Biomedical subjects

Wei-Yi Ong

Publications and source records attributed to Wei-Yi Ong.

At least 19 recordsLinked to original sources

PubMed2007

Expression, activity, and role of serine palmitoyltransferase in the rat hippocampus after kainate injury.

An increase in ceramide species has been shown recently by lipidomic analysis of the rat hippocampus after kainate-induced excitotoxic injury (Guan et al. [2006] FASEB J 20:1152-1161). In this study, we showed increased expression of serine palmitoyltransferase (SPT), the first enzyme in the ceramide biosynthetic pathway, in reactive astrocytes of the hippocampus after kainate injections. The increase in enzyme expression was paralleled by increased SPT enzyme activity in the hippocampus at 2 weeks post-kainate injection. In vitro studies showed that treatment of hippocampal slice cultures with SPT inhibitor ISP-1 (myriocin) or L-cycloserine modulated increases in 16:0, 18:0, and 20:0 ceramide species, and partially reduced kainate-induced cell death. The above findings indicate a role of SPT in ceramide increase after kainate injury, although additional effects of sphingomyelinase cannot be ruled out. They also suggest that SPT activity might contribute to neuronal injury after kainate excitotoxicity.

Animals↗

PubMed2006

Dysbindin-1 is a synaptic and microtubular protein that binds brain snapin.

Variations in the gene encoding the novel protein dysbindin-1 (DTNBP1) are among the most commonly reported genetic variations associated with schizophrenia. Recent studies show that those variations are also associated with cognitive functioning in carriers with and without psychiatric diagnoses, suggesting a general role for dysbindin-1 in cognition. Such a role could stem from the protein's known ability to affect neuronal glutamate release. How dysbindin-1 might affect glutamate release nevertheless remains unknown without the discovery of the protein's neuronal binding partners and its subcellular locus of action. We demonstrate here that snapin is a binding partner of dysbindin-1 in vitro and in the brain. Tissue fractionation of whole mouse brains and human hippocampal formations revealed that both dysbindin-1 and snapin are concentrated in tissue enriched in synaptic vesicle membranes and less commonly in postsynaptic densities. It is not detected in presynaptic tissue fractions lacking synaptic vesicles. Consistent with that finding, immunoelectron microscopy showed that dysbindin-1 is located in (i) synaptic vesicles of axospinous terminals in the dentate gyrus inner molecular layer and CA1 stratum radiatum and in (ii) postsynaptic densities and microtubules of dentate hilus neurons and CA1 pyramidal cells. The labeled synapses are often asymmetric with thick postsynaptic densities suggestive of glutamatergic synapses, which are likely to be derived from dentate mossy cells and CA3 pyramidal cells. The function of dysbindin-1 in presynaptic, postsynaptic and microtubule locations may all be related to known functions of snapin.

Aged↗

PubMed2006

Effects of intracerebroventricular injections of free fatty acids, lysophospholipids, or platelet activating factor in a mouse model of orofacial pain.

The present study was carried out to determine the effects of central nervous free fatty acids, lysophospholipids, or platelet activating factor (PAF), in a mouse facial carrageenan injection model of orofacial pain. Mice that received intracerebroventricular (I.C.V.) injection of arachidonic acid or oleic acid showed significantly reduced allodynia and behavioral responses to von Frey hair stimulation of a carrageenan-injected area of the face, at 8 h post-injection, compared to controls that received I.C.V. injection of vehicle. In contrast to free fatty acids, increased responses were observed in mice at 72 h after I.C.V. lysophosphatidic acid or lysophosphatidylcholine injection, and at 8 and 24 h after PAF injection, compared vehicle injected controls. Information regarding pro-nociceptive effect of specific brain lipids may be a useful basis for further studies to explore mechanism.

Animals↗

PubMed2006

Distribution of calcium-independent phospholipase A2 (iPLA 2) in monkey brain.

