Melatonin protects against common deletion of mitochondrial DNA-augmented mitochondrial oxidative stress and apoptosis

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

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Melatonin exerts differential actions on X-ray radiation-induced apoptosis in normal mice splenocytes and Jurkat leukemia cells

The ability of melatonin as a potent antioxidant was used as a rationale for testing its antiapoptotic ability in normal cells. Recently, melatonin was shown to possess proapoptotic action by increasing reactive oxygen species in certain cancer cells. The modification of radiation-induced apoptosis by melatonin and the expression of apoptosis-associated upstream regulators were studied in normal mice splenocytes and Jurkat T leukemia cells. C57BL/6 mice were exposed to a single whole body X-ray radiation dose of 2 Gy with or without 250 mg/kg melatonin pretreatment. The Jurkat cells were divided into four groups of control, 1 mm melatonin alone, 4 Gy irradiation-only and melatonin pretreatment before irradiation. The highest level of apoptosis in the normal splenic white pulp was detected by TUNEL assay at 8 hr after irradiation. At this time, the apoptotic index of irradiation-only and melatonin pretreatment groups were 35.6% and 20.7%, respectively. This reduced apoptosis by melatonin was associated with the increase of Bcl-2 expression and a reduction of Bax/Bcl-2 ratio through a relative decrease of p53 mRNA and protein. In the Jurkat cells treated with a combination of melatonin and radiation, both Annexin V-FITC(+)/PI(-) and Annexin V-FITC(+) cells were increased at 48 hr after irradiation when compared with irradiation-only or melatonin alone. The expressions of p53 between groups were well correlated with the results of Annexin V binding. The irradiation or melatonin did not influence the JNK1 expression in Jurkat cells. The present results suggest that melatonin enhances radiation-induced apoptosis in Jurkat leukemia cells, while reducing radiation-induced apoptosis in normal mice splenocytes. These differential effects on radiation-induced apoptosis by melatonin might involve the regulation of p53 expression.

Therapeutic potential of melatonin in traumatic central nervous system injury

A vast literature extolling the benefits of melatonin has accumulated during the past four decades. Melatonin was previously considered of importance to seasonal reproduction and circadian rhythmicity. Currently, it appears to be a versatile anti-oxidative and anti-nitrosative agent, a molecule with immunomodulatory actions and profound oncostatic activity, and also to play a role as a potent neuroprotectant. Nowadays, melatonin is sold as a dietary supplement with differential availability as an over-the-counter aid in different countries. There is a widespread agreement that melatonin is nontoxic and safe considering its frequent, long-term usage by humans at both physiological and pharmacological doses with no reported side effects. Endeavors toward a designated drug status for melatonin may be enormously rewarding in clinics for treatment of several forms of neurotrauma where effective pharmacological intervention has not yet been attained. This mini review consolidates the data regarding the efficacy of melatonin as an unique neuroprotective agent in traumatic central nervous system (CNS) injuries. Well-documented actions of melatonin in combating traumatic CNS damage are compiled from various clinical and experimental studies. Research on traumatic brain injury and ischemia/reperfusion are briefly outlined here as they have been recently reviewed elsewhere, whereas the studies on different animal models of the experimental spinal cord injury have been extensively covered in this mini review for the first time.

Long-term melatonin administration protects brain mitochondria from aging

We tested whether chronic melatonin administration in the drinking water would reduce the brain mitochondrial impairment that accompanies aging. Brain mitochondria from male and female senescent prone (SAMP8) mice at 5 and 10 months of age were studied. Mitochondrial oxidative stress was determined by measuring the levels of lipid peroxidation and nitrite, glutathione/glutathione disulfide ratio, and glutathione peroxidase and glutathione reductase activities. Electron transport chain activity and oxidative phosphorylation capability of mitochondria were also determined by measuring the activity of the respiratory chain complexes and the ATP content. The results support a significant age-dependent mitochondrial dysfunction with a diminished efficiency of the electron transport chain and reduced ATP production, accompanied by an increased oxidative/nitrosative stress. Melatonin administration between 1 and 10 months of age completely prevented the mitochondrial impairment, maintaining or even increasing ATP production. There were no major age-dependent differences between males in females, although female mice seemed to be somewhat more sensitive to melatonin treatment than males. Thus, melatonin administration as a single therapy maintained fully functioning brain mitochondria during aging, a finding with important consequences in the pathophysiology of brain aging.

Melatonin protects against heart ischemia-reperfusion injury by inhibiting mitochondrial permeability transition pore opening

Melatonin, a well-known antioxidant, has been shown to protect against ischemia-reperfusion myocardial damage. Mitochondrial permeability transition pore (MPTP) opening is an important event in cardiomyocyte cell death occurring during ischemia-reperfusion and therefore a possible target for cardioprotection. In the present study, we tested the hypothesis that melatonin could protect heart against ischemia-reperfusion injury by inhibiting MPTP opening. Isolated perfused rat hearts were subjected to global ischemia and reperfusion in the presence or absence of melatonin in a Langerdoff apparatus. Melatonin treatment significantly improves the functional recovery of Langerdoff hearts on reperfusion, reduces the infarct size, and decreases necrotic damage as shown by the reduced release of lactate dehydrogenase. Mitochondria isolated from melatonin-treated hearts are less sensitive than mitochondria from reperfused hearts to MPTP opening as demonstrated by their higher resistance to Ca(2+). Similar results were obtained following treatment of ischemic-reperfused rat heart with cyclosporine A, a known inhibitor of MPTP opening. In addition, melatonin prevents mitochondrial NAD(+) release and mitochondrial cytochrome c release and, as previously shown, cardiolipin oxidation associated with ischemia-reperfusion. Together, these results demonstrate that melatonin protects heart from reperfusion injury by inhibiting MPTP opening, probably via prevention of cardiolipin peroxidation.

Induction of matrix metalloproteinase-9 and -3 in nonsteroidal anti-inflammatory drug-induced acute gastric ulcers in mice: regulation by melatonin

The pathogenesis of gastric ulcer is associated with remodeling of extracellular matrix (ECM) by various matrix metalloproteinases (MMPs). However, how MMPs are regulated during nonsteroidal anti-inflammatory drug (NSAID)-induced acute gastric ulceration is not well studied. In this study, different NSAIDs (80 mg/kg b.w.) were applied to generate acute gastric ulcer in the BALB/c mouse and the regulation of MMPs were investigated. NSAIDs caused dose-dependent induction in MMP-9 and -3 activities and expressions in ulcerated gastric tissues along with significant infiltration of inflammatory cells and disruption of gastric mucosal layer. In addition, an increase in tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-8 expression, excessive generation of hydroxyl radical ((*)OH), and protein oxidation and lipid peroxidation were observed in acute ulcerated gastric tissues. In this study, the efficacy of melatonin on activities of MMP-9 and -3 during prevention of gastric ulcers was tested. Melatonin at a dose of 60 mg/kg b.w. downregulated MMP-9 and -3 both at the enzyme and protein levels in mouse gastric tissues during prevention as well as healing of acute gastric ulcers. It also blocked oxidative stress via inhibition of protein oxidation, lipid peroxidation, (*)OH generation and SOD-2 expression. Moreover, it suppressed myeloperoxidase activity and expressions of TNF-alpha, IL-1beta and IL-8. This study documents for the first time that induction of MMP-9 and -3 activities accompany NSAID-induced inflammation and oxidative stress in gastric tissues and indicates that, melatonin may be a preventive or therapeutic remedy for gastric ulcers.

