Measurement of isoprostanes as markers of oxidative stress in neuronal tissue

Tissue pretreatment for LC-MS/MS analysis of PUFA and eicosanoid distribution in mouse brain and liver

Polyunsaturated fatty acids (PUFAs) and eicosanoids are important mediators of inflammation. The functional role of eicosanoids in metabolic-syndrome-related diseases has been extensively studied. However, their role in neuroinflammation and the development of neurodegenerative diseases is still unclear. The aim of this study was the development of a sample pretreatment protocol for the simultaneous analysis of PUFAs and eicosanoids in mouse liver and brain. Liver and brain samples of male wild-type C57BL/6J mice (11-122 mg) were used to investigate conditions for tissue rinsing, homogenization, extraction, and storage. A targeted liquid chromatography-negative electrospray ionization tandem mass spectrometry method was applied to quantify 7 PUFAs and 94 eicosanoids. The final pretreatment protocol consisted of a 5-min homogenization step by sonication in 650 μL n-hexane/2-propanol (60:40 v/v) containing 2,6-di-tert-butyl-4-methylphenol at 50 μg/mL. Homogenates representing 1 mg tissue were extracted in a single step with n-hexane/2-propanol (60:40 v/v) containing 0.1% formic acid. Autoxidation was prevented by addition of 2,6-di-tert-butyl-4-methylphenol at 50 μg/mL and keeping the samples at 4 °C during sample preparation. Extracts were dried under nitrogen and reconstituted in liquid chromatography eluent before analysis. Recovery was determined to range from 45% to 149% for both liver and brain tissue. Within-run and between-run variability ranged between 7% and 18% for PUFAs and between 1% and 24% for eicosanoids. In liver, 7 PUFAs and 15 eicosanoids were quantified; in brain, 6 PUFAs and 21 eicosanoids had significant differences within the brain substructures. In conclusion, a robust and reproducible sample preparation protocol for the multiplexed analysis of PUFAs and eicosanoids by liquid chromatography-tandem mass spectrometry in liver and discrete brain substructures was developed.

Manganese-Induced Neurotoxicity: New Insights Into the Triad of Protein Misfolding, Mitochondrial Impairment, and Neuroinflammation

Occupational or environmental exposure to manganese (Mn) can lead to the development of "Manganism," a neurological condition showing certain motor symptoms similar to Parkinson's disease (PD). Like PD, Mn toxicity is seen in the central nervous system mainly affecting nigrostriatal neuronal circuitry and subsequent behavioral and motor impairments. Since the first report of Mn-induced toxicity in 1837, various experimental and epidemiological studies have been conducted to understand this disorder. While early investigations focused on the impact of high concentrations of Mn on the mitochondria and subsequent oxidative stress, current studies have attempted to elucidate the cellular and molecular pathways involved in Mn toxicity. In fact, recent reports suggest the involvement of Mn in the misfolding of proteins such as α-synuclein and amyloid, thus providing credence to the theory that environmental exposure to toxicants can either initiate or propagate neurodegenerative processes by interfering with disease-specific proteins. Besides manganism and PD, Mn has also been implicated in other neurological diseases such as Huntington's and prion diseases. While many reviews have focused on Mn homeostasis, the aim of this review is to concisely synthesize what we know about its effect primarily on the nervous system with respect to its role in protein misfolding, mitochondrial dysfunction, and consequently, neuroinflammation and neurodegeneration. Based on the current evidence, we propose a 'Mn Mechanistic Neurotoxic Triad' comprising (1) mitochondrial dysfunction and oxidative stress, (2) protein trafficking and misfolding, and (3) neuroinflammation.

Multiwalled carbon nanotube supported Schiff base copper complex inorganic nanocomposite for enhanced electrochemical detection of dopamine

A MWCNT/[Cu(sal-ala)bpy] inorganic nanocomposite for the electrochemical detection of dopamine (DA).

