Melatonin protects against MPTP/MPP+ -induced mitochondrial DNA oxidative damage in vivo and in vitro

Therapeutic potential of melatonin and its derivatives in aging and neurodegenerative diseases

Aging is associated with increasing impairments in brain homeostasis and represents the main risk factor across most neurodegenerative disorders. Melatonin, a neuroendocrine hormone that regulates mammalian chronobiology and endocrine functions is well known for its antioxidant potential, exhibiting both cytoprotective and chronobiotic abilities. Age-related decline of melatonin disrupting mitochondrial homeostasis and cytosolic DNA-mediated inflammatory reactions in neurons is a major contributory factor in the emergence of neurological abnormalities. There is scattered literature on the possible use of melatonin against neurodegenerative mechanisms in the aging process and its associated diseases. We have searched PUBMED with many combinations of key words for available literature spanning two decades. Based on the vast number of experimental papers, we hereby review recent advancements concerning the potential impact of melatonin on cellular redox balance and mitochondrial dynamics in the context of neurodegeneration. Next, we discuss a broader explanation of the involvement of disrupted redox homeostasis in the pathophysiology of age-related diseases and its connection to circadian mechanisms. Our effort may result in the discovery of novel therapeutic approaches. Finally, we summarize the current knowledge on molecular and circadian regulatory mechanisms of melatonin to overcome neurodegenerative diseases (NDDs) such as Alzheimer's, Parkinson's, Huntington's disease, and amyotrophic lateral sclerosis, however, these findings need to be confirmed by larger, well-designed clinical trials. This review is also expected to uncover the associated molecular alterations in the aging brain and explain how melatonin-mediated circadian restoration of neuronal homeodynamics may increase healthy lifespan in age-related NDDs.

A Novel Mitochondria-Targeting Iron Chelator Neuroprotects Multimodally via HIF-1 Modulation Against a Mitochondrial Toxin in a Dopaminergic Cell Model of Parkinson's Disease

Coumarins are plant-derived polyphenolic compounds belonging to the benzopyrones family, possessing wide-ranging pharmaceutical applications including cytoprotection, which may translate into therapeutic potential for multiple diseases, including Parkinson's disease (PD). Here we demonstrate the neuroprotective potential of a new polyhydroxyl coumarin, N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetamide (CT51), against the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP⁺). MPP+'s mechanism of toxicity relates to its ability to inhibit complex I of the mitochondrial electron transport chain (METC), leading to adenosine triphosphate (ATP) depletion, increased reactive oxygen species (ROS) production, and apoptotic cell death, hence mimicking PD-related neuropathology. Dopaminergic differentiated human neuroblastoma cells were briefly pretreated with CT51, followed by toxin exposure. CT51 significantly restored somatic cell viability and neurite processes; hence, the drug targets cell bodies and axons thereby preserving neural function and circuitry against PD-related damage. Moreover, MPP+ emulates the iron dyshomeostasis affecting dopaminergic neurons in PD-affected brains, whilst CT51 was previously revealed as an effective iron chelator that preferentially partitions to mitochondria. We extend these findings by characterising the drug's interactive effects at the METC level. CT51 did not improve mitochondrial coupling efficiency. However, voltammetric measurements and high-resolution respirometry analysis revealed that CT51 acts as an antioxidant agent. Also, the neuronal protection afforded by CT51 associated with downregulating MPP+-induced upregulated expression of hypoxia-inducible factor 1 alpha (HIF-1α), a protein which regulates iron homeostasis and protects against certain forms of oxidative stress after translocating to mitochondria. Our findings support the further development of CT51 as a dual functioning iron chelator and antioxidant antiparkinsonian agent.

Effect of Melatonin Administration on Mitochondrial Activity and Oxidative Stress Markers in Patients with Parkinson's Disease

Mitochondrial dysfunction and oxidative stress are extensively linked to Parkinson's disease (PD) pathogenesis. Melatonin is a pleiotropic molecule with antioxidant and neuroprotective effects. The aim of this study was to evaluate the effect of melatonin on oxidative stress markers, mitochondrial complex 1 activity, and mitochondrial respiratory control ratio in patients with PD. A double-blind, cross-over, placebo-controlled randomized clinical trial study was conducted in 26 patients who received either 25 mg of melatonin or placebo at noon and 30 min before bedtime for three months. At the end of the trial, in patients who received melatonin, we detected a significant diminution of lipoperoxides, nitric oxide metabolites, and carbonyl groups in plasma samples from PD patients compared with the placebo group. Conversely, catalase activity was increased significantly in comparison with the placebo group. Compared with the placebo group, the melatonin group showed significant increases of mitochondrial complex 1 activity and respiratory control ratio. The fluidity of the membranes was similar in the melatonin group and the placebo group at baseline and after three months of treatment. In conclusion, melatonin administration was effective in reducing the levels of oxidative stress markers and restoring the rate of complex I activity and respiratory control ratio without modifying membrane fluidity. This suggests that melatonin could play a role in the treatment of PD.

The DNA Repair Enzyme XPD Is Partially Regulated by PI3K/AKT Signaling in the Context of Bupivacaine-Mediated Neuronal DNA Damage

Bupivacaine, a local anesthetic widely used for regional anesthesia and pain management, has been reported to induce neuronal injury, especially DNA damage. Neurons employ different pathways to repair DNA damage. However, the mechanism underlying bupivacaine-mediated DNA damage repair is unclear. A rat neuronal injury model was established by intrathecal injection of (3%) bupivacaine. An in vitro neuronal injury model was generated by exposing SH-SY5Y cells to bupivacaine (1.5 mmol/L). Then, a cDNA plate array was used to identify the DNA repair genes after bupivacaine exposure. The results showed that xeroderma pigmentosum complementary group D (XPD) of the nuclear excision repair (NER) pathway was closely associated with the repair of DNA damage induced by bupivacaine. Subsequently, Western blot assay and immunohistochemistry indicated that the expression of the repair enzyme XPD was upregulated after DNA damage. Downregulation of XPD expression by a lentivirus aggravated the DNA damage induced by bupivacaine. In addition, phosphatidyl-3-kinase (PI3K)/AKT signaling in neurons was inhibited after exposure to bupivacaine. After PI3K/AKT signaling was inhibited, bupivacaine-mediated DNA damage was further aggravated, and the expression of XPD was further upregulated. However, knockdown of XPD aggravated bupivacaine-mediated neuronal injury but did not affect PI3K/AKT signaling. In conclusion, the repair enzyme XPD, which was partially regulated by PI3K/AKT signaling, responded to bupivacaine-mediated neuronal DNA damage. These results can be used as a reference for the treatment of bupivacaine-induced neurotoxicity.

