Phospholipases as mediators of amyloid beta peptide neurotoxicity: an early event contributing to neurodegeneration characteristic of Alzheimer's disease

Neural excitotoxicity and the toxic mechanism induced by acute hypoxia in Chinese mitten crab (Eriocheir sinensis)

Hypoxia can induce neural excitotoxicity in mammals, but this adverse effect has not been investigated in aquatic animals to date, especially in crustaceans. This study explored the induction effect and toxic mechanism of acute hypoxia stress (1.0 ± 0.1 mg dissolved oxygen /L) for 24 h on neural excitotoxicity in juvenile Chinese mitten crab, Eriocheir sinensis. The results showed that hemolymph glucose and serum lactic acid content were significantly increased, and the mRNA expression of crustacean hyperglycemic hormone and hypoxia-inducible factor 1α were significantly up-regulated in the hypoxia group compared with control. RNA-Seq results confirmed that acute hypoxia stress had a more significant impact on carbohydrate metabolism than lipid and protein metabolism. In addition, the TUNEL assay showed that the apoptosis rate of nerve cells was significantly higher in the hypoxia group than in the control, and similar trends were observed in the expression of apoptosis-related genes. RNA-Seq results also showed that acute hypoxia stress-induced neuronal apoptosis by regulating multiple apoptosis-related pathways. Moreover, free glutamate and GABA contents in the nerve tissue of thoracic ganglia were significantly higher in the hypoxia group than in the control group. Furthermore, the mRNA expression of NMDA related receptors was significantly up-regulated in the hypoxia group compared with the control. Similar trends were observed in the expression of calcium-dependent degrading enzymes and endogenous antioxidant-related proteins or enzymes. Meanwhile, the mRNA expression level of high-affinity neuronal glutamate transporter in the hypoxia group was significantly up-regulated compared with the control, whereas the vesicular glutamate transporter was significantly down-regulated. Furthermore, NMDA-R antagonists (MK-801 and Ro25-6981) injection showed that NMDA-R served as the bridge and core position of glutamate-induced neural neurotoxicity. This study provides a new perspective and theoretical guidance for exploring the regulation of hypoxic tolerance in E. sinensis.

APOE alters glucose flux through central carbon pathways in astrocytes

The Apolipoprotein E (APOE) gene is a major genetic risk factor associated with Alzheimer's disease (AD). APOE encodes for three main isoforms in humans (E2, E3, and E4). Homozygous E4 individuals have more than a 10-fold higher risk for developing late-onset AD, while E2 carriers are protected. A hallmark of AD is a reduction in cerebral glucose metabolism, alluding to a strong metabolic component in disease onset and progression. Interestingly, E4 individuals display a similar regional pattern of cerebral glucose hypometabolism decades prior to disease onset. Mapping this metabolic landscape may help elucidate the underlying biological mechanism of APOE-associated risk for AD. Efficient metabolic coupling of neurons and glia is necessary for proper neuronal function, and disruption in glial energy distribution has been proposed to contribute to neuronal cell death and AD pathology. One important function of astrocytes - canonically the primary source of apolipoprotein E in the brain - is to provide metabolic substrates (lactate, lipids, amino acids and neurotransmitters) to neurons. Here we investigate the effects of APOE on astrocyte glucose metabolism in vitro utilizing scintillation proximity assays, stable isotope tracer metabolomics, and gene expression analyses. Glucose uptake is impaired in E4 astrocytes relative to E2 or E3 with specific alterations in central carbon metabolism. Using stable isotope labeled glucose [U-¹³C] allowed analyses of astrocyte-specific deep metabolic networks affected by APOE, and provided insight to the effects downstream of glucose uptake. Enrichment of ¹³C in early steps of glycolysis was lowest in E4 astrocytes (highest in E2), while synthesis of lactate from glucose was highest in E4 astrocytes (lowest in E2). We observed an increase in glucose flux through the pentose phosphate pathway (PPP), with downstream increases in gluconeogenesis, lipid, and de novo nucleotide biosynthesis in E4 astrocytes. There was also a marked increase in ¹³C enrichment in the TCA cycle of E4 astrocytes - whose substrates were also incorporated into biosynthetic pathways at a higher rate. Pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH) are the two main enzymes controlling pyruvate entry to the TCA cycle. PC gene expression is increased in E4 astrocytes and the activity relative to PDH was also increased, compared to E2 or E3. Decreased enrichment in the TCA cycle of E2 and E3 astrocytes is suggestive of increased oxidation and non-glucose derived anaplerosis, which could be fueling mitochondrial ATP production. Conversely, E4 astrocytes appear to increase carbon flux into the TCA cycle to fuel cataplerosis. Together, these data demonstrate clear APOE isoform-specific effects on glucose utilization in astrocytes, including E4-associated increases in lactate synthesis, PPP flux, and de novo biosynthesis pathways.