Melatonin protects kidney grafts from ischemia/reperfusion injury through inhibition of NF-kB and apoptosis after experimental kidney transplantation

Free radicals are involved in pathophysiology of ischemia/reperfusion injury (IRI). Melatonin is a potent scavenger of reactive oxygen and nitrogen species. Thus, this study was designed to elucidate its effects in a model of rat kidney transplantation. Twenty Lewis rats were randomly divided into 2 groups (n = 10 animals each). Melatonin (50 mg/kg BW) dissolved in 5 mL milk was given to one group via gavage 2 hr before left donor nephrectomy. Controls were given the same volume of milk only. Kidney grafts were then transplanted into bilaterally nephrectomized syngeneic recipients after 24 hr of cold storage in Histidine-Tryptophan-Ketoglutarate solution. Both graft function and injury were assessed after transplantation through serum levels of blood urea nitrogen (BUN), creatinine, transaminases, and lactate dehydrogenase (LDH). Biopsies were taken to evaluate tubular damage, the enzymatic activity of superoxide dismutase (SOD) and lipid hydroperoxide (LPO), and the expression of NF-kBp65, inducible nitric oxide synthase (iNOS), caspase-3 as indices of oxidative stress, necrosis, and apoptosis, respectively. Melatonin improved survival (P < 0.01) while decreasing BUN, creatinine, transaminases, and LDH values up to 39-71% (P < 0.05). Melatonin significantly reduced the histological index for tubular damage, induced tissue enzymatic activity of SOD while reducing LPO. At the same time, melatonin down-regulated the expression of NF-kBp65, iNOS, and caspase-3. In conclusion, donor preconditioning with melatonin protected kidney donor grafts from IRI-induced renal dysfunction and tubular injury most likely through its anti-oxidative, anti-apoptotic and NF-kB inhibitory capacity.

Melatonin reduces induction of Bax, caspase and cell death in methamphetamine-treated human neuroblastoma SH-SY5Y cultured cells

Several studies demonstrated that methamphetamine (MA)-treated human neuroblastoma cells exhibit increased oxidative stress, which regulates intracellular signaling cascades leading to cell death. Melatonin has a potential as a direct free radical scavenger and protects against cell death caused by MA. The objective of this study was to investigate the neuroprotective properties of melatonin on MA-induced induction of death signaling cascade and neuronal cell degeneration in human neuroblastoma SH-SY5Y cultured cells. The results of the present study demonstrate that MA significantly reduced cell viability in SH-SY5Y cultured cells. Desipramine, a monoamine uptake blocker, and melatonin reversed the toxic effect of MA in reducing cell viability. Induction of Bax, Bcl-2 and cleaved caspase-3 protein levels were observed in SH-SY5Y cultured cells treated with MA, whereas the induction of Bax and cleaved caspase-3 was diminished by melatonin. Visualization of the induction of Bax using immunofluorescence but a reduction in mitochondrial sites using red-fluorescent mitochondria-staining dye was more obviously apparent in MA-treated cells than in untreated control cells and, again, this effect was abolished by melatonin. These findings demonstrate important roles of Bax and caspase in death signaling cascade, and the protective effects of melatonin in MA-treated SH-SY5Y cells.

Exogenous melatonin positively influences follicular dynamics, oocyte developmental competence and blastocyst output in a goat model

The role of melatonin in modulating mammalian reproduction is of particular interest; however, its effects on ovarian follicles and their oocytes still remain to be characterized. This study determined the influence of melatonin treatment on follicular growth patterns and on in vitro oocyte developmental competence. In a first experiment, the effects of melatonin supplementation on follicular dynamics were evaluated using daily transrectal ultrasonographies for 21 days, in 7 multiparous Sarda goats receiving a subcutaneous implant of 18 mg of melatonin and in 5 control untreated does. Melatonin caused more follicular waves (5.2 +/- 0.2 versus 4 +/- 0.3; P < 0.05) as the waves were shortened at around 2 days when compared with the non-melatonin treated control goats (P < 0.001). Oocyte developmental competence was evaluated in a second experiment by applying procedures for in vitro embryo production. There were no significant differences in the total number of oocytes obtained from 6 control (n = 192) and 7 melatonin-treated (n = 265) goats given follicle stimulating hormone to induce follicular development. Differences in oocyte developmental competence between the two groups became evident after in vitro fertilization and culture; melatonin increased the rate of cleaved oocytes in comparison with control animals (82.5 versus 63.4%; P < 0.001), advanced timing of embryo development and enhanced blastocyst output (31.5 versus 16.3%; P < 0.01). However, blastocyst quality, as evaluated by cryotolerance and gene expression analysis, was not found to be different between the groups. In conclusion, in vivo melatonin treatment is beneficial for increasing ovarian follicle turnover and improving oocyte developmental competence and kinetics of the blastocyst.

Melatonin induces mitochondrial-mediated apoptosis in human myeloid HL-60 cells

The role of melatonin in the mediation of apoptotic events has recently gained attention, especially after recent studies have reported that melatonin exerts antiapoptotic actions in normal cells but may activate proapoptotic pathways in some tumor cells. Here, we have evaluated the effect of melatonin on apoptosis in the human leukemia cell line HL-60. Melatonin treatment (1 mm) induced a significant increase in caspase-3 and -9 activities. The effect of melatonin on the activation of caspases was time dependent, reaching a maximum after 12 hr of stimulation, and then decreasing to a minimum after 72 hr. Treatment with melatonin also evoked mitochondrial membrane depolarization and permeability transition pore induction, which caused loss of mitochondrial staining by calcein, and increased cell death by apoptosis/necrosis as demonstrated by propidium iodide positive-staining of cells after 72 hr of stimulation. In addition, the exposure of cells to melatonin resulted in an activation and association of the proapoptotic proteins Bax and Bid, as well as promoting detectable increases in the expression of both proteins. We conclude that melatonin has proapoptotic and/or oncostatic effects in the human myeloid cell line HL-60.