The DJ1-Nrf2-STING axis mediates the neuroprotective effects of Withaferin A in Parkinson's disease

The pathogenesis of Parkinson's disease (PD) remains unclear, and there is no disease-modifying agent for PD. Withaferin A (WA), a naturally occurring compound, has emerged as a neuroprotective agent. However, the mechanisms by which WA is neuroprotective in PD are unknown. Here we show that WA protected against loss of dopaminergic neurons, neuroinflammation, and motor deficits in MPTP-induced PD mouse models. Whole-genome deep sequencing analysis combined with Meta-analysis of human PD studies reveal that DJ1, Nrf2, and STING in substantia nigra pars compacta (SNc) are linked to anti-PD effect of WA. We found that WA activated DJ1 and Nrf2, and suppressed STING within SNc; and overexpression of STING in SNc dampened the effect of WA. Using genetically modified mice (DJ1-KO, Nrf2-KO, STINGgt/gt and STING-KO) and immunolabeling technique, we identified that WA targeted DJ1-Nrf2-STING pathway in dopaminergic neurons; and we demonstrate that STING might be an important factor in PD pathogenesis. In addition, WA alleviated accumulation of phosphorylated α-synuclein (p-α-syn) and insoluble α-syn within SNc in adeno-associated virus (AAV)-mediated human α-syn overexpression PD model. Our comparative analysis on whole-genome transcriptome profiles suggests that STING might be a key target of WA and amantadine in PD treatment. This study highlights a multifaceted role for WA in neuroprotection, and suggests that WA can be a potential candidate for treatment of PD.

Protection of melatonin against long-term radon exposure-caused lung injury

Radon is one of the major pathogenic factors worldwide. Recently, epidemiological studies have suggested that radon exposure plays an important role in lung injury, which could further cause cancer. However, the toxic effects and underlying mechanism on lung injury are still not clear. Here, we identified the detailed toxic effects of long-term radon exposure. Specifically, the manifestations were inflammatory response and cell apoptosis in dose- and time-dependent manners. In detail, it caused the mitochondrial dysfunction and oxidative stress as determined by the abnormal levels of mitochondrial DNA copy number, adenosine triphosphate, mitochondrial membrane potential, superoxide dismutase, and cycloxygenase-2. Furthermore, we found that melatonin treatment ameliorated mitochondrial dysfunction and attenuated the levels of oxidative stress caused by long-term radon exposure, which could further inhibit the lung tissue apoptosis as determined by the decreased levels of cleaved caspase 3. Our study would provide potential therapeutic application of melatonin on lung tissue injury caused by long-term radon exposure.

The roles of PARP-1 and XPD and their potential interplay in repairing bupivacaine-induced neuron oxidative DNA damage

Bupivacaine has been widely used in clinical Anesthesia, but its neurotoxicity has been frequently reported, implicating cellular oxidative DNA damage as the major underlying mechanism. However, the mechanism underlying bupivacaine-induced oxidative DNA damage is unknown. We, thus, exposed SH-SY5Y cells to 1.5mM bupivacaine to induce neurotoxicity. Then, iTRAQ proteomic analysis was used to explore the repair of neuronal oxidative DNA damage. By analyzing the STRING version 11.0 database, the bioinformatics relationship between key repair enzymes was tracked. Subsequently, immunofluorescence co-localization and immunoprecipitation were used to investigate the interaction between key repair enzymes. The iTRAQ showed that Poly [ADP-ribose] polymerase 1 (PARP-1) from the base excision repair pathway participated closely in the repair of oxidative DNA damage induced by bupivacaine, and inhibition of PARP-1 expression significantly aggravated bupivacaine-induced DNA damage and apoptosis. Interestingly, this study showed that there were interactions and co-expression between PARP-1 and XPD (xeroderma pigmentosum D), another key protein of the nucleic acid excision repair pathway. After inhibiting XPD, PARP-1 expression was significantly reduced. However, simultaneous inhibition of both XPD and PARP-1 did not further increase DNA damage. It is concluded that PARP-1 may repair bupivacaine-induced oxidative DNA damage through XPD-mediated interactions.

Mitochondrial Dysfunction in Parkinson's Disease: Focus on Mitochondrial DNA

Mitochondria, the energy stations of the cell, are the only extranuclear organelles, containing their own (mitochondrial) DNA (mtDNA) and the protein synthesizing machinery. The location of mtDNA in close proximity to the oxidative phosphorylation system of the inner mitochondrial membrane, the main source of reactive oxygen species (ROS), is an important factor responsible for its much higher mutation rate than nuclear DNA. Being more vulnerable to damage than nuclear DNA, mtDNA accumulates mutations, crucial for the development of mitochondrial dysfunction playing a key role in the pathogenesis of various diseases. Good evidence exists that some mtDNA mutations are associated with increased risk of Parkinson’s disease (PD), the movement disorder resulted from the degenerative loss of dopaminergic neurons of substantia nigra. Although their direct impact on mitochondrial function/dysfunction needs further investigation, results of various studies performed using cells isolated from PD patients or their mitochondria (cybrids) suggest their functional importance. Studies involving mtDNA mutator mice also demonstrated the importance of mtDNA deletions, which could also originate from abnormalities induced by mutations in nuclear encoded proteins needed for mtDNA replication (e.g., polymerase γ). However, proteomic studies revealed only a few mitochondrial proteins encoded by mtDNA which were downregulated in various PD models. This suggests nuclear suppression of the mitochondrial defects, which obviously involve cross-talk between nuclear and mitochondrial genomes for maintenance of mitochondrial functioning.

Antioxidative effect of melatonin on cryopreserved ovarian tissue in mice

Cryopreservation of ovarian tissues (OTs) has become the most effective way to preserve the fertility of female cancer patients. However, cryopreservation of OTs is still relatively at an experimental stage. The aim of study is to examine the effect of melatonin (MTL) on cryopreserved-thawed OTs. Fragments of OTs were cryopreserved in medium containing different concentrations (0 mM, 0.001 mM, 0.01 mM, 0.1 mM and 1 mM) of MLT. The endogenous enzymes (GSH-PX, GSH, SOD, CAT and T-AOC), MDA and ROS levels were all evaluated after cryopreservation. Our results showed that the 0.1 mM of MLT significantly improved the survival and diameter of follicles (P < 0.001). Meanwhile, the antioxidant enzymes activities (including GSH-PX, GSH, SOD, CAT and T-AOC) were enhanced and MDA content were significantly decreased in 0.1 mM of MLT group compared to other groups (P < 0.001). Additionally, compared to the control group, MTL of 0.1 mM resulted in a significantly lower ROS level. In conclusion, MLT protects the quality of cryopreserved OTs by decreasing oxidative stress level and the optimal concentration is 0.1 mM.

