Protective effects of melatonin in reducing oxidative stress and in preserving the fluidity of biological membranes: a review

Melatonin transport into mitochondria

Melatonin is a well-known, nighttime-produced indole found in bacteria, eukaryotic unicellulars, animals or vascular plants. In vertebrates, melatonin is the major product of the pineal gland, which accounts for its increase in serum during the dark phase, but it is also produced by many other organs and cell types. Such a wide distribution is consistent with its multiple and well-described functions which include from the circadian regulation and adaptation to seasonal variations to immunomodulatory and oncostatic actions in different types of tumors. The discovery of its antioxidant properties in the early 1990s opened a new field of potential protective functions in multiple tissues. A special mention should be made regarding the nervous system, where the indole is considered a major neuroprotector. Furthermore, mitochondria appear as one of the most important targets for the indole's protective actions. Melatonin's mechanisms of action vary from the direct molecular interaction with free radicals (free radical scavenger) to the binding to membrane (MLT1A and MLT1B) or nuclear receptors (RZR/RORα). Receptor binding has been associated with some, but not all of the indole functions reported to date. Recently, two new mechanisms of cellular uptake involving the facilitative glucose transporters GLUT/SLC2A and the proton-driven oligopeptide transporter PEPT1/2 have been reported. Here we discuss the potential importance that these newly discovered transport systems could have in determining the actions of melatonin, particularly in the mitochondria. We also argue the relative importance of passive diffusion vs active transport in different parts of the cell.

Melatonin as a mitochondria-targeted antioxidant: one of evolution's best ideas

Melatonin is an ancient antioxidant. After its initial development in bacteria, it has been retained throughout evolution such that it may be or may have been present in every species that have existed. Even though it has been maintained throughout evolution during the diversification of species, melatonin's chemical structure has never changed; thus, the melatonin present in currently living humans is identical to that present in cyanobacteria that have existed on Earth for billions of years. Melatonin in the systemic circulation of mammals quickly disappears from the blood presumably due to its uptake by cells, particularly when they are under high oxidative stress conditions. The measurement of the subcellular distribution of melatonin has shown that the concentration of this indole in the mitochondria greatly exceeds that in the blood. Melatonin presumably enters mitochondria through oligopeptide transporters, PEPT1, and PEPT2. Thus, melatonin is specifically targeted to the mitochondria where it seems to function as an apex antioxidant. In addition to being taken up from the circulation, melatonin may be produced in the mitochondria as well. During evolution, mitochondria likely originated when melatonin-forming bacteria were engulfed as food by ancestral prokaryotes. Over time, engulfed bacteria evolved into mitochondria; this is known as the endosymbiotic theory of the origin of mitochondria. When they did so, the mitochondria retained the ability to synthesize melatonin. Thus, melatonin is not only taken up by mitochondria but these organelles, in addition to many other functions, also probably produce melatonin as well. Melatonin's high concentrations and multiple actions as an antioxidant provide potent antioxidant protection to these organelles which are exposed to abundant free radicals.

Mitochondrial bioenergetics decay in aging: beneficial effect of melatonin

Aging is a biological process characterized by progressive decline in physiological functions, increased oxidative stress, reduced capacity to respond to stresses, and increased risk of contracting age-associated disorders. Mitochondria are referred to as the powerhouse of the cell through their role in the oxidative phosphorylation to generate ATP. These organelles contribute to the aging process, mainly through impairment of electron transport chain activity, opening of the mitochondrial permeability transition pore and increased oxidative stress. These events lead to damage to proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid of the inner mitochondrial membrane, plays a pivotal role in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis and in mitochondrial membrane stability and dynamics. Cardiolipin alterations are associated with mitochondrial bienergetics decline in multiple tissues in a variety of physiopathological conditions, as well as in the aging process. Melatonin, the major product of the pineal gland, is considered an effective protector of mitochondrial bioenergetic function. Melatonin preserves mitochondrial function by preventing cardiolipin oxidation and this may explain, at least in part, the protective role of this compound in mitochondrial physiopathology and aging. Here, mechanisms through which melatonin exerts its protective role against mitochondrial dysfunction associated with aging and age-associated disorders are discussed.

Oxidative stress prediction: A preliminary approach using a response surface based technique

A response surface was built to predict the lipid peroxidation level, generated in an iron-ascorbate in vitro model, of any organ, which is correlated with the oxidative stress injury in biological membranes. Oxidative stress studies are numerous, usually performed on laboratory animals. However, ethical concerns require validated methods to reduce the use of laboratory animals. The response surface described here is a validated method to replace animals. Tissue samples of rabbit liver, kidney, heart, skeletal muscle and brain were oxidized with different concentrations of FeCl₃ (0.1 to 8mM) and ascorbate (0.1mM), during different periods of time (0 to 90min) at 37°C. Experimental data obtained, with lipid content and antioxidant activity of each organ, allowed constructing a multidimensional surface capable of predicting, by interpolation, the lipid peroxidation level of any organ defined by its antioxidant activity and fat content, when exposed to different oxidant conditions. To check the predictive potential of the technique, two more experiments were carried out. First, in vitro oxidation data from lung tissue were collected. Second, the antioxidant capacity of kidney homogenates was modified by adding melatonin. Then, the response surface generated could predict lipid peroxidation levels produced in these new situations. The potential of this technique could be reinforced using collaborative databases to reduce the number of animals in experimental procedures.

Melatonin promotes self-renewal of nestin-positive pancreatic stem cells through activation of the MT2/ERK/SMAD/nestin axis

Although melatonin has been shown to exhibit a wide variety of biological functions, its effects on promotion of self-renewal in pancreatic stem cells remain unknown. In this study, we incubated murine pancreatic stem cells (PSCs) with various concentrations of melatonin (0.01, 0.1, 1, 10 or 100 μM) to screen for the optimum culture medium for increasing cell proliferation. We found that 10 μM melatonin can significantly increase proliferation and enhance expression of a stem cell marker, nestin, in PSCs via melatonin receptor 2 (MT2). Thus, we used 10 μM melatonin to study the melatonin-mediated molecular mechanisms of cell proliferation in PSCs. We applied extracellular signal-regulated kinase (ERK) pathway inhibitor SCH772984 and transforming growth factor beta (TGF-β) pathway inhibitor SB431542, along with interfering RNAs siERK1, siERK2, siSmad2, siSmad3, siSmad4 and siNestin, to melatonin-treated PSCs to research the roles of these genes in self-renewal. The results revealed a novel molecular mechanism by which melatonin promotes self-renewal of PSCs: a chain reaction in the MT2/ERK/SMAD/nestin axis promoted the aforementioned self-renewal as well as inhibited differentiation. In addition, upregulation of nestin created a positive feedback loop in the regulation of the transforming growth factor beta 1 (TGF-β1)/SMADs pathway by promoting expression of Smad4. Conversely, knockdown of nestin significantly suppressed the proliferative effect in melatonin-treated PSCs. These are all novel mechanisms through which the ERK pathway cooperatively crosstalks with the SMAD pathway to regulate nestin expression, thereby enhancing self-renewal in PSCs.

Melatonin Treatment Reduces Oxidative Damage and Normalizes Plasma Pro-Inflammatory Cytokines in Patients Suffering from Charcot-Marie-Tooth Neuropathy: A Pilot Study in Three Children

Charcot-Marie-Tooth neuropathy (CMT) is a motor and sensory neuropathy comprising a heterogeneous group of inherited diseases. The CMT1A phenotype is predominant in the 70% of CMT patients, with nerve conduction velocity reduction and hypertrophic demyelination. These patients have elevated oxidative stress and chronic inflammation. Currently, there is no effective cure for CMT; herein, we investigated whether melatonin treatment may reduce the inflammatory and oxidative damage in CMT1A patients. Three patients, aged 8–10 years, were treated with melatonin (60 mg at 21:00 h plus 10 mg at 09:00 h), and plasma levels of lipid peroxidation (LPO), nitrites (NOx), IL-1β, IL-2, IL-6, TNF-α, INF-γ, oxidized to reduced glutathione (GSSG/GSH) ratio, and the activities of superoxide dismutase (SOD), glutathione-S transferase (GST), glutathione peroxidase (GPx), and reductase (GRd), were determined in erythrocytes at 3 and 6 months of treatment. Healthy age- and sex-matched subjects were used as controls. The results showed increased activities of SOD, GST, GPx, and GRd in CMT1A patients, which were reduced at 3 and 6 months of treatment. The GSSG/GSH ratio significantly increased in the patients, returning to control values after melatonin treatment. The inflammatory process was confirmed by the elevation of all proinflammatory cytokines measured, which were also normalized by melatonin. LPO and NOx, which also were elevated in the patients, were normalized by melatonin. The results document beneficial effects of the use of melatonin in CMT1A patients to reduce the hyperoxidative and inflammatory condition, which may correlate with a reduction of the degenerative process.

