The protective effect of astrocyte-derived 14,15-epoxyeicosatrienoic acid on hydrogen peroxide-induced cell injury in astrocyte-dopaminergic neuronal cell line co-culture

Aflatoxin B1 Increases Soluble Epoxide Hydrolase in the Brain and Induces Neuroinflammation and Dopaminergic Neurotoxicity

Parkinson's disease (PD) is an increasingly common neurodegenerative movement disorder with contributing factors that are still largely unexplored and currently no effective intervention strategy. Epidemiological and pre-clinical studies support the close association between environmental toxicant exposure and PD incidence. Aflatoxin B1 (AFB1), a hazardous mycotoxin commonly present in food and environment, is alarmingly high in many areas of the world. Previous evidence suggests that chronic exposure to AFB1 leads to neurological disorders as well as cancer. However, whether and how aflatoxin B1 contributes to the pathogenesis of PD is poorly understood. Here, oral exposure to AFB1 is shown to induce neuroinflammation, trigger the α-synuclein pathology, and cause dopaminergic neurotoxicity. This was accompanied by the increased expression and enzymatic activity of soluble epoxide hydrolase (sEH) in the mouse brain. Importantly, genetic deletion or pharmacological inhibition of sEH alleviated the AFB1-induced neuroinflammation by reducing microglia activation and suppressing pro-inflammatory factors in the brain. Furthermore, blocking the action of sEH attenuated dopaminergic neuron dysfunction caused by AFB1 in vivo and in vitro. Together, our findings suggest a contributing role of AFB1 to PD etiology and highlight sEH as a potential pharmacological target for alleviating PD-related neuronal disorders caused by AFB1 exposure.

Epoxyeicosatrienoic acids and soluble epoxide hydrolase in physiology and diseases of the central nervous system

Epoxyeicosatrienoic acids (EETs) are fatty acid signaling molecules synthesized by cytochrome P450 epoxygenases from arachidonic acid. The biological activity of EETs is terminated when being metabolized by soluble epoxide hydrolase (sEH), a process that serves as a key regulator of tissue EETs levels. EETs act through several signaling pathways to mediate various beneficial effects, including anti-inflammation, anti-apoptosis, and anti-oxidation with relieve of endoplasmic reticulum stress, thereby sEH has become a potential therapeutic target in cardiovascular disease and cancer therapy. Enzymes for EET biosynthesis and metabolism are both widely detected in both neuron and glial cells in the central nervous system (CNS). Recent studies discovered that astrocyte-derived EETs not only mediate neurovascular coupling and neuronal excitability by maintaining glutamate homeostasis but also glia-dependent neuroprotection. Genetic ablation as well as pharmacologic inhibition of sEH has greatly helped to elucidate the physiologic actions of EETs, and maintaining or elevating brain EETs level has been demonstrated beneficial effects in CNS disease models. Here, we review the literature regarding the studies on the bioactivity of EETs and their metabolic enzyme sEH with special attention paid to their action mechanisms in the CNS, including their modulation of neuronal activity, attenuation of neuroinflammation, regulation of cerebral blood flow, and improvement of neuronal and glial cells survival. We further reviewed the recent advance on the potential application of sEH inhibition for treating cerebrovascular disease, epilepsy, and pain disorder.

Soluble Epoxide Hydrolase Inhibition to Face Neuroinflammation in Parkinson's Disease: A New Therapeutic Strategy

Neuroinflammation is a crucial process associated with the pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Several pieces of evidence suggest an active role of lipid mediators, especially epoxy-fatty acids (EpFAs), in the genesis and control of neuroinflammation; 14,15-epoxyeicosatrienoic acid (14,15-EET) is one of the most commonly studied EpFAs, with anti-inflammatory properties. Soluble epoxide hydrolase (sEH) is implicated in the hydrolysis of 14,15-EET to its corresponding diol, which lacks anti-inflammatory properties. Preventing EET degradation thus increases its concentration in the brain through sEH inhibition, which represents a novel pharmacological approach to foster the reduction of neuroinflammation and by end neurodegeneration. Recently, it has been shown that sEH levels increase in brains of PD patients. Moreover, the pharmacological inhibition of the hydrolase domain of the enzyme or the use of sEH knockout mice reduced the deleterious effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. This paper overviews the knowledge of sEH and EETs in PD and the importance of blocking its hydrolytic activity, degrading EETs in PD physiopathology. We focus on imperative neuroinflammation participation in the neurodegenerative process in PD and the putative therapeutic role for sEH inhibitors. In this review, we also describe highlights in the general knowledge of the role of sEH in the central nervous system (CNS) and its participation in neurodegeneration. We conclude that sEH is one of the most promising therapeutic strategies for PD and other neurodegenerative diseases with chronic inflammation process, providing new insights into the crucial role of sEH in PD pathophysiology as well as a singular opportunity for drug development.