Agomelatine prevents indomethacin-induced gastric ulcer in rats

BACKGROUND

Gastric ulcer is a very common gastrointestinal disease that may be dangerous and even may lead to death. The current study was conducted to detect the prophylactic effects of agomelatine on indomethacin-induced gastric ulcer.

METHODS

In this study, a total of 5 groups were created as the sham, ulcer, omeprazole, agomelatine 1 mg/kg and agomelatine 5 mg/kg groups. The effects of agomelatine on indomethacin-induced gastric injury were investigated. Total antioxidant and oxidant levels; the oxidant parameters like oxidative stress index and the inflammation markers such as tumor necrosis factor-α, interleukin-1β, interleukin-6 and interleukin-10 levels in stomach tissue were determined by ELISA. In addition, the gastric mucosal injury occurred in stomach wall was examined with histopathological methods.

RESULTS

While the levels of the inflammatory markers, total oxidant status and oxidative stress index increased at an obvious level especially in the indomethacin group, the total antioxidant status levels decreased. It was observed that these parameters were improved at a significant level in agomelatine 1 mg/kg and agomelatine 5 mg/kg groups when compared to ulcer group; and the results were similar to omeprazole group. It was also observed that our histopathological findings were consistent with all our other results.

CONCLUSIONS

The results of this study showed that agomelatine usage in indomethacin-induced gastric ulcer model provides beneficial results.

Melatonin and Parkinson Disease: Current Status and Future Perspectives for Molecular Mechanisms

Parkinson disease (PD) is a chronic and neurodegenerative disease with motor and nonmotor symptoms. Multiple pathways are involved in the pathophysiology of PD, including apoptosis, autophagy, oxidative stress, inflammation, α-synuclein aggregation, and changes in the neurotransmitters. Preclinical and clinical studies have shown that melatonin supplementation is an appropriate therapy for PD. Administration of melatonin leads to inhibition of some pathways related to apoptosis, autophagy, oxidative stress, inflammation, α-synuclein aggregation, and dopamine loss in PD. In addition, melatonin improves some nonmotor symptom in patients with PD. Limited studies, however, have evaluated the role of melatonin on molecular mechanisms and clinical symptoms in PD. This review summarizes what is known regarding the impact of melatonin on PD in preclinical and clinical studies.

Parkinsonian Neurotoxins Impair the Pro-inflammatory Response of Glial Cells

In the case of Parkinson's disease (PD), epidemiological studies have reported that pesticide exposure is a risk factor for its pathology. It has been suggested that some chemical agents, such as rotenone and paraquat, that inhibit the mitochondrial respiratory chain (in the same way as the PD mimetic toxin 1-methyl-4-phenylpyridinium, MPP+) are involved in the development of PD. However, although the neurotoxic effect of such compounds has been widely reported using in vivo and in vitro experimental approaches, their direct effect on the glial cells remains poorly characterized. In addition, the extent to which these toxins interfere with the immune response of the glial cells, is also underexplored. We used mouse primary mixed glial and microglial cultures to study the effect of MPP+ and rotenone on glial activation, in the absence and the presence of a pro-inflammatory stimulus (lipopolysaccharide plus interferon-γ, LPS+IFN-γ). We determined the mRNA expression of the effector molecules that participate in the inflammatory response (pro-inflammatory cytokines and enzymes), as well as the nitric oxide (NO) and cytokine production. We also studied the phagocytic activity of the microglial cells. In addition, we evaluated the metabolic changes associated with the observed effects, through the measurement of adenosine triphosphate (ATP) production and the expression of genes involved in the control of metabolic pathways. We observed that exposure of the glial cultures to the neurotoxins, especially rotenone, impaired the pro-inflammatory response induced by LPS/IFN-γ. MPP+ and rotenone also impaired the phagocytic activity of the microglial cells, and this effect was potentiated in the presence of LPS/IFN-γ. The deficit in ATP production that was detected, mainly in MPP+ and rotenone-treated mixed glial cultures, may be responsible for the effects observed. These results show that the response of glial cells to a pro-inflammatory challenge is altered in the presence of toxins inhibiting mitochondrial respiratory chain activity, suggesting that the glial immune response is impaired by such agents. This may have relevant consequences for brain function and the central nervous system's (CNS's) response to insults.

Diplomats' Mystery Illness and Pulsed Radiofrequency/Microwave Radiation

Importance: A mystery illness striking U.S. and Canadian diplomats to Cuba (and now China) "has confounded the FBI, the State Department and US intelligence agencies" (Lederman, Weissenstein, & Lee, 2017). Sonic explanations for the so-called health attacks have long dominated media reports, propelled by peculiar sounds heard and auditory symptoms experienced. Sonic mediation was justly rejected by experts. We assessed whether pulsed radiofrequency/microwave radiation (RF/MW) exposure can accommodate reported facts in diplomats, including unusual ones. Observations: (1) Noises: Many diplomats heard chirping, ringing or grinding noises at night during episodes reportedly triggering health problems. Some reported that noises were localized with laser-like precision or said the sounds seemed to follow them (within the territory in which they were perceived). Pulsed RF/MW engenders just these apparent "sounds" via the Frey effect. Perceived "sounds" differ by head dimensions and pulse characteristics and can be perceived as located behind in or above the head. Ability to hear the "sounds" depends on high-frequency hearing and low ambient noise. (2) Signs/symptoms: Hearing loss and tinnitus are prominent in affected diplomats and in RF/MW-affected individuals. Each of the protean symptoms that diplomats report also affect persons reporting symptoms from RF/MW: sleep problems, headaches, and cognitive problems dominate in both groups. Sensations of pressure or vibration figure in each. Both encompass vision, balance, and speech problems and nosebleeds. Brain injury and brain swelling are reported in both. (3) Mechanisms: Oxidative stress provides a documented mechanism of RF/MW injury compatible with reported signs and symptoms; sequelae of endothelial dysfunction (yielding blood flow compromise), membrane damage, blood-brain barrier disruption, mitochondrial injury, apoptosis, and autoimmune triggering afford downstream mechanisms, of varying persistence, that merit investigation. (4) Of note, microwaving of the U.S. embassy in Moscow is historically documented. Conclusions and relevance: Reported facts appear consistent with pulsed RF/MW as the source of injury in affected diplomats. Nondiplomats citing symptoms from RF/MW, often with an inciting pulsed-RF/MW exposure, report compatible health conditions. Under the RF/MW hypothesis, lessons learned for diplomats and for RF/MW-affected civilians may each aid the other.

