Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts

Structure and mechanism behind the inhibitory effect of water soluble metalloporphyrins on Aβ1-42 aggregation

Although the exact molecular mechanism of the pathogenesis of Alzheimer’s disease (AD) is still unclear, compounds that can inhibit the aggregation of amyloid-β peptide (Aβ1-42) or scavenge the highly toxic...

Methamphetamine, Neurotransmitters and Neurodevelopment

Methamphetamine (MA), as massively abused psychoactive stimulant, has been associated with many neurological diseases. It has various potent and neurotoxic properties. There are many mechanisms of action that contribute to its neurotoxic and degenerative effects, including excessive neurotransmitter (NEU) release, blockage of NEU uptake transporters, degeneration of NEU receptors, process of oxidative stress etc. MA intoxication is caused by blood-brain barrier disruption resulted from MA-induced oxidation stress. In our laboratory we constantly work on animal research of MA. Our current interest is to investigate processes of MA-induced alteration in neurotransmission, especially during development of laboratory rat. This review will describe current understanding in role of NEUs, which are affected by MA-induced neurotoxicity caused by altering the action of NEUs in the central nervous system (CNS). It also briefly brings information about NEUs development in critical periods of development.

A Zebrafish Model of Neurotoxicity by Binge-Like Methamphetamine Exposure

Hyperthermia is a common confounding factor for assessing the neurotoxic effects of methamphetamine (METH) in mammalian models. The development of new models of methamphetamine neurotoxicity using vertebrate poikilothermic animals should allow to overcome this problem. The aim of the present study was to develop a zebrafish model of neurotoxicity by binge-like methamphetamine exposure. After an initial testing at 20 and 40 mg/L for 48 h, the later METH concentration was selected for developing the model and the effects on the brain monoaminergic profile, locomotor, anxiety-like and social behaviors as well as on the expression of key genes of the catecholaminergic system were determined. A concentration- and time-dependent decrease in the brain levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) was found in METH-exposed fish. A significant hyperactivity was found during the first hour of exposure, followed 3 h after by a positive geotaxis and negative scototaxis in the novel tank and in the light/dark paradigm, respectively. Moreover, the behavioral phenotype in the treated fish was consistent with social isolation. At transcriptional level, th1 and slc18a2 (vmat2) exhibited a significant increase after 3 h of exposure, whereas the expression of gfap, a marker of astroglial response to neuronal injury, was strongly increased after 48 h exposure. However, no evidences of oxidative stress were found in the brain of the treated fish. Altogether, this study demonstrates the suitability of the adult zebrafish as a model of METH-induced neurotoxicity and provides more information about the biochemical and behavioral consequences of METH abuse.

The Role of Chinese Herbal Therapy in Methamphetamine Abuse and its Induced Psychiatric Symptoms

Repeated intake of methamphetamine (METH) leads to drug addiction, the inability to control intake, and strong drug cravings. It is also likely to cause psychiatric impairments, such as cognitive impairment, depression, and anxiety. Because the specific neurobiological mechanisms involved are complex and have not been fully and systematically elucidated, there is no established pharmacotherapy for METH abuse. Studies have found that a variety of Chinese herbal medicines have significant therapeutic effects on neuropsychiatric symptoms and have the advantage of multitarget comprehensive treatment. We conducted a systematic review, from neurobiological mechanisms to candidate Chinese herbal medicines, hoping to provide new perspectives and ideas for the prevention and treatment of METH abuse.

Role of autophagy and oxidative stress to astrocytes in fenpropathrin-induced Parkinson-like damage

Fenpropathrin is an insecticide that is widely used in agriculture. It remains unknown whether fenpropathrin exposure increases the risk of Parkinson's disease. We found that fenpropathrin increased oxidative stress both in vitro and in vivo. Additionally, fenpropathrin increased production of ROS, NOS2, and HO-1, and decreased SOD and GSH in astrocytes. We further found that fenpropathrin-mediated oxidative stress might inhibit autophagic flow, including decreased expression of LC3A/B and enhanced expression of SQSTM1 via down-regulation of CDK-5, an upstream marker of autophagy. In mice, autophagy was slightly different from that found in astrocytes, as reflected in the increased expressions of LC3A/B and SQSTM1. Our findings elucidate the toxicological phenomena and pathogenic mechanisms of fenpropathrin and may provide guidance for improved pesticide control and environmental protection.

The interplay between autophagy and apoptosis mediates toxicity triggered by synthetic cathinones in human kidney cells

Synthetic cathinones abuse remains a serious public health problem. Kidney injury has been reported in intoxications associated with synthetic cathinones, but the molecular mechanisms involved have not been explored yet. In this study, the potential in vitro nephrotoxic effects of four commonly abused cathinone derivatives, namely pentedrone, 3,4-dimethylmethcatinone (3,4-DMMC), methylone and 3,4-methylenedioxypyrovalerone (MDPV), were assessed in the human kidney HK-2 cell line. All four derivatives elicited cell death in a concentration- and time-dependent manner, in the following order of potency: 3,4-DMMC >> MDPV > methylone ≈ pentedrone. 3,4-DMMC and methylone were selected to further elucidate the mechanisms behind synthetic cathinones-induced cell death. Both drugs elicited apoptotic cell death and prompted the formation of acidic vesicular organelles and autophagosomes in HK-2 cells. Moreover, the autophagy inhibitor 3-methyladenine significantly potentiated cell death, indicating that autophagy may serve as a cell survival mechanism that protects renal cells against synthetic cathinones toxicity. Both drugs triggered a rise in reactive oxygen and nitrogen species formation, which was completely prevented by antioxidant treatment with N‑acetyl‑L‑cysteine or ascorbic acid. Importantly, these antioxidant agents significantly aggravated renal cell death induced by cathinone derivatives, most likely due to their autophagy-blocking properties. Taken together, our results support an intricate control of cell survival/death modulated by oxidative stress, apoptosis and autophagy in synthetic cathinones-induced renal injury.

Crocin Inhibits Apoptosis and Astrogliosis of Hippocampus Neurons Against Methamphetamine Neurotoxicity via Antioxidant and Anti-inflammatory Mechanisms

Methamphetamine (METH) is a stimulant drug, which can cause neurotoxicity and increase the risk of neurodegenerative disorders. The mechanisms of acute METH intoxication comprise intra-neuronal events including oxidative stress, dopamine oxidation, and excitotoxicity. According to recent studies, crocin protects neurons by functioning as an anti-oxidant, anti-inflammatory, and anti-apoptotic compound. Accordingly, this study aimed to determine if crocin can protect against METH-induced neurotoxicity. Seventy-two male Wistar rats that weighed 260-300 g were randomly allocated to six groups of control (n = 12), crocin 90 mg/kg group (n = 12), METH (n = 12), METH + crocin 30 mg/kg (n = 12), METH + crocin 60 mg/kg (n = 12), and METH + crocin 90 mg/kg (n = 12). METH neurotoxicity was induced by 40 mg/kg of METH in four injections (e.g., 4 × 10 mg/kg q. 2 h, IP). Crocin was intraperitoneally (IP) injected at 30 min, 24 h, and 48 h after the final injection of METH. Seven days after METH injection, the rats' brains were removed for biochemical assessment using the ELISA technique, and immunohistochemistry staining was used for caspase-3 and glial fibrillary acidic protein (GFAP) detection. Crocin treatment could significantly increase superoxide dismutase (P < 0.05) and glutathione (P < 0.01) levels and reduce malondialdehyde and TNF-α in comparison with the METH group (P < 0.05). Moreover, crocin could significantly decline the level of caspase-3 and GFAP-positive cells in the CA1 region (P < 0.01). According to the results, crocin exerts neuroprotective effects on METH neurotoxicity via the inhibition of apoptosis and neuroinflammation.

