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Despite efforts to elucidate the cellular adaptations induced by obesity, cellular bioenergetics is currently considered a crucial target. New strategies to delay the onset of the hazardous adaptations induced by obesity are needed. Therefore, we evaluated the effects of 4 weeks of melatonin treatment on mitochondrial function and lipid metabolism in the livers of leptin-deficient mice. Our results revealed that the absence of leptin increased lipid storage in the liver and induced significant mitochondrial alterations, which were ultimately responsible for defective ATP production and reactive oxygen species overproduction. Moreover, leptin deficiency promoted mitochondrial biogenesis, fusion, and outer membrane permeabilization. Melatonin treatment reduced the bioenergetic deficit found in ob/ob mice, alleviating some mitochondrial alterations in the electron transport chain machinery, biogenesis, dynamics, respiration, ATP production, and mitochondrial outer membrane permeabilization. Given the role of melatonin in maintaining mitochondrial homeostasis, it could be used as a therapeutic agent against adipogenic steatosis.

Acute HSV-1 infection is associated with mild symptoms, such as fever and lesions of the mouth, face and skin. This phase is followed by a latency period before reactivation, which is associated with symptoms ranging from ulcers to encephalitis. Despite available anti-HSV-1 drugs, the development of new antiviral agents is sought due to the presence of resistant viruses. Melatonin, a molecule secreted by the pineal gland, has been shown to be an antioxidant, inducer of antioxidant enzymes, and regulator of various biological processes. Clinical trials have explored its therapeutic utility in conditions including infections. This study focuses on melatonin's role in HSV-1 replication and the underlying mechanisms. Melatonin was found to decrease the synthesis of HSV-1 proteins in infected Vero cells measured by immunofluorescence, indicating an inhibition of HSV-1 replication. Additionally, it regulates the activities of antioxidant enzymes and affects proteasome activity. Melatonin activates the unfolded protein response (UPR) and autophagy and suppresses apoptosis in HSV-1-infected cells. In summary, melatonin demonstrates an inhibitory role in HSV-1 replication by modulating various cellular responses, suggesting its potential utility in the treatment of viral infections.

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

Adult hippocampal neurogenesis is altered during aging and under different neuropsychiatric and neurodegenerative diseases. Melatonin shows neurogenic and neuroprotective properties during aging and neuropathological conditions. In this study, we evaluated the effects of chronic treatment with melatonin on different markers of neurodegeneration and hippocampal neurogenesis using immunohistochemistry in the aged and neurodegenerative brains of SAMP8 mice, which is an animal model of accelerated senescence that mimics aging-related Alzheimer's pathology. Neurodegenerative processes observed in the brains of aged SAMP8 mice at 10 months of age include the presence of damaged neurons, disorganization in the layers of the brain cortex, alterations in neural processes and the length of neuronal prolongations and β-amyloid accumulation in the cortex and hippocampus. This neurodegeneration may be associated with neurogenic responses in the hippocampal dentate gyrus of these mice, since we observed a neurogenic niche of neural stem and progenitor/precursors cells in the hippocampus of SAMP8 mice. However, hippocampal neurogenesis seems to be compromised due to alterations in the cell survival, migration and/or neuronal maturation of neural precursor cells due to the neurodegeneration levels in these mice. Chronic treatment with melatonin for 9 months decreased these neurodegenerative processes and the neurodegeneration-induced neurogenic response. Noticeably, melatonin also induced recovery in the functionality of adult hippocampal neurogenesis in aged SAMP8 mice.

Sexual dimorphism has been reported in many processes. However, sexual bias in favour of the use of males is very present in science. One of the main reasons is that the impact of hormones in diverse pathways and processes such as autophagy have not been properly addressed in vivo. The Harderian gland is a perfect model to study autophagic modulation as it exhibits important changes during the oestrous cycle. The aim of this study is to identify the main processes behind Harderian gland differences under oestrous cycle and their modulator. In the present study we show that redox-sensitive transcription factors have an essential role: NF-κB may activate SQSTM1/p62 in oestrus, promoting selective types of autophagy: mitophagy and lipophagy. Nrf2 activation in dioestrus, leads the retrieval phase and restoration of mitochondrial homeostasis. Melatonin's receptors show higher expression in dioestrus, leading to decreases in pro-inflammatory mediators and enhanced Nrf2 expression. Consequently, autophagy is blocked, and porphyrin release is reduced. All these results point to melatonin as one of the main modulators of the changes in autophagy during the oestrous cycle.