Exogenous melatonin in the treatment of pain: a systematic review and meta-analysis

Melatonin is an important hormone for regulating mammalian circadian biology and cellular homeostasis. Recent evidence has shown that melatonin exerts anti-nociception effects in both animals and humans. However, according to clinical trials, the anti-nociception effects of melatonin are still controversial. The aim of this meta-analysis was to investigate the anti-nociception effects of melatonin premedication. The primary outcome was the effects of melatonin on pain intensity. The secondary outcomes included the number of patients with analgesic requirements, total analgesic consumption, and brain-derived neurotrophic factor (BDNF) levels. In total, 19 studies were included in the current meta-analysis. The pooling data show that melatonin significantly decreased the pain intensity, as evidenced by the pain scores. Moreover, melatonin administration also reduced the proportion of patients with analgesic requirements and BDNF levels. However, the effects of melatonin on total analgesic consumption still require further confirmation. Collectively, the current meta-analysis supports the use of melatonin for anti-nociception.

Melatonin Supplementation Lowers Oxidative Stress and Regulates Adipokines in Obese Patients on a Calorie-Restricted Diet

Obesity is one of the major global health problems. Melatonin deficiency has been demonstrated to correlate with obesity. The aim of the study was to estimate the effect of melatonin on oxidative stress and adipokine levels in obese patients on a calorie-restricted diet. Thirty obese patients were supplemented with a daily dose of 10 mg of melatonin (n = 15) or placebo (n = 15) for 30 days with a calorie-restricted diet. Serum levels of melatonin, 4-hydroxynonenal (HNE), adiponectin, omentin-1, leptin, and resistin, as well as erythrocytic malondialdehyde (MDA) concentration and Zn/Cu-superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities, were measured at baseline and after supplementation. Significant body weight reduction was observed only in the melatonin group. After melatonin supplementation, the adiponectin and omentin-1 levels and GPx activities statistically increased, whereas the MDA concentrations were reduced. In the placebo group, a significant rise in the HNE and a drop in the melatonin concentrations were found. The results show evidence of increased oxidative stress accompanying calorie restriction. Melatonin supplementation facilitated body weight reduction, improved the antioxidant defense, and regulated adipokine secretion. The findings strongly suggest that melatonin should be considered in obesity management. This trial is registered with CTRI/2017/07/009093.

Melatonin successfully rescues hippocampal bioenergetics and improves cognitive function following drug intoxication by promoting Nrf2-ARE signaling activity

Prolonged exposure to gamma-hydroxybutyric acid (GHB) would cause drug intoxication in which impaired cognitive function results from enhanced hippocampal oxidative stress may serve as a major symptom in this deficiency. Considering melatonin possesses significant anti-oxidative efficacy, this study aimed to determine whether melatonin would successfully promote the nuclear factor erythroid 2-related factor 2 and antioxidant responsive element (Nrf2-ARE) signaling, depress oxidative stress, and rescue hippocampal bioenergetics and cognitive function following drug intoxication injury. Adolescent rats subjected to 10 days of GHB were received melatonin at doses of either 10 or 100 mg/kg. Time-of-flight secondary ion mass spectrometry, biochemical assay, quantitative histochemistry, [¹⁴ C]-2-deoxyglucose analysis, together with Morris water maze were employed to detect the molecular signaling, oxidative status, bioenergetic level, as well as the cognitive performances, respectively. Results indicated that in GHB-intoxicated rats, enhanced oxidative stress, increased cholesterol level, and decreased anti-oxidative enzymes activities were detected in hippocampal regions. Intense oxidative stress paralleled well with reduced bioenergetics and poor performance in behavioral testing. However, in rats treated with melatonin following GHB intoxication, all above parameters and cognitive function were gradually returned to nearly normal levels. Melatonin also remarkably promoted the translocation of Nrf2 from cytoplasm to nucleus in a dose-dependent manner, thereby increased the Nrf2-ARE signaling-related downstream anti-oxidative enzymes activities. As melatonin effectively rescues hippocampal bioenergetics through depressing the oxidative stress by promoting Nrf2-ARE molecular machinery, this study thus highlights for the first time that clinical use of melatonin may serve as a therapeutic strategy to improve the cognitive function in unsuspecting victims suffered from GHB intoxication injury.

Melatonin prevents memory impairment induced by high-fat diet: Role of oxidative stress

Consumption of high-fat diet (HFD) induces oxidative stress in the hippocampus that leads to memory impairment. Melatonin has antioxidant and neuroprotective effects. In this study, we hypothesized that chronic administration of melatonin can prevent memory impairment induced by consumption of HFD. Melatonin was administered to rats via oral gavage (100mg/kg/day) for 4 weeks. HFD was also instituted for the same duration. Behavioral studies were conducted to test spatial memory using the radial arm water maze. Additionally, oxidative stress biomarkers were assessed in the hippocampus. Results showed that HFD impaired both short- and long- term memory (P<0.05), while melatonin treatment prevented such effects. Furthermore, melatonin prevented HFD-induced reduction in levels of GSH, and ratio of GSH/GSSG, and increase in GSSG in the hippocampus. Melatonin also prevented reduction in the catalase activity in hippocampus of animals on HFD. In conclusion, HFD induced memory impairment and melatonin prevented this impairment probably by preventing alteration of oxidative stress in the hippocampus.

Melatonin inhibits neuronal dysfunction-associated with neuroinflammation by atopic psychological stress in NC/Nga atopic-like mouse models

Atopic dermatitis (AD), also known as atopic eczema, is chronic pruritic skin disease. AD can increase psychological stress as well, increasing glucocorticoid release and exacerbating the associated symptoms. Chronic glucocorticoid elevation disturbs neuroendocrine signaling and can induce neuroinflammation, neurotoxicity, and cognitive impairment; however, it is unclear whether AD-related psychological stress elevates glucocorticoids enough to cause neuronal damage. Therefore, we assessed the effects of AD-induced stress in a mouse AD model. AD-related psychological stress increased astroglial and microglial activation, neuroinflammatory cytokine expression, and markers of neuronal loss. Notably, melatonin administration inhibited the development of skin lesions, scratching behavior, and serum IgE levels in the model mice, and additionally caused a significant reduction in corticotropin-releasing hormone responsiveness, and a significant reduction in neuronal damage. Finally, we produced similar results in a corticosterone-induced AD-like skin model. This is the first study to demonstrate that AD-related psychological stress increases neuroendocrine dysfunction, exacerbates neuroinflammation, and potentially accelerates other neurodegenerative disease states.

Melatonin potentiates the antitumor effect of curcumin by inhibiting IKKβ/NF-κB/COX-2 signaling pathway

Curcumin, a natural polyphenolic compound, has commonly been used as a food additive or in many traditional medicine remedies for over 2,000 years in many Asian countries. Melatonin is a hormone secreted from pineal glands of mammals and possesses diverse physiological functions. Both curcumin and melatonin have the effective potential to inhibit proliferation of various types of cancers, but there is no report on their combination for bladder cancer treatment, and the underlying mechanism remains poorly understood. In the present study, we investigated whether the combination of curcumin and melatonin leads to an enhanced inhibition of cell proliferation in bladder cancer cells. Our results showed that the combinational treatment enhanced the repression of nuclear translocation of NF-κB and their binding on COX-2 promoter via inhibiting IKKβ activity, resulting in inhibition of COX-2 expression. In addition, combined treatment with curcumin and melatonin induced cell apoptosis in bladder cancer through enhancing the release of cytochrome c from the mitochondrial intermembrane space into the cytosol. These results, therefore, indicated that melatonin synergized the inhibitory effect of curcumin against the growth of bladder cancer by enhancing the anti-proliferation, anti-migration, and pro-apoptotic activities, and provide strong evidence that combined treatment with curcumin and melatonin might exhibit an effective therapeutic option in bladder cancer therapy.

