The induction of amyloid precursor protein and α-synuclein in rat hippocampal astrocytes by diethyldithiocarbamate and copper with or without glutathione

Angiotensin type 1 receptor activation promotes neuronal and glial alpha-synuclein aggregation and transmission

The brain renin-angiotensin system (RAS) has been related to dopaminergic degeneration, and high expression of the angiotensin II (AngII) type 1 receptor (AT1) gene is a marker of the most vulnerable neurons in humans. However, it is unknown whether AngII/AT1 overactivation affects α-synuclein aggregation and transmission. In vitro, AngII/AT1 activation increased α-synuclein aggregation in dopaminergic neurons and microglial cells, which was related to AngII-induced NADPH-oxidase activation and intracellular calcium raising. In mice, AngII/AT1 activation was involved in MPTP-induced increase in α-synuclein expression and aggregation, as they significantly decreased in mice treated with the AT1 blocker telmisartan and AT1 knockout mice. Cell co-cultures (transwells) revealed strong transmission of α-synuclein from dopaminergic neurons to astrocytes and microglia. AngII induced a higher α-synuclein uptake by microglial cells and an increase in the transfer of α-synuclein among astroglial cells. However, AngII did not increase the release of α-synuclein by neurons. The results further support brain RAS dysregulation as a major mechanism for the progression of Parkinson's disease, and AT1 inhibition and RAS modulation as therapeutic targets.

Brain clearance of protein aggregates: a close-up on astrocytes

Protein misfolding and accumulation defines a prevailing feature of many neurodegenerative disorders, finally resulting in the formation of toxic intra- and extracellular aggregates. Intracellular aggregates can enter the extracellular space and be subsequently transferred among different cell types, thus spreading between connected brain districts.Although microglia perform a predominant role in the removal of extracellular aggregated proteins, mounting evidence suggests that astrocytes actively contribute to the clearing process. However, the molecular mechanisms used by astrocytes to remove misfolded proteins are still largely unknown.Here we first provide a brief overview of the progressive transition from soluble monomers to insoluble fibrils that characterizes amyloid proteins, referring to α-Synuclein and Tau as archetypical examples. We then highlight the mechanisms at the basis of astrocyte-mediated clearance with a focus on their potential ability to recognize, collect, internalize and digest extracellular protein aggregates. Finally, we explore the potential of targeting astrocyte-mediated clearance as a future therapeutic approach for the treatment of neurodegenerative disorders characterized by protein misfolding and accumulation.

Effects of glyphosate, mancozeb and their combinations on mouse neuroblastoma cells

Pesticides-related toxicities have long been studied. Data regarding the effects of combined exposure to environmentally relevant pesticides however remain lacking. The herbicide glyphosate and the fungicide mancozeb are extensively used in agriculture. Residues of both compounds are frequently found in food and water and therefore, environmental exposure to both pesticides is a possibility. Neurotoxicity of glyphosate, mancozeb and their combinations were investigated using mouse neuroblastoma cells. Cytotoxicity observed with the glyphosate and mancozeb combinations was higher than that observed when glyphosate was tested alone. Combinations of glyphosate followed by mancozeb increased copper, manganese, and zinc levels. Mixture of mancozeb + glyphosate increased manganese and zinc levels. Combination of mancozeb followed by glyphosate increased copper and zinc levels. Glutathione ratio was decreased as a result of combinations of glyphosate and mancozeb. The decrease in glutathione ratio was greater in the combination groups than in glyphosate alone.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Oxidative Stress Induced Dysfunction of Protein Synthesis in 661W Mice Photoreceptor Cells

Photoreceptor cells are highly susceptible to oxidative-stress-induced damage due to their high metabolic rate. Oxidative stress plays a key role in driving pathological events in several different ocular diseases, which lead to retinal degeneration and ultimately blindness. A growing number of studies have been performed to understand downstream events caused by ROS induced oxidative stress in photoreceptor cells; however, the underlying mechanisms of ROS toxicity are not fully understood. To shed light on ROS induced downstream pathological events, we employed a tandem mass tag (TMT) labelling-based quantitative mass-spectrometric approach to determine proteome changes in 661W photoreceptor cells following oxidative stress induction via the application of different concentrations of H2O2 at different time points. Overall, 5920 proteins were identified and quantified, and 450 differentially expressed proteins (DEPs) were identified, which were altered in a dose and time dependent manner in all treatment groups compared to the control group. These proteins were involved in several biological pathways, including spliceosome and ribosome response, activated glutathione metabolism, decreased ECM-receptor interaction, oxidative phosphorylation, abnormally regulated lysosome, apoptosis, and ribosome biogenesis. Our results highlighted ECM receptor interaction, oxidative phosphorylation and spliceosome pathways as the major targets of oxidative stress that might mediate vascular dysfunction and cellular senescence.

