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1.  Melatonin in Alzheimer's disease and other neurodegenerative disorders 
Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.
doi:10.1186/1744-9081-2-15
PMCID: PMC1483829  PMID: 16674804
2.  Melatonin protects against neurobehavioral and mitochondrial deficits in a chronic mouse model of Parkinson’s disease 
Neuronal oxidative stress and mitochondrial dysfunction have been implicated in Parkinson’s disease. Melatonin is a natural antioxidant and free radical scavenger that has been shown to effectively reduce cellular oxidative stress and protect mitochondrial functions in vitro. However, whether melatonin is capable of slowing down the neurodegenerative process in animal models of Parkinson’s disease remains controversial. In this research, we examined long-term melatonin treatment on striatal mitochondrial and dopaminergic functions and on animal locomotor performance in a chronic mouse model of Parkinson’s disease originally established in our laboratory by gradually treating C57BL/6 mice with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (15 mg/kg, s.c.) and probenecid (250 mg/kg, i.p.) over five weeks. We report here that when the chronic Parkinsonian mice were pre-treated and continuously treated with melatonin (5 mg/kg/day, i.p.) for 18 weeks, the defects of mitochondrial respiration, ATP and antioxidant enzyme levels detected in the striatum of chronic Parkinson’s mice were fully preempted. Meanwhile, the striatal dopaminergic and locomotor deficits seen in the chronic Parkinson’s mice were partially and significantly forestalled. These results imply that long-term melatonin is not only mitochondrial protective but also moderately neuronal protective in the chronic Parkinson’s mice. Melatonin may potentially be effective for slowing down the progression of idiopathic Parkinson’s disease and for reducing oxidative stress and respiratory chain inhibition in other mitochondrial disorders.
doi:10.1016/j.pbb.2011.06.026
PMCID: PMC3156390  PMID: 21741988
Parkinson’s disease; chronic MPTP/probenecid model; neurodegeneration; neuroprotection; mitochondrial dysfunction
3.  Melatonin and Its Agonist Ramelteon in Alzheimer's Disease: Possible Therapeutic Value 
Alzheimer's disease (AD) is an age-associated neurodegenerative disease characterized by the progressive loss of cognitive function, loss of memory and insomnia, and abnormal behavioral signs and symptoms. Among the various theories that have been put forth to explain the pathophysiology of AD, the oxidative stress induced by amyloid β-protein (Aβ) deposition has received great attention. Studies undertaken on postmortem brain samples of AD patients have consistently shown extensive lipid, protein, and DNA oxidation. Presence of abnormal tau protein, mitochondrial dysfunction, and protein hyperphosphorylation all have been demonstrated in neural tissues of AD patients. Moreover, AD patients exhibit severe sleep/wake disturbances and insomnia and these are associated with more rapid cognitive decline and memory impairment. On this basis, the successful management of AD patients requires an ideal drug that besides antagonizing Aβ-induced neurotoxicity could also correct the disturbed sleep-wake rhythm and improve sleep quality. Melatonin is an effective chronobiotic agent and has significant neuroprotective properties preventing Aβ-induced neurotoxic effects in a number of animal experimental models. Since melatonin levels in AD patients are greatly reduced, melatonin replacement has the potential value to be used as a therapeutic agent for treating AD, particularly at the early phases of the disease and especially in those in whom the relevant melatonin receptors are intact. As sleep deprivation has been shown to produce oxidative damage, impaired mitochondrial function, neurodegenerative inflammation, and altered proteosomal processing with abnormal activation of enzymes, treatment of sleep disturbances may be a priority for arresting the progression of AD. In this context the newly introduced melatonin agonist ramelteon can be of much therapeutic value because of its highly selective action on melatonin MT1/MT2 receptors in promoting sleep.
doi:10.4061/2011/741974
PMCID: PMC3004402  PMID: 21197086
4.  Melatonin ameliorates brain injury induced by systemic lipopolysaccharide in neonatal rats 
Neuroscience  2014;267:147-156.
Our previous study showed that lipopolysaccharide (LPS)-induced brain injury in the neonatal rat is associated with nitrosative and oxidative stress. The present study was conducted to examine whether melatonin, an endogenous molecule with antioxidant properties, reduces systemic LPS-induced nitrosative and oxidative damage in the neonatal rat brain. Intraperitoneal (i.p.) injection of LPS (2 mg/kg) was administered to Sprague–Dawley rat pups on postnatal day 5 (P5), and i.p. administration of melatonin (20 mg/kg) or vehicle was performed 5 minutes after LPS injection. Sensorimotor behavioral tests were performed 24 h after LPS exposure, and brain injury was examined after these tests. The results show that systemic LPS exposure resulted in impaired sensorimotor behavioral performance, and acute brain injury, as indicated by the loss of oligodendrocyte immunoreactivity and a decrease in mitochondrial activity in the neonatal rat brain. Melatonin treatment significantly reduced LPS-induced neurobehavioral disturbances and brain damage in neonatal rats. The neuroprotective effect of melatonin was associated with attenuation of LPS-induced nitrosative and oxidative stress, as indicated by the decreased nitrotyrosine- and 4-hydroxynonenal-positive staining in the brain following melatonin and LPS exposure in neonatal rats. Further, melatonin significantly attenuated LPS-induced increases in the number of activated microglia in the neonatal rat brain. The protection provided by melatonin was also associated with a reduced number of inducible nitric oxide synthase (iNOS)+ cells, which were double-labeled with ED1 (microglia). Our results show that melatonin prevents the brain injury and neurobehavioral disturbances induced by systemic LPS exposure in neonatal rats, and its neuroprotective effects are associated with its impact on nitrosative and oxidative stress.
