Melatonin protects SK-N-SH neuroblastoma cells from amphetamine-induced neurotoxicity

Antiviral effect of melatonin on Japanese encephalitis virus infection involves inhibition of neuronal apoptosis and neuroinflammation in SH-SY5Y cells

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, causes high mortality rates in humans and it is the most clinically important and common cause of viral encephalitis in Asia. To date, there is no specific treatment for JEV infection. Melatonin, a neurotropic hormone, is reported to be effective in combating various bacterial and viral infections. However, the effects of melatonin on JEV infection have not yet been studied. The investigation tested the antiviral effects of melatonin against JEV infection and elucidated the possible molecular mechanisms of inhibition. Melatonin inhibited the viral production in JEV-infected SH-SY5Y cells in a time- and dose-dependent manner. Time-of-addition assays demonstrated a potent inhibitory effect of melatonin at the post-entry stage of viral replication. Molecular docking analysis revealed that melatonin negatively affected viral replication by interfering with physiological function and/or enzymatic activity of both JEV nonstructural 3 (NS3) and NS5 protein, suggesting a possible underlying mechanism of JEV replication inhibition. Moreover, treatment with melatonin reduced neuronal apoptosis and inhibited neuroinflammation induced by JEV infection. The present findings reveal a new property of melatonin as a potential molecule for the further development of anti-JEV agents and treatment of JEV infection.

Melatonin ameliorates nickel induced autophagy in mouse brain: diminution of oxidative stress

Nickel（Ni) is a neurotoxic environmental pollutant. Oxidative stress is thought to be the main mechanism behind the development of Ni neurotoxicity. Melatonin (Mt) has significant efficacy as an antioxidant. In this paper, we investigated the damage that Ni causes to the autophagy of the nervous system. Furthermore, Mt has can intervene upon the damage caused by Ni, which can protect the nervous system. Herein, we randomly divided 80 8-week-old male wild-type C57BL/6N mice into four groups, including the C group, Ni group, Mt group, and Mt+Ni group. Ni was gavaged at a concentration of 10mg/kg, while was Mt was administered at a concentration of 2mg/kg for 21 days at 0.1ml/10g body weight of the mice. Histopathological and ultrastructural observations demonstrated altered states, such as neuronal atrophy, as well as typical autophagic features in the Ni group. Mt was able to intervene effectively in Ni-induced neurotoxicity. The antioxidant capacity assay also demonstrated that Ni can lead to a large amount of reactive oxygen species (ROS) production within the mouse brain. Furthermore, the same Mt was effective at reducing ROS production. In order to further illustrate this point, we added the broad-spectrum phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 to NS20Y cells. The presence of inhibitors effectively demonstrates that, within the PI3K/AKT/mTOR pathway, autophagy occurs. In conclusion, these data suggest that Ni causes oxidative stress damage and induces autophagy within the mouse brain by inhibiting the PI3K/AKT/mTOR pathway, and that Mt can effectively alleviate the oxidative stress caused by Ni, and reducing Ni induces autophagy in the mouse brain through the PI3K/AKT/mTOR pathway.

Exploring the multifunctional role of melatonin in regulating autophagy and sleep to mitigate Alzheimer's disease neuropathology

Melatonin (MLT) is a neurohormone that is regulated by the circadian clock and plays multifunctional roles in numerous neurodegenerative disorders, such as Alzheimer's disease (AD). AD is the most common form of dementia and is associated with the degradation of axons and synapses resulting in memory loss and cognitive impairment. Despite extensive research, there is still no effective cure or specific treatment to prevent the progression of AD. The pathogenesis of AD involves atrophic alterations in the brain that also result in circadian alterations, sleep disruption, and autophagic dysfunction. In this scenario, MLT and autophagy play a central role in removing the misfolded protein aggregations. MLT also promotes autophagy through inhibiting methamphetamine toxicity to protect against neuronal cell death in AD brain. Besides, MLT plays critical roles as either a pro-autophagic indicator or anti-autophagic regulator depending on the phase of autophagy. MLT also has antioxidant properties that can counteract mitochondrial damage, oxidative stress, and apoptosis. Aging, a major risk factor for AD, can change sleep patterns and sleep quality, and MLT can improve sleep quality through regulating sleep cycles. The primary purpose of this review is to explore the putative mechanisms of the beneficial effects of MLT in AD patients. Furthermore, we also summarize the findings from preclinical and clinical studies on the multifunctional roles of MLT on autophagic regulation, the control of the circadian clock-associated genes, and sleep regulation.