Exposure to dithiocarbamate fungicide Ziram results in hepatic and renal toxicity in Long Evan rats

Ziram is a dimethyldithiocarbamate fungicide that is complexed to the metal zinc. The focus of this study is to examine the effects of dimethyldithiocarbamate exposure on metal homeostasis, glutathione levels, and the physiological parameters of the kidney and liver in Long-Evan rats. Our results indicate significant accumulation of copper or zinc, and changes in total GSH or GSH/GSSG ratio in the liver and kidneys of animals treated with Ziram only. Histopathological examination of liver and kidney sections indicate the presence of infiltrates in the liver of animals treated with Ziram only, whereas protein aggregates, sloughing of cells and increased KIM-1 positive cells, an indicator of tubule deterioration, are seen in the kidneys of animals treated with Ziram and sodium-dimethyldithiocarbamate, the salt form of the dimethyldithiocarbmate backbone. These findings suggest that the overall toxicological effect of Ziram is mediated by an intrinsic property rather than to dimethyldithiocarbamate backbone or metal moiety.

Fatty Acid Synthesis in Glial Cells of the CNS

Fatty acids (FAs) are of crucial importance for brain homeostasis and neural function. Glia cells support the high demand of FAs that the central nervous system (CNS) needs for its proper functioning. Additionally, FAs can modulate inflammation and direct CNS repair, thereby contributing to brain pathologies such Alzheimer’s disease or multiple sclerosis. Intervention strategies targeting FA synthesis in glia represents a potential therapeutic opportunity for several CNS diseases.

Subtle genomic DNA damage induces intraneuronal production of amyloid-β (1-42) by increasing β-secretase activity

Aberrant accumulation of amyloid-β (Aβ) in brain is the major trigger for pathogenesis in Alzheimer's disease (AD). It is imperative to understand how Aβ attains such toxic levels in the brain parenchyma. We detected that a subtle and tolerable amount of DNA damage, related to aging, increased intraneuronal Aβ_1-42 production both in cultured neuron and in cortex of rodent brain. Strikingly, we also observed elevated levels of mitochondrial fusion and of its major driver protein, MFN2. Hyperfusion of mitochondria may be seen as an adaptive stress response resulting from the induction of ER stress since we detected the activation of both PERK and IRE1α arms of unfolded protein response of ER stress. We found increased phosphorylation of PERK substrate eukaryotic initiation factor 2 α (eIF2α), and upregulation of the downstream effector proteins, ATF4 and CHOP. Concomitantly, increased XBP1 level, the direct effecter protein of IRE-1α, was observed. Reports suggest that eIF2α phosphorylation can increase BACE1 activity, the rate limiting enzyme in Aβ production. Here, we show that inhibiting PERK, decreased Aβ_1-42 level while direct BACE1 inhibition, reduced the mitochondrial fusion. We found increased MFN2 expression in young 5xFAD mice when Aβ plaques and neurodegeneration were absent. Thus, our study indicates that mild DNA damage leads to increased Aβ_1-42 production almost as a consequence of an initial ER stress-directed protective mitochondrial fusion in brain. We propose that an age-related subtle genomic DNA damage may trigger enhanced intraneuronal Aβ_1-42 production in an apparently healthy neuron way before the appearance of clinical symptoms in AD.