doi:10.1016/j.neuroscience.2014.02.032
PMCID: PMC4036489  PMID: 24613717
melatonin; lipopolysaccharide; nitrosative and oxidative damage; mitochondria; microglia
5.  Peripheral and Central Effects of Melatonin on Blood Pressure Regulation 
The pineal hormone, melatonin (N-acetyl-5-methoxytryptamine), shows potent receptor-dependent and -independent actions, which participate in blood pressure regulation. The antihypertensive effect of melatonin was demonstrated in experimental and clinical hypertension. Receptor-dependent effects are mediated predominantly through MT1 and MT2 G-protein coupled receptors. The pleiotropic receptor-independent effects of melatonin with a possible impact on blood pressure involve the reactive oxygen species (ROS) scavenging nature, activation and over-expression of several antioxidant enzymes or their protection from oxidative damage and the ability to increase the efficiency of the mitochondrial electron transport chain. Besides the interaction with the vascular system, this indolamine may exert part of its antihypertensive action through its interaction with the central nervous system (CNS). The imbalance between the sympathetic and parasympathetic vegetative system is an important pathophysiological disorder and therapeutic target in hypertension. Melatonin is protective in CNS on several different levels: It reduces free radical burden, improves endothelial dysfunction, reduces inflammation and shifts the balance between the sympathetic and parasympathetic system in favor of the parasympathetic system. The increased level of serum melatonin observed in some types of hypertension may be a counter-regulatory adaptive mechanism against the sympathetic overstimulation. Since melatonin acts favorably on different levels of hypertension, including organ protection and with minimal side effects, it could become regularly involved in the struggle against this widespread cardiovascular pathology.
doi:10.3390/ijms151017920
PMCID: PMC4227197  PMID: 25299692
melatonin; hypertension; central nervous system (CNS); MT1 and MT2 receptors; reactive oxygen species (ROS)
6.  A melatonin-based fluorescence method for the measurement of mitochondrial complex III function in intact cells 
Journal of pineal research  2013;55(4):364-370.
Mitochondrial complex III (MC-3) plays a pivotal role in electron transfer and oxidative phosphorylation. Impaired MC-3 functions may contribute to a variety of diseases by interrupting normal bioenergetics and increasing reactive oxygen production and oxidative stress. Currently, MC-3 function is assessed by measuring the cytochrome c reductase activity spectrophotometrically in isolated mitochondria or MC-3. The cytoplasmic microenvironment critical for mitochondrial complex functions may be depleted during these isolation processes. The development of a reliable method to measure MC-3 activities in intact cells or tissues is highly desirable. This report describes a novel fluorescence-based method to assess MC-3 functions, i.e. Qi site electron transfer, in the intact cells. Human mesangial and teratocarcinoma NT2 cells were used to demonstrate that melatonin induced oxidation of 2′,7′-dichlorodihydrofluorescein (H2DCF) was inhibited by antimycin A, the MC-3 Qi site specific inhibitor; but not by myxothiazol, the MC-3 Qo site specific inhibitor, nor rotenone, the mitochondrial complex I inhibitor. These results indicate that melatonin induced oxidation of H2DCF is reflecting MC-3 Qi site electron transfer activities. Modifying structures of the side groups at the R3 and R5 positions of the indole ring of melatonin diminished its efficacy for inducing H2DCF oxidation, suggesting a specific interaction of melatonin with the MC-3 Qi site. These results suggest that the fluorogenic property of melatonin-induced H2DCF oxidation provides a MC-3 Qi site electron transfer specific measurement in intact cells. Interestingly, by using this method, the Qi site electron transfer activity in transformed or immortalized cells was found to be significantly higher than the non-transformed cells.
doi:10.1111/jpi.12079
PMCID: PMC4450748  PMID: 23952718
mitochondrial complex III; Qi site; electron transfer; melatonin; H2DCF; cancer
7.  Melatonin maintains mitochondrial membrane potential and attenuates activation of initiator (casp-9) and effector caspases (casp-3/casp-7) and PARP in UVR-exposed HaCaT keratinocytes 
Journal of pineal research  2007;44(4):397-407.
Melatonin is a recognized antioxidant with high potential as a protective agent in many conditions related to oxidative stress such as neurodegenerative diseases, ischemia/reperfusion syndromes, sepsis and aging. These processes may be favorably affected by melatonin through its radical scavenging properties and/or antiapoptotic activity. Also, there is increasing evidence that these effects of melatonin could be relevant in keratinocytes, the main cell population of the skin where it would contribute to protection against damage induced by ultraviolet radiation (UVR). We therefore investigated the kinetics of UVR-induced apoptosis in cultured keratinocytes characterizing the morphological and mitochondrial changes, the caspases-dependent apoptotic pathways and involvement of poly(ADP-ribose) polymerase (PARP) activation as well as the protective effects of melatonin. When irradiated with UVB radiation (50 mJ/cm2), melatonin treated, cultured keratinocytes were more confluent, showed less cell blebbing, more uniform shape and less nuclear condensation as compared to irradiated, nonmelatonin-treated controls. Preincubation with melatonin also led to normalization of the decreased UVR-induced mitochondrial membrane potential. These melatonin effects were followed by suppression of the activation of mitochondrial pathway-related initiator caspase 9 (casp-9), but not of death receptor-dependent casp-8 between 24 and 48 hr after UVR exposure. Melatonin down-regulated effector caspases (casp-3/casp-7) at 24–48 hr post-UV irradiation and reduced PARP activation at 24 hr. Thus, melatonin is particularly active in UV-irradiated keratinocytes maintaining the mitochondrial membrane potential, inhibiting the consecutive activation of the intrinsic apoptotic pathway and reducing PARP activation. In conclusion, these data provide detailed evidence for specific antiapoptotic mechanisms of melatonin in UVR-induced damage of human keratinocytes.
