Melatonin prevents cytoskeletal alterations and oxidative stress induced by okadaic acid in N1E-115 cells

Nootropic effect of Indian Royal Jelly against okadaic acid induced rat model of Alzheimer's disease: Inhibition of neuroinflammation and acetylcholineesterase

Background

Royal jelly is an anti-inflammatory, antioxidant, and neuroprotective bee product. There are several sources for royal jelly and one of them is Indian Royal Jelly (IRJ). However, the neuroprotective actions of IRJ and the underlying molecular mechanisms involved are not well known.

Objective

To evaluate the neuroprotective effect of IRJ in the okadaic acid (OKA)-induced Alzheimer's disease (AD) model in rats.

Methods

In male Wistar rats, OKA was intracerebroventricularly (ICV) administered, and from day 7, they were treated orally with IRJ or memantine for 21 days. Spatial and recognition learning and memory were evaluated from days 27-34; employing the Morris water maze (MWM) and the novel object recognition tests (NORT), respectively. In vitro biochemical measurements were taken of the cholinergic system and oxidative stress markers. In silico docking was used to find the role of tau protein kinase and phosphatase in the pharmacological action.

Results

In OKA-induced rats, IRJ decreased the escape latency and path length in MWM and increased the exploration time for novel objects and the discrimination index in NORT. ICV-OKA rats had higher free radicals and cytokines that caused inflammation and their level of free radical scavengers was back to normal with IRJ treatment. IRJ increased the level of acetylcholine and inhibited acetylcholinesterase. Moreover, the in silico docking study revealed the strong binding affinity of 10-hydroxy-2-decenoic acid (10-HDA), a bioactive constituent of IR, to the tau protein kinases and phosphatases.

Conclusion

IRJ may serve as a nootropic agent in the treatment of dementia, and owing to its capacity to prevent oxidative stress and neuroinflammation, and increase cholinergic tone; it has the potential to be explored as a novel strategy for the treatment of dementia and AD. More studies may be needed to develop 10-HDA as a novel drug entity for AD.

Melatonin Rescues the Dendrite Collapse Induced by the Pro-Oxidant Toxin Okadaic Acid in Organotypic Cultures of Rat Hilar Hippocampus

The pro-oxidant compound okadaic acid (OKA) mimics alterations found in Alzheimer's disease (AD) as oxidative stress and tau hyperphosphorylation, leading to neurodegeneration and cognitive decline. Although loss of dendrite complexity occurs in AD, the study of this post-synaptic domain in chemical-induced models remains unexplored. Moreover, there is a growing expectation for therapeutic adjuvants to counteract these brain dysfunctions. Melatonin, a free-radical scavenger, inhibits tau hyperphosphorylation, modulates phosphatases, and strengthens dendritic arbors. Thus, we determined if OKA alters the dendritic arbors of hilar hippocampal neurons and whether melatonin prevents, counteracts, or reverses these damages. Rat organotypic cultures were incubated with vehicle, OKA, melatonin, and combined treatments with melatonin either before, simultaneously, or after OKA. DNA breaks were assessed by TUNEL assay and nuclei were counterstained with DAPI. Additionally, MAP2 was immunostained to assess the dendritic arbor properties by the Sholl method. In hippocampal hilus, OKA increased DNA fragmentation and reduced the number of MAP2(+) cells, whereas melatonin protected against oxidation and apoptosis. Additionally, OKA decreased the dendritic arbor complexity and melatonin not only counteracted, but also prevented and reversed the dendritic arbor retraction, highlighting its role in post-synaptic domain integrity preservation against neurodegenerative events in hippocampal neurons.

Role of Melatonin in Aluminum-Related Neurodegenerative Disorders: a Review

Aluminum (Al), a potentially neurotoxic element, provokes various adverse effects on human health such as dialysis dementia, osteomalacia, and microcytic anemia. It has been also associated with serious neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis, and Parkinsonism dementia of Guam. The "aluminum hypothesis" of AD assumes that the metal complexes can potentiate the rate of aggregation of amyloid-β (Aβ), enhancing the toxicity of this peptide, and being able of contributing to the pathogenesis of AD. It has been supported by a number of analytical, epidemiological, and neurotoxicological studies. On the other hand, melatonin (Mel) is a potent direct free radical scavenger and indirect antioxidant, which acts increasing the activity of important related antioxidant enzymes, and preventing oxidative stress and cell death of neurons exposed to Aβ-induced neurotoxicity. Therefore, Mel might be useful in the treatment of AD by reducing the Aβ generation and by inhibiting mitochondrial cell death pathways. The present review on the role of Mel in Al-related neurodegenerative disorders concludes that the protective effects of this hormone, together with its low toxicity, support the administration of Mel as a potential supplement in the treatment of neurological disorders, in which oxidative stress is involved.

