Involvement of the 5-lipoxygenase pathway in the neurotoxicity of the prion peptide PrP106-126

Natural and Synthetic Derivatives of Hydroxycinnamic Acid Modulating the Pathological Transformation of Amyloidogenic Proteins

This review presents the main properties of hydroxycinnamic acid (HCA) derivatives and their potential application as agents for the prevention and treatment of neurodegenerative diseases. It is partially focused on the successful use of these compounds as inhibitors of amyloidogenic transformation of proteins. Firstly, the prerequisites for the emergence of interest in HCA derivatives, including natural compounds, are described. A separate section is devoted to synthesis and properties of HCA derivatives. Then, the results of molecular modeling of HCA derivatives with prion protein as well as with α-synuclein fibrils are summarized, followed by detailed analysis of the experiments on the effect of natural and synthetic HCA derivatives, as well as structurally similar phenylacetic and benzoic acid derivatives, on the pathological transformation of prion protein and α-synuclein. The ability of HCA derivatives to prevent amyloid transformation of some amyloidogenic proteins, and their presence not only in food products but also as natural metabolites in human blood and tissues, makes them promising for the prevention and treatment of neurodegenerative diseases of amyloid nature.

Neurotoxicity of Prion Peptides on Cultured Cerebellar Neurons

Prion neurotoxicity has been modeled in vitro using synthetic peptides derived from the PrP^C sequence. The major region of neurotoxicity has been localized to the hydrophobic domain located in the middle of the PrP protein. Neurotoxicity assays are typically performed on cultured mouse cerebellar neurons derived from neonatal pups, and cell viability can be monitored by assays including MTT or MTS, cell death by LDH release, or apoptosis by caspase cleavage assays. These neurotoxicity studies have been useful in identifying cofactors, such as PrP^C and metals, as modulators of PrP peptide-mediated neurotoxicity. Given the biosafety issues associated with handling and purifying infectious prions, the use of synthetic peptides, which display a dependence upon PrP^C expression for toxicity, as per the PrP^Sc agent for infectivity, supports the relevance of using these synthetic peptides for understanding PrP-mediated neurotoxicity.

The Ayurvedic drug Ksheerabala (101) ameliorates alcohol-induced neurotoxicity by down-regulating the expression of transcription factor (NFkB) in rat brain

Introduction:

Most of the pharmaceutical effects of alcohol are due to its accumulation in the brain. Ksheerabala (101) an Ayurvedic formulation mainly used against central nervous system disorders.

Aim:

To determine the antioxidant and neuroprotective effect of Ksheerabala (101) on alcohol-induced oxidative stress in rats.

Materials and Methods:

Male Albino rats of Sprague-Dawley strain were grouped into four; control, alcohol (4 g/kg), Ksheerabala (15 μL/1 ml milk/100 g) and Ksheerabala (15 μL/1 ml milk/100 g) + alcohol (4 g/kg). After the experimental period (90 days), the animals were sacrificed and the effect of Ksheerabala (101) was studied on oxidative stress, inflammatory markers, and induction of transcription factor in brain. Results were statistically analyzed by one-way ANOVA.

Results:

The activities of antioxidant enzymes and reduced glutathione which were decreased in alcohol-treated rats, increased significantly in co-administered groups. The lipid peroxidation products and protein carbonyls which were increased significantly in alcohol-treated rats decreased significantly in co-administered groups. The expression of gamma-glutamyl cysteine synthase decreased significantly in alcohol-treated rats and increased significantly in co-administered groups. The transcription factor nuclear factor-κB (NFκB) which was up-regulated in alcohol-treated rats was down-regulated in co-administered rats. The histopathology reinforced these results.

Conclusion:

Ksheerabala (101) attenuates alcohol-induced oxidative stress and down-regulates the expression of NFκB in rat brain.

The involvement of 5-lipoxygenase activating protein in anxiety-like behavior

The 5-lipoxygenase is an enzyme widely expressed in the central nervous system, where its activity is dependent on the presence the 5-lipoxygenase activating protein (FLAP) for the formation of leukotrienes, potent bioactive lipid mediators. Emerging evidence has shown that the FLAP/leukotriene pathway may play a role in neuropsychiatric disease contexts. In this study we investigated whether genetic deficiency of FLAP (FLAPKO) modulated some behavioral aspects in mice, and if this effect was age-dependent. While we observed that FLAPKO mice at 3 and 6 months of age did not different from wild type animals in the elevated plus maze, at 12 months of age they manifested a significant increase in anxiety-like behavior. By contrast, we observed no differences between FLAPKO mice and their controls at any of the three ages considered when they were tested for working memory in the Y maze paradigm. Additionally, while we found that cFOS protein and message levels were reduced in the brains of animals lacking FLAP, no changes for other transcription factors were detected. Taken together our findings suggest a novel role for FLAP in the pathogenesis of anxiety-like behavior. Future studies of FLAP neurobiology may be attractive for development of anxiolytic therapeutics.