Proteomic Analysis of the Spinophilin Interactome in Rodent Striatum Following Psychostimulant Sensitization

Glutamatergic projections from the cortex and dopaminergic projections from the substantia nigra or ventral tegmental area synapse on dendritic spines of specific GABAergic medium spiny neurons (MSNs) in the striatum. Direct pathway MSNs (dMSNs) are positively coupled to protein kinase A (PKA) signaling and activation of these neurons enhance specific motor programs whereas indirect pathway MSNs (iMSNs) are negatively coupled to PKA and inhibit competing motor programs. An imbalance in the activity of these two programs is observed following increased dopamine signaling associated with exposure to psychostimulant drugs of abuse. Alterations in MSN signaling are mediated by changes in MSN protein post-translational modifications, including phosphorylation. Whereas direct changes in specific kinases, such as PKA, regulate different effects observed in the two MSN populations, alterations in the specific activity of serine/threonine phosphatases, such as protein phosphatase 1 (PP1) are less well known. This lack of knowledge is due, in part, to unknown, cell-specific changes in PP1 targeting proteins. Spinophilin is the major PP1-targeting protein in striatal postsynaptic densities. Using proteomics and immunoblotting approaches along with a novel transgenic mouse expressing hemagglutainin (HA)-tagged spinophilin in dMSNs and iMSNs, we have uncovered cell-specific regulation of the spinophilin interactome following a sensitizing regimen of amphetamine. These data suggest regulation of spinophilin interactions in specific MSN cell types and may give novel insight into putative cell-specific, phosphatase-dependent signaling pathways associated with psychostimulants.

Neuroprotective effects of melatonin on amphetamine-induced dopaminergic fiber degeneration in the hippocampus of postnatal rats

Chronic amphetamine (AMPH) abuse leads to damage of the hippocampus, the brain area associated with learning and memory process. Previous results have shown that AMPH-induced dopamine neurotransmitter release, reactive oxygen species formation, and degenerative protein aggregation lead to neuronal death. Melatonin, a powerful antioxidant, plays a role as a neuroprotective agent. The objective of this study was to investigate whether the protective effect of melatonin on AMPH-induced hippocampal damage in the postnatal rat acts through the dopaminergic pathway. Four-day-old postnatal rats were subcutaneously injected with 5-10 mg/kg AMPH and pretreated with 10 mg/kg melatonin prior to AMPH exposure for seven days. The results showed that melatonin decreased the AMPH-induced hippocampal neuronal degeneration in the dentate gyrus, CA1, and CA3. Melatonin attenuated the reduction in the expression of hippocampal synaptophysin, PSD-95, α-synuclein, and N-methyl-D-aspartate (NMDA) receptor protein and mRNA caused by AMPH. Melatonin attenuated the AMPH-induced reduction in dopamine transporter (DAT) protein expression in the hippocampus and the reduction in mRNA expression in the ventral tegmental area (VTA). Immunofluorescence demonstrated that melatonin not only prevented the AMPH-induced loss of DAT and NMDA receptor but also prevented AMPH-induced α-synuclein overexpression in the dentate gyrus, CA1, and CA3. Melatonin decreased the AMPH-induced reduction in the protein and mRNA of the NMDA receptor downstream signaling molecule, calcium/calmodulin-dependent protein kinase II (CaMKII), and the melatonin receptors (MT1 and MT2). This study showed that melatonin prevented AMPH-induced toxicity in the hippocampus of postnatal rats possibly via its antioxidative effect and mitochondrial protection.

Melatonin as a mitochondrial protector in neurodegenerative diseases

Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.

The muscarinic effect of anhydroecgonine methyl ester, a crack cocaine pyrolysis product, impairs melatonin synthesis in the rat pineal gland

Anhydroecgonine methyl ester (AEME), also called methylecgonidine, is a pyrolysis product of crack cocaine that is neurotoxic and potentiates cocaine-induced sensitization. The sensitization induced by drugs of abuse can be influenced by melatonin, a neuroprotective pineal hormone. In the same way, drugs of abuse like alcohol and methamphetamine can modify melatonin synthesis. The aim of the present work was to investigate the AEME effects on melatonin synthesis in the rat pineal gland. Neurotransmitter systems involved in its effects, antioxidant enzyme activities and the melatonin protective role in AEME-induced toxicity were also evaluated. The animals were injected with AEME i.p. (1.12 mg per kg of body weight per day) or vehicle for 10 consecutive days and the nocturnal pineal melatonin synthesis profile and SOD, GPx and GR activities in the cerebral cortex and hippocampus were assessed. Cultured pineal glands were incubated with AEME for 30 min or 48 h before norepinephrine stimulation and melatonin synthesis, arylalkylamine N-acetyltransferase activity, cAMP and [Ca2+]i were determined. The involvement of cholinergic and glutamatergic systems was analyzed using different antagonists. The protective role of melatonin in AEME toxicity on hippocampal neurons was evaluated by a viability assay. AEME impaired melatonin synthesis both in vivo and in vitro and this effect seems to be mediated by muscarinic receptors and [Ca2+]i elevation. AEME reduced neuronal viability and melatonin was able to protected hippocampal neurons against AEME toxicity. The melatonin synthesis impairment observed could lead to the worsening of the direct AEME neurotoxicity and to the exacerbation of the crack cocaine addiction and sensitization.

Melatonin enhances the anti-tumor effect of sorafenib via AKT/p27-mediated cell cycle arrest in hepatocarcinoma cell lines

Proposed model elucidating the role of MT in regulating the proliferation of hepatocellular carcinoma (HCC) cells treated with sorafenib.