Melatonin: Clinical Perspectives in Neurodegeneration

Prevention of neurodegenerative diseases is presently a major goal for our Society and melatonin, an unusual phylogenetically conserved molecule present in all aerobic organisms, merits consideration in this respect. Melatonin combines both chronobiotic and cytoprotective properties. As a chronobiotic, melatonin can modify phase and amplitude of biological rhythms. As a cytoprotective molecule, melatonin reverses the low degree inflammatory damage seen in neurodegenerative disorders and aging. Low levels of melatonin in blood characterizes advancing age. In experimental models of Alzheimer's disease (AD) and Parkinson's disease (PD) the neurodegeneration observed is prevented by melatonin. Melatonin also increased removal of toxic proteins by the brain glymphatic system. A limited number of clinical trials endorse melatonin's potentiality in AD and PD, particularly at an early stage of disease. Calculations derived from animal studies indicate cytoprotective melatonin doses in the 40-100 mg/day range. Hence, controlled studies employing melatonin doses in this range are urgently needed. The off-label use of melatonin is discussed.

Apoptosis signaling pathways in osteoarthritis and possible protective role of melatonin

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive erosion of articular cartilage. As chondrocytes are the only cell type forming the articular cartilage, their gradual loss is the main cause of OA. There is a substantial body of published research that suggests reactive oxygen species (ROS) are major causative factors for chondrocyte damage and OA development. Oxidative stress elicited by ROS is capable of oxidizing and subsequently disrupting cartilage homeostasis, promoting catabolism via induction of cell death and damaging numerous components of the joint. IL-1β and TNF-α are crucial inflammatory factors that play pivotal roles in the pathogenesis of OA. In this process, the mitochondria are the major source of ROS production in cells, suggesting a role of mitochondrial dysfunction in this type of arthritis. This may also be promoted by inflammatory cytokines such as IL-1β and TNF-α which contribute to chondrocyte death. In patients with OA, the expression of endoplasmic reticulum (ER) stress-associated molecules is positively correlated with cartilage degeneration. Melatonin and its metabolites are broad-spectrum antioxidants and free radical scavengers which regulate a variety of molecular pathways such as inflammation, proliferation, apoptosis, and metastasis in different pathophysiological situations. Herein, we review the effects of melatonin on OA, focusing on its ability to regulate apoptotic processes and ER and mitochondrial activity. We also evaluate likely protective effects of melatonin on OA pathogenesis.

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.

Melatonin Therapy in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is a major health problem and a growing recognition exists that efforts to prevent it must be undertaken by both governmental and non-governmental organizations. In this context, the pineal product, melatonin, has a promising significance because of its chronobiotic/cytoprotective properties potentially useful for a number of aspects of AD. One of the features of advancing age is the gradual decrease in circulating melatonin levels. A limited number of therapeutic trials have indicated that melatonin has a therapeutic value as a neuroprotective drug in the treatment of AD and minimal cognitive impairment (which may evolve to AD). Both in vitro and in vivo, melatonin prevented the neurodegeneration seen in experimental models of AD. For these effects to occur, doses of melatonin about two orders of magnitude higher than those required to affect sleep and circadian rhythmicity are needed. More recently, attention has been focused on the development of potent melatonin analogs with prolonged effects, which were employed in clinical trials in sleep-disturbed or depressed patients in doses considerably higher than those employed for melatonin. In view that the relative potencies of the analogs are higher than that of the natural compound, clinical trials employing melatonin in the range of 50-100 mg/day are urgently needed to assess its therapeutic validity in neurodegenerative disorders such as AD.

Berberine attenuates axonal transport impairment and axonopathy induced by Calyculin A in N2a cells

Berberine is a primary component of the most functional extracts of Coptidis rhizome used in traditional Chinese medicine for centuries. Recent reports indicate that Berberine has the potential to prevent and treat Alzheimer's disease (AD). The previous studies reported that Calyculin A (CA) impaired the axonal transport in neuroblastoma-2a (N2a) cells. Berberine attenuated tau hyperphosphorylation and cytotoxicity induced by CA. Our study aimed at investigating the effects of Berberine on the axonal transport impairment induced by CA in N2a cells. The results showed that Berberine could protect the cell from CA -induced toxicity in metabolism and viability, as well as hyperphosphorylation of tau and neurofilaments (NFs). Furthermore, Berberine could reverse CA-induced axonal transport impairment significantly. Berberine also partially reversed the phosphorylation of the catalytic subunit of PP-2A at Tyrosine 307, a crucial site negatively regulating the activity of PP-2A, and reduced the levels of malondialdehyde and the activity of superoxide dismutase, markers of oxidative stress, induced by CA. The present work for the first time demonstrates that Berberine may play a role in protecting against CA-induced axonal transport impairment by modulating the activity of PP-2A and oxidative stress. Our findings also suggest that Berberine may be a potential therapeutic drug for AD.