HIV-1 Tat and methamphetamine co-induced oxidative cellular injury is mitigated by N-acetylcysteine amide (NACA) through rectifying mTOR signaling

Methamphetamine (Meth) is an addictive psychostimulant whose abuse is intimately linked to increased risks for HIV-1 infection. Converging lines of evidence indicate that Meth also aggravates the symptoms of HIV-associated neurocognitive disorders (HAND), though the underlying mechanisms remain poorly understood. By using the lipophilic antioxidant N-acetylcysteine amide (NACA) as an interventional agent, we examined the roles of oxidative stress in autophagy and apoptosis induced by HIV-Tat (the transactivator of transcription), Meth or their combined treatment in human SH-SY5Y neuroblastoma cells and in the rat striatum. Oxidative stress was monitored in terms of the production of intracellular reactive oxygen species (ROS) and antioxidant reserves including glutathione peroxidase (GPx) and Cu,Zn-superoxide dismutase (SOD). NACA significantly reduced the level of ROS and restored GPx and SOD to levels comparable to that of normal control, implying a cytoprotective effect of NACA against oxidative stress elicited by Tat- and/or Meth. Protein expression of mammalian target of rapamycin (mTOR) was measured in SH-SY5Y cells and in the rat striatum to further explore the underlying mechanism of NACA protect against oxidative stress. The results support a beneficial effect of NACA in vivo and in vitro through rectification of the mTOR signaling pathway. Collectively, our study shows that NACA protects against Meth and/or Tat-induced cellular injury in vitro and in the rat striatum in vivo by attenuating oxidative stress, apoptosis and autophagy, at least in part, via modulation of mTOR signaling.

The differences in bioaccumulation and effects between Se(IV) and Se(VI) in the topmouth gudgeon Pseudorasbora parva

Selenium (Se) might be protective against oxidative stress at nutritional levels, but elevated Se concentrations in the diet has been revealed as the main culprit for the extinction of natural fish populations in Se-contaminated lakes. Though Se predominate as waterborne selenite (IV) and selenate (VI) in the water, the differences in bioaccumulation, effects (e.g., oxidative stress, antioxidants etc.) and molecular mechanisms between Se(IV) and Se(VI) have been relatively understudied in wild fish. In this study, the P. parva were exposed to waterborne Se (10, 200 and 1000 μg/L of Se(IV) or Se(VI)) and sampled at 4, 14 and 28 days. Bioaccumulation, tissue distributions of Se and following effects in different tissues were evaluated. The results showed that the levels of Se in the gills and intestine were significantly elevated with a seemingly concentration-dependent pattern in the Se(IV) treatment, with respectively 173.3% and 57.2% increase after 28 days of exposure, relative to that of Se(VI) treatment. Additionally, significant accumulation of Se was also observed in the muscle of Se(IV) treated fish. Se exposure increased the MDA levels in the brain and gills in the Se(IV) treatment, but less apparent in the Se(VI) treatment. Meanwhile, Se exposure lowered (at least 56%) the activity of GST in the gills, but increased the activity of AChE in the muscle (~69%) and brain (~50%) after 28 d. Most importantly, after 28 d of exposure, Se exposure caused significant decrease in GSH levels in the gills (at least 35%) and in all tissues examined at the highest test concentration. In general, the results showed that Se(IV) led to faster accumulation of Se than Se(VI) in P. parva, and the resulted lipid peroxidation was closely related to the levels of antioxidants, especially GSH. Our results suggest that the ecotoxicological effects of waterborne selenite and selenate differ in this freshwater species in the field.

Methamphetamine Induces Dopamine Release in the Nucleus Accumbens Through a Sigma Receptor-Mediated Pathway

Methamphetamine (METH) is a drug with a high addictive potential that is widely abused across the world. Although it is known that METH dysregulates both dopamine transmission and dopamine reuptake, the specific mechanism of action remains obscure. One promising target of METH is the sigma receptor, a chaperone protein located on the membrane of the endoplasmic reticulum. Using fast-scan cyclic voltammetry, we show that METH-enhancement of evoked dopamine release and basal efflux is dependent on sigma receptor activation. METH-induced activation of sigma receptors results in oxidation of a cysteine residue on VMAT2, which decreases transporter function. Unilateral injections of the sigma receptor antagonist BD-1063 prior to METH administration increased dopamine-related ipsilateral circling behavior, indicating the involvement of sigma receptors. These findings suggest that interactions between METH and the sigma receptor lead to oxidative species (most likely superoxide) that in turn oxidize VMAT2. Altogether, these findings show that the sigma receptor has a key role in METH dysregulation of dopamine release and dopamine-related behaviors.

Effects of sequential ethanol exposure and repeated high-dose methamphetamine on striatal and hippocampal dopamine, serotonin and glutamate tissue content in Wistar rats

Alcohol (ethanol) and methamphetamine (METH) co-abuse is a major public health issue. Ethanol or METH exposure has been associated with changes in neurotransmitter levels in several central brain regions. However, little is known about the effect of sequential exposure to ethanol and METH on glutamate, dopamine and serotonin tissue content in striatum and hippocampus. In this study, we investigated the effects of sequential exposure to ethanol and METH on tissue content of these neurotransmitters. Male Wistar rats were orally gavaged with either ethanol (6g/kg) or water for seven days. Rats were administered with high dose of METH (10mg/kg, i.p. every 2h×4) or saline on Day 8 and euthanized 48h of last METH or saline i.p. injection. In the striatum, sequential exposure to ethanol and METH increased glutamate tissue content while reducing dopamine and serotonin tissue content as compared to the group exposed to ethanol alone. In the hippocampus, sequential exposure to ethanol and METH decreased serotonin tissue content as compared to the group that was exposed to ethanol alone. However, this study showed that ethanol has no additive effect to METH on tissue content of dopamine and serotonin as compared to METH in the striatum and hippocampus. This study demonstrated that sequential exposure of ethanol and METH has an additive effect on tissue content of certain neurotransmitters in the brain.

Age-dependent redox status in the brain stem of NO-deficient hypertensive rats

BACKGROUND

The brain stem contains important nuclei that control cardiovascular function via the sympathetic nervous system (SNS), which is strongly influenced by nitric oxide. Its biological activity is also largely determined by oxygen free radicals. Despite many experimental studies, the role of AT1R-NAD(P)H oxidase-superoxide pathway in NO-deficiency is not yet sufficiently clarified. We determined changes in free radical signaling and antioxidant and detoxification response in the brain stem of young and adult Wistar rats during chronic administration of exogenous NO inhibitors.

METHODS

Young (4 weeks) and adult (10 weeks) Wistar rats were treated with 7-nitroindazole (7-NI group, 10 mg/kg/day), a specific nNOS inhibitor, with N^G-nitro-L-arginine-methyl ester (L-NAME group, 50 mg/kg/day), a nonspecific NOS inhibitor, and with drinking water (Control group) during 6 weeks. Systolic blood pressure was measured by non-invasive plethysmography. Expression of genes (AT1R, AT2R, p22phox, SOD and NOS isoforms, HO-1, MDR1a, housekeeper GAPDH) was identified by real-time PCR. NOS activity was detected by conversion of [3H]-L-arginine to [3H]-L-citrulline and SOD activity was measured using UV VIS spectroscopy.