Peroxiredoxin 6 promotes upregulation of the prion protein (PrP) in neuronal cells of prion-infected mice

Background

It has been widely established that the conversion of the cellular prion protein (PrP^C) into its abnormal isoform (PrP^Sc) is responsible for the development of transmissible spongiform encephalopathies (TSEs). However, the knowledge of the detailed molecular mechanisms and direct functional consequences within the cell is rare. In this study, we aimed at the identification of deregulated proteins which might be involved in prion pathogenesis.

Findings

Apolipoprotein E and peroxiredoxin 6 (PRDX6) were identified as upregulated proteins in brains of scrapie-infected mice and cultured neuronal cell lines. Downregulation of PrP gene expression using specific siRNA did not result in a decrease of PRDX6 amounts. Interestingly, selective siRNA targeting PRDX6 or overexpression of PRDX6 controlled PrP^C and PrP^Sc protein amounts in neuronal cells.

Conclusions

Besides its possible function as a novel marker protein in the diagnosis of TSEs, PDRX6 represents an attractive target molecule in putative pharmacological intervention strategies in the future.

Differential contribution of lipoxygenase isozymes to nigrostriatal vulnerability

The 5- and 12/15-lipoxygenase (LOX) isozymes have been implicated to contribute to disease development in CNS disorders such as Alzheimer's disease. These LOX isozymes are distinct in function, with differential effects on neuroinflammation, and the impact of the distinct isozymes in the pathogenesis of Parkinson's disease has not as yet been evaluated. To determine whether the isozymes contribute differently to nigrostriatal vulnerability, the effects of 5- and 12/15-LOX deficiency on dopaminergic tone under naïve and toxicant-challenged conditions were tested. In naïve mice deficient in 5-LOX expression, a modest but significant reduction (18.0% reduction vs. wildtype (WT)) in striatal dopamine (DA) was detected (n=6-8 per genotype). A concomitant decline in striatal tyrosine hydroxylase (TH) enzyme was also revealed in null 5-LOX vs. WT mice (26.2%); however, no changes in levels of DA or TH immunoreactivity were observed in null 12/15-LOX vs. WT mice. When challenged with the selective dopaminergic toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), WT mice showed a marked reduction in DA (31.9%) and robust astrocytic and microglial activation as compared to saline-treated animals. In contrast, null 5-LOX littermates demonstrated no significant striatal DA depletion or astrogliosis (as noted by Western blot analyses for glial acidic fibrillary protein (GFAP) immunoreactivity). In naïve null 12/15-LOX mice, no significant change in striatal DA values was observed compared to WT, and following MPTP treatment, the transgenics revealed striatal DA reduction similar to the challenged WT mice. Taken together, these data provide the first evidence that: (i) LOX isozymes are involved in the maintenance of normal dopaminergic function in the striatum and (ii) the 5- and 12/15-LOX isozymes contribute differentially to striatal vulnerability in response to neurotoxicant challenge.

Inhibition of cytosolic Phospholipase A2 prevents prion peptide-induced neuronal damage and co-localisation with Beta III Tubulin

Background

Activation of phospholipase A₂ (PLA₂) and the subsequent metabolism of arachidonic acid (AA) to prostaglandins have been shown to play an important role in neuronal death in neurodegenerative disease. Here we report the effects of the prion peptide fragment HuPrP106-126 on the PLA₂ cascade in primary cortical neurons and translocation of cPLA₂ to neurites.

