COX-2-deficient mice are less prone to MPTP-neurotoxicity than wild-type mice

Neuroprotective effect of diclofenac on chlorpromazine induced catalepsy in rats

Neuroinflammation plays a key role in progressive degeneration of dopaminergic cells. Upregulation of prostaglandins and free radicals formation are involved in the mechanisms of cell death in Parkinson's disease (PD). The present study aimed to investigate the neuroprotective effect of diclofenac against chlorpromazine (CPZ) induced catalepsy and motor impairment in mice. Adult Wistar rats treated with CPZ (3 mg/kg/day, IP) were orally dosed with diclofenac and L-dopa/carbidopa for 21 days. Catalepsy was measured after 21 days of dosing by using standard bar test at 30, 60, 90, 120 and 180 min then motor performances were assessed via open field test and wire hanging test. Histopathological investigation and determination of dopamine (DA) and 3,4-Dihydroxyphenylacetic acid (DOPAC) levels of rat's brain was also carried out. We found that CPZ treated group exhibited reduced motor impairment after 21 days of treatment in open field and wire hanging test (P < 0.01) as compared to control group. The cataleptic scores of CPZ treated rats were also significantly increased (P < 0.01) after 21 days of chronic dosing, however diclofenac treated groups showed significant reduction in cataleptic scores with improved motor performances. Histopathology of CPZ treated rats showed marked degeneration with architecture distortion in the mid brain region. Dopaminergic degeneration is confirmed by neurochemical results that showed reduced amount of dopamine and DOPAC levels in mid brain. Moreover, histopathological slides of diclofenac treated rats showed improved architecture with reduced gliosis of mid brain region as well as improved dopamine and DOPAC levels were achieved after 21 days dosing of diclofenac. Taken together, the present work provide an evidence that diclofenac ameliorated behavioral performances by mediating neuroprotection against CPZ induced PD via preventing dopaminergic neuronal cell death.

Are cyclooxygenase-2 and nitric oxide involved in the dyskinesia of Parkinson's disease induced by L-DOPA?

Inflammatory mechanisms are proposed to play a role in L-DOPA-induced dyskinesia. Cyclooxygenase-2 (COX2) contributes to inflammation pathways in the periphery and is constitutively expressed in the central nervous system. Considering that inhibition of nitric oxide (NO) formation attenuates L-DOPA-induced dyskinesia, this study aimed at investigating if a NO synthase (NOS) inhibitor would change COX2 brain expression in animals with L-DOPA-induced dyskinesia. To this aim, male Wistar rats received unilateral 6-hydroxydopamine microinjection into the medial forebrain bundle were treated daily with L-DOPA (21 days) combined with 7-nitroindazole or vehicle. All hemi-Parkinsonian rats receiving l-DOPA showed dyskinesia. They also presented increased neuronal COX2 immunoreactivity in the dopamine-depleted dorsal striatum that was directly correlated with dyskinesia severity. Striatal COX2 co-localized with choline-acetyltransferase, calbindin and DARPP-32 (dopamine-cAMP-regulated phosphoprotein-32), neuronal markers of GABAergic neurons. NOS inhibition prevented L-DOPA-induced dyskinesia and COX2 increased expression in the dorsal striatum. These results suggest that increased COX2 expression after L-DOPA long-term treatment in Parkinsonian-like rats could contribute to the development of dyskinesia.

2-Acetyl-7-hydroxy-6-methoxy-1-methyl-1,2,3,4,-tetrahydroisoquinoline exhibits anti-inflammatory properties and protects the nigral dopaminergic neurons

Parkinson's disease (PD) is a neurodegenerative disorder characterized by degeneration of dopamine(DA)ergic neurons. Neuroinflammation caused by microglial activation is believed to be involved in the pathogenesis of neurodegenerative diseases including PD. In the present study, we tested the effects of a novel compound 2-acetyl-7-hydroxy-6-methoxy-1-methyl-1,2,3,4,-tetarhydroisoquinoline (AMTIQ) on neuroinflammatory response and DAergic neurodegeneration. In lipopolysaccharide-activated BV-2 microglial cells, AMTIQ lowered nitric oxide and tetrahydrobiopterin levels and downregulated gene expression of inducible nitric oxide synthase and GTP cyclohydrolase I. AMTIQ also repressed gene expression of the proinflammatory cytokines IL-1β and TNF-α, and attenuated nuclear translocation of NF-κB. AMTIQ was stable against liver microsomal enzymes from human and mouse and did not interfere with activities of the cytochrome p450 enzymes 1A2, 2D6, 2C9, 2C19 and 3A4. Pharmacokinetic studies revealed the brain to plasma ratio of AMTIQ to be 45%, suggesting it can penetrate the blood brain barrier. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mouse PD model, AMTIQ led to decreased microglial activation, increased survival of DAergic neurons and their fibers, and improved behavioral scores on rotarod and vertical grid tests. Taken together, these results suggest that AMTIQ might serve as a candidate preventive-therapeutic agent for neurodegenerative diseases such as PD.

Neuroinflammation and J2 prostaglandins: linking impairment of the ubiquitin-proteasome pathway and mitochondria to neurodegeneration

The immune response of the CNS is a defense mechanism activated upon injury to initiate repair mechanisms while chronic over-activation of the CNS immune system (termed neuroinflammation) may exacerbate injury. The latter is implicated in a variety of neurological and neurodegenerative disorders such as Alzheimer and Parkinson diseases, amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain injury, HIV dementia, and prion diseases. Cyclooxygenases (COX-1 and COX-2), which are key enzymes in the conversion of arachidonic acid into bioactive prostanoids, play a central role in the inflammatory cascade. J2 prostaglandins are endogenous toxic products of cyclooxygenases, and because their levels are significantly increased upon brain injury, they are actively involved in neuronal dysfunction induced by pro-inflammatory stimuli. In this review, we highlight the mechanisms by which J2 prostaglandins (1) exert their actions, (2) potentially contribute to the transition from acute to chronic inflammation and to the spreading of neuropathology, (3) disturb the ubiquitin-proteasome pathway and mitochondrial function, and (4) contribute to neurodegenerative disorders such as Alzheimer and Parkinson diseases, and amyotrophic lateral sclerosis, as well as stroke, traumatic brain injury (TBI), and demyelination in Krabbe disease. We conclude by discussing the therapeutic potential of targeting the J2 prostaglandin pathway to prevent/delay neurodegeneration associated with neuroinflammation. In this context, we suggest a shift from the traditional view that cyclooxygenases are the most appropriate targets to treat neuroinflammation, to the notion that J2 prostaglandin pathways and other neurotoxic prostaglandins downstream from cyclooxygenases, would offer significant benefits as more effective therapeutic targets to treat chronic neurodegenerative diseases, while minimizing adverse side effects.