Potential Role of Epigenetic Mechanism in Manganese Induced Neurotoxicity

Manganese is a vital nutrient and is maintained at an optimal level (2.5–5 mg/day) in human body. Chronic exposure to manganese is associated with neurotoxicity and correlated with the development of various neurological disorders such as Parkinson's disease. Oxidative stress mediated apoptotic cell death has been well established mechanism in manganese induced toxicity. Oxidative stress has a potential to alter the epigenetic mechanism of gene regulation. Epigenetic insight of manganese neurotoxicity in context of its correlation with the development of parkinsonism is poorly understood. Parkinson's disease is characterized by the α-synuclein aggregation in the form of Lewy bodies in neuronal cells. Recent findings illustrate that manganese can cause overexpression of α-synuclein. α-Synuclein acts epigenetically via interaction with histone proteins in regulating apoptosis. α-Synuclein also causes global DNA hypomethylation through sequestration of DNA methyltransferase in cytoplasm. An individual genetic difference may also have an influence on epigenetic susceptibility to manganese neurotoxicity and the development of Parkinson's disease. This review presents the current state of findings in relation to role of epigenetic mechanism in manganese induced neurotoxicity, with a special emphasis on the development of Parkinson's disease.

Relationship of serum paraoxonase enzyme activity and thermal burn injury

OBJECTIVE

This study investigated changes in serum oxidative stress parameters in burn cases compared to healthy controls.

MATERIALS AND METHODS

This study was performed in 41 burn patients with mild to severe thermal burn injuries and 38 healthy volunteers. The burn cases were selected from patients who were hospitalized in the burn unit for the treatment of second- and third-degree burns. Malondialdehyde (MDA) levels and PON-1 paraoxonase and arylesterase activities were measured in patient serum samples.

RESULTS

PON-1 paraoxonase activity and MDA levels in patients with major thermal burn injury were significantly higher than healthy controls, but PON-1 arylesterase activities were lower. A significant negative correlation was observed between the burn percentage of the total body surface area and the PON-1 arylesterase activities in patients.

CONCLUSION

Human thermal burn injury was associated with an increase in MDA production and a decrease in PON-1 arylesterase activity, which was proportional to the percentage of total burned surface area.

Isoprostanes and neuroprostanes as biomarkers of oxidative stress in neurodegenerative diseases

Accumulating data shows that oxidative stress plays a crucial role in neurodegenerative disorders. The literature data indicate that in vivo or postmortem cerebrospinal fluid and brain tissue levels of F2-isoprostanes (F2-IsoPs) especially F4-neuroprotanes (F4-NPs) are significantly increased in some neurodegenerative diseases: multiple sclerosis, Alzheimer's disease, Huntington's disease, and Creutzfeldt-Jakob disease. Central nervous system is the most metabolically active organ of the body characterized by high requirement for oxygen and relatively low antioxidative activity, what makes neurons and glia highly susceptible to destruction by reactive oxygen/nitrogen species and neurodegeneration. The discovery of F2-IsoPs and F4-NPs as markers of lipid peroxidation caused by the free radicals has opened up new areas of investigation regarding the role of oxidative stress in the pathogenesis of human neurodegenerative diseases. This review focuses on the relationship between F2-IsoPs and F4-NPs as biomarkers of oxidative stress and neurodegenerative diseases. We summarize the knowledge of these novel biomarkers of oxidative stress and the advantages of monitoring their formation to better define the involvement of oxidative stress in neurological diseases.

Lipid peroxidation generates biologically active phospholipids including oxidatively N-modified phospholipids

Peroxidation of membranes and lipoproteins converts "inert" phospholipids into a plethora of oxidatively modified phospholipids (oxPL) that can act as signaling molecules. In this review, we will discuss four major classes of oxPL: mildly oxygenated phospholipids, phospholipids with oxidatively truncated acyl chains, phospholipids with cyclized acyl chains, and phospholipids that have been oxidatively N-modified on their headgroups by reactive lipid species. For each class of oxPL we will review the chemical mechanisms of their formation, the evidence for their formation in biological samples, the biological activities and signaling pathways associated with them, and the catabolic pathways for their elimination. We will end by briefly highlighting some of the critical questions that remain about the role of oxPL in physiology and disease.