Results

Exposure of primary cortical neurons to HuPrP106-126 increased the levels of phosphorylated cPLA₂ and caused phosphorylated cPLA₂ to relocate from the cell body to the cellular neurite in a PrP-dependent manner, a previously unreported observation. HuPrP106-126 also induced significant AA release, an indicator of cPLA₂ activation; this preceded synapse damage and subsequent cellular death. The novel translocation of p-cPLA₂ postulated the potential for exposure to HuPrP106-126 to result in a re-arrangement of the cellular cytoskeleton. However p-cPLA₂ did not colocalise significantly with F-actin, intermediate filaments, or microtubule-associated proteins. Conversely, p-cPLA₂ did significantly colocalise with the cytoskeletal protein beta III tubulin. Pre-treatment with the PLA₂ inhibitor, palmitoyl trifluoromethyl ketone (PACOCF₃) reduced cPLA₂ activation, AA release and damage to the neuronal synapse. Furthermore, PACOCF₃ reduced expression of p-cPLA₂ in neurites and inhibited colocalisation with beta III tubulin, resulting in protection against PrP-induced cell death.

Conclusions

Collectively, these findings suggest that cPLA₂ plays a vital role in the action of HuPrP106-126 and that the colocalisation of p-cPLA₂ with beta III tubulin could be central to the progress of neurodegeneration caused by prion peptides. Further work is needed to define exactly how PLA₂ inhibitors protect neurons from peptide-induced toxicity and how this relates to intracellular structural changes occurring in neurodegeneration.

Caffeic Acid phenethyl ester protects blood-brain barrier integrity and reduces contusion volume in rodent models of traumatic brain injury

A number of studies have established a deleterious role for inflammatory molecules and reactive oxygen species (ROS) in the pathology of traumatic brain injury (TBI). Caffeic acid phenethyl ester (CAPE) has been shown to exert both antioxidant and anti-inflammatory effects. The primary objective of the present study was to examine if CAPE could be used to reduce some of the pathological consequences of TBI using rodent models. Male Sprague-Dawley rats and C57BL/6 mice were subjected to controlled cortical impact (CCI) injury. Blood-brain barrier (BBB) integrity was assessed by examining claudin-5 expression and the extravasation of Evans blue dye. The effect of post-injury CAPE administration on neurobehavioral function was assessed using vestibulomotor, motor, and two hippocampus-dependent learning and memory tasks. We report that post-TBI administration of CAPE reduces Evans blue extravasation both in rats and mice. This improvement was associated with preservation of the levels of the tight junction protein claudin-5. CAPE treatment did not improve performance in either vestibulomotor/motor function (tested using beam balance and foot-fault tests), or in learning and memory function (tested using the Morris water maze and associative fear memory tasks). However, animals treated with CAPE were found to have significantly less cortical tissue loss than vehicle-treated controls. These findings suggest that CAPE may provide benefit in the treatment of vascular compromise following central nervous system injury.

Knockout of 5-lipoxygenase results in age-dependent anxiety-like behavior in female mice

Background

The enzyme 5-lipoxygenase (5LO) has been implicated in a variety of neurological and psychiatric disorders including anxiety. Knockout of 5LO has previously been shown to alter anxiety-like behavior in mice at a young age but the effect of 5LO knockout on older animals has not been characterized.

Methodology/Principal Findings

Here we used the elevated plus maze behavioral paradigm to measure anxiety-like behavior in female mice lacking 5LO (5LO-KO) at three different ages. Adolescent 5LO-KO animals did not significantly differ from wild-type (WT) animals in anxiety-like behavior. However, adult and older mice exhibited increased anxiety-like behavior compared to WT controls.

Conclusions

These results indicate that 5LO plays a role in the development of the anxiety-like phenotype in an age-dependent manner in female mice. Future work should further investigate this interaction as 5LO may prove to be an important molecular target for the development of novel anxiolytic therapies.

Phenidone protects the nigral dopaminergic neurons from LPS-induced neurotoxicity

Anti-inflammatory drugs such as ibuprofen appear to prevent the development of Parkinson's disease (PD); however, long-term use has undesirable side-effects. A new strategy for anti-inflammatory drug therapy is using a dual inhibitor of COX and lipooxygenase (LOX). Here, we compared the dopaminergic neuroprotective property of phenidone (a dual COX and LOX inhibitor) with COX or LOX inhibitors including SC-560 (a COX-1 inhibitor), aspirin (a COX-1/2 inhibitor), meloxicam (a preferential COX-2 inhibitor), caffeic acid (a 5-LOX inhibitor), and esculetin (a 5, 12-LOX inhibitor) in our lipopolysaccharide (LPS)-induced PD animal model. Our results show that COX-2 and 5-LOX play a major role in LPS-induced dopaminergic neurotoxicity, as meloxicam and phenidone attenuated LPS-induced oxidative stress and meloxicam, phenidone, and caffeic acid attenuated dopaminergic neurodegeneration, while SC-560, aspirin, and esculetin did not. In addition, phenidone was superior in attenuating LPS-induced dopaminergic neurodegeneration and microglia activation, probably as a result of dual inhibition of COX-2 and LOX. Therefore, dual inhibition of COX and LOX with phenidone represents a promising new candidate for anti-inflammatory drug therapy, and may provide a novel therapeutic approach for inflammation-related neurodegenerative diseases including PD.