There are several pathologies, syndromes, and physiological processes in which autophagy is involved. This process of self-digestion that cells trigger as a survival mechanism is complex and tightly regulated, according to the homeostatic conditions of the organ. However, in all cases, its relationship with oxidative stress alterations is evident, following a pathway that suggests endoplasmic reticulum stress and/or mitochondrial changes. There is accumulating evidence of the beneficial role that melatonin has in the regulation and restoration of damaged autophagic processes. In this review, we focus on major physiological changes such as aging and essential pathologies including cancer, neurodegenerative diseases, viral infections and obesity, and document the essential role of melatonin in the regulation of autophagy in each of these different situations., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Although numerous studies have demonstrated the harmful effect of excessive fructose consumption at the systemic level, there is little information on its effects in the central nervous system. The purpose of the present work was to study the cellular alterations related to oxidative stress and protein quality control systems induced by a high-fructose diet in the brain of Syrian hamsters and their possible attenuation by exogenous melatonin. High-fructose intake induced type II diabetes together with oxidative damage, led to alterations of the unfolded protein response by activating the eIF2α branch, and impaired the macroautophagic machinery in the brain, favoring the accumulation of aggregates labeled for selective degradation and neurodegeneration markers such as β-amyloid (1-42), tau-p-S199, and tau-p-S404. Melatonin attenuated the manifestation of type II diabetes and reduced oxidative stress, deactivated eIF2α, and decreased tau-p-S404 levels in the brain of animals fed a high-fructose diet.

Obesity is a health problem caused by a diet rich in energy and the sedentary lifestyle of modern societies. A leptin deficiency is one of the worst causes of obesity, since it results in morbid obesity, a chronic disease without a cure. Leptin is an adipokine secreted in a manner dependent on the circadian rhythm that ultimately reduces food intake. We studied cellular alterations in brain of leptin-deficient obese animals and tested whether these alterations are reflected in abnormal behaviors. Obesity induced increases in oxidative stress and the unfolded protein response caused by endoplasmic reticulum stress. However, the subsequent signaling cascade was disrupted, blocking possible systemic improvements and increasing the production of misfolded proteins that trigger autophagy. Up-regulated autophagy was not indefinitely maintained and misfolded proteins accumulated in obese animals, which led to aggresome formation. Finally, neurodegenerative markers together with anxiety and stress-induced behaviors were observed in leptin-deficient mice. As oxidative stress has an essential role in the development of these harmful effects of obesity, melatonin, a powerful antioxidant, might counteract these effects on the brain. Following treatment with melatonin, the animals' antioxidant defenses were improved and misfolded protein, proteasome activity, and autophagy decreased. Aggresome formation was reduced due to the reduction in the levels of misfolded proteins and the reduction in tubulin expression, a key element in aggresome development. The levels of neurodegenerative markers were reduced and the behaviors recovered. The data support the use of melatonin in therapeutic interventions to reduce brain damage induced by leptin deficiency-dependent obesity.

Considering the increased speed at which the world population is aging, sarcopenia could become an epidemic in this century. This condition currently has no means of prevention or treatment. Melatonin is a highly effective and ubiquitously acting antioxidant and free radical scavenger that is normally produced in all organisms. This molecule has been implicated in a huge number of biological processes, from anticonvulsant properties in children to protective effects on the lung in chronic obstructive pulmonary disease. In this review, we summarize the data which suggest that melatonin may be beneficial in attenuating, reducing or preventing each of the symptoms that characterize sarcopenia. The findings are not limited to sarcopenia, but also apply to osteoporosis-related sarcopenia and to age-related neuromuscular junction dysfunction. Since melatonin has a high safety profile and is drastically reduced in advanced age, its potential utility in the treatment of sarcopenic patients and related dysfunctions should be considered., Competing Interests: The authors declare no conflict of interest.