NQO2 inhibition relieves reactive oxygen species effects on mouse oocyte meiotic maturation and embryo development

NRH: quinone oxidoreductase 2 (NQO2) is a cytosolic and ubiquitously expressed flavoprotein that catalyzes the two-electron reduction of quinone to hydroquinones. Herein, we assessed the protein expression, subcellular localization, and possible functions of NQO2 in mouse oocyte meiotic maturation and embryo development. Western blot analysis detected high and stable protein expression of NQO2 in mouse oocytes during meiotic progression. Immunofluorescence illustrated NQO2 distribution on nuclear membrane, chromosomes, and meiotic spindles. Microtubule poisons treatment (nocodazole and taxol) showed that filamentous assembly of NQO2 and its co-localization with microtubules require microtubule integrity and normal dynamics. Increased levels of NQO2, reactive oxygen species (ROS), malondialdehyde (MDA), and autophagy protein Beclin1 expression were detected in oocytes cultured with ROS stimulator vitamin K3 (VK3), combined with decreased antioxidant glutathione (GSH). These oocytes were arrested at metaphase I with abnormal spindle structure and chromosome configuration. However, this impact was counteracted by melatonin or NQO2 inhibitor S29434, and the spindle configuration and first polar body extrusion were restored. Similarly, morpholino oligo-induced NQO2 knockdown suppressed ROS, MDA, and Beclin1, instead increased GSH in oocytes under VK3. Supplementary S29434 or melatonin limited changes in NQO2, ROS, MDA, Beclin1, and GSH during in vitro aging of ovulated oocytes, thereby maintaining spindle structure, as well as ordered chromosome separation and embryo development potential after parthenogenetic activation with SrCl2. Taken together, NQO2 is involved in ROS generation and subsequent cytotoxicity in oocytes, and its inhibition can restore oocyte maturation and embryo development, suggesting NQO2 as a pharmacological target for infertility cure.

Melatonin: A Versatile Protector against Oxidative DNA Damage

Oxidative damage to DNA has important implications for human health and has been identified as a key factor in the onset and development of numerous diseases. Thus, it is evident that preventing DNA from oxidative damage is crucial for humans and for any living organism. Melatonin is an astonishingly versatile molecule in this context. It can offer both direct and indirect protection against a wide variety of damaging agents and through multiple pathways, which may (or may not) take place simultaneously. They include direct antioxidative protection, which is mediated by melatonin's free radical scavenging activity, and also indirect ways of action. The latter include, at least: (i) inhibition of metal-induced DNA damage; (ii) protection against non-radical triggers of oxidative DNA damage; (iii) continuous protection after being metabolized; (iv) activation of antioxidative enzymes; (v) inhibition of pro-oxidative enzymes; and (vi) boosting of the DNA repair machinery. The rather unique capability of melatonin to exhibit multiple neutralizing actions against diverse threatening factors, together with its low toxicity and its ability to cross biological barriers, are all significant to its efficiency for preventing oxidative damage to DNA.

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.

Measurements of morphological and biophysical alterations in individual neuron cells associated with early neurotoxic effects in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease. However, therapeutic methods of PD are still limited due to complex pathophysiology in PD. Here, optical measurements of individual neurons from in vitro PD model using optical diffraction tomography (ODT) are presented. By measuring 3D refractive index distribution of neurons, morphological and biophysical alterations in in-vitro PD model are quantitatively investigated. It was found that neurons show apoptotic features in early PD progression. The present approach will open up new opportunities for quantitative investigation of the pathophysiology of various neurodegenerative diseases. © 2017 International Society for Advancement of Cytometry.

Genetic modification of H2AX renders mesenchymal stromal cell-derived dopamine neurons more resistant to DNA damage and subsequent apoptosis

BACKGROUND AIMS

Aberrant production of reactive oxygen species (ROS) and its impact on the integrity of genomic DNA have been considered one of the major risk factors for the loss of dopaminergic neurons in Parkinson's disease (PD). Stem cell transplantation as a strategy to replenish new functional neurons has great potential for PD treatment. However, limited survival of stem cells post-transplantation has always been an obstacle ascribed to the existence of neurotoxic environment in PD patients.

METHODS

To improve the survival of transplanted stem cells for PD treatment, we explored a new strategy based on the function of the H2AX gene (H2A histone family, member X) in determination of DNA repair and cell apoptosis. We introduced a mutant form Y142F of H2AX into dopamine (DA) neuron-like cells differentiated from bone marrow-derived mesenchymal stromal cells (BMSCs).

RESULTS

Expression of H2AX(Y142F) renders DA neuron-like cells more resistant to DNA damage and subsequent cell death induced by ultraviolet irradiation and 1-methyl-4-phenylpyridinium (MPP+) treatment.

DISCUSSION

This is a meaningful attempt to improve the sustainability of BMSC-derived dopamine neurons under a brain neurotoxic environment. Further studies are needed to evaluate the implications of our findings in stem cell therapy for PD and related diseases.

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.

Neuroprotective Effect of Coptis chinensis in MPP+ and MPTP-Induced Parkinson’s Disease Models

The rhizome of Coptis chinensis is commonly used in traditional Chinese medicine alone or in combination with other herbs to treat diseases characterized by causing oxidative stress including inflammatory diseases, diabetes mellitus and neurodegenerative diseases. In particular, there is emerging evidence that Coptis chinensis is effective in the treatment of neurodegenerative diseases associated with oxidative stress. Hence, the aim of this study was to investigate the neuroprotective effect of Coptis chinensis in vitro and in vivo using MPP[Formula: see text] and MPTP models of Parkinson’s disease. MPP[Formula: see text] treated human SH-SY5Y neuroblastoma cells were used as a cell model of Parkinson’s disease. A 24[Formula: see text]h pre-treatment of the cells with the watery extract of Coptis chinensis significantly increased cell viability, as well as the intracellular ATP concentration and attenuated apoptosis compared to the MPP[Formula: see text] control. Further experiments with the main alkaloids of Coptidis chinensis, berberine, coptisine, jaterorrhizine and palmatine revealed that berberine and coptisine were the main active compounds responsible for the observed neuroprotective effect. However, the full extract of Coptis chinensis was more effective than the tested single alkaloids. In the MPTP-induced animal model of Parkinson’s disease, Coptis chinensis dose-dependently improved motor functions and increased tyrosine hydroxylase-positive neurons in the substantia nigra compared to the MPTP control. Based on the results of this work, Coptis chinensis and its main alkaloids could be considered potential candidates for the development of new treatment options for Parkinson’s disease.