Comparison between 5-aminosalicylic acid (5-ASA) and para-aminosalicylic acid (4-PAS) as potential protectors against Mn-induced neurotoxicity

Manganese (Mn) is an essential metal for biological systems; however, occupational or clinical exposure to high levels of Mn can produce a neurological disorder called manganism. Oxidative stress and neuroinflammation play major roles in the Mn-induced neurodegeneration leading to dysfunction of the basal ganglia. We investigated the toxic effects of MnCl2 in an immortalized rat brain endothelial cell line (RBE4) and the protective effects of the radical scavenging aminosalicylic acids, 5-aminosalicylic acid (5-ASA) and 4-aminosalicylic acid (4-PAS). Mn cytotoxicity was determined with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) activity. A significant decrease in MTT reduction concomitant with increased LDH release was noted in RBE4 cells exposed for 24 h to MnCl2 (600 and 800 μM; p < 0.0001). Our results establish that compared to 4-PAS, 5-ASA has greater efficacy in protecting RBE4 cells from Mn-induced neurotoxicity after preexposure to MnCl2 800 μM (p < 0.0001).

Manganese-exposed developing rats display motor deficits and striatal oxidative stress that are reversed by Trolox

While manganese (Mn) is essential for proper central nervous system (CNS) development, excessive Mn exposure may lead to neurotoxicity. Mn preferentially accumulates in the basal ganglia, and in adults it may cause Parkinson's disease-like disorder. Compared to adults, younger individuals accumulate greater Mn levels in the CNS and are more vulnerable to its toxicity. Moreover, the mechanisms mediating developmental Mn-induced neurotoxicity are not completely understood. The present study investigated the developmental neurotoxicity elicited by Mn exposure (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 to PN27 in rats. Neurochemical analyses were carried out on PN29, with a particular focus on striatal alterations in intracellular signaling pathways (MAPKs, Akt and DARPP-32), oxidative stress generation and cell death. Motor alterations were evaluated later in life at 3, 4 or 5 weeks of age. Mn exposure (20 mg/kg) increased p38(MAPK) and Akt phosphorylation, but decreased DARPP-32-Thr-34 phosphorylation. Mn (10 and 20 mg/kg) increased caspase activity and F2-isoprostane production (a biological marker of lipid peroxidation). Paralleling the changes in striatal biochemical parameters, Mn (20 mg/kg) also caused motor impairment, evidenced by increased falling latency in the rotarod test, decreased distance traveled and motor speed in the open-field test. Notably, the antioxidant Trolox™ reversed the Mn (20 mg/kg)-dependent augmentation in p38(MAPK) phosphorylation and reduced the Mn (20 mg/kg)-induced caspase activity and F2-isoprostane production. Trolox™ also reversed the Mn-induced motor coordination deficits. These findings are the first to show that long-term exposure to Mn during a critical period of neurodevelopment causes motor coordination dysfunction with parallel increment in oxidative stress markers, p38(MAPK) phosphorylation and caspase activity in the striatum. Moreover, we establish Trolox™ as a potential neuroprotective agent given its efficacy in reversing the Mn-induced neurodevelopmental effects.

Chlorpyrifos-, diisopropylphosphorofluoridate-, and parathion-induced behavioral and oxidative stress effects: are they mediated by analogous mechanisms of action?