Oxylipin Profiles as Functional Characteristics of Acute Inflammatory Responses in Astrocytes Pre-Treated with IL-4, IL-10, or LPS

Functional phenotypes, which cells can acquire depending on the microenvironment, are currently the focus of investigations into new anti-inflammatory therapeutic approaches. Glial cells, microglia, and astrocytes are major participants in neuroinflammation, but their roles differ, as microglia are cells of mesodermal origin, while astrocytes are cells of ectodermal origin. The inflammatory phenotype of cells can be modulated by ω-6- and ω-3-polyunsaturated fatty acid-derived oxylipins, although data on changes in oxylipin profiles in different cell adaptations to pro- and anti-inflammatory stimuli are scarce. Our study aimed to compare UPLC-MS/MS-measured oxylipin profiles in various rat astrocyte adaptation states. We used cells treated for 24 h with lipopolysaccharide (LPS) for classical pro-inflammatory adaptation and with interleukin 4 (IL-4) or 10 (IL-10) for alternative anti-inflammatory adaptation, with the resulting phenotypes characterized by quantitative real-time PCR (RT-PCR). We also tested long-term, low-concentration LPS treatment (endotoxin treatment) as a model of astrocyte adaptations. The functional response of astrocytes was estimated by acute (4 h) LPS-induced cell reactivity, measured by gene expression markers and oxylipin synthesis. We discovered that, as well as gene markers, oxylipin profiles can serve as markers of pro- (A1-like) or anti-inflammatory (A2-like) adaptations. We observed predominant involvement of ω-6 polyunsaturated fatty acid (PUFA) and the cyclooxygenase branch for classical (LPS) pro-inflammatory adaptations and ω-3 PUFA and the lipoxygenase branch for alternative (IL-4) anti-inflammatory adaptations. Treatment with IL-4, but not IL-10, primes the ability of astrocytes to activate the innate immunity signaling pathways in response to LPS. Endotoxin-treated astrocytes provide an alternative anti-inflammatory adaptation, which makes cells less sensitive to acute LPS stimulation than the IL-4 induced adaptation. Taken together, the data reveal that oxylipin profiles associate with different states of polarization to generate a pro-inflammatory or anti-inflammatory phenotype. This association manifests itself both in native cells and in their responses to a pro-inflammatory stimulus.

1-Trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) Urea, a Selective and Potent Dual Inhibitor of Soluble Epoxide Hydrolase and p38 Kinase Intervenes in Alzheimer's Signaling in Human Nerve Cells

Alzheimer's disease (AD) is the most common neurodegenerative disorder. Neuroinflammation is a prevalent pathogenic stress leading to neuronal death in AD. Targeting neuroinflammation to keep neurons alive is an attractive strategy for AD therapy. 1-Trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU) is a potent inhibitor of soluble epoxide hydrolase (sEH) and can enter into the brain. It has good efficacy on a wide range of chronic inflammatory diseases in preclinical animal models. However, the anti-neuroinflammatory effects and molecular mechanisms of TPPU for potential AD interventions remain elusive. With an aim to develop multitarget therapeutics for neurodegenerative diseases, we screened TPPU against sEH from different mammalian species and a broad panel of human kinases in vitro for potential new targets relevant to neuroinflammation in AD. TPPU inhibits both human sEH and p38β kinase, two key regulators of inflammation, with nanomolar potencies and distinct selectivity. To further elucidate the molecular mechanisms, differentiated SH-SY5Y human neuroblastoma cells were used as an AD cell model, and we investigated the neuroprotection of TPPU against amyloid oligomers. We found that TPPU effectively prevents neuronal death by mitigating amyloid neurotoxicity, tau hyperphosphorylation, and mitochondrial dysfunction, promoting neurite outgrowth and suppressing activation and nuclear translocation of NF-κB for inflammatory responses in human nerve cells. The results indicate that TPPU is a potent and selective dual inhibitor of sEH and p38β kinase, showing a synergistic action in multiple AD signaling pathways. Our study sheds light upon TPPU and other sEH/p38β dual inhibitors for potential pharmacological interventions in AD.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.