Oxidative Stress in Neurodegenerative Diseases

The pathophysiologies of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD), are far from being fully explained. Oxidative stress (OS) has been proposed as one factor that plays a potential role in the pathogenesis of neurodegenerative disorders. Clinical and preclinical studies indicate that neurodegenerative diseases are characterized by higher levels of OS biomarkers and by lower levels of antioxidant defense biomarkers in the brain and peripheral tissues. In this article, we review the current knowledge regarding the involvement of OS in neurodegenerative diseases, based on clinical trials and animal studies. In addition, we analyze the effects of the drug-induced modulation of oxidative balance, and we explore pharmacotherapeutic strategies for OS reduction.

Rejuvenation of MPTP-induced human neural precursor cell senescence by activating autophagy

Aging of neural stem cell, which can affect brain homeostasis, may be caused by many cellular mechanisms. Autophagy dysfunction was found in aged and neurodegenerative brains. However, little is known about the relationship between autophagy and human neural stem cell (hNSC) aging. The present study used 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) to treat neural precursor cells (NPCs) derived from human embryonic stem cell (hESC) line H9 and investigate related molecular mechanisms involved in this process. MPTP-treated NPCs were found to undergo premature senescence [determined by increased senescence-associated-β-galactosidase (SA-β-gal) activity, elevated intracellular reactive oxygen species level, and decreased proliferation] and were associated with impaired autophagy. Additionally, the cellular senescence phenotypes were manifested at the molecular level by a significant increase in p21 and p53 expression, a decrease in SOD2 expression, and a decrease in expression of some key autophagy-related genes such as Atg5, Atg7, Atg12, and Beclin 1. Furthermore, we found that the senescence-like phenotype of MPTP-treated hNPCs was rejuvenated through treatment with a well-known autophagy enhancer rapamycin, which was blocked by suppression of essential autophagy gene Beclin 1. Taken together, these findings reveal the critical role of autophagy in the process of hNSC aging, and this process can be reversed by activating autophagy.

Melatonin: a well-documented antioxidant with conditional pro-oxidant actions

Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.

Formation and repair of oxidative damage in the mitochondrial DNA

The mitochondrial DNA (mtDNA) encodes for only 13 polypeptides, components of 4 of the 5 oxidative phosphorylation complexes. But despite this apparently small numeric contribution, all 13 subunits are essential for the proper functioning of the oxidative phosphorylation circuit. Thus, accumulation of lesions, mutations and deletions/insertions in the mtDNA could have severe functional consequences, including mitochondrial diseases, aging and age-related diseases. The DNA is a chemically unstable molecule, which can be easily oxidized, alkylated, deaminated and suffer other types of chemical modifications, throughout evolution the organisms that survived were those who developed efficient DNA repair processes. In the last two decades, it has become clear that mitochondria have DNA repair pathways, which operate, at least for some types of lesions, as efficiently as the nuclear DNA repair pathways. The mtDNA is localized in a particularly oxidizing environment, making it prone to accumulate oxidatively generated DNA modifications (ODMs). In this article, we: i) review the major types of ODMs formed in mtDNA and the known repair pathways that remove them; ii) discuss the possible involvement of other repair pathways, just recently characterized in mitochondria, in the repair of these modifications; and iii) address the role of DNA repair in mitochondrial function and a possible cross-talk with other pathways that may potentially participate in mitochondrial genomic stability, such as mitochondrial dynamics and nuclear-mitochondrial signaling. Oxidative stress and ODMs have been increasingly implicated in disease and aging, and thus we discuss how variations in DNA repair efficiency may contribute to the etiology of such conditions or even modulate their clinical outcomes.

Melatonin from cerebrospinal fluid but not from blood reaches sheep cerebral tissues under physiological conditions

The pineal gland secretes melatonin (MLT) that circulates in the blood and cerebrospinal fluid (CSF). We provide data to support the hypothesis that, in sheep and possibly in humans, only the CSF MLT, and not the blood MLT, can provide most of MLT to the cerebral tissue in high concentrations, particularly in the periventricular area. The MLT content of sheep brain, our chosen animal model, was found in significant concentration gradients oriented from the ventricle (close to the CSF) to the cerebral tissue, with concentrations varying by a factor of 1-125. The highest concentrations were observed close to the ventricle wall, whereas the lowest concentrations were furthest from the ventricles (407.0 ± 71.5 pg/ml compared to 84.7 ± 5.2 pg/ml around the third ventricle). This concentration gradient was measured in brain tissue collected at mid-day and at the end of the night. Nocturnal concentrations were higher than daytime concentrations, reflecting the diurnal variation in the pineal gland. The concentration gradient was not detected when MLT was delivered to the brain via the bloodstream. The diffusion of MLT to cerebral tissues via CSF was supported by in vivo scintigraphy and autoradiography. 2-[(123)I]-MLT infused into the CSF quickly and efficiently diffused into the brain tissues, whereas [(123)I]-iodine (control) was mostly washed away by the CSF flow and [(123)I]-bovine serum albumin remained mostly in the CSF. Taken together, these data support a critical role of CSF in providing the brain with MLT.

Secalonic acid A protects dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell death via the mitochondrial apoptotic pathway

Secalonic acid A (SAA) is a natural compound found in marine fungi. We have reported that SAA can attenuate the cytotoxicity of colchicine in rat cortical neurons. Whether SAA can also inhibit the neurotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in dopaminergic neurons has not been investigated. Here, we show that pretreatment with 1 μM SAA significantly rescued tyrosine hydroxylase (TH)-positive neurons from MPP(+)-induced neurotoxicity in primary dopaminergic neuron culture. Moreover, SAA at doses of 0.15 mg/kg and 0.75 mg/kg increased the number of dopaminergic neurons and upregulated striatal dopamine in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease mice experiments. We also show that SAA significantly attenuated cytotoxicity induced by 2.5 mM MPP(+) in SH-SY5Y cells. These results indicate that the activation of JNK, p38 mitogen activated protein kinase (MAPK) and caspase-3 during apoptosis triggered by MPP(+) could be suppressed by SAA; on the other hand, an MPP(+)-induced increase in the expression of Bax in SH-SY5Y cells was blocked by SAA. These results indicate that inhibition of the phosphorylation of JNK and p38 MAPK, down-regulation of Bax expression, and suppression of caspase-3 activation are involved in the protective effects of SAA against MPP(+) toxicity in SH-SY5Y cells. SAA may rescue dopaminergic neurons from MPP(+)-induced cell death through the mitochondrial apoptotic pathway.

