Neuroprotection by melatonin from glutamate-induced excitotoxicity during development of the cerebellum in the chick embryo

The Therapeutic Trip of Melatonin Eye Drops: From the Ocular Surface to the Retina

Melatonin is a ubiquitous molecule found in living organisms, ranging from bacteria to plants and mammals. It possesses various properties, partly due to its robust antioxidant nature and partly owed to its specific interaction with melatonin receptors present in almost all tissues. Melatonin regulates different physiological functions and contributes to the homeostasis of the entire organism. In the human eye, a small amount of melatonin is also present, produced by cells in the anterior segment and the posterior pole, including the retina. In the eye, melatonin may provide antioxidant protection along with regulating physiological functions of ocular tissues, including intraocular pressure (IOP). Therefore, it is conceivable that the exogenous topical administration of sufficiently high amounts of melatonin to the eye could be beneficial in several instances: for the treatment of eye pathologies like glaucoma, due to the IOP-lowering and neuroprotection effects of melatonin; for the prevention of other dysfunctions, such as dry eye and refractive defects (cataract and myopia) mainly due to its antioxidant properties; for diabetic retinopathy due to its metabolic influence and neuroprotective effects; for macular degeneration due to the antioxidant and neuroprotective properties; and for uveitis, mostly owing to anti-inflammatory and immunomodulatory properties. This paper reviews the scientific evidence supporting the use of melatonin in different ocular districts. Moreover, it provides data suggesting that the topical administration of melatonin as eye drops is a real possibility, utilizing nanotechnological formulations that could improve its solubility and permeation through the eye. This way, its distribution and concentration in different ocular tissues may support its pleiotropic therapeutic effects.

The possible protective role of melatonin versus garlic on monosodium Glutamate-induced changes in rat cerebellar cortex: histological, immunohistochemical and electron microscope study

Monosodium glutamate (MSG) is widely used as a flavor enhancer. Melatonin and garlic are well known as antioxidant. The present study was performed to evaluate the microscopic changes in the cerebellar cortex of rats after the administration of MSG and the possible protective effect of melatonin versus garlic on those changes. The rats were divided into four main groups. Group I (control group). Group II received MSG (4 mg/ g/day). Group III received MSG+ melatonin (10 mg/kg bw/day). Group IV received MSG+garlic (300 mg/kg bw/day). Immunohistochemical staining for glial fibrillary acidic protein (GFAP) was done as a marker for astrocyte demonstration. Morphometric study was done to assess the mean number and diameter of Purkinje cells, the number of astrocytes and the percentage area of positive GFAP immune stain. MSG group demonstrated congested blood vessels, vacuolations in the molecular layer, and Purkinje cells appeared irregular with nuclear degeneration. Granule cells appeared shrunken with darkly stained nuclei. The immunohistochemical stain for GFAP was less than expected in the three layers of the cerebellar cortex. Purkinje cells and granule cells appeared irregular in shape with dark small heterochromatic nuclei. The myelinated nerve fibers showed splitting and loss of the lamellar structure of their myelin sheath. Melatonin group showed that the cerebellar cortex was nearly similar to that of control group. Garlic treated group showed partial improvement. In conclusion, melatonin and garlic could partially protect against MSG induced changes and the protective effect of melatonin was better than garlic.

Investigation of the Effects of Monosodium Glutamate on the Embryonic Development of the Eye in Chickens

MSG is the most ubiquitous food additive in the food industry. The aim of this report was to investigate the effects of in ovo MSG administration on embryonic chicken eye development using histological and histometric methods. A total of 410 fertilized eggs obtained from Babcock Brown laying hens (Gallus gallus domesticus) were used and divided into 5 groups: I (untreated control), II (vehicle control), III (0.12 mg/g egg MSG), IV (0.6 mg/g egg MSG), and V (1.2 mg/g egg MSG), and injections were performed via the egg yolk. At incubation day 15, 18, and 21, 6 embryos from each group were sacrificed by decapitation and pieces of eye tissue were obtained. In all MSG groups, it was determined that both corneal epithelium thickness and total corneal thickness decreased at incubation time points 15, 18, and 21 days compared with the controls (p < 0.05). The total retinal thickness, thickness of the outer nuclear layer (ONL), inner nuclear layer (INL), ganglion cell layer (GL), and nerve fibre layers (NFL), as well as the number of ganglion cells decreased significantly at incubation days 15, 18, and 21 (p < 0.05), and degenerative changes such as vacuolar degeneration and retinal pigment epithelial detachment were also observed. In conclusion, MSG in ovo administration can affect the cornea and distinct layers of retinal cells.