doi:10.1111/j.1600-079X.2007.00542.x
PMCID: PMC2365494  PMID: 18086147
antioxidant; apoptosis; caspases; keratinocytes; melatonin; mitochondria; poly(ADP-ribose) polymerase; ultraviolet radiation
8.  Antiinflammatory Activity of Melatonin in Central Nervous System 
Current Neuropharmacology  2010;8(3):228-242.
Melatonin is mainly produced in the mammalian pineal gland during the dark phase. Its secretion from the pineal gland has been classically associated with circadian and circanual rhythm regulation. However, melatonin production is not confined exclusively to the pineal gland, but other tissues including retina, Harderian glands, gut, ovary, testes, bone marrow and lens also produce it. Several studies have shown that melatonin reduces chronic and acute inflammation. The immunomodulatory properties of melatonin are well known; it acts on the immune system by regulating cytokine production of immunocompetent cells. Experimental and clinical data showing that melatonin reduces adhesion molecules and pro-inflammatory cytokines and modifies serum inflammatory parameters. As a consequence, melatonin improves the clinical course of illnesses which have an inflammatory etiology. Moreover, experimental evidence supports its actions as a direct and indirect antioxidant, scavenging free radicals, stimulating antioxidant enzymes, enhancing the activities of other antioxidants or protecting other antioxidant enzymes from oxidative damage. Several encouraging clinical studies suggest that melatonin is a neuroprotective molecule in neurodegenerative disorders where brain oxidative damage has been implicated as a common link. In this review, the authors examine the effect of melatonin on several neurological diseases with inflammatory components, including dementia, Alzheimer disease, Parkinson disease, multiple sclerosis, stroke, and brain ischemia/reperfusion but also in traumatic CNS injuries (traumatic brain and spinal cord injury)
doi:10.2174/157015910792246155
PMCID: PMC3001216  PMID: 21358973
Melatonin; inflammation; neurodegeneration; mitochondria; antioxidant; free radical.
9.  Melatonin protects the integrity of granulosa cells by reducing oxidative stress in nuclei, mitochondria, and plasma membranes in mice 
Melatonin protects luteinized granulosa cells (GCs) from oxidative stress in the follicle during ovulation. However, it is unclear in which cellular components (e.g., nuclei, mitochondria, or plasma membranes) melatonin works as an antioxidant. GCs from immature (3 wks) ICR mice were incubated with hydrogen peroxide (H2O2; 0.01, 0.1, 1, 10 mM) in the presence or absence of melatonin (100 μg/ml) for 2 h. DNA damage was assessed by fluorescence-based immunocytochemistry using specific antibodies for 8-hydroxydeoxyguanosine (8-OHdG), an indicator of oxidative guanine base damage in DNA, and for histone H2AX phosphorylation (γH2AX), a marker of double-strand breaks of DNA. Mitochondrial function was assessed by the fluorescence intensity of MitoTracker Red probes, which diffuse across the membrane and accumulate in mitochondria with active membrane potentials. Lipid peroxidation of plasma membranes was analyzed by measuring hexanoyl-lysine (HEL), a oxidative stress marker for lipid peroxidation. Apoptosis of GCs was assessed by nuclear fragmentation using DAPI staining, and apoptotic activities were evaluated by caspase-3/7 activities. H2O2 treatment significantly increased the fluorescence intensities of 8-OHdG and γH2AX, reduced the intensity of MitoTracker Red in the mitochondria, increased HEL concentrations in GCs, and enhanced the number of apoptotic cells and caspase-3/7 activities. All these changes were significantly decreased by melatonin treatment. Melatonin reduced oxidative stress-induced DNA damage, mitochondrial dysfunction, lipid peroxidation, and apoptosis in GCs, suggesting that melatonin protects GCs by reducing oxidative stress of cellular components including nuclei, mitochondria, and plasma membranes. Melatonin helps to maintain the integrity of GCs as an antioxidant in the preovulatory follicle.
doi:10.1262/jrd.2014-105
PMCID: PMC4354229  PMID: 25366368
Granulosa cells; Melatonin; Oxidative stress; Reactive oxygen species
10.  Analysis of the mechanism by which melatonin inhibits human eosinophil peroxidase 
British Journal of Pharmacology  2008;154(6):1308-1317.
Background and purpose:
Eosinophil peroxidase (EPO) catalyses the formation of oxidants implicated in the pathogenesis of various respiratory diseases including allergy and asthma. Mechanisms for inhibiting EPO, once released, are poorly understood. The aim of this work is to determine the mechanisms by which melatonin, a hormone produced in the brain by the pineal gland, inhibits the catalytic activity of EPO.
Experimental approach:
We utilized H2O2-selective electrode and direct rapid kinetic measurements to determine the pathways by which melatonin inhibits human EPO.