Neurotoxicity of prion peptides on cultured cerebellar neurons

Prion peptide (PrP) neurotoxicity has been modelled in vitro by using synthetic peptides derived from the PrP(C) sequence. The major region of neurotoxicity has been localized to the hydrophobic domain located in the middle of the PrP sequence. The neurotoxicity assays are typically performed on cultured mouse cerebellar neurons derived from neonatal pups, and viability can be monitored by a variety of assays, including MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium); MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) lactate dehydrogenase release; and apoptotic assays. These neurotoxicity studies have been useful in identifying cofactors, such as PrP(C) and metals as modulators of PrP peptide-mediated neurotoxicity. Given the biosafety issues associated with handling and purifying infectious prions, the use of synthetic peptides that display a dependence upon PrP(C) expression for toxicity, as per the PrP(Sc) agent for infectivity, supports the relevance of using these synthetic peptides for understanding PrP-mediated neurotoxicity.

Neuronal apoptosis in neurodegeneration

Apoptosis mediates the precise and programmed natural death of neurons and is a physiologically important process in neurogenesis during maturation of the central nervous system. However, premature apoptosis and/or an aberration in apoptosis regulation is implicated in the pathogenesis of neurodegeneration, a multifaceted process that leads to various chronic disease states, such as Alzheimer's (AD), Parkinson's (PD), Huntington's (HD) diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and diabetic encephalopathy. The current review focuses on two major areas (a) the fundamentals of apoptosis, which includes elements of the apoptotic machinery, apoptosis inducers, and emerging concepts in apoptosis research, and (b) apoptotic involvement in neurodegenerative disorders, neuroprotective treatment strategies/modalities, and the mechanisms of, and signaling in, neuronal apoptosis. Current and new experimental models for apoptosis research in neurodegenerative diseases are also discussed.

Interactions between neural membrane glycerophospholipid and sphingolipid mediators: A recipe for neural cell survival or suicide

The neural membranes contain phospholipids, sphingolipids, cholesterol, and proteins. Glycerophospholipids and sphingolipids are precursors for lipid mediators involved in signal transduction processes. Degradation of glycerophospholipids by phospholipase A(2) (PLA(2)) generates arachidonic acid (AA) and docosahexaenoic acids (DHA). Arachidonic acid is metabolized to eicosanoids and DHA is metabolized to docosanoids. The catabolism of glycosphingolipids generates ceramide, ceramide 1-phosphate, sphingosine, and sphingosine 1-phosphate. These metabolites modulate PLA(2) activity. Arachidonic acid, a product derived from glycerophospholipid catabolism by PLA(2), modulates sphingomyelinase (SMase), the enzyme that generates ceramide and phosphocholine. Furthermore, sphingosine 1-phosphate modulates cyclooxygenase, an enzyme responsible for eicosanoid production in brain. This suggests that an interplay and cross talk occurs between lipid mediators of glycerophospholipid and glycosphingolipid metabolism in brain tissue. This interplay between metabolites of glycerophospholipid and sphingolipid metabolism may play an important role in initiation and maintenance of oxidative stress associated with neurologic disorders as well as in neural cell proliferation, differentiation, and apoptosis. Recent studies indicate that PLA(2) and SMase inhibitors can be used as neuroprotective and anti-apoptotic agents. Development of novel inhibitors of PLA(2) and SMase may be useful for the treatment of oxidative stress, and apoptosis associated with neurologic disorders such as stroke, Alzheimer disease, Parkinson disease, and head and spinal cord injuries.