Protective mechanisms of melatonin against hydrogen-peroxide-induced toxicity in human bone-marrow-derived mesenchymal stem cells

Many obstacles compromise the efficacy of bone marrow mesenchymal stem cells (BM-MSCs) by inducing apoptosis in the grafted BM-MSCs. The current study investigates the effect of melatonin on important mediators involved in survival of BM-MSCs in hydrogen peroxide (H₂O₂) apoptosis model. In brief, BM-MSCs were isolated, treated with melatonin, and then exposed to H₂O₂. Their viability was assessed by MTT assay and apoptotic fractions were evaluated through Annexin V, Hoechst staining, and ADP/ATP ratio. Oxidative stress biomarkers including ROS, total antioxidant power (TAP), superoxide dismutase (SOD) and catalase (CAT) activity, glutathione (GSH), thiol molecules, and lipid peroxidation (LPO) levels were determined. Secretion of inflammatory cytokines (TNF-α and IL-6) were measured by ELISA assay. The protein expression of caspase-3, Bax, and Bcl-2, was also evaluated by Western blotting. Melatonin pretreatment significantly increased viability and decreased apoptotic fraction of H₂O₂-exposed BM-MSCs. Melatonin also decreased ROS generation, as well as increasing the activity of SOD and CAT enzymes and GSH content. Secretion of inflammatory cytokines in H₂O₂-exposed cells was also reduced by melatonin. Expression of caspase-3 and Bax proteins in H₂O₂-exposed cells was diminished by melatonin pretreatment. The findings suggest that melatonin may be an effective protective agent against H₂O₂-induced oxidative stress and apoptosis in MSC.

Melatoninergic System in Parkinson's Disease: From Neuroprotection to the Management of Motor and Nonmotor Symptoms

Melatonin is synthesized by several tissues besides the pineal gland, and beyond its regulatory effects in light-dark cycle, melatonin is a hormone with neuroprotective, anti-inflammatory, and antioxidant properties. Melatonin acts as a free-radical scavenger, reducing reactive species and improving mitochondrial homeostasis. Melatonin also regulates the expression of neurotrophins that are involved in the survival of dopaminergic neurons and reduces α-synuclein aggregation, thus protecting the dopaminergic system against damage. The unbalance of pineal melatonin synthesis can predispose the organism to inflammatory and neurodegenerative diseases such as Parkinson's disease (PD). The aim of this review is to summarize the knowledge about the potential role of the melatoninergic system in the pathogenesis and treatment of PD. The literature reviewed here indicates that PD is associated with impaired brain expression of melatonin and its receptors MT₁ and MT₂. Exogenous melatonin treatment presented an outstanding neuroprotective effect in animal models of PD induced by different toxins, such as 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat, and maneb. Despite the neuroprotective effects and the improvement of motor impairments, melatonin also presents the potential to improve nonmotor symptoms commonly experienced by PD patients such as sleep and anxiety disorders, depression, and memory dysfunction.

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.

Effects of melatonin and its analogues on neural stem cells

Neural stem cells (NSCs) are multipotent cells which are capable of self-replication and differentiation into neurons, astrocytes or oligodendrocytes in the central nervous system (CNS). NSCs are found in two main regions in the adult brain: the subgranular zone (SGZ) in the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ). The recent discovery of NSCs in the adult mammalian brain has fostered a plethora of translational and preclinical studies to investigate novel approaches for the therapy of neurodegenerative diseases. Melatonin is the major secretory product synthesized and secreted by the pineal gland and shows both a wide distribution within phylogenetically distant organisms from bacteria to humans and a great functional versatility. Recently, accumulated experimental evidence showed that melatonin plays an important role in NSCs, including its proliferation, differentiation and survival, which are modulated by many factors including MAPK/ERK signaling pathway, histone acetylation, neurotrophic factors, transcription factors, and apoptotic genes. The purpose of this review is to summarize the beneficial effects of melatonin on NSCs and further to discuss the potential usage of melatonin and its derivatives or analogues in the treatment of CNS neurodegenerative diseases.

Comparison of the Effects of 13-cis Retinoic Acid and Melatonin on the Viabilities of SH-SY5Y Neuroblastoma Cell Line

Objective

Neuroblastoma is one of common childhood tumors. Although its mortality is very high, there is no effective treatment yet. The aim of this project is to evaluate cytotoxic effects of melatonin (MLT) an endogen hormone and 13-cis retinoic acid (13-cis-RA) also named as isotretinoin an analogue of vitamin A on neuroblastoma SH-SY5Y cell line.

Methods

In this study, SH-SY5Y cell line was used. After cell culture, the cells were exposed to different doses of MLT and 13-cis-RA. 24 and 48 hours later. While the viabilities was estimated with MTT cell viability assay test, apoptotic indexes were calculated after staining with TUNEL based apoptosis kit.

Results

It was observed that MLT has very effective cytotoxic potential than 13-cis-RA on neuroblastoma cell line. At the same time, when MLT and 13-cis-RA were combined, this effect was potentiated. On the other hand, it was found that the effect of 13-cis-RA individually on neuroblastoma cells was very slight.

Conclusion

We suggest that in the treatment of patient with neuroblastoma, MLT is very effective and also this effect can be augmented by combination with 13-cis-RA.

Recent advances in methamphetamine neurotoxicity mechanisms and its molecular pathophysiology

Methamphetamine (METH) is a sympathomimetic amine that belongs to phenethylamine and amphetamine class of psychoactive drugs, which are widely abused for their stimulant, euphoric, empathogenic, and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, METH produces persistent damage to dopamine and serotonin release in nerve terminals, gliosis, and apoptosis. This review summarized the numerous interdependent mechanisms including excessive dopamine, ubiquitin-proteasome system dysfunction, protein nitration, endoplasmic reticulum stress, p53 expression, inflammatory molecular, D₃ receptor, microtubule deacetylation, and HIV-1 Tat protein that have been demonstrated to contribute to this damage. In addition, the feasible therapeutic strategies according to recent studies were also summarized ranging from drug and protein to gene level.