Determining the effects of in ovo administration of monosodium glutamate on the embryonic development of brain in chickens

Monosodium glutamate (MSG) is a popular flavor enhancer largely used in the food industry. Although numerous studies have reported the neurotoxic effects of MSG on humans and animals, there is limited information about how it affects embryonic brain development. Thus, this study aimed to determine the effects of in ovo administered MSG on embryonic brain development in chickens. For this purpose, 410 fertilized chicken eggs were divided into 5 groups as control, distilled water, 0.12, 0.6 and 1.2 mg/g egg MSG, and injections were performed via the egg yolk. On days 15, 18, and 21 of the incubation period, brain tissue samples were taken from all embryos and chicks. The mortality rates of MSG-treated groups were significantly higher than those of the control and distilled water groups. The MSG-treated groups showed embryonic growth retardation and various structural abnormalities such as abdominal hernia, unilateral anophthalmia, hemorrhage, brain malformation, and the curling of legs and fingers. The relative embryo and body weights of the MSG-treated groups were significantly lower than those of the control group on incubation days 18 and 21. Histopathological evaluations revealed that MSG caused histopathological changes such as necrosis, neuronophagia, and gliosis in brain on incubation days 15, 18, and 21. There was a significant increase in the number of necrotic neurons in the MSG-treated groups compared to the control and distilled water groups in the hyperpallium, optic tectum and hippocampus regions. Proliferating cell nuclear antigen (PCNA) positive cells in brain were found in the hyperpallium, optic tectum, and hippocampus regions; there were more PCNA(+) immunoreactive cells in MSG-treated groups than in control and distilled water groups. In conclusion, it was determined that in ovo MSG administered could adversely affect embryonic growth and development in addition to causing necrosis in the neurons in the developing brain.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

Melatonin Blocks Morphine-Induced Place Preference: Involvement of GLT-1, NF-κB, BDNF, and CREB in the Nucleus Accumbens

Opioid addiction remains a widespread issue despite continuous attempts by the FDA to help maintain abstinence. Melatonin is a neurohormone considered to be involved only in the neuroendocrine and reproductive systems; however, recent reports have demonstrated its potential to attenuate drug addiction and dependence. Cumulative studies have suggested that melatonin can attenuate the rewarding effects of several drugs of abuse, including opioids. This study aimed to investigate the effect of melatonin (50 mg/kg) on morphine (5 mg/kg) to produce place preference. We also investigated the effect of melatonin and morphine on the expression of GLT-1, BDNF, NF-κB, and CREB within the nucleus accumbens. Male Wistar rats were divided into control, morphine, melatonin, and the morphine + melatonin groups. The study involved a two-phase habituation phase from day 1 to day 3 and an acquisition phase from day 5 to day 14. The conditioned place preference (CPP) score, distance traveled, resting time, ambulatory count, and total activity count were measured for all animals. Rats that received morphine showed a significant increase in CPP score compared to those in the control group. Morphine treatment reduced the mRNA expression of GLT-1, BDNF, and CREB and increased that of NF-κB. However, melatonin treatment administered 30 min before morphine treatment attenuated morphine place preference and reversed GLT-1, BDNF, NF-κB, and CREB expression levels. In conclusion, the study results indicate, for the first time, the new potential targets of melatonin in modulating morphine-induced CPP.