Neurons and Glia Interplay in α-Synucleinopathies

Accumulation of the neuronal presynaptic protein alpha-synuclein within proteinaceous inclusions represents the key histophathological hallmark of a spectrum of neurodegenerative disorders, referred to by the umbrella term a-synucleinopathies. Even though alpha-synuclein is expressed predominantly in neurons, pathological aggregates of the protein are also found in the glial cells of the brain. In Parkinson's disease and dementia with Lewy bodies, alpha-synuclein accumulates mainly in neurons forming the Lewy bodies and Lewy neurites, whereas in multiple system atrophy, the protein aggregates mostly in the glial cytoplasmic inclusions within oligodendrocytes. In addition, astrogliosis and microgliosis are found in the synucleinopathy brains, whereas both astrocytes and microglia internalize alpha-synuclein and contribute to the spread of pathology. The mechanisms underlying the pathological accumulation of alpha-synuclein in glial cells that under physiological conditions express low to non-detectable levels of the protein are an area of intense research. Undoubtedly, the presence of aggregated alpha-synuclein can disrupt glial function in general and can contribute to neurodegeneration through numerous pathways. Herein, we summarize the current knowledge on the role of alpha-synuclein in both neurons and glia, highlighting the contribution of the neuron-glia connectome in the disease initiation and progression, which may represent potential therapeutic target for a-synucleinopathies.

α-Synuclein and astrocytes: tracing the pathways from homeostasis to neurodegeneration in Lewy body disease

α-Synuclein is a soluble protein that is present in abundance in the brain, though its normal function in the healthy brain is poorly defined. Intraneuronal inclusions of α-synuclein, commonly referred to as Lewy pathology, are pathological hallmarks of a spectrum of neurodegenerative disorders referred to as α-synucleinopathies. Though α-synuclein is expressed predominantly in neurons, α-synuclein aggregates in astrocytes are a common feature in these neurodegenerative diseases. How and why α-synuclein ends up in the astrocytes and the consequences of this dysfunctional proteostasis in immune cells is a major area of research that can have far-reaching implications for future immunobiotherapies in α-synucleinopathies. Accumulation of aggregated α-synuclein can disrupt astrocyte function in general and, more importantly, can contribute to neurodegeneration in α-synucleinopathies through various pathways. Here, we summarize our current knowledge on how astrocytic α-synucleinopathy affects CNS function in health and disease and propose a model of neuroglial connectome altered by α-synuclein proteostasis that might be amenable to immune-based therapies.

Dysregulated Lipid Metabolism and Its Role in α-Synucleinopathy in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, the main pathological hallmark of which is the accumulation of α-synuclein (α-syn) and the formation of filamentous aggregates called Lewy bodies in the brainstem, limbic system, and cortical areas. Lipidomics is a newly emerging field which can provide fresh insights and new answers that will enhance our capacity for early diagnosis, tracking disease progression, predicting critical endpoints, and identifying risk in pre-symptomatic persons. In recent years, lipids have been implicated in many aspects of PD pathology. Biophysical and lipidomic studies have demonstrated that α-syn binds preferentially not only to specific lipid families but also to specific molecular species and that these lipid-protein complexes enhance its interaction with synaptic membranes, influence its oligomerization and aggregation, and interfere with the catalytic activity of cytoplasmic lipid enzymes and lysosomal lipases, thereby affecting lipid metabolism. The genetic link between aberrant lipid metabolism and PD is even more direct, with mutations in GBA and SMPD1 enhancing PD risk in humans and loss of GALC function increasing α-syn aggregation and accumulation in experimental murine models. Moreover, a number of lipidomic studies have reported PD-specific lipid alterations in both patient brains and plasma, including alterations in the lipid composition of lipid rafts in the frontal cortex. A further aspect of lipid dysregulation promoting PD pathogenesis is oxidative stress and inflammation, with proinflammatory lipid mediators such as platelet activating factors (PAFs) playing key roles in arbitrating the progressive neurodegeneration seen in PD linked to α-syn intracellular trafficking. Lastly, there are a number of genetic risk factors of PD which are involved in normal lipid metabolism and function. Genes such as PLA2G6 and SCARB2, which are involved in glycerophospholipid and sphingolipid metabolism either directly or indirectly are associated with risk of PD. This review seeks to describe these facets of metabolic lipid dysregulation as they relate to PD pathology and potential pathomechanisms involved in disease progression, while highlighting incongruous findings and gaps in knowledge that necessitate further research.

