum glucose (GLU), triglycerides (TGs), low-density lipoprotein (LDL), and cholesterol (TC) levels in obese mice or rats but increased high-density lipoprotein (HDL) levels. Melatonin showed a slight positive effect on clock-related genes, although the number of studies was limited. Meta-regression analysis and machine learning indicated that the dosage of melatonin was the primary factor influencing body weight, with higher melatonin dosages leading to a stronger weight reduction effect. Together, male obese C57BL/6 mice and Sprague-Dawley rats with an IBW of 100-200 g showed better body weight reduction when supplemented with a dose of 10-30 mg/kg melatonin administered at night via injection for 5-8 weeks.

Astrocyte response to melatonin treatment in rats under high-carbohydrate high-fat diet

The involvement of consumption of high-carbohydrate high-fat (HCHF) diet in cognitive impairment is attributed, at least in part, to the activation of astrocytes, which contributes to the development of neuroinflammation, oxidative stress, and subsequent cognitive deficits. This study aimed to assess the influence of melatonin on cognitive impairment and astrogliosis induced by the HCHF diet in rats. Male Wistar rats were fed an HCHF diet for eight weeks to induce obesity and metabolic syndrome. Subsequently, they received oral melatonin treatment for four weeks at doses of 5 mg/kg, 10 mg/kg, and 30 mg/kg, alongside the HCHF diet. Cognitive function was evaluated using the Y-maze test, while the levels of proinflammatory cytokines, oxidative stress, and the number glial fibrillary acidic protein (GFAP) positive cells were assessed in the hippocampi and hypothalamus. The consumption of the HCHF diet resulted in weight gain, hyperlipidemia, impaired glucose tolerance, cognitive decline, neuroinflammation, oxidative stress damage, and astrogliosis in rats. Although melatonin treatment did not demonstrate beneficial effects on blood glucose and lipid metabolism, it improved the impaired working memory caused by the HCHF diet. Melatonin exhibited a dose-dependent reduction of astrogliosis, neuroinflammation, and lipid peroxidation while restored superoxide dismutase in the hippocampus and hypothalamus of HCHF diet-treated rats. These findings provide evidence that melatonin inhibits astrocyte activation, thereby attenuating inflammation and minimizing oxidative stress damage induced by the HCHF diet.

Significance of Melatonin in the Regulation of Circadian Rhythms and Disease Management

Melatonin, the 'hormone of darkness' is a neuronal hormone secreted by the pineal gland and other extra pineal sites. Responsible for the circadian rhythm and seasonal behaviour of vertebrates and mammals, melatonin is responsible for regulating various physiological conditions and the maintenance of sleep, body weight and the neuronal activities of the ocular sites. With its unique amphiphilic structure, melatonin can cross the cellular barriers and elucidate its activities in the subcellular components, including mitochondria. Melatonin is a potential scavenger of oxygen and nitrogen-reactive species and can directly obliterate the ROS and RNS by a receptor-independent mechanism. It can also regulate the pro- and anti-inflammatory cytokines in various pathological conditions and exhibit therapeutic activities against neurodegenerative, psychiatric disorders and cancer. Melatonin is also found to show its effects on major organs, particularly the brain, liver and heart, and also imparts a role in the modulation of the immune system. Thus, melatonin is a multifaceted candidate with immense therapeutic potential and is still considered an effective supplement on various therapies. This is primarily due to rectification of aberrant circadian rhythm by improvement of sleep quality associated with risk development of neurodegenerative, cognitive, cardiovascular and other metabolic disorders, thereby enhancing the quality of life.

Glycoprotein Non-Metastatic Protein B (GPNMB): The Missing Link Between Lysosomes and Obesity

As a result of an unhealthy diet and limited physical activity, obesity has become a widespread pandemic worldwide and is an important predictor for the development of cardiovascular disease. Obesity is often characterized by a pro-inflammatory environment in white adipose tissue (WAT), mainly due to increased macrophage infiltration. These immune cells boost their lipid concentrations by accumulating the content of dying adipocytes. As the lysosome is highly involved in lipid handling, the progressive lipid accumulation may result in lysosomal stress and a metabolic shift. Recent studies have identified glycoprotein non-metastatic melanoma protein B (GPNMB) as a novel marker of inflammatory diseases. GPNMB is a type I transmembrane protein on the cell surface of various cell types, such as macrophages, dendritic cells, osteoblasts, and microglia, from which it can be proteolytically cleaved into a soluble molecule. It is induced by lysosomal stress via microphthalmia-associated transcription factor and thus has been found to be upregulated in many lysosomal storage disorders. In addition, a clear connection between GPNMB and obesity was recently established. GPNMB was shown to have protective and anti-inflammatory effects in most cases, preventing the progression of obesity-related metabolic disorders. In contrast, soluble GPNMB likely has the opposite effect and promotes lipogenesis in WAT. This review aims to summarize and clarify the role of GPNMB in the progression of obesity and to highlight its potential use as a biomarker for lipid-associated disorders.

Melatonin associated with a high-fat diet during pregnancy and lactation prevents liver changes in the offspring

In the present study, we set out to determine whether melatonin combined with a high-fat diet during pregnancy and lactation can prevent liver disorders in offspring. Forty rats were divided into four groups: DC - pregnant rats submitted to the standard diet; DC + Mel - pregnant rats submitted to the standard diet combined with melatonin; HFD - pregnant rats submitted to a high-fat diet; HFD + Mel - pregnant rats submitted to a high-fat diet combined with melatonin. Morphophysiological and biochemical parameters were analyzed. Melatonin (5 mg/kg) was administered intraperitoneally. The HFD group offspring showed an increase in AST, ALT, alkaline phosphatase, cholesterol, triglycerides, LDL and glucose levels, and a reduction in HDL and lipase levels. In the liver obseved steatosis, hepatocellular ballooning, increased lobular parenchyma and reduced non-lobular parenchyma, beside reduced liver glycogen and fibrosis. These changes were not observed in the HFD + Mel group. In conclusion, melatonin combined with a high-fat diet preserves the liver architecture and function in the offspring.