Molecular mechanisms involved in the protective actions of Selective Estrogen Receptor Modulators in brain cells

Synthetic selective modulators of the estrogen receptors (SERMs) have shown to protect neurons and glial cells against toxic insults. Among the most relevant beneficial effects attributed to these compounds are the regulation of inflammation, attenuation of astrogliosis and microglial activation, prevention of excitotoxicity and as a consequence the reduction of neuronal cell death. Under pathological conditions, the mechanism of action of the SERMs involves the activation of estrogen receptors (ERs) and G protein-coupled receptor for estrogens (GRP30). These receptors trigger neuroprotective responses such as increasing the expression of antioxidants and the activation of kinase-mediated survival signaling pathways. Despite the advances in the knowledge of the pathways activated by the SERMs, their mechanism of action is still not entirely clear, and there are several controversies. In this review, we focused on the molecular pathways activated by SERMs in brain cells, mainly astrocytes, as a response to treatment with raloxifene and tamoxifen.

Soluble epoxide hydrolase inhibitor, APAU, protects dopaminergic neurons against rotenone induced neurotoxicity: Implications for Parkinson's disease

Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid, play a crucial role in cytoprotection by attenuating oxidative stress, inflammation and apoptosis. EETs are rapidly metabolised in vivo by the soluble epoxide hydrolase (sEH). Increasing the half life of EETs by inhibiting the sEH enzyme is a novel strategy for neuroprotection. In the present study, sEH inhibitors APAU was screened in silico and further evaluated for their antiparkinson activity against rotenone (ROT) induced neurodegeneration in N27 dopaminergic cell line and Drosophila melanogaster model of Parkinson disease (PD). In the in vitro study cell viability (MTT and LDH release assay), oxidative stress parameters (total intracellular ROS, hydroperoxides, protein oxidation, lipid peroxidation, superoxide dismutase, catalase, glutathione peroxidise, glutathione reductase, glutathione, total antioxidant status, mitochondrial complex-1activity and mitochondrial membrane potential), inflammatory markers (IL-6, COX-1 and COX-2), and apoptotic markers (JNK, phospho-JNK, c-jun, phospho-c-jun, pro and active caspase-3) were assessed to study the neuroprotective effects. In vivo activity of APAU was assessed in Drosophila melanogaster by measuring survival rate, negative geotaxis, oxidative stress parameters (total intracellular ROS, hydroperoxides, glutathione levels) were measured. Dopamine and its metabolites were estimated by LC-MS/MS analysis. In the in silico study the molecule, APAU showed good binding interaction at the active site of sEH (PDB: 1VJ5). In the in vitro study, APAU significantly attenuated ROT induced changes in oxidative, pro-inflammatory and apoptotic parameters. In the in vivo study, APAU significantly attenuates ROT induced changes in survival rate, negative geotaxis, oxidative stress, dopamine and its metabolites levels (p < 0.05). Our study, therefore, concludes that the molecule APAU, has significant neuroprotection benefits against rotenone induced Parkinsonism.

Stem cell-secreted 14,15- epoxyeicosatrienoic acid rescues cholesterol homeostasis and autophagic flux in Niemann-Pick-type C disease

We previously demonstrated that the direct transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) into the dentate gyrus ameliorated the neurological symptoms of Niemann–Pick type C1 (NPC1)-mutant mice. However, the clinical presentation of NPC1-mutant mice was not fully understood with a molecular mechanism. Here, we found 14,15-epoxyeicosatrienoic acid (14,15-EET), a cytochrome P450 (CYP) metabolite, from hUCB-MSCs and the cerebella of NPC1-mutant mice and investigated the functional consequence of this metabolite. Our screening of the CYP2J family indicated a dysregulation in the CYP system in a cerebellar-specific manner. Moreover, in Purkinje cells, CYP2J6 showed an elevated expression level compared to that of astrocytes, granule cells, and microglia. In this regard, we found that one CYP metabolite, 14,15-EET, acts as a key mediator in ameliorating cholesterol accumulation. In confirming this hypothesis, 14,15-EET treatment reduced the accumulation of cholesterol in human NPC1 patient-derived fibroblasts in vitro by suppressing cholesterol synthesis and ameliorating the impaired autophagic flux. We show that the reduced activity within the CYP system in the cerebellum could cause the neurological symptoms of NPC1 patients, as 14,15-EET treatment significantly rescued cholesterol accumulation and impaired autophagy. We also provide evidence that the intranasal administration of hUCB-MSCs is a highly promising alternative to traumatic surgical transplantation for NPC1 patients.

