Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin

Melatonin treatment counteracts the hyperoxidative status in erythrocytes of patients suffering from Duchenne muscular dystrophy

OBJECTIVES

To analyze whether the antioxidant melatonin could reduce the hyperoxidative status in the blood of patients with Duchenne's muscular dystrophy.

DESIGN AND METHODS

Ten patients aged 12.8±0.9 years were treated with melatonin (60mg at 21:00h plus 10mg at 09:00h) for 9 months, and erythrocyte markers of oxidative stress were determined at 3, 6, and 9 months of treatment. Healthy age- and sex-matched subjects served as controls.

RESULTS

Prior to treatment, the patients had higher glutathione disulfide/glutathione ratio and higher glutathione transferase and superoxide dismutase activities, and lower glutathione reductase activity than controls. After 3 months of melatonin treatment, the hyperoxidative status of these patients was counteracted, being reduced to the normal redox state between 3 and 9 months.

CONCLUSION

These results, together with the reduction in the inflammatory process and in muscle injury recently reported in the same patients, support the efficacy of melatonin therapy in DMD patients.

A new perspective in Oral health: potential importance and actions of melatonin receptors MT1, MT2, MT3, and RZR/ROR in the oral cavity

BACKGROUND

Melatonin is involved in many physiological processes in mammals, amongst others; it is implicated in sleep-wake regulation. It has antioxidant and anti-inflammatory properties. It also acts as an immunomodulator, stimulates bone metabolism and inhibits various tumours. Additionally an abnormal melatonin rhythm may contribute to depression and insomnia. The mechanisms of action of melatonin include the involvement of membrane receptors (MT1, MT2), cytosolic binding sites (MT3 and calmodulin), and nuclear receptors of the RZR/ROR family. Melatonin also has receptor-independent activity and can directly scavenge free radicals. The current review addresses the functions of melatonin in the oral cavity in relation to its receptors.

METHODS

An extensive search was conducted on the following scientific databases Pub Med, Science Direct, ISI Web of Knowledge and Cochrane database in order to review all pertinent literature.

RESULTS

Melatonin from the blood into the saliva may play an important role in suppressing oral diseases. It may have beneficial effects in periodontal disease, herpes and oral cancer, amongst others.

CONCLUSIONS

Melatonin contributes to protecting of oral cavity from tissue damage due to its action of different receptors. From the reviewed literature it is concluded that experimental evidence suggests that melatonin can be useful in treating several common diseases of the oral cavity. Specific studies are necessary to extend the therapeutic possibilities of melatonin to other oral diseases.

Melatonin reduces pancreatic tumor cell viability by altering mitochondrial physiology

Melatonin reduces proliferation in many different cancer cell lines. Thus, melatonin is considered a promising antitumor agent, promoting apoptosis in tumor cells while preserving viability of normal cells. Herein, we examined the effects of melatonin on the pancreatic AR42J tumor cell line. We have analyzed cytosolic-free Ca(2+) concentration ([Ca(2+) ](c) ), mitochondrial-free Ca(2+) concentration ([Ca(2+) ](m) ), mitochondrial membrane potential (Ψm), mitochondrial flavin adenine dinucleotide (FAD) oxidative state, cellular viability and caspase-3 activity. Our results show that melatonin induced transient changes in [Ca(2+) ](c) and [Ca(2+) ](m) . Melatonin also induced depolarization of Ψm and led to a reduction in the level of oxidized FAD. In addition, melatonin reduced AR42J cell viability. Finally, we found a Ca(2+) -dependent caspase-3 activation in response to melatonin. Collectively, these data support the likelihood that melatonin reduces viability of tumor AR42J cells via its action on mitochondrial activity and caspase-3 activation.

Melatonin protects against apoptotic and autophagic cell death in C2C12 murine myoblast cells

In this study, we investigated whether or not melatonin inhibits apoptotic and autophagic cell death in C2C12 murine myoblast cells. Treatment of cells with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, was shown to induce cell death, and treatment with melatonin (100 μm) significantly attenuated the occurrence of NO-induced cell death. Decreased p-Akt expression in response to NO was also arrested by melatonin. Under these conditions, p-Bad (Ser 136) expression increased with melatonin treatment prior to NO treatment. Treatment with Akt inhibitors (LY 294002, wortmannin) plus melatonin reduced p-Akt expression. Compared with NO treatment, Bcl-2 expression increased with melatonin treatment, while Bax expression was inhibited by melatonin treatment. Expression of catalase and Mn-superoxide dismutase (SOD) was elevated with melatonin treatment, whereas Cu/Zn-SOD expression decreased with melatonin, lower than NO treatment, respectively. Next, we investigated the question of whether or not melatonin may restrain autophagic cell death in C2C12 cells. Nutrient starvation induced a rise in expression of the microtubule-associated protein 1 light chain 3 (LC3)-II; however, melatonin treatment suppressed LC3-II expression by nutrient deprivation. Expression of Bcl-2, Bax, catalase, and Cu/Zn-SODs coincided with results of apoptotic cell death. Together, these results suggest that melatonin protects against apoptotic and autophagic cell death through the common pathway resulted in the increment of Bcl-2 expression and the reduction of Bax expression in C2C12 murine myoblast cells.

Melatonin has membrane receptor-independent hypnotic action on neurons: an hypothesis

Melatonin, which is known to have sleep-promoting properties, has no morpho-physiological barriers and readily enters neurons and their subcellular compartments from both the blood and cerebrospinal fluid. It has multiple receptor-dependent and receptor-independent functions. Sleep is a neuronal function, and it can no longer be postulated that one or more anatomical structures fully control sleep. Neurons require sleep for metabolically driven restorative purposes, and as a result, the process of sleep is modulated by peripheral and central mechanisms. This is an important finding because it suggests that melatonin should have intracellular sleep-inducing properties. Based on recent evidence, it is proposed that melatonin induces sleep at the neuronal level independently of its membrane receptors. Thus, the hypnotic action of melatonin and the mechanisms involving the circadian rhythms are separate neurological functions. This is contrary to the presently accepted view.

A protective effect of melatonin on intestinal permeability is induced by diclofenac via regulation of mitochondrial function in mice

AIM

This study investigated the effect of intragastrically administered melatonin on intestinal mucosal permeability induced by diclofenac in mice.

METHODS

Intestinal mucosal permeability was induced in mice by intragastric administration of diclofenac (2.5 mg/kg). Melatonin was given intragastrically (10 mg/kg) once per day for 3 d after diclofenac administration. The small intestine was examined macroscopically and microscopically for pathologic injury to the intestinal mucosa. Intestinal mucosal permeability was evaluated by Evans blue and FITC-dextran methods. Mitochondrial functional parameters, including mitochondrial membrane potential, mitochondrial ATPase and succinate dehydrogenase (SDH) activity, were assessed. The malondialdehyde (MDA) and myeloperoxidase (MPO) levels were determined from small intestinal mucosal homogenates.

RESULTS

As compared with control mice, the permeability, pathologic score, MDA and MPO levels and ulceration of the intestinal mucosa were increased significantly by diclofenac treatment, and a broadened junctional complex and enlarged intercellular space were observed by transmission electron microscopy (TEM). Melatonin treatment significantly reduced the intestinal mucosal permeability, pathologic score, MDA, and MPO levels and ulceration of the intestinal mucosa. By TEM, the small intestine villus morphology and intercellular spaces were nearly normal in melatonin-treated mice. At the level of the mitochondria, melatonin treatment significantly restored the activities of ATPase and SDH.

CONCLUSION

The intestinal damage and increased intestinal permeability induced by diclofenac in mice was limited by melatonin; moreover, melatonin preserved several aspects of mitochondrial function.