Novel Multitarget Directed Triazinoindole Derivatives as Anti-Alzheimer Agents

The multifaceted nature of Alzheimer's disease (AD) demands treatment with multitarget-directed ligands (MTDLs) to confront the key pathological aberrations. A novel series of triazinoindole derivatives were designed and synthesized. In vitro studies revealed that all the compounds showed moderate to good anticholinesterase activity; the most active compound 23e showed an IC₅₀ value of 0.56 ± 0.02 μM for AChE and an IC₅₀ value of 1.17 ± 0.09 μM for BuChE. These derivatives are also endowed with potent antioxidant activity. To understand the plausible binding mode of the compound 23e, molecular docking studies and molecular dynamics simulation studies were performed, and the results indicated significant interactions of 23e within the active sites of AChE as well as BuChE. Compound 23e successfully diminished H₂O₂-induced oxidative stress in SH-SY5Y cells and displayed excellent neuroprotective activity against H₂O₂ as well as Aβ-induced toxicity in SH-SY5Y cells in a concentration dependent manner. Furthermore, it did not show any significant toxicity in neuronal SH-SY5Y cells in the cytotoxicity assay. Compound 23e did not show any acute toxicity in rats at doses up to 2000 mg/kg, and it significantly reversed scopolamine-induced memory deficit in mice model. Additionally, compound 23e showed notable in silico ADMET properties. Taken collectively, these findings project compound 23e as a potential balanced MTDL in the evolution process of novel anti-AD drugs.

Neuroprotective effects of melatonin and celecoxib against ethanol-induced neurodegeneration: a computational and pharmacological approach

PURPOSE

Melatonin and celecoxib are antioxidants and anti-inflammatory agents that exert protective effects in different experimental models. In this study, the neuroprotective effects of melatonin and celecoxib were demonstrated against ethanol-induced neuronal injury by in silico, morphological, and biochemical approaches.

METHODS

For the in silico study, 3-D structures were constructed and docking analysis performed. For in vivo studies, rats were treated with ethanol, melatonin, and celecoxib. Brain samples were collected for biochemical and morphological analysis.

RESULTS

Homology modeling was performed to build 3-D structures for IL1β), TNFα, TLR4, and inducible nitric oxide synthase. Structural refinement was achieved via molecular dynamic simulation and processed for docking and postdocking analysis. Further in vivo experiments showed that ethanol induced marked neuronal injury characterized by downregulated glutathione, glutathione S-transferase, and upregulated inducible nitric oxide synthase. Additionally, ethanol increased the expression of TNFα and IL1β. Finally, neuronal apoptosis was demonstrated in ethanol-intoxicated animals using caspase 3 and activated JNK staining. On the other hand, melatonin and celecoxib treatment ameliorated the biochemical and immunohistochemical alterations induced by ethanol.

CONCLUSION

These results demonstrated that ethanol induced neurodegeneration by activating inflammatory and apoptotic proteins in rat brain, while melatonin and celecoxib may protect rat brain by downregulating inflammatory and apoptotic markers.

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

Bench to cribside: the path for developing a neuroprotectant

The consequences of perinatal brain injury include immeasurable anguish for families and substantial ongoing costs for care and support of effected children. Factors associated with perinatal brain injury in the preterm infant include inflammation and infection, and with increasing gestational age, a higher proportion is related to hypoxic-ischemic events, such as stroke and placental abruption. Over the past decade, we have acquired new insights in the mechanisms underpinning injury and many new tools to monitor outcome in perinatal brain injury in our experimental models. By embracing these new technologies, we can expedite the screening of novel therapies. This is critical as despite enormous efforts of the research community, hypothermia is the only viable neurotherapeutic, and this procedure is limited to term birth and postcardiac arrest hypoxic-ischemic events. Importantly, experimental and preliminary data in humans also indicate a considerable therapeutic potential for melatonin against perinatal brain injury. However, even if this suggested potential is proven, the complexity of the human condition means we are likely to need additional neuroprotective and regenerative strategies. Thus, within this review, we will outline what we consider the key stages of preclinical testing and development for a neuroprotectant or regenerative neurotherapy for perinatal brain injury. We will also highlight examples of novel small animal physiological and behavioral testing that gives small animal preclinical models greater clinical relevance. We hope these new tools and an integrated bench to cribside strategic plan will facilitate the fulfillment of our overarching goal, improving the long-term brain health and quality of life for infants suffering perinatal brain injury.

