Melatonin inhibits arsenite-induced peripheral neurotoxicity

Melatonin regulates endoplasmic reticulum stress in diverse pathophysiological contexts: A comprehensive mechanistic review

The endoplasmic reticulum (ER) is crucial for protein quality control, and disruptions in its function can lead to various diseases. ER stress triggers an adaptive response called the unfolded protein response (UPR), which can either restore cellular homeostasis or induce cell death. Melatonin, a safe and multifunctional compound, shows promise in controlling ER stress and could be a valuable therapeutic agent for managing the UPR. By regulating ER and mitochondrial functions, melatonin helps maintain cellular homeostasis via reduction of oxidative stress, inflammation, and apoptosis. Melatonin can directly or indirectly interfere with ER-associated sensors and downstream targets of the UPR, impacting cell death, autophagy, inflammation, molecular repair, among others. Crucially, this review explores the mechanistic role of melatonin on ER stress in various diseases including liver damage, neurodegeneration, reproductive disorders, pulmonary disease, cardiomyopathy, insulin resistance, renal dysfunction, and cancer. Interestingly, while it alleviates the burden of ER stress in most pathological contexts, it can paradoxically stimulate ER stress in cancer cells, highlighting its intricate involvement in cellular homeostasis. With numerous successful studies using in vivo and in vitro models, the continuation of clinical trials is imperative to fully explore melatonin's therapeutic potential in these conditions.

The protective effect of natural or chemical compounds against arsenic-induced neurotoxicity: Cellular and molecular mechanisms

Arsenic is a notorious metalloid that exists in the earth's crust and is considered toxic for humans and the environment. Both cancerous and non-cancerous complications are possible after arsenic exposure. Target organs include the liver, lungs, kidney, heart, and brain. Arsenic-induced neurotoxicity, the main focus of our study, can occur in central and peripheral nervous systems. Symptoms can develop in a few hours, weeks, or years depending on the quantity of arsenic and the duration of exposure. In this review, we aimed to gather all the compounds, natural and chemical, that have been studied as protective agents in cellular, animal, and human reports. Oxidative stress, apoptosis, and inflammation are frequently described as destructive mechanisms in heavy metal toxicity. Moreover, reduced activity of acetylcholinesterase, the altered release of monoamine neurotransmitters, down-regulation of N-methyl-D-aspartate receptors, and decreased brain-derived neurotrophic factor are important underlying mechanisms of arsenic-induced neurotoxicity. As for neuroprotection, though some compounds have yet limited data, there are others, such as curcumin, resveratrol, taurine, or melatonin which have been studied more deeply and might be closer to a reliable protective agent. We collected the available information on all protective agents and the mechanisms by which they fight against arsenic-induced neurotoxicity.

Cytotoxicity of Acrylic Resins, Particulate Filler Composite Resin and Thermoplastic Material in Artificial Saliva with and without Melatonin

There is limited information on the effect of melatonin on the cytotoxicity of dental materials. The study evaluated the cytotoxic effects of heat- and auto-polymerized acrylic resin, particulate filler composite resin and a thermoplastic material on L-929 fibroblast cell viability at different incubation periods in artificial saliva without and with melatonin. Disk-shaped specimens were prepared according to each manufacturer’s instructions and divided into two groups to be stored either in artificial saliva (AS) and AS with melatonin (ASM). The measurements were performed using an MTT (3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyl tetrazoliumbromide) assay, in which the L-929 mouse fibroblasts cell culture was used. For the MTT test, extracts were examined at 1, 24, 72 h and 1 and 2 weeks. Data were analyzed using 3-way ANOVA and Tukey’s tests. No significant difference was found between groups AS and ASM (F = 0.796; p = 0.373). Incubation period significantly affected all materials tested (p < 0.001). Storing resin-based materials in artificial saliva with melatonin solution for 24 h may reduce cytotoxic effects on the fibroblast cells for which the highest effect was observed. Soaking resin prosthesis or orthodontic appliances in artificial saliva with melatonin at least 24 h before intraoral use or rinsing medium containing melatonin may be recommended for decreasing the cytotoxicity of dental resin materials.