An acid secreted by stem cells can reduce the excess cholesterol caused by a genetic metabolic disorder. Niemann–Pick type C disease is a rare, inherited condition that causes defective muscular development and progressive neurological degeneration. A key disease mechanism is the excessive accumulation of cholesterol within cells. Kyung-Sun Kang at Seoul National University, South Korea, and co-workers have demonstrated that a metabolite molecule called 14,15-epoxyeicosatrienoic acid (14,15-EET) derived from stem cells from human umbilical cord blood significantly reduced cholesterol in Neimann-Pick Type C mouse models and human cell samples. The team administered the stem cell therapy non-invasively via the nose, and observed significant improvements in motor function in the mice. Experiments in both animals and cells showed that the treatment resulted in reduced cholesterol levels and the correction of defective signalling within cells.

14,15-epoxyeicosatrienoic acid produced by cytochrome P450s enhances neurite outgrowth of PC12 and rat hippocampal neuronal cells

Polyunsaturated fatty acids, such as arachidonic acid, are accumulated in brain and induce neuronal differentiation. Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids (HETEs) by cytochrome P450s. In this study, we found that 14,15-EET and 20-HETE-enhanced NGF-induced rat pheochromocytoma PC12 cell neurite outgrowth even at the concentration of 100 nmol L-1. LC-MS analysis revealed that 14,15-EET was effectively produced from arachidonic acid by rat CYP2C11, 2C13, and 2C23, and these P450s were expressed in PC12 cells. An inhibitor of these P450s, ketoconazole, inhibited neurite outgrowth, whereas inhibition of soluble epoxide hydrolase, which hydrolyzes EETs to their corresponding diols enhanced neurite outgrowth. To determine the mechanism of neurite formation enhancement by arachidonic acid metabolites, we focused on transient receptor potential (TRP) channels expressed in PC12 cells. The TRPV4 inhibitor HC067047, but not the TRPV1 inhibitor capsazepine, inhibited the effects of 14,15-EET on neurite outgrowth of PC12. Furthermore, 14,15-EET increased the cytosolic calcium ion concentration and this increase was inhibited by HC067047. 14,15-EET also enhanced neurite outgrowth of primary cultured neuron from rat hippocampus. This study suggests that arachidonic acid metabolites produced by P450 contribute to neurite outgrowth through calcium influx.

P450 Eicosanoids and Reactive Oxygen Species Interplay in Brain Injury and Neuroprotection

Significance: Eicosanoids are endogenous lipid mediators that play important roles in brain function and disease. Acute brain injury such as that which occurs in stroke and traumatic brain injury increases the formation of eicosanoids, which, in turn, exacerbate or diminish injury. In chronic neurodegenerative diseases such as Alzheimer's disease and vascular dementia (VD), eicosanoid synthetic and metabolizing enzymes are altered, disrupting the balance between neuroprotective and neurotoxic eicosanoids. Recent Advances: Human and experimental studies have established the opposing roles of hydroxy- and epoxyeicosanoids and their potential utility as diagnostic biomarkers and therapeutic targets in neural injury. Critical Issues: A gap in knowledge remains in understanding the cellular and molecular mechanisms underlying the neurovascular actions of specific eicosanoids, such as specific isomers of epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic acids (HETEs). Future Directions: EETs and HETEs exert their actions on brain cells by targeting multiple mechanisms, which include surface G-protein coupled receptors. The identification of high-affinity receptors for EETs and HETEs and their cellular localization in the brain will be a breakthrough in our understanding of these eicosanoids as mediators of cell-cell communications and contributors to brain development, function, and disease. Antioxid. Redox Signal. 28, 987-1007.

Cytochrome P450 eicosanoids in cerebrovascular function and disease

Cytochrome P450 eicosanoids play important roles in brain function and disease through their complementary actions on cell-cell communications within the neurovascular unit (NVU) and mechanisms of brain injury. Epoxy- and hydroxyeicosanoids, respectively formed by cytochrome P450 epoxygenases and ω-hydroxylases, play opposing roles in cerebrovascular function and in pathological processes underlying neural injury, including ischemia, neuroinflammation and oxidative injury. P450 eicosanoids also contribute to cerebrovascular disease risk factors, including hypertension and diabetes. We summarize studies investigating the roles P450 eicosanoids in cerebrovascular physiology and disease to highlight the existing balance between these important lipid signaling molecules, as well as their roles in maintaining neurovascular homeostasis and in acute and chronic neurovascular and neurodegenerative disorders.