PACAP27 prevents Parkinson-like neuronal loss and motor deficits but not microglia activation induced by prostaglandin J2

Neuroinflammation is a major risk factor in Parkinson's disease (PD). Alternative approaches are needed to treat inflammation, as anti-inflammatory drugs such as NSAIDs that inhibit cyclooxygenase-2 (COX-2) can produce devastating side effects, including heart attack and stroke. New therapeutic strategies that target factors downstream of COX-2, such as prostaglandin J2 (PGJ2), hold tremendous promise because they will not alter the homeostatic balance offered by COX-2 derived prostanoids. In the current studies, we report that repeated microinfusion of PGJ2 into the substantia nigra of non-transgenic mice, induces three stages of pathology that mimic the slow-onset cellular and behavioral pathology of PD: mild (one injection) when only motor deficits are detectable, intermediate (two injections) when neuronal and motor deficits as well as microglia activation are detectable, and severe (four injections) when dopaminergic neuronal loss is massive accompanied by microglia activation and motor deficits. Microglia activation was evaluated in vivo by positron emission tomography (PET) with [(11)C](R)PK11195 to provide a regional estimation of brain inflammation. PACAP27 reduced dopaminergic neuronal loss and motor deficits induced by PGJ2, without preventing microglia activation. The latter could be problematic in that persistent microglia activation can exert long-term deleterious effects on neurons and behavior. In conclusion, this PGJ2-induced mouse model that mimics in part chronic inflammation, exhibits slow-onset PD-like pathology and is optimal for testing diagnostic tools such as PET, as well as therapies designed to target the integrated signaling across neurons and microglia, to fully benefit patients with PD.

Fish oil, melatonin and vitamin E attenuates midbrain cyclooxygenase-2 activity and oxidative stress after the administration of 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine

Parkinson's disease is a neurodegenerative disease whose hallmark pathological features include a selective loss of dopaminergic neurons in the midbrain. Ciclooxygenase-2 activity induction and oxidative stress have been implicated in the aetiology of Parkinson's disease and in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson disease. Upon administration of fish oil, melatonin and vitamin E, neuroprotective effects on MPTP-induced neurotoxicity have been indicated. The aim of this study was to investigate the time course and compare the potency of these agents alone, on several parameters such as COX-2 and lipid peroxides (LPO) products associated with MPTP neurotoxicity in midbrain homogenates of C57BL/6 mice. Using fish oil (0.0368 g EPA and 0.0184 g DHA, per day), melatonin (10 mg/kg/day), and vitamin E (50 mg/Kg/day) we have now shown that COX-2 activity, LPO and nitrite/nitrate levels were significantly increased in MPTP treated mice (p < 0.001) while fish oil, melatonin and vitamin E treatment were capable of decreasing significantly the outcome of all above noted parameters (p < 0.05). The effect of fish oil on COX-2 activity and nitrite/nitrate levels was more profound than that of vitamin E or melatonin while the latter was more effective on reducing the LPO levels compared to fish oil and vitamin E. In conclusion, the outcome of the neuroprotective effects of these agents is long lasting and of variable potency indicating a different anti-inflammatory mode of action.

Glial-mediated inflammation underlying parkinsonism

The interest in studying neuroimmune interactions is increasing in the scientific community, and for many researchers, immunity is becoming a crucial factor in the understanding of the physiology of the normal brain as well as the biology underlying neurodegenerative diseases. Mounting data over the last two decades point toward immune and inflammatory alterations as important mediators of the progressive dopaminergic degeneration in Parkinson's disease. The purpose of this review is to address, under a historical perspective, as well as in the light of recent reports, the glial-mediated inflammatory and immune responses that occur in Parkinsonism. In line with this, this review also evaluates and highlights available anti-inflammatory drugs and putative targets for Parkinson's disease therapy for the near future.

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

PGE2 EP1 receptor deletion attenuates 6-OHDA-induced Parkinsonism in mice: old switch, new target

Recent experimental data on Parkinson's disease (PD) predicts the critical role of inflammation in the progression of neurodegeneration and the promising preventive effects of nonsteroidal anti-inflammatory drugs (NSAIDs). Previous studies suggest that NSAIDs minimize cyclooxygenase-2 (COX-2) activity and thereby attenuate free radical generation. Prostaglandin E2 (PGE2) is an important product of COX activity and plays an important role in various physiologic and pathophysiologic conditions through its EP receptors (EP1-EP4). Part of the toxic effect of PGE2 in the central nervous system has been reported to be through the EP1 receptor; however, the effect of the EP1 receptor in PD remains elusive. Therefore, in our pursuit to determine if deletion of the PGE2 EP1 receptor will attenuate 6-hydroxy dopamine (6-OHDA)-induced Parkinsonism, mice were given a unilateral 6-OHDA injection into the medial forebrain bundle. We found that apomorphine-induced contralateral rotations were significantly attenuated in the 6-OHDA-lesioned EP1(-/-) mice compared with the 6-OHDA-lesioned WT mice. Quantitative analysis showed significant protection of dopaminergic neurons in the substantia nigra pars compacta of the 6-OHDA-lesioned EP1(-/-) mice. To the best of our knowledge, this is the first in vivo study to implicate the PGE2 EP1 receptor in toxin-induced Parkinsonism. We propose the PGE2 EP1 receptor as a new target to better understand some of the mechanisms leading to PD.

Role of prostaglandins in neuroinflammatory and neurodegenerative diseases

Increasing data demonstrates that inflammation participates in the pathophysiology of neurodegenerative diseases. Among the different inflammatory mediators involved, prostaglandins play an important role. The effects induced by prostaglandins might be mediated by activation of their known receptors or by nonclassical mechanisms. In the present paper, we discuss the evidences that link prostaglandins, as well as the enzymes that produce them, to some neurological diseases.

Glia: initiators and progressors of pathology in Parkinson's disease

BACKGROUND

Glia are traditionally known as support cells for neurons, and their role in neurodegeneration has been largely considered secondary to neuronal dysfunction. We review newer concepts on glial function and assess glial changes in Parkinson's disease (PD) at the time of disease initiation when α-synuclein is accumulating in brain tissue but there is limited neuronal loss, and also as the disease progresses and neuronal loss is evident.

RESULTS

Of the two main types of astrocytes, only protoplasmic astrocytes are involved in PD, where they become nonreactive and accumulate α-synuclein. Experimental evidence has shown that astrocytic α-synuclein deposition initiates the noncell autonomous killing of neurons through microglial signaling. As the disease progresses, more protoplasmic astrocytes are affected by the disease with an increasing microglial response. Although there is still controversy on the role microglia play in neurodegeneration, there is evidence that microglia are activated early in PD and possibly assist with the clearance of extracellular α-synuclein at this time. Microglia transform to phagocytes and target neurons as the disease progresses but appear to become dysfunctional with increasing amounts of ingested debris. Only nonmyelinating oligodendroglial cells are affected in PD, and only late in the disease process.