The sedentary lifestyle of modern society along with the high intake of energetic food has made obesity a current worldwide health problem. Despite great efforts to study the obesity and its related diseases, the mechanisms underlying the development of these diseases are not well understood. Therefore, identifying novel strategies to slow the progression of these diseases is urgently needed. Experimental observations indicate that melatonin has an important role in energy metabolism and cell signalling; thus, the use of this molecule may counteract the pathologies of obesity. In this study, wild-type and obese (ob/ob) mice received daily intraperitoneal injections of melatonin at a dose of 500 μg/kg body weight for 4 weeks, and the livers of these mice were used to evaluate the oxidative stress status, proteolytic (autophagy and proteasome) activity, unfolded protein response, inflammation and insulin signalling. Our results show, for the first time, that melatonin could significantly reduce endoplasmic reticulum stress in leptin-deficient obese animals and ameliorate several symptoms that characterize this disease. Our study supports the potential of melatonin as a therapeutic treatment for the most common type of obesity and its liver-associated disorders., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, anti-inflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5-3.2 billion years ago, was as an antioxidant. The evolution of melatonin as an antioxidant by this organism was necessary as photosynthesis is associated with the generation of toxic-free radicals. The other secondary functions of melatonin came about much later in evolution. We also surmise that mitochondria and chloroplasts may be primary sites of melatonin synthesis in all eukaryotic cells that possess these organelles. This prediction is made on the basis that mitochondria and chloroplasts of eukaryotes developed from purple nonsulfur bacteria (which also produce melatonin) and cyanobacteria when they were engulfed by early eukaryotes. Thus, we speculate that the melatonin-synthesizing actions of the engulfed bacteria were retained when these organelles became mitochondria and chloroplasts, respectively. That mitochondria are likely sites of melatonin formation is supported by the observation that this organelle contains high levels of melatonin that are not impacted by blood melatonin concentrations. Melatonin has a remarkable array of means by which it thwarts oxidative damage. It, as well as its metabolites, is differentially effective in scavenging a variety of reactive oxygen and reactive nitrogen species. Moreover, melatonin and its metabolites modulate a large number of antioxidative and pro-oxidative enzymes, leading to a reduction in oxidative damage. The actions of melatonin on radical metabolizing/producing enzymes may be mediated by the Keap1-Nrf2-ARE pathway. Beyond its direct free radical scavenging and indirect antioxidant effects, melatonin has a variety of physiological and metabolic advantages that may enhance its ability to limit oxidative stress., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Despite efforts to curb the incidence of obesity and its comorbidities, this condition remains the fifth leading cause of death worldwide. To identify ways to reduce this global effect, we investigated the actions of daily melatonin administration on oxidative stress parameters and autophagic processes as a possible treatment of obesity in ob/ob mice. The involvement of melatonin in many physiological functions, such as the regulation of seasonal body weight variation, glucose uptake, or adiposity, and the role of this indoleamine as an essential antioxidant, has become the focus of numerous anti-obesity studies. Here, we examined the oxidative status in the livers of obese melatonin-treated and untreated mice, observing a decrease in the oxidative stress levels through elevated catalase activity. ROS-mediated autophagy was downregulated in the liver of melatonin-treated animals and was accompanied by significant accumulation of p62. Autophagy is closely associated with adipogenesis; in this study, we report that melatonin-treated obese mice also showed reduced adiposity, as demonstrated by diminished body weight and reduced peroxisome proliferator-activated receptor gamma expression. Based on these factors, it is reasonable to assume that oxidative stress and autophagy play important roles in obesity, and therefore, melatonin could be an interesting target molecule for the development of a potential therapeutic agent to curb body weight., (© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Oxidative stress plays an essential role in triggering many cellular processes including programmed cell death. Proving a relationship between apoptosis and reactive oxygen species has been the goal of numerous studies. Accumulating data point to an essential role for oxidative stress in the activation of autophagy. The term autophagy encompasses several processes including not only survival or death mechanisms, but also pexophagy, mitophagy, ER-phagy or ribophagy, depending of which organelles are targeted for specific autophagic degradation. However, whether the outcome of autophagy is survival or death and whether the initiating conditions are starvation, pathogens or death receptors, reactive oxygen species are invariably involved. The role of antioxidants in the regulation of these processes, however, has been sparingly investigated. Among the known antioxidants, melatonin has high efficacy and, in both experimental and clinical situations, its protective actions against oxidative stress are well documented. Beneficial effects against mitochondrial dysfunction have also been described for melatonin; thus, this indoleamine seems to be linked to mitophagy. The present review focuses on data and the most recent advances related to the role of melatonin in health and disease, on autophagy activation in general, and on mitophagy in particular., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Melatonin (N-acetyl-5-methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein., (Copyright © 2012 John Wiley & Sons, Ltd.)

Melatonin was considered to be the sole member of this natural family. The emergence of naturally occurring melatonin isomers (MIs) has opened an exciting new research area. Currently, several MIs have been identified in wine, and these molecules are believed to be synthesized by either yeasts or bacteria. A tentative nomenclature for the MIs is proposed in this article. It will be important to explore whether all organisms have the capacity to synthesize MIs, especially under the conditions of environmental stress. These isomers probably share many of the biological functions of melatonin, but their activities seem to exceed those of melatonin. On basis of the limited available information, it seems that MIs differ in their biosynthetic pathways from melatonin. Especially in those compounds in which the aliphatic side chain is not attached to ring atom 3, the starting material may not be tryptophan. Also, the metabolic pathways of MIs remain unknown. This, therefore, is another promising area of research to explore. It is our hypothesis that MIs would increase the performance of yeasts and probiotic bacteria during the processes of fermentation. Therefore, yeasts producing elevated levels of these isomers might have a superior alcohol tolerance and be able to produce higher levels of alcohol. This can be tested by comparing existing yeast strains differing in alcohol tolerance. Selection for MIs may become a strategy for isolating more resistant yeast and Lactobacillus strains, which can be of interest for industrial alcohol production and quality improvements in bacterially fermented foods such as kimchi., (© 2012 John Wiley & Sons A/S.)

The senescence-accelerated prone 8 (SAMP8) mouse strain shows early cognitive loss that mimics the deterioration of learning and memory in the elderly and is widely used as an animal model of aging. SAMP8 mouse brain suffers oxidative stress, as well as tau- and amyloid-related pathology. Mitochondrial dysfunction and the subsequent increase in cellular oxidative stress are central to the aging processes of the organism. Here, we examined the mitochondrial status of neocortical neurons cultured from SAMP8 and senescence-accelerated-resistant (SAMR1) mice. SAMP8 mouse mitochondria showed a reduced membrane potential and higher vulnerability to inhibitors and uncouplers than SAMR1 mitochondria. DL-buthionine-[S,R]-sulfoximine (BSO) caused greater oxidative damage in neurons from SAMP8 mice than in those from SAMR1 mice. This increased vulnerability, indicative of frailty-associated senescence, was protected by the anti-aging agents melatonin and resveratrol. The sirtuin 1 inhibitor, sirtinol, demonstrated that the neuroprotection against BSO was partially mediated by increased sirtuin 1 expression. Melatonin, like resveratrol, enhanced sirtuin 1 expression in neuron cultures of SAMR1 and SAMP8 mice. Therefore, a deficiency in the neuroprotection and longevity of the sirtuin 1 pathway in SAMP8 neurons may contribute to the early age-related brain damage in these mice. This supports the therapeutic use of sirtuin 1-enhancing agents against age-related nerve cell dysfunction and brain frailty., (© 2011 John Wiley & Sons A/S.)