New Users of Herbal Medicine Containing Aristolochic Acids and the Risk of Dementia in the Elderly: A Nationwide, Population-Based Study in Taiwan

BACKGROUND

Herbal medicine containing aristolochic acids (HMCAA) was used for inflammatory and infectious diseases. This study aimed to investigate the association between the usage of HMCAA and the risk of dementia.

METHODS

A total of 199 new users of HMCAA were enrolled, along with 597 controls without the usage of HMCAA, at a ratio of 1:3 - matched by age, sex, and comorbidity, between 2000 and 2003 - from the National Health Research Institutes Database (NHRID) of Taiwan, which contains two million randomly sampled subjects, in this cohort study. We used Fine and Gray's survival analysis (competing with mortality) to compare the risk of developing dementia during a 15-year follow-up period (2000-2015).

RESULTS

In general, HMCAA was not significantly associated with dementia (adjusted subdistribution hazard ratio [SHR] = 0.861, 95% confidence interval [CI] = 0.484-1.532, p = 0.611) for the HMCAA-cohort, although differential risk was observed among the groups at risk. The patients with usage of HMCAA aged ≧ 85 years were associated with a higher risk in dementia (adjusted SHR: 6.243, 95% CI=1.258-21.084, p = 0.001), in comparison to those aged 50-54 years. Furthermore, the patients with usage of HMCAA that had cerebrovascular accidents were associated with an increased risk of dementia.

CONCLUSION

The usage of HMCAA was associated with the risk of developing dementia in the patients aged ≧ 85 years.

Mammalian phospholipase D: Function, and therapeutics

Despite being discovered over 60 years ago, the precise role of phospholipase D (PLD) is still being elucidated. PLD enzymes catalyze the hydrolysis of the phosphodiester bond of glycerophospholipids producing phosphatidic acid and the free headgroup. PLD family members are found in organisms ranging from viruses, and bacteria to plants, and mammals. They display a range of substrate specificities, are regulated by a diverse range of molecules, and have been implicated in a broad range of cellular processes including receptor signaling, cytoskeletal regulation and membrane trafficking. Recent technological advances including: the development of PLD knockout mice, isoform-specific antibodies, and specific inhibitors are finally permitting a thorough analysis of the in vivo role of mammalian PLDs. These studies are facilitating increased recognition of PLD's role in disease states including cancers and Alzheimer's disease, offering potential as a target for therapeutic intervention.

Effects of Acetylcholine on β-Amyloid-Induced cPLA2 Activation in the TB Neuroectodermal Cell Line: Implications for the Pathogenesis of Alzheimer's Disease