The role of melatonin in anaesthesia and critical care

Melatonin is a neurohormone secreted by the pineal gland. It is widely present in both plant and animal sources. In several countries, it is sold over the counter as tablets and as food supplement or additive. Currently, it is most often used to prevent jet lag and to induce sleep. It has been and is being used in several clinical trials with different therapeutic approaches. It has sedative, analgesic, anti-inflammatory, anti-oxidative and chronobiotic effects. In the present review, the potential therapeutic benefits of melatonin in anaesthesia and critical care are presented. This article aims to review the physiological properties of melatonin and how these could prove useful for several clinical applications in perioperative management, critical care and pain medicine. The topic was handsearched from textbooks and journals and electronically from PubMed, and Google scholar using text words.

Molecular mechanisms of melatonin's inhibitory actions on breast cancers

Melatonin is involved in many physiological functions and it plays an important role in many pathological processes as well. Melatonin has been shown to reduce the incidence of experimentally induced cancers and can significantly inhibit the growth of some human tumors, namely hormone-dependent cancers. The anticancer effects of melatonin have been observed in breast cancer, both in in vivo with models of chemically induced rat mammary tumors, and in vitro studies on human breast cancer cell lines. Melatonin acts at different physiological levels and its antitumoral properties are supported by a set of complex, different mechanisms of action, involving apoptosis activation, inhibition of proliferation, and cell differentiation.

Melatonin anticancer effects: review

Melatonin (N-acetyl-5-methoxytryptamine, MLT), the main hormone produced by the pineal gland, not only regulates circadian rhythm, but also has antioxidant, anti-ageing and immunomodulatory properties. MLT plays an important role in blood composition, medullary dynamics, platelet genesis, vessel endothelia, and in platelet aggregation, leukocyte formula regulation and hemoglobin synthesis. Its significant atoxic, apoptotic, oncostatic, angiogenetic, differentiating and antiproliferative properties against all solid and liquid tumors have also been documented. Thanks, in fact, to its considerable functional versatility, MLT can exert both direct and indirect anticancer effects in factorial synergy with other differentiating, antiproliferative, immunomodulating and trophic molecules that form part of the anticancer treatment formulated by Luigi Di Bella (Di Bella Method, DBM: somatostatin, retinoids, ascorbic acid, vitamin D3, prolactin inhibitors, chondroitin-sulfate). The interaction between MLT and the DBM molecules counters the multiple processes that characterize the neoplastic phenotype (induction, promotion, progression and/or dissemination, tumoral mutation). All these particular characteristics suggest the use of MLT in oncological diseases.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Identification of differentially expressed genes in SHSY5Y cells exposed to okadaic acid by suppression subtractive hybridization

Background

Okadaic acid (OA), a toxin produced by several dinoflagellate species is responsible for frequent food poisonings associated to shellfish consumption. Although several studies have documented the OA effects on different processes such as cell transformation, apoptosis, DNA repair or embryogenesis, the molecular mechanistic basis for these and other effects is not completely understood and the number of controversial data on OA is increasing in the literature.

Results

In this study, we used suppression subtractive hybridization in SHSY5Y cells to identify genes that are differentially expressed after OA exposure for different times (3, 24 and 48 h). A total of 247 subtracted clones which shared high homology with known genes were isolated. Among these, 5 specific genes associated with cytoskeleton and neurotransmission processes (NEFM, TUBB, SEPT7, SYT4 and NPY) were selected to confirm their expression levels by real-time PCR. Significant down-regulation of these genes was obtained at the short term (3 and 24 h OA exposure), excepting for NEFM, but their expression was similar to the controls at 48 h.

Conclusions

From all the obtained genes, 114 genes were up-regulated and 133 were down-regulated. Based on the NCBI GenBank and Gene Ontology databases, most of these genes are involved in relevant cell functions such as metabolism, transport, translation, signal transduction and cell cycle. After quantitative PCR analysis, the observed underexpression of the selected genes could underlie the previously reported OA-induced cytoskeleton disruption, neurotransmission alterations and in vivo neurotoxic effects. The basal expression levels obtained at 48 h suggested that surviving cells were able to recover from OA-caused gene expression alterations.