Molecular Evidence of the Inhibitory Potential of Melatonin against NaAsO2-Induced Aging in Male Rats

Arsenic (As) poisoning is widespread due to exposure to pollution. The toxic level of (As) causes oxidative stress-induced aging and tissue damage. Since melatonin (MLT) has anti-oxidant and anti-aging properties, we aimed to evaluate the protective effect of MLT against the toxicity of sodium arsenite (NaAsO₂). Healthy male NMRI mice were divided into eight different groups. The control group received a standard regular diet. Other groups were treated with varying diets, including MLT alone, NaAsO₂, and NaAsO₂ plus MLT. After one month of treatment, biochemical and pathological tests were performed on blood, heart, and lung tissue samples. NaAsO₂ increased the levels of TNF-α, 8-hydroxy-2-deoxy guanosine (8OHdG), malondialdehyde (MDA), reactive oxygen species (ROS), and high mobility group box 1 (HMGB1), increased the expression of TNF receptor type 1-associated death domain (TRADD) mRNA and telomerase reverse transcriptase, and decreased the expression of Klotho (KL) mRNA in both plasma and tissues. In contrast, MLT reduced MDA, ROS, HMGB1, lactate, and TNF-α enhanced the mRNA expression of KL, and suppressed the mRNA expression of the TERT and TRADD genes. Thus, MLT confers potent protection against NaAsO₂- induced tissue injury and oxidative stress.

Role and Therapeutic Potential of Melatonin in the Central Nervous System and Cancers

Melatonin (MLT) is a powerful chronobiotic hormone that controls a multitude of circadian rhythms at several levels and, in recent times, has garnered considerable attention both from academia and industry. In several studies, MLT has been discussed as a potent neuroprotectant, anti-apoptotic, anti-inflammatory, and antioxidative agent with no serious undesired side effects. These characteristics raise hopes that it could be used in humans for central nervous system (CNS)-related disorders. MLT is mainly secreted in the mammalian pineal gland during the dark phase, and it is associated with circadian rhythms. However, the production of MLT is not only restricted to the pineal gland; it also occurs in the retina, Harderian glands, gut, ovary, testes, bone marrow, and lens. Although most studies are limited to investigating the role of MLT in the CNS and related disorders, we explored a considerable amount of the existing literature. The objectives of this comprehensive review were to evaluate the impact of MLT on the CNS from the published literature, specifically to address the biological functions and potential mechanism of action of MLT in the CNS. We document the effectiveness of MLT in various animal models of brain injury and its curative effects in humans. Furthermore, this review discusses the synthesis, biology, function, and role of MLT in brain damage, and as a neuroprotective, antioxidative, anti-inflammatory, and anticancer agent through a collection of experimental evidence. Finally, it focuses on the effect of MLT on several neurological diseases, particularly CNS-related injuries.

Identification of potential target genes of ROR-alpha in THP1 and HUVEC cell lines

ROR-alpha is a nuclear receptor, activity of which can be modulated by natural or synthetic ligands. Due to its possible involvement in, and potential therapeutic target for atherosclerosis, we aimed to identify ROR-alpha target genes in monocytic and endothelial cell lines. We performed chromatin immunoprecipitation (ChIP) followed by tiling array (ChIP-on-chip) for ROR-alpha in monocytic cell line THP1 and endothelial cell line HUVEC. Following bioinformatic analysis of the array data, we tested four candidate genes in terms of dependence of their expression level on ligand-mediated ROR-alpha activity, and two of them in terms of promoter occupancy by ROR-alpha. Bioinformatic analyses of ChIP-on-chip data suggested that ROR-alpha binds to genomic regions near the transcription start site (TSS) of more than 3000 genes in THP1 and HUVEC. Potential ROR-alpha target genes in both cell types seem to be involved mainly in membrane receptor activity, signal transduction and ion transport. While SPP1 and IKBKA were shown to be direct target genes of ROR-alpha in THP1 monocytes, inflammation related gene HMOX1 and heat shock protein gene HSPA8 were shown to be potential target genes of ROR-alpha. Our results suggest that ROR-alpha may regulate signaling receptor activity, and transmembrane transport activity through its potential target genes. ROR-alpha seems also to play role in cellular sensitivity to environmental substances like arsenite and chloroprene. Although, the expression analyses have shown that synthetic ROR-alpha ligands can modulate some of potential ROR-alpha target genes, functional significance of ligand-dependent modulation of gene expression needs to be confirmed with further analyses.