RESULTS

We observed a blood pressure elevation and decrease in NOS activity only after L-NAME application in both age groups. Gene expression of nNOS (youngs) and eNOS (adults) in the brain stem decreased after both inhibitors. The radical signaling pathway triggered by AT1R and p22phox was elevated in L-NAME adults, but not in young rats. Moreover, L-NAME-induced NOS inhibition increased antioxidant response, as indicated by the observed elevation of mRNA SOD3, HO-1, AT2R and MDR1a in adult rats. 7-NI did not have a significant effect on AT1R-NADPH oxidase-superoxide pathway, yet it affected antioxidant response of mRNA expression of SOD1 and stimulated total activity of SOD in young rats and mRNA expression of AT2R in adult rats.

CONCLUSION

Our results show that chronic NOS inhibition by two different NOS inhibitors has age-dependent effect on radical signaling and antioxidant/detoxificant response in Wistar rats. While 7-NI had neuroprotective effect in the brain stem of young Wistar rats, L-NAME- induced NOS inhibition evoked activation of AT1R-NAD(P)H oxidase pathway in adult Wistar rats. Triggering of the radical pathway was followed by activation of protective compensation mechanism at the gene expression level.

Neurotoxicology of Synthetic Cathinone Analogs

The present review briefly explores the neurotoxic properties of methcathinone, mephedrone, methylone, and methylenedioxypyrovalerone (MDPV), four synthetic cathinones most commonly found in "bath salts." Cathinones are β-keto analogs of the commonly abused amphetamines and display pharmacological effects resembling cocaine and amphetamines, but despite their commonalities in chemical structures, synthetic cathinones possess distinct neuropharmacological profiles and produce unique effects. Among the similarities of synthetic cathinones with their non-keto analogs are their targeting of monoamine systems, the release of neurotransmitters, and their stimulant properties. Most of the literature on synthetic cathinones has focused on describing their properties as psychostimulants, their behavioral effects on locomotion, memory, and potential for abuse, whereas descriptions of their neurotoxic properties are not abundant. The biochemical gauges of neurotoxicity induced by non-keto analogs are well studied in humans and experimental animals and include their ability to induce neuroinflammation, oxidative stress, excitotoxicity, temperature alterations as well as dysregulation of neurotransmitter systems and induce changes in monoamine transporters and receptors. These neurotoxicity gauges will serve as parameters to discuss the effects of the four previously mentioned synthetic cathinones alone or in combination with either another cathinone or with some of their non-keto analogs. Bath salts are not a defined combination of drugs and may consist of one synthetic cathinone compound or combinations of more cathinones. Furthermore, this review also presents some of the mechanisms that are thought to underlie this toxicity. A better understanding of the cellular and molecular mechanisms involved in the synthetic cathinones-induced neurotoxicity should contribute to generate modern therapeutic approaches to prevent or attenuate the adverse consequences of use of these drugs in humans.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

Nucleus accumbens invulnerability to methamphetamine neurotoxicity

Methamphetamine (Meth) is a neurotoxic drug of abuse that damages neurons and nerve endings throughout the central nervous system. Emerging studies of human Meth addicts using both postmortem analyses of brain tissue and noninvasive imaging studies of intact brains have confirmed that Meth causes persistent structural abnormalities. Animal and human studies have also defined a number of significant functional problems and comorbid psychiatric disorders associated with long-term Meth abuse. This review summarizes the salient features of Meth-induced neurotoxicity with a focus on the dopamine (DA) neuronal system. DA nerve endings in the caudate-putamen (CPu) are damaged by Meth in a highly delimited manner. Even within the CPu, damage is remarkably heterogeneous, with ventral and lateral aspects showing the greatest deficits. The nucleus accumbens (NAc) is largely spared the damage that accompanies binge Meth intoxication, but relatively subtle changes in the disposition of DA in its nerve endings can lead to dramatic increases in Meth-induced toxicity in the CPu and overcome the normal resistance of the NAc to damage. In contrast to the CPu, where DA neuronal deficiencies are persistent, alterations in the NAc show a partial recovery. Animal models have been indispensable in studies of the causes and consequences of Meth neurotoxicity and in the development of new therapies. This research has shown that increases in cytoplasmic DA dramatically broaden the neurotoxic profile of Meth to include brain structures not normally targeted for damage. The resistance of the NAc to Meth-induced neurotoxicity and its ability to recover reveal a fundamentally different neuroplasticity by comparison to the CPu. Recruitment of the NAc as a target of Meth neurotoxicity by alterations in DA homeostasis is significant in light of the numerous important roles played by this brain structure.

Methamphetamine induces DNA damage in specific regions of the female rat brain

Methamphetamine (METH) is a highly addictive psychostimulant that has been shown to produce neurotoxicity. Methamphetamine increases the release of dopamine by reversing the direction of monoamine transporter proteins, leading to the formation of reactive oxygen species in the brain. In this study, we examined the effect of METH on DNA damage in vivo using the single cell gel electrophoresis assay (comet assay) under two different conditions. Rats treated with multiple doses of METH (10 mg/kg × 4) showed significant levels of DNA damage in the nucleus accumbens and striatum, both dopamine-rich areas. In contrast, a single dose of METH did not lead to significant levels of DNA damage in any of the dopamine-rich brain regions that were tested. Overall, the results of our study demonstrate that METH produces greater oxidative DNA damage in brain areas that receive greater dopamine innervation.

Drug-induced neurotoxicity in addiction medicine: From prevention to harm reduction

Neurotoxicity is considered as a major cause of neurodegenerative disorders. Most drugs of abuse have nonnegligible neurotoxic effects many of which are primarily mediated by several dopaminergic and glutamatergic neurotransmitter systems. Although many researchers have investigated the medical and cognitive consequences of drug abuse, the neurotoxicity induced by these drugs still requires comprehensive attention. The science of neurotoxicity promises to improve preventive and therapeutic strategies for brain disorders such as Alzheimer disease and Parkinson's disease. However, its clinical applications for addiction medicine remain to be defined adequately. This chapter reviews the most commonly discussed mechanisms underlying neurotoxicity induced by common drugs of abuse including amphetamines, cocaine, opiates, and alcohol. In addition, the known factors that trigger and/or predispose to drug-induced neurotoxicity are discussed. These factors include drug-related, individual-related, and environmental insults. Moreover, we introduce some of the potential pharmacological antineurotoxic interventions deduced from experimental animal studies. These interventions involve various targets such as dopaminergic system, mitochondria, cell death signaling, and NMDA receptors, among others. We conclude the chapter with a discussion of addicted patients who might benefit from such interventions.