CONCLUSIONS

Glial cells are responsible for the progression of PD and play an important role in initiating the early tissue response. In particular, early dysfunction and α-synuclein accumulation in astrocytes causes recruitment of phagocytic microglia that attack selected neurons in restricted brain regions causing the clinical symptoms of PD.

Oxidation of 3,4-dihydroxyphenylacetaldehyde, a toxic dopaminergic metabolite, to a semiquinone radical and an ortho-quinone

The oxidation and toxicity of dopamine is believed to contribute to the selective neurodegeneration associated with Parkinson disease. The formation of reactive radicals and quinones greatly contributes to dopaminergic toxicity through a variety of mechanisms. The physiological metabolism of dopamine to 3,4-dihydroxyphenylacetaldehyde (DOPAL) via monoamine oxidase significantly increases its toxicity. To more adequately explain this enhanced toxicity, we hypothesized that DOPAL is capable of forming radical and quinone species upon oxidation. Here, two unique oxidation products of DOPAL are identified. Several different oxidation methods gave rise to a transient DOPAL semiquinone radical, which was characterized by electron paramagnetic resonance spectroscopy. NMR identified the second oxidation product of DOPAL as the ortho-quinone. Also, carbonyl hydration of DOPAL in aqueous media was evident via NMR. Interestingly, the DOPAL quinone exists exclusively in the hydrated form. Furthermore, the enzymatic and chemical oxidation of DOPAL greatly enhance protein cross-linking, whereas auto-oxidation results in the production of superoxide. Also, DOPAL was shown to be susceptible to oxidation by cyclooxygenase-2 (COX-2). The involvement of this physiologically relevant enzyme in both oxidative stress and Parkinson disease underscores the potential importance of DOPAL in the pathogenesis of this condition.

Expression of mutant alpha-synuclein modulates microglial phenotype in vitro

Background

Increased reactive microglia are a histological characteristic of Parkinson's disease (PD) brains, positively correlating with levels of deposited α-synuclein protein. This suggests that microglial-mediated inflammatory events may contribute to disease pathophysiology. Mutations in the gene coding for α-synuclein lead to a familial form of PD. Based upon our prior findings that α-synuclein expression regulates microglial phenotype we hypothesized that expression of mutant forms of the protein may contribute to the reactive microgliosis characteristic of PD brains.

Methods

To quantify the effects of wild type and mutant α-synuclein over-expression on microglial phenotype a murine microglial cell line, BV2, was transiently transfected to express human wild type (WT), and mutant α-synuclein (A30P and A53T) proteins. Transfected cells were used to assess changes in microglia phenotype via Western blot analysis, ELISA, phagocytosis, and neurotoxicity assays.

Results

As expected, over-expression of α-synuclein induced a reactive phenotype in the transfected cells. Expression of α-synuclein increased protein levels of cycloxygenase-2 (Cox-2). Transfected cells demonstrated increased secretion of the proinflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), as well as increased nitric oxide production. Transfected cells also had impaired phagocytic ability correlating with decreased protein levels of lysosomal-associated membrane protein 1 (LAMP-1). In spite of the increased cytokine secretion profile, the transfected cells did not exhibit increased neurotoxic ability above control non-transfected BV2 cells in neuron-microglia co-cultures.

Conclusions

These data demonstrated that over-expression of α-synuclein drives microglial cells into a form of reactive phenotype characterized by elevated levels of arachidonic acid metabolizing enzymes, cytokine secretion, and reactive nitrogen species secretion all superimposed upon impaired phagocytic potential.

Interferon-γ plays a role in paraquat-induced neurodegeneration involving oxidative and proinflammatory pathways

Exposure to environmental contaminants, particularly pesticides, may be an important etiological factor in Parkinson's disease (PD); and evidence suggests a role for microglia-dependent inflammatory and oxidative processes in nigrostriatal pathology induced by such toxins. Yet, the events mediating microglial activation and their effects are not fully known. To this end, we hypothesized that the proinflammatory cytokine, interferon-gamma (IFN-γ), may be a prime factor in the pathogenesis of PD, given its critical role in regulating microglial responses to pathogens. Indeed, the present investigation demonstrated that genetic deletion of IFN-γ protected substantia nigra pars compacta (SNc) dopamine (DA) neurons from the toxic effects of the pesticide, paraquat, and normalized changes in inflammatory and oxidative factors within this brain region. Specifically, IFN-γ knockout prevented the paraquat-induced morphological signs of microglial activation and expression of key nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, while also preventing time-dependent changes in proinflammatory enzymes (inducible nitric oxide synthase [iNOS], cyclooxygenase-2 [COX-2]), cytokines (interleukin-1β [IL-1β], tumor necrosis factor-α [TNF-α]), and signaling factors (c-Jun N-terminal kinase [JNK], p38 MAP kinase [p38], Signal transducer and activator of transcription-1 [STAT1], nuclear factor kappa B [NF-κB]). Moreover, paraquat transiently suppressed substantia nigra pars compacta expression of trophic and proneuroplastic factors (cyclic-AMP response element binding protein [CREB], brain-derived neurotrophic factor [BDNF]), and IFN-γ deficiency again reversed these effects. These data suggest that IFN-γ is important for paraquat-induced neurodegeneration and the accompanying oxidative, inflammatory, and trophic changes that characterize the response to the toxin. Targeting IFN-γ could thus have therapeutic implications for PD and other neurodegenerative conditions that involve multiple inflammatory pathways.

Lipid-mediated oxidative stress and inflammation in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative movement disorder of unknown etiology. PD is characterized by the progressive loss of dopaminergic neurons in the substantia nigra, depletion of dopamine in the striatum, abnormal mitochondrial and proteasomal functions, and accumulation of α-synuclein that may be closely associated with pathological and clinical abnormalities. Increasing evidence indicates that both oxidative stress and inflammation may play a fundamental role in the pathogenesis of PD. Oxidative stress is characterized by increase in reactive oxygen species (ROS) and depletion of glutathione. Lipid mediators for oxidative stress include 4-hydroxynonenal, isoprostanes, isofurans, isoketals, neuroprostanes, and neurofurans. Neuroinflammation is characterized by activated microglial cells that generate proinflammatory cytokines, such as TNF-α and IL-1β. Proinflammatory lipid mediators include prostaglandins and platelet activating factor, together with cytokines may play a prominent role in mediating the progressive neurodegeneration in PD.