Possible role of pineal allopregnanolone in Purkinje cell survival

It is believed that neurosteroids are produced in the brain and other nervous systems. Here, we show that allopregnanolone (ALLO), a neurosteroid, is exceedingly produced in the pineal gland compared with the brain and that pineal ALLO acts on the Purkinje cell, a principal cerebellar neuron, to prevent apoptosis in the juvenile quail. We first demonstrated that the pineal gland is a major organ of neurosteroidogenesis. A series of experiments using molecular and biochemical techniques has further demonstrated that the pineal gland produces a variety of neurosteroids de novo from cholesterol in the juvenile quail. Importantly, ALLO was far more actively produced in the pineal gland than in the brain. Pinealectomy (Px) decreased ALLO concentration in the cerebellum and induced apoptosis of Purkinje cells, whereas administration of ALLO to Px quail chicks prevented apoptosis of Purkinje cells. We further found that Px significantly increased the number of Purkinje cells that expressed active caspase-3, a key protease in apoptotic pathway, and daily injection of ALLO to Px quail chicks decreased the number of Purkinje cells expressing active caspase-3. These results indicate that the neuroprotective effect of pineal ALLO is associated with the decrease in caspase-3 activity during the early stage of neuronal development. We thus provide evidence that the pineal gland is an important neurosteroidogenic organ and that pineal ALLO may be involved in Purkinje cell survival during development. This is an important function of the pineal gland in the formation of neuronal circuits in the developing cerebellum.

Accumulation of exogenous amyloid-beta peptide in hippocampal mitochondria causes their dysfunction: a protective role for melatonin

Amyloid-beta (Aβ) pathology is related to mitochondrial dysfunction accompanied by energy reduction and an elevated production of reactive oxygen species (ROS). Monomers and oligomers of Aβ have been found inside mitochondria where they accumulate in a time-dependent manner as demonstrated in transgenic mice and in Alzheimer's disease (AD) brain. We hypothesize that the internalization of extracellular Aβ aggregates is the major cause of mitochondrial damage and here we report that following the injection of fibrillar Aβ into the hippocampus, there is severe axonal damage which is accompanied by the entrance of Aβ into the cell. Thereafter, Aβ appears in mitochondria where it is linked to alterations in the ionic gradient across the inner mitochondrial membrane. This effect is accompanied by disruption of subcellular structure, oxidative stress, and a significant reduction in both the respiratory control ratio and in the hydrolytic activity of ATPase. Orally administrated melatonin reduced oxidative stress, improved the mitochondrial respiratory control ratio, and ameliorated the energy imbalance.

Pinoline and N-acetylserotonin reduce glutamate-induced lipid peroxidation in retinal homogenates

Glutamate is a neurotransmitter associated with oxidative retinal disorders. Pinoline (PIN) and N-acetylserotonin (NAS) are newly identified neural protectors. We investigated the glutamate-induced lipid peroxidation (LPO) and the protective effects of PIN and NAS in the retina. Porcine retinal homogenates were treated with different concentrations of glutamate. The malondialdehyde (MDA) level per unit weight of protein was quantified spectro-photometrically as an index of LPO. The glutamate concentration that induced a significant increase in retinal MDA was determined. The glutamate-treated retinal homogenate was then co-incubated with 5 different concentrations (0, 35.7, 71.5, 143 and 286 microM) of PIN, NAS or their combinations (concentration corresponding to 25, 50 and 75% of protection). Glutamate induced a significant dose-dependent increase in retinal MDA (p<0.0001). Co-incubation with PIN or NAS significantly suppressed the glutamate-induced MDA (p<0.01) in a dose-dependent manner (p<0.0001). The concentrations to inhibit 50% of LPO were 132.8 and 98.6 microM for PIN and NAS, respectively. In summary, elevated glutamate induced retinal LPO. Both PIN and NAS suppressed the glutamate-induced LPO and a synergic protection was evident after incubation in PIN/NAS mixtures.