Opposing effects of ketamine and acetyl L-carnitine on the serotonergic system of zebrafish

Ketamine, a pediatric anesthetic, is a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist. Studies show that ketamine is neurotoxic in developing mammals and zebrafish. In both mammals and zebrafish, acetyl L-carnitine (ALCAR) has been shown to be protective against ketamine toxicity. Ketamine is known to modulate the serotonergic system in mammals. Here, we measured the levels of serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the embryos exposed to ketamine in the presence and absence of ALCAR. Ketamine, at lower doses, did not produce significant changes in the 5-HT or 5-HIAA levels in 3 dpf (day post-fertilization) embryos. However, 2 mM ketamine (internal embryo exposure levels comparable to human anesthetic plasma concentration) significantly reduced 5-HT level, and 5-HIAA was not detectable indicating that 5-HT metabolism was abolished. In the presence or absence of 2 mM ketamine, ALCAR by itself did not significantly alter 5-HT or 5-HIAA levels compared to the control. Ratios of metabolite/5-HT indicated that 2 mM ketamine inhibited 5-HT metabolism to 5-HIAA whereas lower doses (0.1-0.3 mM) of ketamine did not have any effect. ALCAR reversed the effects of 2 mM ketamine not only by restoring 5-HT and 5-HIAA levels but also 5-HT turnover rate to control levels. Whole mount immunohistochemical studies showed that 2 mM ketamine reduced the serotonergic area in the brain whereas ALCAR expanded it with increased axonal sprouting and branching. These results indicate that ketamine and ALCAR have opposing effects on the zebrafish serotonergic system.

Oxidative stress, neurotoxicity, and non-specific immune responses in juvenile red sea bream, Pagrus major, exposed to different waterborne selenium concentrations

Juvenile Pagrus major (mean length 15.8±1.6 cm, and mean weight 90.4±4.7 g) were exposed for 4 weeks with waterborne selenium concentration (0, 50, 100, 200, and 400 μg L(-1)). In oxidative stress indicators, liver and gill superoxide dismutase (SOD) activity and glutathione S-transferase (GST) activity were markedly elevated after 4 weeks exposure. Similarly, glutathione (GSH) level in liver and gill was also increased in response to the highest Se exposure after 4 weeks exposure. In neurotoxicity, AChE activity was inhibited in brain and muscle tissues by waterborne Se exposure. In the non-specific immune responses, lysozyme activity of plasma and kidney was significantly increased by waterborne Se exposure. Peroxidase activity and anti-protease activity were decreased at high Se concentration. The results suggest that waterborne Se exposure can induce significant oxidative stress, inhibition of AChE activity, and immunological alterations.

Neuronal changes and oxidative stress in adolescent rats after repeated exposure to mephedrone

Mephedrone is a new designer drug of abuse. We have investigated the neurochemical/enzymatic changes after mephedrone administration to adolescent rats (3×25 mg/kg, s.c. in a day, with a 2 h interval between doses, for two days) at high ambient temperature (26±2 °C), a schedule that intends to model human recreational abuse. In addition, we have studied the effect of mephedrone in spatial learning and memory. The drug caused a transient decrease in weight gain. After the first dose, animals showed hypothermia but, after the subsequent doses, temperature raised over the values of saline-treated group. We observed the development of tolerance to these thermoregulatory effects of mephedrone. Mephedrone induced a reduction of the densities of dopamine (30% in the frontal cortex) and serotonin (40% in the frontal cortex and the hippocampus and 48% in the striatum) transporters without microgliosis. These deficits were also accompanied by a parallel decrease in the expression of tyrosine hydroxylase and tryptophan hydroxylase 2. These changes matched with a down-regulation of D2 dopamine receptors in the striatum. Mephedrone also induced an oxidative stress evidenced by an increase of lipid peroxidation in the frontal cortex, and accompanied by a rise in glutathione peroxidase levels in all studied brain areas. Drug-treated animals displayed an impairment of the reference memory in the Morris water maze one week beyond the cessation of drug exposure, while the spatial learning process seems to be preserved. These findings raise concerns about the neuronal long-term effects of mephedrone.

Methamphetamine effects on blood-brain barrier structure and function

Methamphetamine (Meth) is a widely abuse psychostimulant. Traditionally, studies have focused on the neurotoxic effects of Meth on monoaminergic neurotransmitter terminals. Recently, both in vitro and in vivo studies have investigated the effects of Meth on the BBB and found that Meth produces a decrease in BBB structural proteins and an increase in BBB permeability to various molecules. Moreover, preclinical studies are validated by clinical studies in which human Meth users have increased concentrations of toxins in the brain. Therefore, this review will focus on the structural and functional disruption of the BBB caused by Meth and the mechanisms that contribute to Meth-induced BBB disruption. The review will reveal that the mechanisms by which Meth damages dopamine and serotonin terminals are similar to the mechanisms by which the blood-brain barrier (BBB) is damaged. Furthermore, this review will cover the factors that are known to potentiate the effects of Meth (McCann et al., 1998) on the BBB, such as stress and HIV, both of which are co-morbid conditions associated with Meth abuse. Overall, the goal of this review is to demonstrate that the scope of damage produced by Meth goes beyond damage to monoaminergic neurotransmitter systems to include BBB disruption as well as provide a rationale for investigating therapeutics to treat Meth-induced BBB disruption. Since a breach of the BBB can have a multitude of consequences, therapies directed toward the treatment of BBB disruption may help to ameliorate the long-term neurodegeneration and cognitive deficits produced by Meth and possibly even Meth addiction.

Liposomal melatonin rescues methamphetamine-elicited mitochondrial burdens, pro-apoptosis, and dopaminergic degeneration through the inhibition PKCδ gene

We have demonstrated that mitochondrial oxidative damage and PKCδ overexpression contribute to methamphetamine-induced dopaminergic degeneration. Although it is recognized that antioxidant melatonin is effective in preventing neurotoxicity induced by methamphetamine, its precise mechanism remains elusive. C57BL/6J wild-type mice exhibited a similar degree of dopaminergic deficit when methamphetamine was administered during light and dark phases. Furthermore, dopaminergic neuroprotection by genetic inhibition of PKCδ during the light phase was comparable to that during the dark phase. Thus, we have focused on the light phase to examine whether melatonin modulates PKCδ-mediated neurotoxic signaling after multiple high doses of methamphetamine. To enhance the bioavailability of melatonin, we applied liposomal melatonin. Treatment with methamphetamine resulted in hyperthermia, mitochondrial translocation of PKCδ, oxidative damage (mitochondria > cytosol), mitochondrial dysfunction, pro-apoptotic changes, ultrastructural mitochondrial degeneration, dopaminergic degeneration, and behavioral impairment in wild-type mice. Treatment with liposomal melatonin resulted in a dose-dependent attenuation against degenerative changes induced by methamphetamine in wild-type mice. Attenuation by liposomal melatonin might be comparable to that by genetic inhibition (using PKCδ((-/-)) mice or PKCδ antisense oligonucleotide). However, liposomal melatonin did not show any additional protective effects on the attenuation by genetic inhibition of PKCδ. Our results suggest that the circadian cycle cannot be a key factor in modulating methamphetamine toxicity under the current experimental condition and that PKCδ is one of the critical target genes for melatonin-mediated protective effects against mitochondrial burdens (dysfunction), oxidative stress, pro-apoptosis, and dopaminergic degeneration induced by methamphetamine.