Soluble epoxide hydrolase as a therapeutic target for pain, inflammatory and neurodegenerative diseases

Eicosanoids are biologically active lipid signaling molecules derived from polyunsaturated fatty acids. Many of the actions of eicosanoid metabolites formed by cyclooxygenase and lipoxygenase enzymes have been characterized, however, the epoxy-fatty acids (EpFAs) formed by cytochrome P450 enzymes are newly described by comparison. The EpFA metabolites modulate a diverse set of physiologic functions that include inflammation and nociception among others. Regulation of EpFAs occurs primarily via release, biosynthesis and enzymatic transformation by the soluble epoxide hydrolase (sEH). Targeting sEH with small molecule inhibitors has enabled observation of the biological activity of the EpFAs in vivo in animal models, greatly contributing to the overall understanding of their role in the inflammatory response. Their role in modulating inflammation has been demonstrated in disease models including cardiovascular pathology and inflammatory pain, but extends to neuroinflammation and neuroinflammatory disease. Moreover, while EpFAs demonstrate activity against inflammatory pain, interestingly, this action extends to blocking chronic neuropathic pain as well. This review outlines the role of modulating sEH and the biological action of EpFAs in models of pain and inflammatory diseases.

Cysteinyl Leukotrienes as Potential Pharmacological Targets for Cerebral Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid mediators widely known for their actions in asthma and in allergic rhinitis. Accumulating data highlights their involvement in a broader range of inflammation-associated diseases such as cancer, atopic dermatitis, rheumatoid arthritis, and cardiovascular diseases. The reported elevated levels of CysLTs in acute and chronic brain lesions, the association between the genetic polymorphisms in the LTs biosynthesis pathways and the risk of cerebral pathological events, and the evidence from animal models link also CysLTs and brain diseases. This review will give an overview of how far research has gone into the evaluation of the role of CysLTs in the most prevalent neurodegenerative disorders (ischemia, Alzheimer's and Parkinson's diseases, multiple sclerosis/experimental autoimmune encephalomyelitis, and epilepsy) in order to understand the underlying mechanism by which they might be central in the disease progression.

Possible role of Epoxyeicosatrienoic acid in prevention of oxidative stress mediated neuroinflammation in Parkinson disorders

Parkinson's disease (PD) is a multifactorial neurodegenerative disease involving oxidative stress, neuroinflammation and apoptosis. Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites and they play a role in cytoprotection by modulating various cell signaling pathways. This cytoprotective role of EETs are well established in cerebral stroke, cardiac failure, and hypertension, and it is due to their ability to attenuate oxidative stress, endoplasmic reticulum stress, inflammation, caspase activation and apoptosis. The actions of EETs in brain closely parallel the effects which is observed in the peripheral tissues. Since many of these effects could potentially contribute to neuroprotection, EETs are, therefore, one of the potential therapeutic candidates in PD. Therefore, by increasing the half life of endogenous EETs in vivo via inhibition of sEH, its metabolizing enzyme can, therefore, constitutes an important therapeutic strategy in PD.

14,15-epoxyeicosatrienoic acid promotes production of brain derived neurotrophic factor from astrocytes and exerts neuroprotective effects during ischaemic injury

AIMS

14,15-Epoxyeicosatrienoic acid (14,15-EET) is abundantly expressed in brain and exerts protective effects against ischaemia. 14,15-EET is hydrolysed by soluble epoxide hydrolase (sEH). sEH^-/- mice show a higher level of 14,15-EET in the brain. Astrocytes play a pivotal role in neuronal survival under ischaemic conditions. However, it is unclear whether the neuroprotective effect of 14,15-EET is associated with astrocytes.

METHODS

A mouse model of focal cerebral ischaemia was induced by middle cerebral artery occlusion. Oxygen-glucose deprivation/reoxygenation (OGD/R) was performed on cultured murine astrocytes, neurons and a human cell line. Cell viabilities were measured by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay. The mRNA expressions were quantified by real-time PCR. Brain derived neurotrophic factor (BDNF) concentration was measured by ELISA. Protein expressions were quantified by Western blotting. BDNF and peroxisome proliferators-activated receptor gamma (PPAR-γ) expressions were analysed by confocal microscopy.

RESULTS

Decreased infarct volumes, elevated BDNF expression and increased numbers of BDNF/GFAP Glial Fibrillary Acidic Protein double-positive cells were observed in the ischaemic penumbra of sEH^-/- mice. The decreased infarct volumes of sEH^-/- mice were diminished by intracerebroventricular injection of a blocker of BDNF receptor. 14,15-EET increases BDNF expression and cell viability of murine astrocytes and U251 cells by BDNF-TrkB Tyrosine receptor kinase-B-extracellular signal-regulated kinase 1/2 signalling during OGD/R. 14,15-EET protects neurons from OGD/R by stimulating the production of astrocyte-derived BDNF. 14,15-EET stimulates the production of astrocyte-derived BDNF through PPAR-γ/p-cAMP-response element binding protein signal pathways.