Mitochondria: key players in the neurotoxic effects of amphetamines

Amphetamines are a class of psychotropic drugs with high abuse potential, as a result of their stimulant, euphoric, emphathogenic, entactogenic, and hallucinogenic properties. Although most amphetamines are synthetic drugs, of which methamphetamine, amphetamine, and 3,4-methylenedioxymethamphetamine ("ecstasy") represent well-recognized examples, the use of natural related compounds, namely cathinone and ephedrine, has been part of the history of humankind for thousands of years. Resulting from their amphiphilic nature, these drugs can easily cross the blood-brain barrier and elicit their well-known psychotropic effects. In the field of amphetamines' research, there is a general consensus that mitochondrial-dependent pathways can provide a major understanding concerning pathological processes underlying the neurotoxicity of these drugs. These events include alterations on tricarboxylic acid cycle's enzymes functioning, inhibition of mitochondrial electron transport chain's complexes, perturbations of mitochondrial clearance mechanisms, interference with mitochondrial dynamics, as well as oxidative modifications in mitochondrial macromolecules. Additionally, other studies indicate that amphetamines-induced neuronal toxicity is closely regulated by B cell lymphoma 2 superfamily of proteins with consequent activation of caspase-mediated downstream cell death pathway. Understanding the molecular mechanisms at mitochondrial level involved in amphetamines' neurotoxicity can help in defining target pathways or molecules mediating these effects, as well as in developing putative therapeutic approaches to prevent or treat the acute- or long-lasting neuropsychiatric complications seen in human abusers.

Melatonin regulates aging and neurodegeneration through energy metabolism, epigenetics, autophagy and circadian rhythm pathways

Brain aging is linked to certain types of neurodegenerative diseases and identifying new therapeutic targets has become critical. Melatonin, a pineal hormone, associates with molecules and signaling pathways that sense and influence energy metabolism, autophagy, and circadian rhythms, including insulin-like growth factor 1 (IGF-1), Forkhead box O (FoxOs), sirtuins and mammalian target of rapamycin (mTOR) signaling pathways. This review summarizes the current understanding of how melatonin, together with molecular, cellular and systemic energy metabolisms, regulates epigenetic processes in the neurons. This information will lead to a greater understanding of molecular epigenetic aging of the brain and anti-aging mechanisms to increase lifespan under healthy conditions.

1-Methyl-4-phenylpyridinium-induced cell death via autophagy through a Bcl-2/Beclin 1 complex-dependent pathway

Several lines of evidence suggest that the mechanism underlying drug-induced neuronal apoptosis is initiated by the increased production of reactive oxygen species (ROS). 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin, has been shown to initiate an apoptotic cascade by increasing ROS in the dopaminergic neurons of the substantia nigra, leading to the morphological and physiological features associated with Parkinson's disease. Recently, it has been reported that autophagy, a type of programmed cell death independent of the apoptotic cascade, also plays a role in neuronal damage. Although autophagy is negatively regulated by the mammalian target of rapamycin receptor (mTOR), there is some evidence showing a novel function for the anti-apoptotic protein Bcl-2. Bcl-2 is proposed to play a role in negatively regulating autophagy by blocking an essential protein in the signaling pathway, Beclin 1. Nevertheless, it is unclear whether autophagy is also correlated with apoptotic signaling in 1-methyl-4-phenylpyridinium (MPP(+)) toxicity. Therefore, we hypothesized that the MPP(+) toxicity generally associated with initiating the apoptotic signaling cascade also increases an autophagic phenotype in neuronal cells. Using the SK-N-SH dopaminergic cell lines, we demonstrate that MPP(+) increases the expression of microtubule-associated protein light chain 3 (LC3-II), an autophagosome membrane marker and the mTOR signaling pathway, and Beclin 1 while decreasing the Bcl-2 levels. Moreover, these expressions correlate with a decreased binding ratio between Bcl-2 and Beclin 1, in effect limiting the regulation of the downstream autophagic markers, such as LC3-II. Our results indicate that MPP(+) can induce autophagy in SK-N-SH cells by decreasing the Bcl-2/Beclin 1 complex.

Melatonin attenuates methamphetamine-induced disturbances in mitochondrial dynamics and degeneration in neuroblastoma SH-SY5Y cells

Methamphetamine (METH) is a psychostimulant drug that can cause toxicity and degeneration in the brain. The toxicity due to METH involves multiple pathways, including the mitochondrial-dependent death pathway. Several pieces of evidence have emphasized that the fragmentation of mitochondria into smaller structures plays some role in the cell-death process. In this study, we investigated the role of mitochondrial dynamics in METH-induced toxicity in human dopaminergic neuroblastoma SH-SY5Y cultured cell lines. In addition, the protective effect of melatonin against METH-induced toxicity was investigated. Our results show that METH significantly decreased cell viability and increased the levels of the mitochondrial fission protein, Fis1 and the Drp1 oligomer. However, the levels of the mitochondrial fusion proteins OPA1 and Mfn1 did not change in METH-treated cells. Melatonin can reverse the toxic effects of the METH-induced reduction in cell viability and the production of the Fis1 protein and the Drp1 oligomer. Moreover, the morphological alteration of mitochondria was investigated in METH-treated cells in the presence of melatonin using transmission electron microscopy (TEM). At 24 hr after METH exposure, typical cell shrinkage was observed in SH-SY5Y cells. Mitochondria were fragmented into small globular structures in a large proportion of METH-treated cells, but tubular networks of mitochondria were present in large proportions of control-untreated cells and METH-treated cells in the presence of melatonin. The results of the present study demonstrate the potential of melatonin to reduce cell death and restore mitochondrial function in neurons affected by METH-induced toxicity.