Antioxidant and Membrane Binding Properties of Serotonin Protect Lipids from Oxidation

Serotonin (5-hydroxytryptamine, 5-HT) is a well-known neurotransmitter that is involved in a growing number of functions in peripheral tissues. Recent studies have shown nonpharmacological functions of 5-HT linked to its chemical properties. Indeed, it was reported that 5-HT may, on the one hand, bind lipid membranes and, on the other hand, protect red blood cells through a mechanism independent of its specific receptors. To better understand these underevaluated properties of 5-HT, we combined biochemical, biophysical, and molecular dynamics simulations approaches to characterize, at the molecular level, the antioxidant capacity of 5-HT and its interaction with lipid membranes. To do so, 5-HT was added to red blood cells and lipid membranes bearing different degrees of unsaturation. Our results demonstrate that 5-HT acts as a potent antioxidant and binds with a superior affinity to lipids with unsaturation on both alkyl chains. We show that 5-HT locates at the hydrophobic-hydrophilic interface, below the glycerol group. This interfacial location is stabilized by hydrogen bonds between the 5-HT hydroxyl group and lipid headgroups and allows 5-HT to intercept reactive oxygen species, preventing membrane oxidation. Experimental and molecular dynamics simulations using membrane enriched with oxidized lipids converge to further reveal that 5-HT contributes to the termination of lipid peroxidation by direct interaction with active groups of these lipids and could also contribute to limit the production of new radicals. Taken together, our results identify 5-HT as a potent inhibitor of lipid peroxidation and offer a different perspective on the role of this pleiotropic molecule.

Effects of Melatonin on Early Pregnancy in Mouse: Involving the Regulation of StAR, Cyp11a1, and Ihh Expression

To test whether melatonin plays an important role in the process of early pregnancy, melatonin was given in drinking water to pregnant mice at different gestation stages. These included mice who were given melatonin 14 days prior to their successful mating (confirmed by vaginal plug) (Group A), after successful mating (Group B), and 14 days prior to and until after successful mating (Group C). Melatonin administration significantly enhanced serum as well as ovarian melatonin levels in the mice. It was observed that melatonin did not affect the natural estrous of mice. On day 0.5 of gestation (D0.5), melatonin not only elevated progesterone (P) secretion, but also upregulated expressions of StAR and Cyp11a1, the two marker genes of corpus luteum in ovaries (p < 0.05). Group A had a significantly lower estradiol (E₂) secretion and a higher number of implantation sites as well as litter size than controls (p < 0.05) and also had an increased Ihh expression in endometrium of D7.5 gestation. Melatonin treatment after successful mating improved the progesterone (P) secretion at D7.5 of gestation (p < 0.05) and significantly induced leukaemia inhibitory factor (LIF) expression (p < 0.05). Our study indicates that melatonin treatment up-regulated the genes involved in pregnenolone synthesis in ovary and Ihh expression in uterine endometrium. The mechanisms of melatonin to improve embryo implantation related to their actions on promoting the development of corpus luteum before gestation and helping to specify uterine receptivity in early pregnant mice.

Coupling of lipid membrane elasticity and in-plane dynamics

Biomembranes exhibit liquid and solid features concomitantly with their in-plane fluidity and elasticity tightly regulated by cells. Here, we present experimental evidence supporting the existence of the dynamics-elasticity correlations for lipid membranes and propose a mechanism involving molecular packing densities to explain them. This paper thereby unifies, at the molecular level, the aspects of the continuum mechanics long used to model the two membrane features. This ultimately may elucidate the universal physical principles governing the cellular phenomena involving biomembranes.

Melatonin suppresses hepatocellular carcinoma progression via lncRNA-CPS1-IT-mediated HIF-1α inactivation

Melatonin is the primary pineal hormone that relays light/dark cycle information to the circadian system. It was recently reported to exert intrinsic antitumor activity in various cancers. However, the regulatory mechanisms underlying the antitumor activity of melatonin are poorly understood. Moreover, a limited number of studies have addressed the role of melatonin in hepatocellular carcinoma (HCC), a major life-threatening malignancy in both sexes in Taiwan. In this study, we investigated the antitumor effects of melatonin in HCC and explored the regulatory mechanisms underlying these effects. We observed that melatonin significantly inhibited the proliferation, migration, and invasion of HCC cells and significantly induced the expression of the transcription factor FOXA2 in HCC cells. This increase in FOXA2 expression resulted in upregulation of lncRNA-CPS1 intronic transcript 1 (CPS1-IT1), which reduced HIF-1α activity and consequently resulted in the suppression of epithelial-mesenchymal transition (EMT) progression and HCC metastasis. Furthermore, the results of the in vivo experiments confirmed that melatonin exerts tumor suppressive effects by reducing tumor growth. In conclusion, our findings suggested that melatonin inhibited HCC progression by reducing lncRNA-CPS1-IT1-mediated EMT suppression and indicated that melatonin could be a promising treatment for HCC.

Omega-3 fatty acids inhibit oxidative stress in a rat model of liver regeneration

Purpose

Lipid peroxidation and consequent reactive oxygen species in the setting of oxidative stress have crucial roles in liver regeneration, which may adversely affect the regeneration itself and lead to liver failure. The aim of the current study is to investigate whether omega-3 fatty acid supplementation inhibits oxidative stress in an experimental model of liver regeneration.

Methods

Forty rats were allocated to four groups. Rats in group A received a sham operation. Rats in group B were subjected to right portal vein ligation (RPVL) and saline infusion. Rats in groups C and D were subjected to RPVL and total parenteral nutrition (TPN) with an all-in-one admixture containing a soybean oil based lipid emulsion. Rats in group D were additionally supplemented with omega-3 fatty acid infusion. Oxidative stresses in the blood and liver were measured by glutathione, superoxide dismutase, catalase, glutathione peroxidase, malondialdehyde, and nitric oxide.

Results

Omega-3 supplementation to the TPN solution significantly corrected alterations in the blood and tissue concentrations of oxidants and anti-oxidants during regeneration (P < 0.05).

Conclusion

Omega-3 fatty acid supplementation to the TPN solution revealed promising results in removal of oxidative stress that emerges during liver regeneration.

Melatonin inhibits Sirt1-dependent NAMPT and NFAT5 signaling in chondrocytes to attenuate osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease mainly characterized by cartilage degradation. Interleukin-1β (IL-1β) contributes to OA pathogenesis by enhancing oxidative stress and inflammation. Melatonin reportedly elicits potent protection against OA. However, the role of melatonin and underlying mechanism in IL-1β-stimulated chondrocytes remain largely unclear. In this study, we found that melatonin inhibited IL-1β-induced toxicity and sirtuin 1 (Sirt1) enhancement in human chondrocytes. Melatonin reduced the IL-1β-increased nicotinamide phosphoribosyltransferase (NAMPT) expression and the NAD⁺ level in chondrocytes in a Sirt1-dependent manner. In turn, the inhibitory effect of melatonin on Sirt1 was mediated by NAMPT. Moreover, melatonin suppressed IL-1β-induced Sirt1-mediated matrix metalloproteinase (MMP)-3 and MMP-13 production. Melatonin also decreased the Sirt1-steered nuclear factor of activated T cells 5 (NFAT5) expression in IL-1β-challenged chondrocytes. NFAT5 depletion mimicked the suppressive effects of melatonin on IL-1β-elevated production of inflammatory mediators, including tumor necrosis factor-α (TNF-α), IL-1β, prostaglandin E2 (PGE₂), and nitric oxide (NO) in chondrocytes. TNF-α, IL-1β, PGE₂, or NO decrease caused the similar reduction of MMP-3 and MMP-13 by melatonin in IL-1β-insulted chondrocytes. Highly consistent with in vitro findings, in vivo results demonstrated that melatonin repressed the expression of relevant genes in rat OA pathogenesis in anterior cruciate ligament transection model. Overall, these results indicate that melatonin effectively reduced IL-1β-induced MMP production by inhibiting Sirt1-dependent NAMPT and NFAT5 signaling in chondrocytes, suggesting melatonin as a potential therapeutic alternative for chondroprotection of OA patients.