Perturbation of endoplasmic reticulum homeostasis facilitates prion replication

Prion diseases are fatal and infectious neurodegenerative disorders characterized by the accumulation of an abnormally folded form of the prion protein (PrP), termed PrP(Sc). Prion replication triggers endoplasmic reticulum (ER) stress, neuronal dysfunction, and apoptosis. In this study we analyze the effect of perturbations in ER homeostasis on PrP biochemical properties and prion replication. ER stress led to the generation of a mis-folded PrP isoform, which is detergent-insoluble and protease-sensitive. To understand the mechanism by which ER stress generates PrP misfolding, we assessed the contribution of different signaling pathways implicated in the unfolded protein response. Expression of a dominant negative form of IRE1 alpha or XBP-1 significantly increased PrP aggregation, whereas overexpression of ATF4 or an active mutant form of XBP-1 and ATF6 had the opposite affect. Analysis of prion replication in vitro revealed that the PrP isoform generated after ER stress is more efficiently converted into PrP(Sc) compared with the protein extracted from untreated cells. These findings indicate that ER-damaged cells might be more susceptible to prion replication. Because PrP(Sc) induces ER stress, our data point to a vicious cycle accelerating prion replication, which may explain the rapid progression of the disease.

Inhibitors of brain phospholipase A2 activity: their neuropharmacological effects and therapeutic importance for the treatment of neurologic disorders

The phospholipase A(2) family includes secretory phospholipase A(2), cytosolic phospholipase A(2), plasmalogen-selective phospholipase A(2), and calcium-independent phospholipase A(2). It is generally thought that the release of arachidonic acid by cytosolic phospholipase A(2) is the rate-limiting step in the generation of eicosanoids and platelet activating factor. These lipid mediators play critical roles in the initiation and modulation of inflammation and oxidative stress. Neurological disorders, such as ischemia, spinal cord injury, Alzheimer's disease, multiple sclerosis, prion diseases, and epilepsy are characterized by inflammatory reactions, oxidative stress, altered phospholipid metabolism, accumulation of lipid peroxides, and increased phospholipase A(2) activity. Increased activities of phospholipases A(2) and generation of lipid mediators may be involved in oxidative stress and neuroinflammation associated with the above neurological disorders. Several phospholipase A(2) inhibitors have been recently discovered and used for the treatment of ischemia and other neurological diseases in cell culture and animal models. At this time very little is known about in vivo neurochemical effects, mechanism of action, or toxicity of phospholipase A(2) inhibitors in human or animal models of neurological disorders. In kainic acid-mediated neurotoxicity, the activities of phospholipase A(2) isoforms and their immunoreactivities are markedly increased and phospholipase A(2) inhibitors, quinacrine and chloroquine, arachidonyl trifluoromethyl ketone, bromoenol lactone, cytidine 5-diphosphoamines, and vitamin E, not only inhibit phospholipase A(2) activity and immunoreactivity but also prevent neurodegeneration, suggesting that phospholipase A(2) is involved in the neurodegenerative process. This also suggests that phospholipase A(2) inhibitors can be used as neuroprotectants and anti-inflammatory agents against neurodegenerative processes in neurodegenerative diseases.

Caffeic acid attenuates neuronal damage, astrogliosis and glial scar formation in mouse brain with cryoinjury

Traumatic brain injury induces neuron damage in early phase, and astrogliosis and the formation of the glial scar in late phase. Caffeic acid (3, 4-dihydroxycinnamic acid), one of the natural phenolic compounds, exerts neuroprotective effects against ischemic brain injuries with anti-oxidant and anti-inflammatory properties, and by scavenging reactive species. However, whether caffeic acid has protective effects against traumatic brain injury is unknown. Therefore, we determined the effect of caffeic acid on the lesion in the early (1 day) and late phases (7 to 28 days) of cryoinjury in mice. We found that caffeic acid (10 and 50 mg/kg, i.p., for 7 days after cryoinjury) reduced the lesion area and attenuated the neuron loss around the lesion core 1 to 28 days, but attenuated the neuron loss in the lesion core only 1 day after cryoinjury. Moreover, caffeic acid attenuated astrocyte proliferation, glial scar wall formation and glial fibrillary acidic protein (GFAP) protein expression in the late phase of cryoinjury (7 to 28 days). Caffeic acid also inhibited the reduction of superoxide dismutase activity and the increase in malondialdehyde content in the brain 1 day after cryoinjury. These results indicate that caffeic acid exerts a protective effect in traumatic brain injury, especially on glial scar formation in the late phase, which at least is associated with its anti-oxidant ability.

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.