The anti-inflammatory effect of melatonin on methamphetamine-induced proinflammatory mediators in human neuroblastoma dopamine SH-SY5Y cell lines

Methamphetamine (METH) is a highly addictive drug that is commonly abused worldwide. This psychostimulant drug causes the disturbances in the dopaminergic and serotonergic neurons of several brain areas. Exposure to METH has been shown to induce oxidative stress, reactive oxygen species, reactive nitrogen species, and neuroinflammation. However, the mechanism underlying METH-induced inflammation in neurons is still unclear. In this study, we investigated whether METH caused inflammatory effects in human dopaminergic neuroblastoma SH-SY5Y cells and whether this effect involved the nuclear factor-κB (NF-κB) transcription factor pathway. The present results showed that METH significantly increased inducible nitric oxide synthase (iNOS) expression in a concentration-dependent manner and significantly increased the levels of tumor necrosis factor (TNF)-α mRNA and phosphorylated NF-κB, which is translocated into the nucleus. Moreover, our results also show that METH downregulated another transcription factor, the nuclear factor erythroid 2-related factor (Nrf2), a transcription factor implicated in the expression of several antioxidant/detoxificant enzymes. Furthermore, we also examined the anti-inflammatory effect of melatonin against these METH-induced neuroinflammatory functions. The results show that melatonin significantly decreases the iNOS protein expression and TNF-α mRNA levels caused by METH. The activation and the level of pNF-κB were decreased while Nrf2 expression was increased when cells were pre-incubated with 100 nM of melatonin. In order to show the relationship between cell death and the increase of iNOS, 100 μM of L-NAME, an iNOS inhibitor pretreatment significantly prevented cell death caused by METH. These results demonstrate, for the first time, that METH directly induces inflammation in neurons via an NF-κB-dependent pathway and that the anti-neuroinflammatory effects of melatonin result from the inhibition of activated NF-κB in parallel with potentiated antioxidant/detoxificant defense by activated Nrf2 pathway.

Fluoxetine ameliorates behavioral and neuropathological deficits in a transgenic model mouse of α-synucleinopathy

The term α-synucleinopathies refers to a group of age-related neurological disorders including Parkinson's disease (PD), Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA) that display an abnormal accumulation of alpha-synuclein (α-syn). In contrast to the neuronal α-syn accumulation observed in PD and DLB, MSA is characterized by a widespread oligodendrocytic α-syn accumulation. Transgenic mice expressing human α-syn under the oligodendrocyte-specific myelin basic protein promoter (MBP1-hαsyn tg mice) model many of the behavioral and neuropathological alterations observed in MSA. Fluoxetine, a selective serotonin reuptake inhibitor, has been shown to be protective in toxin-induced models of PD, however its effects in an in vivo transgenic model of α-synucleinopathy remain unclear. In this context, this study examined the effect of fluoxetine in the MBP1-hαsyn tg mice, a model of MSA. Fluoxetine administration ameliorated motor deficits in the MBP1-hαsyn tg mice, with a concomitant decrease in neurodegenerative pathology in the basal ganglia, neocortex and hippocampus. Fluoxetine administration also increased levels of the neurotrophic factors, GDNF (glial-derived neurotrophic factor) and BDNF (brain-derived neurotrophic factor) in the MBP1-hαsyn tg mice compared to vehicle-treated tg mice. This fluoxetine-induced increase in GDNF and BDNF protein levels was accompanied by activation of the ERK signaling pathway. The effects of fluoxetine administration on myelin and serotonin markers were also examined. Collectively these results indicate that fluoxetine may represent a novel therapeutic intervention for MSA and other neurodegenerative disorders.

Melatonin synergistically enhances cisplatin-induced apoptosis via the dephosphorylation of ERK/p90 ribosomal S6 kinase/heat shock protein 27 in SK-OV-3 cells

To evaluate melatonin's ability to enhance ovarian cancer cells to cisplatin treatment for ovarian cancer, this study was performed. Melatonin by itself had no significant cytotoxicity against SK-OV-3 cells, while cisplatin suppressed the cell viability in a dose-dependent manner. Combined treatment with cisplatin and melatonin synergistically inhibited the viability of SK-OV-3 cells with the synergism between two drugs (1 > combination index). In contrast, melatonin revealed the protective effect against cisplatin-induced cytotoxicity in OSEN normal ovarian epithelial cells. Cotreatment with cisplatin and melatonin increased the sub-G1 DNA contents and TdT-mediated dUTP nick end-labeling (TUNEL)-positive cells compared with cisplatin control in SK-OV-3 cells, suggesting that melatonin augments cisplatin-induced apoptosis. Consistently, combined treatment of cisplatin and melatonin increased the cleavage of caspase-3 and poly-(ADP-ribose) polymerase (PARP). Importantly, melatonin synergistically inhibited the phosphorylation of extracellular signal-regulated kinase (ERK) along with dephosphorylation of 90-kDa ribosomal S6 kinase (p90RSK) and heat shock protein 27 (HSP27) induced by cisplatin. Furthermore, melatonin remarkably blocked the expression and colocalization of p90RSK and HSP27 by combination treatment with cisplatin. Taken together, our findings demonstrate that melatonin enhances cisplatin-induced apoptosis via the inactivation of ERK/p90RSK/HSP27 cascade in SK-OV-3 cells as a potent synergist to cisplatin treatment.