Non-bonding interactions and non-covalent delocalization effects play a critical role in the relative stability of group 12 complexes arising from interaction of diethanoldithiocarbamate with the cations of transition metals Zn(II), Cd(II), and Hg(II): a theoretical study

The chelating properties of diethanoldithiocarbamate (DEDC) and π-electron flow from the nitrogen atom to the sulfur atom via a plane-delocalized π-orbital system (quasi ring) was studied using a density functional theory method. The molecular structure of DEDC and its complexes with Zn(II), Cd(II), and Hg(II) were also considered. First, the geometries of this ligand and DEDC-Zn(II), DEDC-Cd(II), and DEDC-Hg(II) were optimized, and the formation energies of these complexes were then calculated based on the electronic energy, or sum of electronic energies, with the zero point energy of each species. Formation energies indicated the DEDC-Zn(II) complex as the most stable complex, and DEDC-Cd(II) as the least stable. Structural data showed that the N1-C2 π-bond was localized in the complexes rather than the ligand, and a delocalized π-bond over S7-C2-S8 was also present. The stability of DEDC-Zn(II), DEDC-Cd(II), and DEDC-Hg(II) complexes increased in the presence of the non-specific effects of the solvent (PCM model), and their relative stability did not change. There was π-electron flow or resonance along N1-C2-S7 and along S7-C2-S8 in the ligand. The π-electron flow or resonance along N1-C2-S7 was abolished when the metal interacted with sulfur atoms. Energy belonging to van der Waals interactions and non-covalent delocalization effects between the metal and sulfur atoms of the ligand was calculated for each complex. The results of nucleus-independent chemical shift (NICS) indicated a decreasing trend as Zn(II) < Cd(II) < Hg(II) for the aromaticity of the quasi-rings. Finally, by ignoring van der Waals interactions and non-covalent delocalization effects between the metal and sulfur atoms of the ligand, the relative stability of the complexes was changed as follows:[Formula: see text] Graphical Abstract Huge electronic cloud localized on Hg(II) in the Hg(II)-DEDC complex.

Overexpression of alpha-synuclein at non-toxic levels increases dopaminergic cell death induced by copper exposure via modulation of protein degradation pathways

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson's disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of wild type (WT) or mutant A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic and yeast cells in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.

Uptake of silica nanoparticles: neurotoxicity and Alzheimer-like pathology in human SK-N-SH and mouse neuro2a neuroblastoma cells

Growing concern has been raised over the potential adverse effects of engineered nanoparticles on human health due to their increasing use in commercial and medical applications. Silica nanoparticles (SiNPs) are one of the most widely used nanoparticles in industry and have been formulated for cellular and non-viral gene delivery in the central nerve system. However, the potential neurotoxicity of SiNPs remains largely unclear. In this study, we investigated the cellular uptake of SiNPs in human SK-N-SH and mouse neuro2a (N2a) neuroblastoma cells treated with 10.0 μg/ml of 15-nm SiNPs for 24 h by transmission electron microscopy. We found that SiNPs were mainly localized in the cytoplasm of the treated cells. The treatment of SiNPs at various concentrations impaired the morphology of SK-N-SH and N2a cells, characterized by increased number of round cells, diminishing of dendrite-like processes and decreased cell density. SiNPs significantly decreased the cell viability, induced cellular apoptosis, and elevated the levels of intracellular reactive oxygen species (ROS) in a dose-dependent manner in both cell lines. Additionally, increased deposit of intracellular β-amyloid 1-42 (Aβ(1-42)) and enhanced phosphorylation of tau at Ser262 and Ser396, two specific pathological hallmarks of Alzheimer's disease (AD), were observed in both cell lines with SiNPs treatment. Concomitantly, the expression of amyloid precursor protein (APP) was up-regulated, while amyloid-β-degrading enzyme neprilysin was down-regulated in SiNP-treated cells. Finally, activity-dependent phosphorylation of glycogen syntheses kinase (GSK)-3β at Ser9 (inactive form) was significantly decreased in SiNP-treated SK-N-SH cells. Taken together, these data demonstrated that exposure to SiNPs induced neurotoxicity and pathological signs of AD. The pre-Alzheimer-like pathology induced by SiNPs might result from the dys-regulated expression of APP/neprilysin and activation of GSK-3β. This is the first study with direct evidence indicating that in addition to neurotoxicity induced by SiNPs, the application of SiNPs might increase the risk of developing AD.