Profiling of melatonin in the model tomato (Solanum lycopersicum L.) cultivar Micro-Tom

Melatonin exists in a considerable variety of plant species. However, the physiological roles of melatonin in plants are not well understood. In this study, the distribution and accumulation of melatonin during leaf and fruit development were analyzed in Micro-Tom, a model cultivar of tomato (Solanum lycopersicum L.). Melatonin was extracted using an acetone-methanol method and measured by enzyme-linked immunosorbent assay. Melatonin was detected in leaves, stems, roots, flowers, fruits, seedlings and seeds in the range of 1.5-66.6 ng/g fresh weight, with seeds containing the highest concentration of melatonin. In fruits and leaves, melatonin concentrations varied depending on the developmental stage, suggesting that melatonin controls some of the processes involved in plant maturation.

Melatonin delivery in solid lipid nanoparticles: prevention of cyclosporine A induced cardiac damage

Melatonin is a potent antioxidant molecule with a capacity to protect tissues from damage caused by oxidative stress. It reduces cyclosporine A (CsA)-induced cardiotoxicity; this improvement required melatonin's binding to its membrane receptors. This experimental study examined whether melatonin is a useful tool for counteracting CsA-induced apoptosis in the heart of rats. We investigated melatonin's antiapoptotic efficacy in protecting the heart and tested whether this effect was totally dependent on its binding to membrane receptors or also involved radical scavenging. In some animals, solid lipid nanoparticles (SLN) as a melatonin delivery system were used. In one group of rats, melatonin (1 mg/kg/day i.p.) was given concurrently with CsA (15 mg/kg/day s.c.; CsA-MT) for 21 days. In other animals, melatonin loaded in SLN was injected with CsA (CsA-MTSLN). Oxidative stress in heart tissue was estimated using the evaluation of lipid peroxidation and the expression of the isoform of inducible nitric oxide (iNOS). The antiapoptotic effect of melatonin was evaluated using TUNEL staining and Bcl-2 protein family expression. CsA administration produced morphological and biochemical changes in the heart of rats, while melatonin reversed the changes. In particular, since the antiapoptotic melatonin's efficacy is mainly observed when it is loaded in SLN, we suggest that MT1/MT2 pathway is not sufficient for apoptosis antagonism and the additional intracellular effects may be required. Finally, we show that, (i) melatonin significantly reduces CsA cardiotoxicity acting also on apoptotic processes, and (ii) the reduction in CsA-induced cardiotoxicity is mediated mainly by its antioxidant effect.

Melatonin reduces indomethacin-induced gastric mucosal cell apoptosis by preventing mitochondrial oxidative stress and the activation of mitochondrial pathway of apoptosis

Augmentation of gastric mucosal cell apoptosis due to development of oxidative stress is one of the main pathogenic events in the development of nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy. Identification of a nontoxic, anti-apoptotic molecule is warranted for therapy against NSAID-induced gastropathy. The objective of the present study was to define the mechanism of the anti-apoptotic effect of melatonin, a nontoxic molecule which scavenges reactive oxygen species. Using an array of experimental approaches, we have shown that melatonin prevents the development of mitochondrial oxidative stress and activation of mitochondrial pathway of apoptosis induced by indomethacin (a NSAID) in the gastric mucosa. Melatonin inhibits the important steps of indomethacin-induced activation of mitochondrial pathway of apoptosis such as upregulation of the expression of Bax and Bak, and the downregulation of Bcl-2 and BclxL. Melatonin also prevents indomethacin-induced mitochondrial translocation of Bax and prevents the collapse of mitochondrial membrane potential. Moreover, melatonin reduces indomethacin-mediated activation of caspase-9 and caspase-3 by blocking the release of cytochrome c and finally rescues gastric mucosal cells from indomethacin-induced apoptosis as measured by the TUNEL assay. Histologic studies of gastric mucosa further document that melatonin almost completely protects against gastric damage induced by indomethacin. Thus, melatonin has significant anti-apoptotic effects to protect gastric mucosa from NSAID-induced apoptosis and gastropathy, which makes its use as potential therapy against gastric damage during NSAID treatment.

Fibroblast growth factor 9 prevents MPP+-induced death of dopaminergic neurons and is involved in melatonin neuroprotection in vivo and in vitro

Oxidative stress and down-regulated trophic factors are involved in the pathogenesis of nigrostriatal dopamine(DA)rgic neurodegeneration in Parkinson's disease. Fibroblast growth factor 9 (FGF9) is a survival factor for various cell types; however, the effect of FGF9 on DA neurons has not been studied. The antioxidant melatonin protects DA neurons against neurotoxicity. We used MPP(+) to induce neuron death in vivo and in vitro and investigated the involvement of FGF9 in MPP(+) intoxication and melatonin protection. We found that MPP(+) in a dose- and time-dependent manner inhibited FGF9 mRNA and protein expression, and caused death in primary cortical neurons. Treating neurons in the substantia nigra and mesencephalic cell cultures with FGF9 protein inhibited the MPP(+)-induced cell death of DA neurons. Melatonin co-treatment attenuated MPP(+)-induced FGF9 down-regulation and DA neuronal apoptosis in vivo and in vitro. Co-treating DA neurons with melatonin and FGF9-neutralizing antibody prevented the protective effect of melatonin. In the absence of MPP(+), the treatment of FGF9-neutralizing antibody-induced DA neuronal apoptosis whereas FGF9 protein reduced it indicating that endogenous FGF9 is a survival factor for DA neurons. We conclude that MPP(+) down-regulates FGF9 expression to cause DA neuron death and that the prevention of FGF9 down-regulation is involved in melatonin-provided neuroprotection.

Modulation of the cGMP signaling pathway by melatonin in pancreatic beta-cells

Melatonin influences the second messenger cyclic guanosine 3',5'-monophosphate (cGMP) signaling pathway in pancreatic beta-cells via a receptor-mediated mechanism. In the present study, it was determined how the regulation of cGMP concentrations by melatonin proceeds. The results provide evidence that melatonin acts via the soluble guanylate cyclase (sGC), as molecular investigations demonstrated that long-term incubation with melatonin significantly reduced the expression levels of the sGC mRNA in rat insulinoma beta-cells (INS1) cells, whereas mRNA expression of membrane guanylate cyclases was unaffected. Incubation with melatonin abolished the S-nitrosoacetyl penicillamine-induced increase of cGMP concentrations in INS1 cells. In addition, the cGMP-inhibitory effect of melatonin was reversed by preincubation with the sGC inhibitors 1H-(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1-one and 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one. Nitric oxide (NO) production was not influenced after 1 hr of melatonin application, but was influenced after a 4 hr incubation period. Preincubation of INS1 cells with the NO synthase inhibitor N(G)-monomethyl-l-arginine did not abolish the cGMP-inhibitory effect of melatonin. Transcripts of cyclic nucleotide-gated (CNG) channels were significantly reduced after melatonin treatment in a dose-dependent manner, indicating the involvement of these channels in mediating the melatonin effect in INS1 cells. The results of this study demonstrate that melatonin mediates its inhibitory effect on cGMP concentrations in pancreatic beta-cells by inhibiting the sGC, but does not influence NO concentration or NO synthase activity in short-term incubation experiments. In addition, it was demonstrated that melatonin is involved in modulation of CNG channel mRNA.