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

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

Impaired Melatonin Secretion, Oxidative Stress and Metabolic Syndrome in Night Shift Work

Metabolic syndrome has been associated in many studies with working in shifts. Even if the mechanistic details are not fully understood, forced sleep deprivation and exposure to light, as happens during night shifts, or irregular schedules with late or very early onset of the working program, lead to a sleep-wake rhythm misalignment, metabolic dysregulation and oxidative stress. The cyclic melatonin secretion is regulated by the hypothalamic suprachiasmatic nuclei and light exposure. At a central level, melatonin promotes sleep and inhibits wake-signals. Beside this role, melatonin acts as an antioxidant and influences the functionality of the cardiovascular system and of different metabolic processes. This review presents data about the influence of night shifts on melatonin secretion and oxidative stress. Assembling data from epidemiological, experimental and clinical studies contributes to a better understanding of the pathological links between chronodisruption and the metabolic syndrome related to working in shifts.

Melatonin ameliorates myocardial infarction in obese diabetic individuals: The possible involvement of macrophage apoptotic factors

In recent days, the hike in obesity-mediated epidemics across the globe and the prevalence of obesity-induced cardiovascular disease has become one of the chief grounds for morbidity and mortality. This epidemic-driven detrimental events in the cardiac tissues start with the altered distribution and metabolism pattern of high-density lipoprotein and low-density lipoprotein (LDL) leading to cholesterol (oxidized LDL) deposition on the arterial wall and atherosclerotic plaque generation, followed by vascular spasms and infarction. Subsequently, obesity-triggered metabolic malfunctions induce free radical generation which may further trigger pro-inflammatory signaling and nuclear factor kappa-light-chain-enhancer of activated B cells transcriptional factor, thus inducing interferon-gamma, tumor necrosis factor-alpha, and inducible nitric oxide synthase. This terrifying cardiomyopathy can be further aggravated in type 2 diabetes mellitus, thereby making obese diabetic patients prone toward the development of myocardial infarction (MI) or stroke in comparison to their nondiabetic counterparts. The accelerated oxidative stress and pro-inflammatory response induced cardiomyocyte hypertrophy, followed by apoptosis in obese diabetic individuals, causing progression of athero-thrombotic vascular disease. Being an efficient antioxidative and anti-inflammatory indolamine, melatonin effectively inhibits lipid peroxidation, pro-inflammatory reactions, thereby resolving free radical-induced myocardial damages along with maintaining antioxidant reservoir to preserve cardiovascular integrity. Prolonged melatonin treatment maintains balanced body weight and serum total cholesterol concentration by inhibiting cholesterol synthesis and promoting cholesterol catabolism. Additionally, melatonin promotes macrophage polarization toward the anti-inflammatory state, providing a proper shield during the recovery period. Therefore, the protective role of melatonin in maintaining the lipid metabolism homeostasis and blocking the atherosclerotic plaque rupture could be targeted as the possible therapeutic strategy for the management of obesity-induced acute MI. This review aimed at orchestrating the efficacy of melatonin in ameliorating irrevocable oxidative cardiovascular damage induced by the obesity-diabetes correlation.

Melatonin and Aging

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

Melatonin protects against body weight gain induced by sleep deprivation in mice

Sleep deprivation is an epidemic phenomenon in modern society. Lack of sleep has been shown to result in metabolic and endocrine disorders that predispose to obesity and other chronic metabolic diseases. Melatonin is a sleep-related neurohormone and affected by the circadian rhythm and light/dark cycles. Melatonin has recently been used to ameliorate diet-induced or night light-induced energy metabolic imbalance. However, the effect of melatonin on sleep deprivation-induced obesity has been poorly characterized. This study focuses on the protective effects of melatonin on lipid metabolism and body weight homeostasis in sleep-deprived mice. Mice subjected to sleep deprivation had significantly decreased plasma melatonin content and increased food intake and body weight gain compared to that of control. Meanwhile, the transcription factor PPARγ protein in liver increased, but there were no significant changes in hepatic circadian proteins BMAL1 and REV-ERBα after 10 consecutive days of sleep deprivation. Moreover, melatonin supplementation increased liver AMPKα/PPARα signaling pathway activity, which leads to lipid catabolism and reduced fat accumulation. These findings suggested that melatonin may be a potential agent for protecting against sleep deprivation-induced obesity.

Dose-Dependent Effect of Melatonin on BAT Thermogenesis in Zücker Diabetic Fatty Rat: Future Clinical Implications for Obesity