Health consequences of shift work and implications for structural design

The objective of the study was to perform a literature review on the health consequences of working rotating shifts and implications for structural design. A literature search was performed in June 2012 and a selection of the most relevant peer-review articles was included in the present review. Shift workers are more likely to suffer from a circadian sleep disorder characterized by sleepiness and insomnia. Shift work is associated with decreased productivity, impaired safety, diminished quality of life and adverse effects on health. Circadian disruption resulting from rotating shift work has also been associated with increased risk for metabolic syndrome, diabetes, cardiovascular disease and cancer. This article summarizes the known health effects of shift work and discusses how light can be used as a countermeasure to minimize circadian disruption at night while maintaining alertness. In the context of the lighted environment, implications for the design of newborn intensive care units are also discussed.

Astrocyte activation: a key step in rotenone induced cytotoxicity and DNA damage

Astrocytes are the most abundant glial cells, which provide metabolic support for neurons. Rotenone is a botanical pesticide of natural origin, known to exhibit neurotoxic potential via inhibition of mitochondrial complex-I. This study was carried out to explore the effect of rotenone on C6 cells. The cell line C6 derived from rat glioma cells represents astrocyte-like cell. C6 cells were treated with rotenone (0.1, 1 and 10 μM) for 4 h. The effect of rotenone was studied on cell survival (MTT reduction and PI uptake); free radicals (ROS and RNS) and DNA damage (comet assay and Hoechst staining). The glial cell activation and apoptotic cell death was evaluated by expression of Glial fibrillary acidic protein (GFAP) and caspase-3 respectively. The treatment with rotenone resulted in decreased cell survival and increased free radical generation. Altered nuclear morphology and DNA damage were evident following rotenone treatment in Hoechst staining and Comet assay. Rotenone elevated expression of GFAP and caspase-3 that indicates glial cell activation and apoptosis, respectively. We further studied the effect of melatonin, an antioxidant, on the observed toxic effects. Co-incubation of antioxidant, melatonin (300 μM), significantly suppressed rotenone induced above-mentioned effects in C6 cells. Inhibitory effects of melatonin suggest that free radicals play a major role in rotenone induced astrocyte activation and cellular toxicity leading to apoptosis of astroglial cells.

Ogg1 null mice exhibit age-associated loss of the nigrostriatal pathway and increased sensitivity to MPTP

Cumulative damage to cellular macromolecules via oxidative stress is a hallmark of aging and neurodegenerative disease. Whether such damage is a cause or a subsequent effect of neurodegeneration is still unknown. This paper describes the development of an age-associated mild parkinsonian model in mice that lack the DNA repair enzyme 8-oxoguanine glycosylase 1 (Ogg1). Aged OGG1 knock-out (OGG1 KO) mice show a decreased spontaneous locomotor behavior and evidence a decrease in striatal dopamine levels, a loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra (SN), and an increase in ubiquitin-positive inclusions in their remaining SN neurons. In addition, young OGG1 KO mice are more susceptible to the dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) than their wild-type (WT) counterparts. Age-associated increases in 7,8-dihydro-2'-deoxyguanine (oxo(8)dG) have been reported in brain regions and neuronal populations affected in Parkinson's disease (PD), toxin-induced parkinsonian models, and mice harboring genetic abnormalities associated with PD. Because of these increased oxo(8)dG levels, the OGG1 KO mouse strain could shed light on molecular events leading to neuronal loss as a consequence of cumulative oxidative damage to DNA during aging and after toxicological challenge.

The role of melatonin as an antioxidant in the follicle

Melatonin (N-acetyl-5-methoxytryptamine) is secreted during the dark hours at night by pineal gland, and it regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction. It has been believed that melatonin regulates ovarian function by the regulation of gonadotropin release in the hypothalamus-pituitary gland axis via its specific receptors. In addition to the receptor mediated action, the discovery of melatonin as a direct free radical scavenger has greatly broadened the understanding of melatonin's mechanisms which benefit reproductive physiology. Higher concentrations of melatonin have been found in human preovulatory follicular fluid compared to serum, and there is growing evidence of the direct effects of melatonin on ovarian function especially oocyte maturation and embryo development. Many scientists have focused on the direct role of melatonin on oocyte maturation and embryo development as an anti-oxidant to reduce oxidative stress induced by reactive oxygen species, which are produced during ovulation process. The beneficial effects of melatonin administration on oocyte maturation and embryo development have been confirmed by in vitro and in vivo experiments in animals. This review also discusses the first application of melatonin to the clinical treatment of infertile women and confirms that melatonin administration reduces intrafollicular oxidative damage and increase fertilization rates. This review summarizes our recent works and new findings related to the reported beneficial effects of melatonin on reproductive physiology in its role as a reducer of oxidative stress, especially on oocyte maturation and embryo development.

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.

Melatonin combats molecular terrorism at the mitochondrial level

The intracellular environmental is a hostile one. Free radicals and related oxygen and nitrogen-based oxidizing agents persistently pulverize and damage molecules in the vicinity of where they are formed. The mitochondria especially are subjected to frequent and abundant oxidative abuse. The carnage that is left in the wake of these oxygen and nitrogen-related reactants is referred to as oxidative damage or oxidative stress. When mitochondrial electron transport complex inhibitors are used, e.g., rotenone, 1-methyl-1-phenyl-1,2,3,6-tetrahydropyridine, 3-nitropropionic acid or cyanide, pandemonium breaks loose within mitochondria as electron leakage leads to the generation of massive amounts of free radicals and related toxicants. The resulting oxidative stress initiates a series of events that leads to cellular apoptosis. To alleviate mitochondrial destruction and the associated cellular implosion, the cell has at its disposal a variety of free radical scavengers and antioxidants. Among these are melatonin and its metabolites. While melatonin stimulates several antioxidative enzymes it, as well as its metabolites (cyclic 3-hydroxymelatonin, N¹-acetyl-N²-formyl-5-methoxykynuramine and N¹-acetyl-5-methoxykynuramine), likewise effectively neutralize free radicals. The resulting cascade of reactions greatly magnifies melatonin's efficacy in reducing oxidative stress and apoptosis even in the presence of mitochondrial electron transport inhibitors. The actions of melatonin at the mitochondrial level are a consequence of melatonin and/or any of its metabolites. Thus, the molecular terrorism meted out by reactive oxygen and nitrogen species is held in check by melatonin and its derivatives.