On the mechanisms of melatonin in protection of aluminum phosphide cardiotoxicity

Aluminum phosphide (AlP), one of the most commonly used pesticides worldwide, has been the leading cause of self-poisoning mortalities among many Asian countries. The heart is the main organ affected in AlP poisoning. Melatonin has been previously shown to be beneficial in reversing toxic changes in the heart. The present study reveals evidence on the probable protective effects of melatonin on AlP-induced cardiotoxicity in rats. The study groups included a control (almond oil only), ethanol 5% (solvent), sole melatonin (50 mg/kg), AlP (16.7 mg/kg), and 4 AlP + melatonin groups which received 20, 30, 40 and 50 mg/kg of melatonin by intraperitoneal injections following AlP treatment. An electronic cardiovascular monitoring device was used to record the electrocardiographic (ECG) parameters. Heart tissues were studied in terms of oxidative stress biomarkers, mitochondrial complexes activities, ADP/ATP ratio and apoptosis. Abnormal ECG records as well as declined heart rate and blood pressure were found to be related to AlP administration. Based on the results, melatonin was highly effective in controlling AlP-induced changes in the study groups. Significant improvements were observed in the activities of mitochondrial complexes, oxidative stress biomarkers, the activities of caspases 3 and 9, and ADP/ATP ratio following treatment with melatonin at doses of 40 and 50 mg/kg. Our results indicate that melatonin can counteract the AlP-induced oxidative damage in the heart. This is mainly done by maintaining the normal balance of intracellular ATP as well as the prevention of oxidative damage. Further research is warranted to evaluate the possibility of using melatonin as an antidote in AlP poisoning.

Melatonin attenuates behavioural deficits and reduces brain oxidative stress in a rodent model of schizophrenia

Melatonin is a neurohormone that is linked to the aetiopathogenesis of schizophrenia. The aim of this study was to assess the potentials of oral melatonin supplement in the management of induced schizophrenia-like behavioural and brain oxidative status changes, using an animal model. The relative degrees of modulation of ketamine-induced behaviours by haloperidol, olanzapine or melatonin were assessed in the open-field, Y-maze, elevated plus maze and the social interaction tests. 12-week old, male mice were assigned to six groups of ten each (n=10). They were pretreated with daily intraperitoneal ketamine at 15mg/kg (except vehicle) for 10days, before commencement of 14day treatment with standard drug (haloperidol or olanzapine) or melatonin. Ketamine injection also continued alongside melatonin or standard drugs administration for the duration of treatment. Melatonin, haloperidol and olanzapine were administered by gavage. Treatments were given daily, and behaviours assessed on days 11 and 24. On day 24, animals were sacrificed and whole brain homogenates used for the estimation of glutathione, nitric oxide and malondialdehyde levels. Ketamine injection increased open-field behaviours; while it decreased working-memory, social-interaction and glutathione activity. Nitric oxide and malondialdehyde levels also increased after ketamine injection. Administration of melatonin was associated with variable degrees of reversal of these effects. In conclusion, melatonin may have the potential of a possible therapeutic agent and/or adjunct in the management of schizophrenia.

Melatonin Attenuates Pulmonary Hypertension in Chronically Hypoxic Rats

Chronic hypoxia induces pulmonary hypertension and vascular remodeling, which are clinically relevant to patients with chronic obstructive pulmonary disease (COPD) associated with a decreased level of nitric oxide (NO). Oxidative stress and inflammation play important roles in the pathophysiological processes in COPD. We examined the hypothesis that daily administration of melatonin (10 mg/kg) mitigates the pulmonary hypertension and vascular remodeling in chronically hypoxic rats. The right ventricular systolic pressure (RVSP) and the thickness of pulmonary arteriolar wall were measured from normoxic control, vehicle- and melatonin-treated hypoxic rats exposed to 10% O₂ for 14 days. Levels of markers for oxidative stress (malondialdhyde) and inflammation (tumor necrosis factor-α (TNFα), inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2)) and the expressions of total endothelial NO synthase (eNOS) and phosphorylated eNOS at serine1177 (ser1177) were determined in the lung tissue. We found that the RVSP and the thickness of the arteriolar wall were significantly increased in the vehicle-treated hypoxic animals with elevated levels of malondialdhyde and mRNA expressions of the inflammatory mediators, when compared with the normoxic control. In addition, the phosphorylated eNOS (ser1177) level was significantly decreased, despite an increased eNOS expression in the vehicle-treated hypoxic group. Melatonin treatment significantly attenuated the levels of RVSP, thickness of the arteriolar wall, oxidative and inflammatory markers in the hypoxic animals with a marked increase in the eNOS phosphorylation in the lung. These results suggest that melatonin attenuates pulmonary hypertension by antagonizing the oxidative injury and restoration of NO production.

Mechanism of salutary effects of melatonin-mediated liver protection after trauma-hemorrhage: p38 MAPK-dependent iNOS/HIF-1α pathway

Although melatonin attenuates the increases in inflammatory mediators and reduces organ injury during trauma-hemorrhage, the mechanisms remain unclear. This study explored whether melatonin prevents liver injury after trauma-hemorrhage through the p38 mitogen-activated protein kinase (MAPK)-dependent, inducible nitrite oxide (iNOS)/hypoxia-inducible factor (HIF)-1α pathway. After a 5-cm midline laparotomy, male rats underwent hemorrhagic shock (mean blood pressure ~40 mmHg for 90 min) followed by fluid resuscitation. At the onset of resuscitation, rats were treated with vehicle, melatonin (2 mg/kg), melatonin plus p38 MAPK inhibitor SB203580 (2 mg/kg), or melatonin plus the melatonin receptor antagonist luzindole (2.5 mg/kg). At 2 h after trauma-hemorrhage, histopathology score of liver injury, liver tissue myeloperoxidase activity, malondialdehyde, adenosine triphosphate, serum alanine aminotransferase, and asparate aminotransferase levels were significantly increased compared with sham-operated control. Trauma-hemorrhage resulted in a significant decrease in the p38 MAPK activation compared with that in the sham-treated animals. Administration of melatonin after trauma-hemorrhage normalized liver p38 MAPK phosphorylation and iNOS and HIF-1α expression and attenuated cleaved caspase 3 and receptor interacting protein kinase-1 levels. Coadministration of SB203580 or luzindole abolished the melatonin-mediated attenuation of the trauma-hemorrhage-induced increase of iNOS/HIF-1α protein expression and liver injury markers. Taken together, our results suggest that melatonin prevents trauma-hemorrhage-induced liver injury in rats, at least in part, through melatonin receptor-related, p38 MAPK-dependent iNOS/HIF-1α pathway.NEW & NOTEWORTHY Trauma-hemorrhage resulted in a significant decrease in liver p38 MAPK activation and increase in nitrite oxide synthase (iNOS) and hypoxia-inducible factor (HIF)-1α expression. Administration of melatonin after trauma-hemorrhage normalized liver p38 MAPK phosphorylation and iNOS and HIF-1α expression, which was abolished by coadministration of SB203580 or luzindole. Melatonin prevents trauma-hemorrhage-induced liver injury in rats via the melatonin receptor-related, p38 MAPK-dependent iNOS/HIF-1α pathway.