CONCLUSIONS

Our study demonstrates the importance of 14,15-EET-mediated production of astrocyte-derived BDNF for enhancing viability of astrocytes and protecting neurons from the ischaemic injury and provides insights into the mechanism by which 14,15-EET is involved in neuroprotection.

Ascorbate protects neurons against oxidative stress: a Raman microspectroscopic study

Oxidative stress due to excessive accumulation of reactive oxygen or nitrogen species in the brain as seen in certain neurodegenerative diseases can have deleterious effects on neurons. Hydrogen peroxide, endogenously generated in neurons under normal physiological conditions, can produce an excess of hydroxyl radical via a Fenton mediated mechanism. This may induce acute oxidative injury if not scavenged or removed effectively by antioxidants. There are several biochemical assay methods to estimate oxidative injury in cells; however, they do not provide information on the biochemical changes as the cells get damaged progressively under oxidative stress. Raman microspectroscopy offers the possibility of real time monitoring of the chemical composition of live cells undergoing oxidative stress under physiological conditions. In the present study, a hippocampal neuron coculture was used to observe the acute impact of hydroxyl radicals generated by hydrogen peroxide in the presence of Fe(2+) (Fenton reaction). Raman peaks related to nucleic acids (725, 782, 1092, 1320, 1340, 1420, and 1576 cm(-1)) showed time-dependent changes over the experimental period (60 min), indicating the breakdown of the phosphodiester backbone as well as nuclear bases. Interestingly, ascorbic acid (a potent antioxidant) when cotreated with Fenton reactants showed protection of cells as inferred from the Raman spectra, presumably by scavenging hydroxyl radicals. Little or no change in the Raman spectra was observed for untreated control cells and for cells exposed to Fe(2+) only, H2O2 only, and ascorbate only. A live-dead assay study also supported the current observations. Hence, Raman microspectroscopy has the potential to be an excellent noninvasive tool for early detection of oxidative stress that is seen in neurodegenerative diseases.

A multimodal disease modifying approach to treat neuropathic pain--inhibition of soluble epoxide hydrolase (sEH)

Both neuronal and non-neuronal mechanisms have been proposed to contribute to neuropathic pain (NP). All currently approved treatments for NP modulate neuronal targets and provide only symptomatic relief. Here we review evidence that inhibition of soluble epoxide hydrolase (sEH), the enzyme that degrades epoxyeicosatrienoic acids (EETs), has potential to be a multimodal, disease modifying approach to treat NP: (1) EET actions involve both endogenous opioid system and the GABAergic systems thus provide superior pain relief compared to morphine or gabapentin, (2) EETs are directly anti-inflammatory and inhibit expression of inflammatory cytokines and adhesion molecules thus can prevent continued nerve damage; and (3) EETs promote nerve regeneration in cultured neurons. Thus, an sEH inhibitor will not only provide effective pain relief, but would also block further nerve damage and promote healing.

Post-exposure administration of diazepam combined with soluble epoxide hydrolase inhibition stops seizures and modulates neuroinflammation in a murine model of acute TETS intoxication

Tetramethylenedisulfotetramine (TETS) is a potent convulsant poison for which there is currently no approved antidote. The convulsant action of TETS is thought to be mediated by inhibition of type A gamma-aminobutyric acid receptor (GABAAR) function. We, therefore, investigated the effects of post-exposure administration of diazepam, a GABAAR positive allosteric modulator, on seizure activity, death and neuroinflammation in adult male Swiss mice injected with a lethal dose of TETS (0.15mg/kg, ip). Administration of a high dose of diazepam (5mg/kg, ip) immediately following the second clonic seizure (approximately 20min post-TETS injection) effectively prevented progression to tonic seizures and death. However, this treatment did not prevent persistent reactive astrogliosis and microglial activation, as determined by GFAP and Iba-1 immunoreactivity and microglial cell morphology. Inhibition of soluble epoxide hydrolase (sEH) has been shown to exert potent anti-inflammatory effects and to increase survival in mice intoxicated with other GABAAR antagonists. The sEH inhibitor TUPS (1mg/kg, ip) administered immediately after the second clonic seizure did not protect TETS-intoxicated animals from tonic seizures or death. Combined administration of diazepam (5mg/kg, ip) and TUPS (1mg/kg, ip, starting 1h after diazepam and repeated every 24h) prevented TETS-induced lethality and influenced signs of neuroinflammation in some brain regions. Significantly decreased microglial activation and enhanced reactive astrogliosis were observed in the hippocampus, with no changes in the cortex. Combining an agent that targets specific anti-inflammatory mechanisms with a traditional antiseizure drug may enhance treatment outcome in TETS intoxication.