Role of melatonin in mitigating nonylphenol-induced toxicity in frontal cortex and hippocampus of rat brain

Nonylphenol (NP), an environmental endocrine disruptor mimics estrogen and is a potential toxicant both under in vitro and in vivo conditions. In this study, the effect of melatonin on NP- induced neurotoxicity and cognitive alteration was investigated in adult male Wistar rats. Melatonin supplementation has been known to protect cells from neurotoxic injury. The animals were divided into three groups namely, control (vehicle) which received olive oil orally and treated rats received NP (25 mg/kg, per os) thrice a week for 45 days while the third group i.e., NP + melatonin, animals were co-administered melatonin (10 mg/kg, i.p.) along with NP. On the 46th day, rats were assessed for anxiety, motor co-ordination, grip strength and cognitive performance using Morris water maze test and then sacrificed for biochemical and histopathological assays in brain tissues. Melatonin improved the behavioral performance in NP exposed group. The results showed that NP significantly decreased the activity of acetylcholine esterase (AchE), monoamine oxidase (MAO) and Na⁺/K⁺-ATPase, in rat brain tissue along with other enzymes of antioxidant milieu. The outcome of the study shows that NP, like other persistent endocrine disrupting pollutants, creates a potential risk of cognitive, neurochemical and histopathological perturbations as a result of environmental exposure. Taken together, our study demonstrates that melatonin is protective against NP-induced neurotoxicity.

Snapshot: implications for melatonin in endoplasmic reticulum homeostasis

The endoplasmic reticulum (ER) is an important intracellular membranous organelle. Previous studies have demonstrated that the ER is responsible for protein folding and trafficking, lipid synthesis and the maintenance of calcium homeostasis. Interestingly, the morphology and structure of the ER were recently found to be important. Melatonin is a hormone that anticipates the daily onset of darkness in mammals, and it is well known that melatonin acts as an antioxidant by scavenging free radicals and increasing the activity of antioxidant enzymes in the body. Notably, the existing evidence demonstrates that melatonin is involved in ER homeostasis, particularly in the morphology of the ER, indicating a potential protective role of melatonin. This review discusses the existing knowledge regarding the implications for the involvement of melatonin in ER homeostasis.

Melatonin Protects SH-SY5Y Neuronal Cells Against Methamphetamine-Induced Endoplasmic Reticulum Stress and Apoptotic Cell Death

Methamphetamine (METH), a psychostimulant with highly neurotoxic effects, has been known to induce neuronal apoptosis in part through an endoplasmic reticulum (ER) stress pathway. Melatonin is an endogenous antioxidant compound that exerts protective effects against several neurodegenerative conditions, including METH-induced neurotoxicity, via various mechanisms. However, the role of melatonin in ER stress is still relatively unclear. In the present study, we investigated ER stress and neuronal apoptosis following METH treatment and the role of melatonin in METH-mediated ER stress-induced cell death in the SH-SY5Y neuroblastoma cell line. We found that METH caused the overexpression of ER stress-related genes, including C/EBP homologous protein and spliced X-box binding protein 1, in dose- and time-dependent manners. Moreover, METH time-dependently activated caspase-12 and -3, leading to cellular apoptosis. Furthermore, we demonstrated that pretreatment with melatonin attenuated the overexpression of ER stress-related genes and the cleavages of caspase-12 and -3 caused by METH exposure. Flow cytometry revealed that METH-mediated neuronal apoptosis was also prevented by melatonin. These findings suggest the protective effects of melatonin against ER stress and apoptosis caused by METH and other harmful agents.