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD., (© 2011 John Wiley & Sons A/S.)

The Syrian hamster Harderian gland exhibits sexually dimorphic porphyrin biosynthesis, wherein the female glands display an extraordinarily high concentration of porphyrins. Damage derived from this production of porphyrins, mediated by reactive oxygen species, causes the glands to develop autophagic processes, which culminate in detachment-derived cell death; these cells normally play a central role in the secretory activity of the gland. The main aim of this study was to analyze how a change in the redox state impacts autophagy. Female Syrian hamsters were treated daily with melatonin (25 μg, subcutaneously) at ZT 10 for 1-2 months (N-acetyl-5-methoxytryptamine), an endogenous antioxidant that ameliorates the deleterious effects of free radicals via a variety of mechanisms. The length of treatment affected the redox balance, the autophagy machinery, and the activation of p53 and NF-κB. One-month treatment displaces redox balance to the antioxidant side, promotes autophagy through a p53-mediated mechanism, and increases cell detachment. Meanwhile, 2-month treatment restores redox balance to the oxidant side, activates NF-κB reducing autophagy to basal levels, increases number of type II cells, and reduces number of detached cells. Our results conclude that the redox state can modulate autophagy through redox-sensitive transcriptions factors. Additionally, these findings support a hypothesis that ascribes differences in the autophagic-lysosomal pathway to epithelial cell types, thereby restricting detachment-induced autophagic cell death to epithelial cell type I., (© 2011 John Wiley & Sons A/S.)

Novel functions of melatonin continue to be uncovered. Those summarized in this report include actions at the level of the peripheral reproductive organs and include functions as an antioxidant to protect the maturing oocyte in the vesicular follicle and during ovulation, melatonin actions on the developing fetus particularly in relation to organizing the circadian system, its potential utility in combating the consequences of pre-eclampsia, reducing intrauterine growth restriction, suppressing endometriotic growths and improving the outcomes of in vitro fertilization/embryo transfer. The inhibitory effects of melatonin on many cancer types have been known for decades. Until recently, however, melatonin had not been tested as a protective agent against exocrine pancreatic tumors. This cancer type is highly aggressive and 5 year survival rate in individuals with pancreatic cancer is very low. Recent studies with melatonin indicate it may have utility in the treatment of these otherwise almost untreatable pancreatic cancers. The discovery of melatonin in plants has also opened a vast new field of research which is rapidly being exploited although the specific functions(s) of melatonin in plant organs remains enigmatic. Finally, the described application of melatonin's use as a chemical reductant in industry could well serve as a stimulus to further define the utility of this versatile molecule in new industrial applications.

Aging is commonly defined as a physiological phenomenon associated with morphological and functional deleterious changes in which oxidative stress has a fundamental impact; therefore, readjusting the oxidative balance should have beneficial effects. In our study, we tested the antioxidant melatonin in old mouse brains and showed positive effects at the cellular and mitochondrial levels. Melatonin attenuated β-amyloid protein expression and α-synuclein deposits in the brain compared to aged group. Furthermore, oxidative stress was increased by aging and induced the nuclear translocation of nuclear factor-kappa B (NF-κB), which was suppressed by melatonin treatment. The antioxidant mitochondrial expression, superoxide dismutase 2 (SOD2), was increased in both control and melatonin-treated old mice, despite the different activation states of the NF-κB pathway. The NF-κB pathway was activated in the old mice, which may be explained by this group's response to the increased oxidative insult; this insult was inhibited in melatonin-treated animals, showing this group an increase in active mitochondria population that was not observed in old group. We also report that melatonin is capable of restoring the mitochondrial potential of age-damaged neurons. In conclusion, melatonin's beneficial effects on brain aging are linked to the increase in mitochondrial membrane potential and SOD2 expression, which probably reduces the mitochondrial contribution to the oxidative stress imbalance., (© 2010 The Authors. Journal of Pineal Research © 2010 John Wiley & Sons A/S.)