Potential therapeutic use of melatonin in migraine and other headache disorders

There is increasing evidence that headache disorders are connected with melatonin secretion and pineal function. Some headaches have a clearcut seasonal and circadian pattern, such as cluster and hypnic headaches. Melatonin levels have been found to be decreased in both migraine and cluster headaches. Melatonin mechanisms are related to headache pathophysiology in many ways, including its anti-inflammatory effect, toxic free radical scavenging, reduction of pro-inflammatory cytokine upregulation, nitric oxide synthase activity and dopamine release inhibition, membrane stabilisation, GABA and opioid analgesia potentitation, glutamate neurotoxicity protection, neurovascular regulation, 5-HT modulation and the similarity in chemical structure to indometacin. The treatment of headache disorders with melatonin and other chronobiotic agents, such as melatonin agonists (ramelteon and agomelatin), is promising and there is a great potential for their use in headache treatment.

Antioxidative protection by melatonin: multiplicity of mechanisms from radical detoxification to radical avoidance

Melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. Signaling effects comprise the upregulation of antioxidant enzymes, such as superoxide dismutases, peroxidases, and enzymes of glutathione supply, down-regulation of prooxidant enzymes, such as nitric oxide synthases and lipoxygenases, and presumably also the control of quinone reductase 2. Other mechanisms are based on direct interactions with several reactive oxygen and nitrogen species. Among these reactions, the capacity of easily undergoing single-electron transfer reactions is of particular importance. Electron donation by melatonin is not only an aspect of direct radical scavenging, but additionally represents the basis for formation of the protective metabolites AFMK (N1-ace-tyl-N2-formyl-5-methoxykynuramine) and AMK (N1-acetyl-5-methoxykynuramine). Recent investigations on mitochondrial metabolism indicate that melatonin as well as AMK are capable of supporting the electron flux through the respiratory chain, of preventing the breakdown of the mitochondrial membrane potential, and of decreasing electron leakage, thereby reducing the formation of superoxide anions. Radical avoidance is a new line of investigation, which exceeds mitochondrial actions and also comprises antiexcitatory effects and contributions to the maintenance of internal circadian phase relationships.

Melatonin, the pineal gland and their implications for headache disorders

There is now evidence that melatonin may have a role in the biological regulation of circadian rhythms, sleep, mood, and ageing. Altered melatonin levels in cluster headache and migraine have been documented. Melatonin mechanisms are related to headache pathophysiology in many ways, including its anti-inflammatory effect, toxic free radical scavenging, reduction of proinflammatory cytokine up-regulation, nitric oxide synthase activity and dopamine release inhibition, membrane stabilization, GABA and opioid analgesia potentiation, glutamate neurotoxicity protection, neurovascular regulation, serotonin modulation, and the similarity of chemical structure to that of indomethacin. Treatment of headache disorders with melatonin and other chronobiotic agents is promising. A double-blind, placebo-controlled trial shows melatonin is effective in cluster headache prevention, other studies also show benefit in other disorders. Melatonin plays an important role in headache disorders, offering new avenues for studying their pathophysiology and treatment.

A randomized, double-blind, placebo controlled trial of melatonin add-on therapy in epileptic children on valproate monotherapy: effect on glutathione peroxidase and glutathione reductase enzymes

AIMS

To compare the effect of add-on melatonin with placebo on the antioxidant enzymes (glutathione peroxidase and glutathione reductase) in epileptic children on valproate monotherapy.

METHODS

In a double-blind, randomized, placebo controlled trial, the effect of add-on melatonin administration on the antioxidant enzymes in epileptic children on valproate (VPA) monotherapy was assessed. A total of 31 patients met the entry criteria. 16 patients were randomly allocated to receive add-on melatonin, and 15 to receive add-on placebo. Blood samples (5 ml) were collected just before the morning dose of valproate for baseline values of glutathione peroxidase and glutathione reductase enzymes, and then after 14 days of add-on melatonin/placebo. Blood was then centrifuged at 3500 r.p.m., serum separated and stored in deep freezer at -20 degrees C until assay of glutathione reductase. Heparinized blood was collected and stored at -20 degrees C in eppendorfs in the deep freezer for assay of glutathione peroxidase. All activity assays were performed on the Ames (Technicon) RA 50 chemistry analyser.