The role of β-amyloid (Aβ) in the pathogenesis of Alzheimer's disease (AD) is still considered crucial. The state of Aβ aggregation is critical in promoting neuronal loss and neuronal function impairment. Recently, we demonstrated that Acetylcholine (ACh) is neuroprotective against the toxic effects of Aβ in the cholinergic LAN-2 cells. In biophysical experiments, ACh promotes the soluble Aβ peptide conformation rather than the aggregation-prone β-sheet conformation. In order to better understand the biological role of ACh in AD, we studied the effect of Aβ on the phosphorylation of the cytosolic phospholipase A2 (cPLA2) in the TB neuroectodermal cell line, which differentiates toward a neuronal phenotype when cultured in the presence of retinoic acid (RA). We chose the phosphorylated form of cPLA2 (Ser505, Phospho-cPLA2) as a biomarker to test the influence of ACh on the effects of Aβ in both undifferentiated and RA-differentiated TB cells. Our results show that TB cells are responsive to Aβ. Moreover, in undifferentiated cells 1 h treatment with Aβ induces a 2.5-fold increase of the Phospho-cPLA2 level compared to the control after 24 h in vitro, while no significant difference is observed between Aβ-treated and non-treated cells after 4 and 7 days in vitro. The RA-differentiated cells are not sensitive to Aβ. In TB cell line ACh is able to blunt the effects of Aβ. The ability of ACh to protect non-cholinergic cells against Aβ reinforces the hypothesis that, in addition to its role in cholinergic transmission, ACh could also act as a neuroprotective agent.

Phospholipase A₂-Generated Lipid Mediators in the Brain: The Good, the Bad, and the Ugly

Phospholipase A2 (PLA2) generates arachidonic acid, docosahexaenoic acid, and lysophospholipids from neural membrane phospholipids. These metabolites have a variety of physiological effects by themselves and also are substrates for the synthesis of more potent lipid mediators such as eicosanoids, platelet activating factor, and 4-hydroxynonenal (4-HNE). At low concentrations, these mediators act as second messengers. They affect and modulate several cell functions, including signal transduction, gene expression, and cell proliferation, but at high concentrations, these lipid mediators cause neurotoxicity. Among the metabolites generated by PLA2, 4-HNE is the most cytotoxic metabolite and is associated with the apoptotic type of neural cell death. Levels of 4-HNE are markedly increased in neurological disorders such as Alzheimer disease, Parkinson disease, ischemia, spinal cord trauma, and head injury. The purpose of this review is to summarize and integrate the vast literature on metabolites generated by PLA2 for a wider audience. The authors hope that this discussion will jump-start more studies not only on the involvement of PLA2 in neurological disorders but also on the importance of PLA2-generated lipid mediators in physiological and pathological processes.

Lipid metabolism in Alzheimer's disease

Lipids play crucial roles in cell signaling and various physiological processes, especially in the brain. Impaired lipid metabolism in the brain has been implicated in neurodegenerative diseases, such as Alzheimer's disease (AD), and other central nervous system insults. The brain contains thousands of lipid species, but the complex lipid compositional diversity and the function of each of lipid species are currently poorly understood. This review integrates current knowledge about major lipid changes with the molecular mechanisms that underlie AD pathogenesis.

The dark sides of amyloid in Alzheimer's disease pathogenesis

Although widely explored, the pathogenesis of Alzheimer's disease (AD) has yet to be cleared. Over the past twenty years the so call amyloid cascade hypothesis represented the main research paradigm in AD pathogenesis. In spite of its large consensus, the proposed role of β-amyloid (Aβ) remain to be elucidated. Many evidences are starting to cast doubt on Aβ as the primary causative factor in AD. For instance, Aβ is deposited in the brain following many different kinds of injury. Also, concentration of Aβ needed to induce toxicity in vitro are never reached in vivo. In this review we propose an amyloid-independent interpretation of several AD pathogenic features, such as synaptic plasticity, endo-lysosomal trafficking, cell cycle regulation and neuronal survival.

Phospholipase d2 ablation ameliorates Alzheimer's disease-linked synaptic dysfunction and cognitive deficits