Key results:
In the presence of plasma levels of bromide (Br−), melatonin inactivates EPO at two different points in the classic peroxidase cycle. First, it binds to EPO and forms an inactive complex, melatonin-EPO-Br, which restricts access of H2O2 to the catalytic site of the oxidation enzyme. Second, melatonin competes with Br− and switches the reaction from a two electron (2e−) to a one electron (1e−) pathway allowing the enzyme to function with catalase-like activity. Melatonin is a bulky molecule and binds to the entrance of the EPO haem pocket (regulatory sites). Furthermore, Br− seems to enhance the affinity of this binding. In the absence of Br−, melatonin accelerated formation of EPO Compound II and its decay by serving as a 1e− substrate for EPO Compounds I and II.
Conclusions and implications:
The interplay between EPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new mechanism for melatonin to control EPO and its downstream inflammatory pathways.
doi:10.1038/bjp.2008.173
PMCID: PMC2483384  PMID: 18516076
allergy; asthma; halides; inflammation; mammalian peroxidases; stopped flow
11.  Melatonin as a potential therapy for sepsis: a phase I dose escalation study and an ex vivo whole blood model under conditions of sepsis 
Journal of Pineal Research  2014;56(4):427-438.
Sepsis is a massive inflammatory response mediated by infection, characterized by oxidative stress, release of cytokines, and mitochondrial dysfunction. Melatonin accumulates in mitochondria, and both it and its metabolites have potent antioxidant and anti-inflammatory activities and may be useful in sepsis. We undertook a phase I dose escalation study in healthy volunteers to assess the tolerability and pharmacokinetics of 20, 30, 50, and 100 mg oral doses of melatonin. In addition, we developed an ex vivo whole blood model under conditions mimicking sepsis to determine the bioactivity of melatonin and the major metabolite 6-hydroxymelatonin at relevant concentrations. For the phase I trial, oral melatonin was given to five subjects in each dose cohort (n = 20). Blood and urine were collected for measurement of melatonin and 6-hydroxymelatonin, and symptoms and physiological measures were assessed. Validated sleep scales were completed. No adverse effects after oral melatonin, other than mild transient drowsiness with no effects on sleeping patterns, were seen, and no symptoms were reported. Melatonin was rapidly cleared at all doses with a median [range] elimination half-life of 51.7 [29.5–63.2] min across all doses. There was considerable variability in maximum melatonin levels within each dose cohort, but 6-hydoxymelatonin sulfate levels were less variable and remained stable for several hours. For the ex vivo study, blood from 20 volunteers was treated with lipopolysaccharide and peptidoglycan plus a range of concentrations of melatonin/6-hydroxymelatonin. Both melatonin and 6-hydroxymelatonin had beneficial effects on sepsis-induced mitochondrial dysfunction, oxidative stress, and cytokine responses at concentrations similar to those achieved in vivo.
doi:10.1111/jpi.12134
PMCID: PMC4279949  PMID: 24650045
6-hydroxymelatonin; cytokines; melatonin; phase I clinical trial; sepsis
12.  Aging and oxygen toxicity: Relation to changes in melatonin 
Age  1997;20(4):201-213.
Melatonin (N-acetyl-5-methoxytryptamine) is a chemical mediator produced in the pineal gland and other sites in the body. The melatonin found in the blood is derived almost exclusively from the pineal gland. Since the pineal synthesizes melatonin primarily at night, blood levels of the indole are also higher at night (5–15 fold) than during the day. Some individuals on a nightly basis produce twice as much melatonin as others of the same age. Throughout life, the melatonin rhythm gradually wanes such that, in advanced age, melatonin production is usually at a minimum. Melatonin was recently found to be a free radical scavenger and antioxidant. It has been shown, in the experimental setting, to protect against both free radical induced DNA damage and oxidative stress-mediated lipid peroxidation. Pharmacologically, melatonin has been shown to reduce oxidative damage caused by such toxins as the chemical carcinogen safrole, carbon tetrachloride, paraquat, bacterial lipopolysaccharide, kainic acid, δ-aminolevulinic and amyloid β peptide of Alzheimer’s disease as well as a model of Parkinson’s disease involving the drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additionally, the oxidative damage caused by agents such as ionizing radiation and excessive exercise is reduced by melatonin. Since free radical-induced molecular injury may play a significant role in aging, melatonin’s ability to protect against it suggests a potential function of melatonin in deferring aging and age-related, free radical-based diseases. Besides its ability to abate oxidative damage, other beneficial features of melatonin may be important in combating the signs of aging; these include melatonin’s immune-stimulating function, its sleep-promoting ability, its function as an anti-viral agent, and general protective actions at the cellular level. Definitive tests of the specific functions of physiological levels of melatonin in processes of aging are currently being conducted.
doi:10.1007/s11357-997-0020-2
PMCID: PMC3455256  PMID: 23604322
13.  Differential expression of the nuclear-encoded mitochondrial transcriptome in pediatric septic shock 
Critical Care  2014;18(6):623.
Introduction
Increasing evidence supports a role for mitochondrial dysfunction in organ injury and immune dysregulation in sepsis. Although differential expression of mitochondrial genes in blood cells has been reported for several diseases in which bioenergetic failure is a postulated mechanism, there are no data about the blood cell mitochondrial transcriptome in pediatric sepsis.
Methods
We conducted a focused analysis using a multicenter genome-wide expression database of 180 children ≤10 years of age with septic shock and 53 healthy controls. Using total RNA isolated from whole blood within 24 hours of PICU admission for septic shock, we evaluated 296 nuclear-encoded mitochondrial genes using a false discovery rate of 1%. A series of bioinformatic approaches were applied to compare differentially expressed genes across previously validated gene expression-based subclasses (groups A, B, and C) of pediatric septic shock.