Melatonin improves D-galactose-induced aging effects on behavior, neurogenesis, and lipid peroxidation in the mouse dentate gyrus via increasing pCREB expression

Melatonin (N-acetyl-5-methoxytryptamine) has multiple functions. In this study, we investigated the effects of melatonin on memory, cell proliferation, and neuroblast differentiation in the dentate gyrus of a mouse model of D-galactose-induced aging. D-galactose was subcutaneously administered to 7-wk-old mice for 10 wk, and age-matched mice were used as controls. Seven weeks after D-galactose administration, vehicle (water) or melatonin (6 mg/L in water) was administered ad libitum to the mice for 3 wk. The administration of D-galactose significantly increased the escape latency compared with that in the control mice on days 1-3. In addition, cells in the subgranular zone and in the granule cell layer of the dentate gyrus showed severe damage (cytoplasmic condensation) in the D-galactose-treated mice. However, melatonin supplementation to these mice for 3 wk significantly ameliorated the D-galactose-induced increase in escape latency and neuronal damage compared with the vehicle-treated group. The administration of melatonin also significantly restored the D-galactose-induced reduction of proliferating cells (Ki67-positive cells) and differentiating neuroblasts (doublecortin-positive neuroblasts) in the dentate gyrus. Furthermore, the administration of melatonin significantly increased Ser133-phosphorylated cyclic AMP response element binding protein in the dentate gyrus. The administration of melatonin significantly reduced D-galactose-induced lipid peroxidation in the dentate gyrus. These results suggest that melatonin may be helpful in reducing age-related phenomena in the brain.

Melatonin: neuritogenesis and neuroprotective effects in crustacean x-organ cells

Melatonin has both neuritogenic and neuroprotective effects in mammalian cell lines such as neuroblastoma cells. The mechanisms of action include receptor-coupled processes, direct binding and modulation of calmodulin and protein kinase C, and direct scavenging of free radicals. While melatonin is produced in invertebrates and has influences on their physiology and behavior, little is known about its mechanisms of action. We studied the influence of melatonin on neuritogenesis in well-differentiated, extensively-arborized crustacean x-organ neurosecretory neurons. Melatonin significantly increased neurite area in the first 24h of culture. The more physiological concentrations, 1 nM and 1 pM, increased area at 48 h also, whereas the pharmacological 1 μM concentration appeared to have desensitizing effects by this time. Luzindole, a vertebrate melatonin receptor antagonist, had surprising and significant agonist-like effects in these invertebrate cells. Melatonin receptors have not yet been studied in invertebrates. However, the presence of membrane-bound receptors in this population of crustacean neurons is indicated by this study. Melatonin also has significant neuroprotective effects, reversing the inhibition of neuritogenesis by 200 and 500 μM hydrogen peroxide. Because this is at least in part a direct action not requiring a receptor, melatonin's protection from oxidative stress is not surprisingly phylogenetically-conserved.

Melatonin reduces the impairment of axonal transport and axonopathy induced by calyculin A

Previous studies have reported that calyculin A (CA), a selective inhibitor of protein phosphatase (PP)-2A and PP-1, impairs axonal transport in neuroblastoma N2a cells. Melatonin prevents Alzheimer-like hyperphosphorylation of cytoskeletal proteins and the impairment of spatial memory retention induced by CA. In this study, we tested the effects of melatonin on the impairment of axonal transport induced by CA in neuroblastoma N2a cells. We found that melatonin protected the cells from CA-induced toxicity in metabolism and viability as well as hyperphosphorylation of tau and neurofilaments. Furthermore, melatonin partially reversed the CA-induced phosphorylation of the catalytic subunit of PP-2A at tyrosine 307, a crucial site that negatively regulates the activity of PP-2A, and reduced the levels of malondialdehyde and the activity of superoxide dismutase, which are markers of oxidative stress. Melatonin also significantly reversed the CA-induced impairment of axonal transport. These results suggest that melatonin may have a role in protecting against the CA-induced impairment of axonal transport by modulating the activity of PP-2A and oxidative stress.

Melatonin and its agonist ramelteon in Alzheimer's disease: possible therapeutic value

Alzheimer's disease (AD) is an age-associated neurodegenerative disease characterized by the progressive loss of cognitive function, loss of memory and insomnia, and abnormal behavioral signs and symptoms. Among the various theories that have been put forth to explain the pathophysiology of AD, the oxidative stress induced by amyloid β-protein (Aβ) deposition has received great attention. Studies undertaken on postmortem brain samples of AD patients have consistently shown extensive lipid, protein, and DNA oxidation. Presence of abnormal tau protein, mitochondrial dysfunction, and protein hyperphosphorylation all have been demonstrated in neural tissues of AD patients. Moreover, AD patients exhibit severe sleep/wake disturbances and insomnia and these are associated with more rapid cognitive decline and memory impairment. On this basis, the successful management of AD patients requires an ideal drug that besides antagonizing Aβ-induced neurotoxicity could also correct the disturbed sleep-wake rhythm and improve sleep quality. Melatonin is an effective chronobiotic agent and has significant neuroprotective properties preventing Aβ-induced neurotoxic effects in a number of animal experimental models. Since melatonin levels in AD patients are greatly reduced, melatonin replacement has the potential value to be used as a therapeutic agent for treating AD, particularly at the early phases of the disease and especially in those in whom the relevant melatonin receptors are intact. As sleep deprivation has been shown to produce oxidative damage, impaired mitochondrial function, neurodegenerative inflammation, and altered proteosomal processing with abnormal activation of enzymes, treatment of sleep disturbances may be a priority for arresting the progression of AD. In this context the newly introduced melatonin agonist ramelteon can be of much therapeutic value because of its highly selective action on melatonin MT₁/MT₂ receptors in promoting sleep.