Melatonin reduces the expression of alpha-synuclein in the dopamine containing neuronal regions of amphetamine-treated postnatal rats

Alpha-synuclein (α-syn) is a neuronal protein that is involved in various degenerative disorders such as Parkinson's disease. It is found in the presynaptic terminals and perinuclear zones of many brain regions. Amphetamine (AMPH), a psychostimulant drug abused progressively more commonly in recent years, has been known to induce neurotoxicity in the central dopaminergic pathway, which is associated with increased oxidative stress. Recently, AMPH has been shown to significantly increase the level of α-syn in dopaminergic neuroblastoma cell cultures. Melatonin is recognized as an antioxidant for the nervous system. This study tested whether melatonin can attenuate the effect of AMPH on the expression of α-syn in the dopaminergic pathway of the neonatal rat. Four-day old postnatal rats (P4) were injected subcutaneously with either AMPH (increasing dose, 5-10 mg/kg daily) alone or AMPH with melatonin (2 mg/kg) daily at 10:00 AM for 7 consecutive days. As determined using Western blot, the level of α-syn was significantly increased in the substantia nigra, dorsal striatum, nucleus accumbens, and prefrontal cortex of the AMPH-treated group, while melatonin treatment either prior to AMPH or alone decreased the accumulation of the protein to 77%, 96%, 78%, and 77% of the control value, respectively. Furthermore, an immunofluorescent study showed that the α-syn-immunoreactivity increased noticeably in the nuclei of cell bodies and nerve terminals of the AMPH-treated group. Again, melatonin lowered this immunoreactivity. These results indicate that melatonin has a direct or indirect effect in reducing the expression of α-syn in the postnatal rat. The exact mechanism of this mitigation should be further investigated.

Melatonin as a neuroprotective agent in the rodent models of Parkinson's disease: is it all set to irrefutable clinical translation?

Parkinson's disease (PD), a neurodegenerative disorder, is characterized by the selective degeneration of the nigrostriatal dopaminergic neurons, continuing or permanent deficiency of dopamine, accretion of an abnormal form of alpha synuclein in the adjacent neurons, and dysregulation of ubiquitin proteasomal system, mitochondrial metabolism, permeability and integrity, and cellular apoptosis resulting in rigidity, bradykinesia, resting tremor, and postural instability. Melatonin, an indoleamine produced almost in all the organisms, has anti-inflammatory, anti-apoptotic, and anti-oxidant nature. Experimental studies employing 1-methyl 4-phenyl 1, 2, 3, 6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), methamphetamine, rotenone, and maneb and paraquat models have shown an enormous potential of melatonin in amelioration of the symptomatic features of PD. Although a few reviews published previously have described the multifaceted efficacy of melatonin against MPTP and 6-OHDA rodent models, due to development and validation of the newer models as well as the extensive studies on the usage of melatonin in entrenched PD models, it is worthwhile to bring up to date note on the usage of melatonin as a neuroprotective agent in PD. This article presents an update on the usage and applications of melatonin in PD models along with incongruous observations. The impending implications in the clinics, success, limitations, and future prospective have also been discussed in this article.

Nickel exposure induces oxidative damage to mitochondrial DNA in Neuro2a cells: the neuroprotective roles of melatonin

Recent studies suggest that oxidative stress and mitochondrial dysfunction play important roles in the neurotoxicity of nickel. Because mitochondrial DNA (mtDNA) is highly vulnerable to oxidative stress and melatonin can efficiently protect mtDNA against oxidative damage in various pathological conditions, the aims of this study were to determine whether mtDNA oxidative damage was involved in the neurotoxicity of nickel and to assay the neuroprotective effects of melatonin in mtDNA. In this study, we exposed mouse neuroblastoma cell lines (Neuro2a) to different concentrations of nickel chloride (NiCl(2), 0.125, 0.25, and 0.5 mm) for 24 hr. We found that nickel significantly increased reactive oxygen species (ROS) production and mitochondrial superoxide levels. In addition, nickel exposure increased mitochondrial 8-hydroxyguanine (8-OHdG) content and reduced mtDNA content and mtDNA transcript levels. Consistent with this finding, nickel was found to destroy mtDNA nucleoid structure and decrease protein levels of Tfam, a key protein component for nucleoid organization. However, all the oxidative damage to mtDNA induced by nickel was efficiently attenuated by melatonin pretreatment. Our results suggest that oxidative damage to mtDNA may account for the neurotoxicity of nickel. Melatonin has great pharmacological potential in protecting mtDNA against the adverse effects of nickel in the nervous system.