Results
In total, 118 genes were differentially regulated in subjects with septic shock compared to healthy controls, including 48 genes that were upregulated and 70 that were downregulated. The top scoring canonical pathway was oxidative phosphorylation, with general downregulation of the 51 genes corresponding to the electron transport system (ETS). The top two gene networks were composed primarily of mitochondrial ribosomal proteins highly connected to ETS complex I, and genes encoding for ETS complexes I, II, and IV that were highly connected to the peroxisome proliferator activated receptor (PPAR) family. There were 162 mitochondrial genes differentially regulated between groups A, B, and C. Group A, which had the highest maximum number of organ failures and mortality, exhibited a greater downregulation of mitochondrial genes compared to groups B and C.
Conclusions
Based on a focused analysis of a pediatric septic shock transcriptomic database, nuclear-encoded mitochondrial genes were differentially regulated early in pediatric septic shock compared to healthy controls, as well as across genotypic and phenotypic distinct pediatric septic shock subclasses. The nuclear genome may be an important mechanism contributing to alterations in mitochondrial bioenergetic function and outcomes in pediatric sepsis.
Electronic supplementary material
The online version of this article (doi:10.1186/s13054-014-0623-9) contains supplementary material, which is available to authorized users.
doi:10.1186/s13054-014-0623-9
PMCID: PMC4247726  PMID: 25410281
14.  High-fat diet decreases activity of the oxidative phosphorylation complexes and causes nonalcoholic steatohepatitis in mice 
Disease Models & Mechanisms  2014;7(11):1287-1296.
Nonalcoholic fatty liver disease (NAFLD) is the most frequent histological finding in individuals with abnormal liver-function tests in the Western countries. In previous studies, we have shown that oxidative phosphorylation (OXPHOS) is decreased in individuals with NAFLD, but the cause of this mitochondrial dysfunction remains uncertain. The aims of this study were to determine whether feeding mice a high-fat diet (HFD) induces any change in the activity of OXPHOS, and to investigate the mechanisms involved in the pathogenesis of this defect. To that end, 30 mice were distributed between five groups: control mice fed a standard diet, and mice on a HFD and treated with saline solution, melatonin (an antioxidant), MnTBAP (a superoxide dismutase analog) or uric acid (a scavenger of peroxynitrite) for 28 weeks intraperitoneously. In the liver of these mice, we studied histology, activity and assembly of OXPHOS complexes, levels of subunits of these complexes, gene expression of these subunits, oxidative and nitrosative stress, and oxidative DNA damage. In HFD-fed mice, we found nonalcoholic steatohepatitis, increased gene expression of TNFα, IFNγ, MCP-1, caspase-3, TGFβ1 and collagen α1(I), and increased levels of 3-tyrosine nitrated proteins. The activity and assembly of all OXPHOS complexes was decreased to about 50–60%. The amount of all studied OXPHOS subunits was markedly decreased, particularly the mitochondrial-DNA-encoded subunits. Gene expression of mitochondrial-DNA-encoded subunits was decreased to about 60% of control. There was oxidative damage to mitochondrial DNA but not to genomic DNA. Treatment of HFD-fed mice with melatonin, MnTBAP or uric acid prevented all changes observed in untreated HFD-fed mice. We conclude that a HFD decreased OXPHOS enzymatic activity owing to a decreased amount of fully assembled complexes caused by a reduced synthesis of their subunits. Antioxidants and antiperoxynitrites prevented all of these changes, suggesting that nitro-oxidative stress played a key role in the pathogenesis of these alterations. Treatment with these agents might prevent the development of NAFLD in humans.
doi:10.1242/dmm.016766
PMCID: PMC4213732  PMID: 25261569
Mitochondrial respiratory chain; Nonalcoholic steatohepatitis; NADPH oxidase; Oxidative phosphorylation; Proteomic; Nitro-oxidative stress
15.  The inhibition of apoptosis by melatonin in VSC4.1 motoneurons exposed to oxidative stress, glutamate excitotoxicity, or TNF-α toxicity involves membrane melatonin receptors 
Journal of pineal research  2010;48(2):157-169.
Loss of motoneurons may underlie some of the deficits in motor function associated with CNS injuries and diseases. We tested whether melatonin, a potent antioxidant and free radical scavenger, would prevent motoneuron apoptosis following exposure to toxins and whether this neuroprotection is mediated by melatonin receptors. Exposure of VSC4.1 motoneurons to either 50 μM H2O2, 25 μM glutamate (LGA), or 50 ng/ml tumor necrosis factor-alpha (TNF-α) for 24 h caused significant increases in apoptosis, as determined by Wright staining and ApopTag assay. Analyses of mRNA and proteins showed increased expression and activities of stress kinases and cysteine proteases and loss of mitochondrial membrane potential during apoptosis. These insults also caused increases in intracellular free [Ca2+] and activities of calpain and caspases. Cells exposed to stress stimuli for 15 min were then treated with 200 nM melatonin. Post-treatment of cells with melatonin attenuated production of reactive oxygen species (ROS) and phosphorylation of p38, MAPK, and JNK1, prevented cell death, and maintained whole-cell membrane potential, indicating functional neuroprotection. Melatonin receptors (MT1 and MT2) were upregulated following treatment with melatonin. To confirm the involvement of MT1 and MT2 in providing neuroprotection, cells were post-treated (20 min) with 10 μM luzindole (melatonin receptor antagonist). Luzindole significantly attenuated melatonin-induced neuroprotection, suggesting that melatonin worked, at least in part, via its receptors to prevent VSC4.1 motoneuron apoptosis. Results suggest that neuroprotection rendered by melatonin to motoneurons is receptor mediated and melatonin may be an effective neuroprotective agent to attenuate motoneuron death in CNS injuries and diseases.
doi:10.1111/j.1600-079X.2009.00739.x
PMCID: PMC2862889  PMID: 20082663
apoptosis; cytoprotective; glutamate; H2O2; melatonin; motoneurons; TNF-α
16.  Mitochondrial and Metabolic Dysfunction in Renal Convoluted Tubules of Obese Mice: Protective Role of Melatonin 
PLoS ONE  2014;9(10):e111141.