Melatonin treatment improves blood pressure, lipid profile, and parameters of oxidative stress in patients with metabolic syndrome

Experimental studies have proven that melatonin has many beneficial pleiotropic actions. The aim of this study was to assess melatonin efficacy in patients with metabolic syndrome (MS). The study included 33 healthy volunteers (who were not treated with melatonin) and 30 patients with MS, who did not respond to 3-month lifestyle modification. Patients with MS were treated with melatonin (5 mg/day, 2 hr before bedtime) for 2 months. The following parameters were studied: systolic and diastolic blood pressure (SBP, DBP), levels of glucose, serum lipids, C-reactive protein, fibrinogen, activities of antioxidative enzymes: catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), thiobarbituric acid reactive substrates (TBARS). After 2-month therapy in comparison with baseline, the following significant changes were measured: systolic blood pressure (132.8±9.8 versus 120.5±11.0 mmHg, P<0.001), DBP (81.7±8.8 versus 75±7.4 mmHg, P<0.01), low-density lipoprotein cholesterol (LDL-C) (149.7±26.4 versus 139.9±30.2 mg/dL, P<0.05), TBARS (0.5±0.2 versus 0.4±0.1 μm/gHb, P<0.01), and CAT (245.9±46.9 versus 276.8±39.4 U/gHb). Melatonin administered for 2 months significantly improved antioxidative defense (increase in CAT activity, decrease in TBARS level) and lipid profile (decrease in LDL-C), and lowered blood pressure. We conclude that melatonin therapy may be of benefit for patients with MS, particularly with arterial hypertension. Further studies with higher doses of melatonin or prolonged supplementation are awaited.

Melatonin ameliorates ischemic-like injury-evoked nitrosative stress: Involvement of HtrA2/PED pathways in endothelial cells

Peroxynitrite contributes to diverse cellular stresses in the pathogenesis of ischemic complications. Here, we investigate the downstream effector signaling elements of nitrosative stress which regulate ischemia-like cell death in endothelial cells and protective effect of melatonin. When the mitochondrial membrane potential (ΔΨm) of oxygen-glucose deprivation (OGD)-treated cells was assessed using the fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol -carbocyanine iodide, we observed spontaneous changes in peroxynitrite formation. Concomitantly, western blot and confocal microscopy analyses indicated that prolonged OGD exposure initiates the release of mitochondrial HtrA2 and dramatically decreases phosphoprotein enriched in astrocytes (PED or PEA-15) protein levels. Consistently, cultured endothelial cells treated with peroxynitrite (1-50 μm) exhibited a concentration-dependent release of mitochondrial HtrA2 and concomitant PED degradation in vitro. Notably, HtrA2 activation coincided with increased nitrotyrosine immunoreactivity in microvessels of rats following microsphere embolism. Additionally, the protective effect of PED overexpression in OGD-induced apoptosis was abolished by transfection with the PED(S104A/S116A) mutant. Furthermore, the effect of melatonin, an potential antioxidant, on endothelial apoptotic cascade was examined in OGD-evoked nitrosative stress. Our data showed that the application of melatonin provided significant protection against OGD-induced peroxynitrite formation and mitochondrial HtrA2 release, accompanied with a decrease in degradation PED and x-linked inhibitor of apoptosis protein, which is associated with activation of the caspase cascade. Taken together, the protective effect of melatonin is likely mediated, in part, by inhibition of peroxynitrate-mediated nitrosative stress, which in turn relieves imbalance of mitochondrial HtrA2-PED signaling and endothelial cell death.

Melatonin protects ram spermatozoa from cryopreservation injuries in a dose-dependent manner

Cryopreservation harms spermatozoa at different levels and thus impairs their fertilizing ability. The role of melatonin in protecting spermatozoa from different kind injuries has been widely reported. Thus, this study tested whether the addition of melatonin to ram semen freezing extender could exert a protective effect and ameliorate postthawing sperm function. Melatonin was added to recommended ram extender to yield five different final concentrations: 0.001, 0.01, 0.1, 1, and 10 mm. A control group without melatonin supplementation was included. Spermatozoa viability, motility parameters, and intracellular ATP concentrations were evaluated both before and after cryopreservation, while DNA integrity and in vitro fertilizing ability were evaluated only after thawing. Obtained results showed that the concentration of 1 mm melatonin led to higher viability rates, higher percentages of total motile and progressive motile spermatozoa, higher percentages of spermatozoa with average rapid and medium velocity, higher intracellular ATP concentrations, and higher DNA integrity among semen frozen in control and melatonin-supplemented extenders (P<0.05). In addition, results obtained after the IVF test showed that at 1 mm concentration, melatonin led to a faster first embryonic division and to higher total cleavage rates compared to the other experimental groups (P<0.05). No difference in embryo output was observed among the six experimental groups. In conclusion, the addition of melatonin to ram semen freezing extender protected spermatozoa during cryopreservation in a dose-dependent manner. These results are likely to be mediated by its well-known antioxidant properties, even if a direct action of the indolamine cannot be ruled out.

Human amniotic epithelial cells express melatonin receptor MT1, but not melatonin receptor MT2: a new perspective to neuroprotection

Recent studies have demonstrated that the human placenta is a novel source of adult stem cells. We have provided laboratory evidence that transplantation of these human placenta-derived cells in vitro and in vivo stroke models promotes functional recovery. However, the mechanisms underlying these observed therapeutic benefits of human placenta-derived cells unfortunately remain poorly understood. Here, we examined the expression of two discrete types of melatonin receptors and their roles in proliferation and differentiation of cultured human amniotic epithelial cells (AECs). Cultured AECs express melatonin receptor type 1A (MT1), but not melatonin receptor type 1B (MT2). The proliferation of cultured AECs was increased in the melatonin-treated group in a dose-dependent manner, and the viability of cultured AECs could be further enhanced by melatonin. Moreover, the viability of AECs significantly decreased with H(2) O(2) exposure, which was reversed by pretreatment with melatonin, resulting in increased cell survival rate and cell proliferation. Immunocytochemically, administration of melatonin significantly suppressed nestin proliferation, but enhanced TUJ1 differentiation of MT1-expressing AECs. Additional experiments incorporating antibody blocking and synergistic AEC-melatonin treatments further showed AEC therapeutic benefits via MT1 modulation. Finally, analysis of trophic factors revealed cultured AECs secreted VEGF in the presence of melatonin. These data indicate that melatonin by stimulating MT1 increased cell proliferation and survival rate while enhancing neuronal differentiation of cultured AECs, which together with VEGF upregulation, rendered neuroprotection against experimental in vitro models of ischemic and oxidative stress injury.

Cadmium-Induced Disruption in 24-h Expression of Clock and Redox Enzyme Genes in Rat Medial Basal Hypothalamus: Prevention by Melatonin

In a previous study we reported that a low daily p.o. dose of cadmium (Cd) disrupted the circadian expression of clock and redox enzyme genes in rat medial basal hypothalamus (MBH). To assess whether melatonin could counteract Cd activity, male Wistar rats (45 days of age) received CdCl₂ (5 ppm) and melatonin (3 μg/mL) or vehicle (0.015% ethanol) in drinking water. Groups of animals receiving melatonin or vehicle alone were also included. After 1 month, MBH mRNA levels were measured by real-time PCR analysis at six time intervals in a 24-h cycle. In control MBH Bmal1 expression peaked at early scotophase, Per1 expression at late afternoon, and Per2 and Cry2 expression at mid-scotophase, whereas neither Clock nor Cry1 expression showed significant 24-h variations. This pattern was significantly disrupted (Clock, Bmal1) or changed in phase (Per1, Per2, Cry2) by CdCl₂ while melatonin counteracted the changes brought about by Cd on Per1 expression only. In animals receiving melatonin alone the 24-h pattern of MBH Per2 and Cry2 expression was disrupted. CdCl₂ disrupted the 24-h rhythmicity of Cu/Zn- and Mn-superoxide dismutase (SOD), nitric oxide synthase (NOS)-1, NOS-2, heme oxygenase (HO)-1, and HO-2 gene expression, most of the effects being counteracted by melatonin. In particular, the co-administration of melatonin and CdCl₂ increased Cu/Zn-SOD gene expression and decreased that of glutathione peroxidase (GPx), glutathione reductase (GSR), and HO-2. In animals receiving melatonin alone, significant increases in mean Cu/Zn and Mn-SOD gene expression, and decreases in that of GPx, GSR, NOS-1, NOS-2, HO-1, and HO-2, were found. The results indicate that the interfering effect of melatonin on the activity of a low dose of CdCl₂ on MBH clock and redox enzyme genes is mainly exerted at the level of redox enzyme gene expression.