Haloperidol causes cytoskeletal collapse in N1E-115 cells through tau hyperphosphorylation induced by oxidative stress: Implications for neurodevelopment

Haloperidol a typical antipsychotic commonly used in the treatment of schizophrenia causes neuronal damage and extrapiramidal symptoms after several years of treatment. These symptoms have been associated with increased levels of oxidative stress. Reactive oxygen species produce cytoskeletal collapse and an excessive phosphorylation of tau, a microtubule-associated protein that plays a key role in microtubule stabilization, and in growth cone and neurite formation, which are cytoskeletal phenotypes that participate in neurodevelopment. Thus, we hypothesized that haloperidol produces neurocytoskeletal disorganization by increasing free radicals and tau hyperphosphorylation, and consequently, the loss of neurodevelopmental cytoskeletal phenotypes, neurites and growth cones. The purpose of this work was the characterization of neuronal cytoskeletal changes caused by haloperidol in neuroblastoma N1E-115 cells. We also studied the mechanisms by which haloperidol causes cytoskeletal changes. The results showed that haloperidol at 100microM caused a complete cytoskeleton collapse in the majority of the cells. Melatonin, a free radical scavenger, blocks tau hyperphosphorylation, and microtubule disorganization caused by haloperidol in a dose-response mode. Additionally, the indole blocks lipoperoxide formation in haloperidol treated cells. The results indicate that free radicals and tau hyperphosphorylation produced by haloperidol caused a cytoskeletal collapse and the lost of growth cones and neurites. These effects were blocked by melatonin. Data suggest that extrapiramidal symptoms in schizophrenic patients can be produced by cytoskeletal disorganization during adult brain neurodevelopment after prolonged haloperidol treatment that can be prevented by melatonin.

Microtubules modulate melatonin receptors involved in phase-shifting circadian activity rhythms: in vitro and in vivo evidence

MT1 melatonin receptors expressed in Chinese hamster ovary (CHO) cells remain sensitive to a melatonin re-challenge even following chronic melatonin exposure when microtubules are depolymerized in the cell, an exposure that normally results in MT1 receptor desensitization. We extended our findings to MT2 melatonin receptors using both in vitro and in vivo approaches. Using CHO cells expressing human MT2 melatonin receptors, microtubule depolymerization prevents the loss in the number of high potency states of the receptor when compared to melatonin-treated cells. In addition, microtubule depolymerization increases melatonin-induced PKC activity but not PI hydrolysis via Gi proteins similar to that shown for MT1Rs. Furthermore, microtubule depolymerization in MT2-CHO cells enhances the exchange of GTP on Gi-proteins using a photoaffinity analog of GTP. To test whether microtubules are capable of modulating melatonin-induced phase-shifts, microtubules are depolymerized specifically within the suprachiasmatic nucleus of the hypothalamus (SCN) of the Long Evans rat and the efficacy of melatonin to phase shift their circadian activity rhythms was assessed and compared to animals with intact SCN microtubules. We find that microtubule depolymerization in the SCN using either Colcemid or nocodazole enhances the efficacy of 10 pm melatonin to phase-shift the activity rhythms of the Long Evans rat. No enhancement occurs in the presence of beta-lumicolchicine, the inactive analog of Colcemid. Taken together, these data suggest that microtubule dynamics can modulate melatonin-induced phase shifts of circadian activity rhythms which may explain, in part, why circadian disturbances occur in individuals afflicted with diseases associated with microtubule disturbances.

Melatonin attenuates the decrement of dendritic protein MAP-2 immuno-staining in the hippocampal CA1 and CA3 fields of the aging male rat

Neuronal death during brain aging results, at least in part, from the disruption of synaptic connectivity caused by oxidative stress. Synaptic elimination might be caused by increased instability of the neuronal processes. In vitro evidence shows that melatonin increases MAP-2 expression, a protein that improves the stability of the dendritic cytoskeleton, opening the possibility that melatonin could prevent synaptic elimination by increasing dendritic stability. One way to begin exploring this issue in vivo is to evaluate whether long-term melatonin treatment changes the intensity of MAP-2 immuno-staining in areas commonly afflicted by aging that are rich in dendritic processes. Accordingly, we evaluated the effects of administering melatonin for 6 or 12 months on the intensity of MAP-2 immuno-staining in the strata oriens and lucidum of the hippocampal CA1 and CA3 fields of aging male rats, through semi-quantitative densitometry. Melatonin treated rats showed a relative increment in the intensity of MAP-2 immuno-staining in both regions after 6 or 12 months of treatment, as compared with age matched control rats. Although melatonin untreated and treated rats showed a decrease of MAP-2 immuno-staining in the hippocampus with increasing age, such decrement was less pronounced following melatonin treatment. These findings were confirmed by qualitative Western blot analyses. The melatonin effect seems specific because MAP-2 staining in the primary somatosensory cortex was not affected by the treatment. Thus, chronic melatonin administration increases MAP-2 immuno-staining and attenuates its decay in the adult aging hippocampus. These results are compatible with the idea that melatonin could improve dendritic stability and thus diminish synaptic elimination in the aging brain.