Protective effect of melatonin on 3-NP induced striatal interneuron injury in rats

To confirm the effect of melatonin on 3-nitropropionic acid (3-NP)-induced striatal interneuron injury in rats, behavioral test, histology, immunohistochemistry and Western blotting were respectively used to characterize the behavioral changes of experimental animals in motor and cognition, the morphological changes of striatal interneurons and the expression level of protein markers induced by 3-NP. The results showed that (1) 3-NP induced dysfunction of experimental animals in movement, motor coordination and cognition could be relieved by melatonin treatment; (2) The 3-NP-induced lesion area was unvaryingly in dorsolateral striatum, with almost all neuronal loss in the lesion core, however, lots of neurons survived after melatonin treatment; (3) Immunohistochemical staining of the four interneuron types (parvalbuminergic, cholinergic, calretinergic, and neuropeptide Y-neuronal nitric oxide synthase co-containing) showed that, in the lesion core of 3-NP group, loss of the four interneuron types was obvious, but in transition zone, the processes and varicosities of calretinergic, and neuropeptide Y-neuronal nitric oxide synthase co-containing interneurons increased significantly. Melatonin treatment reduced the loss of the four interneuron types in the lesion core, and inhibited the increase of processes and varicosities in the transition zone; (4) Consistent with above results, the expression level of five interneuron protein markers were significantly increased in the striatum after melatonin treatment. Notably, in both the transition zone and the lesion core induced by 3-NP, TUNEL-positive cells were detected, but decreased significantly after melatonin treatment. The present results indicate that melatonin effectively protects the striatal neurons against the injury induced by 3-NP in rats.

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.

1-Methyl-4-phenyl-pyridinium time-dependently alters expressions of oxoguanine glycosylase 1 and xeroderma pigmentosum group F protein in PC12 cells

OBJECTIVE

To determine if DNA excision repair enzymes oxoguanine glycosylase 1 (OGG1) and xeroderma pigmentosum group F protein (XPF) are involved in the pathogenesis of Parkinson's disease (PD) in a cell model.

METHODS

PC12 cells were treated with 1-Methyl-4-phenylpyridine ion (MPP(+)) for various periods of time to induce oxidative DNA damage. MTT assay was used to determine cell viability. Immunocytochemistry with antibody against 8-hydroxy-2'-deoxyguanosine (8-oxodG) was used to evaluate oxidative DNA damage. Immunoblotting was used to detect the protein levels of OGG1 and XPF.

RESULTS

MPP(+) treatment (1 mmol/L) for 18 h and 24 h reduced cell viability to 78.6% and 70.3% of the control, respectively, in a time-dependent way. MPP(+) increased the immunoreactivity of 8-oxodG in the cytoplasm at 3 h and in the nucleus at 24 h of treatment. With the treatment of MPP(+), the expression of OGG1 was significantly increased at 1 h, reaching a peak at 3 h, and then it was decreased at 24 h, as compared to that with vehicle treatment. The same effect was exerted on XPF level, except that the XPF level reached a peak at 18 h of MPP(+) treatment. Moreover, the maximally-increased protein level of OGG1 by MPP(+) was approximately 2-fold higher than that of XPF.

CONCLUSION

MPP(+) treatment could time-dependently induce increases in OGG1 and XPF expressions in PC12 cells. Also, this study indicates that the base and nucleotide excision repair pathways may be compensatory activated in the early stage of pathogenesis in the cells after MPP(+) treatment.

Differential effects of melatonin on amyloid-beta peptide 25-35-induced mitochondrial dysfunction in hippocampal neurons at different stages of culture

beta-Amyloid (Abeta) is strongly involved in the pathogenesis of Alzheimer's disease (AD), and mitochondria play an important role in neurodegenerative disorders. To determine whether any different effect of melatonin on cultured neurons treated with Abeta in vitro and which may be produced through its different action on mitochondria at different stages of culture, we investigated the damage of cultured rat hippocampal neurons mitochondrial function induced by Abeta in young neurons [days in vitro 10 (DIV 10)] and senescent neurons (DIV 25) and the protective effect of melatonin. Rat hippocampal neurons were incubated with amyloid-beta peptide 25-35 (Abeta25-35) alone or pretreatment with melatonin. Cell viability, mitochondrial membrane potential (Deltapsim), ATP and the activity of the respiratory chain complexes were measured. Data showed that Abeta25-35 caused a reduction in Deltapsim, inhibited the activity of the respiratory chain complexes and led to ATP depletion, melatonin attenuated Abeta25-35-induced mitochondrial impairment in young neurons, whereas melatonin had no effect on Abeta25-35-induced mitochondrial damage in senescent neurons. These results demonstrate that melatonin has differential effect on Abeta25-35-induced mitochondrial dysfunction at different stages of culture and suggest that melatonin is useful for the prevention of AD, rather than treatment.

The carboxyproxyl-derived spin trap (CP-H) is an appropriate detector-compound for oxidative stress

Reperfusion of ischemic tissue disturbs the balance between reactive oxygen species (ROS) and the cellular antioxidative defense. This imbalance is known as oxidative stress. In this study the spin trap 3-carboxy-2,2,5,5-tetramethylpyrrolin-1-hydroxide (CP-H) with its ESR-detectable paramagnetic analogue 3-carboxy-2,2,5,5-tetramethylpyrrolin-1-oxyl (*CP) was analyzed in vitro and in vivo. In preliminary in vitro experiments we studied the interaction of CP-H with reactive compounds like hydroxyl radicals (*OH) and alkylperoxyl radicals (ROO*) which are formed during organ reperfusion or tissue reoxygenation. The increase in the peak intensity of the ESR signal of the *CP-radical was used as a measure for CP-H oxidation by the above-mentioned oxidizing radicals. It could be clearly shown that *OH as well as ROO* induce CP-H oxidation. The intensity of the ESR signal (*CP) depends on the concentration of the applied oxidant. In a further set of in vitro experiments we analyzed some factors influencing the stability of the generated *CP. Cellular reductants are able to interact with many radicals whereby their paramagnetic signal intensity decreases. We could show that glutathione (GSH) up to 5 mM does not influence *CP concentration. On the other hand, ascorbate at a concentration of 0.6 mM significantly reduces 55% of *CP within 60 min to the ESR-silent CP-H. At 1 mM ascorbate the *CP derived ESR signal is reduced within 60 min by 90%. Lower concentrations of ascorbate (0.1-0.3 mM) do not significantly decrease signal intensity within 1 h. Homogenization of ischemic rat kidney in the presence of an air-equilibrated buffer obviously induces the formation of oxidizing radicals which in turn are able to convert diamagnetic CP-H into paramagnetic *CP. The intensity of the formed *CP was analyzed in a 600 g supernatant with ESR spectroscopy at 25 degrees C. It could be demonstrated that at least 3.0 +/- 0.5 microM *CP is formed 15 min after starting tissue homogenization and reoxygenation. Subsequent measurements of the *CP concentration indicated that its signal intensity continuously decreases. After 75 min a residual *CP concentration of 0.7 +/- 0.3 microM was monitored. Removal of mitochondria from the homogenate by centrifugation at 6,000g decelerates the disappearance of *CP but does not block it completely. In summary it could be shown that the marker (CP-H) is able to indicate the formation of oxidizing radicals during reoxygenation of ischemic tissue. This method underestimates the amount of produced oxidizing radicals. One reason for this is the reduction of *CP by some cellular reductants. Other reasons will be discussed. We assume that the used method allows a nearly real-time determination of radical production during organ reoxygenation.