RESULTS

Fifteen patients in the add-on melatonin group and 14 patients in the add-on placebo group were finally assessed. There was an increase in the activity of antioxidant enzymes, glutathione peroxidase (GSH-Px) and glutathione reductase (GSSG-Rd), in the add-on melatonin (MEL) group as compared with a reduction in the same in the add-on placebo group (P). After the addition of melatonin/placebo in the respective groups, there was a 7.5% decrease in GSH-Px in the valproate + placebo group, whereas a 11.9% increase in the valproate + melatonin group was observed, the difference between the groups being not statistically significant (P = 0.29). On administration of melatonin/placebo, the post-treatment concentrations of GSSG-Rd in the valproate + placebo group decreased from 92.0 U l(-1) to 67.0 U l(-1) and increased from 82.0 U l(-1) to 113.0 U l(-1), in the valproate + melatonin group, respectively, the difference between them being statistically significant (P = 0.05). The percentage change in the values of GSSG-Rd in the two groups was statistically significant (P = 0.005).

CONCLUSIONS

Melatonin exerts neuroprotection due to its antioxidant, antiexcitotoxic and free radical scavenging properties within the central nervous system. Melatonin, thus, as an adjunct, can be a putative neuroprotector in conditions involving oxidative stress like epilepsies.

Effect of melatonin on the retinal glutamate/glutamine cycle in the golden hamster retina

Glutamate is the main excitatory neurotransmitter in the retina, but it is neurotoxic when present in excessive amounts. The metabolic dependence of glutamatergic neurons upon glia via the glutamate/glutamine cycle to provide the precursor for neurotransmitter glutamate is well established. Since melatonin has been shown to be neuroprotective in several systems, in the present report, its effect on the glutamate/glutamine cycle activity was examined in the golden hamster retina. Melatonin (0.1-10 nM) significantly increased retinal glutamine synthetase activity but it did not affect L-glutamine release. A characterization of the hamster retinal L-glutamine uptake mechanism was performed. This mechanism was partly Na+-dependent, and it was significantly inhibited by 2-aminobicyclo (2, 2, 1) heptane 2-carboxylic acid (BCH, a selective antagonists for the L-type system) and by alpha-(methylamino)-isobutyric acid (MeAIB, substrate characteristic for the A -type transporter) suggesting the coexistence of these transport systems in the hamster retina. Melatonin (0.1-10 nM) significantly increased total glutamine uptake as well as the BCH and the MeAIB-insensitive transporters activity. On the other hand, melatonin significantly decreased retinal glutaminase activity. On the basis of these results, it might be presumed that hamster retinal glutamate/glutamine cycle activity is regulated by physiological concentrations of melatonin. Furthermore, these findings suggest that a treatment with melatonin could be considered as a new approach to handling glutamate-mediated neuronal degeneration.

Add-on melatonin improves quality of life in epileptic children on valproate monotherapy: a randomized, double-blind, placebo-controlled trial

This randomized, double-blind, placebo-controlled study in epileptic children aged 3-12 years evaluated the effects of add-on melatonin administration on the quality of life of these children on sodium valproate (VPA) monotherapy using a parental questionnaire. Quality of Life in Childhood Epilepsy is a questionnaire designed to assess a variety of age-relevant domains such as physical function, emotional well-being, cognitive function, social function, behavior, and general health. Of the 31 patients, 16 randomly received add-on melatonin (MEL), whereas 15 received add-on placebo (P). The questionnaire had good internal consistency reliability, because for most of the multi-item scales Cronbach's alpha reliability exceeded 0.5 (range: 0.59-0.94). To our knowledge, this is the first study assessing quality of life in epileptic children with add-on melatonin administration in the form of a randomized, double-blind, placebo-controlled trial. The study suggests a potential use of melatonin as an adjunct to antiepileptic therapy due to its diverse spectrum of action as an antioxidant, neuroprotector, and free radical scavenger, thus offering the advantage of reducing oxidant stress and subsequent damage. The beneficial effects of melatonin on sleep, its wide safety window, and its ability to cross the blood-brain barrier have the potential to improve quality of life in pediatric epilepsy.

Neuroprotection against Abeta and glutamate toxicity by melatonin: are GABA receptors involved?