Obesity is a common and complex health problem, which impacts crucial organs; it is also considered an independent risk factor for chronic kidney disease. Few studies have analyzed the consequence of obesity in the renal proximal convoluted tubules, which are the major tubules involved in reabsorptive processes. For optimal performance of the kidney, energy is primarily provided by mitochondria. Melatonin, an indoleamine and antioxidant, has been identified in mitochondria, and there is considerable evidence regarding its essential role in the prevention of oxidative mitochondrial damage. In this study we evaluated the mechanism(s) of mitochondrial alterations in an animal model of obesity (ob/ob mice) and describe the beneficial effects of melatonin treatment on mitochondrial morphology and dynamics as influenced by mitofusin-2 and the intrinsic apoptotic cascade. Melatonin dissolved in 1% ethanol was added to the drinking water from postnatal week 5–13; the calculated dose of melatonin intake was 100 mg/kg body weight/day. Compared to control mice, obesity-related morphological alterations were apparent in the proximal tubules which contained round mitochondria with irregular, short cristae and cells with elevated apoptotic index. Melatonin supplementation in obese mice changed mitochondria shape and cristae organization of proximal tubules, enhanced mitofusin-2 expression, which in turn modulated the progression of the mitochondria-driven intrinsic apoptotic pathway. These changes possibly aid in reducing renal failure. The melatonin-mediated changes indicate its potential protective use against renal morphological damage and dysfunction associated with obesity and metabolic disease.
doi:10.1371/journal.pone.0111141
PMCID: PMC4210266  PMID: 25347680
17.  Significance of High Levels of Endogenous Melatonin in Mammalian Cerebrospinal Fluid and in the Central Nervous System 
Current Neuropharmacology  2010;8(3):162-167.
Levels of melatonin in mammalian circulation are well documented; however, its levels in tissues and other body fluids are yet only poorly established. It is obvious that melatonin concentrations in cerebrospinal fluid (CSF) of mammals including humans are substantially higher than those in the peripheral circulation. Evidence indicates that melatonin produced in pineal gland is directly released into third ventricle via the pineal recess. In addition, brain tissue is equipped with the synthetic machinery for melatonin production and the astrocytes and glial cells have been proven to produce melatonin. These two sources of melatonin may be responsible for its high levels in CNS. The physiological significance of the high levels of melatonin in CNS presumably is to protect neurons and glia from oxidative stress. Melatonin as a potent antioxidant has been reported to be a neuroprotector in animals and in clinical studies. It seems that long term melatonin administration which elevates CSF melatonin concentrations will retard the progression of neurodegenerative disorders, for example, Alzheimer disease.
doi:10.2174/157015910792246182
PMCID: PMC3001210  PMID: 21358967
Melatonin; pineal gland; CNS; CSF; oxidative stress; neurodegenerative disease.
18.  New Prophylactic and Therapeutic Strategies for Spinal Cord Injury 
Journal of Lifestyle Medicine  2013;3(1):34-40.
Melatonin production by the pineal gland in the vertebrate brain has attracted much scientific attention. Pineal melatonin is regulated by photoperiodicity, whereas circadian secretion of melatonin produced in the gastrointestinal tract is regulated by food intake. Thus, the circadian rhythm of pineal melatonin depends upon whether a species is diurnal or nocturnal. Spinal cord injury (SCI) involves damage to the spinal cord caused by trauma or disease that results in compromise or loss of body function. Melatonin is the most efficient and commonly used pharmacological antioxidant treatment for SCI. Melatonin is an indolamine secreted by the pineal gland during the dark phase of the circadian cycle. Neurorehabilitation is a complex medical process that focuses on improving function and repairing damaged connections in the brain and nervous system following injury. Physical activity associated with an active lifestyle reduces the risk of obesity, cardiovascular disease, type 2 diabetes, osteoporosis, and depression and protects against neurological conditions, including Parkinson’s disease, Alzheimer’s disease, and ischemic stroke. Physical activity has been shown to increase the gene expression of several brain neurotrophins (brain-derived neurotrophic factor [BDNF], nerve growth factor, and galanin) and the production of mitochondrial uncoupling protein 2, which promotes neuronal survival, differentiation, and growth. In summary, melatonin is a neural protectant, and when combined with therapeutic exercise, the hormone prevents the progression of secondary neuronal degeneration in SCI. The present review briefly describes the pathophysiological mechanisms underlying SCI, focusing on therapeutic targets and combined melatonin and exercise therapy, which can attenuate secondary injury mechanisms with minimal side effects.
PMCID: PMC4390748  PMID: 26064835
Spinal cord injury; Melatonin; Exercise therapy; Secondary damage; Neuroprotectant
19.  Melatonin Metabolism in the Central Nervous System 
Current Neuropharmacology  2010;8(3):168-181.