Melatonin protects human cells from clustered DNA damages, killing and acquisition of soft agar growth induced by X-rays or 970 MeV/n Fe ions

PURPOSE

We tested the ability of melatonin (N-acetyl-5 methoxytryptamine), a highly effective radical scavenger and human hormone, to protect DNA in solution and in human cells against induction of complex DNA clusters and biological damage induced by low or high linear energy transfer radiation (100 kVp X-rays, 970 MeV/nucleon Fe ions).

MATERIALS AND METHODS

Plasmid DNA in solution was treated with increasing concentrations of melatonin (0.0-3.5 mM) and were irradiated with X-rays. Human cells (28SC monocytes) were also irradiated with X-rays and Fe ions with and without 2 mM melatonin. Agarose plugs containing genomic DNA were subjected to Contour Clamped Homogeneous Electrophoretic Field (CHEF) followed by imaging and clustered DNA damages were measured by using Number Average length analysis. Transformation experiments on human primary fibroblast cells using soft agar colony assay were carried out which were irradiated with Fe ions with or without 2 mM melatonin.

RESULTS

In plasmid DNA in solution, melatonin reduced the induction of single- and double-strand breaks. Pretreatment of human 28SC cells for 24 h before irradiation with 2 mM melatonin reduced the level of X-ray induced double-strand breaks by ∼50%, of abasic clustered damages about 40%, and of Fe ion-induced double-strand breaks (41% reduction) and abasic clusters (34% reduction). It decreased transformation to soft agar growth of human primary cells by a factor of 10, but reduced killing by Fe ions only by 20-40%.

CONCLUSION

Melatonin's effective reduction of radiation-induced critical DNA damages, cell killing, and striking decrease of transformation suggest that it is an excellent candidate as a countermeasure against radiation exposure, including radiation exposure to astronaut crews in space travel.

Melatonin modulates neuroinflammation and oxidative stress in experimental diabetic neuropathy: effects on NF-κB and Nrf2 cascades

Melatonin exhibits an array of biological activities, including antioxidant and anti-inflammatory actions. Diabetic neuropathy is one of the complications of diabetes with a prevalence rate of 50-60%. We have previously reported the protective effect of melatonin in experimental diabetic neuropathy. In this study, we investigated the role of nuclear factor-kappa B (NF-κB) and nuclear erythroid 2-related factor 2 (Nrf2) in melatonin-mediated protection against streptozotocin-induced diabetic neuropathy. Melatonin at doses of 3 and 10 mg/kg was administered daily in seventh and eighth week after diabetes induction. Motor nerve conduction velocity and nerve blood flow were improved in melatonin-treated animals. Melatonin also reduced the elevated expression of NF-κB, IκB-α, and phosphorylated IκB-α. Further, melatonin treatment also reduced the elevated levels of proinflammatory cytokines (TNF-α and IL-6), iNOS and COX-2 in sciatic nerves of animals. The capacity of melatonin to modulate Nrf2 pathway was associated with increased heme oxygenase-1 (HO-1) expression, which strengthens antioxidant defense. This fact was also established by decreased DNA fragmentation (because inhibition of excessive oxidant-induced DNA damage) in the sciatic nerve of melatonin-treated animals. The results of this study suggest that melatonin modulates neuroinflammation by decreasing NF-κB activation cascade and oxidative stress by increasing Nrf2 expression, which might be responsible at least in part, for its neuroprotective effect in diabetic neuropathy.

Melatonin or silymarin reduces maneb- and paraquat-induced Parkinson's disease phenotype in the mouse

Oxidative stress is reported as one of the most widely accepted mechanisms of maneb (MB)- and paraquat (PQ)-induced nigrostriatal dopaminergic neurodegeneration leading to the Parkinson's disease (PD) phenotype. The study investigated the effects of silymarin, an antioxidant of plant origin, and melatonin, an indoleamine produced in all species, in MB- and PQ-induced mouse model of PD. The mice were treated intraperitoneally daily with silymarin (40mg/kg) or melatonin (30mg/kg) along with respective controls for 9wk. Subsets of these animals were also treated with MB (30mg/kg) and PQ (10mg/kg), twice a week, for 9wk, 2hr after silymarin/melatonin treatment. Locomotor activities along with striatal dopamine content, tyrosine hydroxylase (TH) immunoreactivity, number of degenerating neurons, lipid peroxidation and nitrite content were estimated. Additionally, mRNA expression of vesicular monoamine transporter, cytochrome P-450 2E1 (CYP2E1), and glutathione-S-transferase A4-4 (GSTA4-4), catalytic activities of CYP2E1 and GSTA4-4 and protein expressions of unphosphorylated and phosphorylated p53 (p53 and P-p53), Bax and caspase 9 were measured in control and MB- and PQ-treated mice with either silymarin or melatonin treatments. Silymarin/melatonin significantly offset MB- and PQ-mediated reductions in locomotor activities, dopamine content, TH immunoreactivity, VMAT 2 mRNA expression and the expression of p53 protein. Silymarin/melatonin attenuated the increases in lipid peroxidation, number of degenerating neurons, nitrite content, mRNA expressions of cytochrome P-450 2E1 (CYP2E1) and GSTA4-4, catalytic activities of CYP2E1 and GST and P-p53, Bax and caspase 9 protein expressions. The results demonstrate that silymarin and melatonin offer nigrostriatal dopaminergic neuroprotection against MB- and PQ-induced PD by the modulation of oxidative stress and apoptotic machinery.

Melatonin protects steatotic and nonsteatotic liver grafts against cold ischemia and reperfusion injury

Chronic organ-donor shortage has required the acceptance of steatotic livers for transplantation purposes despite the higher risk of graft dysfunction or nonfunction associated with the cold ischemia-reperfusion injury. This study evaluated the use of melatonin as an additive to Institute Georges Lopez (IGL-1) solution for protecting nonsteatotic and steatotic liver grafts against cold ischemia-reperfusion injury. In the current investigation, we used an ex vivo isolated perfused rat liver model. Steatotic and nonsteatotic livers were preserved for 24 hr (4°C) in University of Wisconsin or IGL-1 solutions with or without melatonin, as well as in University of Wisconsin solution alone. Thereafter, livers were subjected to 2-hr reperfusion (37°C). We assessed hepatic injury (transaminases) and function [bile production and sulfobromophthalein (BSP) clearance, vascular resistance], as well as other factors potentially implicated in the high vulnerability of steatotic livers against ischemia-reperfusion injury (oxidative stress and related inflammatory mediators including nitric oxide and cytokines). We also evaluated well-known cytoprotective factors as hemeoxygenase 1 (HO-1). Fatty livers preserved in IGL-1 solution enriched with melatonin showed lower transaminase levels and higher bile production and BSP clearance when compared to those obtained for livers maintained in IGL-1 solution alone. A significant diminution of vascular resistance was also observed when melatonin was added to the IGL-1 solution. The melatonin benefits correlated with the generation of nitric oxide (through constitutive e-NOS activation) and the prevention of oxidative stress and inflammatory cytokine release including tumor necrosis factor and adiponectin, respectively. The addition of melatonin to IGL-1 solution improved nonsteatotic and steatotic liver graft preservation, limiting their risk against cold ischemia-reperfusion injury.