Amphetamine- and methamphetamine-induced hyperthermia: Implications of the effects produced in brain vasculature and peripheral organs to forebrain neurotoxicity

The adverse effects of amphetamine- (AMPH) and methamphetamine- (METH) induced hyperthermia on vasculature, peripheral organs and peripheral immune system are discussed. Hyperthermia alone does not produce amphetamine-like neurotoxicity but AMPH and METH exposures that do not produce hyperthermia (≥40°C) are minimally neurotoxic. Hyperthermia likely enhances AMPH and METH neurotoxicity directly through disruption of protein function, ion channels and enhanced ROS production. Forebrain neurotoxicity can also be indirectly influenced through the effects of AMPH- and METH- induced hyperthermia on vasculature. The hyperthermia and the hypertension produced by high doses amphetamines are a primary cause of transient breakdowns in the blood-brain barrier (BBB) resulting in concomitant regional neurodegeneration and neuroinflammation in laboratory animals. This BBB breakdown can occur in the amygdala, thalamus, striatum, sensory and motor cortex and hippocampus. Under these conditions, repetitive seizures greatly enhance neurodegeneration in hippocampus, thalamus and amygdala. Even when the BBB is less disrupted, AMPH- or METH- induced hyperthermia effects on brain vasculature may play a role in neurotoxicity. In this case, striatal and cortical vascular function are adversely affected, and even greater ROS, immune and damage responses are seen in the meninges and cortical surface vasculature. Finally, muscle and liver damage and elevated cytokines in blood can result when amphetamines produce hyperthermia. Proteins, from damaged muscle may activate the peripheral immune system and exacerbate liver damage. Liver damage can further increase cytokine levels, immune system activation and increase ammonia levels. These effects could potentially enhance vascular damage and neurotoxicity.

Methylphenidate ameliorates depressive comorbidity in ADHD children without any modification on differences in serum melatonin concentration between ADHD subtypes

The vast majority of Attention-deficit/hyperactivity disorder (ADHD) patients have other associated pathologies, with depressive symptoms as one of the most prevalent. Among the mediators that may participate in ADHD, melatonin is thought to regulate circadian rhythms, neurological function and stress response. To determine (1) the serum baseline daily variations and nocturnal excretion of melatonin in ADHD subtypes and (2) the effect of chronic administration of methylphenidate, as well as the effects on symptomatology, 136 children with ADHD (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision: DSM-IV-TR criteria) were divided into subgroups using the “Children’s Depression Inventory” (CDI). Blood samples were drawn at 20:00 and 09:00 h, and urine was collected between 21:00 and 09:00 h, at inclusion and after 4.61 ± 2.29 months of treatment. Melatonin and its urine metabolite were measured by radioimmunoassay RIA. Factorial analysis was performed using STATA 12.0. Melatonin was higher predominantly in hyperactive-impulsive/conduct disordered children (PHI/CD) of the ADHD subtype, without the influence of comorbid depressive symptoms. Methylphenidate ameliorated this comorbidity without induction of any changes in the serum melatonin profile, but treatment with it was associated with a decrease in 6-s-melatonin excretion in both ADHD subtypes. Conclusions: In untreated children, partial homeostatic restoration of disrupted neuroendocrine equilibrium most likely led to an increased serum melatonin in PHI/CD children. A differential cerebral melatonin metabolization after methylphenidate may underlie some of the clinical benefit.

Metalloporphyrins as therapeutic catalytic oxidoreductants in central nervous system disorders

SIGNIFICANCE

Metalloporphyrins, characterized by a redox-active transitional metal (Mn or Fe) coordinated to a cyclic porphyrin core ligand, mitigate oxidative/nitrosative stress in biological systems. Side-chain substitutions tune redox properties of metalloporphyrins to act as potent superoxide dismutase mimics, peroxynitrite decomposition catalysts, and redox regulators of transcription factor function. With oxidative/nitrosative stress central to pathogenesis of CNS injury, metalloporphyrins offer unique pharmacologic activity to improve the course of disease.

RECENT ADVANCES

Metalloporphyrins are efficacious in models of amyotrophic lateral sclerosis, Alzheimer's disease, epilepsy, neuropathic pain, opioid tolerance, Parkinson's disease, spinal cord injury, and stroke and have proved to be useful tools in defining roles of superoxide, nitric oxide, and peroxynitrite in disease progression. The most substantive recent advance has been the synthesis of lipophilic metalloporphyrins offering improved blood-brain barrier penetration to allow intravenous, subcutaneous, or oral treatment.

CRITICAL ISSUES

Insufficient preclinical data have accumulated to enable clinical development of metalloporphyrins for any single indication. An improved definition of mechanisms of action will facilitate preclinical modeling to define and validate optimal dosing strategies to enable appropriate clinical trial design. Due to previous failures of "antioxidants" in clinical trials, with most having markedly less biologic activity and bioavailability than current-generation metalloporphyrins, a stigma against antioxidants has discouraged the development of metalloporphyrins as CNS therapeutics, despite the consistent definition of efficacy in a wide array of CNS disorders.

FUTURE DIRECTIONS

Further definition of the metalloporphyrin mechanism of action, side-by-side comparison with "failed" antioxidants, and intense effort to optimize therapeutic dosing strategies are required to inform and encourage clinical trial design.

Neuroprotective and anti-apoptotic propensity of Bacopa monniera extract against sodium nitroprusside induced activation of iNOS, heat shock proteins and apoptotic markers in PC12 cells

Sodium nitroprusside (SNP) is a widely used nitric oxide (NO) donor, known to exert nitrative stress by up-regulation of inducible nitric oxide synthase (iNOS). Nω-nitro-L-arginine-methyl esther (L-NAME) is a NO inhibitor, which inhibits iNOS expression, is used as positive control. The present study was designed to assess neuroprotective propensity of Bacopa monniera extract (BME) in SNP-induced neuronal damage and oxido-nitrative stress in PC12 cells via modulation of iNOS, heat shock proteins and apoptotic markers. Our results elucidate that pre-treatment of PC12 cells with BME ameliorates the mitochondrial and plasma membrane damage induced by SNP (200 μM) as evidenced by MTT and LDH assays. BME pre-treatment inhibited NO generation by down regulating iNOS expression. BME replenished the depleted antioxidant status induced by SNP treatment. SNP-induced damage to cellular, nuclear and mitochondrial integrity was also restored by BME, which was confirmed by ROS estimation, comet assay and mitochondrial membrane potential assays respectively. BME pre-treatment efficiently attenuated the SNP-induced apoptotic protein biomarkers such as Bax, Bcl-2, cytochrome-c and caspase-3, which orchestrate the proteolytic damage of the cell. Q-PCR results further elucidated up-regulation of neuronal cell stress markers like HO-1 and iNOS and down-regulation of BDNF upon SNP exposure was attenuated by BME pre-treatment. By considering all these findings, we report that BME protects PC12 cells against SNP-induced toxicity via its free radical scavenging and neuroprotective mechanism.

Methamphetamine decreases levels of glutathione peroxidases 1 and 4 in SH-SY5Y neuronal cells: protective effects of selenium

Methamphetamine interferes with dopamine reuptake, and the resulting increased dopamine oxidation that creates oxidative stress can lead to degeneration of dopaminergic terminals. Previous studies have shown that the trace element selenium protects against methamphetamine toxicity. However, the specific selenoproteins responsible for protection have not been elucidated. Glutathione peroxidases 1 and 4 (GPx1 and GPx4) incorporate selenium into the amino acid selenocysteine, and their known antioxidant functions make them good candidates for protection from methamphetamine-induced oxidative damage. We differentiated SH-SY5Y neuronal cells in serum-free media with defined supplement containing 0, 10 and 100 nM selenium, and then challenged the cells with a 24-h exposure to methamphetamine. We found that 100 μM methamphetamine decreased GPx1 and GPx4 protein levels. However, both proteins were upregulated with increasing media selenium concentration. GPx enzymatic activity was also increased by selenium and decreased by methamphetamine and correlated with GPx protein levels. Total glutathione levels were reduced by methamphetamine at lower selenium conditions, while the oxidized fraction of GSH was increased at higher selenium levels. Additionally, we observed an increased generation of reactive oxygen species with methamphetamine exposure in media with 0 nM selenium, which was ameliorated by selenium supplementation. These results show that methamphetamine increases oxidative stress by reducing GPx levels, and this can be reversed with addition of selenium. These findings have important implications for treating patients with acute methamphetamine toxicity.