We studied the effect of age and melatonin on cell death processes in brain aging. Senescence-accelerated prone mice 8 (SAMP8) and senescence-accelerated resistant mice (SAMR1) at 5 and 10 months of age were used as models of the study. Melatonin (10 mg/kg) or its vehicle (ethanol at 0.066%) was administered in the drinking water from 1 to 9 months of age. Neurodegeneration, previously shown in the aged brain of SAMP8 and SAMR1 at 10 months of age, may be due to a drop in age-related proteolytic activities (cathepsin D, calpains, and caspase-3). Likewise, lack of apoptotic and macroautophagic processes were found, without apparent modification by melatonin. However, the caspase-independent cell death, owing to high p53 and apoptosis-inducing factor (AIF) levels, might be an alternative pathway of cell death in the aged brain. The main effects of melatonin treatment were observed in the aged SAMR1 mice; in this strain we observed a marked increase in antioxidant activity (catalase and superoxide dismutase). Likewise, a key antioxidant role of apoptosis-related proteins, Bcl-2 and AIF, was suggested in the aged brain of SAM mice, which was clearly influenced by melatonin. Moreover, the age-related increase of lysosomal activity of cathepsin B and a lysosomal membrane-associated protein 2 supports the possibility of the maintenance of lysosomal viability in addition to age-related impairments of the proteolytic or macroautophagic activities. The effectiveness of melatonin against the oxidative stress-related impairments and apoptosis during the aging process is, once more, corroborated in this article.

We examined the effect of melatonin on pro-survival processes in three groups of mice. Untreated senescence-accelerated mice (SAMP8), melatonin-treated SAMP8 and untreated senescence-accelerated resistant mice (SAMR1) of 10 months old were studied. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) was supplied in the drinking water from the end of the first month until the end of the ninth month of life. Differences in the Akt/Erk1-2 pathway and downstream targets were examined and no significant changes were observed, except for beta-catenin. However, sirtuin 1 expression was significantly lower in SAMP8 than in SAMR1. In addition, acetylated p53 and NFkappaB expression were lower in SAMP8 than in SAMR1. These changes were prevented by melatonin. Moreover, the concentration/expression of alpha-secretase was lower and that of amyloid beta aggregates (Abeta) was higher in untreated SAMP8 than in SAMR1. Likewise, the levels of Bid were higher, whereas Bcl-2(XL) levels were lower in SAMP8 than in SAMR1. Melatonin reduced all these changes. We conclude that melatonin improves pro-survival signals and reduces pro-death signals in age-related impairments of neural processes.

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

The Syrian hamster Harderian gland (HG) is a juxtaorbital organ exhibiting marked gender-associated morphological differences. Regarding contents of porphyrins, this gland is a good model for studying physiological oxidative stress effects, since both sexes present strong (in females) and moderate (in males) levels of this stress in normal conditions. We have recently showed that autophagic processes are in the Syrian hamster HG as the first result of an elevated porphyrin metabolism observed in both sexes. In this case, autophagy is not a cell death mechanism per se but a constant renovation system which allows to continuing with the normal gland activity. Moreover, we have also reported that this gland presents invasive processes, resembling to tumoral progression, and are, additionally, a consequence of a strong oxidative stress environment that is mainly observed in female Syrian hamster HG and in minor proportion in male HG. Here, we present additional data and discuss a model of melatonin action on these cited processes by which melatonin would be able to destroy the equilibrium between both detoxifying actions. We postulate that melatonin reduces oxidative stress level into HG as direct antioxidant. This decrease of free radicals produces the autophagy inhibition due to outbreak signal disappearance in HG. Under these events and regarding the huge contents of porphyrins that this gland supports, the invasive process triggers.

To assess whether oxidative damage in some tissues was related to their melatonin concentration, endogenous melatonin levels and the age-linked protein and lipid damage in spleen, thymus and liver in 5-month-old SAM P8 mice were examined. The results show that high levels of melatonin in spleen and thymus correlate with lower protein and lipid damage. The liver, which had much lower melatonin concentrations than the other two tissues, had much higher levels of oxidatively damaged protein, as measured by carbonyl values. These results add new evidence concerning the protective role of endogenous melatonin as an antioxidant agent, and suggest that a treatment with this molecule might help to reduce age-associated functional deficits in many organs, including those of the immune system.

Quinolinic acid is a well-known excitotoxin that induces oxidative stress and damage. In the present study, oxidative damage to biomolecules was followed by measuring lipid peroxidation and protein carbonyl formation in rat brain tissue culture over a period of 24 hr of exposure to this prooxidant agent at a concentration of 0.5 mm. Quinolinic acid enhanced lipid peroxidation in an early stage of tissue culture, and protein carbonyl at a later stage. These data confirm and extend previous studies demonstrating that quinolinic acid can induce significant oxidative damage. Melatonin, an antioxidant and neuroprotective agent with multiple actions as a radical scavenger and signaling molecule, completely prevented these prooxidant actions of quinolinic acid at a concentration of 1 mm. Morphological lesions and neurotoxicity induced by quinolinic acid were evaluated by light microscopy. Quinolinic acid produced extensive apoptosis/necrosis which was significantly attenuated by melatonin. Cotreatment with melatonin exerted a profound protective effect antagonizing the neurotoxicity induced by quinolinic acid. Glutathione reductase and catalase activities were increased by quinolinic acid and these effects were antagonized by melatonin. Furthermore, melatonin induced superoxide dismutase activity. Quinolinic acid and melatonin acted independently and by different mechanisms in modulating antioxidant enzyme activities. Our findings using quinolinic acid and melatonin clearly demonstrate that such changes should always be seen in the context of oxidative neurotoxicity and antioxidant neuroprotection.