Adaptive immune regulation of glial homeostasis as an immunization strategy for neurodegenerative diseases

Neurodegenerative diseases, notably Alzheimer's and Parkinson's diseases, are amongst the most devastating disorders afflicting the elderly. Currently, no curative treatments or treatments that interdict disease progression exist. Over the past decade, immunization strategies have been proposed to combat disease progression. Such strategies induce humoral immune responses against misfolded protein aggregates to facilitate their clearance. Robust adaptive immunity against misfolded proteins, however, accelerates disease progression, precipitated by induced effector T cell responses that lead to encephalitis and neuronal death. Since then, mechanisms that attenuate such adaptive neurotoxic immune responses have been sought. We propose that shifting the balance between effector and regulatory T cell activity can attenuate neurotoxic inflammatory events. This review summarizes advances in immune regulation to achieve a homeostatic glial response for therapeutic gain. Promising new ways to optimize immunization schemes and measure their clinical efficacy are also discussed.

Alpha-synuclein, lipids and Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease, after Alzheimer's disease, among the aging human population. The main symptoms of Parkinson's disease such as tremor and movement disabilities are the result of degeneration of dopaminergic neurons in substantia nigra pars compacta. The widely-accepted subcellular factor which underlies Parkinson's disease neuropathology is the presence of Lewy bodies with characteristic inclusions of aggregated alpha-synuclein. This small soluble protein has been implicated in a range of interactions with phospholipid membranes and free fatty acids. The precise biological function of this protein is, however, still under investigation. Here we review the evidence linking alpha-synuclein, lipid metabolism, fatty acid oxidation, mitochondrial damage and Parkinson's disease. We propose that association of alpha-synuclein with oxidized lipid metabolites can lead to mitochondrial dysfunction in turn leading to dopaminergic neuron death and thus to Parkinson's disease.

Acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administrations elicit similar microglial activation in the substantia nigra of monkeys

Increasing evidence suggests a pivotal role for neuroinflammation in the pathogenesis of Parkinson disease, but whether activated microglia participate in disease progression remains unclear. To clarify this issue, we determined the numbers of activated microglial cells in the substantia nigra pars compacta and ventral tegmental area of monkeys subacutely and chronically exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Monkeys in the subacute MPTP treatment group were killed 1 week after the last MPTP injection; chronically treated monkeys were killed either 6 or 35 months after the last MPTP injection. Subacute MPTP administration induced loss of dopaminergic neurons in the substantia nigra pars compacta and ventral tegmental area and microglial activation in the same areas. Chronic MPTP treatment resulted in greater dopaminergic neuron depletion in both treatment groups. Both groups of chronic MPTP-treated monkeys showed increased numbers of activated microglial cells in the substantia nigra pars compacta that were similar to those of the subacute MPTP treatment group. These results indicate that microglial activation seems to be induced mainly by the toxic effects of MPTP and that it does not further progress once the toxin administration has been terminated. This suggests that the progressive degeneration of nigral cells in Parkinson disease may not necessarily be associated with progressively increased microglial activation.

Interferon-gamma deficiency modifies the motor and co-morbid behavioral pathology and neurochemical changes provoked by the pesticide paraquat

In addition to nigrostriatal pathology and corresponding motor disturbances, Parkinson's disease (PD) is often characterized by co-morbid neuropsychiatric symptoms, most notably anxiety and depression. Separate lines of evidence indicate that inflammatory processes associated with microglial activation and cytokine release may be fundamental to the progression of both PD and its co-morbid psychiatric pathology. Accordingly, we assessed the contribution of the pro-inflammatory cytokine, interferon-gamma (IFN-gamma), to a range of PD-like pathology provoked by the ecologically relevant herbicide and dopamine (DA) toxin, paraquat. To this end, paraquat provoked overt motor impairment (reduced home-cage activity and impaired vertical climbing) and signs of anxiety-like behavior (reduced open field exploration) in wild-type but not IFN-gamma-deficient mice. Correspondingly, paraquat promoted somewhat divergent variations in neurochemical activity among wild-type and IFN-gamma null mice at brain sites important for both motor (striatum) and co-morbid affective pathologies (dorsal hippocampus, medial prefrontal cortex, and locus coeruleus). Specifically, the herbicide provoked a dosing regimen-dependent reduction in striatal DA levels that was prevented by IFN-gamma deficiency. In addition, the herbicide influenced serotonergic and noradrenergic activity within the dorsal hippocampus and medial prefrontal cortex; and elevated noradrenergic activity within the locus coeruleus. Although genetic ablation of IFN-gamma had relatively few effects on monoamine variations within the locus coeruleus and prefrontal cortex, loss of the pro-inflammatory cytokine did normalize the paraquat-induced noradrenergic alterations within the hippocampus. These findings further elucidate the functional implications of paraquat intoxication and suggest an important role for IFN-gamma in the striatal and motor pathology, as well as the co-morbid behavioral and hippocampal changes induced by paraquat.

Innate and adaptive immunity for the pathobiology of Parkinson's disease

Innate and adaptive immunity affect the pathogenesis of Parkinson's disease (PD). In particular, activation of microglia influences degeneration of dopaminergic neurons. Cell-to-cell interactions and immune regulation critical for neuronal homeostasis also influence immune responses. The links between T cell immunity and nigrostriatal degeneration are supported by laboratory, animal model, and human pathologic investigations. Immune-associated biomarkers in spinal fluids and brain tissue of patients with idiopathic or familial forms of PD provide means to improve diagnosis and therapeutic monitoring. Relationships between oxidative stress, inflammation, and immune-mediated cell death pathways are examined in this review as they are linked to PD pathogenesis. Harnessing the immune system by drugs or by vaccination remain promising future therapeutic options.

Activation of p38 MAPK in the substantia nigra leads to nuclear translocation of NF-kappaB in MPTP-treated mice: implication in Parkinson's disease

Activation and translocation of the transcription factor nuclear factor kappa B (NF-kappaB) from cytoplasm to the nucleus has been reported in models of Parkinson's disease (PD). Our focus was to discern the upstream events which ultimately lead to NF-kappaB nuclear translocation using animal model of PD. We demonstrate that p38 activation results in downstream phosphorylation of NF-kappaB and accumulation of p65 subunit of NF-kappaB selectively in ventral midbrain but not in striatum. Treatment with p38 inhibitor, SB239063, prevented downstream phosphorylation of IkappaB alpha and p65 translocation to the nucleus in the ventral midbrain. Phosphorylation of anti-apoptotic Bcl2, an NF-kappaB target gene by p38 to inactive pBcl2ser87 was also attenuated by SB239063. Increased staining of p65 in the nuclei of cells in the substantia nigra but not in the ventral tegmental area of MPTP-treated mice further suggests a role for NF-kappaB in PD. In agreement with the above, sustained caspase activation is seen in the ventral midbrain but not in striatum. We demonstrate the region specific p38-mediated activation of NF-kappaB following MPTP treatment demonstrating the role of p38/NF-kappaB signaling in the pathogenesis and progression of the disease. Selective inhibitors of p38 may therefore, help preserve the surviving neurons in PD and slow down the disease progression.