Oxidative stress of the newborn in the pre- and postnatal period and the clinical utility of melatonin

Newborns, and especially those delivered preterm, are probably more prone to oxidative stress than individuals later in life. Also during pregnancy, increased oxygen demand augments the rate of production of reactive oxygen species (ROS) and women, even with normal pregnancies, experience elevated oxidative stress and lipid peroxidation compared with nonpregnant women. Also, there appears to be an increase in ROS generation in the placenta of pre-eclamptic women. In comparison with healthy adults, newborn infants have lower levels of plasma antioxidants such as vitamin E, beta-carotene, and sulphydryl groups, lower levels of plasma metal binding proteins including ceruloplasmin and transferrin, and reduced activity of erythrocyte superoxide dismutase. This review summarizes conditions of newborns where there is elevated oxidative stress. Included in this group of conditions is asphyxia, respiratory distress syndrome and sepsis and the review also summarizes the literature related to clinical trials of antioxidant therapies and of melatonin, a highly effective antioxidant and free radical scavenger. The authors document there is general agreement that short-term melatonin therapy may be highly effective and that it has a remarkably benign safety profile, even when neonates are treated with pharmacological doses. Significant complications with long-term melatonin therapy in children and adults also have not been reported. None of the animal studies of maternal melatonin treatment or in postnatal life have shown any treatment-related side effects. The authors conclude that treatment with melatonin might result in a wide range of health benefits, improved quality of life and reduced healthcare costs and may help reduce complications in the neonatal period.

Melatonin attenuates methamphetamine-induced deactivation of the mammalian target of rapamycin signaling to induce autophagy in SK-N-SH cells

Methamphetamine (METH) is a commonly abused drug that damages nerve terminals by causing reactive oxygen species (ROS) formation, apoptosis, and neuronal damage. Autophagy, a type of programmed cell death independent of apoptosis, is negatively regulated by the mammalian target of the rapamycin (mTOR) signaling pathway. It is not known, however, whether autophagy is involved in METH-induced neurotoxicity. Therefore, we investigated the effect of METH on autophagy and its upstream regulator, the mTOR signaling pathway. Using the SK-N-SH dopaminergic cell line, we found that METH induces the expression of LC3-II, a protein associated with the autophagosome membrane, in a dose-dependent manner. Moreover, METH inhibits the phosphorylation of mTOR and the action of its downstream target, the eukaryotic initiation factor (eIF)4E-binding protein, 4EBP1. Melatonin, a major secretory product of pineal, is a potent naturally produced antioxidant that acts through various mechanisms to ameliorate the toxic effects of ROS. We found that a pretreatment with melatonin enhances mTOR activity and 4EBP1 phosphorylation and protects against the formation of LC3-II in SK-N-SH cells exposed to METH. This work demonstrates a novel role for melatonin as a neuroprotective agent against METH.

Evidence for a biphasic apoptotic pathway induced by melatonin in MCF-7 breast cancer cells

Previous investigations demonstrated that melatonin exerts an oncostatic action on estrogen-responsive breast cancer, both in vitro and in vivo. Nevertheless, the pro-apoptotic effect of melatonin is still a matter of debate. An experimental study was undertaken to focus on melatonin-related apoptosis and to identify the apoptotic pathways involved. Whole cell-count, flow-cytometry analysis and proteins involved in apoptotic pathways [p53, p73, murine double minute 2 (MDM2), caspases-9,-7,-6, cleaved-poly ADP ribose polymerase (PARP), Bcl-2, Bax and apoptotic inducing factor (AIF)] were investigated in human MCF-7 breast cancer cells treated with physiological (1 nM) concentration of melatonin. Melatonin exerts a significant growth-inhibitory effect on MCF-7 cells, becoming evident after 72 hr and thereafter increasing linearly up to 144 hr. In this model, the growth-inhibition is transforming growth factor beta 1 (TGFbeta1)-dependent and it might be reversed by adding an anti-TGFbeta1 antibody. Melatonin induces a significant rise in apoptotic rate, at both 24 and 96 hr. The anti-TGFbeta1 antibody almost completely suppresses melatonin-related late apoptosis; however, early apoptosis is unaffected. Early programmed cell death is associated with a significant increase in the p53/MDM2 ratio and in AIF release, without modifications in caspase activity or cleaved-PARP levels. Activated caspases-9 and -7 and cleaved-PARP increased significantly at 96 hr, concomitantly with a down-regulation of the Bcl-2/Bax ratio. These data suggest that two distinct apoptotic processes are triggered by melatonin in MCF-7 cells: an early, TGFbeta1 and caspase-independent response, and a late apoptotic TGFbeta1-dependent process in which activated-caspase-7 is likely to be the terminal effector.

Protective effects of melatonin against oxidative stress in Fmr1 knockout mice: a therapeutic research model for the fragile X syndrome

Fragile X syndrome is the most common form of inherited mental retardation. It is typically caused by a mutation of the Fragile X mental-retardation 1 (Fmr1) gene. To better understand the role of the Fmr1 gene and its gene product, the fragile X mental-retardation protein in central nervous system functions, an fmr1 knockout mouse that is deficient in the fragile X mental-retardation protein was bred. In the present study, fragile X mental retardation 1-knockout and wild-type mice are used to determine behaviour and oxidative stress alterations, including reduced glutathione, oxidized glutathione and thiobarbituric acid-reactive substances, before and after chronic treatment with melatonin or tianeptine. Reduced glutathione levels were reduced in the brain of fmr1-knockout mice and chronic melatonin treatment normalized the glutathione levels compared with the control group. Lipid peroxidation was elevated in brain and testes of fmr1-knockout mice and chronic melatonin treatment prevents lipid peroxidation in both tissues. Interestingly, chronic treatment with melatonin alleviated the altered parameters in the fmr1-knockout mice, including abnormal context-dependent exploratory and anxiety behaviours and learning abnormalities. Chronic treatment with tianeptine (a serotonin reuptake enhancer) did not normalize the behaviour in fmr1-knockout mice. The prevention of oxidative stress in the fragile X mouse model, by an antioxidant compound such as melatonin, emerges as a new and promising approach for further investigation on treatment trials for the disease.