Favorable effects of a prolonged treatment with melatonin on the level of oxidative damage and neurodegeneration in senescence-accelerated mice

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Inhibition of protein phosphatases impairs the ability of astrocytes to detoxify hydrogen peroxide

We have used protein phosphatase (PP) inhibitors and rat cerebellar glial cells in primary culture to investigate the role of PP activity in the ability of glial cells to detoxify exogenously applied hydrogen peroxide (H2O2). The marine toxin okadaic acid (OKA), a potent PP1 and PP2A inhibitor, caused a concentration-dependent degeneration of astrocytes and increased the formation of hydroperoxide radicals significantly. Subtoxic exposures to OKA significantly potentiated toxicity by exogenous H2O2. The concentration of H2O2 that reduced by 50% the survival of astrocytes after 3 h was estimated at 720+/-40 microM in the absence and 85+/-30 microM in the presence of the toxin. The PP inhibitors calyculin A and endothall also potentiated H2O2 toxicity in cerebellar astrocytes. OKA caused a time-dependent inhibition of both glial catalase and glutathione peroxidase, reducing by approximately 50% the activity of these enzymes after 3 h, whereas other enzymatic activities remained unaffected. Also, OKA reduced the cellular content of total glutathione and elevated oxidized glutathione to about 25% of total glutathione. OKA-treated astrocytes cleared H2O2 from the incubation medium approximately two times more slowly than control cultures. Our results suggest a prominent role for PP activity in the antioxidant mechanisms protecting astrocytes against damage by H2O2.

Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau

Hyperphosphorylated tau has long been proposed as the key molecule disrupting normal neuronal microtubule dynamics and leading to neurofibrillary degeneration in Alzheimer disease. Here we provide a direct evidence of hyperphosphorylated tau-induced disruption of microtubule network. Using Nocodozole-treated and detergent-extracted cells, we created a neuronal environment in mouse embryonic fibroblasts, 3T3 cells, by replacing their cytoplasm with adult rat brain cytosol. By recreating neuronal microtubule network in these cells, we were able to follow the effects of hyperphosphorylated tau on microtubule dynamics in real time. Whereas recombinant human brain tau promoted assembly and bundling of microtubules, abnormally hyperphosphorylated tau isolated from Alzheimer disease brain cytosol (AD P-tau) inhibited the assembly and disrupted preformed microtubule network by sequestering normal brain tau and MAP2. This breakdown of the microtubule network was reversed by treatment of the extracted cells with protein phosphatase-2A. This study, for the first time, provides direct mechanistic insights into the molecular basis of both axonal and dendritic neurodegeneration seen in Alzheimer disease.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Melatonin as a cytoskeletal modulator: implications for cell physiology and disease

The cytoskeleton is a phylogenetically well-preserved structure that plays a key role in cell physiology. Dynamic and differential changes in cytoskeletal organization occur in cellular processes according to the cell type and the specific function. In neurons, microtubules, microfilaments and intermediate filament (IF) rearrangements occur during axogenesis, and neurite formation which eventually differentiate into axons and dendrites to constitute synaptic patterns of connectivity. In epithelial cells, dynamic modifications occur in the three main cytoskeletal components and phosphorylation of cytoskeletal associated proteins takes place during the formation of the epithelial cell monolayer that eventually will transport water. In pathological processes such as neurodegenerative and psychiatric diseases an abnormal cytoskeletal organization occurs. Melatonin, the main product secreted by pineal gland during dark phase of the photoperiod, is capable of influencing microfilament, microtubule and IF organization by acting as a cytoskeletal modulator. In this paper we will summarize the evidence which provides the data that melatonin regulates cytoskeletal organization and we describe recent findings, which indicate that melatonin effects on microfilament rearrangements in stress fibers are involved in the mechanism by which the indole synchronizes water transport in kidney-derived epithelial cells. In addition, we review recent data, which indicates that melatonin protects the neuro-cytoskeletal organization from damage caused by free radicals contributing to cell survival, in addition to the already described mechanism elicited by the indole to prevent apoptosis and to scavenge free radicals. Moreover, we discuss the implications of an altered cytoskeletal organization for neurodegenerative and psychiatric illnesses and its re-establishment by melatonin.