The present study was carried out to elucidate the distribution of calcium-independent phospholipase A(2) (iPLA(2)) in the normal monkey brain. iPLA(2) immunoreactivity was observed in structures derived from the telencephalon, including the cerebral neocortex, amygdala, hippocampus, caudate nucleus, putamen, and nucleus accumbens, whereas structures derived from the diencephalon, including the thalamus, hypothalamus and globus pallidus were lightly labeled. The midbrain, vestibular, trigeminal and inferior olivary nuclei, and the cerebellar cortex were densely labeled. Immunoreactivity was observed on the nuclear envelope of neurons, and dendrites and axon terminals at electron microscopy. Western blot analysis showed higher levels of iPLA(2) protein in the cytosolic, than the nuclear fraction, but little or no protein in the membrane fraction. Similarly, subcellular fractionation studies of iPLA(2) activity in rat brain cortical cell cultures showed greater enzymatic activity in the cytosolic, than the nuclear fraction, and the least activity in non-nuclear membranes. The association of iPLA(2) with the nuclear envelope suggests a role of the enzyme in nuclear signaling, such as during neuronal proliferation and differentiation or death. In addition, the localization of iPLA(2) in dendrites and axon terminals suggests a role of the enzyme in neuronal signaling.

Active Transport, Cell Nucleus↗

PubMed2006

Differential effects of polyunsaturated fatty acids on membrane capacitance and exocytosis in rat pheochromocytoma-12 cells.

The fusion of synaptic vesicles with the plasma membrane during exocytosis can be recorded by membrane capacitance measurements under voltage-clamp conditions. These measurements enable high time-resolution quantitation of exocytosis. The present study was carried out using the above technique to elucidate the effects of various polyunsaturated fatty acids on exocytosis in a neuroendocrine cell, the rat pheochromocytoma-12 (PC12) cell. External application of eicosapentaenoic acid and arachidonic acid resulted in an increase in capacitance of PC12 cells, indicating fusion of secretory vesicles with cell membranes and exocytosis. In contrast, docosahexaenoic acid, linoleic acid, oleic acid, and vehicle control had no significant effect on capacitance. The above findings show differential effects of polyunsaturated fatty acids on exocytosis in PC12 cells. It is postulated that besides arachidonic acid, eicosapentaenoic acid could also play an important role in exocytosis and neurotransmitter release, in neurons and hormone-secreting cells.

Animals↗

PubMed2006

Non-targeted profiling of lipids during kainate-induced neuronal injury.

Kainate is a glutamate analog that has been widely used in pharmacological studies of neuronal injury related to ischemic conditions and epilepsy. While altered lipid metabolism has been implicated in kainate action, no study has yet investigated the associated changes in lipid metabolites on a systems scale. Here we describe a mass spectrometry-based approach for profiling of lipid mixtures in a nontargeted fashion. Combined with tandem mass spectrometry, this method aims to identify lipids that are altered between two conditions, the kainate-treated and the control hippocampal tissues. In addition to reductions in major phospholipids with mainly polyunsaturated fatty acyl chains, we find elevated levels of ions that correspond to acylated forms of phosphatidylethanolamines and ceramides. Acylated phosphatidylethanolamines are neuroprotective lipids and precursors for anandamide, which signals via cannabinoid receptors. Quantitative analysis of ceramides shows that many molecular species with different acyl compositions are increased during kainate treatment. This increase is mainly restricted to neurons rather than other brain cells in the hippocampus as revealed by immunohistochemistry of brain slices.

Animals↗

PubMed2006

Lovastatin modulates increased cholesterol and oxysterol levels and has a neuroprotective effect on rat hippocampal neurons after kainate injury.

This study was carried out to elucidate the effect of a brain-permeable statin (lovastatin) on cholesterol and oxysterol levels of the hippocampus after neuronal injury induced by the excitotoxin, kainic acid. Increased immunolabeling to cholesterol and the oxysterol biosynthetic enzyme, cholesterol 24-hydroxylase, was observed in the rat hippocampus after kainate lesions. This was accompanied by increased levels of cholesterol, 24-hydroxycholesterol (product of cholesterol 24-hydroxylase enzymatic activity), and 7-ketocholesterol in homogenates of the degenerating hippocampus as detected by gas chromatography/mass spectrometry. Hippocampi from rats or organotypic slices that had been treated with kainate plus lovastatin showed significantly lower levels of cholesterol, 24-hydroxycholesterol, and 7-ketocholesterol compared with those that had been treated with kainate only. Lovastatin also modulated hippocampal neuronal loss after kainate treatment in vivo and in vitro. The level of 24-hydroxycholesterol detected in vivo after kainate treatment (>50 microM) was found to be neurotoxic in hippocampal slice cultures. These results suggest that brain-permeable statins such as lovastatin could have a neuroprotective effect by limiting the levels of oxysterol in brain areas undergoing neurodegeneration.