Neonatal +-methamphetamine exposure in rats alters adult locomotor responses to dopamine D1 and D2 agonists and to a glutamate NMDA receptor antagonist, but not to serotonin agonists

Neonatal exposure to (+)-methamphetamine (Meth) results in long-term behavioural abnormalities but its developmental mechanisms are unknown. In a series of experiments, rats were treated from post-natal days (PD) 11-20 (stage that approximates human development from the second to third trimester) with Meth or saline and assessed using locomotor activity as the readout following pharmacological challenge doses with dopamine, serotonin and glutamate agonists or antagonists during adulthood. Exposure to Meth early in life resulted in an exaggerated adult locomotor hyperactivity response to the dopamine D1 agonist SKF-82958 at multiple doses, a high dose only under-response activating effect of the D2 agonist quinpirole, and an exaggerated under-response to the activating effect of the N-methyl-d-aspartic acid (NMDA) receptor antagonist, MK-801. No change in locomotor response was seen following challenge with the 5-HT releaser p-chloroamphetamine or the 5-HT2/3 receptor agonist, quipazine. These are the first data to show that PD 11-20 Meth exposure induces long-lasting alterations to dopamine D1, D2 and glutamate NMDA receptor function and may suggest how developmental Meth exposure leads to many of its long-term adverse effects.

Oxidative stress status in recently abstinent methamphetamine abusers

AIM

Methamphetamine (METH) administration is associated with excessive oxidative stress. It is not known whether the systemic oxidative stress indices would alter during early abstinence in METH abusers with positive urine testing for recent METH exposure.

METHODS

Sixty-four non-treatment-seeking METH abusers enrolled from a controlled environment and 60 healthy controls participated in the study. Fasting serum malondialdehyde (MDA) levels and anti-oxidant indices, including superoxide dismutase (SOD) and catalase (CAT) activity, and glutathione (GSH) levels, were measured at baseline and 2 weeks after the first measurement. We compared the differences of these oxidative stress indices between METH abusers and controls and examined the changes of the indices 2 weeks after baseline in the METH group.

RESULTS

At baseline, the recently abstinent METH abusers had significantly higher MDA levels, lower SOD activity, and higher CAT activity and GSH levels compared to healthy controls. CAT and GSH values were positively correlated with MDA but negatively correlated with SOD. These oxidative stress indices did not significantly correlate with age, smoking amount, Alcohol Use Disorder Identification Test scores, or METH use variables. After 2 more weeks of abstinence, the indices did not alter nor normalize.

CONCLUSION

Compared to controls, we found that METH abusers have persistently higher systemic oxidative stress throughout early abstinence. The compromised SOD as well as elevated CAT activity and GSH levels may act together as a compensatory mechanism to counteract excessive oxidative stress induced by METH. Whether the oxidative stress could improve after a longer period of abstinence needs to be examined in future studies.

A dysphoric-like state during early withdrawal from extended access to methamphetamine self-administration in rats

RATIONALE

Negative emotional states during drug withdrawal may contribute to compulsive drug intake and seeking in humans. Studies suggest that extended access to methamphetamine induces compulsive drug intake in rats.

OBJECTIVE

The present study tested the hypothesis that compulsive methamphetamine intake in rats with extended access is associated with negative emotional states during drug withdrawal.

METHODS

Rats with short (1 h, ShA) and extended access (6 h, LgA) to methamphetamine self-administration (0.05 mg/kg/infusion) were tested for reward thresholds using intracranial self-stimulation (ICSS). Different groups of ShA and LgA rats were examined for depression-like and anxiety-like states in the novelty-suppressed feeding, open field, defensive burying, and forced swim tests.

RESULTS

With extended access, ICSS thresholds gradually increased, which was correlated with the increase of drug intake. During drug withdrawal, the increased ICSS thresholds returned to levels observed before exposure to extended access to methamphetamine. Upon re-exposure to extended access to methamphetamine, ICSS thresholds showed a more rapid escalation than during the initial exposure. LgA rats showed a longer latency to approach chow in the center of a novel field and remained immobile longer in the forced swim test than ShA rats did during early withdrawal. In contrast, ShA rats actively buried an aversive shock probe whereas LgA rats remained immobile in the defensive burying test.

CONCLUSION

The data suggest that extended access to methamphetamine produces a more depressive-like state than anxiety-like state in rats during early withdrawal.

Effect of diet on serotonergic neurotransmission in depression

Depression is characterized by sadness, purposelessness, irritability, and impaired body functions. Depression causes severe symptoms for several weeks, and dysthymia, which may cause chronic, low-grade symptoms. Treatment of depression involves psychotherapy, medications, or phototherapy. Clinical and experimental evidence indicates that an appropriate diet can reduce symptoms of depression. The neurotransmitter, serotonin (5-HT), synthesized in the brain, plays an important role in mood alleviation, satiety, and sleep regulation. Although certain fruits and vegetables are rich in 5-HT, it is not easily accessible to the CNS due to blood brain barrier. However the serotonin precursor, tryptophan, can readily pass through the blood brain barrier. Tryptophan is converted to 5-HT by tryptophan hydroxylase and 5-HTP decarboxylase, respectively, in the presence of pyridoxal phosphate, derived from vitamin B(6). Hence diets poor in tryptophan may induce depression as this essential amino acid is not naturally abundant even in protein-rich foods. Tryptophan-rich diet is important in patients susceptible to depression such as certain females during pre and postmenstrual phase, post-traumatic stress disorder, chronic pain, cancer, epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, and drug addiction. Carbohydrate-rich diet triggers insulin response to enhance the bioavailability of tryptophan in the CNS which is responsible for increased craving of carbohydrate diets. Although serotonin reuptake inhibitors (SSRIs) are prescribed to obese patients with depressive symptoms, these agents are incapable of precisely regulating the CNS serotonin and may cause life-threatening adverse effects in the presence of monoamine oxidase inhibitors. However, CNS serotonin synthesis can be controlled by proper intake of tryptophan-rich diet. This report highlights the clinical significance of tryptophan-rich diet and vitamin B(6) to boost serotonergic neurotransmission in depression observed in various neurodegenerative diseases. However pharmacological interventions to modulate serotonergic neurotransmission in depression, remains clinically significant. Depression may involve several other molecular mechanisms as discussed briefly in this report.