Neuroinflammation in Parkinson's disease: a target for neuroprotection?

Parkinson's disease is characterised by a slow and progressive degeneration of dopaminergic neurons in the substantia nigra. Despite intensive research, the cause of the neuronal loss in Parkinson's disease is poorly understood. Neuroinflammatory mechanisms might contribute to the cascade of events leading to neuronal degeneration. In this Review, we describe the evidence for neuroinflammatory processes from post-mortem and in vivo studies in Parkinson's disease. We further identify the cellular and molecular events associated with neuroinflammation that are involved in the degeneration of dopaminergic neurons in animal models of the disease. Overall, available data support the importance of non-cell-autonomous pathological mechanisms in Parkinson's disease, which are mostly mediated by activated glial and peripheral immune cells. This cellular response to neurodegeneration triggers deleterious events (eg, oxidative stress and cytokine-receptor-mediated apoptosis), which might eventually lead to dopaminergic cell death and hence disease progression. Finally, we highlight possible therapeutic strategies (including immunomodulatory drugs and therapeutic immunisation) aimed at downregulating these inflammatory processes that might be important to slow the progression of Parkinson's disease.

Inflammatory response in Parkinsonism

Inflammatory responses have been proposed as important factors in dopaminergic neuro-degeneration in Parkinsonism. Increasing evidence suggests that the alteration of the glial microenvironment induced by neuronal degeneration could be deleterious to the remaining neurons. The activation of microglia/macrophages and reactive astrocytes may have a negative effect on the surrounding parenchyma, perpetuating the neurodegenerative process. However, this alteration may also go beyond the brain parenchyma and stimulate other inflammatory changes in other systems, inducing the release of proinflammatory cytokines and probably Acute Phase Proteins (APP) and Glucocorticoids (GC). In this work we review the latest advances in the field to provide a picture of the state of the art of studies of inflammatory responses and Parkinsonism, hopefully opening up new therapeutic perspectives for patients with Parkinson's disease.

The novel cyclooxygenase-2 inhibitor GW637185X protects against l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity

The possible neuroprotective role of a novel and highly selective cyclooxygenase-2 inhibitor GW637185X was studied in a model of acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced injury of nigrostriatal dopaminergic (DA) neurons in the mouse. Stereological and microdensitometrical analysis of nigral tyrosine hydroxylase-immunoreactive cell bodies and striatal tyrosine hydroxylase-immunoreactive terminals, respectively, showed that GW637185X exerted a full protection against MPTP-induced degeneration of the nigro-striatal pathway. In contrast to earlier studies, these findings demonstrate that acute inhibition of cyclooxygenase-2 can result in a full neuroprotective effect not only on nigral DA cell bodies, but also on striatal DA terminals in the mouse MPTP model.

Altered GABAergic neurotransmission is associated with increased kainate-induced seizure in prostaglandin-endoperoxide synthase-2 deficient mice

Excitotoxicity involves over activation of brain excitatory glutamate receptors and has been implicated in neurological, neurodegenerative and neuropsychiatric diseases. Metabolism of arachidonic acid (AA) through the phospholipase A(2) (PLA(2))/prostaglandin-endoperoxide synthase (PTGS) pathway is increased after excitotoxic stimulation. However, the individual roles of the PTGS isoforms in this process are not well established. We assessed the role of the PTGS isoforms in the process of excitotoxicity by exposing mice deficient in either PTGS-1 (PTGS-1(-/-)) or PTGS-2 (PTGS-2(-/-)) to the prototypic excitotoxin, kainic acid (KA). Seizure intensity and neuronal damage were significantly elevated in KA-exposed PTGS-2(-/-), but not in PTGS-1(-/-), mice. The increased susceptibility was not associated with an alteration in KA receptor binding activity or mediated through the CB1 endocannabinoid receptor. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was decreased in the CA1 pyramidal neurons of PTGS-2(-/-) mice, suggesting an alteration of GABAergic function. In wild-type mice, six weeks treatment with the PTGS-2 selective inhibitor celecoxib recapitulated the increased susceptibility to KA-induced excitotoxicity observed in PTGS-2(-/-) mice, further supporting the role of PTGS-2 in the excitotoxic process. The increased susceptibility to KA was also associated with decreased brain levels of PGE(2), a biomarker of PTGS-2 activity. Our results suggest that PTGS-2 activity and its specific products may modulate neuronal excitability by affecting GABAergic neurotransmission. Further, inhibition of PTGS-2, but not PTGS-1, may increase the susceptibility to seizures.

The roles of NADPH oxidase and phospholipases A2 in oxidative and inflammatory responses in neurodegenerative diseases

Reactive oxygen species (ROS) are produced in mammalian cells through enzymic and non-enzymic mechanisms. Although some ROS production pathways are needed for specific physiological functions, excessive production is detrimental and is regarded as the basis of numerous neurodegenerative diseases. Among enzymes producing superoxide anions, NADPH oxidase is widespread in mammalian cells and is an important source of ROS in mediating physiological and pathological processes in the cardiovascular and the CNS. ROS production is linked to the alteration of intracellular calcium homeostasis, activation of Ca(2+)-dependent enzymes, alteration of cytoskeletal proteins, and degradation of membrane glycerophospholipids. There is evolving evidence that ROS produced by NADPH oxidase regulate neuronal functions and degrade membrane phospholipids through activation of phospholipases A(2) (PLA(2)). This review is intended to cover recent studies describing ROS generation from NADPH oxidase in the CNS and its downstream activation of PLA(2), namely, the group IV cytosolic cPLA(2) and the group II secretory sPLA(2). A major focus is to elaborate the dual role of NADPH oxidase and PLA(2) in mediating the oxidative and inflammatory responses in neurodegenerative diseases, including cerebral ischemia and Alzheimer's disease. Elucidation of the signaling pathways linking NADPH oxidase with the multiple forms of PLA(2) will be important in understanding the oxidative and degradative mechanisms that underline neuronal damage and glial activation and will facilitate development of therapeutic intervention for prevention and treatment of these and other neurodegenerative diseases.

Differential gene expression patterns in cyclooxygenase-1 and cyclooxygenase-2 deficient mouse brain

Microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in cyclooxygenase-1 or cyclooxygenase-2 reveals that the two enzymes differentially modulate brain gene expression.