Melatonin synergistically increases resveratrol-induced heme oxygenase-1 expression through the inhibition of ubiquitin-dependent proteasome pathway: a possible role in neuroprotection

Melatonin is an indoleamine secreted by the pineal gland as well as a plant-derived product, and resveratrol (RSV) is a naturally occurring polyphenol synthesized by a variety of plant species; both molecules act as a neuroprotector and antioxidant. Recent studies have demonstrated that RSV reduced the incidence of Alzheimer's disease and stroke, while melatonin supplementation was found to reduce the progression of the cognitive impairment in AD. The heme oxygenase-1 (HO-1) is an inducible and redox-regulated enzyme that provides tissue-specific antioxidant effects. We assessed whether the co-administration of melatonin and RSV shows synergistic effects in terms of their neuroprotective properties through HO-1. RSV significantly increased the expression levels of HO-1 protein in a concentration-dependent manner both in primary cortical neurons and in astrocytes, while melatonin per se did not. Melatonin + RSV showed a synergistic increase in the expression levels of HO-1 protein but not in the HO-1 mRNA level compared to either melatonin or RSV alone, which is mediated by the activation of PI3K-Akt pathway. Treatment of melatonin + RSV significantly attenuated the neurotoxicity induced by H(2) O(2) in primary cortical neurons and also in organotypic hippocampal slice culture. The blockade of HO-1 induction by shRNA attenuated HO-1 induction by melatonin + RSV and hindered the neuroprotective effects against oxidative stress induced by H(2) O(2) . The treatment of MG132 + RSV mimicked the effects of melatonin + RSV, and melatonin + RSV inhibited ubiquitination of HO-1. These data suggest that melatonin potentiates the neuroprotective effect of RSV against oxidative injury, by enhancing HO-1 induction through inhibiting ubiquitination-dependent proteasome pathway, which may provide an effective means to treat neurodegenerative disorders.

Beneficial effects of melatonin on obesity and lipid profile in young Zucker diabetic fatty rats

The study objective was to investigate the effects of melatonin on obesity and obesity-associated systolic hypertension and dyslipidemia in young male Zucker diabetic fatty (ZDF) rats, an experimental model of the metabolic syndrome. ZDF rats (n=30) and lean littermates (ZL) (n=30) were used. At 6wk of age, both lean and fatty animals were subdivided into three groups (n=10): naive (N), vehicle-treated (V), and melatonin-treated (M) (10mg/kg/day) for 6wk. Vehicle and melatonin were added to the drinking water. Melatonin reduced mean weight gain (51±2/100g BW) versus N-ZDF group (58±3, P<0.05) without food intake differences. M-ZDF rats showed an apparent reduction in systolic hypertension that proved not to be statistically significant, and a significant improvement in dyslipidemia, with a reduction in hypertriglyceridemia from 580±40 to 420.6±40.9mg/dL (P<0.01). Melatonin raised high-density-lipoprotein (HDL) cholesterol in ZDF (from 81.6±4.9 to 103.1±4.5mg/dL, P<0.01) and ZL rats (from 62.8±4.8 to 73.5±4.8mg/dL, P<0.05) and significantly reduced low-density-lipoprotein (LDL) cholesterol in ZDF rats from 5.20±0.4 to 4.14±0.3 mg/dL (P<0.05) but had no effect on total cholesterol levels. To our knowledge, this is the first evidence of a positive effect of melatonin on overweight and lipid pattern of obese Zucker diabetic rats, supporting the proposition that melatonin administration may ameliorate overweight and lipid metabolism in humans. Because these benefits occurred in youth, before advanced metabolic and vascular complications, melatonin might help to prevent cardiovascular disease associated with obesity and dyslipidemia.

Melatonin in septic shock: some recent concepts

Melatonin is a versatile molecule, synthesized not only in the pineal gland, but also in many other organs. Melatonin plays an important physiologic role in sleep and circadian rhythm regulation, immunoregulation, antioxidant and mitochondrial-protective functions, reproductive control, and regulation of mood. Melatonin has also been reported as effective in combating various bacterial and viral infections. Melatonin is an effective anti-inflammatory agent in various animal models of inflammation and sepsis, and its anti-inflammatory action has been attributed to inhibition of nitric oxide synthase with consequent reduction of peroxynitrite formation, to the stimulation of various antioxidant enzymes thus contributing to enhance the antioxidant defense, and to protective effects on mitochondrial function and in preventing apoptosis. In a number of animal models of septic shock, as well as in patients with septic disease, melatonin reportedly exerts beneficial effects to arrest cellular damage and multiorgan failure. The significance of these actions in septic shock and its potential usefulness in the treatment of multiorgan failure are discussed.

Matrix metalloproteinases in health and disease: regulation by melatonin

Matrix metalloproteinases (MMPs) are part of a superfamily of metal-requiring proteases that play important roles in tissue remodeling by breaking down proteins in the extracellular matrix that provides structural support for cells. The intricate balance in protease/anti-protease stoichiometry is a contributing factor in a number of diseases. Melatonin possesses multifunctional bioactivities including antioxidative, anti-inflammatory, endocrinologic and behavioral effects. As melatonin affects the redox status of tissues, the association of reactive oxygen species (ROS) with tissue injury under different circumstances may be mitigated by melatonin. Redox signaling is expanding into all areas of basic and clinical sciences, and this timely review focuses on the topic of regulation of MMP activities by melatonin. This is a rapidly growing field. Accumulating evidence indicates that oxidative stress plays an important role in regulating the activities of MMPs that are involved in various cellular processes such as cellular proliferation, angiogenesis, apoptosis, invasion and metastasis. This review offers sections on MMPs, melatonin, major physiological and pathophysiological conditions in the context to MMPs, followed by redox signaling mechanisms that are known to influence the cellular processes. Finally, we discuss the emerging molecular mechanisms relevant to regulatory actions of melatonin on the activities of MMPs. The possibility that melatonin might have therapeutic significance via regulation of MMPs may be a novel approach in the treatment of some diseases.

Chronic treatment with melatonin stimulates dendrite maturation and complexity in adult hippocampal neurogenesis of mice

In the course of adult hippocampal neurogenesis, the postmitotic maturation and survival phase is associated with dendrite maturation. Melatonin modulates the survival of new neurons with relative specificity. During this phase, the new neurons express microtubule-associated protein doublecortin (DCX). Here, we show that the entire population of cells expressing DCX is increased after 14 days of treatment with melatonin. As melatonin also affects microtubule polymerization which is important for neuritogenesis and dendritogenesis, we studied the consequences of chronic melatonin administration on dendrite maturation of DCX-positive cells. Treatment with melatonin increased the number of DCX-positive immature neurons with more complex dendrites. Sholl analysis revealed that melatonin treatment lead to greater complexity of the dendritic tree. In addition, melatonin increased the total volume of the granular cell layer. Besides its survival-promoting effect, melatonin thus also increases dendritic maturation in adult neurogenesis. This might open the opportunity of using melatonin as an adjuvant in attempts to extrinsically stimulate adult hippocampal neurogenesis in neuropsychiatric disease, dementia or cognitive ageing.

Update on the use of melatonin in pediatrics

Melatonin, an endogenously produced indoleamine, is a highly effective antioxidant, free radical scavenger, and a primary circadian regulator. Melatonin has important antioxidant properties owing to direct and indirect effects. It directly scavenges reactive oxygen and reactive nitrogen species, prevents molecular oxidation, improves mitochondrial physiology, and restores glutathione homeostasis. Its indirect antioxidant effects stem from its ability to stimulate the activities of the enzymes involved in the glutathione cycling and production. Melatonin, by reducing free radical damage, may be an effective protective agent for the fetus as it is in adults. Several clinical studies on melatonin have shown that it reduces oxidative stress in human newborns with sepsis, hypoxic distress, or other conditions, where there is excessive free radical generation. A role of melatonin in infant development has also been suggested. Pineal dysfunction may be associated with deleterious outcomes in infants and may contribute to an increased prevalence of sudden infant death syndrome. Delayed melatonin production is evident in infants who had experienced an apparent life-threatening event. Melatonin has been used as a pharmacologic treatment for insomnias associated with shift work, jet lag, and delayed sleep onset in adults for decades. In children as well, melatonin has value as a sleep-promoting agent. Evidence suggests that melatonin has utility as an analgesic agent presumably related to its ability to release β-endorphin. The data support the notion that melatonin, or one of its analogs, might find use as an anesthetic agent in children.