The metabolism of melatonin in the central nervous system is of interest for several reasons. Melatonin enters the brain either via the pineal recess or by uptake from the blood. It has been assumed to be also formed in some brain areas. Neuroprotection by melatonin has been demonstrated in numerous model systems, and various attempts have been undertaken to counteract neurodegeneration by melatonin treatment. Several concurrent pathways lead to different products. Cytochrome P450 subforms have been demonstrated in the brain. They either demethylate melatonin to N-acetylserotonin, or produce 6-hydroxymelatonin, which is mostly sulfated already in the CNS. Melatonin is deacetylated, at least in pineal gland and retina, to 5-methoxytryptamine. N1-acetyl-N2-formyl-5-methoxykynuramine is formed by pyrrole-ring cleavage, by myeloperoxidase, indoleamine 2,3-dioxygenase and various non-enzymatic oxidants. Its product, N1-acetyl-5-methoxykynuramine, is of interest as a scavenger of reactive oxygen and nitrogen species, mitochondrial modulator, downregulator of cyclooxygenase-2, inhibitor of cyclooxygenase, neuronal and inducible NO synthases. Contrary to other nitrosated aromates, the nitrosated kynuramine metabolite, 3-acetamidomethyl-6-methoxycinnolinone, does not re-donate NO. Various other products are formed from melatonin and its metabolites by interaction with reactive oxygen and nitrogen species. The relative contribution of the various pathways to melatonin catabolism seems to be influenced by microglia activation, oxidative stress and brain levels of melatonin, which may be strongly changed in experiments on neuroprotection. Many of the melatonin metabolites, which may appear in elevated concentrations after melatonin administration, possess biological or pharmacological properties, including N-acetylserotonin, 5-methoxytryptamine and some of its derivatives, and especially the 5-methoxylated kynuramines.
doi:10.2174/157015910792246244
PMCID: PMC3001211  PMID: 21358968
Kynuramines; melatonin; 5-methoxytryptamine; N-acetylserotonin; reactive nitrogen species; reactive oxygen species; 6-sulfatoxymelatonin.
20.  Melatonin protects lung mitochondria from aging 
Age  2011;34(3):681-692.
We assessed whether melatonin administration would prevent the hyperoxidative status that occurs in lung mitochondria with age. Mitochondria from lungs of male and female senescent prone mice at 5 and 10 months of age were studied. Age-dependent mitochondrial oxidative stress was evaluated by measuring the levels of lipid peroxidation and nitrite, glutathione/glutathione disulfide ratio, and glutathione peroxidase and reductase activities. Mitochondrial respiratory chain and oxidative phosphorylation capability were also measured. Age induces a significant oxidative/nitrosative status in lung mitochondria, which exhibited a significantly reduced activity of the respiratory chain and ATP production. These manifestations of age were more pronounced in males than in females. After 9 months of melatonin administration in the drinking water, the hyperoxidative status and functional deficiency of aged lung mitochondria were totally counteracted, and had increased ATP production. The beneficial effects of melatonin were generally similar in both mice genders. Thus, melatonin administration, as a single therapy, maintained fully functioning lung mitochondria during aging, a finding with important consequences in the pathophysiology of lung aging. In view of these data melatonin, the production of which decreases with age, should be considered a preventive therapy against the hyperoxidative status of the aged lungs, and its use may lead to the avoidance of respiratory complications in the elderly.
doi:10.1007/s11357-011-9267-8
PMCID: PMC3337938  PMID: 21614449
Lung; Aging; Mitochondria; Respiratory chain; Oxidative phosphorylation; Oxidative stress; Life Sciences; Molecular Medicine; Geriatrics/Gerontology; Cell Biology
21.  Melatonin, a potent agent in antioxidative defense: Actions as a natural food constituent, gastrointestinal factor, drug and prodrug 
Melatonin, originally discovered as a hormone of the pineal gland, is also produced in other organs and represents, additionally, a normal food constituent found in yeast and plant material, which can influence the level in the circulation. Compared to the pineal, the gastrointestinal tract contains several hundred times more melatonin, which can be released into the blood in response to food intake and stimuli by nutrients, especially tryptophan. Apart from its use as a commercial food additive, supraphysiological doses have been applied in medical trials and pure preparations are well tolerated by patients. Owing to its amphiphilicity, melatonin can enter any body fluid, cell or cell compartment. Its properties as an antioxidant agent are based on several, highly diverse effects. Apart from direct radical scavenging, it plays a role in upregulation of antioxidant and downregulation of prooxidant enzymes, and damage by free radicals can be reduced by its antiexcitatory actions, and presumably by contributions to appropriate internal circadian phasing, and by its improvement of mitochondrial metabolism, in terms of avoiding electron leakage and enhancing complex I and complex IV activities. Melatonin was shown to potentiate effects of other antioxidants, such as ascorbate and Trolox. Under physiological conditions, direct radical scavenging may only contribute to a minor extent to overall radical detoxification, although melatonin can eliminate several of them in scavenger cascades and potentiates the efficacy of antioxidant vitamins. Melatonin oxidation seems rather important for the production of other biologically active metabolites such as N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) and N1-acetyl-5-methoxykynuramine (AMK), which have been shown to also dispose of protective properties. Thus, melatonin may be regarded as a prodrug, too. AMK interacts with reactive oxygen and nitrogen species, conveys protection to mitochondria, inhibits and downregulates cyclooxygenase 2.