Expression patterns of 5-lipoxygenase in human brain with traumatic injury and astrocytoma

5-Lipoxygenase (5-LOX) is a key enzyme in the metabolism of arachidonic acid to leukotrienes. The levels of leukotrienes increase after brain injury and when tumors are present. It has been reported that 5-LOX is widely expressed in the brain and that 5-LOX inhibition provides neuroprotection. However, there is still no information available for the expression patterns of 5-LOX in human brain following trauma or with astrocytomas. We investigated its expression patterns by immunohistochemistry. We found that 5-LOX is normally expressed in neurons and glial cells. In neurons, it was expressed in two patterns: in the cytosol and nucleus or only in the cytosol. In traumatic brain injury, 5-LOX expression increased in glial cells and neutrophils. Double-labeling immunohistochemistry showed that part of the 5-LOX-positive glial cells were GFAP positive. No 5-LOX expression was found in brain microvessel endothelia, except in the regenerated endothelia of a patient 8 days following brain trauma. Furthermore, 5-LOX expression increased and showed a granular pattern in high-grade (grade III/IV) astrocytoma. These results indicate that 5-LOX has multiple expression patterns, and can be induced by brain injury, which implies that 5-LOX might have pathophysiological roles in the human brain.

ONO-1078 reduces NMDA-induced brain injury and vascular cell adhesion molecule-1 expression in rats

AIM

To determine whether ONO-1078 (pranlukast), a potent cysteinyl leukotriene receptor 1 (CysLT1) antagonist, has an effect on N-methyl-D-aspartate (NMDA)-induced brain injury and vascular cell adhesion molecule-1 (VCAM-1) expression in rats.

METHODS

Brain injury was induced by direct microinjection of NMDA (0.3 mumol in 1 muL of sterile 0.1 mol/L PBS, pH 7.4) into the cerebral cortex. The lesion volume (area), brain edema and neuron density were assessed by an image analyzer and the expression of VCAM-1 in the cortex was detected by Western blot 24 h after NMDA injection. ONO-1078 (0.03, 0.1, or 0.3 mg/kg) and edaravone (MCI-186, 10 mg/kg), a neuroprotective agent, were ip injected 30 min before and after NMDA injection.

RESULTS

NMDA microinjection produced well-defined focal lesions dose- and time-dependently. ONO-1078 (0.1, 0.3 mg/kg) and edaravone (10 mg/kg) decreased the total lesion volume, lesion area and brain edema induced by NMDA. Furthermore, ONO-1078 (0.1, 0.3 mg/kg) significantly inhibited the enhanced expression of VCAM-1 in the injured cortices, but edaravone did not have this effect.

CONCLUSION

CysLT1 receptor antagonist ONO-1078 attenuates NMDA-induced brain damage in rats, and this might relate to the attenuation of NMDA receptor-dependent neurotoxicity and the inhibition of the upregulation of VCAM-1 expression.

The neurotoxicity of prion protein (PrP) peptide 106–126 is independent of the expression level of PrP and is not mediated by abnormal PrP species

A synthetic peptide homologous to region 106-126 of the prion protein (PrP) is toxic to cells expressing PrP, but not to PrP knockout neurons, arguing for a specific role of PrP in mediating the peptide's activity. Whether this is related to a gain of toxicity or a loss of function of PrP is not clear. We explored the possibility that PrP106-126 triggered formation of PrP(Sc) or other neurotoxic PrP species. We found that PrP106-126 did not induce detergent-insoluble and protease-resistant PrP, nor did it alter its membrane topology or cellular distribution. We also found that neurons expressing endogenous or higher level of either wild-type PrP or a nine-octapeptide insertional mutant were equally susceptible to PrP106-126, and that sub-physiological PrP expression was sufficient to restore vulnerability to the peptide. These results indicate that PrP106-126 interferes with a PrP function that requires only low protein levels, and is not impaired by a pathogenic insertion in the octapeptide region.

Blockade of 12-lipoxygenase expression protects cortical neurons from apoptosis induced by β-amyloid peptide

The cyclo-oxygenase (COX) and lipoxygenase (LOX) pathways belong to the eicosanoid synthesis pathway, a major component of the chronic inflammatory process occurring in Alzheimer's disease (AD). Clinical studies reported beneficial effects of COX inhibitors, but little is known about the involvement of LOXs in AD pathogenesis. beta-amyloid peptide (A beta) accumulation contributes to neurodegeneration in AD, but mechanisms underlying A beta toxicity have not been fully elucidated yet. Here, using an antisense oligonucleotide-based strategy, we show that blockade of 12-LOX expression prevents both A beta-induced apoptosis and overexpression of c-Jun, a factor required for the apoptotic process, in cortical neurons. Conversely, the 12-LOX metabolite, 12(S)-HETE (12(S)-hydroxy-(5Z, 8Z, 10E, 14Z)-eicosatetraenoic acid), promoted c-Jun-dependent apoptosis. Specificity of the 12-LOX involvement was further supported by the observed lack of contribution of 5-LOX in this process. These data indicate that blockade of 12-LOX expression disrupts a c-Jun-dependent apoptosis pathway, and suggest that 12-LOX may represent a new target for the treatment of AD.