Role of melatonin in Alzheimer-like neurodegeneration

Alzheimer disease (AD), an age-related neurodegenerative disorder with progressive loss of memory and deterioration of comprehensive cognition, is characterized by extracellular senile plaques of aggregated beta-amyloid (Abeta), and intracellular neurofibrillary tangles that contain hyperphosphorylated tau protein. Recent studies showed that melatonin, an indoleamine secreted by the pineal gland, may play an important role in aging and AD as an antioxidant and neuroprotector. Melatonin decreases during aging and patients with AD have a more profound reduction in this hormone. Data from clinical trials indicate that melatonin supplementation improves sleep, ameliorates sundowning, and slows down the progression of cognitive impairment in Alzheimer patients. Melatonin efficiently protects neuronal cells from Abeta-mediated toxicity via antioxidant and anti-amyloid properties: it not only inhibits Abeta generation, but also arrests the formation of amyloid fibrils by a structure-dependent interaction with Abeta. Our recent studies have demonstrated that melatonin efficiently attenuates Alzheimer-like tau hyperphosphorylation. Although the exact mechanism is still not fully understood, a direct regulatory influence of melatonin on the activities of protein kinases and protein phosphatases is proposed. Additionally, melatonin also plays a role in protecting cholinergic neurons and in anti-inflammation. Here, the neuroprotective effects of melatonin and the underlying mechanisms by which it exerts its effects are reviewed. The capacity of melatonin to prevent or ameliorate tau and Abeta pathology further enhances its potential in the prevention or treatment of AD.

Parachlorophenylalanine Exacerbates Oxidative Stress Induced by Gentamicin in Rats

The present work studies the effect of parachlorophenylalanine (PCPA, 200 mg/kg intraperitoneally/48 hr for 7 days) on the oxidative stress and nephropathy induced by gentamicin (80 mg/kg intraperitoneally/daily for 7 days) in Wistar rats. The effect of PCPA on lipid peroxidation products and reduced glutathione content in renal and brain tissue, as well as on 5HT content in brain was assessed. Catalase and superoxide dismutase activities were determined in brain tissue. Blood urea nitrogen and creatinine in plasma and total protein content in urine were also measured. Gentamicin caused significant increases in proteinuria, non-protein nitrogen compounds and lipid peroxidation markers, together with decreases in both reduced glutathione content in renal and brain tissue and enzymatic activities in brain homogenates. PCPA harnessed the effect of gentamicin in the brain and the kidney, while PCPA alone induced brain oxidative stress. These results support the prooxidant action of PCPA in brain tissue and its capacity to exacerbate the oxidative stress and renal dysfunction induced by gentamicin, as well as the possible antioxidant property of serotonin.

Melatonin reduces oxidative stress and increases gene expression in the cerebral cortex and cerebellum of aluminum-exposed rats

The pro-oxidant activity of aluminum (Al), the protective role of exogenous melatonin, as well as the mRNA levels of some antioxidant enzymes, were determined in cortex and cerebellum of rats following exposure to Al and/or melatonin. Two groups of male rats received intraperitoneal injections of Al lactate or melatonin at doses of 7 mg Al/kg/day and 10 mg/kg/day, respectively, for 11 wk. A third group of animals received concurrently Al lactate (7 mg Al/kg/day) plus melatonin (10 mg/kg/day) during the same period. A fourth group of rats was used as control. At the end of the treatment, the cerebral cortex and cerebellum were removed and processed to examine the following oxidative stress markers: glutathione transferase (GST), reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), glutathione reductase, glutathione peroxidase (GPx), catalase (CAT), thiobarbituric acid reactive substances (TBARS), as well as protein content. Moreover, gene expression of Cu-ZnSOD, MnSOD, GPx and CAT was evaluated by real-time RT-PCR. On the other hand, Al, Fe, Mn, Cu and Zn concentrations were determined in cortex and cerebellum of rats. Oxidative stress was promoted in both neural regions following Al administration, resulting from the pro-oxidant activity related with an increase in tissue Al concentrations. In contrast, melatonin exerted an antioxidant action which was related with an increase in the mRNA levels of the antioxidant enzymes evaluated. The results of the present investigation emphasize the potential use of melatonin as a supplement in the therapy of neurological disorders in which oxidative stress is involved.

Effect of melatonin on calyculin A-induced tau hyperphosphorylation

We have found in the present study that incubation of neuroblastma N2a with calyculin A, an inhibitor of protein phosphatase-2A (PP-2A) and protein phosphatase-1 (PP-1), reduces cell viability in a dose-dependent manner, and leads to tau hyperphosphorylation at tau-1 (Ser198/199/202) and PHF-1 (Ser396/404) epitopes. In addition to inhibit PP-2A, calyculin A treatment also results in significant activation of glycogen synthase kinase-3 (GSK-3). Calyculin A induces oxidative stress manifested by elevated level of malondialdehyde and decreased activity of superoxide dismutase. When the cells were incubated simultaneously with calyculin A and melatonin (25 microM or 50 microM), the calyculin A-induced decrease in cell viability, tau hyperphosphorylation, PP-2A/GSK-3 imbalance and oxidative stress were attenuated accordingly. These results suggest (i) that calyculin A induces tau hyperphosphorylation not only by inhibition of PP-2A, but also by activation of GSK-3 in N2a cells; (ii) that melatonin efficiently attenuates the calyculin A-induced damages through not only its antioxidant effect but also its modulation to the phosphorylation system.