Melatonin, the main secretory product of the pineal gland, is known to collaborate against oxidative stress within cells, but its mechanism of action in terms of stimulating antioxidant enzymes remains unclear. Herein, we propose that melatonin modulates antioxidant enzyme activities via its interaction with calmodulin, which in turn inhibits downstream processes that lead to the inactivation of nuclear RORalpha melatonin receptor. Eventually, this nuclear transcription factor downregulates NF-kappaB-induced antioxidant enzyme expression. Therefore, the increment in antioxidant enzyme activities induced by melatonin involves the inhibition of the RORalpha pathway. Thus, in addition to its direct free radical scavenging activities, melatonin has important actions in oxidative defense by stimulating enzymes which metabolize free radicals and radical products to innocuous metabolites.

Melatonin binding sites were characterized in the nuclei of mouse mammary glands. The specific binding of 2-125I-iodomelatonin by homogenates of purified mammary gland cell nuclei was found to be rapid, reversible and saturable. Binding of 125I-melatonin exhibited day-night variations with the highest binding affinity observed during the dark period and the lowest affinity at midday. However, when the animals were maintained under continuous light exposure, binding of 125I-melatonin to cell nuclei showed a higher affinity than the daytime values found in animals maintained in normal photoperiod. Scatchard analysis of the binding data revealed the existence of a significant night-day variation in the binding kinetics, compatible with the existence of two classes of binding sites: a high-affinity binding site expressed during the night, with KD = 185 +/- 36 pm and a binding capacity of 6.24 +/- 0.4 fmol/mg protein, and a low-affinity site with KD = 562 +/- 57 nm and Bmax = 7.56 +/- 0.49 pmol/mg protein during the day. Interestingly, after 2 wk of continuous exposure to light, the animals killed at an equivalent midday time showed a significant increase in binding affinity, with KD = 1.43 +/- 0.2 nm and Bmax = 24.75 +/- 3.5 fmol/mg protein. Displacement experiments show an IC50 value compatible with the affinity constants obtained in the saturation experiments. These results indicate that the low-affinity binding site may be saturated by the high levels of melatonin found in the mouse mammary gland, and sustain the hypothesis of a circadian regulation of these melatonin binding sites by the photoperiod.

In the present paper, binding of melatonin to purified cell nuclei from harderian glands of male and female hamsters was assessed. Binding of 125I-melatonin to cell nuclei fulfills the criteria for binding to a receptor site. Binding kinetics exhibit properties such as dependence on time and temperature as well as reversibility, saturability, high affinity and specificity. The dissociation constants (K(D)) and the number of binding sites (B(max)) for the binding of 125I-melatonin to harderian gland nuclei were 260 +/- 56 pm and 12.2 +/- 0.8 fmol/mg protein in male glands, and 280 +/- 43 pm and 9.8 +/- 0.6 fmol/mg protein in female glands, respectively. Competition experiments showed IC50 values for melatonin of 250 +/- 45 pm and 290 +/- 68 pm in male and female glands, respectively. Other indoleamines such as N-acetylserotonine and 5-metoxytryptamine showed IC50 values in the micromolar range, suggesting that the binding sites are specific for melatonin. Hill analyses of the data show nH values of 0.96-0.98, suggesting the existence of a single class of binding sites. These data indicate that specific 125I-melatonin binding sites exist in the cell nuclei of Harderian glands in male as well as in female hamsters, without significant differences between them. The K(D) and B(max) values obtained from the binding in both sexes correlates well with the concentration of melatonin described in these respective Harderian glands. It is hypothesized that the nuclear binding sites of melatonin here described could be a physiological melatonin receptor, which may be involved in the genomic-dependent antioxidant effects of melatonin on hamster Harderian glands elsewhere reported.

Effects of delta-aminolevulinic acid (ALA) and melatonin were investigated in the female Syrian hamster Harderian gland. This is an organ physiologically exposed to strong oxidative stress due to the highest porphyrinogenic rates known in nature. Enzyme activities of porphyrin biosynthesis and of antioxidative protection, oxidative protein modification, and histological integrity were studied. In the porphyrin biosynthetic pathway, ALA and melatonin acted synergistically by downregulating ALA synthase (ALA-S) and stimulating product formation from ALA; the combination of ALA and melatonin suppressed ALA-S activity, down to about 1% of that in controls. While ALA effects on porphyrinogenesis can be interpreted in terms of homeostasis, melatonin's actions may be seen in relation to seasonality and/or reduction of oxidative stress. Among antioxidant enzymes, superoxide dismutase (SOD) and glutathione reductase (GR) activities were diminished by ALA, presumably due to the vulnerability of their active centers to free radicals, whereas melatonin moderately increased SOD. Both ALA and melatonin strongly stimulated catalase (CAT), thereby counteracting the oxidative stress induced by ALA and its metabolites. Nevertheless, exogenous ALA caused a strong net rise in protein carbonyl and considerable damage of tissue. When given together with ALA, melatonin antagonized these effects and largely protected the integrity of glandular structures.