Experimental data have revealed that melatonin at high doses reduced obesity and improved metabolic outcomes in experimental models of obesity, mainly by enhancing brown adipose tissue (BAT) thermogenesis. A potential dose-response relationship has yet to be performed to translate these promising findings into potential clinical therapy. This study aimed to assess the effects of different doses of melatonin on interscapular BAT (iBAT) thermogenic capacity in Zücker diabetic fatty (ZDF) rats. At 6 wk of age, male ZDF rats were divided into four groups (n = 4 per group): control and those treated with different doses of melatonin (0.1, 1, and 10 mg/kg of body weight) in their drinking water for 6 wk. Body weight (BW) was significantly decreased at doses of 1 and 10 mg/kg of melatonin, but not at 0.1 mg/kg compared with the control, with a similar rate of BW decrease being reached at the dose of 1 mg/kg (by ~11%) and 10 mg/kg (by ~12%). This effect was associated with a dose-dependent increase in the thermal response to the baseline condition or acute cold challenge in the interscapular area measurable by infrared thermography, with the highest thermal response being recorded at the 10 mg/kg dose. Upon histology, melatonin treatment markedly restored the typical brownish appearance of the tissue and promoted a shift in size distribution toward smaller adipocytes in a dose-dependent fashion, with the most pronounced brownish phenotype being observed at 10 mg/kg of melatonin. As a hallmark of thermogenesis, the protein level of uncoupled protein 1 (UCP1) from immunofluorescence and Western blot analysis increased significantly and dose-dependently at all three doses of melatonin, reaching the highest level at the dose of 10 mg/kg. Likewise, all three doses of melatonin modulated iBAT mitochondrial dynamics by increasing protein expression of the optic atrophy protein type 1 (OPA1) fusion marker and decreasing that of the dynamin-related protein1 (DRP1) fission marker, again dose-dependently, with the highest and lowest expression levels, respectively, being reached at the 10 mg/kg dose. These findings highlight for the first time the relevance of the dose-dependency of melatonin toward BW control and BAT thermogenic activation, which may have potential therapeutic implications for the treatment of obesity. To clinically apply the potential therapeutic of melatonin for obesity, we consider that the effective animal doses that should be extrapolated to obese individuals may be within the dose range of 1 to 10 mg/kg.

Hepatic Encephalopathy and Melatonin

Hepatic encephalopathy (HE) is a severe metabolic syndrome linked with acute/chronic hepatic disorders. HE is also a pernicious neuropsychiatric complication associated with cognitive decline, coma, and death. Limited therapies are available to treat HE, which is formidable to oversee in the clinic. Thus, determining a novel therapeutic approach is essential. The pathogenesis of HE has not been well established. According to various scientific reports, neuropathological symptoms arise due to excessive accumulation of ammonia, which is transported to the brain via the blood–brain barrier (BBB), triggering oxidative stress and inflammation, and disturbing neuronal-glial functions. The treatment of HE involves eliminating hyperammonemia by enhancing the ammonia scavenging mechanism in systemic blood circulation. Melatonin is the sole endogenous hormone linked with HE. Melatonin as a neurohormone is a potent antioxidant that is primarily synthesized and released by the brain’s pineal gland. Several HE and liver cirrhosis clinical studies have demonstrated impaired synthesis, secretion of melatonin, and circadian patterns. Melatonin can cross the BBB and is involved in various neuroprotective actions on the HE brain. Hence, we aim to elucidate how HE impairs brain functions, and elucidate the precise molecular mechanism of melatonin that reverses the HE effects on the central nervous system.

The role of melatonin in the molecular mechanisms underlying metaflammation and infections in obesity: A narrative review

Obesity is a chronic condition whose management is a critical challenge for physicians. The scientific community has increased its focus on the molecular mechanisms involved in obesity etiopathogenesis to better manage patients with obesity and its associated complications. The tight connection between adipose tissue and the immune system has been demonstrated to play a crucial role in inflammation, and melatonin is important for circadian rhythm regulation and metabolic homeostasis, in which it orchestrates several molecular mechanisms involved in obesity and associated inflammation. Melatonin also regulates innate and adaptive immunity; its antioxidant properties are linked to reduced predisposition to infection and weight gain in patients with obesity through the modulation of the immune response, which has a significant beneficial effect on inflammation and, consequently, on the metabolic state. Low melatonin levels have been linked to obesity, and melatonin supplementation can reduce body weight, improve metabolic profile, and ameliorate immune responses and pro-inflammatory stimuli. The role of melatonin in obesity is mainly related to improved oxidative stress signaling, modulation of adipokine secretion, and a switching from white-to-brown adipose tissue phenotype and activity. Moreover, the role of melatonin in obesity modulation by controlling circadian rhythm has recently emerged as a pivotal mechanism for lipid and glucose metabolism dysfunction in adipose, muscle, and liver tissues. Melatonin may also regulate the immune system by acting directly on thymus morphology and activity as well as by modulating oxidative stress and inflammatory states during infections. The tight association between melatonin and immune response regulation is coordinated by Toll-like receptors, which are rhythmically expressed during the day. Their expression may be strongly modulated by melatonin as their signaling is highly inhibited by melatonin. The current review summarizes studies of melatonin-induced mechanisms involved in infection regulation, particularly the modulation of obesity-associated inflammation and systemic complications.

Protective Effects of Melatonin against Obesity-Induced by Leptin Resistance

Consumption of an exceedingly high-fat diet with irregular eating and sleeping habits is typical in the current sedentary lifestyle, leading to chronic diseases like obesity and diabetes mellitus. Leptin is a primary appetite-regulating hormone that binds to its receptors in the hypothalamic cell membrane and regulates downstream appetite-regulating neurons NPY/AgRp and POMC in the hypothalamus. Based on the fat content of the adipose tissue, leptin is secreted, and excess accumulation of fat in adipose tissue stimulates the abnormal secretion of leptin. The secreted leptin circulating in the bloodstream uses its transporters to cross the blood-brain barrier (BBB) and reach the CSF. There is a saturation limit for leptin bound to its transporters to cross the BBB, and increased leptin secretion in adipose tissue has a defect in its transport across the BBB. Leptin resistance is due to excess leptin, a saturation of its transporters, and deficiency in either the receptor level or signalling in the hypothalamus. Leptin resistance leads to obesity due to excess food intake and less energy expenditure. Normal leptin secretion follows a rhythm, and alteration in the lifestyle leads to hormonal imbalances and increases ROS generation leading to oxidative stress. The sleep disturbance causes obesity with increased lipid accumulation in adipose tissue. Melatonin is the master regulator of the sleep-wake cycle secreted by the pineal gland during the night. It is a potent antioxidant with anti-inflammatory properties. Melatonin is secreted in a pattern called the circadian rhythm in humans as well. Research indicates that melatonin plays a vital role in hormonal regulation and energy metabolism, including leptin signalling and secretion. Studying the role of melatonin in leptin regulation will help us combat the pathologies of obesity caused by leptin resistance.