Melatonin protects against taurolithocholic-induced oxidative stress in rat liver

Cholestasis, encountered in a variety of clinical disorders, is characterized by intracellular accumulation of toxic bile acids in the liver. Furthermore, oxidative stress plays an important role in the pathogenesis of bile acids. Taurolithocholic acid (TLC) was revealed in previous studies as the most pro-oxidative bile acid. Melatonin, a well-known antioxidant, is a safe and widely used therapeutic agent. Herein, we investigated the hepatoprotective role of melatonin on lipid and protein oxidation induced by TLC alone and in combination with FeCl(3) and ascorbic acid in rat liver homogenates and hepatic membranes. The lipid peroxidation products, malondialdehyde and 4-hydroxyalkenals (MDA + 4-HDA), and carbonyl levels were quantified as indices of oxidative damage to hepatic lipids and proteins, respectively. In the current study, the rise in MDA + 4-HDA levels induced by TLC was inhibited by melatonin in a concentration-dependent manner in both liver homogenates and in hepatic membranes. Melatonin also had protective effects against structural damage to proteins induced by TLC in membranes. These results suggest that the indoleamine melatonin may potentially act as a protective agent in the therapy of those diseases that involve bile acid toxicity.

Melatonin and vitamin C increase umbilical blood flow via nitric oxide-dependent mechanisms

Inadequate umbilical blood flow leads to intrauterine growth restriction, a major killer in perinatal medicine today. Nitric oxide (NO) is important in the maintenance of umbilical blood flow, and antioxidants increase NO bioavailability. What remains unknown is whether antioxidants can increase umbilical blood flow. Melatonin participates in circadian, seasonal, and reproductive physiology, but has also been reported to act as a potent endogenous antioxidant. We tested the hypothesis that treatment during pregnancy with melatonin increases umbilical blood flow via NO-dependent mechanisms. This was tested in pregnant sheep by investigating in vivo the effects on continuous measurement of umbilical blood flow of melatonin before and after NO blockade with a NO clamp. These effects of melatonin were compared with those of the traditional antioxidant, vitamin C. Under anesthesia, 12 pregnant sheep and their fetuses (0.8 of gestation) were fitted with catheters and a Transonic probe around an umbilical artery, inside the fetal abdomen. Following 5 days of recovery, cardiovascular variables were recorded during fetal i.v. treatment with either melatonin (n=6, 0.5±0.1 μg/kg/min) or vitamin C (n=6, 8.9±0.4 mg/kg/min) before and after fetal NO blockade with the NO clamp. Fetal treatment with melatonin or vitamin C increased umbilical blood flow, independent of changes in fetal arterial blood pressure. Fetal NO blockade prevented the increase in umbilical blood flow induced by melatonin or vitamin C. Antioxidant treatment could be a useful clinical tool to increase or maintain umbilical blood flow in complicated pregnancy.

Proteomic identification of proteins differentially expressed by melatonin in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion (I-R) injury induces hepatic dysfunction or failure. Melatonin is a potent free radical scavenger and a strong antioxidant. Although many studies have demonstrated the protective effect of melatonin in hepatic injury, the molecular mechanisms of this protection are unclear. We identified specific proteins that are differentially expressed by melatonin treatment in hepatic I-R injury. Adult mice were subjected to 1 hr of ischemia and 3 hr of reperfusion. Animals were treated with vehicle or melatonin (10 mg/kg, i.p.) 15 min prior to ischemia and just before reperfusion. Serum aspartate aminotransferase and alanine aminotransferase levels were higher in I-R group than in sham-operated group, and these increases were reduced by melatonin treatment. Proteins that were differentially expressed following melatonin treatment during hepatic I-R injury were detected using two-dimensional gel electrophoresis. Hepatic I-R injury induced down-regulation of glyoxalase I, glutaredoxin-3, spermidine synthase, proteasome subunit beta type-4, and dynamin like protein-1 (DLP-1). However, melatonin prevented the reductions in these proteins induced by I-R injury. Among the identified proteins, we focused on DLP-1, which is essential for the maintenance of mitochondrial and endoplasmic reticulum morphology. Western blot analysis confirmed that melatonin prevents the hepatic I-R injury-induced decrease in DLP-1. These results suggest that melatonin protects hepatic cells against hepatic I-R injury and that its protective effects involve the regulation of specific proteins.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Melatonin reduces hyperalgesia associated with inflammation

The perception of pain is altered by inflammatory processes. Anti-inflammatory drugs block this by raising the pain threshold and by reducing the inflammatory process. Melatonin is claimed to have anti-inflammatory activity in animal models of acute and chronic inflammation. However, little is known whether melatonin can reverse the hyperalgesia that is secondary to the inflammation. This study assessed the effect of melatonin on in a well-established model of hyperalgesia associated with inflammation in rats. Peroxynitrite, as generated by the interaction between superoxide anion radical exogenously supplied (O(2)(˙-) ) and endogenous nitric oxide (NO), led to the development of hyperalgesia. This subplantar injection of O(2)(˙-) into the right hindpaw evoked potent thermal hyperalgesia measured by changes in withdrawal latency. Melatonin (25-100 mg/kg, given ip 30 min prior to O(2)(˙-) ) dose dependently attenuated the hyperalgesic responses to O(2)(˙-) . Moreover, melatonin (100 mg/kg) significantly improved tissue damage and inflammation, blocked protein nitration affecting cyclooxygenase-2 and inducible nitric oxide synthase expression in paw tissue. To investigate the antinociceptive activity of melatonin and characterize the underlying mechanisms involved in this action, mitogen-activated protein kinase and NF-κB pathways were explored. Moreover, antihyperalgesic effect of melatonin derived partly from the inhibition of superoxide-driven PARP activation. These results suggest that melatonin has ameliorative potential in attenuating the hyperalgesia associated with inflammation.

Melatonin attenuates methotrexate-induced oxidative stress and renal damage in rats

Nephrotoxicity is an adverse side effect of methotrexate (MTX) chemotherapy. The present study verifies whether melatonin, an endogenous antioxidant prevents MTX-induced renal damage. Adult rats were administered 7 mg/kg body weight MTX intraperitoneally for 3 days. In the melatonin pretreated rats, 40 mg/ kg body weight melatonin was administered daily intraperitoneally 1 h before the administration of MTX. The rats were killed 12 h after the final dose of MTX/vehicle. The kidneys were used for light microscopic and biochemical studies. The markers of oxidative stress were measured along with the activities of the antioxidant enzymes and myeloperoxidase activity in the kidney homogenates. Pretreatment with melatonin reduced MTX induced renal damage both histologically and biochemically as revealed by normal plasma creatinine levels. Melatonin pretreatment reduced MTX induced oxidative stress, alteration in the activity of antioxidant enzymes as well as elevation in myeloperoxidase activity. The results suggest that melatonin has the potential to reduce MTX induced oxidative stress, neutrophil infiltration as well as renal damage. As melatonin is an endogenous antioxidant and is non-toxic even in high doses it is suggested that melatonin may be beneficial in minimizing MTX induced renal damage in humans.

Melatonin induces pro-apoptotic signaling pathway in human pancreatic carcinoma cells (PANC-1)

Pancreatic cancer is a highly lethal disease with a poor prognosis for long-term survival rate at all stages of invasiveness. It responds poorly to radio- and chemotherapy because the tumor cells are resistant to apoptosis. Melatonin has been reported to inhibit pancreatic cancer growth in experimental studies in animals but the effect of melatonin on cultured human pancreatic carcinoma cells has not been tested. Moreover, we have recently shown that melatonin stimulates production of two major anti-apoptotic heat shock proteins, HSP27 and HSP 90, in pancreatic carcinoma cells. This study investigated the changes in intrinsic pathway of apoptosis at the mitochondrial level and cascade of caspases in human pancreatic carcinoma cells (PANC-1) cells subjected to melatonin and/or luzindole. Melatonin (10⁻⁸ -10⁻¹² m), the nonselective melatonin receptor antagonist, luzindole (10⁻⁸ -10⁻¹² m) or a combination of both agents were added to PANC-1 cell cultures. Cells were harvested, and the cytoplasmic proteins were isolated after 24 and 48 hr of incubation and analyzed employing co-immunoprecipitation and western blot. Administration of melatonin to the PANC-1 cells resulted in the stimulation of Bcl-2/Bax and caspase-9 proteins levels. The strongest signal of these pro-apoptotic factors was observed at the low concentration (10⁻¹² m) of melatonin. Pretreatment with luzindole alone and prior to the addition of melatonin reversed the stimulatory effect of this indoloamine on Bcl-2/Bax and caspase-9 proteins expression in PANC-1 cells. This is the first study to demonstrate a pro-apoptotic effect of low (physiological) concentration of melatonin on the pancreatic carcinoma cells. In conclusion, melatonin induced pro-apoptotic pathways in human pancreatic carcinoma, probably by interaction with the Mel-1 A/B receptors.