Growing evidence implicates aberrant lipid signaling in Alzheimer's disease (AD). While phospholipases A2 and C have been recently shown to mediate key actions of amyloid β-peptide (Aβ) through a dysregulation of arachidonic acid and phosphatidylinositol-4,5-bisphosphate metabolism, respectively, the role of phospholipase D (PLD) has so far remained elusive. PLD produces phosphatidic acid (PA), a bioactive lipid involved in multiple aspects of cell physiology, including signaling and membrane trafficking processes. Here we show that oligomeric Aβ enhances PLD activity in cultured neurons and that this stimulatory effect does not occur upon ablation of PLD2 via gene targeting. Aβ fails to suppress long-term potentiation in PLD2-deficient hippocampal slices, suggesting that PLD2 is required for the synaptotoxic action of this peptide. In vivo PLD activity, as assessed by detection of phosphatidylethanol levels using mass spectrometry (MS) following ethanol injection, is also increased in the brain of a transgenic mouse model of AD (SwAPP). Furthermore, Pld2 ablation rescues memory deficits and confers synaptic protection in SwAPP mice despite a significant Aβ load. MS-based lipid analysis of Pld2 mutant brains in the presence or absence of the SwAPP transgene unmasks striking crosstalks between different PA species. This lipid analysis shows an exquisite acyl chain specificity and plasticity in the perturbation of PA metabolism. Collectively, our results point to specific molecular species of PA as key modulators of AD pathogenesis and identify PLD2 as a novel potential target for therapeutics.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.

MR spectroscopy, functional MRI, and diffusion-tensor imaging in the aging brain: a conceptual review

In vivo magnetic resonance spectroscopy (MRS), functional magnetic resonance imaging (fMRI), and diffusion-tensor imaging (DTI) have recently opened new possibilities for noninvasively assessing the metabolic, functional, and connectivity correlates of aging in research and clinical settings. The purpose of this article is to provide a conceptual review intended for a multidisciplinary audience, covering physical principles and main findings related to normal aging and senile cognitive impairment. This article is divided into 3 sections, dedicated to MRS, to fMRI, and to DTI. The spectroscopy section surveys physiological function of the observable metabolites, concentration changes in normal aging and their interpretation, and correlation with cognitive performance. The functional MRI section surveys the hemispheric asymmetry reduction model from compensation and de-differentiation viewpoints, memory encoding, retrieval and consolidation, inhibitory control, perception and action, resting-state networks, and functional deactivations. The DTI section surveys age-related changes, correlation with behavioral scores, and transition to cognitive impairment.

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.

Phospholipase D1 is up-regulated in the mitochondrial fraction from the brains of Alzheimer's disease patients

Mitochondrial dysfunction may play an important role in sporadic Alzheimer's disease (AD) progression. Recently, we have reported that amyloid precursor protein (APP) stimulates phospholipase D (PLD) activity and beta-amyloid (Abeta) region of APP is involved in the interaction with PLD1. To elucidate the involvement of PLD in the pathophysiology of AD, we examined the expression of PLD1 and alteration of membrane phospholipid in mitochondrial membranes of control and AD brains using Western blot and phospholipid analysis by thin layer chromatography (TLC). We have found that protein expression of PLD1 was significantly increased in mitochondrial fraction of brains of AD patients compared with that in control brains. Furthermore, the concentration of mitochondrial phospholipids such as phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was increased and the content of phosphatidic acid (PA), a product of PLD activity, was up-regulated in the mitochondrial membrane fractions of AD brain compared with that of control brain. These results suggest that up-regulation of PLD1 in the mitochondrial fraction of AD brain might affect the composition of membrane phospholipids and provide a clue to the mechanism underlying the mitochondrial dysfunction associated with AD.

Phospholipase D1 is associated with amyloid precursor protein in Alzheimer's disease

Amyloid precursor protein (APP) is a widely expressed transmembrane protein of unknown function that is involved in the pathogenesis of Alzheimer's disease (AD). We investigated the involvement of phospholipase D (PLD) in the pathophysiology of AD. We showed dramatic upregulation of PLD1 immunoreactivity in reactive astroglial cells in brain tissue sections from authentic AD patients. Expression and activity of PLD1 were up-regulated in brain tissues from AD patients, especially caveolae membrane fraction, compared with those of control brains. Interestingly, PLD1 physically interacts and colocalizes with APP and caveolin-3. We found that APP was associated with the pleckstrin homology domain of PLD1, and the amyloid region of APP interacted with PLD. Elevated expression of APP stimulated PLD activity in human astroglioma cells. These results suggest that up-regulation of PLD might have a role in the neuronal pathology associated with AD.