Melatonin set out to ER stress signaling thwarts epithelial mesenchymal transition and peritoneal dissemination via calpain-mediated C/EBPβ and NFκB cleavage

Peritoneal dissemination of tumor has high mortality and is associated with the loss of epithelial features, acquisition of motile mesenchymal morphology characteristics, and invasive properties by tumor cells. Melatonin is an endogenously produced molecule in all plant species that is known to exert antitumor activity, but to date, its underlying mechanisms and antiperitoneal metastasis efficacy is not well defined. This study determined the antiperitoneal dissemination potential of melatonin in vivo and assessed its association with the inhibition of epithelial-to-mesenchymal transition (EMT) signaling mechanism by endoplasmic reticulum (ER) stress, which may be a major molecular mechanism of melatonin against cancer. The results demonstrate that melatonin inhibited peritoneal metastasis in vivo and activated ER stress in Cignal ERSE Reporter Assay, organelle structure in transmission electron microscopy images, calpain activity, and protein biomarkers like p-elf2α. Moreover, the overexpression of transcription factor C/EBPβ in gastric cancer interacted with NFκB and further regulates COX-2 expression. These were dissociated and downregulated by melatonin, as proven by immunofluorescence imaging, immunoprecipitation, EMSA, and ChIP assay. Melatonin or gene silencing of C/EBPβ decreased the EMT protein markers (E-cadherin, Snail, and Slug) and Wnt/beta-catenin activity by Topflash activity, and increased ER stress markers. In an animal study, the results of melatonin therapy were consistent with those of in vitro findings and attenuated systemic proangiogenesis factor production. In conclusion, C/EBPβ and NFκB inhibition by melatonin may impede both gastric tumor growth and peritoneal dissemination by inducing ER stress and inhibiting EMT.

Melatonin and endoplasmic reticulum stress: relation to autophagy and apoptosis

Endoplasmic reticulum (ER) is a dynamic organelle that participates in a number of cellular functions by controlling lipid metabolism, calcium stores, and proteostasis. Under stressful situations, the ER environment is compromised, and protein maturation is impaired; this causes misfolded proteins to accumulate and a characteristic stress response named unfolded protein response (UPR). UPR protects cells from stress and contributes to cellular homeostasis re-establishment; however, during prolonged ER stress, UPR activation promotes cell death. ER stressors can modulate autophagy which in turn, depending of the situation, induces cell survival or death. Interactions of different autophagy- and apoptosis-related proteins and also common signaling pathways have been found, suggesting an interplay between these cellular processes, although their dynamic features are still unknown. A number of pathologies including metabolic, neurodegenerative and cardiovascular diseases, cancer, inflammation, and viral infections are associated with ER stress, leading to a growing interest in targeting components of the UPR as a therapeutic strategy. Melatonin has a variety of antioxidant, anti-inflammatory, and antitumor effects. As such, it modulates apoptosis and autophagy in cancer cells, neurodegeneration and the development of liver diseases as well as other pathologies. Here, we review the effects of melatonin on the main ER stress mechanisms, focusing on its ability to regulate the autophagic and apoptotic processes. As the number of studies that have analyzed ER stress modulation by this indole remains limited, further research is necessary for a better understanding of the crosstalk between ER stress, autophagy, and apoptosis and to clearly delineate the mechanisms by which melatonin modulates these responses.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Elevated serum dopamine increases while coffee consumption decreases the occurrence of reddish streaks in the intact stomach

BACKGROUND AND AIM

Reddish streaks in an intact stomach are an endoscopic feature of duodenogastric reflux. This study aimed to identify which factors are associated with gastric reddish streaks and thus help prevent mucosal damage from duodenogastric reflux.