Melatonin increases proliferation of cultured neural stem cells obtained from adult mouse subventricular zone

Melatonin, a circadian rhythm-promoting molecule secreted mainly by the pineal gland, has a variety of biological functions and neuroprotective effects including control of sleep-wake cycle, seasonal reproduction, and body temperature as well as preventing neuronal cell death induced by neurotoxic substances. Melatonin also modulates neural stem cell (NSC) function including proliferation and differentiation in embryonic brain tissue. However, the involvement of melatonin in adult neurogenesis is still not clear. Here, we report that precursor cells from adult mouse subventricular zone (SVZ) of the lateral ventricle, the main neurogenic area of the adult brain, express melatonin receptors. In addition, precursor cells derived from this area treated with melatonin exhibited increased proliferative activity. However, when cells were treated with luzindole, a competitive inhibitor of melatonin receptors, or pertussis toxin, an uncoupler of Gi from adenylate cyclase, melatonin-induced proliferation was reduced. Under these conditions, melatonin induced the differentiation of precursor cells to neuronal cells without an upregulation of the number of glia cells. Because stem cell replacement is thought to play an important therapeutic role in neurodegenerative diseases, melatonin might be beneficial for stimulating endogenous neural stem cells.

Lowering intercellular melatonin levels by transgenic analysis of indoleamine 2,3-dioxygenase from rice in tomato plants

Melatonin exists in numerous living organisms including vertebrates, insects, fungi, bacteria, and plants. Extensive studies have been conducted on the physiological roles of melatonin in various plant species. In plants, melatonin seems to act in antioxidant protection, as a growth promoter, and in photoperiodism. However, the mechanisms by which melatonin carries out these roles remain unclear. We manipulated the endogenous melatonin content in tomato plants by modifying the metabolic enzyme indoleamine 2,3-dioxygenase (IDO). The OsIDO gene was isolated from rice (Oryza sativa) and characterized using 3-D homology modeling and reverse genetic approaches. The amino acid sequence of OsIDO showed high homology to the Ustilago maydis IDO. The 3-D model structure of OsIDO is composed of a small and a large domain. Transgenic tomato plants constitutively expressing the OsIDO gene exhibited a decrease in their melatonin content. Moreover, the number of lateral leaflets decreased in transgenic plants. Protein extracts taken from these plants showed activity degradation, demonstrating the function of OsIDO. These results suggest the involvement of IDO in plant melatonin metabolism and a possible role in plant leaf development.

Melatonin induces calcium release from CCK-8- and thapsigargin-sensitive cytosolic stores in pancreatic AR42J cells

Melatonin is produced following circadian rhythm with high levels being released at night and has been implicated in the regulation of physiological processes in major tissues, including the pancreas. The aim of our study was to examine the effects of melatonin on intracellular free Ca(2+) concentration ([Ca(2+) ](c)) in AR42J pancreatic cells. Our results show that stimulation of cells with 1 nm cholecystokinin (CCK)-8 led to a transient increase in [Ca(2+) ](c) followed by a decrease towards a value close to the prestimulation level. Melatonin (at the concentrations 1, 10, 100 μm and 1 mm) induced changes in [Ca(2+) ](c) that consisted of single or short lasting spikes in the form of oscillations or slow transient increases followed by a slow reduction towards a value close to the resting level. Depletion of intracellular Ca(2+) stores by stimulation of cells with 1 nm CCK-8 or 1 μm thapsigargin (Tps) blocked Ca(2+) responses evoked by melatonin in the majority of cells. Conversely, prior stimulation of cells with 1 mm melatonin in the absence of extracellular Ca(2+) inhibited Ca(2+) mobilization in response to a secondary application of CCK-8 or Tps. In summary, our results show that melatonin releases Ca(2+) from intracellular stores and can therefore modulate the responses of the pancreas to CCK-8. The source for Ca(2+) mobilization most probably is the endoplasmic reticulum. These data raise the possibility that melatonin also involves Ca(2+) signalling, in addition to other intracellular messengers, to modulate cellular function.

Melatonin enhances antioxidant action of alpha-tocopherol and ascorbate against NADPH- and iron-dependent lipid peroxidation in human placental mitochondria

Human placental mitochondria might be a significant source of NADPH- and iron-dependent production of reactive oxygen species (ROS). Preeclampsia is believed to be a consequence of overproduction of ROS in human placenta. The experimental results presented here show that melatonin inhibits NADPH- and iron-dependent lipid peroxidation of human placental mitochondria in a concentration-dependent manner. At 1.5 mm concentration, melatonin suppressed this process nearly completely. Melatonin does not influence significantly the iron oxidation at this conditions, indicating that free radical scavenging rather than metal-chelating phenomenon is the basis of its antioxidant action. The fact of inhibition of lipid peroxidation by melatonin at conditions excluding iron participation also supports this hypothesis. Elucidation of the nature of common interaction among melatonin, ascorbate, and alpha-tocopherol in human placental mitochondria was the main aim of this study. In presence of 90 mum ascorbate, the inhibition of lipid peroxidation by melatonin was strong and had a feature of synergistic interaction. At presence of 30 mum ascorbate, which stimulated lipid peroxidation, melatonin caused a loss of pro-oxidant effect of ascorbate. While the interaction of melatonin with ascorbate indicated synergism, the joint action of melatonin and alpha-tocopherol was additive. When all three antioxidants were applied together, the strongest inhibition of lipid peroxidation was observed. The experimental results presented here indicated that melatonin could be considered as an effective component of antioxidant treatment of preeclampsia, allowing the use of reduced doses of vitamin C and E owing to elevated efficiency of their antioxidant activity in placenta when used in combination.

Neurotoxins: free radical mechanisms and melatonin protection

Toxins that pass through the blood-brain barrier put neurons and glia in peril. The damage inflicted is usually a consequence of the ability of these toxic agents to induce free radical generation within cells but especially at the level of the mitochondria. The elevated production of oxygen and nitrogen-based radicals and related non-radical products leads to the oxidation of essential macromolecules including lipids, proteins and DNA. The resultant damage is referred to as oxidative and nitrosative stress and, when the molecular destruction is sufficiently severe, it causes apoptosis or necrosis of neurons and glia. Loss of brain cells compromises the functions of the central nervous system expressed as motor, sensory and cognitive deficits and psychological alterations. In this survey we summarize the publications related to the following neurotoxins and the protective actions of melatonin: aminolevulinic acid, cyanide, domoic acid, kainic acid, metals, methamphetamine, polychlorinated biphenyls, rotenone, toluene and 6-hydroxydopamine. Given the potent direct free radical scavenging activities of melatonin and its metabolites, their ability to indirectly stimulate antioxidative enzymes and their efficacy in reducing electron leakage from mitochondria, it would be expected that these molecules would protect the brain from oxidative and nitrosative molecular mutilation. The studies summarized in this review indicate that this is indeed the case, an action that is obviously assisted by the fact that melatonin readily crosses the blood brain barrier.