Sex-dependent Actions of Amyloid Beta Peptides on Hippocampal Choline Carriers of Postnatal Rats

It is suggested that amyloid beta peptides (Abeta) play a role in the pathogenesis of Alzheimer disease but their physiological function is still unknown. However, low pM-nM concentrations mediate a hypofunction of a basal forebrain cholinergic system without marked signs of neurotoxicity. In this study, we compared in vitro effects of soluble nonaggregated human Abeta 1-40 and 1-42 either on synaptosomal hemicholinium-3 sensitive choline carriers or on membrane fluidity in hippocampi of male and female Wistar rats aged 7 and 14 days or 2-3 months. The results indicate age- and sex-dependent effects mediated by peptides at nM concentrations but no significant differences between both fragments. Namely, opposite actions were observed in 14-day (the increase in the choline uptake and membrane fluidity) when compared to 7-day old and adult males (the mild drops). Lineweaver-Burk plot analysis revealed that the enhancement of the high-affinity choline transport in 14-day old males occurs via alterations in K (M )and the change was accompanied by a mild increase in the specific binding of [3H]hemicholinium-3. On the other hand, no age-dependent differences were found in females. Rat Abeta 1-40 mediated similar effects on 14-day old rats as the corresponding human fragment. Moreover, higher levels of soluble peptides were detected in immature when compared to mature male brains by means of competitive ELISA. Our study indicates that Abeta could play a role in postnatal sexual differentiation of hippocampal cholinergic system.

Glycerophosphocholine is elevated in cerebrospinal fluid of Alzheimer patients

Experimental and clinical studies give evidence for breakdown of membrane phospholipids during neurodegeneration. In the present study, we measured the levels of glycerophosphocholine (GPCh), phosphocholine (PCh), and choline, that is, water-soluble metabolites of phosphatidylcholine (PtdCho), in human cerebrospinal fluid (CSF). Among 30 cognitively normal patients the average CSF levels of GPCh, phosphocholine and choline were 3.64, 1.28, and 1.93 microM, respectively; metabolite levels did not change with increasing age. When compared with age-matched controls, patients with Alzheimer's disease had elevated levels of all choline metabolites: GPCh was significantly increased by 76% (P<0.01), phosphocholine by 52% (P<0.05), and free choline (Ch) by 39%. Six patients with vascular dementia had lower choline and elevated phosphocholine levels, when compared to controls, but normal levels of GPCh. These data demonstrate that Alzheimer's disease is accompanied by an increased PtdCho hydrolysis in the brain. PtdCho breakdown seems to be mediated by phospholipase A2 and leads to significantly elevated levels of GPCh in CSF.

Retinoic acid-mediated phospholipase A2 signaling in the nucleus

Retinoic acid modulates a wide variety of biological processes including proliferation, differentiation, and apoptosis. It interacts with specific receptors in the nucleus, the retinoic acid receptors (RARs). The molecular mechanism by which retinoic acid mediates cellular differentiation and growth suppression in neural cells remains unknown. However, retinoic acid-induced release of arachidonic acid and its metabolites may play an important role in cell proliferation, differentiation, and apoptosis. In brain tissue, arachidonic acid is mainly released by the action of phospholipase A2 (PLA2) and phospholipase C (PLC)/diacylglycerol lipase pathways. We have used the model of differentiation in LA-N-1 cells induced by retinoic acid. The treatment of LA-N-1 cells with retinoic acid produces an increase in phospholipase A2 activity in the nuclear fraction. The pan retinoic acid receptor antagonist, BMS493, can prevent this increase in phospholipase A2 activity. This suggests that retinoic acid-induced stimulation of phospholipase A2 activity is a retinoic acid receptor-mediated process. LA-N-1 cell nuclei also have phospholipase C and phospholipase D (PLD) activities that are stimulated by retinoic acid. Selective phospholipase C and phospholipase D inhibitors block the stimulation of phospholipase C and phospholipase D activities. Thus, both direct and indirect mechanisms of arachidonic acid release exist in LA-N-1 cell nuclei. Arachidonic acid and its metabolites markedly affect the neurite outgrowth and neurotransmitter release in cells of neuronal and glial origin. We propose that retinoic acid receptors coupled with phospholipases A2, C and D in the nuclear membrane play an important role in the redistribution of arachidonic acid in neuronal and non-nuclear neuronal membranes during differentiation and growth suppression. Abnormal retinoid metabolism may be involved in the downstream transcriptional regulation of phospholipase A2-mediated signal transduction in schizophrenia and Alzheimer disease (AD). The development of new retinoid analogs with diminished toxicity that can cross the blood-brain barrier without harm and can normalize phospholipase A2-mediated signaling will be important in developing pharmacological interventions for these neurological disorders.