Background

Cyclooxygenase (COX)-1 and COX-2 produce prostanoids from arachidonic acid and are thought to have important yet distinct roles in normal brain function. Deletion of COX-1 or COX-2 results in profound differences both in brain levels of prostaglandin E₂ and in activation of the transcription factor nuclear factor-κB, suggesting that COX-1 and COX-2 play distinct roles in brain arachidonic acid metabolism and regulation of gene expression. To further elucidate the role of COX isoforms in the regulation of the brain transcriptome, microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in COX-1 (COX-1^-/-) or COX-2 (COX-2^-/-) was performed.

Results

A majority (>93%) of the differentially expressed genes in both the cortex and hippocampus were altered in one COX isoform knockout mouse but not the other. The major gene function affected in all genotype comparisons was 'transcriptional regulation'. Distinct biologic and metabolic pathways that were altered in COX^-/- mice included β oxidation, methionine metabolism, janus kinase signaling, and GABAergic neurotransmission.

Conclusion

Our findings suggest that COX-1 and COX-2 differentially modulate brain gene expression. Because certain anti-inflammatory and analgesic treatments are based on inhibition of COX activity, the specific alterations observed in this study further our understanding of the relationship of COX-1 and COX-2 with signaling pathways in brain and of the therapeutic and toxicologic consequences of COX inhibition.

Arachidonic acid metabolism in brain physiology and pathology: lessons from genetically altered mouse models

The arachidonic acid (AA) cascade involves the release of AA from the membrane phospholipids by a phospholipase A(2), followed by its subsequent metabolism to bioactive prostanoids by cyclooxygenases coupled with terminal synthases. Altered brain AA metabolism has been implicated in neurological, neurodegenerative, and psychiatric disorders. The development of genetically altered mice lacking specific enzymes of the AA cascade has helped to elucidate the individual roles of these enzymes in brain physiology and pathology. The roles of AA and its metabolites in brain physiology, with a particular emphasis on the phospholipase A(2)/cyclooxygenases pathway, are summarized, and the specific phenotypes of genetically altered mice relevant to brain physiology and neurotoxic models are discussed.

Angiotensin-(1-7)-induced plasticity changes in the lateral amygdala are mediated by COX-2 and NO

It is known from studies outside the brain that upon binding to its receptor, angiotensin-(1-7) elicits the release of prostanoids and nitric oxide (NO). Cyclooxygenase (COX) is a key enzyme that converts arachidonic acid to prostaglandins. Since there are no data available so far on the role of COX-2 in the amygdala, in a first step we demonstrated that the selective COX-2 inhibitor NS-398 significantly reduced the probability of long-term potentiation (LTP) induction in the lateral nucleus of the amygdala. Similarly, in COX-2(-/-) mice, LTP induced by external capsule (EC) stimulation was impaired. Second, we evaluated the action of angiotensin-(1-7) in the amygdala. In wild-type mice, angiotensin-(1-7) increased LTP. This LTP-enhancing effect of Ang-(1-7) was not observed in COX-2(+/-) mice. However, in COX-2(-/-) mice, Ang-(1-7) caused an enhancement of LTP similar to that in wild-type mice. The NO synthetase inhibitor L-NAME blocked this angiotensin-(1-7)-induced increase in LTP in COX-2(-/-) mice. Low-frequency stimulation of external capsule fibers did not cause long-term depression (LTD) in drug-free and angiotensin-(1-7)-treated brain slices in wild-type mice. In contrast, in COX-2(-/-) mice, angiotensin-(1-7) caused stable LTD. Increasing NO concentration by the NO-donor SNAP also caused LTD in wild-type mice. Our study shows for the first time that LTP in the amygdala is dependent on COX-2 activity. Moreover, COX-2 is involved in the mediation of angiotensin-(1-7) effects on LTP. Finally, it is recognized that there is a molecular cross-talk between COX-2 and NO that may regulate synaptic plasticity.

Non-steroidal anti-inflammatory drugs in Parkinson's disease

Parkinson's disease (PD) is known to be a chronic and progressive neurodegenerative disease caused by a selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). A large body of experimental evidence indicates that the factors involved in the pathogenesis of this disease are several, occurring inside and outside the DAergic neuron. Recently, the role of the neuron-glia interaction and the inflammatory process, in particular, has been the object of intense study by the research community. It seems to represent a new therapeutic approach opportunity for this neurological disorder. Indeed, it has been demonstrated that the cyclooxygenase type 2 (COX-2) is up-regulated in SNc DAergic neurons in both PD patients and animal models of PD and, furthermore, non-steroidal anti-inflammatory drugs (NSAIDs) pre-treatment protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6 hydroxydopamine (6-OHDA)-induced nigro-striatal dopamine degeneration. Moreover, recent epidemiological studies have revealed that the risk of developing PD is reduced in humans who make therapeutical use of NSAIDs. Consequently, it is hypothesized that they might delay or prevent the onset of PD. However, whether or not these common drugs may also be of benefit to those individuals who already have Parkinson's disease has not as yet been shown. In this paper, evidence relating to the protective effects of aspirin or other NSAIDs on DAergic neurons in animal models of Parkinson's disease will be discussed. In addition, the pharmacological mechanisms by which these molecules can exert their neuroprotective effects will be reviewed. Finally, epidemiological data exploring the effectiveness of NSAIDs in the prevention of PD and their possible use as adjuvants in the therapy of this neurodegenerative disease will also be examined.

Discovery of Ecopladib, an indole inhibitor of cytosolic phospholipase A2alpha

The synthesis and structure-activity relationship of a series of indole inhibitors of cytosolic phospholipase A2alpha (cPLA2alpha, type IVA phospholipase) are described. Inhibitors of cPLA2alpha are predicted to be efficacious in treating asthma as well as the signs and symptoms of osteoarthritis, rheumatoid arthritis, and pain. The introduction of a benzyl sulfonamide substituent at C2 was found to impart improved potency of these inhibitors, and the SAR of these sulfonamide analogues is disclosed. Compound 123 (Ecopladib) is a sub-micromolar inhibitor of cPLA2alpha in the GLU micelle and rat whole blood assays. Compound 123 displayed oral efficacy in the rat carrageenan air pouch and rat carrageenan-induced paw edema models.