Melatonin in traditional Mediterranean diets

Compared with other industrialized countries, the lower incidence of chronic-degenerative disorders in Mediterranean populations has been emphasized in recent decades. The health-promoting effects arising from Mediterranean dietary habits have been attributed to the large intake of plant foodstuffs rich in bioactive phytochemicals, such as melatonin. Recently, it has been suggested that melatonin present in edible plants may improve human health, by virtue of its biological activities and its good bioavailability. Plant melatonin, besides contributing to optimize the physiological functions regulated, in humans, by endogenous melatonin, may be involved in nutritional therapy to reduce the risk of cancer, cardiovascular and neurodegenerative diseases in western populations. In this view, the presence of melatonin in some Mediterranean foods and beverages adds a new element to the hypothesis of health benefits associated to Mediterranean dietary patterns, although the available data are still preliminary and incomplete.

Synergistic neuroprotective effect of combined low concentrations of galantamine and melatonin against oxidative stress in SH-SY5Y neuroblastoma cells

Melatonin is a potent free radical scavenger, antioxidant and neuroprotective drug. On the other hand, galantamine is a cholinergic drug with antioxidant and neuroprotective properties linked to inhibition of acetylcholinesterase and allosteric modulation of nicotinic receptors. This investigation evaluated a possible synergistic neuroprotective effect of subeffective concentrations of combined galantamine and melatonin. Human neuroblastoma SH-SY5Y cells were subjected to a mitochondrial oxidative stress, by blockade of mitochondrial complexes I and V with rotenone and oligomycin-A (R/O); cells were treated for 24 hr with R/O. This caused 40% of the cell to die as measured by lactate dehydrogenase (LDH) release. Cell incubation with increasing concentrations of galantamine (10-300 nm) or melatonin (0.3-10 nm) for 24 hr, followed by a 24-hr period with R/O, caused a concentration-dependent protection; maximum protection was achieved with 300 nm galantamine (56% protection) and 10 nm melatonin (50% protection). Combination of subeffective concentrations of melatonin (0.3 nm) and galantamine (30 nm) caused a synergistic and significant protection that was similar to the maximum protection afforded by effective concentrations of melatonin or galantamine alone. This protective effect was completely reversed when nicotinic and melatonin receptors were blocked respectively by mecamylamine and luzindole. The neuroprotective effect was prevented by chelerythrine, LY294002, and Sn (IV) protoporphyrin IX dichloride (SnPP), indicating the participation of the PKC/PI3K/Akt activation and induction of the antioxidant enzyme heme oxygenase-1. The synthesis of novel multitarget compounds having in a single molecule the combined neuroprotective properties of galantamine and melatonin could be a new strategy for potential therapeutic agents in neurodegenerative diseases.

Single-nucleotide polymorphisms and mRNA expression for melatonin synthesis rate-limiting enzyme in recurrent depressive disorder

Depressive disorder (DD) is characterised by disturbances in blood melatonin concentration. It is well known that melatonin is involved in the control of circadian rhythms, sleep included. The use of melatonin and its analogues has been found to be effective in depression therapy. Melatonin synthesis is a multistage process, where the last stage is catalysed by acetylserotonin methyltransferase (ASMT), the reported rate-limiting melatonin synthesis enzyme. Taking into account the significance of genetic factors in depression development, the gene for ASMT may become an interesting focus for studies in patients with recurrent DD. The goal of the study was to evaluate two single-nucleotide polymorphisms (SNPs) (rs4446909; rs5989681) of the ASMT gene, as well as mRNA expression for ASMT in recurrent DD-affected patients. We genotyped two polymorphisms in a group of 181 recurrent DD patients and in 149 control subjects. The study was performed using the polymerase chain reaction/restriction fragment length polymorphism method. The distribution of genotypes in both studied SNPs in the ASMT gene differed significantly between DD and healthy subjects. The presence of AA genotype of rs4446909 polymorphism and of GG genotype of rs5989681 polymorphism was associated with lower risk for having recurrent DD. In turn, patients with depression were characterised by reduced mRNA expression for ASMT. In addition, ASMT transcript level in both recurrent DD patients and in healthy subjects depended significantly on genotype distributions in both polymorphisms. In conclusion, our results suggest the ASMT gene as a susceptibility gene for recurrent DD.

Melatonin decreases cell proliferation and induces melanogenesis in human melanoma SK-MEL-1 cells

Melatonin is an indoleamine synthesized in the pineal gland, and after its release into the blood, it has an extensive repertoire of biological activities, including antitumoral properties. In this study, we found that melatonin reduced the growth of the human melanoma cells SK-MEL-1. The antiproliferative effect was associated with an alteration in the progression of the phases of the cell cycle and also with an increase in tyrosinase activity, the key regulatory enzyme of melanogenesis. Antagonists for melatonin membrane receptors (luzindole and 4-P-PDOT) and the general G-coupled receptor inhibitor, pertussis toxin, did not prevent the melatonin-induced cell growth arrest; this suggests a mechanism independent of G-coupled membrane receptors. In contrast, p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway seems to play a significant role in cell growth inhibition by melatonin. The indoleamine-induced phosphorylation of p38 MAPK and the effect on cell proliferation were abrogated by the specific inhibitor SB203580. Furthermore, comparative studies with known antioxidants such as N-acetyl-l-cysteine and trolox indicate that the growth of SK-MEL-1 cells is highly sensitive to antioxidants.

Melatonin as a therapeutic tool in ophthalmology: implications for glaucoma and uveitis

Several lines of evidence support the view that increased free radical generation and altered nitric oxide (NO) metabolism play a role in the pathogenesis of highly prevalent ocular diseases, such as glaucoma and uveitis. Data are discussed indicating that melatonin, being an efficient antioxidant that displays antinitridergic properties, has a promising role in the treatment of these ocular dysfunctions. Melatonin synthesis occurs in the eye of most species, and melatonin receptors are localized in different ocular structures. In view of the fact that melatonin lacks significant adverse collateral effects even at high doses, the application of melatonin could potentially protect ocular tissues by effectively scavenging free radicals and excessive amounts of NO generated in the glaucomatous or uveitic eye.

Abnormal proliferation and differentiation of osteoblasts from girls with adolescent idiopathic scoliosis to melatonin

Melatonin deficiency has been postulated as an etiologic factors in adolescent idiopathic scoliosis (AIS). In previous studies, melatonin was shown to regulate skeletal growth and bone formation in both humans and rats. Although it remains controversial whether there are differences in serum melatonin level between AIS and control subjects, melatonin signaling pathway dysfunction in osteoblasts has been reported in patients with AIS. Recently, our group found that melatonin receptor 1B (MT2) gene polymorphism was associated with the occurrence of AIS. Hence, the present study investigated the effect of melatonin on AIS osteoblasts. In vitro assays were performed with osteoblasts isolated from 17 severe AIS girls and nine control subjects. The osteoblasts were exposed to different concentrations of melatonin for 3 days. The effects of melatonin on cell proliferation (as evidenced by MTT assay) and differentiation (demonstrated by alkaline phosphatase activity) were determined. In the control group, melatonin significantly stimulated osteoblasts to proliferate and differentiate. However, in the AIS group, the stimulatory effects of melatonin were not discernible. Importantly, this finding demonstrated that there is a significant difference between AIS and control osteoblasts in functional response toward melatonin. Melatonin-stimulated proliferation of control osteoblasts was inhibited by the MT2 antagonist, 4-phenyl-2-propionamidotetraline, as well as by luzindole, a nonselective melatonin receptor antagonist, suggesting that MT2 is associated with the proliferative action of melatonin. The lack of response in AIS osteoblasts might be because of dysfunction of the melatonin signaling pathway, which may contribute to the low bone mineral density and abnormal skeletal growth observed in patients with AIS.