Human transporters, PEPT1/2, facilitate melatonin transportation into mitochondria of cancer cells: An implication of the therapeutic potential

Melatonin is present in virtually all organisms from bacteria to mammals, and it exhibits a broad spectrum of biological functions, including synchronization of circadian rhythms and oncostatic activity. Several functions of melatonin are mediated by its membrane receptors, but others are receptor-independent. For the latter, melatonin is required to penetrate membrane and enters intracellular compartments. However, the mechanism by which melatonin enters cells remains debatable. In this study, it was identified that melatonin and its sulfation metabolites were the substrates of oligopeptide transporter (PEPT) 1/2 and organic anion transporter (OAT) 3, respectively. The docking analysis showed that the binding of melatonin to PEPT1/2 was attributed to their low binding energy and suitable binding conformation in which melatonin was embedded in the active site of PEPT1/2 and fitted well with the cavity in three-dimensional space. PEPT1/2 transporters play a pivotal role in melatonin uptake in cells. Melatonin's membrane transportation via PEPT1/2 renders its oncostatic effect in malignant cells. For the first time, PEPT1/2 were identified to localize in the mitochondrial membrane of human cancer cell lines of PC3 and U118. PEPT1/2 facilitated the transportation of melatonin into mitochondria. Melatonin accumulation in mitochondria induced apoptosis of PC3 and U118 cells. Thus, PEPT1/2 can potentially be used as a cancer cell-targeted melatonin delivery system to improve the therapeutic effects of melatonin in cancer treatment.

Melatonin Improves Mitochondrial Respiration in Syncytiotrophoblasts From Placentas of Obese Women

Maternal obesity is associated with increased oxidative stress but decreased placental mitochondrial respiration and expression of mitochondrial electron transport chain (ETC) complexes I to V. Melatonin acts as an antioxidant and prevents oxidative stress-induced changes in cytotrophoblasts. Placentas were collected at term by cesarean delivery from obese (first trimester body mass index [BMI] ≥30, n = 10) or lean (BMI < 25, n = 6) women. Cytotrophoblasts were isolated and allowed to syncytialize for 72 hours with or without melatonin (0.1-100 µM) for the last 24 hours. Mitochondrial respiratory parameters were measured in a Seahorse XF24. Expression of ETC complexes I to V and antioxidant enzymes was measured by Western blot. Maternal clinical characteristics of patients were similar except for BMI. No significant improvement in mitochondrial respiration occurred with addition of melatonin to trophoblasts of lean women. However, in trophoblasts from obese women, melatonin (10 and 100 µmol/L) significantly increased maximal respiration ( P = .01 and P = .009, respectively) and spare capacity ( P = .02 and P = .003, respectively) compared to the untreated control. No differences were detected in the expression of ETC complexes and superoxide dismutase 1 or 2 in trophoblasts treated with melatonin. The expression of glutathione peroxidase, which was significantly greater in trophoblast of obese compared to lean women ( P < .05), was decreased back to the level seen in trophoblast of lean women with addition of melatonin ( P = .02). Improved spare respiratory capacity, the cellular reserve, could impart a protective effect to the placenta and fetus in an adverse intrauterine environment or in response to additional stressors.

Melatonin enhances survival and preserves functional integrity of stem cells: A review

Despite state-of-the-art pharmaceutical regimens, continuous improvements in diagnostic techniques as well as refinements in equipment and interventional procedures, many diseases remain refractory to conventional therapies. Recent advances in stem cell (SC) biology have opened an avenue to exploring its therapeutic potential in various disease entities, especially those that are ischemia-related and refractory to conventional treatment. A number of experimental studies and clinical trials have already demonstrated promising outcomes. On the other hand, SC therapy is associated with major problems. For instance, ischemia, inflammation, and oxidative stress are some of the factors unfavorable for SC survival once SCs are implanted into the ischemic area in an attempt to enhance tissue regeneration and restore organ function. Melatonin, which is originally derived from pineal gland in the regulation of human circadian rhythms and sleep, is a potent free radical scavenger and metal chelator with the capacity to alleviate oxidative stress and inflammatory reactions as well as stabilizing cell membranes. Accumulating data have demonstrated that melatonin-supported SC therapy is superior to SC alone for improving ischemia-related organ dysfunction. In this review, we describe and interpret the potential role of melatonin in sustaining the survival and preserving the functional integrity of SC.

Potentiation of biological effects of mesenchymal stem cells in ischemic conditions by melatonin via upregulation of cellular prion protein expression

Mesenchymal stem cells (MSCs) are promising candidates for stem cell-based therapy in ischemic diseases. However, ischemic injury induces pathophysiological conditions, such as oxidative stress and inflammation, which diminish therapeutic efficacy of MSC-based therapy by reducing survival and functionality of transplanted MSCs. To overcome this problem, we explored the effects of melatonin on the proliferation, resistance to oxidative stress, and immunomodulatory properties of MSCs. Treatment with melatonin enhanced MSC proliferation and self-renewal via upregulation of cellular prion protein (PrP^C ) expression. Melatonin diminished the extent of MSC apoptosis in oxidative stress conditions by regulating the levels of apoptosis-associated proteins, such as BCL-2, BAX, PARP-1, and caspase-3, in a PrP^C -dependent manner. In addition, melatonin regulated the immunomodulatory effects of MSCs via the PrP^C -IDO axis. In a murine hind-limb ischemia model, melatonin-stimulated MSCs improved the blood flow perfusion, limb salvage, and vessel regeneration by lowering the extent of apoptosis of affected local cells and transplanted MSCs as well as by reducing infiltration of macrophages. These melatonin-mediated therapeutic effects were inhibited by silencing of PrP^C expression. Our findings for the first time indicate that melatonin promotes MSC functionality and enhances MSC-mediated neovascularization in ischemic tissues through the upregulation of PrP^C expression. In conclusion, melatonin-treated MSCs could provide a therapeutic strategy for vessel regeneration in ischemic disease, and the targeting of PrP^C levels may prove instrumental for MSC-based therapies.

Sleep Problems as Predictors in Attention-Deficit Hyperactivity Disorder: Causal Mechanisms, Consequences and Treatment

Attention-deficit hyperactivity disorder (ADHD) is notorious for its debilitating consequences and early age of onset. The need for early diagnosis and intervention has frequently been underscored. Previous studies have attempted to clarify the bidirectional relationship between ADHD and sleep problems, proposing a potential role for sleep problems as early predictors of ADHD. Sleep deprivation, sleep-disordered breathing, and circadian rhythm disturbances have been extensively studied, yielding evidence with regard to their induction of ADHD-like symptoms. Genetic-phenotypic differences across individuals regarding the aforementioned sleep problems have been elucidated along with the possible use of these characteristics for early prediction of ADHD. The long-term consequences of sleep problems in individuals with ADHD include obesity, poor academic performance, and disrupted parent-child interactions. Early intervention has been proposed as an approach to preventing these debilitating outcomes of ADHD, with novel treatment approaches ranging from melatonin and light therapy to myofunctional therapy and adjustments of the time point at which school starts.

Activation of melatonin receptor (MT1/2) promotes P-gp transporter in methamphetamine-induced toxicity on primary rat brain microvascular endothelial cells

Melatonin has been known as a neuroprotective agent for the central nervous system (CNS) and the blood-brain barrier (BBB), which is the primary structure that comes into contact with several neurotoxins including methamphetamine (METH). Previous studies have reported that the activation of melatonin receptors (MT1/2) by melatonin could protect against METH-induced toxicity in brain endothelial cells via several mechanisms. However, its effects on the P-glycoprotein (P-gp) transporter, the active efflux pump involved in cell homeostasis, are still unclear. Thus, this study investigated the role of melatonin and its receptors on the METH-impaired P-gp transporter in primary rat brain microvascular endothelial cells (BMVECs). The results showed that METH impaired the function of the P-gp transporter, significantly decreasing the efflux of Rho123 and P-gp expression, which caused a significant increase in the intracellular accumulation of Rho123, and these responses were reversed by the interaction of melatonin with its receptors. Blockade of the P-gp transporter by verapamil caused oxidative stress, apoptosis, and cell integrity impairment after METH treatment, and these effects could be reversed by melatonin. Our results, together with previous findings, suggest that the interaction of melatonin with its receptors protects against the effects of the METH-impaired P-gp transporter and that the protective role in METH-induced toxicity was at least partially mediated by the regulation of the P-gp transporter. Thus, melatonin and its receptors (MT1/2) are essential for protecting against BBB impairment caused by METH.