Neuroinflammation, Oxidative Stress and the Pathogenesis of Parkinson's Disease

Neuroinflammatory processes play a significant role in the pathogenesis of Parkinson's disease (PD). Epidemiologic, animal, human, and therapeutic studies all support the presence of an neuroinflammatory cascade in disease. This is highlighted by the neurotoxic potential of microglia . In steady state, microglia serve to protect the nervous system by acting as debris scavengers, killers of microbial pathogens, and regulators of innate and adaptive immune responses. In neurodegenerative diseases, activated microglia affect neuronal injury and death through production of glutamate, pro-inflammatory factors, reactive oxygen species, quinolinic acid amongst others and by mobilization of adaptive immune responses and cell chemotaxis leading to transendothelial migration of immunocytes across the blood-brain barrier and perpetuation of neural damage. As disease progresses, inflammatory secretions engage neighboring glial cells, including astrocytes and endothelial cells, resulting in a vicious cycle of autocrine and paracrine amplification of inflammation perpetuating tissue injury. Such pathogenic processes contribute to neurodegeneration in PD. Research from others and our own laboratories seek to harness such inflammatory processes with the singular goal of developing therapeutic interventions that positively affect the tempo and progression of human disease.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

NO-cGMP signaling and regenerative medicine involving stem cells

Nitric oxide (NO) is a short lived diatomic free radical species synthesized by nitric oxide synthases (NOS). The physiological roles of NO depend on its local concentrations as well as availability and the nature of downstream target molecules. At low nanomolar concentrations, activation of soluble guanylyl cyclase (sGC) is the major event initiated by NO. The resulting elevation in the intracellular cyclic GMP (cGMP) levels serves as signals for regulating diverse cellular and physiological processes. The participation of NO and cGMP in diverse physiological processes is made possible through cell type specific spatio-temporal regulation of NO and cGMP synthesis and signal diversity downstream of cGMP achieved through specific target selection. Thus cyclic GMP directly regulates the activities of its downstream effectors such as Protein Kinase G (PKG), Cyclic Nucleotide Gated channels (CNG) and Cyclic nucleotide phosphodiesterases, which in turn regulate the activities of a number of proteins that are involved in regulating diverse cellular and physiological processes. Localization and activity of the NO-cGMP signaling pathway components are regulated by G-protein coupled receptors, receptor and non receptor tyrosine kinases, phosphatases and other signaling molecules. NO also serves as a powerful paracrine factor. At micromolar concentrations, NO reacts with superoxide anion to form reactive peroxinitrite, thereby leading to the oxidation of important cellular proteins. Extensive research efforts over the past two decades have shown that NO is an important modulator of axon outgrowth and guidance, synaptic plasticity, neural precursor proliferation as well as neuronal survival. Excessive NO production as that evoked by inflammatory signals has been identified as one of the major causative reasons for the pathogenesis of a number of neurodegenerative diseases such as ALS, Alzheimers and Parkinson diseases. Regenerative therapies involving transplantation of embryonic stem cells (ES cells) and ES cell derived lineage committed neural precursor cells have recently shown promising results in animal models of Parkinson disease (PD). Recent studies from our laboratory have shown that a functional NO-cGMP signaling system is operative early during the differentiation of embryonic stem cells. The cell type specific, spatio-temporally regulated NO-cGMP signaling pathways are well suited for inductive signals to use them for important cell fate decision making and lineage commitment processes. We believe that manipulating the NO-cGMP signaling system will be an important tool for large scale generation of lineage committed precursor cells to be used for regenerative therapies.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Oxidation and cytotoxicity of 6-OHDA are mediated by reactive intermediates of COX-2 overexpressed in PC12 cells

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons, likely associated with dysregulation of oxidation of catechols, such as dopamine (DA) and 6-hydroxydopamine (6-OHDA), and resulting in oxidative stress. The involvement of cyclooxygenase-2 (COX-2) in pathogenesis of Parkinson's disease has been suggested. However, specific COX-2 triggered mechanisms participating in catalysis of DA oxidation and enhanced catechol-induced cytotoxicity remain poorly characterized. Here, we demonstrate that in a model biochemical system, recombinant heme-reconstituted COX-2 induced oxidation of 6-OHDA in the course of its peroxidase (H(2)O(2)-dependent) and cyclooxygenase (arachidonic acid (AA)-dependent) catalytic half-cycles. Similarly, COX-2 was able to stimulate 6-OHDA oxidation during its peroxidase- and cyclooxygenase half-cycles and caused oxidative stress in homogenates of PC12 cells stably overexpressing the enzyme (but not in mock-transfected cells). In addition, the increased levels of COX-2 were associated with enhanced cytotoxicity of 6-OHDA in stably transfected PC12 cells. Finally, co-oxidation of 6-OHDA by COX-2 triggered production of superoxide radicals critical for both propagation of 6-OHDA oxidation and induction of oxidative stress in COX-2 overexpressing cells. Thus, we conclude that both peroxidase and cyclooxygenase half-cycles of COX-2-catalyzed reactions are essential for COX-2-dependent activation of 6-OHDA oxidation, oxygen radical production, oxidative stress, and cytotoxicity.

Aspirin protects striatal dopaminergic neurons from neurotoxin-induced degeneration: An in vivo microdialysis study

The effect of aspirin on dopaminergic neuronal damage induced by in vivo infusion of 1-methyl-4-phenylpiridinium iodide (MPP(+)) and 6-hydroxydopamine (6-OHDA) was studied in rats, using microdialysis. Rat striata were perfused with 1 mM MPP(+) or 6-OHDA for 10 min, causing peak levels of dopamine (DA) in the dialytic fluid, after 40 min. After 24 h, 1 mM MPP(+) was perfused again for 10 min and DA levels measured in the dialytic fluid, as an index of neuronal cell integrity. Pretreatment with Aspidol (lysine acetylsalicylate), 180 mg/kg i.p., 1 h before MPP(+) or 6-OHDA perfusion, did not modify DA extracellular output, on day 1, but restored MPP(+)-induced DA release on day 2, indicating a neuroprotective effect of Aspidol. Conversion of 0.5 mM 4-hydroxybenzoic acid (4-HBA) to 3,4-dihydroxybenzoic acid (3,4-DHBA) was measured as an index of reactive oxygen species (ROS). 6-OHDA, but not MPP(+), significantly enhanced 3,4-DHBA levels in the perfusion fluid. Aspidol (180 mg/kg, i.p.) reduced 6-OHDA-dependent increase of 3,4-DHBA levels. Meloxicam (50 mg/kg, i.p.), a specific cyclooxygenase-2 (COX-2) inhibitor, was ineffective against both neurotoxins. These data suggest that the protective effect of aspirin is due to different mechanisms of action according to the neurotoxin used, and it is independent from COX-2 inhibition.