The beta-amyloid peptide (Abeta) is centrally related to the pathogenesis of Alzheimer's disease (AD). Previous studies have suggested that the neurotoxicity of Abeta may be related to the overactivation of glutamatergic transmission and excitotoxicity, and that blockade of glutamate receptors prevents Abeta-induced cell death. Here, we show that melatonin, a pineal hormone, protects chick retinal neurons in culture against the neurotoxicity of Abeta and glutamate. Right-angle light scattering and thioflavin T fluorescence measurements, as well as light microscopy analysis, indicated that, under our experimental conditions, melatonin had no effect on the aggregation of Abeta. Interestingly, the neuroprotective action of melatonin against the toxicity of Abeta was significantly decreased in the presence of picrotoxin, an antagonist of GABA(A)-like receptors. By itself, picrotoxin had no effect. These results suggest that the neuroprotective effects of melatonin against Abeta neurotoxicity could be at least in part related to a decrease in the excitatory tonus, mediated by activation of GABA receptors and the resulting hyper-polarization of the neurons. Thus, selective pharmacological manipulation of neuronal excitatory/inhibitory tonus could be a potentially interesting new approach in the treatment of AD.

Pretreatment with melatonin reduces volume of cerebral infarction in a rat middle cerebral artery occlusion stroke model

Melatonin is a potent scavenger of free radicals and an indirect antioxidant. Recent studies have shown that melatonin possesses beneficial effects in experimental models of brain trauma and global cerebral ischemia. The effects of pretreatment with melatonin on volume of cerebral infarction were investigated in the present study. Adult male Sprague-Dawley rats were anesthetized with sodium pentobarbital to undergo right-sided endovascular middle cerebral artery occlusion (MCAO) for 3 hr. A single dose of melatonin (1.5, 5, 15, or 50 mg/kg in 1 mL normal saline) or its vehicle was given via an intraperitoneal injection at 0.5 hr before MCAO. Relative infarction volumes on day 3 after MCAO were significantly reduced in the groups treated with melatonin at 5 (mean +/- S.E.M., 15.7 +/- 2.5%) or 15 (21.4 +/- 3.1 %) mg/kg but not at 1.5 (30.6 +/- 3.5%) or 50 (26.7 +/- 2.8%) mg/ kg when compared with the vehicle group (33.9 +/- 3.5%). There was no significant difference in the arterial blood pressure (BP), heart rate (HR) and relative cerebral blood flow among the experimental groups. These results indicate that pretreatment with melatonin at a dose between 5 and 15 mg/kg protects against focal cerebral ischemia.

Synthesis of valproic acid amides of a melatonin derivative, a piracetam and amantadine for biological tests

Three new amide derivatives of valproic acid have been synthesized and characterized by spectrophotometric studies. The rationale for the preparation of such agents has been based on the observation that chemical combination of the anticonvulsant pharmacophore, valproic acid with amine moieties produces more effective and less toxic amides. The amine components selected in this work also exhibit neuroactivity with the prospect of these agents being biologically active in controlling not just seizures and but also possessing neuroprotective properties. We report here the synthesis and properties of the valproylamides of 5-methoxytryptamine, related to melatonin (1), of N-substituted 2-pyrrolidinone related to piracetam (2), and of adamantylamine related to amantadine (3). In preliminary tests these compounds showed low toxicity and a variety of anticonvulsive properties, including a delay in onset of activity. These compounds and their derivatives are now available to be tested additionally for control of subclinical seizures, enhancement of cognition, behavior modification and alleviation of symptoms and disorders due to neuronal damage.

Actions of melatonin in the reduction of oxidative stress. A review

Melatonin was discovered to be a direct free radical scavenger less than 10 years ago. Besides its ability to directly neutralize a number of free radicals and reactive oxygen and nitrogen species, it stimulates several antioxidative enzymes which increase its efficiency as an antioxidant. In terms of direct free radical scavenging, melatonin interacts with the highly toxic hydroxyl radical with a rate constant equivalent to that of other highly efficient hydroxyl radical scavengers. Additionally, melatonin reportedly neutralizes hydrogen peroxide, singlet oxygen, peroxynitrite anion, nitric oxide and hypochlorous acid. The following antioxidative enzymes are also stimulated by melatonin: superoxide dismutase, glutathione peroxidase and glutathione reductase. Melatonin has been widely used as a protective agent against a wide variety of processes and agents that damage tissues via free radical mechanisms.