Melatonin protects the mitochondria from oxidative damage reducing oxygen consumption, membrane potential, and superoxide anion production

The role of melatonin in improving mitochondrial respiratory chain activity and increasing ATP production in different experimental conditions has been widely reported. To date, however, the mechanism(s) involved are largely unknown. Using high-resolution respirometry, fluorometry and spectrophotometry we studied the effects of melatonin on normal mitochondrial functions. Mitochondria were recovered from mouse liver cells and incubated in vitro with melatonin at concentrations ranging from 1 nm to 1 mm. Melatonin decreased oxygen consumption concomitantly with its concentration, inhibited any increase in oxygen flux in the presence of an excess of ADP, reduced the membrane potential, and consequently inhibited the production of superoxide anion and hydrogen peroxide. At the same time it maintained the efficiency of oxidative phosphorylation and ATP synthesis while increasing the activity of the respiratory complexes (mainly complexes I, III, and IV). The effects of melatonin appeared to be due to its presence within the mitochondria, since kinetic experiments clearly showed its incorporation into these organelles. Our results support the hypothesis that melatonin, together with hormones such as triiodothyronine, participates in the physiological regulation of mitochondrial homeostasis.

Free iron, total F-isoprostanes and total F-neuroprostanes in a model of neonatal hypoxic-ischemic encephalopathy: neuroprotective effect of melatonin

Oxidative stress due to free radical formation and initiation of abnormal oxidative reactions is involved in several diseases of newborns, such as hypoxic-ischemic encephalopathy. Melatonin, an endogenously produced indoleamine primarily formed in the pineal gland, is a potent free radical scavenger as well as an indirect antioxidant. The present study was conducted to evaluate the formation of oxidative damage mediators and the possible effect of melatonin treatment in a model of hypoxic-ischemic encephalopathy in 7-day-old rats. Pups were subjected to permanent ligation of the right common carotid artery and exposed for 2.5 hr to a nitrogen-oxygen mixture (92% and 8%, respectively) (hypoxia-ischemia, HI). Melatonin was injected intraperitoneally to a group of rats at the dose of 15 mg/kg 30 min before starting the ischemic procedure (HI-Melatonin). After 24 hr of treatment, in homogenized cerebral cortex, desferoxamine (DFO)-chelatable free iron, total F(2)-isoprostanes and total F(4)-neuroprostanes, originating from the free radical-catalyzed peroxidation of arachidonic and docosahexaenoic acids, respectively, were determined. HI induced a significant increase in DFO-chelatable iron, total F(2)-isoprostanes and F(4)-neuroprostanes in both right and left side of the cerebral cortex. In HI-Melatonin-treated animals the levels of free iron, F(2)-isoprostanes, and F(4)-neuroprostanes were significantly lower than that in HI rats and the values were similar to controls. These data show the important neuroprotective role of melatonin in reducing oxidative damage resulting from HI. Melatonin could represent a potential safe approach to perinatal brain damage in humans.

Protection against cell death and sustained tyrosine hydroxylase phosphorylation in hydrogen peroxide- and MPP-treated human neuroblastoma cells with melatonin

Neuroprotective effects of melatonin against oxidative stress-induced neuronal cell degeneration in human SH-SY5Y neuroblastoma cells were investigated in this report. The results demonstrate that exogenous administration of H(2)O(2) and 1-methyl, 4-phenyl, pyridinium ion (MPP(+)) significantly decreased cell viability in SH-SY5Y cultured cells. Desipramine, a monoamine uptake blocker was able to abolish the toxic effects of MPP(+) but not H(2)O(2) in reduction of cell viability. Conversely, melatonin reversed the toxic effects of H(2)O(2) and MPP(+) on cell viability. In addition, the reduction of phosphorylation of tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis, and phosphorylation of cyclic AMP responsive element-binding protein by H(2)O(2) and MPP(+) was also diminished by melatonin. These results demonstrate some effective roles of melatonin on neuroprotection and its action on the modulation of tyrosine hydroxylase phosphorylation.

Effects of melatonin on in vitro maturation of porcine oocyte and expression of melatonin receptor RNA in cumulus and granulosa cells

Melatonin is a multifunctional molecule that mediates several circadian and seasonal processes in animal reproduction. Melatonin and its metabolites are antioxidants and free radical scavengers. We investigated the effects of melatonin on porcine oocyte maturation and embryo development. We then investigated the local expression of the melatonin receptor 1 (MT1) gene in cumulus cells, granulosa cells, and the oocytes with the reverse transcription-polymerase chain reaction (RT-PCR) method. We further evaluated the antioxidant effects [reactive oxygen species (ROS) levels in cumulus-oocytes complexes] of melatonin supplementation during in vitro maturation (IVM). Compared with control, melatonin supplementation (10 ng/mL) during IVM resulted in a greater proportion of oocytes extruding the polar body (75.6% versus 84.6%). Significantly greater proportion of parthenogenetically activated oocytes developed to blastocysts when the in vitro medium was supplemented with melatonin; however, cleavage frequency and blastocyst cell number were not affected by the treatment. RT-PCR analysis revealed the expression of MT1 gene in cumulus and granulosa cells but not in oocytes. Melatonin-treated oocytes had significantly lower levels of ROS than did control (untreated) oocytes. We conclude that exogenous melatonin has beneficial effects on nuclear and cytoplasmic maturation during porcine IVM. Some of the observed effects may be mediated by receptor binding and while others may have been receptor independent, e.g., direct free radical scavenging.

Melatonin inhibits arsenite-induced peripheral neurotoxicity

In this study, the effect of melatonin on sodium arsenite (arsenite)-induced peripheral neurotoxicity was investigated using dorsal root ganglion (DRG) explants. After 24-hr incubation, arsenite (30 microm) consistently elevated the expression of heat shock protein 70 and haeme oxygenase-1, two well-known stress proteins, in the treated DRG explants. Co-incubation with melatonin (4 and 20 mm) concentration-dependently attenuated arsenite-induced elevation in stress proteins. Furthermore, melatonin inhibited arsenite-induced phosphorylation of p38 and DNA fragmentation. Inhibition by melatonin of arsenite-induced apoptosis was mediated via inactivating both endoplasmic reticulum (ER) and mitochondrial pathways. In the ER pathway, melatonin suppressed arsenite-induced elevation in activating transcription factor-6 and CCAAT/enhancer-binding protein homologous protein in the nuclear fraction of the treated DRG explants. Moreover, melatonin attenuated arsenite-induced activation of caspase 12, an ER-specific enzyme. In the mitochondrial pathway, arsenite-induced increases in Bcl-2 levels and cytosolic cytochrome c were reduced by melatonin. At the same time, melatonin inhibited arsenite-induced activation of caspase 3 in the treated DRG explants. Compared with glutathione and N-acetyl cysteine, melatonin was more potent than either in inhibiting arsenite-induced elevation in stress proteins. Taken together, our study demonstrates that melatonin is protective against arsenite-induced neurotoxicity in DRG explants. In addition, melatonin prevented arsenite-induced apoptosis via suppression of ER and mitochondrial activation. Our data suggest that melatonin is potentially a therapy for arsenite-induced peripheral neuropathy.