Mercury induced the Accumulation of Amyloid Beta (Aβ) in PC12 Cells: The Role of Production and Degradation of Aβ

Extracellular accumulation of amyloid beta protein (Aβ) plays a central role in Alzheimer’s disease (AD). Some metals, such as copper, lead, and aluminum can affect the Aβ accumulation in the brain. However, the effect of mercury on Aβ accumulation in the brain is not clear. Thus, this study was proposed to estimate whether mercury concentration affects Aβ accumulation in PC12 cells. We treated 10, 100, and 1000 nM HgCl₂ (Hg) or CH₃HgCl₂ (MeHg) for 48 hr in PC12 cells. After treatment, Aβ₄₀ in culture medium increased in a dose- and time-dependent manner. Hg and MeHg increased amyloid precursor protein (APP), which is related to Aβ production. Neprilysin (NEP) levels in PC12 cells were decreased by Hg and MeHg treatment. These results suggested that Hg induced Aβ accumulation through APP overproduction and reduction of NEP.

Exposure of rat hippocampal astrocytes to Ziram increases oxidative stress

Pesticides have been shown in several studies to be the leading candidates of environmental toxins and may contribute to the pathogenesis of several neurodegenerative diseases. Ziram (zinc-bis(dimethyldithiocarbamate)) is an agricultural dithiocarbamate fungicide that is used to treat a variety of plant diseases. In spite of their generally acknowledged low toxicity, dithiocarbamates are known to cause a wide range of neurobehavioral effects as well as neuropathological changes in the brain. Astrocytes play a key role in normal brain physiology and in the pathology of the nervous system. This investigation studied the effects of 1.0 µM Ziram on rat hippocampal astrocytes. The thiobarbituric acid reactive substance assay performed showed a significant increase in malondialdehyde, a product of lipid peroxidation, in the Ziram-treated cells. Biochemical analysis also revealed a significant increase in the induction of 70 kDa heat shock and heme oxygenase 1 stress proteins. In addition, an increase of glutathione peroxidase (GPx) and a significant increase in oxidized glutathione (GSSG) were observed in the Ziram-treated cells. The ratio GSH to GSSG calculated from the treated cells was also decreased. Light and transmission electron microscopy supported the biochemical findings in Ziram-treated astrocytes. This data suggest that the cytotoxic effects observed with Ziram treatments may be related to the increase of oxidative stress.

Melatonin protects against amyloid-β-induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid-β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ-induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1-42 or Aβ31-35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long-term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1-42 or Aβ31-35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1-42- or Aβ31-35-induced impairments in LTP induction. Intrahippocampal injection of Aβ31-35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD.

Impact of ω-3 fatty acids in Parkinson's disease

Current epidemiological, preclinical and clinical data suggest that omega-3 polyunsaturated fatty acids (n-3 PUFAs) may constitute therapeutic strategy for several disorders of the central nervous system, including Parkinson's disease (PD). PD is a neurodegenerative disorder primarily characterized by motor symptoms but which also includes several other pathological features such as autonomic system failures, mood disorders, and cognitive deficits. Current pharmacological options for the disease are limited to symptom management and their long-term use leads to important side effects. In this review, we discuss the evidence for the effects of n-3 PUFAs in PD both from an epidemiological perspective as well as in light of data gathered on various pathological features of the disease. Effects of n-3 PUFAs on the dopaminergic system, α-synucleinopathy, their possible mechanisms of action as well as their therapeutic potential for PD patients are also reviewed. n-3 PUFAs are inexpensive, readily transferable to the clinical setting and their use could represent a neuroprotective strategy or a disease-modifying option to delay the appearance of symptoms. It could also be beneficial as a symptomatologic treatment or serve as an add-on therapy to current pharmacological approaches. Review of the current literature as well as the undertaking of future clinical trials will shed light on these possibilities.