Exposure to organophosphates (OPs) can lead to cognitive deficits and oxidative damage. Little is known about the relationship between behavioral deficits and oxidative stress within the context of such exposures. Accordingly, the first experiment was carried out to address this issue. Male Wistar rats were administered 250 mg/kg of chlorpyrifos (CPF), 1.5 mg/kg of diisopropylphosphorofluoridate (DFP), or 15 mg/kg of parathion (PTN). Spatial learning in the water maze task was evaluated, and F(2)-isoprostanes (F(2)-IsoPs) and prostaglandin (PGE(2)) were analyzed in the hippocampus. A second experiment was designed to determine the degree of inhibition of brain acetylcholinesterase (AChE) activity, both the soluble and particulate forms of the enzyme, and to assess changes in AChE gene expression given evidence on alternative splicing of the gene in response to OP exposures. In addition, brain acylpeptide hydrolase (APH) activity was evaluated as a second target for OP-mediated effects. In both experiments, rats were sacrificed at various points to determine the time course of OPs toxicity in relation to their mechanism of action. Results from the first experiment suggest cognitive and emotional deficits after OPs exposure, which could be due to, at least in part, increased F(2)-IsoPs levels. Results from the second experiment revealed inhibition of brain AChE and APH activity at various time points post OP exposure. In addition, we observed increased brain read-through splice variant AChE (AChE-R) mRNA levels after 48 h PTN exposure. In conclusion, this study provides novel data on the relationship between cognitive alterations and oxidative stress, and the diverse mechanisms of action along a temporal axis in response to OP exposures in the rat.

In vivo manganese exposure modulates Erk, Akt and Darpp-32 in the striatum of developing rats, and impairs their motor function

Manganese (Mn) is an essential metal for development and metabolism. However, exposures to high Mn levels may be toxic, especially to the central nervous system (CNS). Neurotoxicity is commonly due to occupational or environmental exposures leading to Mn accumulation in the basal ganglia and a Parkinsonian-like disorder. Younger individuals are more susceptible to Mn toxicity. Moreover, early exposure may represent a risk factor for the development of neurodegenerative diseases later in life. The present study was undertaken to investigate the developmental neurotoxicity in an in vivo model of immature rats exposed to Mn (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 (PN8) to PN12. Neurochemical analysis was carried out on PN14. We focused on striatal alterations in intracellular signaling pathways, oxidative stress and cell death. Moreover, motor alterations as a result of early Mn exposure (PN8-12) were evaluated later in life at 3-, 4- and 5-weeks-of-age. Mn altered in a dose-dependent manner the activity of key cell signaling elements. Specifically, Mn increased the phosphorylation of DARPP-32-Thr-34, ERK1/2 and AKT. Additionally, Mn increased reactive oxygen species (ROS) production and caspase activity, and altered mitochondrial respiratory chain complexes I and II activities. Mn (10 and 20 mg/kg) also impaired motor coordination in the 3^rd, 4^th and 5^th week of life. Trolox™, an antioxidant, reversed several of the Mn altered parameters, including the increased ROS production and ERK1/2 phosphorylation. However, Trolox™ failed to reverse the Mn (20 mg/kg)-induced increase in AKT phosphorylation and motor deficits. Additionally, Mn (20 mg/kg) decreased the distance, speed and grooming frequency in an open field test; Trolox™ blocked only the decrease of grooming frequency. Taken together, these results establish that short-term exposure to Mn during a specific developmental window (PN8-12) induces metabolic and neurochemical alterations in the striatum that may modulate later-life behavioral changes. Furthermore, some of the molecular and behavioral events, which are perturbed by early Mn exposure are not directly related to the production of oxidative stress.

Protective effect of a novel peptide against methylmercury-induced toxicity in rat primary astrocytes

Methylmercury (MeHg) is an environmental neurotoxicant associated with aberrant central nervous system (CNS) functions. In this study, we examined the protective effect of a novel anti-inflammatory and cytoprotective nonapeptide, termed IIIM1, against MeHg-induced toxicity in cultured rat neonatal primary astrocytes. Astrocytes were pretreated for 66 h with 5 μg/ml IIIM1 (4.95 μM) followed by 6 h exposure to MeHg (5 μM). MeHg significantly increased F(2)-isoprostane generation, a lipid peroxidation biomarker of oxidative injury and this effect was significantly reduced upon pre-treatment with IIIM1. The MeHg-induced increase in levels of prostaglandin E(2) (PGE(2)), biomarkers of inflammatory responses, was also decreased in the peptide-treated cells. Mass spectrometry analysis revealed no chemical or binding interaction between MeHg and IIIM1, indicating that intracellular cytoprotective mechanism of action accounts for the neuroprotection rather than direct intracellular neutralization of the neurotoxicant with the peptide. These findings point to therapeutic potential for IIIM1 in a plethora of conditions associated with reactive oxygen species (ROS) generation. The implication of these findings may prove beneficial in designing new treatment modalities that efficiently suppress neurotoxicity, triggered not only by MeHg, but also by other metals and environmental agents, as well as chronic disease conditions that inherently increase reactive radical production and inflammatory signaling.