The mechanism for the neuroprotective effect of melatonin against methamphetamine-induced autophagy

Methamphetamine (METH) is a common drug of abuse that induces toxicity in the central nervous system and is connected to neurological disorders such as Parkinson's disease. METH neurotoxicity is induced by reactive oxygen species (ROS) production and apoptosis. Moreover, autophagy is an alternative to cell death and a means for eliminating dysfunctional organelles. In other cases, autophagy can end up in cell death. Nonetheless, it is not clear whether autophagy is also correlated with apoptotic signaling in drug-induced neurotoxicity. Therefore, we hypothesized that METH-generated toxicity associated with initiating the apoptotic signaling cascade can also increase the autophagic phenotype in neuronal cells. Using the SK-N-SH dopaminergic cell line as our model system, we found that METH-induced autophagy by inhibiting dissociation of Bcl-2/Beclin 1 complex and its upstream pathway that thereby led to cell death. We uncovered a novel function for the anti-apoptotic protein Bcl-2, as it played a role in negatively regulating autophagy by blocking an essential protein in the signaling pathway, Beclin 1. Furthermore, Bcl-2 was activated by c-Jun N-terminal kinase 1 (JNK 1), which is upstream of Bcl-2 phosphorylation, to induce Bcl-2/Beclin 1 dissociation. Furthermore, we demonstrated a novel role for melatonin in protecting cells from autophagic cell death triggered by the Bcl-2/Beclin 1 pathway by inhibiting the activation of the JNK 1, Bcl-2 upstream pathway. This study provides information regarding the link between apoptosis and autophagy signaling, which could lead to the development of therapeutic strategies that exploit the neurotoxicity of drugs of abuse.

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

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

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

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

Increased blood oxidative stress in amphetamine users

Amphetamine derivatives have been shown to be a potential brain neurotoxin based on the production of free radicals that occurs after administration. The purpose of this study was to examine the lipid peroxidation and antioxidant enzymes in the blood of amphetamine users. The plasma lipid peroxidation was determined and reported as thiobarbituric acid reactive substance and was significantly increased (+21%), whereas the activities of the erythrocyte antioxidant enzymes glutathione peroxidase, catalase, and superoxide dismutase were significantly decreased (-32%, -14% and -31%, respectively) in amphetamine users. These results implicated the potential role of oxidative stress in amphetamine-induced neurotoxicity.

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.

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.

Potential adverse effects of amphetamine treatment on brain and behavior: a review

Amphetamine stimulants have been used medically since early in the twentieth century, but they have a high abuse potential and can be neurotoxic. Although they have long been used effectively to treat attention deficit hyperactivity disorder (ADHD) in children and adolescents, amphetamines are now being prescribed increasingly as maintenance therapy for ADHD and narcolepsy in adults, considerably extending the period of potential exposure. Effects of prolonged stimulant treatment have not been fully explored, and understanding such effects is a research priority. Because the pharmacokinetics of amphetamines differ between children and adults, reevaluation of the potential for adverse effects of chronic treatment of adults is essential. Despite information on the effects of stimulants in laboratory animals, profound species differences in susceptibility to stimulant-induced neurotoxicity underscore the need for systematic studies of prolonged human exposure. Early amphetamine treatment has been linked to slowing in height and weight growth in some children. Because the number of prescriptions for amphetamines has increased several fold over the past decade, an amphetamine-containing formulation is the most commonly prescribed stimulant in North America, and it is noteworthy that amphetamines are also the most abused prescription medications. Although early treatment does not increase risk for substance abuse, few studies have tracked the compliance and usage profiles of individuals who began amphetamine treatment as adults. Overall, there is concern about risk for slowed growth in young patients who are dosed continuously, and for substance abuse in patients first medicated in late adolescence or adulthood. Although most adult patients also use amphetamines effectively and safely, occasional case reports indicate that prescription use can produce marked psychological adverse events, including stimulant-induced psychosis. Assessments of central toxicity and adverse psychological effects during late adulthood and senescence of adults who receive prolonged courses of amphetamine treatment are warranted. Finally, identification of the biological factors that confer risk and those that offer protection is also needed to better specify the parameters of safe, long-term, therapeutic administration of amphetamines to adults.

Abuse of amphetamines and structural abnormalities in the brain

We review evidence that structural brain abnormalities are associated with abuse of amphetamines. A brief history of amphetamine use/abuse and evidence for toxicity is followed by a summary of findings from structural magnetic resonance imaging (MRI) studies of human subjects who had abused amphetamines and children who were exposed to amphetamines in utero. Evidence comes from studies that used a variety of techniques including manual tracing, pattern matching, voxel-based, tensor-based, or cortical thickness mapping, quantification of white matter signal hyperintensities, and diffusion tensor imaging. Ten studies compared controls to individuals who were exposed to methamphetamine. Three studies assessed individuals exposed to 3-4-methylenedioxymethamphetamine (MDMA). Brain structural abnormalities were consistently reported in amphetamine abusers, as compared to control subjects. These included lower cortical gray matter volume and higher striatal volume than control subjects. These differences might reflect brain features that could predispose to substance dependence. High striatal volumes might also reflect compensation for toxicity in the dopamine-rich basal ganglia. Prenatal exposure was associated with striatal volume that was below control values, suggesting that such compensation might not occur in utero. Several forms of white matter abnormality are also common and may involve gliosis. Many of the limitations and inconsistencies in the literature relate to techniques and cross-sectional designs, which cannot infer causality. Potential confounding influences include effects of pre existing risk/protective factors, development, gender, severity of amphetamine abuse, abuse of other drugs, abstinence, and differences in lifestyle. Longitudinal designs in which multimodal datasets are acquired and are subjected to multivariate analyses would enhance our ability to provide general conclusions regarding the associations between amphetamine abuse and brain structure.