Astrocytic regulation of NMDA receptor subunit composition modulates the toxicity of prion peptide PrP106–126

Prion diseases are neurodegenerative conditions. The main pathological alterations common to these diseases include the loss of neurones, gliosis and the deposition of an abnormal isoform of the prion protein in aggregates in the nervous tissue. Prevention of the devastating effects of prion disease requires prevention of neuronal death. Therefore, understanding the mechanism by which this occurs is essential. Cell culture studies using the synthetic peptide PrP106-126 have been central to developing a model of this mechanism. Using a coculture system, we have shown that PrP106-126 caused neuronal death mediated by glutamate. This neuronal death resulted from modification of the expression of NMDA receptor subtypes stimulated by the exposure of neurones to the combination of astrocytic factors, elevated Cu and PrP106-126. The results of these experiments suggest neuronal death in prion disease might be reduced by the use of NMDA receptor antagonists such as MK801 or inhibitors of the arachidonic acid metabolism pathway.

Channels formed with a mutant prion protein PrP(82-146) homologous to a 7-kDa fragment in diseased brain of GSS patients

A major prion protein (PrP) mutant that forms amyloid fibrils in the diseased brain of patients with Gerstmann-Sträussler-Scheinker syndrome (GSS) is a fragment of 7 kDa spanning from residues 81-82 to 144-153 of PrP. Analysis of ionic membrane currents, recorded with a lipid bilayer technique, revealed that the wild-type fragment PrP(82-146) WT and the partially scrambled PrP(82-146) (127-146) SC are capable of forming heterogeneous ion channels that are similar to those channels formed with PrP(106-126). In contrast, PrP(82-146) peptides in which the region from residue 106 to 126 had been scrambled (SC) showed a reduction in interaction with lipid membranes and did not form channels. The PrP(82-146) WT- and PrP(82-146) (127-146) SC-formed cation channels with fast kinetics are Cu2+ sensitive and rifampicin (RIF) insensitive, whereas the time-dependent inactivating channels formed by these same peptides are both Cu2+ and RIF insensitive. The presence of RIF in the solution before the addition of PrP(82-146) WT or PrP(82-146) (127-146) SC affected their incorporation into the lipid bilayers. PrP(82-146) WT and PrP(82-146) (127-146) SC fast cation channels formed in the presence of RIF appeared in an electrically semisilent state or an inactivated state. Increasing [Cd2+]cis enhanced the incorporation of PrP(82-146) WT and PrP(82-146) (127-146) SC channels formed in the presence of RIF. We conclude that the major PrP mutant fragment in the diseased brain of GSS patients is prone to form channels in neuronal membranes, causing their dysfunction. We propose that Cd2+ may accentuate the neurotoxicity of this channel-forming PrP fragment by enhancing its incorporation into the membrane.

Copper modulation of ion channels of PrP[106-126] mutant prion peptide fragments

We have shown previously that the protease-resistant and neurotoxic prion peptide fragment PrP[106-126] of human PrP incorporates into lipid bilayer membranes to form heterogeneous ion channels, one of which is a Cu(2+)-sensitive fast cation channel. To investigate the role of PrP[106-126]'s hydrophobic core, AGAAAAGA, on its ability to form ion channels and their regulation with Cu(2+), we used the lipid-bilayer technique to examine membrane currents induced as a result of PrP[106-126] (AA/SS) and PrP[106-126] (VVAA/SSSS) interaction with lipid membranes and channel formation. Channel analysis of the mutant (VVAAA/SSS), which has a reduced hydrophobicity due to substitution of hydrophobic residues with the hydrophilic serine residue, showed a significant change in channel activity, which reflects a decrease in the beta-sheet structure, as shown by CD spectroscopy. One of the channels formed by the PrP[106-126] mutant has fast kinetics with three modes: burst, open and spike. The biophysical properties of this channel are similar to those of channels formed with other aggregation-prone amyloids, indicating their ability to form the common beta sheet-based channel structure. The current-voltage (I-V) relationship of the fast cation channel, which had a reversal potential, E(rev), between -40 and -10 mV, close to the equilibrium potential for K(+) ( E(K) = -35 mV), exhibited a sigmoidal shape. The value of the maximal slope conductance (g(max)) was 58 pS at positive potentials between 0 and 140 mV. Cu(2+) shifted the kinetics of the channel from being in the open and "burst" states to the spike mode. Cu(2+) reduced the probability of the channel being open (P(o)) and the mean open time (T(o)) and increased the channel's opening frequency (F(o)) and the mean closed time (T(c)) at a membrane potential ( V(m)) between +20 and + 140 mV. The fact that Cu(2+) induced changes in the kinetics of this channel with no changes in its conductance, indicates that Cu(2+) binds at the mouth of the channel via a fast channel block mechanism. The Cu(2+)-induced changes in the kinetic parameters of this channel suggest that the hydrophobic core is not a ligand Cu(2+) site, and they are in agreement with the suggestion that the Cu(2+)-binding site is located at M(109) and H(111) of this prion fragment. Although the data indicate that the hydrophobic core sequence plays a role in PrP[106-126] channel formation, it is not a binding site for Cu(2+). We suggest that the role of the hydrophobic region in modulating PrP toxicity is to influence PrP assembly into neurotoxic channel conformations. Such conformations may underlie toxicity observed in prion diseases. We further suggest that the conversions of the normal cellular isoform of prion protein (PrP(c)) to abnormal scrapie isoform (PrP(Sc)) and intermediates represent conversions to protease-resistant neurotoxic channel conformations.