The inhibitory effect of manganese on acetylcholinesterase activity enhances oxidative stress and neuroinflammation in the rat brain

BACKGROUND

Manganese (Mn) is a naturally occurring element and an essential nutrient for humans and animals. However, exposure to high levels of Mn may cause neurotoxic effects. The pathological mechanisms associated with Mn neurotoxicity are poorly understood, but several reports have established it is mediated, at least in part, by oxidative stress.

OBJECTIVES

The present study was undertaken to test the hypothesis that a decrease in acetylcholinesterase (AChE) activity mediates Mn-induced neurotoxicity.

METHODS

Groups of 6 rats received 4 or 8 intraperitoneal (i.p.) injections of 25mg MnCl(2)/kg/day, every 48 h. Twenty-four hours after the last injection, brain AChE activity and the levels of F(2)-isoprostanes (F(2)-IsoPs) and F(4)-neuroprostanes (F(4)-NPs) (biomarkers of oxidative stress), as well as prostaglandin E(2) (PGE(2)) (biomarker of neuroinflammation) were analyzed.

RESULTS

The results showed that after either 4 or 8 Mn doses, brain AChE activity was significantly decreased (p<0.05), to 60 ± 16% and 55 ± 13% of control levels, respectively. Both treated groups exhibited clear signs of neurobehavioral toxicity, characterized by a significant (p<0.001) decrease in ambulation and rearings in open-field. Furthermore, Mn treatment caused a significant increase (p<0.05) in brain F(2)-IsoPs and PGE(2) levels, but only after 8 doses. In rats treated with 4 Mn doses, a significant increase (p<0.05) in brain F(4)-NPs levels was found. To evaluate cellular responses to oxidative stress, we assessed brain nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) and Mn-superoxide dismutase (Mn-SOD, SOD2) protein expression levels. A significant increase in Mn-SOD protein expression (p<0.05) and a trend towards increased Nrf2 protein expression was noted in rat brains after 4 Mn doses vs. the control group, but the expression of these proteins was decreased after 8 Mn doses. Taken together, these results suggest that the inhibitory effect of Mn on AChE activity promotes increased levels of neuronal oxidative stress and neuroinflammatory biomarkers.

Chemokines, macrophage inflammatory protein-2 and stromal cell-derived factor-1α, suppress amyloid β-induced neurotoxicity

Alzheimer's disease (AD) is characterized by a progressive cognitive decline and accumulation of neurotoxic oligomeric peptides amyloid-β (Aβ). Although the molecular events are not entirely known, it has become evident that inflammation, environmental and other risk factors may play a causal, disruptive and/or protective role in the development of AD. The present study investigated the ability of the chemokines, macrophage inflammatory protein-2 (MIP-2) and stromal cell-derived factor-1α (SDF-1α), the respective ligands for chemokine receptors CXCR2 and CXCR4, to suppress Aβ-induced neurotoxicity in vitro and in vivo. Pretreatment with MIP-2 or SDF-1α significantly protected neurons from Aβ-induced dendritic regression and apoptosis in vitro through activation of Akt, ERK1/2 and maintenance of metalloproteinase ADAM17 especially with SDF-1α. Intra-cerebroventricular (ICV) injection of Aβ led to reduction in dendritic length and spine density of pyramidal neurons in the CA1 area of the hippocampus and increased oxidative damage 24h following the exposure. The Aβ-induced morphometric changes of neurons and increase in biomarkers of oxidative damage, F(2)-isoprostanes, were significantly inhibited by pretreatment with the chemokines MIP-2 or SDF-1α. Additionally, MIP-2 or SDF-1α was able to suppress the aberrant mislocalization of p21-activated kinase (PAK), one of the proteins involved in the maintenance of dendritic spines. Furthermore, MIP-2 also protected neurons against Aβ neurotoxicity in CXCR2-/- mice, potentially through observed up regulation of CXCR1 mRNA. Understanding the neuroprotective potential of chemokines is crucial in defining the role for their employment during the early stages of neurodegeneration.