Therapeutic potential of melatonin in colorectal cancer: Focus on lipid metabolism and gut microbiota

Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies. The occurrence and development of CRC are complicated processes. Obesity and dysbacteriosis have been increasingly regarded as the main risk factors for CRC. Understanding the etiology of CRC from multiple perspectives is conducive to screening for some potential drugs or new treatment strategies to limit the serious side effects of conventional treatment and prolong the survival of CRC patients. Melatonin, a natural indoleamine, is mainly produced by the pineal gland, but it is also abundant in other tissues, including the gastrointestinal tract, retina, testes, lymphocytes, and Harder's glands. Melatonin could participate in lipid metabolism by regulating adipogenesis and lipolysis. Additionally, many studies have focused on the potential beneficial effects of melatonin in CRC, such as promotion of apoptosis; inhibition of cell proliferation, migration, and invasion; antioxidant activity; and immune regulation. Meaningfully, gut microbiota is the main determinant of all aspects of health and disease (including obesity and tumorigenesis). The gut microbiota is of great significance for understanding the relationship between obesity and increased risk of CRC. Although the current understanding of how the melatonin-mediated gut microbiota coordinates a variety of physiological and pathological activities is fairly comprehensive, there are still many unknown topics to be explored in the face of a complex nutritional status and a changeable microbiota. This review summarizes the potential links among melatonin, lipid metabolism, gut microbiota, and CRC to promote the development of melatonin as a preventive and therapeutic agent for CRC.

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 reactive astrogliosis and glial scar formation following cerebral ischemia and reperfusion injury mediated by GSK-3β and RIP1K

Even though astrocytes have been widely reported to support several brain functions, studies have emerged that they exert deleterious effects on the brain after ischemia and reperfusion (I/R) injury. The present study investigated the neuroprotective effects of melatonin on the processes of reactive astrogliosis and glial scar formation, as well as axonal regeneration after transient middle cerebral artery occlusion. Male Wistar rats were randomly divided into four groups: sham-operated, I/R, I/R treated with melatonin, and I/R treated with edaravone. All drugs were administered via intraperitoneal injection at the onset of reperfusion and were continued until the rats were sacrificed on Day 7 or 14 after the surgery. Melatonin presented long-term benefits on cerebral damage after I/R injury, as demonstrated by a decreased infarct volume, histopathological changes, and reduced neuronal cell death. We also found that melatonin attenuated reactive astrogliosis and glial scar formation and, consequently, enhanced axonal regeneration and promoted neurobehavioral recovery. Furthermore, glycogen synthase kinase-3 beta (GSK-3β) and receptor-interacting serine/threonine-protein 1 kinase (RIP1K), which had previously been revealed as proteins involved in astrocyte responses, were significantly reduced after melatonin administration. Taken together, melatonin effectively counteracted the deleterious effects due to astrocyte responses and improved axonal regeneration to promote functional recovery during the chronic phase of cerebral I/R injury by inhibiting GSK-3β and RIP1K activities.

Melatonin supplementation and anthropometric indicators of obesity: A systematic review and meta-analysis

OBJECTIVE

According to in vivo and in vitro studies, melatonin appears to be a potential supplement for obesity reduction. The aim of this study was to review the literature on randomized clinical trials that evaluated the effects of melatonin supplementation on anthropometric indicators of obesity in humans.

METHODS

We conducted a systematic review with meta-analysis in the following databases: Pubmed, LILACS, Scielo, Scopus, Web of Science, Cochrane, and Embase. We included studies that evaluated melatonin supplementation's effects, compared with placebo, on anthropometric measures, including body weight, body mass index (BMI), and waist circumference, in people ≥18 y of age. This systematic review and meta-analysis were registered on PROSPERO: CRD42021241079.

RESULTS

Of the 23 studies included, 11 showed significant results from melatonin supplementation on weight loss, BMI, or waist circumference, compared with placebo. In the meta-analysis, melatonin supplementation significantly reduced body weight (standardized mean difference, -0.48; 95% confidence interval, -0.94 to -0.02; P = <0.01; I² = 92%). Results for BMI and waist circumference were null. The I² tests were significant for the analyses with significant results.

CONCLUSION

The results demonstrated that melatonin supplementation was responsible for significantly reducing body weight. More studies are needed before melatonin can be recommended for weight loss.

Exogenous melatonin decreases circadian misalignment and body weight among early types

Shift workers experience chronic circadian misalignment, which can manifest itself in reduced melatonin production, and has been associated with metabolic disorders. In addition, chronotype modulates the effect of night shift work, with early types presenting greater circadian misalignment when working night shift as compared to late types. Melatonin supplementation has shown positive results reducing weight gain in animal models, but the effect of exogenous melatonin in humans on body weight in the context of shift work remains inconsistent. The aim of this study was thus to evaluate the effects of exogenous melatonin on circadian misalignment and body weight among overweight night shift workers, according to chronotype, under real-life conditions. We conducted a double-blind, randomized, placebo-controlled, crossover trial where melatonin (3 mg) or placebo was administered on non-night shift nights for 12 weeks in 27 female nurses (37.1 yo, ±5.9 yo; BMI 29.9 kg/m2 , ±3.3 kg/m2 ). Melatonin (or placebo) was only taken on nights when the participants did not work night shifts, that is, on nights when they slept (between night shifts and on days off). Composite Phase Deviations (CPD) of actigraphy-based mid-sleep timing were calculated to measure circadian misalignment. The analyses were performed for the whole group and by chronotype. We found approximately 20% reduction in circadian misalignment after exogenous melatonin administration considering all chronotypes. Moreover, melatonin supplementation in those who presented high circadian misalignment, as observed in early chronotypes, reduced body weight, BMI, waist circumference, and hip circumference, without any change in the participants' calorie intake or physical activity levels.