Effect of okadaic acid on integrins and structural proteins in BE(2)-M17 cells

Okadaic acid (OA), an algal toxin, is known to induce Diarrhetic Shellfish Poisoning and apoptosis in a variety of cell lines. One of the main targets of OA is the actin cytoskeleton which can be modulated by integrins and other structural proteins. In this paper we studied the role of these proteins and skeletal structures on OA-induced apoptosis in neuroblastoma cells. Results show that beta1 integrin and vinculin are down-regulated when cells were exposed to OA. We observed an interaction between talin and beta1 integrin that is impaired in OA treated cells.

Role of melatonin in neurodegenerative diseases

The pineal product melatonin has remarkable antioxidant properties. It scavenges hydroxyl, carbonate and various organic radicals, peroxynitrite and other reactive nitrogen species. Melatonyl radicals formed by scavenging combine with and, thereby, detoxify superoxide anions in processes terminating the radical reaction chains. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and glutathione reductase, and by augmenting glutathione levels. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases, e.g., Alzheimer's disease. Melatonin has been shown to be effective in arresting neurodegenerative phenomena seen in experimental models of Alzheimer's disease, Parkinsonism and ischemic stroke. Melatonin preserves mitochondrial homeostasis, reduces free radical generation, e.g., by enhancing mitochondrial glutathione levels, and safeguards proton potential and ATP synthesis by stimulating complex I and IV activities. Therapeutic trials with melatonin have been effective in slowing the progression of Alzheimer's disease but not of Parkinson's disease. Melatonin's efficacy in combating free radical damage in the brain suggests that it may be a valuable therapeutic agent in the treatment of cerebral edema after traumatic brain injury.

Protective effect of melatonin on 3-nitropropionic acid-induced oxidative stress in synaptosomes in an animal model of Huntington's disease

The effect of melatonin (1 mg/kg BW i.p./day) on the oxidative changes produced by 3-nitropropionic acid (20 mg/kg BW/day for 4 days) in rat striatal and cortical synaptosomes was investigated. The effects of 3-nitropropionic acid were evaluated as changes in the quantity of lipid peroxidation products, protein carbonyl groups and superoxide dismutase and succinate dehydrogenase activities. 3-Nitropropionic acid caused a rise in lipid peroxidation levels and protein carbonyls content whereas it induced a reduction in the activity of succinate dehydrogenase and triggered an enhancement in superoxide dismutase activity. These changes were prevented by previous administration of melatonin. Our results reveal: (i) 3-nitropropionic acid induces a status of oxidative stress in some brain regions of the Wistar rat; (ii) melatonin prevents the deleterious effects induced by the acid. In conclusion, the results show the ability of melatonin to modify the neural response to 3-nitropropionic acid with the protective mechanism likely involving the antioxidative processes of melatonin.

Melatonin protects human retinal pigment epithelial (RPE) cells against oxidative stress

Oxidative stress is involved in the pathogenesis of age-related macular degeneration (AMD). Administration of conventional antioxidants has been shown to slow the progression of AMD and vision loss. Melatonin, an endogenous neurohormone produced by the pineal gland and retina, has been reported to be a potent antioxidant and free radical scavenger. In this study we tested whether melatonin can protect retinal pigment epithelial (RPE) cells against hydrogen peroxide (H(2)O(2))-induced cell death. Since mitochondrial DNA (mtDNA) is preferentially susceptible to oxidative damage, we tested whether melatonin can reduce H(2)O(2)-induced mtDNA lesions. A human RPE cell line (ARPE-19) was cultured and exposed to H(2)O(2) (100 and 200 microm) for 1 hr to induce cell death. Prior to H(2)O(2) treatment, cells were treated with various concentrations (0.1-200 microm) of melatonin for 2, 24 or 72 hr. Control cells received either melatonin or ethanol alone. Cell viability, as determined by MTT assay, showed no significant (P>0.05) protection against H(2)O(2) toxicity in cells receiving 2- and 24-hr pretreatment of melatonin at either concentration. However, when melatonin was administered diurnally for 3 consecutive days, this prolonged treatment markedly reduced H(2)O(2)-induced cell death (P>0.05) MtDNA damage, as assessed with quantitative PCR, was significantly decreased (P<0.05) in RPE cells pretreated with melatonin as compared to those without melatonin treatment. These results suggest that melatonin may play a role in protecting RPE cells from oxidative stress.