Lack of alpha-synuclein modulates microglial phenotype in vitro

Alpha (α)-synuclein neuronal effects are continually being defined although its role in regulating glial phenotypes remains unclear. An ability to regulate microglial activation was investigated using primary cultures from wild type and α-synuclein deficient mice (Snca-/-). Snca-/- microglia demonstrated increased secretion of the cytokine tumor necrosis factor-alpha (TNF-α), impaired phagocytic ability, elevated prostaglandin levels, and increased protein levels of key enzymes in lipid-mediated signaling events, cytosolic phospholipase (cPLA(2)), cyclooxygenase-2 (Cox-2) and phospholipase D2 (PLD2) when compared to wild type cells. Increased cytokine secretion and cPLA(2) and Cox-2 levels in Snca-/- microglia were partially attenuated by inhibiting PLD-dependent signaling with n-butanol treatment.

Oxidative stress mediates the pathogenic effect of different Alzheimer's disease risk factors

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting the elderly population. Mechanistically, the major cause of the disease bases on the altered processing of the amyloid-β (Aβ) precursor protein (APP), resulting in the accumulation and aggregation of neurotoxic forms of Aβ. Aβ derives from the sequential proteolytic cleavage of the β- and γ-secretases on APP. The causes of Aβ accumulation in the common sporadic form of AD are not completely known, but they are likely to include oxidative stress (OS). OS and Aβ are linked to each other since Aβ aggregation induces OS in vivo and in vitro, and oxidant agents increase the production of Aβ. Moreover, OS produces several effects that may contribute to synaptic function and cell death in AD. We and others have shown that the expression and activity of β-secretase (named BACE1; β-site APP cleaving enzyme) is increased by oxidant agents and by lipid peroxidation product 4-hydroxynonenal and that there is a significant correlation between BACE1 activity and oxidative markers in sporadic AD. OS results from several cellular insults such as aging, hyperglycemia, hypoxic insults that are all well known risk factors for AD development. Thus, our data strengthen the hypothesis that OS is a basic common pathway of Aβ accumulation, common to different AD risk factors.

Up-regulation of cytosolic phospholipase A2α expression by N,N-diethyldithiocarbamate in PC12 cells; involvement of reactive oxygen species and nitric oxide

Disulfiram (an alcohol-aversive drug) and related compounds are known to provoke several side effects involving behavioral and neurological complications. N,N-diethyldithiocarbamate (DDC) is considered as one of the main toxic species of disulfiram and acts as an inhibitor of superoxide dismutase. Since arachidonic acid (AA) formation is regulated by reactive oxygen species (ROS) and related to toxicity in neuronal cells, we investigated the effects of DDC on AA release and expression of the alpha type of cytosolic phospholipase A(2) (cPLA(2)alpha) in PC12 cells. Treatment with 80-120 microM DDC that causes a moderate increase in ROS levels without cell toxicity stimulated cPLA(2)alpha mRNA and its protein expression. The expression was mediated by extracellular-signal-regulated kinase (ERK1/2), one of the mitogen-activated protein kinases. Treatment with N(G) nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase, 1 mM) and oxy-hemoglobin (a scavenger of nitric oxide, 2 mg/mL) abolished the DDC-induced responses (ERK1/2 phosphorylation and cPLA(2)alpha expression). We also showed DDC-induced up-regulation of the mRNA expression of lipocortin 1, an inhibitor of PLA(2). Furthermore, DDC treatment of the cells enhanced Ca(2+)-ionophore-induced AA release in 30 min, although the effect was limited. Changes in AA metabolism in DDC-treated cells may have a potential role in mediating neurotoxic actions of disulfiram. In this study, we show the first to demonstrate the up-regulation of cPLA(2)alpha expression by DDC treatment in neuronal cells.

Acyl-CoA synthetase activity links wild-type but not mutant alpha-synuclein to brain arachidonate metabolism