Anti-Inflammatory Activity of Melatonin: a Focus on the Role of NLRP3 Inflammasome

Melatonin is a hormone of the pineal gland that contributes to the regulation of physiological activities, such as sleep, circadian rhythm, and neuroendocrine processes. Melatonin is found in several plants and has pharmacological activities including antioxidant, anti-inflammatory, hepatoprotective, cardioprotective, and neuroprotective. It also has shown therapeutic efficacy in treatment of cancer and diabetes. Melatonin affects several molecular pathways to exert its protective effects. The NLRP3 inflammasome is considered a novel target of melatonin. This inflammasome contributes to enhanced level of IL-1β, caspase-1 activation, and pyroptosis stimulation. The function of NLRP3 inflammasome has been explored in various diseases, including cancer, diabetes, and neurological disorders. By inhibiting NLRP3, melatonin diminishes inflammation and influences various molecular pathways, such as SIRT1, microRNA, long non-coding RNA, and Wnt/β-catenin. Here, we discuss these molecular pathways and suggest that melatonin-induced inhibition of NLRP3 should be advanced in disease therapy.

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.

Melatonin activates ABCA1 via the BiP/NRF1 pathway to suppress high-cholesterol-induced apoptosis of mesenchymal stem cells

BACKGROUND

Retarded wound healing in patients with obesity contributes to a risk of complications associated with vascular insufficiency and oxidative stress. The high cholesterol levels of patients with obesity are associated with apoptosis of engrafted umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). Melatonin contributes to the prevention of cholesterol accumulation in patients with obesity via a mechanism that is poorly understood. We therefore investigated the regulatory mechanism of melatonin in cholesterol-induced apoptosis.

METHODS

The protective effects of melatonin on cholesterol-induced apoptosis were investigated in UCB-MSCs. We used a mouse model of induced obesity to show that melatonin treatment restored the survival rate of transplanted UCB-MSCs and their wound-healing capacity. The mean values of the treatment groups were compared with those of the control group using Student's t test, and differences among three or more groups were analyzed using one-way analysis of variance with Dunnett's multiple comparison test.

RESULTS

Melatonin treatment increased the expression of ATP-binding cassette subfamily A member 1 (ABCA1), which reduced cholesterol accumulation and cholesterol-induced apoptosis. The mouse skin wound healing model showed that melatonin treatment restored the survival rate of transplanted UCB-MSCs and the wound-healing capacity of obese mice. Melatonin inhibited the expression of binding immunoglobulin protein (BiP) through the regulation of MT2/Sp1-dependent microRNA-597-5p. Melatonin decreased the co-localization of BiP with nuclear factor erythroid 2-related factor 1 (NRF1), which resulted in increased ABCA1 expression.

CONCLUSION

Melatonin induced the efflux of intracellular cholesterol through ABCA1 to decrease apoptosis of UCB-MSCs via an MT2-dependent BiP/NRF1 pathway.

Ischemic stroke, obesity, and the anti-inflammatory role of melatonin

Obesity is a predominant risk factor in ischemic stroke and is commonly comorbid with it. Pathologies following these conditions are associated with systemic and local inflammation. Moreover, there is increasing evidence that the susceptibility for ischemic brain damage increases substantially in experimental models of ischemic stroke with concomitant obesity. Herein, we explore the proinflammatory events that occur during ischemic stroke and obesity, and we discuss the influence of obesity on the inflammatory response and cerebral damage outcomes in experimental models of brain ischemia. In addition, because melatonin is a neurohormone widely reported to exhibit protective effects in various diseases, this study also demonstrates the anti-inflammatory role and possible mechanistic actions of melatonin in both epidemic diseases. A summary of research findings suggests that melatonin administration has great potential to exert an anti-inflammatory role and provide protection against obesity and ischemic stroke conditions. However, the efficacy of this hormonal treatment on ischemic stroke with concomitant obesity, when more serious inflammation is generated, is still lacking.

The use of melatonin to mitigate the adverse metabolic side effects of antipsychotics

Antipsychotic drugs are efficacious first-line treatments for many individuals diagnosed with a psychiatric illness. However, their adverse metabolic side-effect profile, which resembles the metabolic syndrome, represents a significant clinical problem that increases morbidity and limits treatment adherence. Moreover, the mechanisms involved in antipsychotic-induced adverse metabolic effects (AMEs) are unknown and mitigating strategies and interventions are limited. However, recent clinical trials show that nightly administration of exogenous melatonin may mitigate or even prevent antipsychotic-induced AMEs. This clinical evidence in combination with recent preclinical data implicate the circadian system in antipsychotic-induced AMEs and their mitigation. In this chapter, we provide an overview on the circadian system and its involvement in antipsychotic-induced AMEs, as well as the potential beneficial effect of nightly melatonin administration to mitigate them.

Association of Serum Melatonin Level with Mild Cognitive Impairment in Type 2 Diabetic Patients: A Cross-Sectional Study

OBJECTIVES

Melatonin is an essential neuroendocrine hormone that participates in the regulation of sleep rhythm and cognitive function. This study aimed to determine serum melatonin levels with mild cognitive impairment (MCI) in patients with type 2 diabetes (T2DM).