Association between light at night, melatonin secretion, sleep deprivation, and the internal clock: Health impacts and mechanisms of circadian disruption

Exposure to Artificial Light At Night (ALAN) results in a disruption of the circadian system, which is deleterious to health. In industrialized countries, 75% of the total workforce is estimated to have been involved in shift work and night work. Epidemiologic studies, mainly of nurses, have revealed an association between sustained night work and a 50-100% higher incidence of breast cancer. The potential and multifactorial mechanisms of the effects include the suppression of melatonin secretion by ALAN, sleep deprivation, and circadian disruption. Shift and/or night work generally decreases the time spent sleeping, and it disrupts the circadian time structure. In the long run, this desynchronization is detrimental to health, as underscored by a large number of epidemiological studies that have uncovered elevated rates of several diseases, including cancer, diabetes, cardiovascular risks, obesity, mood disorders and age-related macular degeneration. It amounts to a public health issue in the light of the very substantial number of individuals involved. The IARC has classified shift work in group 2A of "probable carcinogens to humans" since "they involve a circadian disorganization". Countermeasures to the effects of ALAN, such as melatonin, bright light, or psychotropic drugs, have been proposed as a means to combat circadian clock disruption and improve adaptation to shift and night work. We review the evidence for the ALAN impacts on health. Furthermore, we highlight the importance of an in-depth mechanistic understanding to combat the detrimental properties of exposure to ALAN and develop strategies of prevention.

Melatonin, a novel selective ATF-6 inhibitor, induces human hepatoma cell apoptosis through COX-2 downregulation

AIM

To clarify the mechanisms involved in the critical endoplasmic reticulum (ER) stress initiating unfolded protein response pathway modified by melatonin.

METHODS

Hepatoma cells, HepG2, were cultured in vitro. Flow cytometry and TUNEL assay were used to measure HepG2 cell apoptosis. Western blotting and quantitative reverse transcription-polymerase chain reaction methods were used to determine the protein and messenger RNA levels of ER stress and apoptosis related genes’ expression, respectively. Tissue microarray construction from patients was verified by immunohistochemical analysis.

RESULTS

In the present study, we first identified that melatonin selectively blocked activating transcription factor 6 (ATF-6) and then inhibited cyclooxygenase-2 (COX-2) expression, leading to enhanced liver cancer cell apoptosis under ER stress condition. Dramatically increased CCAAT-enhancer-binding protein homologous protein level, suppressed COX-2 and decreased Bcl-2/Bax ratio by melatonin or ATF-6 siRNA contributed the enhanced HepG2 cell apoptosis under tunicamycin (an ER stress inducer) stimulation. In clinical hepatocellular carcinoma patients, the close relationship between ATF-6 and COX-2 was further confirmed.

CONCLUSION

These findings indicate that melatonin as a novel selective ATF-6 inhibitor can sensitize human hepatoma cells to ER stress inducing apoptosis.

Aging and Oxidative Stress Decrease Pineal Elongation Factor 2: In Vivo Protective Effect of Melatonin in Young Rats Treated With Cumene Hydroperoxide

We studied the alterations of Elongation Factor 2 (eEF2) in the pineal gland of aged rats as well as the possible protective role of exogenous melatonin on these changes in young rats treated with cumene hydroperoxide (CH), a compound that promotes lipid peroxidation and inhibits protein synthesis. The study was performed using male Wistar rats of 3 (control), 12, and 24 months and 3-month-old rats treated with CH, melatonin, and CH plus melatonin. We found that pineal eEF-2 is affected by aging and CH, these changes being prevented by exogenous melatonin in the case of CH-treated rats. The proteomic studies show that many other proteins are affected by aging and oxidative stress in the pineal gland. The results suggest that one of the possible mechanisms underlying pineal gland dysfunction during aging is the effect of lipid peroxidation on eEF-2, which is a key component of protein synthesis machinery. J. Cell. Biochem. 118: 182-190, 2017. © 2016 Wiley Periodicals, Inc.

Effect and possible mechanisms of melatonin treatment on the quality and developmental potential of aged bovine oocytes

After reaching the metaphase II (MII) stage, unfertilised oocytes undergo a time-dependent process of quality deterioration referred to as oocyte aging. The associated morphological and cellular changes lead to decreased oocyte developmental potential. This study investigated the effect of exogenous melatonin supplementation on in vitro aged bovine oocytes and explored its underlying mechanisms. The levels of cytoplasmic reactive oxygen species and DNA damage response in bovine oocytes increased during in vitro aging. Meanwhile, maturation promoting factor activity significantly decreased and the proportion of morphologically abnormal oocytes significantly increased. Melatonin supplementation significantly decreased quality deterioration in aged bovine MII oocytes (P < 0.05). Additionally, it decreased the frequency of aberrant spindle organisation and cortical granule release during oocyte aging (P < 0.05). In the melatonin-supplemented group, mitochondrial membrane potential and ATP production were significantly increased compared with control. Furthermore, melatonin treatment significantly increased the speed of development of bovine oocytes to the blastocyst stage after in vitro fertilisation and significantly decreased the apoptotic rate in the blastocysts (P < 0.05). The expression of Bax and Casp3 in the blastocysts was significantly reduced after treatment with melatonin, whereas expression of Bcl2 significantly increased (P < 0.05). In conclusion, these findings suggest that supplementation of aged bovine oocytes with exogenous melatonin improves oocyte quality, thereby enhancing the developmental capacity of early embryos.

Melatonin alleviates postinfarction cardiac remodeling and dysfunction by inhibiting Mst1

Melatonin reportedly protects against several cardiovascular diseases including ischemia/reperfusion (I/R), atherosclerosis, and hypertension. The present study investigated the effects and mechanisms of melatonin on cardiomyocyte autophagy, apoptosis, and mitochondrial injury in the context of myocardial infarction (MI). We demonstrated that melatonin significantly alleviated cardiac dysfunction after MI. Four weeks after MI, echocardiography and Masson staining indicated that melatonin notably mitigated adverse left ventricle remodeling. The mechanism may be associated with increased autophagy, reduced apoptosis, and alleviated mitochondrial dysfunction. Furthermore, melatonin significantly inhibited Mst1 phosphorylation while promoting Sirt1 expression after MI, which indicates that Mst1/Sirt1 signaling may serve as the downstream target of melatonin. We thus constructed a MI model using Mst1 transgenic (Mst1 Tg) and Mst1 knockout (Mst1^-/- ) mice. The absence of Mst1 abolished the favorable effects of melatonin on cardiac injury after MI. Consistently, melatonin administration did not further increase autophagy, decrease apoptosis, or alleviate mitochondrial integrity and biogenesis in Mst1 knockout mice subjected to MI injury. These results suggest that melatonin alleviates postinfarction cardiac remodeling and dysfunction by upregulating autophagy, decreasing apoptosis, and modulating mitochondrial integrity and biogenesis. The attributed mechanism involved, at least in part, Mst1/Sirt1 signaling.

Apoptosis signaling pathways in osteoarthritis and possible protective role of melatonin

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive erosion of articular cartilage. As chondrocytes are the only cell type forming the articular cartilage, their gradual loss is the main cause of OA. There is a substantial body of published research that suggests reactive oxygen species (ROS) are major causative factors for chondrocyte damage and OA development. Oxidative stress elicited by ROS is capable of oxidizing and subsequently disrupting cartilage homeostasis, promoting catabolism via induction of cell death and damaging numerous components of the joint. IL-1β and TNF-α are crucial inflammatory factors that play pivotal roles in the pathogenesis of OA. In this process, the mitochondria are the major source of ROS production in cells, suggesting a role of mitochondrial dysfunction in this type of arthritis. This may also be promoted by inflammatory cytokines such as IL-1β and TNF-α which contribute to chondrocyte death. In patients with OA, the expression of endoplasmic reticulum (ER) stress-associated molecules is positively correlated with cartilage degeneration. Melatonin and its metabolites are broad-spectrum antioxidants and free radical scavengers which regulate a variety of molecular pathways such as inflammation, proliferation, apoptosis, and metastasis in different pathophysiological situations. Herein, we review the effects of melatonin on OA, focusing on its ability to regulate apoptotic processes and ER and mitochondrial activity. We also evaluate likely protective effects of melatonin on OA pathogenesis.