Chronic estradiol-17β exposure suppresses hypothalamic norepinephrine release and the steroid-induced luteinizing hormone surge: role of nitration of tyrosine hydroxylase

Chronic exposure to estrogens is known to produce a variety of deleterious effects in women including breast and ovarian cancer and anovulation. In female rats, exposure to low levels of estradiol-17β (E2) decreases hypothalamic norepinephrine (NE) to suppress luteinizing hormone (LH) secretion and cause failure of ovulation. We hypothesized that E2 exposure most likely decreases NE release in the medial preoptic area (MPA) of the hypothalamus to produce this effect and that this may be due to E2-induced inflammatory changes in noradrenergic nuclei leading to nitration of an enzyme involved in NE synthesis. To test this, female Sprague Dawley rats were sham implanted or implanted with slow release E2 pellets (20ng/day) for 30, 60 or 90 days (E30, E60 and E90 respectively). At the end of the treatment period, the rats were implanted with a push-pull cannula in the MPA, ovariectomized and steroid primied to induce a LH surge and subjected to push-pull perfusion. Perfusates were analyzed for NE levels using HPLC-EC. Blood samples collected simultaneously were analyzed for LH levels. We measured interleukin-1β (IL-1β) and nitrate levels in brainstem noradrenergic nuclei that innervate the MPA. In control animals, there was a marked increase in NE levels in response to steroid priming at 1600h that was reduced in the E30 group, and completely abolished after 60 and 90 days of E2 exposure. LH profiles were similar to NE release profiles in control and E2-treated animals. We found that IL-1β levels increased in all three (A1, A2 and A6) noradrenergic nuclei with chronic E2 exposure, while nitrate levels increased only in the A6 region. There was an increase in the nitration of the NE synthesizing enzyme in the MPA in this group as well probably contributing to reduced NE synthesis. This could be a possible mechanism by which chronic E2 exposure decreases NE levels in the MPA to suppress the LH surge.

N-Acetylcysteine amide protects against methamphetamine-induced tissue damage in CD-1 mice

Methamphetamine (METH), a highly addictive drug used worldwide, induces oxidative stress in various animal organs, especially the brain. This study evaluated oxidative damage caused by METH to tissues in CD-1 mice and identified a therapeutic drug that could protect against METH-induced toxicity. Male CD-1 mice were pretreated with a novel thiol antioxidant, N-acetylcysteine amide (NACA, 250 mg/kg body weight) or saline. Following this, METH (10 mg/kg body weight) or saline intraperitoneal injections were administered every 2 h over an 8-h period. Animals were killed 24 h after the last exposure. NACA-treated animals exposed to METH experienced significantly lower oxidative stress in their kidneys, livers, and brains than the untreated group, as indicated by their levels of glutathione, malondialdehyde, and protein carbonyl and their catalase and glutathione peroxidase activity. This suggests that METH induces oxidative stress in various organs and that a combination of NACA as a neuro- or tissue-protective agent, in conjunction with current treatment, might effectively treat METH abusers.

Huperzine A derivative M3 protects PC12 cells against sodium nitroprusside-induced apoptosis

AIM

To investigate the effects of M3, a derivative of huperzine A, on the apoptosis induced by sodium nitroprusside (SNP) in PC12 cells.

METHODS

Cell viability was detected using MTT method. Apoptosis was examined with annexin V/prodium iodide (PI) stain. The levels of reactive oxygen species (ROS) were measured using fluorophotometric quantitation. The amount of malonaldehyde (MDA) was determined with MDA detection kits. The expression of caspase-3 and Hsp70 were analyzed using Western blotting.

RESULTS

Exposure of PC12 cells to SNP (200 μmol/L) for 24 h decreased the cell viability to 69.0% of that in the control group. Pretreatment with M3 (10 μmol/L) or huperzine A (10 μmol/L) significantly protected the cells against SNP-induced injury and apoptosis; the ratio of apoptotic bodies in PC12 cells was decreased from 27.3% to 15.0%. Pretreatment with M3 (10 μmol/L) significantly decreased ROS and MDA levels, and increased the expression of Hsp70 in the cells. Quercetin (10 μmol/L) blocked the protective effect of M3, while did not influence on that of huperzine A.

CONCLUSION

M3 protects PC12 cells against SNP-induced apoptosis, possible due to ROS scavenging and Hsp70 induction.

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

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

Oxidative stress in neurodegeneration

It has been demonstrated that oxidative stress has a ubiquitous role in neurodegenerative diseases. Major source of oxidative stress due to reactive oxygen species (ROS) is related to mitochondria as an endogenous source. Although there is ample evidence from tissues of patients with neurodegenerative disorders of morphological, biochemical, and molecular abnormalities in mitochondria, it is still not very clear whether the oxidative stress itself contributes to the onset of neurodegeneration or it is part of the neurodegenerative process as secondary manifestation. This paper begins with an overview of how oxidative stress occurs, discussing various oxidants and antioxidants, and role of oxidative stress in diseases in general. It highlights the role of oxidative stress in neurodegenerative diseases like Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. The last part of the paper describes the role of oxidative stress causing deregulation of cyclin-dependent kinase 5 (Cdk5) hyperactivity associated with neurodegeneration.

Methamphetamine induces endoplasmic reticulum stress related gene CHOP/Gadd153/ddit3 in dopaminergic cells

We examined the toxicity of methamphetamine and dopamine in CATH.a cells, which were derived from mouse dopamine-producing neural cells in the central nervous system. Use of the quantitative real-time polymerase chain reaction revealed that transcripts of the endoplasmic reticulum stress related gene (CHOP/Gadd153/ddit3) were considerably induced at 24–48 h after methamphetamine administration (but only under apoptotic conditions), whereas dopamine slightly induced CHOP/Gadd153/ddit3 transcripts at an early stage. We also found that dopamine and methamphetamine weakly induced transcripts for the glucose-regulated protein 78 gene (Grp78/Bip) at the early stage. Analysis by immunofluorescence microscopy demonstrated an increase of　CHOP/Gadd153/ddit3 and Grp78/Bip proteins at 24 h after methamphetamine administration. Treatment of CATH.a cells with methamphetamine caused a re-distribution of dopamine inside the cells, which mimicked the presynaptic activity of neurons with cell bodies located in the ventral tegmental area or the substantia nigra. Thus, we have demonstrated the existence of endoplasmic reticulum stress in a model of presynaptic dopaminergic neurons for the first time. Together with the recent evidence suggesting the importance of presynaptic toxicity, our findings provide new insights into the mechanisms of dopamine toxicity, which might represent one of the most important mechanisms of methamphetamine toxicity and addiction.

Mouse strain- and age-dependent effects of binge methamphetamine on dopaminergic signaling

We have shown that a single "binge" dose of methamphetamine (Meth) in mice has long-lasting effects on open-field behavior dependent on mouse strain and age. Here we further investigated the impact of genotype and age on tyrosine hydroxylase (TH) loss and dopamine (DA) metabolism due to a high binge dose of Meth (4 × 5 mg/kg × 2 h × 2 days). Administration of high dose Meth or saline (Sal) to adolescent (PND 40) and adult (PND 80) C57BL/6 (B6), DBA/2 (DBA), and 129S6SvEv/Tac (129) mice was followed by a 1mg/kg Meth or Sal (control) challenge 40 days later. Striatal and prefrontal cortex tissues were collected 1h following the challenge. Meth-pretreated adolescent B6 and DBA mice exhibited losses in striatal DA concentrations; DBA adolescents also showed losses in striatal 3,4-dihydroxyphenylacetic acid (DOPAC) and increased DA turnover. Pre-exposed B6 and 129 adults demonstrated significant decreases in striatal DA, DOPAC, and increased DA turnover; DBA adults showed significant losses in striatal DA and increased DA turnover. 129 and DBA adults exhibited increases and decreases, respectively, in prefrontal cortex DA. Adult pretreated B6 mice produced significant losses in striatal TH. The results again show age and genotype dependent differences in Meth-induced DA alterations.