Phospholipase A2 in the central nervous system

Phospholipase A2 (PLA2) belongs to a family of enzymes that catalyze the cleavage of fatty acids from the sn-2 position of phospholipids. There are more than 19 different isoforms of PLA2 in the mammalian system, but recent studies have focused on three major groups, namely, the group IV cytosolic PLA2, the group II secretory PLA2 (sPLA2), and the group VI Ca(2+)-independent PLA2. These PLA2s are involved in a complex network of signaling pathways that link receptor agonists, oxidative agents, and proinflammatory cytokines to the release of arachidonic acid (AA) and the synthesis of eicosanoids. PLA2s acting on membrane phospholipids have been implicated in intracellular membrane trafficking, differentiation, proliferation, and apoptotic processes. All major groups of PLA2 are present in the central nervous system (CNS). Therefore, this review is focused on PLA2 and AA release in neural cells, especially in astrocytes and neurons. In addition, because many neurodegenerative diseases are associated with increased oxidative and inflammatory responses, an attempt was made to include studies on PLA2 in cerebral ischemia, Alzheimer's disease, and neuronal injury due to excitotoxic agents. Information from these studies has provided clear evidence for the important role of PLA2 in regulating physiological and pathological functions in the CNS.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

L-homocysteine sulfinic acid and other acidic homocysteine derivatives are potent and selective metabotropic glutamate receptor agonists

Moderate hyperhomocysteinemia is associated with several diseases, including coronary artery disease, stroke, Alzheimer's disease, schizophrenia, and spina bifida. However, the mechanisms for their pathogenesis are unknown but could involve the interaction of homocysteine or its metabolites with molecular targets such as neurotransmitter receptors, channels, or transporters. We discovered that L-homocysteine sulfinic acid (L-HCSA), L-homocysteic acid, L-cysteine sulfinic acid, and L-cysteic acid are potent and effective agonists at several rat metabotropic glutamate receptors (mGluRs). These acidic homocysteine derivatives 1) stimulated phosphoinositide hydrolysis in the cells stably expressing the mGluR1, mGluR5, or mGluR8 (plus Galpha(qi9)) and 2) inhibited the forskolin-induced cAMP accumulation in the cells stably expressing mGluR2, mGluR4, or mGluR6, with different potencies and efficacies depending on receptor subtypes. Of the four compounds, L-HCSA is the most potent agonist at mGluR1, mGluR2, mGluR4, mGluR5, mGluR6, and mGluR8. The effects of the four agonists were selective for mGluRs because activity was not discovered when L-HCSA and several other homocysteine derivatives were screened against a large panel of cloned neurotransmitter receptors, channels, and transporters. These findings imply that mGluRs are candidate G-protein-coupled receptors for mediating the intracellular signaling events induced by acidic homocysteine derivatives. The relevance of these findings for the role of mGluRs in the pathogenesis of homocysteine-mediated phenomena is discussed.

Activation of phospholipases A2 and D of a human neuroblastoma cell line (LA-N-2) by N-dodecyl-L-lysine amide (compound 24), a putative G protein activator: characteristics of inhibition by (-)-nicotine

Compound 24, an alkyl-substituted amino acid amide, previously found to activate pertussis toxin-sensitive G proteins in cell membranes and membrane protein fractions, was used as a tool to determine the mechanism/location of nicotine inhibition of amyloid beta peptide-stimulated phospholipase A2 and D activities in a human neuroblastoma cell line, LA-N-2, in vitro. In contrast to our previous findings with amyloid beta peptide, these phospholipase activations by compound 24 were not inhibited by (-)-nicotine, cholera toxin or tetanus toxin pretreatment. The contrasting activation of these phospholipases by amyloid beta peptide and compound 24 are discussed.