Because alpha-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that the loss of alpha-synuclein had on brain arachidonic acid (20:4n-6) metabolism in vivo using Snca-/- mice. We measured [1-(14)C]20:4n-6 incorporation and turnover kinetics in brain phospholipids using an established steady-state kinetic model. Liver was used as a negative control, and no changes were observed between groups. In Snca-/- brains, there was a marked reduction in 20:4n-6-CoA mass and in microsomal acyl-CoA synthetase (Acsl) activity toward 20:4n-6. Microsomal Acsl activity was completely restored after the addition of exogenous wild-type mouse or human alpha-synuclein, but not by A30P, E46K, and A53T forms of alpha-synuclein. Acsl and acyl-CoA hydrolase expression was not different between groups. The incorporation and turnover of 20:4n-6 into brain phospholipid pools were markedly reduced. The dilution coefficient lambda, which indicates 20:4n-6 recycling between the acyl-CoA pool and brain phospholipids, was increased 3.3-fold, indicating more 20:4n-6 was entering the 20:4n-6-CoA pool from the plasma relative to that being recycled from the phospholipids. This is consistent with the reduction in Acsl activity observed in the Snca-/- mice. Using titration microcalorimetry, we determined that alpha-synuclein bound free 20:4n-6 (Kd = 3.7 microM) but did not bind 20:4n-6-CoA. These data suggest alpha-synuclein is involved in substrate presentation to Acsl rather than product removal. In summary, our data demonstrate that alpha-synuclein has a major role in brain 20:4n-6 metabolism through its modulation of endoplasmic reticulum-localized acyl-CoA synthetase activity, although mutant forms of alpha-synuclein fail to restore this activity.

Possible implication of ciliary neurotrophic factor (CNTF) and beta-synuclein in the ammonia effect on cultured rat astroglial cells: a study using DNA and protein microarrays

Astrocytes are considered the key cell in hepatic encephalopathy; although their precise role in the disease has not yet been determined, exposure to ammonia appears to have an important pathogenic effect. We exposed confluent cultures of rat astroglial cells to ammonia (5mM NH(4)Cl) for 1, 3, 5 and 7 days, and determined astroglial levels of actin, glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), GLAST glutamate transporter, 25kDa heat-shock protein (HSP25), HSP60 and HSP70 by Western blot; the glutamine content in culture medium was measured by mass spectrometry. Significant increases were observed for GS, HSP60 and glutamine, and significant reductions for actin and GFAP. Astrocytes exposed to ammonia for 4 days were used to analyze the effect of ammonia in protein and DNA microarrays. After protein microarray data filtration by signal intensity, x-fold change and z-score, 11 proteins were selected, among which the significant increase in beta-synuclein was confirmed by Western blot. DNA microarray data filtration by intensity signal, x-fold change and p-value selected almost 600 genes. The significant increase in alpha-synuclein mRNA was confirmed by quantitative RT-PCR, but no change was observed in alpha-synuclein protein levels. A notable decrease in ciliary neurotrophic factor (CNTF) was demonstrated by Western blot after ammonia treatment, concurring with the reduction in CNTF mRNA observed in DNA microarrays. We discuss the possibility of a pathogenic role for CNTF and a protective role for beta-synuclein in experimental hyperammonemia. This study demonstrates the use of microarrays as tools to ascertain the possible implication of previously unidentified proteins in the pathogenesis of hepatic encephalopathy.

Fatty acid incorporation is decreased in astrocytes cultured from alpha-synuclein gene-ablated mice

Because alpha-synuclein may function as a fatty acid binding protein, we measured fatty acid incorporation into astrocytes isolated from wild-type and alpha-synuclein gene-ablated mice. alpha-Synuclein deficiency decreased palmitic acid (16:0) incorporation 31% and arachidonic acid [20:4 (n-6)] incorporation 39%, whereas 22:6 (n-3) incorporation was unaffected. In neutral lipids, fatty acid targeting of 20:4 (n-6) and 22:6 (n-3) (docosahexaenoic acid) to the neutral lipid fraction was increased 1.7-fold and 1.6-fold, respectively, with an increase in each of the major neutral lipids. This was consistent with a 3.4- to 3.8-fold increase in cholesteryl ester and triacylglycerol mass. In the phospholipid fraction, alpha-synuclein deficiency decreased 16:0 esterification 39% and 20:4 (n-6) esterification 43% and decreased the distribution of these fatty acids, including 22:6 (n-3), into this lipid pool. alpha-Synuclein gene-ablation significantly decreased the trafficking of these fatty acids to phosphatidylinositol. This observation is consistent with changes in phospholipid fatty acid composition in the alpha-synuclein-deficient astrocytes, including decreased 22:6 (n-3) content in the four major phospholipid classes. In summary, these studies demonstrate that alpha-synuclein deficiency significantly disrupted astrocyte fatty acid uptake and trafficking, with a marked increase in fatty acid trafficking to cholesteryl esters and triacylglycerols and decreased trafficking to phospholipids, including phosphatidylinositol.