Effects of the prooxidant delta-aminolevulinic acid (ALA) and the antioxidant melatonin (MEL) were investigated in the male Syrian hamster Harderian gland (HG). Rodent Harderian glands are highly porphyrogenic organs, which may be used as model systems for studying damage by delta-aminolevulinic acid and its metabolites, as occurring in porphyrias. Chronic administration of delta-aminolevulinic acid (2 weeks) markedly decreased activities of the porphyrogenic enzymes delta-aminolevulinate synthase (ALA-S) and delta-aminolevulinate dehydratase (ALA-D) and of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR) and catalase (CAT), whereas porphobilinogen deaminase (PBG-D) remained unaffected. This treatment led to increased lipid peroxidation (LPO) and oxidatively modified protein (protein carbonyl) as well as to morphologically apparent tissue damage. Melatonin also caused decreases in delta-aminolevulinate synthase, delta-aminolevulinate dehydratase, superoxide dismutase, glutathione reductase and catalase. Despite lower activities of antioxidant enzymes, lipid peroxidation and protein carbonyl were markedly diminished. The combination of delta-aminolevulinic acid and melatonin led to approximately normal levels of delta-aminolevulinate dehydratase, glutathione reductase, catalase and protein carbonyl, and to rises in superoxide dismutase and porphobilinogen deaminase activities; lipid peroxidation remained even lower than in controls and the appearance of the tissue revealed a protective influence of melatonin. These results suggest that melatonin may have profound effects on the oxidant status of the Harderian gland.

Leptin is critically compromised in the major common forms of obesity. Skeletal muscle is the main effector tissue for energy modification that occurs as a result of the effect of endocrine axes, such as leptin signaling. Our study was carried out using skeletal muscle from a leptin-deficient animal model, in order to ascertain the importance of this hormone and to identify the major skeletal muscle mechanisms affected. We also examined the therapeutic role of melatonin against leptin-induced muscle wasting. Here, we report that leptin deficiency stimulates fatty acid β-oxidation, which results in mitochondrial uncoupling and the suppression of mitochondrial oxidative damage; however, it increases cytosolic oxidative damage. Thus, different nutrient-sensing pathways are disrupted, impairing proteostasis and promoting lipid anabolism, which induces myofiber degeneration and drives oxidative type I fiber conversion. Melatonin treatment plays a significant role in reducing cellular oxidative damage and regulating energy homeostasis and fuel utilization. Melatonin is able to improve both glucose and mitochondrial metabolism and partially restore proteostasis. Taken together, our study demonstrates melatonin to be a decisive mitochondrial function-fate regulator in skeletal muscle, with implications for resembling physiological energy requirements and targeting glycolytic type II fiber recovery. [ABSTRACT FROM AUTHOR]

The sedentary lifestyle of modern society along with the high intake of energetic food has made obesity a current worldwide health problem. Despite great efforts to study the obesity and its related diseases, the mechanisms underlying the development of these diseases are not well understood. Therefore, identifying novel strategies to slow the progression of these diseases is urgently needed. Experimental observations indicate that melatonin has an important role in energy metabolism and cell signalling; thus, the use of this molecule may counteract the pathologies of obesity. In this study, wild-type and obese (ob/ob) mice received daily intraperitoneal injections of melatonin at a dose of 500 μg/kg body weight for 4 weeks, and the livers of these mice were used to evaluate the oxidative stress status, proteolytic (autophagy and proteasome) activity, unfolded protein response, inflammation and insulin signalling. Our results show, for the first time, that melatonin could significantly reduce endoplasmic reticulum stress in leptin-deficient obese animals and ameliorate several symptoms that characterize this disease. Our study supports the potential of melatonin as a therapeutic treatment for the most common type of obesity and its liver-associated disorders. [ABSTRACT FROM AUTHOR]

Despite efforts to curb the incidence of obesity and its comorbidities, this condition remains the fifth leading cause of death worldwide. To identify ways to reduce this global effect, we investigated the actions of daily melatonin administration on oxidative stress parameters and autophagic processes as a possible treatment of obesity in ob/ob mice. The involvement of melatonin in many physiological functions, such as the regulation of seasonal body weight variation, glucose uptake, or adiposity, and the role of this indoleamine as an essential antioxidant, has become the focus of numerous anti-obesity studies. Here, we examined the oxidative status in the livers of obese melatonin-treated and untreated mice, observing a decrease in the oxidative stress levels through elevated catalase activity. ROS-mediated autophagy was downregulated in the liver of melatonin-treated animals and was accompanied by significant accumulation of p62. Autophagy is closely associated with adipogenesis; in this study, we report that melatonin-treated obese mice also showed reduced adiposity, as demonstrated by diminished body weight and reduced peroxisome proliferator-activated receptor gamma expression. Based on these factors, it is reasonable to assume that oxidative stress and autophagy play important roles in obesity, and therefore, melatonin could be an interesting target molecule for the development of a potential therapeutic agent to curb body weight. [ABSTRACT FROM AUTHOR]