Melatonin attenuates lipopolysaccharide-induced acute lung inflammation in sleep-deprived mice

Sleep disorders are great problems in modern society. Even minimal changes of sleep can affect health. Especially, patients with pulmonary diseases complain of sleep problems such as sleep disturbance and insomnia. Recent studies have shown an association between sleep deprivation (SD) and inflammation, however, the underlying mechanisms remain unclear. In the present study, we investigated whether melatonin protects against acute lung inflammation in SD. Male ICR mice were deprived sleep using modified multiplatform water bath for 3 days. Acute lung inflammation was induced by lipopolysaccharide (LPS; 5 mg/kg). Melatonin (5 mg/kg) and LPS was administered in SD mice at day 2. Mice were divided into five groups as control, SD, LPS, LPS + SD, and LPS + SD + melatonin (each group, n = 11). Mice were killed on day 3 after treatment of melatonin and LPS for 24 hr. Lung tissues were collected for histological examination and protein analysis. The malondialdehyde (MDA) level was determined for the effect of oxidative stress. Melatonin restored weight loss in LPS + SD. Histological findings revealed alveolar damages with inflammatory cell infiltration in LPS + SD. Melatonin remarkably attenuated the alveolar damages. In western blot analysis, LPS reduced the levels of Bcl-XL and procaspase-3 in SD mice. After treatment with melatonin, the levels of Bcl-XL and procaspase-3 increased when compared with LPS + SD. LPS treatment showed an increase of TUNEL-positive cells, whereas melatonin prevented the increase of cell death in LPS + SD animals. In lipid peroxidation assay, melatonin significantly reduced the elevated MDA level in LPS + SD. Our results suggest that melatonin attenuates acute lung inflammation during SD via anti-apoptotic and anti-oxidative actions.

PHARMACOLOGICAL TREATMENTS FOR TINNITUS: NEW AND OLD

Subjective tinnitus, the phantom ringing or buzzing sensation that occurs in the absence of sound, affects 12-14% of adults; in some cases the tinnitus is so severe or disabling that patients seek medical treatment. However, although the economic and emotional impact of tinnitus is large, there are currently no FDA-approved drugs to treat this condition. Clinical trials are now underway to evaluate the efficacy of N-methyl-d-aspartate (NMDA) and dopamine D(2) antagonists, selective serotonin reuptake inhibitors (SSRIs), γ-aminobutyric acid (GABA) agonists and zinc dietary supplements. Previous off-label clinical studies, while not definitive, suggest that patients with severe depression may experience improvement in their tinnitus after treatment with antidepressants such as nortriptyline or sertraline. A small subpopulation of patients with what has been described as "typewriter tinnitus" have been shown to gain significant relief from the anticonvulsant carbamazepine. Preliminary studies with misoprostol, a synthetic prostaglandin E1 analogue, and sulpiride, a dopamine D(2) antagonist, have shown promise. Animal behavioral studies suggest that GABA transaminase inhibitors and potassium channel modulators can suppress tinnitus. Additionally, improvements in tinnitus have also been noted in patients taking melatonin for significant sleep disturbances. Like other complex neurological disorders, one drug is unlikely to resolve tinnitus in all patients; therapies targeting specific subgroups are likely to yield the greatest success.

Melatonin induces cell cycle arrest and apoptosis in hepatocarcinoma HepG2 cell line

Melatonin reduces proliferation in many different cancer cell lines. However, studies on the oncostatic effects of melatonin in the treatment of hepatocarcinoma are limited. In this study, we examined the effect of melatonin administration on HepG2 human hepatocarcinoma cells, analyzing cell cycle arrest, apoptosis and mitogen-activated protein kinase (MAPK) signalling pathways. Melatonin was dissolved in the cell culture media in 0.2% dimethyl sulfoxide and administered at different concentrations for 2, 4, 6, 8 and 10 days. Melatonin at concentrations 1000-10,000 microM caused a dose- and time-dependent reduction in cell number. Furthermore, melatonin treatment induced apoptosis with increased caspase-3 activity and poly(ADP-ribose) polymerase proteolysis. Proapoptotic effects of melatonin were related to cytosolic cytochrome c release, upregulation of Bax and induction of caspase-9 activity. Melatonin treatment also resulted in increased caspase-8 activity, although no significant change was observed in Fas-L expression. In addition, JNK 1,-2 and -3 and p38, members of the MAPK family, were upregulated by melatonin treatment. Growth inhibition by melatonin altered the percentage or cells in G0-G1 and G2/M phases indicating cell cycle arrest in the G2/M phase. The reduced cell proliferation and alterations of cell cycle were coincident with a significant increase in the expression of p53 and p21 proteins. These novel findings show that melatonin, by inducing cell death and cell cycle arrest, might be useful as adjuvant in hepatocarcinoma therapy.

Can disturbances in the atmospheric electric field created by powerline corona ions disrupt melatonin production in the pineal gland?

Recent epidemiological studies have reported an increased risk of leukemia in adults and children near overhead high voltage powerlines at distances beyond the measured range of the direct electric and magnetic fields. Corona ions are emitted by powerlines, forming a plume that is carried away from the line by the wind. The plume generates highly variable disturbances in the atmospheric electric field of tens to a few hundred V/m on time scales from seconds to minutes. Such disturbances can be seen up to several hundred meters from powerlines. It is hypothesized that these random disturbances result in the disruption of nocturnal melatonin synthesis and related circadian rhythms, in turn leading to increased risk of a number of adverse health effects including leukemia. In support of the hypothesis, it is noted that melatonin is highly protective of oxidative damage to the human hemopoietic system. A review of electric field studies provides evidence that (i) diurnal variation in the natural atmospheric electric field may itself act as a weak Zeitgeber; (ii) melatonin disruption by electric fields occurs in rats; (iii) in humans, disturbances in circadian rhythms have been observed with artificial fields as low at 2.5 V/m. Specific suggestions are made to test the aspects of the hypothesis.