Enhancement of phospholipase D activity by overexpression of amyloid precursor protein in P19 mouse embryonic carcinoma cells

It has been shown that phospholipase D (PLD) activity is stimulated by the beta-amyloid protein in neuronal cells. The aim of this study was to determine whether overexpression of the amyloid precursor protein (APP) affects the activity and the level of PLD expression in P19 embryonic carcinoma cells. We observed that the unstimulated basal PLD activity was higher in wild-type APP(695)-transfected cells than in non-transfected control cells. The protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), has been shown to activate PLD. PMA-stimulated PLD activity was 3-fold higher in the APP overexpressing cells than in the control cells. P19 cells express two distinct PLD isozymes, PLD1 and PLD2. The level of PLD2 expression was increased by APP overexpression. Although the PKC inhibitor, GF109203X, inhibited PMA-stimulated PLD activity, it did not affect the high basal PLD activity induced by APP overexpression. Neuronal differentiation of the P19 cells by retinoic acid did not affect the basal or PMA stimulated-PLD activity. Interestingly, APP overexpression in the differentiated P19 cells also led to an increase in PLD activity. The PLD activity of the P19 cells is apparently regulated by amyloid protein through both PKC-dependent and -independent mechanisms.

(1)H-MR spectroscopy differentiates mild cognitive impairment from normal brain aging

This study aimed to characterize the white matter biochemical profile of healthy elderly subjects, mild cognitive impairment (MCI) subjects, and early Alzheimer's disease (AD) patients. We used proton magnetic resonance spectroscopy ((1)H-MRS) to measure myo-inositol, creatine, N-acetylaspartate (NAA) and choline levels from a volume of interest located in the paratrigonal white matter bilaterally. A significantly higher myo-inositol/creatine ratio was found in MCI subjects and AD patients than in controls. The NAA/creatine ratio was reduced in AD patients in the left hemisphere compared to control subjects. The choline/creatine ratio was not significantly different among the three groups. These data suggest that MCI is different from normal brain aging, having a white matter biochemical pattern similar to AD.

Amyloid beta peptide 1-40 and the function of rat hippocampal hemicholinium-3 sensitive choline carriers: effects of a proteolytic degradation in vitro

Effects of amyloid beta peptide 1-40 (Abeta) and of plant cysteine proteases bromelain and papain on the high-affinity uptake of choline (HACU) and the specific binding of [3H]hemicholinium-3 ([3H]HC-3) have been investigated on hippocampal synaptosomes from young adult male Wistar rats under basal and stimulated conditions (55 mM KCl). Depolarization increased significantly the HACU levels (the changes were predominantly in Vmax) and mildly the [3H]HC-3 binding (the changes especially in K(D)). Nonaggregated Abeta at low nM concentrations suppressed the depolarization effects but was ineffective under basal conditions during a short-term incubation. Higher microM concentrations decreased the HACU and binding under basal conditions in a time-dependent manner. The binding changes were firstly associated with alterations in K(D) and secondarily were accompanied also by a drop in Bmax. The results suggest that Abeta directly influences high-affinity carriers, inhibits their transport activity and enhances their sensitivity to proteoLytic cleavage. Stimulation increases the sensitivity of carriers to the interaction with Abeta.