Melatonin acts through several specific receptors, including membrane receptors (MT1 and MT2) and members of the RZR/ROR nuclear receptors family, which have been identified in a large variety of mammalian and nonmammalian cells types. Both membrane and nuclear melatonin receptors have been partially characterized in Harderian gland of the Syrian hamster. Nevertheless, the identities of these receptors were unknown until this study, where the coexistence of MT1 and ROR α1 in this gland was determined by nested RT-PCR followed by amplicon sequencing and Western-blot. Furthermore, the cellular localization of both receptors was determined by immunohistochemistry. Thus, MT1 receptor was localized exclusively at the basal side of the cell acini, supporting the hypothesis that this receptor is activated by the pineal-synthesized melatonin. On the contrary, although a ROR α1-immunoreactivity was observed in nuclei of epithelial cells of both sexes, an extranuclear specific staining, which was more frequently among those cells of males, was also seen. The implication of this possible nuclear exclusion of ROR α1 on the role of this indoleamine against oxidative stress is discussed. [ABSTRACT FROM AUTHOR]

Endogenous circadian and exogenously driven daily rhythms of antioxidative enzyme activities and of low molecular weight antioxidants (LMWAs) are described in various phylogenetically distant organisms. Substantial amplitudes are detected in several cases, suggesting the significance of rhythmicity in avoiding excessive oxidative stress. Mammalian and/or avian glutathione peroxidase and, as a consequence, glutathione reductase activities follow the rhythm of melatonin. Another hint for an involvement of melatonin in the control of redox processes is seen in its high-affinity binding to cytosolic quinone reductase 2, previously believed to be a melatonin receptor. Although antioxidative protection by pharmacological doses of melatonin is repeatedly reported, explanations of these findings are still insufficient and their physiological and chronobiological relevance is not yet settled. Recent data indicate a role of melatonin in the avoidance of mitochondrial radical formation, a function which may prevail over direct scavenging. Rhythmic changes in oxidative damage of protein and lipid molecules are also reported. Enhanced oxidative protein modification accompanied by a marked increase in the circadian amplitude of this parameter is detected in the Drosophila mutant rosy, which is deficient in the LMWA urate. Preliminary evidence for the significance of circadian rhythmicity in diminishing oxidative stress comes from clock mutants. In Drosophila, moderately enhanced protein damage is described for the arrhythmic and melatonin null mutant per0, but even more elevated, periodic damage is found in the short-period mutant pers, synchronized to LD 12:12. Remarkably large increases in oxidative protein damage, along with impairment of tissue integrity and—obviously insufficient—compensatory elevations in protective enzymes are observed in a particularly vulnerable organ, the Harderian gland, of another short-period mutant tau, in the Syrian hamster. Mice deficient in the per2 gene homolog are reported to be cancer-prone, a finding which might also relate to oxidative stress. In the dinoflagellate Lingulodinium polyedrum [Gonyaulax polyedra], various treatments that cause oxidative stress result in strong suppressions of melatonin and its metabolite 5-methoxytryptamine (5-MT) and to secondary effects on overt rhythmicity. The glow maximum, depending on the presence of elevated 5-MT at the end of subjective night, decreases in a dose-dependent manner already under moderate, non-lethal oxidative stress, but is restored by replenishing melatonin. Therefore, a general effect of oxidative stress may consist in declines of easily oxidizable signaling molecules such as melatonin, and this can have consequences on the circadian intraorganismal organization and expression of overt rhythms. Recent findings on a redox-sensitive input into the core oscillator via modulation of NPAS2/BMAL1 or CLK/BMAL1 heterodimer binding to DNA indicate a direct influence of cellular redox balance, including oxidative stress, on the circadian clock. [ABSTRACT FROM AUTHOR]

Metabolic syndrome is a global health problem in adults and its prevalence among children and adolescents is rising. It is strongly linked to a lifestyle with high-caloric food, which causes obesity and lipid metabolism anomalies. Molecular damage due to excessive oxidative stress plays a major role during the development of metabolic syndrome complications. Among the different hormones, melatonin presents strong antioxidant properties, and it is used to treat metabolic diseases. However, there is not a consensus about its use as a metabolic syndrome treatment. The aim of this study was to identify melatonin effects in a metabolic syndrome model. Golden hamsters were fed with 60% fructose-enriched food to induce metabolic syndrome and were compared to hamsters fed with regular chow diet. Both groups were also treated with melatonin. Fructose-fed hamsters showed altered blood lipid levels (increased cholesterol and LDL) and phenotypes restored with the melatonin treatment. The Harderian gland (HG), which is an ideal model to study autophagy modulation through oxidative stress, was the organ that was most affected by a fructose diet. Redox balance was altered in fructose-fed HG, inducing autophagic activation. However, since LC3-II was not increased, the impairment must be in the last steps of autophagy. Lipophagy HG markers were also disturbed, contributing to the dyslipidemia. Melatonin treatment improved possible oxidative homeostasis through autophagic induction. All these results point to melatonin as a possible treatment of the metabolic syndrome. [ABSTRACT FROM AUTHOR]