Cytoprotective effects of melatonin on C6 astroglial cells exposed to glutamate excitotoxicity and oxidative stress

To preserve the central nervous system (CNS) function after a traumatic injury, therapeutic agents must be administered to protect neurons as well as glial cells. Cell death in CNS injuries and diseases are attributed to many factors including glutamate toxicity and oxidative stress. We examined whether melatonin, a potent anti-oxidant and free radical scavenger, would attenuate apoptotic death of rat C6 astroglial cells under glutamate excitotoxicity and oxidative stress. Exposure of C6 cells to 500 microM L-glutamic acid (LGA) and 100 microm hydrogen peroxide (H(2)O(2)) for 24 hr caused significant increases in apoptosis. Apoptosis was evaluated by Wright staining and ApopTag assay. Melatonin receptor 1 appeared to be involved in the protection of these cells from excitotoxic and oxidative damage. Cells undergoing excitotoxic and oxidative stress for 15 min were then treated with 150 nM melatonin, which prevented Ca(2+)influx and cell death. Western blot analyses showed alterations in Bax and Bcl-2 expression resulting in increased Bax:Bcl-2 ratio during apoptosis. Western blot analyses also showed increases in calpain and caspase-3 activities, which cleaved 270 kD alpha-spectrin at specific sites to generate 145 kD spectrin breakdown product (SBDP) and 120 kD SBDP, respectively. However, 15-min post-treatment of C6 cells with melatonin dramatically reduced Bax:Bcl-2 ratio and proteolytic activities, decreasing LGA or H(2)O(2)-induced apoptosis. Our data showed that melatonin prevented proteolysis and apoptosis in C6 astroglial cells. The results suggest that melatonin may be an effective cytoprotective agent against glutamate excitotoxicity and oxidative stress in CNS injuries and diseases.

Age-related alterations in Ca2+ signals and mitochondrial membrane potential in exocrine cells are prevented by melatonin

Information regarding age-induced Ca(2+) signal alterations in nonexcitable cells is limited. In addition, little evidence exists on the ability of melatonin to palliate the effects of aging on Ca(2+) signals and mitochondrial potential, a parameter involved in both Ca(2+) signaling and aging. We studied the ability of melatonin to prevent the effects of aging on intracellular Ca(2+) homeostasis and mitochondrial potential in exocrine cells. Pancreatic acinar cells were obtained from adult (3 months old) and aged (22-24 months old) mice by collagenase dispersion. Ca(2+) signals, in situ mitochondrial potential and in vitro amylase secretion were determined. Secretion in response to increasing levels of the secretagogues, acetylcholine and cholecystokinin (CCK), were impaired in aged pancreatic acini. This decrease was accompanied by an inhibition in the amplitude of the peak response to maximal concentrations of the agonists, and by a decrease in the pattern of Ca(2+) oscillations induced by postprandial levels of CCK. Both the size of the calcium pools, assessed by low levels of ionomycin, and capacitative calcium entry, induced by depletion of the stores with thapsigargin, were diminished in aged cells. These changes in Ca(2+) homeostasis were associated with depolarization of intracellular mitochondria. Oral administration of melatonin for 3 months to aged mice restored the secretory response, the amplitude and frequency of Ca(2+) responses, the size of intracellular calcium pools, the capacitative calcium entry, and the mitochondrial potential. In conclusion, melatonin restores secretory function, Ca(2+) signals and mitochondrial potential of aged exocrine cells.

Presowing seed treatment with melatonin protects red cabbage seedlings against toxic copper ion concentrations

One of the targets of modern plant physiology is to identify tools for improving seed germination and plant growth under unfavorable environmental conditions. Seeds of Brassica oleracea rubrum were pretreated with melatonin at concentrations: 1, 10, and 100 microM using a hydropriming method. Air-dried seeds of each experimental variants that were nonpretreated (control), hydroprimed (H) or hydroprimed with melatonin (HM1, HM10, and HM100) were germinated in darkness for 3 days at 25 degrees C. Young seedlings were then transferred to the light and grown for an additional 5 days. Both germination and growth tests were performed in water and in CuSO(4) water solutions in concentrations of 0.5 and 1 mM. H, HM1 and HM10 improved seed germination both in water and in the presence of Cu(2+). One or 10 microM melatonin eliminated the inhibitory effect of the 0.5 mM metal concentration on the fresh weight of seedlings. HM100 had a negative effect; thus seed germination was lower and seedlings had poor establishment. The toxic effect of Cu(2+) manifested by membrane peroxidation and DNA endoreplication blocking in the seedlings grown from nontreated (control) and H seeds was not observed in the seedlings grown from HM1 and HM10 seeds; in contrast, HM100 enhanced the toxic effect of Cu(2+).

Melatonin and ischemia-reperfusion injury of the brain

This review summarizes the reports that have documented the neuroprotective effects of melatonin against ischemia/reperfusion brain injury. The studies were carried out on several species, using models of acute focal or global cerebral ischemia under different treatment schedules. The neuroprotective actions of melatonin were observed during critical evolving periods for cell processes of immediate or delayed neuronal death and brain injury, early after the ischemia/reperfusion episode. Late neural phenomena accounting either for brain damage or neuronal repair, plasticity and functional recovery taking place after ischemia/reperfusion have been rarely examined for the protective actions of melatonin. Special attention has been paid to the advantageous characteristics of melatonin as a neuroprotective drug: bioavailability into brain cells and cellular organelles targeted by morpho-functional derangement; effectiveness in exerting several neuroprotective actions, which can be amplified and prolonged by its metabolites, through direct and indirect antioxidant activity; prevention and reversal of mitochondrial malfunction, reducing inflammation, derangement of cytoskeleton organization, and pro-apoptotic cell signaling; lack of interference with thrombolytic and neuroprotective actions of other drugs; and an adequate safety profile. Thus, the immediate results of melatonin actions in reducing infarct volume, necrotic and apoptotic neuronal death, neurologic deficits, and in increasing the number of surviving neurons, may improve brain tissue preservation. The potential use of melatonin as a neuroprotective drug in clinical trials aimed to improve the outcome of patients suffering acute focal or global cerebral ischemia should be seriously considered.