Animals↗

PubMed2006

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.

Animals↗

PubMed2005

Changes in AMPA subunit expression in the mouse brain after chronic treatment with the antidepressant maprotiline: a link between noradrenergic and glutamatergic function?

Potentiation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function has been proposed as being useful in the treatment of depression, but thus far, little is known about the possible changes in AMPA receptor expression in the brain, after antidepressant treatment. The present study was carried out to study the expression of AMPA receptor subunits in different brain regions of mice that had been chronically injected with maprotiline. The latter is a modified tricyclic antidepressant that functions as a noradrenaline uptake inhibitor. Daily intraperitoneal injection with 10 mg/kg maprotiline for 30 days resulted in significantly increased GluR1 and GluR2/3 subunit expression in the nucleus accumbens and dorsal striatum as detected by immunohistochemistry; and significantly increased GluR1 and GluR2/3 expression in the hippocampus, as demonstrated by Western blot analysis. No change, or a decrease in GluR2 expression was detected in all the brain regions by both immunohistochemistry and Western blots. The increase in GluR1 and GluR2/3, but no increase in GluR2 subunits suggests that there could be an increase in calcium permeability of AMPA receptors in limbic/striatal brain regions after maprotiline treatment. This could lead to increased synaptic activity or plasticity in the hippocampus and striatum, and may underlie the therapeutic effect of maprotline, and possibly, other antidepressant drugs.

Animals↗

PubMed2005

Upregulation of iron regulatory proteins and divalent metal transporter-1 isoforms in the rat hippocampus after kainate induced neuronal injury.

Iron regulatory proteins (IRP1 and IRP2) bind to iron response elements (IRE) on specific mRNAs, to affect the translation of many proteins involved in iron metabolism. An increase in iron levels and divalent metal transporter-1 (DMT1) expression have been observed in the rat hippocampus after excitotoxic injury induced by kainate, but thus far, it is not known whether these could be associated with changes in IRPs. The present study was therefore carried out to elucidate the expression of IRP1 or IRP2 and the IRE or non-IRE forms of DMT1 (DMT1 or -IRE DMT1) in the hippocampus after neuronal injury induced by kainate. A sustained upregulation of IRP1, IRP2, DMT1 and -IRE DMT1 protein was detected in the lesioned hippocampus by western blot and immunohistochemical analyses up to 2 months post-injection. Double immunofluorescence labeling showed that IRP1, IRP2, DMT1 and -IRE DMT1 were mostly expressed in GFAP positive astrocytes. The increased IRP expression could lead to increased expression of the +IRE form of DMT1. On the other hand, the increased expression of the -IRE DMT1 indicates that IRPs are unlikely to be only factor determining the expression of DMT1. It is postulated that transcription factors acting on putative AP-1, NF-kappaB binding sites, or gamma-interferon responsive elements on the DMT1 promoter may also play a role in upregulating the expression of the transporter. This could lead to increased iron influx into the brain areas undergoing neurodegeneration, and might be a factor contributing to neuronal damage after the initial excitotoxic injury.

Animals↗

PubMed2005

The iron chelator desferrioxamine inhibits atherosclerotic lesion development and decreases lesion iron concentrations in the cholesterol-fed rabbit.