Protective effects of antioxidants and anti-inflammatory agents against manganese-induced oxidative damage and neuronal injury

Exposure to excessive manganese (Mn) levels leads to neurotoxicity, referred to as manganism, which resembles Parkinson's disease (PD). Manganism is caused by neuronal injury in both cortical and subcortical regions, particularly in the basal ganglia. The basis for the selective neurotoxicity of Mn is not yet fully understood. However, several studies suggest that oxidative damage and inflammatory processes play prominent roles in the degeneration of dopamine-containing neurons. In the present study, we assessed the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates and associated neuronal dysfunctions both in vitro and in vivo. Results from our in vitro study showed a significant (p<0.01) increase in biomarkers of oxidative damage, F(2)-isoprostanes (F(2)-IsoPs), as well as the depletion of ATP in primary rat cortical neurons following exposure to Mn (500 μM) for 2h. These effects were protected when neurons were pretreated for 30 min with 100 of an antioxidant, the hydrophilic vitamin E analog, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), or an anti-inflammatory agent, indomethacin. Results from our in vivo study confirmed a significant increase in F(2)-IsoPs levels in conjunction with the progressive spine degeneration and dendritic damage of the striatal medium spiny neurons (MSNs) of mice exposed to Mn (100mg/kg, s.c.) 24h. Additionally, pretreatment with vitamin E (100mg/kg, i.p.) or ibuprofen (140 μg/ml in the drinking water for two weeks) attenuated the Mn-induced increase in cerebral F(2)-IsoPs? and protected the MSNs from dendritic atrophy and dendritic spine loss. Our findings suggest that the mediation of oxidative stress/mitochondrial dysfunction and the control of alterations in biomarkers of oxidative injury, neuroinflammation and synaptodendritic degeneration may provide an effective, multi-pronged therapeutic strategy for protecting dysfunctional dopaminergic transmission and slowing of the progression of Mn-induced neurodegenerative processes.

Prostanoid signaling: dual role for prostaglandin E2 in neurotoxicity

The prostanoids, a naturally occurring subclass of eicosanoids, are lipid mediators generated through oxidative pathways from arachidonic acid. These cyclooxygenase metabolites, consisting of the prostaglandins (PG), prostacyclin and tromboxane, are released in response to a variety of physiological and pathological stimuli in almost all organs, including the brain. They are produced by various cell types and act upon targeted cells via specific G protein-coupled receptors. The existence of multiple receptors, cross-reactivity and coupling to different signal transduction pathways for each prostanoid, collectively establish their diverse effects. Notably, these effects can occur in functionally opposing directions within the same cell or organ. Prostaglandin E(2) (PGE(2)) is the most versatile prostanoid because of its receptors, E Prostanoid (EP) receptor subtypes 1 through 4, its biological heterogeneity and its differential expression on neuronal and glial cells throughout the central nervous system. Since PGE(2) plays an important role in processes associated with various neurological diseases, this review focuses on its dual neuroprotective and neurotoxic role in EP receptor subtype signaling pathways in different models of brain injury.

Progression of neurodegeneration and morphologic changes in the brains of juvenile mice with selenoprotein P deleted