METHODS

Demographic data, personal habits, stressful life events, and psychological distress were compared between subjects with only gastric reddish streaks and those with normal mucosa who underwent upper gastrointestinal endoscopy as part of a self-paid physical checkup. Stress hormones dopamine and cortisol were also checked by high-performance liquid chromatography and radioimmunoassay methods respectively.

RESULTS

There were 95 subjects with gastric reddish streaks and 52 subjects with normal mucosa. No significant differences in age, gender, blood groups, education levels, marital status, religion, aspirin or nonsteroidal anti-inflammatory drug (NSAID) use, smoking habit, alcohol consumption, and intake of tea was found between the two groups, but intake of coffee was borderline more common in subjects with normal mucosa (38.5% vs 22.1%, P = 0.055). Subjects with gastric reddish streaks had lower Helicobacter pylori infection rate (37.8% vs 19.3%, P < 0.05). There were no significant differences in psychological distress and stressful life events between the two groups. Multivariate analysis shows that serum dopamine concentrations (odds ratio = 11.31, 95% confidence interval = 2.11-60.48, P = 0.005) and being without the consumption of coffee (odds ratio = 2.97, 95% confidence interval = 1.27-6.94, P = 0.012) were associated with gastric reddish streaks.

CONCLUSIONS

Elevated serum dopamine and less coffee consumption are associated with gastric reddish streaks. These findings implicate that increased dopamine level plays a role for abnormal duodenogastric reflux.

Melatonin and oral cavity

While initially the oral cavity was considered to be mainly a source of various bacteria, their toxins and antigens, recent studies showed that it may also be a location of oxidative stress and periodontal inflammation. Accordingly, this paper focuses on the involvement of melatonin in oxidative stress diseases of oral cavity as well as on potential therapeutic implications of melatonin in dental disorders. Melatonin has immunomodulatory and antioxidant activities, stimulates the proliferation of collagen and osseous tissue, and acts as a protector against cellular degeneration associated with aging and toxin exposure. Arising out of its antioxidant actions, melatonin protects against inflammatory processes and cellular damage caused by the toxic derivates of oxygen. As a result of these actions, melatonin may be useful as a coadjuvant in the treatment of certain conditions of the oral cavity. However, the most important effect of melatonin seems to result from its potent antioxidant, immunomodulatory, protective, and anticancer properties. Thus, melatonin could be used therapeutically for instance, locally, in the oral cavity damage of mechanical, bacterial, fungal, or viral origin, in postsurgical wounds caused by tooth extractions and other oral surgeries. Additionally, it can help bone formation in various autoimmunological disorders such as Sjorgen syndrome, in periodontal diseases, in toxic effects of dental materials, in dental implants, and in oral cancers.

Ascorbic acid protects against cadmium-induced endoplasmic reticulum stress and germ cell apoptosis in testes

Cadmium (Cd) is a testicular toxicant which induces endoplasmic reticulum (ER) stress and germ cell apoptosis in testes. This study investigated the effects of ascorbic acid on Cd-evoked ER stress and germ cell apoptosis in testes. Male mice were intraperitoneally injected with CdCl(2) (2.0 mg/kg). As expected, a single dose of Cd induced testicular germ cell apoptosis. Interestingly, Cd-triggered testicular germ cell apoptosis was almost completely inhibited in mice treated with ascorbic acid. Interestingly, ascorbic acid significantly attenuated Cd-induced upregulation of GRP78 in testes. In addition, ascorbic acid significantly attenuated Cd-triggered testicular IRE1α and eIF2α phosphorylation and XBP-1 activation, indicating that this antioxidant counteracts Cd-induced unfolded protein response (UPR) in testes. Finally, ascorbic acid significantly attenuated Cd-evoked upregulation of CHOP and JNK phosphorylation, two components in ER stress-mediated apoptotic pathway. In conclusion, ascorbic acid protects mice from Cd-triggered germ cell apoptosis via inhibiting ER stress and UPR in testes.