METHODS

A total of 247 T2DM patients were recruited in this retrospective study and divided into 75 subjects with MCI and 172 with normal cognition. Cognitive function was evaluated by the Montreal Cognitive Assessment (MoCA). Their blood sample was examined for the level of melatonin and other biochemical parameters.

RESULTS

Melatonin concentration was decreased in MCI patients to non-MCI patients (P < 0.001). Melatonin level was negatively correlated with age (r = -0.202; P = 0.001), diabetes duration (r = -0.282; P < 0.001), serum HbA1c (r = -0.195; P = 0.002), hs-CRP (r = -0.324; P < 0.001), and TSH (r = -0.184; P = 0.004) levels and positively correlated with MoCA score, serum HDL-C (r = 0.145; P < 0.001), FT3 (r = 0.241; P < 0.001), and FT4 (r = 0.169; P = 0.008) levels. The multivariable analysis indicated that fewer years of formal education, longer diabetes duration, higher serum HbA1c, higher serum hs-CRP, and lower serum melatonin are the predisposing factors for MCI.

CONCLUSION

Lower melatonin level was associated with cognitive impairment in patients with T2DM. Melatonin might serve as a potential protective molecule against cognitive dysfunction in T2DM.

Removal of melatonin receptor type 1 signalling induces dyslipidaemia and hormonal changes in mice subjected to environmental circadian disruption

Background

Melatonin is a hormone secreted by the pineal gland in a circadian rhythmic manner with peak synthesis at night. Melatonin signalling was suggested to play a critical role in metabolism during the circadian disruption.

Methods

Melatonin-proficient (C3H-f+/+ or WT) and melatonin receptor type 1 knockout (MT1 KO) male and female mice were phase-advanced (6 hours) once a week for 6 weeks. Every week, we measured weight, food intake and basal glucose levels. At the end of the experiment, we sacrificed the animals and measured the blood's plasma for lipids profile (total lipids, phospholipids, triglycerides and total cholesterol), metabolic hormones profiles (ghrelin, leptin, insulin, glucagon, glucagon-like-peptide and resistin) and the body composition.

Results

Environmental circadian disruption (ECD) did not produce any significant effects in C3H-f+/+, while it increased lipids profile in MT1 KO with the significant increase observed in total lipids and triglycerides. For metabolic hormones profile, ECD decreased plasma ghrelin and increased plasma insulin in MT1 KO females. Under control condition, MT1 KO females have significantly different body weight, fat mass, total lipids and total cholesterol than the control C3H-f+/+ females.

Conclusion

Our data show that melatonin-proficient mice are not affected by ECD. When the MT1 receptors are removed, ECD induced dyslipidaemia in males and females with females experiencing the most adverse effect. Overall, our data demonstrate that MT1 signalling is an essential modulator of lipid and metabolic homeostasis during ECD.

CLOCK 3111TT Genotype Is Associated with Increased Total Cholesterol and Low-Density Lipoprotein Levels in Menopausal Women with a Body Mass Index of at Least 25 kg/m2

Lipid profile comparative analysis was performed to reveal the interdependence of lipids with Circadian locomoter output cycles protein kaput (CLOCK) 3111T/C gene polymorphism in menopausal women with/without a body mass index (BMI) of ≥25 kg/m². Methods: A total of 193 female volunteers aged 45 to 60 years were divided into two groups: Those with BMI < 25 kg/m² (control) and those with BMI ≥ 25 kg/m². Each group was then divided into two subgroups: Those with the CLOCK TT-genotype and those with the CLOCK TC-, CC-genotypes. Lipid metabolism parameters were determined by the enzymatic method. Single-nucleotide polymorphisms (SNPs) were detected via polymerase chain reaction–restriction fragment length polymorphism technology. Results: There were no differences in CLOCK 3111T/C genotypes or allele frequency between the control and main groups. In addition, there were no differences in lipid profile parameters between women of the control group and different CLOCK 3111T/C genotypes. The total cholesterol (p = 0.041) and low-density lipoprotein cholesterol (p = 0.036) levels were higher in the subgroup of women with a BMI ≥ 25 kg/m² and CLOCK TT-genotype as compared to the subgroup with a BMI ≥ 25 kg/m² and minor allele 3111C. Conclusions: SNP 3111T/C of the CLOCK gene is not associated with BMI however, data suggest that the minor allele of the CLOCK 3111T/C gene polymorphism may have a protective role in atherogenic lipid levels in women with a BMI greater than or equal to 25 kg/m².

Adipose tissue inflammation and metabolic dysfunction in obesity

Several lines of preclinical and clinical research have confirmed that chronic low-grade inflammation of adipose tissue is mechanistically linked to metabolic disease and organ tissue complications in the overweight and obese organism. Despite this widely confirmed paradigm, numerous open questions and knowledge gaps remain to be investigated. This is mainly due to the intricately intertwined cross-talk of various pro- and anti-inflammatory signaling cascades involved in the immune response of expanding adipose depots, particularly the visceral adipose tissue. Adipose tissue inflammation is initiated and sustained over time by dysfunctional adipocytes that secrete inflammatory adipokines and by infiltration of bone marrow-derived immune cells that signal via production of cytokines and chemokines. Despite its low-grade nature, adipose tissue inflammation negatively impacts remote organ function, a phenomenon that is considered causative of the complications of obesity. The aim of this review is to broadly present an overview of adipose tissue inflammation by highlighting the most recent reports in the scientific literature and summarizing our overall understanding of the field. We also discuss key endogenous anti-inflammatory mediators and analyze their mechanistic role(s) in the pathogenesis and treatment of adipose tissue inflammation. In doing so, we hope to stimulate studies to uncover novel physiological, cellular, and molecular targets for the treatment of obesity.