Melatonin protects against Nickel-induced neurotoxicity in vitro by reducing oxidative stress and maintaining mitochondrial function

Nickel is a potential neurotoxic pollutant. Oxidative stress is supposed to be involved in the mechanism underlying nickel-induced neurotoxicity. Melatonin has efficient protective effects against various oxidative damages in nervous system. The purpose of this study was to investigate whether melatonin could efficiently protect against neurotoxicity induced by nickel. Here, we exposed primary cultured cortical neurons and mouse neuroblastoma cell lines (neuro2a) to different concentrations of nickel chloride (NiCl(2)) (0.125, 0.25, 0.5, and 1 mm) for 12 hr or 0.5 mm NiCl(2) for various periods (0, 3, 6, 12, and 24 hr). We found that nickel significantly increased reactive oxygen species production and caused the loss of cell viability both in cortical neurons and neuro2a cells. In addition, nickel exposure obviously inhibited the mitochondrial function, disrupted the mitochondrial membrane potential (DeltaPsim), reduced ATP production, and decreased mitochondrial DNA (mtDNA) content. However, each of these oxidative damages was efficiently attenuated by melatonin pretreatment. These protective effects of melatonin may be attributable to its roles in reducing oxidative stress and improving mitochondrial function in nickel-treated nerve cells. Our results suggested that melatonin may have great pharmacological potential in protecting against the adverse effects of nickel in the nervous system.

Jerte Valley cherry-enriched diets improve nocturnal rest and increase 6-sulfatoxymelatonin and total antioxidant capacity in the urine of middle-aged and elderly humans

Tryptophan, serotonin, and melatonin, present in Jerte Valley cherries, participate in sleep regulation and exhibit antioxidant properties. The effect of the intake of seven different Jerte Valley cherry cultivars on the sleep-wake cycle, 6-sulfatoxymelatonin levels, and urinary total antioxidant capacity in middle-aged and elderly participants was evaluated. Volunteers were subjected to actigraphic monitoring to record and display the temporal patterns of their nocturnal activity and rest. 6-sulfatoxymelatonin and total antioxidant capacity were quantified by enzyme-linked immunosorbent assay and colorimetric assay kits, respectively. The intake of each of the cherry cultivars produced beneficial effects on actual sleep time, total nocturnal activity, assumed sleep, and immobility. Also, there were significant increases in 6-sulfatoxymelatonin levels and total antioxidant capacity in urine after the intake of each cultivar. These findings suggested that the intake of Jerte Valley cherries exerted positive effect on sleep and may be seen as a potential nutraceutical tool to counteract oxidation.

Melatonin signaling and cell protection function

Besides its well-known regulatory role on circadian rhythm, the pineal gland hormone melatonin has other biological functions and a distinct metabolism in various cell types and peripheral tissues. In different tissues and organs, melatonin has been described to act as a paracrine and also as an intracrine and autocrine agent with overall homeostatic functions and pleiotropic effects that include cell protection and prosurvival factor. These latter effects, documented in a number of in vitro and in vivo studies, are sustained through both receptor-dependent and -independent mechanisms that control detoxification and stress response genes, thus conferring protection against a number of xenobiotics and endobiotics produced by acute and chronic noxious stimuli. Redox-sensitive components are included in the cell protection signaling of melatonin and in the resulting transcriptional response that involves the control of NF-κB, AP-1, and Nrf2. By these pathways, melatonin stimulates the expression of antioxidant and detoxification genes, acting in turn as a glutathione system enhancer. A further and converging mechanism of cell protection by this indoleamine described in different models seems to lie in the control of damage and signaling function of mitochondria that involves decreased production of reactive oxygen species and activation of the antiapoptotic and redox-sensitive element Bcl2. Recent evidence suggests that upstream components in this mitochondrial route include the calmodulin pathway with its central role in melatonin signaling and the survival-promoting component of MAPKs, ERK1/2. In this review article, we will discuss these and other molecular aspects of melatonin signaling relevant to cell protection and survival mechanisms.

Scientific basis for the potential use of melatonin in bone diseases: osteoporosis and adolescent idiopathic scoliosis

The objective of this paper was to analyze the data supporting the possible role of melatonin on bone metabolism and its repercussion in the etiology and treatment of bone pathologies such as the osteoporosis and the adolescent idiopathic scoliosis (AIS). Melatonin may prevent bone degradation and promote bone formation through mechanisms involving both melatonin receptor-mediated and receptor-independent actions. The three principal mechanisms of melatonin effects on bone function could be: (a) the promotion of the osteoblast differentiation and activity; (b) an increase in the osteoprotegerin expression by osteoblasts, thereby preventing the differentiation of osteoclasts; (c) scavenging of free radicals generated by osteoclast activity and responsible for bone resorption. A variety of in vitro and in vivo experimental studies, although with some controversial results, point toward a possible role of melatonin deficits in the etiology of osteoporosis and AIS and open a new field related to the possible therapeutic use of melatonin in these bone diseases.

Beneficial effects of melatonin in cardiovascular disease

The experimental data obtained from both human and rodent studies suggest that melatonin may have utility in the treatment of several cardiovascular conditions. In particular, melatonin's use in reducing the severity of essential hypertension should be more widely considered. In rodent studies melatonin has been shown to be highly effective in limiting abnormal cardiac physiology and the loss of critical heart tissue resulting from ischemia/reperfusion injury. Melatonin may also be useful in reducing cardiac hypertrophy in some situations and thereby limiting the frequency of heart failure. Finally, some conventional drugs currently in use have cardiotoxicity as a side-effect. Based on studies in rodents, melatonin, due to its multiple anti-oxidative actions, is highly effective in abrogating drug-mediated damage to the heart. Taken together, the findings from human and animal studies support the consideration of melatonin as a cardioprotective agent.

Melatonin: a novel neuroprotectant for the treatment of glaucoma

Glaucoma is a leading cause of blindness. Although ocular hypertension is the most important risk factor, several concomitant factors such as elevation of glutamate and decrease in gamma-aminobutyric acid (GABA) levels, disorganized NO metabolism, and oxidative damage could significantly contribute to the neurodegeneration. The aim of this report was to analyze the effect of melatonin on retinal glutamate clearance, GABA concentrations, NO synthesis, and retinal redox status, as well as on functional and histological alterations provoked by chronic ocular hypertension induced by intracameral injections of hyaluronic acid (HA) in the rat eye. In normal retinas, melatonin increased glutamate uptake, glutamine synthase activity, GABA turnover rate, glutamic acid decarboxylase activity, superoxide dismutase activity, and reduced glutathione (GSH) levels, whereas it decreased NOS activity, L-arginine uptake, and lipid peroxidation. To assess the effect of melatonin on glaucomatous neuropathy, weekly injections of HA were performed in the eye anterior chamber. A pellet of melatonin was implanted subcutaneously 24 hr before the first injection or after six weekly injections of HA. Melatonin, which did not affect intraocular pressure (IOP), prevented and reversed the effect of ocular hypertension on retinal function (assessed by electroretinography) and diminished the vulnerability of retinal ganglion cells to the deleterious effects of ocular hypertension. These results indicate that melatonin could be a promissory resource in the management of glaucoma.

Amyloid-beta neurotoxicity in organotypic culture is attenuated by melatonin: involvement of GSK-3beta, tau and neuroinflammation

Alzheimer's disease (AD) is a progressive neurodegenerative disorder marked by accumulation of extracellular deposits of amyloid-beta (Abeta) peptide in brain regions that are important for memory and cognition. The buildup of Abeta aggregates in the AD is followed by the formation of intracellular neurofibrillary tangles and activation of neuroinflammatory reactions. The present study investigated whether melatonin possesses a neuroprotective effect against Abeta-induced toxicity. For this purpose, organotypic hippocampal slices were cultured and exposed to 25 microm of Abeta(25-35) in the absence or in the presence of melatonin (25, 50, or 100 microm). In addition, the authors have investigated the involvement of GSK-3beta, tau protein, astroglial, and microglial activation, and cytokine levels in the melatonin protection against Abeta-induced neurotoxicity. Melatonin prevented the cell damage in hippocampus induced by the exposure to Abeta(25-35). In addition, melatonin significantly reduced the activation of GSK-3beta, the phosphorylation of tau protein, the glial activation and the Abeta-induced increase of TNF-alpha and IL-6 levels. On the basis of these findings, we speculate that melatonin may provide an effective therapeutic strategy for AD, by attenuating Abeta-induced phosphorylation of tau protein, and preventing GSK-3beta activation and neuroinflammation.