Selenoprotein P (Sepp1) is an important protein involved in selenium (Se) transport and homeostasis. Severe neurologic dysfunction develops in Sepp1 null mice (Sepp1(-/-)) fed a selenium-deficient diet. Sepp1(-/-) mice fed a selenium-deficient diet have extensive degeneration of the brainstem and thalamus, and even when supplemented with selenium exhibit subtle learning deficits and altered basal synaptic transmission and short-term plasticity in the CA1 region of the hippocampus. The goal of this study was to delineate the regional progression of neurodegeneration in the brain, determine the extent of neuronal cell death, and evaluate neurite structural changes within the hippocampus of Sepp1(-/-) mice. Whole brain serial sections of wild-type and Sepp1(-/-) mice maintained on selenium-deficient or supplemented diets over the course of 12 days from weaning were evaluated with amino cupric silver neurodegeneration stain. The neurodegeneration was present in all regions upon weaning and progressed over 12 days in Sepp1(-/-) mice fed selenium-deficient diet, except in the medial forebrain bundle and somatosensory cortex where the neurodegeneration developed post-weaning. The neurodegeneration was predominantly axonal, however the somatosensory cortex and lateral striatum showed silver-stained neurons. Morphologic analysis of the hippocampus revealed decreased dendritic length and spine density, suggesting that loss of Sepp1 also causes subtle changes in the brain that can contribute to functional deficits. These data illustrate that deletion of Sepp1, and presumably selenium deficiency in the brain, produce both neuronal and axonal degeneration as well as more moderate and potentially reversible neurite changes in the developing brain.

Mefloquine neurotoxicity is mediated by non-receptor tyrosine kinase

Among several available antimalarial drugs, mefloquine has proven to be effective against drug-resistant Plasmodium falciparum and remains the drug of choice for both therapy and chemoprophylaxis. However, mefloquine is known to cause adverse neurological and/or psychiatric symptoms, which offset its therapeutic advantage. The exact mechanisms leading to the adverse neurological effects of mefloquine are poorly defined. Alterations in neurotransmitter release and calcium homeostasis, the inhibition of cholinesterases and the interaction with adenosine A(2A) receptors have been hypothesized to play prominent roles in mediating the deleterious effects of this drug. Our recent data have established that mefloquine can also trigger oxidative damage and subsequent neurodegeneration in rat cortical primary neurons. Furthermore, we have utilized a system biology-centered approach and have constructed a pathway model of cellular responses to mefloquine, identifying non-receptor tyrosine kinase 2 (Pyk2) as a critical target in mediating mefloquine neurotoxicity. In this study, we sought to establish an experimental validation of Pyk2 using gene-silencing techniques (siRNA). We have examined whether the downregulation of Pyk2 in primary rat cortical neurons alters mefloquine neurotoxicity by evaluating cell viability, apoptosis and oxidative stress. Results from our study have confirmed that mefloquine neurotoxicity is associated with apoptotic response and oxidative injury, and we have demonstrated that mefloquine affects primary rat cortical neurons, at least in part, via Pyk2. The implication of these findings may prove beneficial in suppressing the neurological side effects of mefloquine and developing effective therapeutic modalities to offset its adverse effects.

Extracellular dopamine potentiates mn-induced oxidative stress, lifespan reduction, and dopaminergic neurodegeneration in a BLI-3-dependent manner in Caenorhabditis elegans

Parkinson's disease (PD)-mimicking drugs and pesticides, and more recently PD-associated gene mutations, have been studied in cell cultures and mammalian models to decipher the molecular basis of PD. Thus far, a dozen of genes have been identified that are responsible for inherited PD. However they only account for about 8% of PD cases, most of the cases likely involving environmental contributions. Environmental manganese (Mn) exposure represents an established risk factor for PD occurrence, and both PD and Mn-intoxicated patients display a characteristic extrapyramidal syndrome primarily involving dopaminergic (DAergic) neurodegeneration with shared common molecular mechanisms. To better understand the specificity of DAergic neurodegeneration, we studied Mn toxicity in vivo in Caenorhabditis elegans. Combining genetics and biochemical assays, we established that extracellular, and not intracellular, dopamine (DA) is responsible for Mn-induced DAergic neurodegeneration and that this process (1) requires functional DA-reuptake transporter (DAT-1) and (2) is associated with oxidative stress and lifespan reduction. Overexpression of the anti-oxidant transcription factor, SKN-1, affords protection against Mn toxicity, while the DA-dependency of Mn toxicity requires the NADPH dual-oxidase BLI-3. These results suggest that in vivo BLI-3 activity promotes the conversion of extracellular DA into toxic reactive species, which, in turn, can be taken up by DAT-1 in DAergic neurons, thus leading to oxidative stress and cell degeneration.