Cytochrome P450 epoxygenase pathway of polyunsaturated fatty acid metabolism

Polyunsaturated fatty acids (PUFA) are oxidized by cytochrome P450 epoxygenases to PUFA epoxides which function as potent lipid mediators. The major metabolic pathways of PUFA epoxides are incorporation into phospholipids and hydrolysis to the corresponding PUFA diols by soluble epoxide hydrolase. Inhibitors of soluble epoxide hydrolase stabilize PUFA epoxides and potentiate their functional effects. The epoxyeicosatrienoic acids (EETs) synthesized from arachidonic acid produce vasodilation, stimulate angiogenesis, have anti-inflammatory actions, and protect the heart against ischemia-reperfusion injury. EETs produce these functional effects by activating receptor-mediated signaling pathways and ion channels. The epoxyeicosatetraenoic acids synthesized from eicosapentaenoic acid and epoxydocosapentaenoic acids synthesized from docosahexaenoic acid are potent inhibitors of cardiac arrhythmias. Epoxydocosapentaenoic acids also inhibit angiogenesis, decrease inflammatory and neuropathic pain, and reduce tumor metastasis. These findings indicate that a number of the beneficial functions of PUFA may be due to their conversion to PUFA epoxides. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Cytoprotective propensity of Bacopa monniera against hydrogen peroxide induced oxidative damage in neuronal and lung epithelial cells

Hydrogen peroxide (H2O2), a major reactive oxygen species (ROS) produced during oxidative stress, is toxic to the cells. Hence, H2O2 has been extensively used to study the effects of antioxidant and cytoprotective role of phytochemicals. In the present investigation H2O2 was used to induce oxidative stress via ROS production within PC12 and L132 cells. Cytoprotective propensity of Bacopa monniera extract (BME) was confirmed by cell viability assays, ROS estimation, lipid peroxidation, mitochondria membrane potential assay, comet assay followed by gene expression studies of antioxidant enzymes in PC12 and L132 cells treated with H2O2 for 24 h with or without BME pre-treatment. Our results elucidate that BME possesses radical scavenging activity by scavenging 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), superoxide radical, and nitric oxide radicals. The IC50 value of BME against these radicals was found to be 226.19, 15.17, 30.07, and 34.55 µg/ml, respectively). The IC50 of BME against ROS, lipid peroxidation and protein carbonylation was found to be 1296.53, 753.22, and 589.04 µg/ml in brain and 1137.08, 1079.65, and 11101.25 µg/ml in lung tissues, respectively. Further cytoprotective potency of the BME ameliorated the mitochondrial and plasma membrane damage induced by H2O2 as evidenced by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase leakage assays in both PC12 and L132 cells. H2O2 induced cellular, nuclear and mitochondrial membrane damage was restored by BME pre-treatment. H2O2 induced depleted antioxidant status was also replenished by BME pre-treatment. This was confirmed by spectrophotometric analysis, semi-quantitative RT-PCR and western blot studies. These results justify the traditional usage of BME based on its promising antioxidant and cytoprotective property.

Damage of neuroblastoma cell SH-SY5Y mediated by MPP+ inhibits proliferation of T-cell leukemia Jurkat by co-culture system

The adaptive immune system has implications in pathology of Parkinson’s disease (PD). Research data demonstrated that the peripheral CD4⁺ T-cell population decreased in pathogenesis of PD. The effect of damaged dopaminergic neurons on peripheral T cells of PD is still unknown. In this study, we constructed a neuronal and glial cells co-culture model by using human neuroblastoma cells SH-SY5Y and gliomas cells U87. After the co-culture cells were treated with neurotoxin 1-methyl-4-phenylpyridinium (MPP⁺) for 24 h, the conditioned media was harvested and used to cultivate T-cell leukemia Jurkat cells for another 24 h. We then analyzed the cell proliferation, cell cycle and necrosis effect of Jurkat cells. The results showed that co-culture medium of SH-SY5Y and U87 cells with MPP⁺ treatment inhibited the proliferation of Jurkat cells compared to control medium without MPP⁺, even though the same concentration of MPP⁺ had very little toxicity to the Jurkat cell. Furthermore, co-culture medium with low concentration of MPP⁺ (100 µM) arrested Jurkat cells cycle in G2/M phase through increasing cell cycle division 2 (CDC2) and CyclinB1 expression level, whereas co-culture medium with high concentration of MPP⁺ (500 µM) induced Jurkat cell necrosis through cellular swelling and membrane breakage. Our data implies that damaged dopamine neurons with glial cells can lead to the reduced number or inhibited proliferation activity of peripheral T cells.