Cyclo-oxygenase inhibitors protect against prion-induced neurotoxicity in vitro

The mechanisms of neuronal loss during the course of the prion diseases are not fully understood. In this study, neurones treated with certain non-steroidal anti-inflammatory drugs (NSAIDs) were protected against the otherwise toxic effects of a peptide derived from the prion protein, or extracts containing infectious prions (PrP ). These NSAIDs inhibit the cyclo-oxygenase (cox) enzymes that metabolise arachidonic acid to prostaglandins (PG). Conversely, drugs that inhibited the metabolism of arachidonic acid to leucotrienes enhanced neurotoxicity. Studies with selective inhibitors highlighted the importance of the cox-1 isoform in prion-induced neurotoxicity. The cox-1 inhibitors also inhibited neuronal PGE production and protected both neuroblastoma cells and primary cortical neurones against prions. They also reduced microglia-mediated killing of prion-treated neurones.

Mayhem of the multiple mechanisms: modelling neurodegeneration in prion disease

This review examines recent attempts to advance the understanding of the mechanism by which neurones die in prion disease. Prion diseases or transmissible spongiform encephalopathies are characterized by the conversion of a normal glycoprotein, the prion protein, to a protease-resistant form that is suggested to be both the infectious agent and the cause of the rapid neurodegeneration in the disease. Death of the patient results from this widespread neuronal loss. Thus understanding the mechanism by which the abnormal form of the prion protein causes neuronal death might lead to treatments that would prevent the life-threatening nature of these diseases.

Oxidative nerve cell death in Alzheimer's disease and stroke: antioxidants as neuroprotective compounds

Many neurodegenerative disorders and syndromes are associated with an excessive generation of reactive oxygen species (ROS) and oxidative stress. The pathways to nerve cell death induced by diverse potential neurotoxins such as peptides, excitatory amino acids, cytokines or synthetic drugs commonly share oxidative downstream processes, which can cause either an acute oxidative destruction or activate secondary events leading to apoptosis. The pathophysiological role of ROS has been intensively studied in in vitro and in vivo models of chronic neurodegenerative diseases such as Alzheimer's disease (AD) and of syndromes associated with rapid nerve cell loss as occuring in stroke. In AD, oxidative neuronal cell dysfunction and cell death caused by protofibrils and aggregates of the AD-associated amyloid beta protein (Abeta) may causally contribute to pathogenesis and progression. ROS and reactive nitrogen species also take part in the complex cascade of events and the detrimental effects occuring during ischemia and reperfusion in stroke. Direct antioxidants such as chain-breaking free radical scavengers can prevent oxidative nerve cell death. Although there is ample experimental evidence demonstrating neuroprotective activities of direct antioxidants in vitro, the clinical evidence for antioxidant compounds to act as protective drugs is relatively scarce. Here, the neuroprotective potential of antioxidant phenolic structures including alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) in vitro is summarized. In addition, the antioxidant and cytoprotective activities of lipophilic tyrosine- and tryptophan-containing structures are discussed. Finally, an outlook is given on the neuroprotective potential of aromatic amines and imines, which may comprise novel lead structures for antioxidant drug design.