Lipid constituents in oligodendroglial cells alter susceptibility to H2O2-induced apoptotic cell death via ERK activation

The present work examines the effect of membrane lipid composition on activation of extracellular signal-regulated protein kinases (ERK) and cell death following oxidative stress. When subjected to 50 microM docosahexaenoic acid (DHA, 22 : 6 n-3), cellular phospholipids of OLN 93 cells, a clonal line of oligodendroglia origin low in DHA, were enriched with this polyunsaturated fatty acid. In the presence of 1 mM N,N-dimethylethanolamine (dEa) a new phospholipid species analog was formed in lieu of phosphatidylcholine. Exposure of DHA-enriched cells to 0.5 mM H2O2, caused sustained activation of ERK up to 24 h. At this time massive apoptotic cell death was demonstrated by ladder and TUNEL techniques. H2O2-induced stress applied to dEa or DHA/dEa co-supplemented cells showed only a transient ERK activation and no cell death after 24 h. Moreover, while ERK was rapidly translocated into the nucleus in DHA-enriched cells, dEa supplements completely blocked ERK nuclear translocation. This study suggests that H2O2-induced apoptotic cell death is associated with prolonged ERK activation and nuclear translocation in DHA-enriched OLN 93 cells, while both phenomena are prevented by dEa supplements. Thus, the membrane lipid composition ultimately modulates ERK activation and translocation and therefore can promote or prevent apoptotic cell death.

Ethanol and oxidative mechanisms in the brain

There is strong evidence showing that chronic and excessive ethanol consumption may enhance oxidative damage to neurons and result in cell death. Although not yet well understood, ethanol may enhance ROS production in brain through a number of pathways including increased generation of hydroxyethyl radicals, induction of CYP2E1, alteration of the cytokine signaling pathways for induction of iNOS and sPLA(2), and production of prostanoids through the PLA(2)/COX pathways. Since many neurodegenerative diseases are also associated with oxidative and inflammatory mechanisms in the brain, it would be important to find out whether chronic and excessive ethanol consumption may exacerbate the progression of these diseases. There is evidence that the polyphenolic antioxidants, especially those extracted from grape skin and seed, may protect the brain from neuronal damage due to chronic ethanol administration. Among the polyphenols from grapes, resveratrol seems to have unique antioxidant properties. The possible use of this compound as a therapeutic agent to ameliorate neurodegenerative processes should be further explored.

Biogerontological research in Canada

There is an ever increasing interest in the study of the aging process. This review is aimed to make an overview of the biological aging research in Canada. I will summarize, to the best of my knowledge, the biological aging research undertaken actually in Canadian institutions dealing with various aspects of this research using many different experimental approaches, models from animals to humans and a huge array of techniques. The biological aging research is developing continuously in Canada, however, it is very important that we assist in a near future to its huge explosion if we would respond to the needs of an ever increasing aging population. Initiatives recently proposed by the Canadian government concerning the creation of Canadian Institutes on Health Research will provide good opportunities to establish a performant, cost-effective, and innovative biological aging research.

Amyloid beta peptide membrane perturbation is the basis for its biological effects

Experimental studies have indicated that the mechanisms offered for explaining the neurotoxicity of amyloid beta peptide (AbetaP) are diverse, and include altered enzyme activities, disrupted calcium homeostasis, and increased free radical formation. AbetaP appears to interact at the cell membrane with a multitude of receptor sites and also inserts physically into the membrane matrix. This membrane insertion affects the membrane fluidity and potentially influences the function of resident membrane proteins. We propose a unifying hypothesis to explain the experimental observations of the diverse cellular responses to AbetaP. The indiscriminate physical insertion of AbetaP into the cell membrane unspecifically activates a host of membrane processes by perturbation of the membrane proteins. This recurrent activation of membrane processes eventually culminates in neuronal cell death. We recommend that successful therapeutic interventions should be directed at reducing or preventing the interaction of AbetaP with neuronal cell membranes.

New gene targets related to schizophrenia and other psychiatric disorders: enzymes, binding proteins and transport proteins involved in phospholipid and fatty acid metabolism

Phospholipids make up about 60% of the brain's dry weight. In spite of this, phospholipid metabolism has received relatively little attention from those seeking genetic factors involved in psychiatric and neurological disorders. However, there is now increasing evidence from many quarters that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. To date the possible specific proteins and genes involved have been relatively ill-defined. This paper reviews the main pathways of phospholipid metabolism, emphasizing the roles of phospholipases of the A2 and C series in signal transduction processes. It identifies some likely protein candidates for involvement in psychiatric and neurological disorders. It also reviews the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.