Melatonin attenuates I/R-induced mitochondrial dysfunction in skeletal muscle

BACKGROUND

Our recent studies have shown that ischemia/reperfusion (I/R) produces significant necrosis and apoptosis in the cells of skeletal muscle. Our previous studies also demonstrated that melatonin provides significant protection against superoxide generation, endothelial dysfunction, and cell death in the skeletal muscle after I/R. Mitochondria are essential for cell survival, because of their roles as ATP producers as well as regulators of cell death. However, the efficacy of melatonin on I/R-induced mitochondrial dysfunction in the skeletal muscle in vivo has not been demonstrated in the literature.

MATERIALS AND METHODS

Vascular pedicle isolated rat gracilis muscle model was used. After 4 h of ischemia followed by 24 h of reperfusion, gracilis muscle was harvested, and mitochondrial as well as cytosolic fractions were isolated. Mitochondrial dysfunction was determined by the alteration of mitochondrial membrane potential and the release of the proapoptotic protein, cytochrome c. Three groups were designed; sham I/R, I/R-V (I/R with vehicle), and I/R-Mel (I/R with melatonin). Melatonin or vehicle was given intravenously 10 min prior to reperfusion and 10 min after reperfusion.

RESULTS

We found that the capability of uptake of fluorescent JC-1 dye in skeletal muscle cells was substantially improved in I/R-Mel group compared with I/R-V group. Melatonin significantly inhibited the outflow of cytochrome c from mitochondria to cytoplasm, which was demonstrated in the I/R-V group.

CONCLUSIONS

Melatonin significantly attenuates I/R-induced mitochondrial dysfunction, such as the depolarization of mitochondrial membrane potential and the release of the proapoptotic protein, cytochrome c, from the mitochondria.

Exposure to 1800 MHz radiofrequency radiation induces oxidative damage to mitochondrial DNA in primary cultured neurons

Increasing evidence indicates that oxidative stress may be involved in the adverse effects of radiofrequency (RF) radiation on the brain. Because mitochondrial DNA (mtDNA) defects are closely associated with various nervous system diseases and mtDNA is particularly susceptible to oxidative stress, the purpose of this study was to determine whether radiofrequency radiation can cause oxidative damage to mtDNA. In this study, we exposed primary cultured cortical neurons to pulsed RF electromagnetic fields at a frequency of 1800 MHz modulated by 217 Hz at an average special absorption rate (SAR) of 2 W/kg. At 24 h after exposure, we found that RF radiation induced a significant increase in the levels of 8-hydroxyguanine (8-OHdG), a common biomarker of DNA oxidative damage, in the mitochondria of neurons. Concomitant with this finding, the copy number of mtDNA and the levels of mitochondrial RNA (mtRNA) transcripts showed an obvious reduction after RF exposure. Each of these mtDNA disturbances could be reversed by pretreatment with melatonin, which is known to be an efficient antioxidant in the brain. Together, these results suggested that 1800 MHz RF radiation could cause oxidative damage to mtDNA in primary cultured neurons. Oxidative damage to mtDNA may account for the neurotoxicity of RF radiation in the brain.

Mitochondria targeted peptides protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

A large body of evidence suggests that mitochondrial dysfunction and oxidative damage play a role in the pathogenesis of Parkinson's disease (PD). A number of antioxidants have been effective in animal models of PD. We have developed a family of mitochondria-targeted peptides that can protect against mitochondrial swelling and apoptosis (SS peptides). In this study, we examined the ability of two peptides, SS-31 and SS-20, to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. SS-31 produced dose-dependent complete protection against loss of dopamine and its metabolites in striatum, as well as loss of tyrosine hydroxylase immunoreactive neurons in substantia nigra pars compacta. SS-20, which does not possess intrinsic ability in scavenging reactive oxygen species, also demonstrated significant neuroprotective effects on dopaminergic neurons of MPTP-treated mice. Both SS-31 and SS-20 were very potent (nM) in preventing MPP+ (1-methyl-4-phenylpyridinium)-induced cell death in cultured dopamine cells (SN4741). Studies with isolated mitochondria showed that both SS-31 and SS-20 prevented MPP+-induced inhibition of oxygen consumption and ATP production, and mitochondrial swelling. These findings provide strong evidence that these neuroprotective peptides, which target both mitochondrial dysfunction and oxidative damage, are a promising approach for the treatment of PD.

Novel imine antioxidants at low nanomolar concentrations protect dopaminergic cells from oxidative neurotoxicity

Strong evidence indicates that oxidative stress may be causally involved in the pathogenesis of Parkinson's disease. We have employed human dopaminergic neuroblastoma cells and rat primary mesencephalic neurons to assess the protective potential of three novel bisarylimine antioxidants on dopaminergic cell death induced by complex I inhibition or glutathione depletion. We have found that exceptionally low concentrations (EC(50) values approximately 20 nM) of these compounds (iminostilbene, phenothiazine, and phenoxazine) exhibited strong protective effects against the toxicities of MPP(+), rotenone, and l-buthionine sulfoximine. Investigating intracellular glutathione levels, it was found that MPP(+), L-buthionine sulfoximine, and rotenone disrupted different aspects of the native glutathione equilibrium, while the aromatic imines did not further influence glutathione levels or redox state on any baseline. However, the imines independently reduced protein oxidation and total oxidant flux, saved the mitochondrial membrane potential, and provided full cytoprotection under conditions of complete glutathione depletion. The unusually potent antioxidant effects of the bisarylimines could be reproduced in isolated mitochondria, which were instantly protected from lipid peroxidation and pathological swelling. Aromatic imines may be interesting lead structures for a potential antioxidant therapy of Parkinson's disease and other disorders accompanied by glutathione dysregulation.