Protection of DFP-induced oxidative damage and neurodegeneration by antioxidants and NMDA receptor antagonist

Prophylactic agents acutely administered in response to anticholinesterases intoxication can prevent toxic symptoms, including fasciculations, seizures, convulsions and death. However, anticholinesterases also have long-term unknown pathophysiological effects, making rational prophylaxis/treatment problematic. Increasing evidence suggests that in addition to excessive cholinergic stimulation, organophosphate compounds such as diisopropylphosphorofluoridate (DFP) induce activation of glutamatergic neurons, generation of reactive oxygen (ROS) and nitrogen species (RNS), leading to neurodegeneration. The present study investigated multiple affectors of DFP exposure critical to cerebral oxidative damage and whether antioxidants and NMDA receptor antagonist memantine provide neuroprotection by preventing DFP-induced biochemical and morphometric changes in rat brain. Rats treated acutely with DFP (1.25 mg/kg, s.c.) developed onset of toxicity signs within 7-15 min that progressed to maximal severity of seizures and fasciculations within 60 min. At this time point, DFP caused significant (p<0.01) increases in biomarkers of ROS (F2-isoprostanes, F2-IsoPs; and F4-neuroprostanes, F4-NeuroPs), RNS (citrulline), and declines in high-energy phosphates (HEP) in rat cerebrum. At the same time, quantitative morphometric analysis of pyramidal neurons of the hippocampal CA1 region revealed significant (p<0.01) reductions in dendritic lengths and spine density. When rats were pretreated with the antioxidants N-tert-butyl-alpha-phenylnitrone (PBN, 200 mg/kg, i.p.), or vitamin E (100 mg/kg, i.p./day for 3 days), or memantine (18 mg/kg, i.p.), significant attenuations in DFP-induced increases in F2-IsoPs, F4-NeuroPs, citrulline, and depletion of HEP were noted. Furthermore, attenuation in oxidative damage following antioxidants or memantine pretreatment was accompanied by rescue from dendritic degeneration of pyramidal neurons in the CA1 hippocampal area. These findings closely associated DFP-induced lipid peroxidation with dendritic degeneration of pyramidal neurons in the CA1 hippocampal area and point to possible interventions to limit oxidative injury and dendritic degeneration induced by anticholinesterase neurotoxicity.

Oxidative damage and neurodegeneration in manganese-induced neurotoxicity

Exposure to excessive manganese (Mn) levels results in neurotoxicity to the extrapyramidal system and the development of Parkinson's disease (PD)-like movement disorder, referred to as manganism. Although the mechanisms by which Mn induces neuronal damage are not well defined, its neurotoxicity appears to be regulated by a number of factors, including oxidative injury, mitochondrial dysfunction and neuroinflammation. To investigate the mechanisms underlying Mn neurotoxicity, we studied the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates (HEP), neuroinflammation mediators and associated neuronal dysfunctions both in vitro and in vivo. Primary cortical neuronal cultures showed concentration-dependent alterations in biomarkers of oxidative damage, F2-isoprostanes (F2-IsoPs) and mitochondrial dysfunction (ATP), as early as 2 h following Mn exposure. Treatment of neurons with 500 microM Mn also resulted in time-dependent increases in the levels of the inflammatory biomarker, prostaglandin E2 (PGE2). In vivo analyses corroborated these findings, establishing that either a single or three (100 mg/kg, s.c.) Mn injections (days 1, 4 and 7) induced significant increases in F2-IsoPs and PGE2 in adult mouse brain 24 h following the last injection. Quantitative morphometric analyses of Golgi-impregnated striatal sections from mice exposed to single or three Mn injections revealed progressive spine degeneration and dendritic damage of medium spiny neurons (MSNs). These findings suggest that oxidative stress, mitochondrial dysfunction and neuroinflammation are underlying mechanisms in Mn-induced neurodegeneration.