doi:10.1186/1743-7075-2-22
PMCID: PMC1262766  PMID: 16153306
22.  Therapeutic potential of melatonin and its analogs in Parkinson’s disease: focus on sleep and neuroprotection 
Sleep disorders constitute major nonmotor features of Parkinson’s disease (PD) that have a substantial effect on patients’ quality of life and can be related to the progression of the neurodegenerative disease. They can also serve as preclinical markers for PD, as it is the case for rapid eye movement (REM)-associated sleep behavior disorder (RBD). Although the etiology of sleep disorders in PD remains undefined, the assessment of the components of the circadian system, including melatonin secretion, could give therapeutically valuable insight on their pathophysiopathology. Melatonin is a regulator of the sleep/wake cycle and also acts as an effective antioxidant and mitochondrial function protector. A reduction in the expression of melatonin MT1 and MT2 receptors has been documented in the substantia nigra of PD patients. The efficacy of melatonin for preventing neuronal cell death and for ameliorating PD symptoms has been demonstrated in animal models of PD employing neurotoxins. A small number of controlled trials indicate that melatonin is useful in treating disturbed sleep in PD, in particular RBD. Whether melatonin and the recently developed melatonergic agents (ramelteon, tasimelteon, agomelatine) have therapeutic potential in PD is also discussed.
doi:10.1177/1756285611406166
PMCID: PMC3187674  PMID: 22010042
agomelatine; insomnia; light therapy; melatonin; oxidative stress; Parkinson’s disease; ramelteon; REM sleep behavior disorder; tasimelteon
23.  Hepatoprotective actions of melatonin: Possible mediation by melatonin receptors 
Melatonin, the hormone of darkness and messenger of the photoperiod, is also well known to exhibit strong direct and indirect antioxidant properties. Melatonin has previously been demonstrated to be a powerful organ protective substance in numerous models of injury; these beneficial effects have been attributed to the hormone’s intense radical scavenging capacity. The present report reviews the hepatoprotective potential of the pineal hormone in various models of oxidative stress in vivo, and summarizes the extensive literature showing that melatonin may be a suitable experimental substance to reduce liver damage after sepsis, hemorrhagic shock, ischemia/reperfusion, and in numerous models of toxic liver injury. Melatonin’s influence on hepatic antioxidant enzymes and other potentially relevant pathways, such as nitric oxide signaling, hepatic cytokine and heat shock protein expression, are evaluated. Based on recent literature demonstrating the functional relevance of melatonin receptor activation for hepatic organ protection, this article finally suggests that melatonin receptors could mediate the hepatoprotective actions of melatonin therapy.
doi:10.3748/wjg.v16.i48.6087
PMCID: PMC3012585  PMID: 21182223
Antioxidant enzymes; Hemorrhagic shock; Hepatoprotection; Ischemia; Liver; Liver function; Melatonin; Melatonin receptor; Ramelteon; Reperfusion; Sepsis; Toxic liver injury
24.  Impaired mitochondrial complex III and melatonin responsive reactive oxygen species generation in kidney mitochondria of db/db mice 
Journal of pineal research  2011;51(3):338-344.
We have previously demonstrated that melatonin, at pharmacological concentrations, causes rapid reactive oxygen species (ROS) generation at the antimycin-A sensitive site of mitochondrial complex III (MC-3). In the current work, we used this melatonin response to investigate the role of mitochondrial dysfunction in the development of diabetic nephropathy. We find that the development of diabetic nephropathy, as indicated by hyperfiltration and histopathological lesions in the kidney of db/db mice, is associated with diminished melatonin-induced ROS generation and MC-3 activity, indicating impaired MC-3 at the antimycin-A site. The MC-3 protein level in the renal mitochondria was equivalent in db/db and the non-diabetic db/m mice whereas mitochondrial complex I (MC-1) protein was dramatically upregulated in the db/db mice. This differential regulation in mitochondrial complexes may alter the equilibrium of the electron transport in renal mitochondria and contribute to ROS overproduction. The study provides one mechanism of enhanced oxidative stress that may be involved in the pathogenesis of diabetic nephropathy in db/db mice.
doi:10.1111/j.1600-079X.2011.00894.x
PMCID: PMC3165143  PMID: 21615785
melatonin; mitochondria; mitochondrial complex I and III; reactive oxygen species; glomerular filtration rate; hyperfiltration; diabetic nephropathy
25.  Delayed onset of the diurnal melatonin rise in patients with Huntington’s disease 
Journal of Neurology  2009;256(12):1961-1965.
Sleep disturbances are very prevalent in Huntington’s disease (HD) patients and can substantially impair their quality of life. Accumulating evidence suggests considerable dysfunction of the hypothalamic suprachiasmatic nucleus (SCN), the biological clock, in both HD patients and transgenic mouse models of the disease. As melatonin has a major role in the regulation of sleep and other cyclical bodily activities and its synthesis is directly regulated by the SCN, we postulated that disturbed SCN function is likely to give rise to abnormal melatonin secretion in HD. Therefore, we compared 24 h melatonin secretion profiles between early stage HD patients and age-, sex- and body mass index-matched controls. Although mean diurnal melatonin levels were not different between the two groups (p = 0.691), the timing of the evening rise in melatonin levels was significantly delayed by more than 01:30 h in HD patients (p = 0.048). Moreover, diurnal melatonin levels strongly correlated with both motor (r = −0.70, p = 0.036) and functional impairment (r = +0.78, p = 0.013). These findings suggest a delayed sleep phase syndrome-like circadian rhythm disorder in early stage HD patients and suggest that melatonin levels may progressively decline with advancing disease.
doi:10.1007/s00415-009-5196-1
PMCID: PMC2780627  PMID: 19562249
Huntington’s disease; Melatonin; Sleep; Circadian rhythm; Hypothalamus

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