Phenolic Melatonin-Related Compounds: Their Role as Chemical Protectors against Oxidative Stress

There is currently no doubt about the serious threat that oxidative stress (OS) poses to human health. Therefore, a crucial strategy to maintain a good health status is to identify molecules capable of offering protection against OS through chemical routes. Based on the known efficiency of the phenolic and melatonin (MLT) families of compounds as antioxidants, it is logical to assume that phenolic MLT-related compounds should be (at least) equally efficient. Unfortunately, they have been less investigated than phenols, MLT and its non-phenolic metabolites in this context. The evidence reviewed here strongly suggests that MLT phenolic derivatives can act as both primary and secondary antioxidants, exerting their protection through diverse chemical routes. They all seem to be better free radical scavengers than MLT and Trolox, while some of them also surpass ascorbic acid and resveratrol. However, there are still many aspects that deserve further investigations for this kind of compounds.

Melatonin as an antioxidant: under promises but over delivers

Melatonin is uncommonly effective in reducing oxidative stress under a remarkably large number of circumstances. It achieves this action via a variety of means: direct detoxification of reactive oxygen and reactive nitrogen species and indirectly by stimulating antioxidant enzymes while suppressing the activity of pro-oxidant enzymes. In addition to these well-described actions, melatonin also reportedly chelates transition metals, which are involved in the Fenton/Haber-Weiss reactions; in doing so, melatonin reduces the formation of the devastatingly toxic hydroxyl radical resulting in the reduction of oxidative stress. Melatonin's ubiquitous but unequal intracellular distribution, including its high concentrations in mitochondria, likely aid in its capacity to resist oxidative stress and cellular apoptosis. There is credible evidence to suggest that melatonin should be classified as a mitochondria-targeted antioxidant. Melatonin's capacity to prevent oxidative damage and the associated physiological debilitation is well documented in numerous experimental ischemia/reperfusion (hypoxia/reoxygenation) studies especially in the brain (stroke) and in the heart (heart attack). Melatonin, via its antiradical mechanisms, also reduces the toxicity of noxious prescription drugs and of methamphetamine, a drug of abuse. Experimental findings also indicate that melatonin renders treatment-resistant cancers sensitive to various therapeutic agents and may be useful, due to its multiple antioxidant actions, in especially delaying and perhaps treating a variety of age-related diseases and dehumanizing conditions. Melatonin has been effectively used to combat oxidative stress, inflammation and cellular apoptosis and to restore tissue function in a number of human trials; its efficacy supports its more extensive use in a wider variety of human studies. The uncommonly high-safety profile of melatonin also bolsters this conclusion. It is the current feeling of the authors that, in view of the widely diverse beneficial functions that have been reported for melatonin, these may be merely epiphenomena of the more fundamental, yet-to-be identified basic action(s) of this ancient molecule.

Melatonin mediates selenium-induced tolerance to cadmium stress in tomato plants

Both selenium (Se) and melatonin reduce cadmium (Cd) uptake and mitigate Cd toxicity in plants. However, the relationship between Se and melatonin in Cd detoxification remains unclear. In this study, we investigated the influence of three forms of Se (selenocysteine, sodium selenite, and sodium selenate) on the biosynthesis of melatonin and the tolerance against Cd in tomato plants. Pretreatment with different forms of Se significantly induced the biosynthesis of melatonin and its precursors (tryptophan, tryptamine, and serotonin); selenocysteine had the most marked effect on melatonin biosynthesis. Furthermore, Se and melatonin supplements significantly increased plant Cd tolerance as evidenced by decreased growth inhibition, photoinhibition, and electrolyte leakage (EL). Se-induced Cd tolerance was compromised in melatonin-deficient plants following tryptophan decarboxylase (TDC) gene silencing. Se treatment increased the levels of glutathione (GSH) and phytochelatins (PCs), as well as the expression of GSH and PC biosynthetic genes in nonsilenced plants, but the effects of Se were compromised in TDC-silenced plants under Cd stress. In addition, Se and melatonin supplements reduced Cd content in leaves of nonsilenced plants, but Se-induced reduction in Cd content was compromised in leaves of TDC-silenced plants. Taken together, our results indicate that melatonin is involved in Se-induced Cd tolerance via the regulation of Cd detoxification.

Melatonin attenuates neuronal apoptosis through up-regulation of K(+) -Cl(-) cotransporter KCC2 expression following traumatic brain injury in rats

Traumatic brain injury (TBI) initiates a complex cascade of neurochemical and signaling changes that leads to neuronal apoptosis, which contributes to poor outcomes for patients with TBI. The neuron-specific K(+) -Cl(-) cotransporter-2 (KCC2), the principal Cl(-) extruder in adult neurons, plays an important role in Cl(-) homeostasis and neuronal function. This present study was designed to investigate the expression pattern of KCC2 following TBI and to evaluate whether or not melatonin is able to prevent neuronal apoptosis by modulating KCC2 expression in a Sprague Dawley rat controlled cortical impact model of TBI. The time course study showed decreased mRNA and protein expression of KCC2 in the ipsilateral peri-core parietal cortex after TBI. Double immunofluorescence staining demonstrated that KCC2 is located in the plasma membrane of neurons. In addition, melatonin (10 mg/kg) was injected intraperitoneally at 5 minutes and repeated at 1, 2, 3, and 4 hours after brain trauma, and brain samples were extracted 24 hours after TBI. Compared to the vehicle group, melatonin treatment altered the down-regulation of KCC2 expression in both mRNA and protein levels after TBI. Also, melatonin treatment increased the protein levels of brain-derived neurotrophic factor (BDNF) and phosphorylated extracellular signal-regulated kinase (p-ERK). Simultaneously, melatonin administration ameliorated cortical neuronal apoptosis, reduced brain edema, and attenuated neurological deficits after TBI. In conclusion, our findings suggested that melatonin restores KCC2 expression, inhibits neuronal apoptosis and attenuates secondary brain injury after TBI, partially through activation of BDNF/ERK pathway.

Elevated heart rate and nondipping heart rate as potential targets for melatonin: a review

Elevated heart rate is a risk factor for cardiovascular and all-cause mortalities in the general population and various cardiovascular pathologies. Insufficient heart rate decline during the night, that is, nondipping heart rate, also increases cardiovascular risk. Abnormal heart rate reflects an autonomic nervous system imbalance in terms of relative dominance of sympathetic tone. There are only a few prospective studies concerning the effect of heart rate reduction in coronary heart disease and heart failure. In hypertensive patients, retrospective analyses show no additional benefit of slowing down the heart rate by beta-blockade to blood pressure reduction. Melatonin, a secretory product of the pineal gland, has several attributes, which predict melatonin to be a promising candidate in the struggle against elevated heart rate and its consequences in the hypertensive population. First, melatonin production depends on the sympathetic stimulation of the pineal gland. On the other hand, melatonin inhibits the sympathetic system in several ways representing potentially the counter-regulatory mechanism to normalize excessive sympathetic drive. Second, administration of melatonin reduces heart rate in animals and humans. Third, the chronobiological action of melatonin may normalize the insufficient nocturnal decline of heart rate. Moreover, melatonin reduces the development of endothelial dysfunction and atherosclerosis, which are considered a crucial pathophysiological disorder of increased heart rate and pulsatile blood flow. The antihypertensive and antiremodeling action of melatonin along with its beneficial effects on lipid profile and insulin resistance may be of additional benefit. A clinical trial investigating melatonin actions in hypertensive patients with increased heart rate is warranted.