Hyperacetylation of histone H3K9 involved in the promotion of abnormally high transcription of the gdnf gene in glioma cells

The mechanism underlying abnormally high transcription of the glial cell line-derived neurotrophic factor (GDNF) gene in glioma cells is not clear. In this study, to assess histone H3K9 acetylation levels in promoters I and II of the gdnf gene in normal human brain tissue, low- and high-grade glioma tissues, normal rat astrocytes, and rat C6 glioblastoma cells, we employed chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR), real-time PCR, and a pGL3 dual fluorescence reporter system. We also investigated the influence of treatment with curcumin, a histone acetyltransferase inhibitor, and trichostatin A (TSA), a deacetylase inhibitor, on promoter acetylation and activity and messenger RNA (mRNA) expression level of the gdnf gene in C6 cells. Compared to normal brain tissue, H3K9 acetylation in promoters I and II of the gdnf gene increased significantly in high-grade glioma tissues but not in low-grade glioma tissues. Moreover, H3K9 promoter acetylation level of the gdnf gene in C6 cells was also remarkably higher than in normal astrocytes. In C6 cells, curcumin markedly decreased promoter II acetylation and activity and GDNF mRNA expression. Conversely, all three measurements were significantly increased following TSA treatment. Our results suggest that histone H3K9 hyperacetylation in promoter II of the gdnf gene might be one of the reasons for its abnormal high transcription in glioma cells.

Epoxyeicosatrienoic acids pretreatment improves amyloid β-induced mitochondrial dysfunction in cultured rat hippocampal astrocytes

Amyloid-β (Aβ) has long been implicated as a causative protein in Alzheimer's disease. Cellular Aβ accumulation is toxic and causes mitochondrial dysfunction, which precedes clinical symptoms of Alzheimer's disease pathology. In the present study, we explored the possible use of epoxyeicosatrienoic acids (EETs), epoxide metabolites of arachidonic acid, as therapeutic target against Aβ-induced mitochondrial impairment using cultured neonatal hippocampal astrocytes. Inhibition of endogenous EET production by a selective epoxygenase inhibitor, MS-PPOH, caused a greater reduction in mitochondrial membrane potential in the presence of Aβ (1, 10 μM) exposure versus absence of Aβ. MS-PPOH preincubation also aggravated Aβ-induced mitochondrial fragmentation. Preincubation of the cells with either 14,15- or 11,12-EET prevented this mitochondrial depolarization and fragmentation. EET pretreatment also further improved the reduction observed in mitochondrial oxygen consumption in the presence of Aβ. Preincubation of the cells with EETs significantly improved cellular respiration under basal condition and in the presence of the protonophore, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP). The uncoupling of ATP synthase from the electron transfer chain that occurred in Aβ-treated cells was also prevented by preincubation with EETs. Lastly, cellular reactive oxygen species production, a hallmark of Aβ toxicity, also showed significant reduction in the presence of EETs. We have previously shown that Aβ reduces EET synthesis in rat brain homogenates and cultured hippocampal astrocytes and neurons (Sarkar P, Narayanan J, Harder DR. Differential effect of amyloid beta on the cytochrome P450 epoxygenase activity in rat brain. Neuroscience 194: 241-249, 2011). We conclude that reduction of endogenous EETs may be one of the mechanisms through which Aβ inflicts toxicity and thus supplementing the cells with exogenous EETs improves mitochondrial dynamics and prevents metabolic impairment.

Pluripotent stem cell-derived dopaminergic neurons as models of neurodegeneration

Researchers utilize a number of models of Parkinson’s disease ranging in complexity from immortalized cell lines to nonhuman primates. These models are used to investigate everything from the mechanisms underlying neurodegeneration, to drugs that may improve patient outcomes. Each model system has advantages and disadvantages, depending on their application. In this review, the authors assess the potential value of embryonic stem and induced-pluripotent stem cells as additions to the crowded Parkinson’s disease in vitro model landscape.