Zinc rescues dopaminergic SK-N-SH cell lines from methamphetamine-induced toxicity

Methamphetamine (METH) is a potent inducer of dopamine (DA) release, and is toxic to DA neurons. It has been reported that the formation of free radicals is an early signaling event that mediates cell death caused by METH. Currently, studies suggest that the generation of free radicals by oxidative catabolism of DA and dysfunction of the mitochondrial respiration chain are important mediators of neuronal death in Parkinson's disease (PD) and one process may counter the effect of the other. In our previous study, we investigated the deleterious effects of METH-induced reactive oxygen species (ROS) and mitochondrial dysfunction in dopaminergic SK-N-SH cells in culture, and assessed whether zinc-metallothionein induction provided mitochondrial protection against METH-induced mitochondrial dysfunction. Our present data demonstrate that METH enhances lipid peroxidation and mitochondrial manganese superoxide dismutase (MnSOD) enzyme levels, and decreases the antioxidant-reduced glutathione (GSH) together with an inhibition of mitochondrial complex-I activity. Pre-treatment with zinc markedly prevents the increase of lipid peroxidation and provides mitochondrial protection by scavenging free radicals via metallothionein and by increasing mitochondrial GSH and complex-I levels, thus rescuing SK-N-SH cells from METH toxicity. It should be emphasized that, however, it is still not clear that effects of METH on cultured SK-N-SH reliably model the effects of METH in the intact animal. Further studies in the intact animal are needed.

Melatonin inhibits amphetamine-induced increase in alpha-synuclein and decrease in phosphorylated tyrosine hydroxylase in SK-N-SH cells

alpha-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegeneration disorders. Understanding alpha-synuclein function in dopaminergic cells could add to our knowledge of this key protein which is implicated in Parkinson's disease. Chronic or intermittent amphetamine (AMPH) abuse may create temporary or permanent disturbances in the dopaminergic system of the brain that may predispose individuals to Parkinsonism. Our previous studies showed that neurotoxicity induced by AMPH was mediated by enhanced oxidative stress and these effects were abolished by melatonin, a main secretory product of pineal gland. The present study was conducted to investigate the effect of AMPH on alpha-synuclein in regulating tyrosine hydroxylase (TH), a rate limiting enzyme for dopamine synthesis, in cultured human dopaminergic SK-N-SH cells. Of these, phosphorylation of Ser40 (pSer40) contributes significantly to TH activation and dopamine synthesis. Our data indicated that AMPH significantly increased the level of alpha-synuclein to 183% of the control value while reducing the levels of phosphorylated TH (TH-pSer40) enzyme and mitochondrial complex I to 78 and 52.9% of the control values, respectively and these effects were attenuated by melatonin. Further studies are needed to explore the mechanism by which alpha-synuclein contributes to TH-pSer40 dephosphorylation and the mechanism by which melatonin contributes to this interaction.

Melatonin reduces the neuronal loss, downregulation of dopamine transporter, and upregulation of D2 receptor in rotenone-induced parkinsonian rats

Parkinson's disease (PD) is a movement disorder resulting from nigrostriatal dopaminergic neurodegeneration. The impairment of mitochondrial function and dopamine synaptic transmission are involved in the pathogenesis of PD. Two mitochondrial inhibitors, 1-methyl-4-phenylpyridine (MPP(+)) and rotenone, have been used to induce dopaminergic neuronal death both in in vitro and in vivo models of PD. Because the uptake of MPP(+) is mediated by the dopamine transporter (DAT), we used a cell-permeable rotenone-induced PD model to investigate the role of DAT and dopamine D2 receptor (D2R) on dopaminergic neuronal loss. Rotenone subcutaneously infused for 14 days induced PD symptoms in rats, as indicated by reduced spontaneous locomotor activity (hypokinesis), loss of tyrosine hydroxylase (TH, a marker enzyme for dopamine neurons) immunoreactivity in the substantia nigra and striatum, obvious alpha-synuclein accumulation, downregulated DAT protein expression, and upregulated D2R expression. Interestingly, rotenone also caused significant noradrenergic neuronal loss in the locus coeruleus. Melatonin, an antioxidant, prevented nigrostriatal neurodegeneration and alpha-synuclein aggregation without affecting the rotenone-induced weight loss and hypokinesis. However, rotenone-induced hypokinesis was markedly reversed by the DAT antagonist nomifensine and body weight loss was attenuated by the D2R antagonist sulpiride. In addition, both antagonists significantly prevented the reduction of striatal TH or DAT immunoreactivity but not the loss of nigral TH- and DAT-immunopositive neurons. These results suggested that oxidative stress and DAT downregulation are involved in the rotenone-induced pathogenesis of nigrostriatal dopaminergic neurodegeneration, whereas D2R upregulation may simply represent a compensatory response.