Circadian Melatonin Secretion In Obese Adolescents With Or Without Obstructive Sleep Apnea

Objective — To compare melatonin levels in saliva during a 24-hr day in order to identify the specificities of circadian melatonin secretion in obese adolescents with or without obstructive sleep apnea (OSA). Material and Methods — We examined 18 obese adolescents with OSA, 12 obese adolescents without OSA, and 15 healthy adolescents with a normal body weight, from whom saliva was sampled four time during the 24-hr day. Polysomnography was used to diagnose OSA. Saliva samples (n=180) were subjected to enzyme-linked immunosorbent assay. Results — Obese adolescents with OSA had higher evening melatonin levels than obese adolescents without OSA. For example, this indicator in OSA patients was 5.3 times higher than in participants without OSA, who had the lowest evening melatonin level among all groups. In both obese groups, nighttime melatonin levels were significantly lower than in the control group. A positive correlation was detected between the levels of morning and afternoon melatonin and body mass index only in obese adolescents without OSA (r=0.58; p=0.03 and r=0.68; p=0.01, respectively). It was found that evening melatonin correlated with minimum blood oxygen saturation (SaO2) in the entire sample of adolescents with OSA (r=-0.69; p=0.008), and it also correlated with time with SaO2 <90% in the group with clinical manifestations of OSA (r=0.76; p=0.003). Nighttime melatonin levels negatively correlated with the minimum SaO2 value solely in the group with clinical manifestations of OSA (r=-0.58; p=0.035). Conclusion — The circadian melatonin secretion in obese adolescents differed, depending on the presence or absence of OSA, and correlated with the level of oxygen desaturation in OSA patients, to a greater extent – in the presence of clinical manifestations.

Comparative protective effects of N-acetylcysteine and melatonin against obesity-induced testicular dysfunction in rats

N-acetylcysteine (NAC) and melatonin were reported to exert protective effects on testicular tissues. Thus, this study aimed to determine which of these is more efficient against obesity-induced testicular dysfunction in albino rats. A total of 32 adult male rats (195 ± 10 g) were divided into four groups: control, obese rats fed a high-fat diet (HFD), HFD+NAC (150 mg/kg per day, i.p.) and HFD+melatonin (10 mg/kg per day, i.p.), for 5 weeks. Testes and epididymis were weighed. Lipid profile, pituitary-testicular hormones, tumor necrosis factor α (TNFα), epididymal sperm parameters, testicular oxidant-antioxidant system, testicular and the epididymal histopathology and immunohistochemical localization for androgen receptors (AR) and Bax reaction were analyzed. Administration of NAC or melatonin significantly improved the lipid parameters, gonadal hormones, TNFα level, sperm count and abnormal morphology, oxidant-antioxidant system and the absolute testicular and epididymal mass with an enhancement of testicular architecture, AR expression and apoptosis as compared with that in the obese group. Additionally, as compared with the NAC group, the melatonin group had significantly reduced body mass index, total cholesterol, triglyceride, and TNFα and increased testosterone, sperm count, motility, superoxide dismutase activity, mitigated histomorphometrical changes, Bax expression, and increased testicular AR expression. Therefore, melatonin was more efficient than NAC in affording fortification against HFD-induced testicular dysfunction.

Melatonin supplementation in the management of obesity and obesity-associated disorders: A review of physiological mechanisms and clinical applications

Despite the evolving advances in clinical approaches to obesity and its inherent comorbidities, the therapeutic challenge persists. Among several pharmacological tools already investigated, recent studies suggest that melatonin supplementation could be an efficient therapeutic approach in the context of obesity. In the present review, we have amalgamated the evidence so far available on physiological effects of melatonin supplementation in obesity therapies, addressing its effects upon neuroendocrine systems, cardiometabolic biomarkers and body composition. Most studies herein appraised employed melatonin supplementation at dosages ranging from 1 to 20 mg/day, and most studies followed up participants for periods from 3 weeks to 12 months. Overall, it was observed that melatonin plays an important role in glycaemic homeostasis, in addition to modulation of white adipose tissue activity and lipid metabolism, and mitochondrial activity. Additionally, melatonin increases brown adipose tissue volume and activity, and its antioxidant and anti-inflammatory properties have also been demonstrated. There appears to be a role for melatonin in adiposity reduction; however, several questions remain unanswered, for example melatonin baseline levels in obesity, and whether any seeming hypomelatonaemia or melatonin irresponsiveness could be clarifying factors. Supplementation dosage studies and more thorough clinical trials are needed to ascertain not only the relevance of such findings but also the efficacy of melatonin supplementation.

Melatonin is a potential adjuvant to improve clinical outcomes in individuals with obesity and diabetes with coexistence of Covid-19

Coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a newly discovered highly pathogenic virus that was declared pandemic in March 2020 by the World Health Organization. The virus affects the respiratory system, produces an inflammatory storm that causes lung damage and respiratory dysfunction. It infects humans of all ages. The Covid-19 takes a more severe course in individuals with chronic metabolic diseases such as obesity, diabetes mellitus, and hypertension. This category of persons exhibits weak immune activity and decreased levels of endogenous antioxidants. Melatonin is a multifunctional signaling hormone synthesized and secreted primarily by the pineal gland. It is a potent antioxidant with immunomodulatory action and has remarkable anti-inflammatory effects under a variety of circumstances. Regarding Covid-19 and metabolic syndrome, adequate information about the relationship between these two comorbidities is required for better management of these patients. Since Covid-19 infection and complications involve severe inflammation and oxidative stress in people with obesity and diabetes, we anticipated the inclusion of melatonin, as powerful antioxidant, within proposed treatment protocols. In this context, melatonin is a potential and promising agent to help overcome Covid-19 infection and boost the immune system in healthy persons and obese and diabetic patients. This review summarizes some evidence from recently published reports on the utility of melatonin as a potential adjuvant in Covid-19-infected individuals with diabetes and obesity.