Melatonin alleviates cadmium-induced cellular stress and germ cell apoptosis in testes

Increasing evidence demonstrates that melatonin has an anti-apoptotic effect in somatic cells. However, whether melatonin can protect against germ cell apoptosis remains obscure. Cadmium (Cd) is a testicular toxicant and induces germ cell apoptosis. In this study, we investigated the effects of melatonin on Cd-evoked germ cell apoptosis in testes. Male ICR mice were intraperitoneally (i.p.) injected with melatonin (5 mg/kg) every 8 hr, beginning at 8 hr before CdCl(2) (2.0 mg/kg, i.p.). As expected, acute Cd exposure resulted in germ cell apoptosis in testes, as determined by terminal dUTP nick-end labeling (TUNEL) staining. Melatonin significantly alleviated Cd-induced testicular germ cell apoptosis. An additional experiment showed that spliced form of XBP-1, the target of the IRE-1 pathway, was significantly increased in testes of mice injected with CdCl(2). GRP78, an endoplasmic reticulum (ER) chaperone, and CHOP, a downstream target of the PERK pathway, were upregulated in testes of Cd-treated mice. In addition, acute Cd exposure significantly increased testicular eIF2α and JNK phosphorylation, indicating that the unfolded protein response (UPR) pathway was activated by CdCl(2). Interestingly, melatonin almost completely inhibited Cd-induced ER stress and the UPR in testes. In addition, melatonin obviously attenuated Cd-induced heme oxygenase (HO)-1 expression and protein nitration in testes. Taken together, these results suggest that melatonin alleviates Cd-induced cellular stress and germ cell apoptosis in testes. Melatonin may be useful as pharmacological agents to protect against Cd-induced testicular toxicity.

Perspectives on the use of melatonin to reduce cytotoxic and genotoxic effects of methacrylate-based dental materials

Melatonin (5-methoxy-N-acetyltryptamine), an indoleamine produced in the pineal gland and many other organs, displays a wide spectrum of protective effects against cell injury of various origins. Contemporary dental restorative materials mainly consist of methacrylate polymers with some additives. However, because of the incompleteness of polymerization process in situ as well as mechanical shearing and enzymatic degradation, methacrylate monomers are released from the restoration into the oral cavity and the pulp, from where they gain access to other tissues and organs. Such monomers have displayed toxic properties in many in vivo and in vitro studies, including cytotoxicity and genotoxicity and a considerable portion of these effects is underlined by the oxidative action of these compounds. As melatonin shows biocompatibility with the oral cavity and displays antioxidative properties, it may be considered as a protective agent against harmful effects of methacrylate monomers derived from dental restorations. Melatonin decreases cytotoxic and genotoxic effects of methacrylate monomers used in dentistry, and it does not influence the bond strength of dental composites. This opens a new possible application of melatonin to improve properties of biomaterials used in dentistry.

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 provides neuroprotection by reducing oxidative stress and HSP70 expression during chronic cerebral hypoperfusion in ovariectomized rats

Oxidative stress is believed to contribute to functional and histopathologic disturbances associated with chronic cerebral hypoperfusion (CCH) in rats. Melatonin has protective effects against cerebral ischemia/reperfusion injury. This effect has mainly been attributed to its antioxidant properties. In the present study, we evaluate the effects of melatonin on chronic cerebral hypoperfused rats and examined its possible influence on oxidative stress, superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels, and heat shock protein (HSP) 70 induction. CCH was induced by permanent bilateral common carotid artery occlusion in ovariectomized female rats. Extensive neuronal loss in the hippocampus at day 14 following CCH was observed. The ischemic changes were preceded by increases in malondialdehyde (MDA) concentration and HSP70 induction as well as reductions in GSH and SOD. Melatonin treatment restored the levels of MDA, SOD, GSH, and HSP70 induction as compared to the ischemic group. Histopathologic analysis confirmed the protective effect of melatonin against CCH-induced morphologic alterations. Taken together, our results document that melatonin provides neuroprotective effects in CCH by attenuating oxidative stress and stress protein expression in neurons. This suggests melatonin may be helpful for the treatment of vascular dementia and cerebrovascular insufficiency.