Several epidemiological studies have suggested that increased iron stores are associated with increased atherosclerotic events. In order to test the hypothesis that decreasing the vascular level of iron slows lesion growth, we examined the effects of the iron chelator Desferal (72 mg/kg/day, 5 days/week) on atherosclerosis and lesion iron content in cholesterol-fed New Zealand White rabbits. Rabbits were fed with a 1% w/w cholesterol diet for either 8 weeks (and for the last 5 weeks injected daily with Desferal) or 12 weeks (and for the last 9 weeks injected with Desferal). Controls were injected with saline. A significant reduction in average lesion area (p = 0.038) was observed in the 12-week treated animals compared with the 12-week controls. The average lesion iron level of the 12-week treated animals (58 ppm dry wt) was also significantly lower (p = 0.030) than in 12-week control animals (95 ppm dry wt), as measured using nuclear microscopy with the combination of scanning transmission ion microscopy, Rutherford back-scattering spectroscopy, and particle-induced X-ray emission. No reduction in lesion area or iron content was observed in the 8-week treated animals compared with controls, and no change in lesion zinc concentration was observed for either group. Our data strengthen the concept that iron contributes to the early stages of the development of atherosclerosis.

Animals↗

PubMed2005

Heme oxygenase-1 activity after excitotoxic injury: immunohistochemical localization of bilirubin in neurons and astrocytes and deleterious effects of heme oxygenase inhibition on neuronal survival after kainate treatment.

An increased expression of the inducible form of heme oxygenase (HO), HO-1, is found in the hippocampus after kainate injection, but thus far it is unclear whether the HO-1 is enzymatically active. The present study was carried out, using monoclonal antibodies to bilirubin and HO-1 and histochemical staining for iron, to compare the products of HO enzymatic activity, bilirubin and iron, with HO-1 expression in the kainate-lesioned hippocampus. There was a close correlation between bilirubin and HO-1 expression, and both bilirubin and HO-1 were observed in damaged neurons at early times, and astrocytes at later times (weeks), after kainate injection. These results indicate that the increased HO-1 in the hippocampus is enzymatically active. Too determine whether HO-1 activity after kainate could have a protective or, perhaps, destructive effect, kainate-injected rats were injected intraperitoneally with a blood-brain barrier-permeable inhibitor of HO, tin protoporphyrin (SnPP), and the effects of such treatment were compared with effects in rats that received kainate and saline injection. It was found that SnPP treatment did not improve neuronal survival. Instead, increased mortality was observed in rats treated with SnPP. Four SnPP-injected rats vs. one saline-injected rats died after kainate treatment. The surviving SnPP-treated rats showed significantly less hippocampal field that containing Nissl or MAP2 staining (an indicator of surviving neurons) compared with the saline-injected rats. These results indicate that HO-1 induction had a net protective effect on neurons in the kainate model of excitotoxic injury.

Animals↗

PubMed2005

Iron, neuroinflammation, and Alzheimer's disease.

The present article reviews the roles and interactions of iron and neuroinflammation in Alzheimer's disease. It highlights the importance of neuroinflammatory changes in the glial scar after neuronal injury, in promoting iron accumulation, and iron-dependent oxidative damage. Elevation of iron in Alzheimer's disease not only affects amyloid precursor protein processing and mitochondrial function but also induces the aggregation of Abeta peptide and abnormalities in signal transduction processes associated with oxidative damage. Collective evidence suggests that although alterations in iron homeostasis may not be the primary triggering event that starts the pathological cascade of Alzheimer's disease, it is an important factor involved in neuroinflammation and progression of this disease.

Alzheimer Disease↗

PubMed2004

Distribution of ferritin in the rat hippocampus after kainate-induced neuronal injury.

A gradual increase in iron occurs in the lesioned hippocampus after neuronal injury induced by the excitotoxin kainate, and the present study was carried out to investigate whether this increase in iron might be associated with changes in expression of the iron binding protein, ferritin. An increase in ferritin immunoreactivity was observed in glial cells of the hippocampus, as early as three days after intracerebroventricular injections of kainate. The number of ferritin positive cells peaked four weeks after the kainate injection, and decreased eight and twelve weeks after injection. They were found to be mostly microglia and oligodendrocytes by double immunofluorescence labeling with glial markers. A number of ferritin-labeled endothelial cells were also observed via electron microscopy. The decline in ferritin immunoreactivity four weeks after the injection of kainate is accompanied by an increase in the number of ferric and ferrous iron positive cells in the lesioned tissue. A substantial non-overlap between ferritin and iron-containing cells was observed. In particular, spherical ferric or ferrous iron-laden cells in the degenerating hippocampus were unlabeled for ferritin for long time periods after the kainate injection. An increase in iron, together with a reduced expression of iron binding proteins such as ferritin at long time intervals after kainate lesions, could result in a relative decrease in ferritin-induced ferroxidase activity and the presence of some of the iron in the ferrous form. It is postulated that this may contribute to chronic neuronal injury, following acute kainate-induced neurodegeneration.