Minocycline attenuates microglial activation but fails to mitigate striatal dopaminergic neurotoxicity: role of tumor necrosis factor-alpha

Activated microglia are implicated in the pathogenesis of disease-, trauma- and toxicant-induced damage to the CNS, and strategies to modulate microglial activation are gaining impetus. A novel action of the tetracycline derivative minocycline is the ability to inhibit inflammation and free radical formation, factors that influence microglial activation. Minocycline is therefore being tested as a neuroprotective agent to alleviate CNS damage, although findings so far have yielded mixed results. Here, we showed that administration of a single low dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH), a paradigm that causes selective degeneration of striatal dopaminergic nerve terminals without affecting the cell body in substantia nigra, increased the expression of mRNAs encoding microglia-associated factors F4/80, interleukin (IL)-1alpha, IL-6, monocyte chemoattractant protein-1 (MCP-1, CCL2) and tumor necrosis factor (TNF)-alpha. Minocycline treatment attenuated MPTP- or METH-mediated microglial activation, but failed to afford neuroprotection. Lack of neuroprotection was shown to be due to the inability of minocycline to abolish the induction of TNF-alpha and its receptors, thereby failing to modulate TNF signaling. Thus, TNF-alpha appeared to be an obligatory component of dopaminergic neurotoxicity. To address this possibility, we examined the effects of MPTP or METH in mice lacking genes encoding IL-6, CCL2 or TNF receptor (TNFR)1/2. Deficiency of either IL-6 or CCL2 did not alter MPTP neurotoxicity. However, deficiency of both TNFRs protected against the dopaminergic neurotoxicity of MPTP. Taken together, our findings suggest that attenuation of microglial activation is insufficient to modulate neurotoxicity as transient activation of microglia may suffice to initiate neurodegeneration. These findings support the hypothesis that TNF-alpha may play a role in the selective vulnerability of the nigrostriatal pathway associated with dopaminergic neurotoxicity and perhaps Parkinson's disease.

Down-regulation of brain nuclear factor-kappa B pathway in the cyclooxygenase-2 knockout mouse

Cyclooxygenase (COX) is the rate-limiting enzyme in the synthesis of prostaglandins (PGs) from arachidonic acid. Evidence suggests that neuronal COX-2 gene expression is mainly regulated by the transcription factor nuclear factor kappa-B (NF-kappaB). The present study was undertaken to determine whether there is a shared regulation of NF-kappaB or of nuclear factor of activated T-cells cytoplasmic (NFATc) with COX-2 and whether these transcription factors known to regulate COX-2 expression are altered in brain from COX-2 knockout (COX-2-/-) mice compared to wild type. We found a decrease in NF-kappaB DNA-protein binding activity, which was accompanied by a reduction of the phosphorylation state of both I-kappaBalpha and p65 proteins in the COX-2-/- mice. The mRNA and protein levels of p65 were also reduced in COX-2-/- mice, whereas total cytoplasmic I-kappaB protein level was not significantly changed. Taken together, these changes may be responsible for the observed decrease in NF-kappaB DNA binding activity. NF-kappaB DNA binding activity was selectively affected in the COX-2-/- mice compared to the wild type as there was no significant change in NFATc DNA binding activity. Overall, our data indicate that constitutive brain NF-kappaB activity is decreased in COX-2 deficient mice and suggest a reciprocal coupling between NF-kappaB and COX-2.

Microarray analysis of rat brain gene expression after chronic administration of sodium valproate

Valproic acid has been used to treat mania and bipolar disorder, but its mechanism of action is not agreed on. We used rat genome U34A Affymetrix oligonucleotide microarrays, containing 8799 known probesets, to determine the effect of 30-day daily intraperitoneal administration of valproate (200mg/kg) on rat brain gene expression. We found 87 down-regulated genes and 34 up-regulated genes of at least a 1.4-fold change in valproate-treated compared to control rats. The experiments were done on five independent samples for each group, each in duplicate. The genes affected are known to be involved in a variety of pathways, including synaptic transmission, ion channels and transport, G-protein signaling, lipid, glucose and amino-acid metabolism, transcriptional and translational regulation, phosphoinositol cycle, protein kinases and phosphatases, and apoptosis. Our results suggest that the therapeutic effect of valproate may involve the modulation of multiple signaling pathways.

KW-6002 protects from MPTP induced dopaminergic toxicity in the mouse

The risk of Parkinson's disease (PD) is associated with a lower intake of caffeine, a non-selective adenosine A2A antagonist. In agreement, genetic or pharmacological inactivation of adenosine A2A receptors in animal models of PD has demonstrated both symptomatic and neuroprotective effects. These findings and the lack of disease modifying therapies have led to intense research on adenosine A2A antagonists as a novel treatment for PD. In the present study the neuroprotective effect of the A2A receptor antagonist KW-6002 was investigated using different models of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice, which induced dopaminergic terminal and or dopaminergic cell loss and inflammation. Treatment with KW-6002 prevented the loss of dopaminergic striatal terminals and nigral cell bodies and inhibited the nigral microglia activation. Our results confirm previous findings that pharmacological inactivation of A2A receptors inhibits MPTP-induced dopaminergic damage at the level of striatum. In addition, we demonstrate for the first time that, after MPTP treatment in mice, an A2A antagonist is neuroprotective, and has anti-inflammatory effects, at the level of the substantia nigra. Thus, our data further support the use of A2A receptor antagonists as a novel neuroprotective therapy for PD.

Prostaglandin E2 and microsomal prostaglandin E synthase-2 expression are decreased in the cyclooxygenase-2-deficient mouse brain despite compensatory induction of cyclooxygenase-1 and Ca2+-dependent phospholipase A2

We previously demonstrated that brain cyclooxygenase (COX)-2 mRNA and protein levels, and prostaglandin E2 (PGE2) level, are down-regulated in cytosolic phospholipase A2 (cPLA2) -deficient mice. To further investigate the interaction between upstream and downstream enzymes involved in brain prostaglandin synthesis, we examined expression and activity of COX-1, of different PLA2 enzymes and of prostaglandin E synthase (PGES) enzymes in COX-2(-/-) mice. We found that the PGE2 level was decreased by 51.5% in the COX-2(-/-) mice brains, indicating a significant role of COX-2 in brain formation of PGE2. However, when we supplied exogenous arachidonic acid (AA) to brain homogenates, COX activity was increased in the COX-2(-/-) mice, suggesting a compensatory activation of COX-1 and an intracellular compartmentalization of the COX isozymes. Consistent with COX-1 increased activity, brain expression of COX-1 protein and mRNA also was increased. Activity and expression of cPLA2 and secretory PLA2 (sPLA2) enzymes, supplying AA to COX, were significantly increased. Also, the PGE2 biosynthetic pathway downstream from COX-2 was affected in the COX-2(-/-) mice, as decreased expression of microsomal prostaglandin E synthase-2 (mPGES-2), but not mPGES-1 or cytosolic PGES, was observed. Overall, the data suggest that compensatory mechanisms exist in COX-2(-/-) mice and that mPGES-2 is functionally coupled with COX-2.