Melatonin Orchestrates Lipid Homeostasis through the Hepatointestinal Circadian Clock and Microbiota during Constant Light Exposure

Misalignment between natural light rhythm and modern life activities induces disruption of the circadian rhythm. It is mainly evident that light at night (LAN) interferes with the human endocrine system and contributes to the increasing rates of obesity and lipid metabolic disease. Maintaining hepatointestinal circadian homeostasis is vital for improving lipid homeostasis. Melatonin is a chronobiotic substance that plays a main role in stabilizing bodily rhythm and has shown beneficial effects in protecting against obesity. Based on the dual effect of circadian rhythm regulation and antiobesity, we tested the effect of melatonin in mice under constant light exposure. Exposure to 24-h constant light (LL) increased weight and insulin resistance compared with those of the control group (12-h light–12-h dark cycle, LD), and simultaneous supplementation in the melatonin group (LLM) ameliorated this phenotype. Constant light exposure disturbed the expression pattern of a series of transcripts, including lipid metabolism, circadian regulation and nuclear receptors in the liver. Melatonin also showed beneficial effects in improving lipid metabolism and circadian rhythm homeostasis. Furthermore, the LL group had increased absorption and digestion of lipids in the intestine as evidenced by the elevated influx of lipids in the duodenum and decrease in the efflux of lipids in the jejunum. More interestingly, melatonin ameliorated the gut microbiota dysbiosis and improved lipid efflux from the intestine. Thus, these findings offer a novel clue regarding the obesity-promoting effect attributed to LAN and suggest a possibility for obesity therapy by melatonin in which melatonin could ameliorate rhythm disorder and intestinal dysbiosis.

Palmitoleic Acid Decreases Non-alcoholic Hepatic Steatosis and Increases Lipogenesis and Fatty Acid Oxidation in Adipose Tissue From Obese Mice

We recently demonstrated that palmitoleic acid (C16:1n7), a monounsaturated fatty acid, increases the metabolic and oxidative capacity of 3T3-L1 adipocytes. Herein, the effect of 16:1n7 supplementation on metabolic parameters on white adipose tissue (WAT) and liver of obese mice induced by a high-fat diet (HFD) was addressed by analyzing metabolic (dys)function and altered genes expression in adipose tissue, as well as liver and serum biochemistry analysis. For this purpose, mice were induced to obesity for 8 weeks, and from the 5th week, they received 16:1n7 (300 mg/kg per day) or water for 30 days, by gavage. Subcutaneous inguinal (ING) and epididymal (EPI) WAT were removed for analysis of metabolic, (anti)inflammatory, adipogenic, and thermogenic genes expression by real-time reverse transcriptase-polymerase chain reaction. Additionally, metabolic activities of isolated adipocytes, such as glucose uptake, lipogenesis (triacylglycerol esterification), β-oxidation, and lipolysis in ING adipocytes, were also assessed. Despite the higher fat intake, the HFD group showed lower food intake but higher body weight, increased glucose, significant dyslipidemia, and increased liver and adipose depot mass, accompanied by liver steatosis. The 16:1n7 supplementation slowed down the body mass gain and prevented the increase of lipids in the liver. HFD+n7 animals presented increased fatty acid oxidation and lipogenesis compared to control, but no effect was observed on lipolysis and glucose uptake in ING isolated adipocytes. Besides, 16:1n7 increased the content of the mRNA encoding FABP4, but partially prevented the expression of genes encoding ATGL, HSL, perilipin, lipin, C/EBP-α, PPAR-γ, C/EBP-β, CPT1, NRF1, TFAM, PRDM16, and nitric oxide synthase 2 in ING depot from HFD group of animals. Finally, HFD increased Mcp1 and Tnfα expression, and 16:1n7 promoted a more marked increase in it. In summary, the data show that palmitoleic acid promotes metabolic changes and partially prevents the increase in gene expression on adipocytes triggered by obesity, suggesting that HFD+n7 animals do not require the same magnitude of metabolic adaptation to cope with energy demand from the HFD. In the long term, the effects of 16:1n7 may be more evident and beneficial for the function/dysfunction of WAT from an obese organism, with relevant repercussions in the systemic metabolic homeostasis.

Melatonin Alleviates Glucose and Lipid Metabolism Disorders in Guinea Pigs Caused by Different Artificial Light Rhythms

Modern lifestyle-associated factors, such as high-calorie intake, high-fat diet (HFD), and excessive artificial light, are risk factors for glucose and lipid metabolism disturbances. Melatonin may be beneficial for managing obesity and diabetes; however, the underlying molecular mechanisms are not well elucidated. We aimed to assess whether melatonin has beneficial effects on constant artificial light-induced fat deposition, lipid metabolism, and insulin resistance. Guinea pigs were randomly divided into five experimental groups: control (C), HFD (H), 12 h light (12HL), 24 h light (24HL), and melatonin (M). The majority of indexes, including insulin resistance and obesity, were measured after 10 weeks. AMP-activated protein kinase α (AMPKα)/peroxisome proliferator-activated receptor-α (PPARα) pathway expression was analyzed by quantitative reverse transcription PCR and western blotting. Although insulin resistance and obesity indexes were higher in the 24HL group than in the 12HL group, they were significantly lower in the M group than in the 24HL group. Melatonin treatment markedly upregulated AMPKα, phosphorylated AMPKα (p-AMPKα), PPARα, and carnitine palmitoyl-CoA transferase 1 A (CPT1A) gene and protein expression. Melatonin may alleviate insulin resistance and obesity caused by persistent artificial light exposure in guinea pigs, likely via activation of the AMPKα/PPARα signaling pathway.