Animals↗

PubMed2004

Changes in GABA transporters in the rat hippocampus after kainate-induced neuronal injury: decrease in GAT-1 and GAT-3 but upregulation of betaine/GABA transporter BGT-1.

The gamma-aminobutyric acid (GABA) transporters GAT-1, GAT-2, GAT-3, and BGT-1 have been cloned and identified according to their differential amino acid sequences and pharmacologic properties. In contrast to GAT-1, -2, or -3, BGT-1 is capable of utilizing both GABA and betaine as substrates. Betaine has been suggested to be a protective osmolyte in the brain. Because changes in expression of GABA transporters/BGT-1 might result in alterations in levels of GABA/betaine in the extracellular space, with consequent effects on neuronal excitability or osmolarity, the present study was carried out to explore expression of GABA transporters in the rat hippocampus after kainate-induced neuronal injury. A decrease in GAT-1 and GAT-3 immunostaining but no change in GAT-2 staining was observed in the degenerating CA subfields. In contrast, increased BGT-1 immunoreactivity was observed in astrocytes after kainate injection. BGT-1 is a weak transporter of GABA in comparison to other GABA transporters and the increased expression of BGT-1 in astrocytes might be a protective mechanism against increased osmotic stress known to occur after excitotoxic injury. On the other hand, excessive or prolonged BGT-1 expression might be a factor contributing to astrocytic swelling after brain injury.

Animals↗

PubMed2004

Biochemical aspects of neurodegeneration in human brain: involvement of neural membrane phospholipids and phospholipases A2.

Neural membrane phospholipids are hydrolyzed by a group of enzymes known as phospholipases. This process results in the generation of second messengers such as arachidonic acid, eicosanoids, platelet activating factor, and diacylglycerols. High levels of these metabolites are neurotoxic and are associated with neurodegeneration. The collective evidence from many studies suggests that neural membrane phospholipid metabolism is disturbed in neural trauma and neurodegenerative diseases. This disturbance is caused by the stimulation of phospholipases A2. Stimulation of these enzymes produces changes in membrane permeability, fluidity, and alteration in ion homeostasis. Low calcium influx produces mild oxidative stress and results in neurodegeneration promoted by apoptosis, whereas a calcium overload generates high oxidative stress and causes neurodegeneration associated with necrosis. Alterations in phospholipid metabolism along with the accumulation of lipid peroxides and compromised energy metabolism may be responsible for neurodegeneration in ischemia, spinal cord trauma, head injury, and Alzheimer disease. The synthesis of phospholipases A2 inhibitors that cross the blood-brain barrier without harm may be useful for the treatment of acute neural trauma and neurodegenerative diseases.

Animals↗

PubMed2004

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.

Alzheimer Disease↗

PubMed2004

Increased iron staining in the cerebral cortex of cholesterol fed rabbits.

The link between hypercholesterolemia and neuronal damage is not clear. In the present study, we studied some of the possible effects of hypercholesterolemia on the brain, using the cholesterol fed New Zealand White rabbit as a model. An increase in the number of iron positive cells (i.e. oligodendrocytes) was observed in the brain parenchyma, in rabbits treated with a high cholesterol diet for 8 weeks. At this time, no neuronal death was observed, indicating that the increased iron did not occur as a consequence of neuronal injury. No heme oxygenase-1 (HO-1) or bilirubin immunoreactivity was observed in the brains in these rabbits, indicating that the iron accumulation did not occur as a consequence of increased breakdown of heme. It is postulated that cholesterol could have subtly damaged brain endothelial cells, resulting in increased iron transport across brain endothelial cells. Hypercholesterolaemia is known to be associated with increased plasma lipid peroxidation which might contribute to such damage.

Animals↗