Melatonin enhances mitochondrial ATP synthesis, reduces reactive oxygen species formation, and mediates translocation of the nuclear erythroid 2-related factor 2 resulting in activation of phase-2 antioxidant enzymes (γ-GCS, HO-1, NQO1) in ultraviolet radiation-treated normal human epidermal keratinocytes (NHEK)

Melatonin is an ubiquitous molecule with a variety of functions including potent antioxidative properties. Due to its lipophilic character, it easily crosses cellular and intracellular membranes and reaches all subcellular organelles. Because of its ability to scavenge free radicals, melatonin protects against oxidative stress, for example, induced by ultraviolet radiation (UVR). Here, we investigated, in a dose-dependent (0, 10, 25, and 50 mJ/cm(2) ) and time-dependent (0, 4, 24, 48 hr post-UVR) manner, whether melatonin prevents the UVR-mediated alterations in ATP synthesis and the generation of reactive oxygen species (ROS) in normal human epidermal keratinocytes (NHEK). Additionally, we evaluated the molecular mechanism of action of melatonin with regard to activation of phase-2 antioxidative enzymes via nuclear erythroid 2-related factor (Nrf2). We found that (i) melatonin counteracted UVR-induced alterations in the ATP synthesis and reduced free radical formation; (ii) melatonin induced the translocation of Nrf2 transcription factor from the cytosol into the nucleus resulting in, (iii) melatonin enhanced gene expression of phase-2 antioxidative enzymes including γ-glutamylcysteine synthetase (γ-GCS), heme oxygenase-1 (HO-1), and NADPH: quinone dehydrogenase-1 (NQO1) representing an elevated antioxidative response of keratinocytes. These results suggest that melatonin not only directly scavenges ROS, but also significantly induces the activation of phase-2 antioxidative enzymes via the Nrf2 pathway uncovering a new action mechanism that supports the ability of keratinocytes to protect themselves from UVR-mediated oxidative stress.

Melatonin improves reprogramming efficiency and proliferation of bovine-induced pluripotent stem cells

Melatonin can modulate neural stem cell (NSC) functions such as proliferation and differentiation into NSC-derived pluripotent stem cells (N-iPS) in brain tissue, but the effect and mechanism underlying this are unclear. Thus, we studied how primary cultured bovine NSCs isolated from the retinal neural layer could transform into N-iPS cell. NSCs were exposed to 0.01, 0.1, 1, 10, or 100 μm melatonin, and cell viability studies indicated that 10 μm melatonin can significantly increase cell viability and promote cell proliferation in NSCs in vitro. Thus, 10 μm melatonin was used to study miR-302/367-mediated cell reprogramming of NSCs. We noted that this concentration of melatonin increased reprogramming efficiency of N-iPS cell generation from primary cultured bovine NSCs and that this was mediated by downregulation of apoptosis-related genes p53 and p21. Then, N-iPS cells were treated with 1, 10, 100, or 500 μm melatonin, and N-iPS (M-N-iPS) cell proliferation was measured. We noted that 100 μm melatonin increased proliferation of N-iPS cells via increased phosphorylation of intracellular ERK1/2 via activation of its pathway in M-N-iPS via melatonin receptors 1 (MT1). Finally, we verified that N-iPS cells and M-N-iPS cells are similar to typical embryonic stem cells including the expression of pluripotency markers (Oct4 and Nanog), the ability to form teratomas in vivo, and the capacity to differentiate into all three embryonic germ layers.

Inhibitory effect of melatonin on cerebral endothelial cells dysfunction induced by methamphetamine via NADPH oxidase-2

Melatonin is a hormone that mostly produced from the pineal gland, and it performs as a strong neuroprotectant to both neuron and glial cells against methamphetamine (METH)-induced neurotoxicity. Recently, it has been found that METH also damages the blood brain barrier (BBB) structure and function. However, the protective mechanism of melatonin on the BBB impairment caused by METH has not been investigated. In this study, the primary rat brain microvascular endothelium cells (BMVECs) isolated from neonatal rats was used to investigate the protective effect of melatonin on METH-induced BBB impairment and the underlying mechanism. The results demonstrated that melatonin decreased the level of reactive oxygen species (ROS), reactive nitrogen species (RNS), and apoptosis induced by METH via NADPH oxidase (NOX)-2 since apocynin, a NOX-2 inhibitor abolished those changes. In addition, melatonin was found to improve cell integrity by increasing the transendothelial electric resistance (TEER) values, and up-regulate the tight junction proteins ZO-1, occludin, and claudin-5, thereby decreasing the paracellular permeability caused by METH mediated by NOX-2. Our data suggest that METH induces BBB impairment by mediating NOX-2 activity, and then induces oxidative and nitrative stress, as well as apoptosis, which causes the impairment of cell integrity, and that melatonin reduces these negative effects of METH by mediating via MT1/2 receptors.

3-Hydroxy-3-methylglutaric and 3-methylglutaric acids impair redox status and energy production and transfer in rat heart: relevance for the pathophysiology of cardiac dysfunction in 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency

3-Hydroxy-3-methylglutaryl-coenzyme A lyase (HL) deficiency is characterized by tissue accumulation of 3-hydroxy-3-methylglutaric (HMG), and 3-methylglutaric (MGA) acids. Affected patients present cardiomyopathy, whose pathomechanisms are not yet established. We investigated the effects of HMG and MGA on energy and redox homeostasis in rat heart using in vivo and in vitro models. In vivo experiments showed that intraperitoneal administration of HMG and MGA decreased the activities of the respiratory chain complex II and creatine kinase (CK), whereas HMG also decreased the activity of complex II-III. Furthermore, HMG and MGA injection increased reactive species production and carbonyl formation, and decreased glutathione concentrations. Regarding the enzymatic antioxidant defenses, HMG and MGA increased glutathione peroxidase (GPx) and glutathione reductase (GR) activities, while only MGA diminished the activities of superoxide dismutase (SOD) and catalase, as well as the protein content of SOD1. Pre-treatment with melatonin (MEL) prevented MGA-induced decrease of CK activity and SOD1 levels. In vitro results demonstrated that HMG and MGA increased reactive species formation, induced lipid peroxidation and decreased glutathione. We also verified that reactive species overproduction and glutathione decrease provoked by HMG and MGA were abrogated by MEL and lipoic acid (LA), while only MEL prevented HMG- and MGA-induced lipoperoxidation. Allopurinol (ALP) also prevented reactive species overproduction caused by both metabolites. Our data provide solid evidence that bioenergetics dysfunction and oxidative stress are induced by HMG and MGA in heart, which may explain the cardiac dysfunction observed in HL deficiency, and also suggest that antioxidant supplementation could be considered as adjuvant therapy for affected patients.

Melatonin pretreatment enhances the therapeutic effects of exogenous mitochondria against hepatic ischemia-reperfusion injury in rats through suppression of mitochondrial permeability transition

We tested the hypothesis that melatonin (Mel) enhances exogenous mitochondria (Mito) treatment against rodent hepatic ischemia-reperfusion (IR) injury. In vitro study utilized three groups of hepatocytes (i.e. nontreatment, menadione, and menadione-melatonin treatment, 4.0 × 10(5) each), while in vivo study used adult male Sprague Dawley rats (n = 40) equally divided into sham-control (SC), IR (60-min left-lobe ischemia + 72-hr reperfusion), IR-Mel (melatonin at 30 min/6/8 hr after reperfusion), IR-Mito (mitochondria 15,000 μg/rat 30 min after reperfusion), and IR-Mel-Mito. Following menadione treatment in vitro, oxidative stress (NOX-1/NOX-2/oxidized protein), apoptotic (cleaved caspase-3/PARP), DNA damage (γ-H2AX/CD90/XRCC1), mitochondria damage (cytosolic cytochrome c) biomarkers, and mitochondrial permeability transition were found to be lower, whereas mitochondrial cytochrome c were found to be higher in hepatocytes with melatonin treatment compared to those without (all P < 0.001). In vivo study demonstrated highest liver injury score and serum AST in IR group, but lowest in SC group and higher in IR-Mito group than that in groups IR-Mel and IR-Mel-Mito, and higher in IR-Mel group than that in IR-Mel-Mito group after 72-hr reperfusion (all P < 0.003). Protein expressions of inflammatory (TNF-α/NF-κB/IL-1β/MMP-9), oxidative stress (NOX-1/NOX-2/oxidized protein), apoptotic (caspase-3/PARP/Bax), and mitochondria damage (cytosolic cytochrome c) biomarkers displayed an identical pattern, whereas mitochondria integrity marker (mitochondrial cytochrome c) showed an opposite pattern compared to that of liver injury score (all P < 0.001) among five groups. Microscopically, expressions of apoptotic nuclei, inflammatory (MPO(+) /CD68(+) /CD14(+) cells), and DNA damage (γ-H2AX(+) cells) biomarkers exhibited an identical pattern compared to that of liver injury score (all P < 0.001) among five groups. Melatonin-supported mitochondria treatment offered an additional benefit of alleviating hepatic IR injury.