Alpha-synuclein gene deletion decreases brain palmitate uptake and alters the palmitate metabolism in the absence of alpha-synuclein palmitate binding

Alpha-synuclein is an abundant protein in the central nervous system that is associated with a number of neurodegenerative disorders, including Parkinson's disease. Its physiological function is poorly understood, although recently it was proposed to function as a fatty acid binding protein. To better define a role for alpha-synuclein in brain fatty acid uptake and metabolism, we infused awake, wild-type, or alpha-synuclein gene-ablated mice with [1-(14)C]palmitic acid (16:0) and assessed fatty acid uptake and turnover kinetics in brain phospholipids. Alpha-synuclein deficiency decreased brain 16:0 uptake 35% and reduced its targeting to the organic fraction. The incorporation coefficient for 16:0 entering the brain acyl-CoA pool was significantly decreased 36% in alpha-synuclein gene-ablated mice. Because incorporation coefficients alone are not predictive of fatty acid turnover in individual phospholipid classes, we calculated kinetic values for 16:0 entering brain phospholipid pools. Alpha-synuclein deficiency decreased the incorporation rate and fractional turnover of 16:0 in a number of phospholipid classes, but also increased the incorporation rate and fractional turnover of 16:0 in the choline glycerophospholipids. No differences in incorporation rate or turnover were observed in liver phospholipids, confirming that these changes in lipid metabolism were brain specific. Using titration microcalorimetry, we observed no binding of 16:0 or oleic acid to alpha-synuclein in vitro. Thus, alpha-synuclein has effects on 16:0 uptake and metabolism similar to those of an FABP, but unlike FABP, it does not directly bind 16:0; hence, the mechanism underlying these effects is different from that of a classical FABP.

Metals and amyloid-beta in Alzheimer's disease

Mounting evidence is demonstrating roles for the amyloid precursor protein (APP) and its proteolytic product Abeta in metal homeostasis. Furthermore, aberrant metal homeostasis is observed in patients with Alzheimer's disease (AD), and this may contribute to AD pathogenesis, by enhancing the formation of reactive oxygen species and toxic Abeta oligomers and facilitating the formation of the hallmark amyloid deposits in AD brain. Indeed, zinc released from synaptic activity has been shown to induce parenchymal and cerebrovascular amyloid in transgenic mice. On the other hand, abnormal metabolism of APP and Abeta may impair brain metal homeostasis as part of the AD pathogenic process. Abeta and APP expression have both been shown to decrease brain copper (Cu) levels, whereas increasing brain Cu availability results in decreased levels of Abeta and amyloid plaque formation in transgenic mice. Lowering Cu concentrations can downregulate the transcription of APP, strengthening the hypothesis that APP and Abeta form part of the Cu homeostatic machinery in the brain. This is a complex pathway, and it appears that when the sensitive metal balance in the brain is sufficiently disrupted, it can lead to the self-perpetuating pathogenesis of AD. Clinical trials are currently studying agents that can remedy abnormal Abeta-metal interactions.

Oxidative stress mediates drug-induced hepatotoxicity in rats: a possible role of DNA fragmentation

Sodium diethyldithiocarbamate, diclofenac and ketoconazol are three important chemotherapeutic agents that are commonly associated with hepatotoxicity. This study was undertaken to provide a better understanding of the mechanism through which these drugs induce hepatotoxicity. Some of the possible mechanisms underlying such modulation were investigated. The hepatotoxic activity of sodium diethyldithiocarbamate (800 mg kg(-1)); diclofenac (200 mg kg(-1)) and ketoconazol (100 mg kg(-1)) were investigated in vivo through the assessment of liver functions, lipid peroxidation and histopathological examination. It was found that all drugs have induced severe hepatic damage as evidenced by the elevation serum aminotransferase activities and confirmed by histological changes of liver. In addition, the drug-induced hepatotoxicity was also associated with massive liver DNA fragmentation and an increase in lipid peroxidation. These results strongly suggest a positive correlation between hepatotoxicity and DNA fragmentation. Moreover, this study also implicates calcium as a potential mediator of the drug-induced oxidative stress associated with hepatotoxicity.