Impairment of adult hippocampal neural progenitor proliferation by methamphetamine: role for nitrotyrosination

Methamphetamine (METH) abuse has reached epidemic proportions, and it has become increasingly recognized that abusers suffer from a wide range of neurocognitive deficits. Much previous work has focused on the deleterious effects of METH on mature neurons, but little is known about the effects of METH on neural progenitor cells (NPCs). It is now well established that new neurons are continuously generated from NPCs in the adult hippocampus, and accumulating evidence suggests important roles for these neurons in hippocampal-dependent cognitive functions. In a rat hippocampal NPC culture system, we find that METH results in a dose-dependent reduction of NPC proliferation, and higher concentrations of METH impair NPC survival. NPC differentiation, however, is not affected by METH, suggesting cell-stage specificity of the effects of METH. We demonstrate that the effects of METH on NPCs are, in part, mediated through oxidative and nitrosative stress. Further, we identify seventeen NPC proteins that are post-translationally modified via 3-nitrotyrosination in response to METH, using mass spectrometric approaches. One such protein was pyruvate kinase isoform M2 (PKM2), an important mediator of cellular energetics and proliferation. We identify sites of PKM2 that undergo nitrotyrosination, and demonstrate that nitration of the protein impairs its activity. Thus, METH abuse may result in impaired adult hippocampal neurogenesis, and effects on NPCs may be mediated by protein nitration. Our study has implications for the development of novel therapeutic approaches for METH-abusing individuals with neurologic dysfunction and may be applicable to other neurodegenerative diseases in which hippocampal neurogenesis is impaired.

Neuronal Nicotinic Receptors as New Targets for Amphetamine-Induced Oxidative Damage and Neurotoxicity

Amphetamine derivatives such as methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”) are widely abused drugs in a recreational context. This has led to concern because of the evidence that they are neurotoxic in animal models and cognitive impairments have been described in heavy abusers. The main targets of these drugs are plasmalemmal and vesicular monoamine transporters, leading to reverse transport and increased monoamine efflux to the synapse. As far as neurotoxicity is concerned, increased reactive oxygen species (ROS) production seems to be one of the main causes. Recent research has demonstrated that blockade of α7 nicotinic acetylcholine receptors (nAChR) inhibits METH- and MDMA-induced ROS production in striatal synaptosomes which is dependent on calcium and on NO-synthase activation. Moreover, α7 nAChR antagonists (methyllycaconitine and memantine) attenuated in vivo the neurotoxicity induced by METH and MDMA, and memantine prevented the cognitive impairment induced by these drugs. Radioligand binding experiments demonstrated that both drugs have affinity to α7 and heteromeric nAChR, with MDMA showing lower K_i values, while fluorescence calcium experiments indicated that MDMA behaves as a partial agonist on α7 and as an antagonist on heteromeric nAChR. Sustained Ca increase led to calpain and caspase-3 activation. In addition, modulatory effects of MDMA on α7 and heteromeric nAChR populations have been found.

Methamphetamine-induced locomotor changes are dependent on age, dose and genotype

Adolescence is a critical age for addiction formation as a large percentage of pathological drug-seeking behaviors manifest during this time. The extent to which the neurotoxic effects of drugs of abuse influence subsequent drug seeking behaviors and impulsivity is an understudied area of research. Methamphetamine (METH) is a widely abused drug that produces locomotor responses ranging from behavioral sensitization to tolerance, both of which are behaviors that may relate to risk of abuse. Here we investigated the effects of age, genotype, METH dose, including a neurotoxic dose, and METH metabolism on open-field activity (OFA) to gain insight into the complex disease of drug abuse. C57Bl/6 (B6), DBA/2 (D2), and 129S6SvEv/Tac (129) mouse strains were administered saline or either a high dose (4×5 mg/kg in 2 h intervals for 2 days) or low dose (2×1 mg/kg in 24 h intervals) METH pretreatment during adolescence (post natal day (PND) 40) or early adulthood (PND 80) followed by behavioral testing with a METH (1 mg/kg) or saline challenge 40 days later. Striatal concentrations of METH and AMPH were also determined. Significant findings include: 1) METH pretreated adolescent B6 mice displayed significant sensitization for horizontal locomotion due to high dose METH pretreatment; 2) METH pretreated B6 adults showed significant tolerance for the vertical activity measure caused by low dose METH pretreatment; 3) METH pretreated adult D2 mice exhibited significant sensitization for vertical activity induced by low dose METH pretreatment, and 4) 129 mice metabolized METH significantly faster than the B6 and D2 mice, but METH pretreatment did not alter metabolism. No significant behavioral responses to either METH pretreatment dose were observed for the D2 adolescent studies or either 129 age group. Our results highlight the importance of the interactions of age, strain and METH dose on locomotor behavioral outcomes.

(2)H,(15)N-substituted nitroxides as sensitive probes for electron paramagnetic resonance imaging

Electron paramagnetic resonance imaging (EPRI) using nitroxides is an emergent imaging method for studying in vivo physiology, including O(2) distribution in various tissues. Such imaging capabilities would allow O(2) mapping in tumors and in different brain regions following hypoxia or drug abuse. We have recently demonstrated that the anion of 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (2) can be entrapped in brain tissue to quantitate O(2) concentration in vivo. To increase the sensitivity of O(2) measurement by EPR imaging, we synthesized 3-carboxy-2,2,5,5-tetra((2)H(3))methyl-1-(3,4,4-(2)H(3),1-(15)N)pyrrolidinyloxyl (7). EPR spectroscopic measurements demonstrate that this fully isotopically substituted nitroxide markedly improves signal-to-noise ratio and, therefore, the sensitivity of EPR imaging. The new isotopically substituted nitroxide shows increased sensitivity to changes in O(2) concentration, which will enable more accurate O(2) measurement in tissues using EPRI.

Chronic estradiol exposure induces oxidative stress in the hypothalamus to decrease hypothalamic dopamine and cause hyperprolactinemia

Estrogens are known to cause hyperprolactinemia, most probably by acting on the tuberoinfundibular dopaminergic (TIDA) system of the hypothalamus. Dopamine (DA) produced by TIDA neurons directly inhibits prolactin secretion and, therefore, to stimulate prolactin secretion, estrogens inhibit TIDA neurons to decrease DA production. However, the mechanism by which estrogen produces this effect is not clear. In the present study, we used a paradigm involving chronic exposure to low levels of estradiol-17β (E(2)) to mimic prolonged exposures to environmental and endogenous estrogens. We hypothesized that chronic exposure to low levels of E(2) induces oxidative stress in the arcuate nucleus (AN) of the hypothalamus that contains TIDA neurons and causes nitration of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of DA. This results in a significant decrease in DA and consequently, hyperprolactinemia. To investigate this, adult, intact female cycling rats were implanted with slow-release E(2) pellets (20 ng/day) for 30, 60, or 90 days and were compared with old (16-18 mo old) constant estrous (OCE) rats. Chronic E(2) exposure significantly increased the expression of glial fibrillary acidic protein and the concentrations of interleukin-1β (IL-1β) and nitrate in the AN that contains perikarya of TIDA neurons and increased nitration of TH in the median eminence (ME) that contains the terminals. These levels were comparable to those seen in OCE rats. We observed a significant decrease in DA concentrations in the ME and hyperprolactinemia in an exposure-dependent manner similar to that seen in OCE rats. It was concluded that chronic exposure to low levels of E(2) evokes oxidative stress in the AN to inhibit TIDA neuronal function, most probably leading to hyperprolactinemia.