Consumption of vegetables alters morning urinary 6-sulfatoxymelatonin concentration

Melatonin, which is contained in certain vegetables, may have an influence on circulatory melatonin concentrations. This study examined the effects of the consumption of vegetables on 6-sulfatoxymelatonin concentrations in morning urine. Ninety-four healthy women aged 24-55 were recruited through a city public health center in Japan. The women randomly allocated to the intervention group were requested to consume high amounts of six selected vegetables, with a target of 350 g/day for 65 days, while those in the control group were asked to avoid the same six vegetables during the same period. First-void morning urine was collected before and at the end of the intervention period, and creatinine-adjusted 6-sulfatoxymelatonin concentrations were measured. At the end of the intervention period, daily mean intake of melatonin from the six vegetables was 1288.0 ng in the intervention group and 5.3 ng in the control group. In the intervention group, the mean concentration of 6-sulfatoxymelatonin changed from 48.1 [95% confidence interval (CI): 40.4-57.2] ng/mg creatinine to 49.6 (95% CI: 42.8-57.3) ng/mg creatinine across the intervention period. In the control group, the mean concentration of 6-sulfatoxymelatonin changed from 55.5 (95% CI: 48.7-63.2) ng/mg creatinine to 50.8 (95% CI: 44.0-58.7) ng/mg creatinine across the intervention period. A comparison of the two groups with regard to the changes in the 6-sulfatoxymelatonin concentrations across the intervention period showed a significant difference (P = 0.03). The results indicate that increased consumption of vegetables raises circulatory melatonin concentrations.

Day/night differences in stress-induced gastric lesions in rats with an intact pineal gland or after pinealectomy

The formation of acute gastric lesions depends upon the balance between the aggressive factors promoting mucosal damage and the natural defense mechanisms. Previous studies have shown that melatonin inhibits gastric acid secretion, enhances the release of gastrin, augments gastric blood flow (GBF), increases the cyclooxygenase-2 (COX-2)-prostaglandin (PG) system and scavenges free radicals, resulting in the prevention of stress-induced gastric lesions. Besides the pineal gland, melatonin is also generated in large amounts in the gastrointestinal tract and due to its antioxidant and anti-inflammatory properties; this indole might serve as local protective endogen preventing the development of acute gastric damage. The results of the present study indicate that stress-induced gastric lesions show circadian variations with an increase in the day time and a decline at night. These changes are inversely related to plasma melatonin levels. Following pinealectomy, stress-induced gastric mucosal lesions were more pronounced both during the day and at night, and were accompanied by markedly reduced plasma melatonin levels with a pronounced reduction in mucosal generation of prostaglandin E(2) (PGE(2)), GBF and increased free radical formation and by small rise in plasma melatonin during the dark phase. We conclude that stress-induced gastric ulcerations exhibit a circadian variation with an increase in the day and attenuation at night and that these fluctuations of gastric stress ulcerogenesis occur also after pinealectomy, depending upon the interaction of COX-PG and free radicals, probably mediated by the changes in local gastric melatonin.

Melatonin protects against endosulfan-induced oxidative tissue damage in rats

Endosulfan is a chlorinated cyclodiene insecticide which induces oxidative stress. In this study, we investigated the possible protective effect of melatonin, an antioxidant agent, against endosulfan (Endo)-induced toxicity in rats. Wistar albino rats (n = 8) were administered endosulfan (22 mg/kg/day orally) followed by either saline (Endo group) or melatonin (10 mg/kg/day, Endo + Mel group) for 5 days. In other rats, saline (control group) or melatonin (10 mg/kg/day, Mel group) was injected for 5 days, following corn oil administration (vehicle of endosulfan). Measurement of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity and collagen content were performed in liver and kidney. Furthermore, aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), and creatinine levels, lactate dehydrogenase (LDH) activity were measured in the serum samples, while tumor necrosis factor-alpha (TNF-alpha), interleukin-beta (IL-beta) and total antioxidant capacity (AOC) were assayed in plasma samples. Endosulfan administration caused a significant decrease in tissue GSH and plasma AOC, which was accompanied with significant rises in tissue MDA and collagen levels and MPO activity. Moreover, the proinflammatory mediators (TNF-alpha and IL-beta), LDH activity, AST, ALT, creatinine and BUN levels were significantly elevated in the endosulfan-treated rats. On the other hand, melatonin treatment reversed all these biochemical alterations induced by endosulfan. Our results suggest that oxidative mechanisms play an important role in endosulfan-induced tissue damage and melatonin, by inhibiting neutrophil infiltration, balancing oxidant-antioxidant status and regulating the generation of inflammatory mediators, ameliorates oxidative organ injury as a result of endosulfan toxicity.

Melatonin represses oxidative stress-induced activation of the MAP kinase and mTOR signaling pathways in H4IIE hepatoma cells through inhibition of Ras

Reactive oxygen species (ROS) have been implicated in the pathogenesis of a variety of diseases, and antioxidant treatment is currently being investigated as a potential therapy to attenuate the detrimental effects of ROS-mediated oxidative stress. Melatonin is a potent naturally produced antioxidant, which acts through various mechanisms to ameliorate the toxic effects of ROS. However, little is known about the mechanisms of signaling pathways through which melatonin acts to reverse the effects of ROS. In the present study, the effect of melatonin treatment on the hydrogen peroxide (H(2)O(2))-induced activation of the mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) signaling pathways was assessed in H4IIE hepatoma cells. It was found that melatonin strongly attenuated H(2)O(2)-induced activation of the ERK1/2 and p38 MAP kinases, as well as several of their downstream targets. Melatonin also attenuated the H(2)O(2)-induced phosphorylation of Akt and the Akt substrate mTOR, as well as a downstream target of mTOR action, 4E-BP1. Upregulation of ERK1/2, p38, and Akt signaling by H(2)O(2) was accompanied by activation of Ras, an effect that was blocked by melatonin. Overall, the results suggest that melatonin acts to prevent many of the H(2)O(2)-induced alterations in the MAPK and mTOR signaling pathways through inhibition of Ras, at least in H4IIE hepatoma cells.

Melatonin in relation to the "strong" and "weak" versions of the free radical theory of aging

That free radicals and the damage they inflict are related to deteriorative cellular and organismal changes associated with aging and also with the development of a variety of age-related diseases is widely debated. There seems to be little doubt that free radical mutilation of essential molecules contributes to these conditions. Numerous investigators, on the basis of their experimental results, have drawn this conclusion. If the free radical theory of aging and disease development has validity, antioxidants could presumably be successfully used to delay the molecular destruction, cellular loss, and organismal death. In the current review we summarize the experimental data related to the utility of melatonin in protecting against reactive oxygen and reactive nitrogen species-induced cellular damage. While the data supporting a role for melatonin in forestalling aging and prolonging life span per se is not compelling, the findings related to melatonin's ability to reduce the severity of a variety of age-related diseases that have as their basis free radical damage is convincing. To date, the bulk of these investigations have been performed in experimental models of diseases in animals. It is now imperative that similar studies be conducted using humans whose quality of life may benefit from treatment with melatonin.