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Biomedical subjects

D W Choi

Publications and source records attributed to D W Choi.

At least 55 records · Page 3Linked to original sources
PubMed1999

Calcium ionophores can induce either apoptosis or necrosis in cultured cortical neurons.

Cultured cortical neurons exposed for 24 h to low concentrations of the Ca2+ ionophores, ionomycin (250 nM) or A-23187 (100 nM), underwent apoptosis, accompanied by early degeneration of neurites, cell body shrinkage, chromatin condensation and internucleosomal DNA fragmentation. This death could be blocked by protein synthesis inhibitors, as well as by the growth factors brain-derived neurotrophic factor or insulin-like growth factor I. If the ionomycin concentration was increased to 1-3 microM, then neurons underwent necrosis, accompanied by early cell body swelling without DNA laddering, or sensitivity to cycloheximide or growth factors. Calcium imaging with Fura-2 suggested a possible basis for the differential effects of low and high concentrations of ionomycin. At low concentrations, ionomycin induced greater increases in intracellular Ca2+ concentration in neurites than in neuronal cell bodies, whereas at high concentrations, ionomycin produced large increases in intracellular Ca2+ concentration in both neurites and cell bodies. We hypothesize that the ability of low concentrations of Ca2+ ionophores to raise intracellular Ca2+ concentration preferentially in neurites caused early neurite degeneration, leading to loss of growth factor availability to the cell body and consequent apoptosis, whereas high concentrations of ionophores produced global cellular Ca2+ overload and consequent necrosis.

Animals↗
PubMed1999

Prevention of neuronal apoptosis by phorbol ester-induced activation of protein kinase C: blockade of p38 mitogen-activated protein kinase.

Consistent with previous studies on cell lines and non-neuronal cells, specific inhibitors of protein kinase C induced mouse primary cultured neocortical neurons to undergo apoptosis. To examine the complementary hypothesis that activating protein kinase C would attenuate neuronal apoptosis, the cultures were exposed for 1 h to phorbol-12-myristate-13-acetate, which activated protein kinase C as evidenced by downstream enhancement of the mitogen-activated protein kinase pathway. Exposure to phorbol-12-myristate-13-acetate, or another active phorbol ester, phorbol-12,13-didecanoate, but not to the inactive ester, 4alpha-phorbol-12,13-didecanoate, markedly attenuated neuronal apoptosis induced by serum deprivation. Phorbol-12-myristate-13-acetate also attenuated neuronal apoptosis induced by exposure to beta-amyloid peptide 1-42, or oxygen-glucose deprivation in the presence of glutamate receptor antagonists. The neuroprotective effects of phorbol-12-myristate-13-acetate were blocked by brief (non-toxic) concurrent exposure to the specific protein kinase C inhibitors, but not by a specific mitogen-activated protein kinase 1 inhibitor. Phorbol-12-myristate-13-acetate blocked the induction of p38 mitogen-activated protein kinase activity and specific inhibition of this kinase by SB 203580 attenuated serum deprivation-induced apoptosis. c-Jun N-terminal kinase 1 activity was high at rest and not modified by phorbol-12-myristate-13-acetate treatment. These data strengthen the idea that protein kinase C is a key modulator of several forms of central neuronal apoptosis, in part acting through inhibition of p38 mitogen-activated protein kinase regulated pathways.

Amyloid beta-Peptides↗
PubMed1999

Transplanted embryonic stem cells survive, differentiate and promote recovery in injured rat spinal cord.

Transplantation approaches using cellular bridges, fetal central nervous system cells, fibroblasts expressing neurotrophin-3 (ref. 6), hybridoma cells expressing inhibitory protein-blocking antibodies, or olfactory nerves ensheathing glial cells transplanted into the acutely injured spinal cord have produced axonal regrowth or functional benefits. Transplants of rat or cat fetal spinal cord tissue into the chronically injured cord survive and integrate with the host cord, and may be associated with some functional improvements. In addition, rats transplanted with fetal spinal cord cells have shown improvements in some gait parameters, and the delayed transplantation of fetal raphe cells can enhance reflexes. We transplanted neural differentiated mouse embryonic stem cells into a rat spinal cord 9 days after traumatic injury. Histological analysis 2-5 weeks later showed that transplant-derived cells survived and differentiated into astrocytes, oligodendrocytes and neurons, and migrated as far as 8 mm away from the lesion edge. Furthermore, gait analysis demonstrated that transplanted rats showed hindlimb weight support and partial hindlimb coordination not found in 'sham-operated' controls or control rats transplanted with adult mouse neocortical cells.

Animals↗
PubMed1999

Gö 6976 is a potent inhibitor of neurotrophin-receptor intrinsic tyrosine kinase.

We report here that addition of the protein kinase C inhibitor Gö 6976 blocked neurotrophin-induced signaling and autophosphorylation of neurotrophin-specific tyrosine kinase (Trk) receptors, either Trk B in cortical neurons or Trk A in GT1-1-trk9 cells. The effect of Gö 6976 on Trk autophosphorylation was not inhibited by 100 microM orthovanadate, suggesting that the block was not due to the activation of tyrosine phosphatases. Moreover, addition of 10-100 nM concentrations of Gö 6976 inhibited either Trk B or Trk A intrinsic kinase activity in cell-free assays. Gö 6976 also blocked the ability of brain-derived neurotrophic factor to promote cortical neuronal survival and the ability of nerve growth factor to promote PC12 cell survival and differentiation. These results suggest that Gö 6976, besides its known inhibitory effects on lipid- and calcium-dependent isoforms of protein kinase C, can also inhibit neurotrophin signaling by directly inhibiting the intrinsic Trk.

Animals↗
PubMed1999

Role of the outward delayed rectifier K+ current in ceramide-induced caspase activation and apoptosis in cultured cortical neurons.

We studied the novel hypothesis that an up-modulation of channels for outward delayed rectifier K+ current (I(K)) plays a key role in ceramide-induced neuronal apoptosis. Exposure for 6-10 h to the membrane-permeable C2-ceramide (25 microM) or to sphingomyelinase (0.2 unit/ml), but not to the inactive ceramide analogue C2-dihydroceramide (25 microM), enhanced the whole-cell I(K) current without affecting the transient A-type K+ current and increased caspase activity, followed by neuronal apoptosis 24 h after exposure onset. Tetraethylammonium (TEA) or 4-chloro-N,N-diethyl-N-heptylbenzenebutanaminium tosylate (clofilium), at concentrations inhibiting I(K), attenuated the C2-ceramide-induced caspase-3-like activation as well as neuronal apoptosis. Raising extracellular K+ to 25 mM similarly blocked the C2-ceramide-induced cell death; the neuroprotection by 25 mM K+ or TEA was not eliminated by blocking voltage-gated Ca2+ channels. An inhibitor of tyrosine kinases, herbimycin A (10 nM) or lavendustin A (0.1-1 microM), suppressed I(K) enhancement and/or apoptosis induced by C2-ceramide. It is suggested that ceramide-induced I(K) current enhancement is mediated by tyrosine phosphorylation and plays a critical role in neuronal apoptosis.

Animals↗
PubMed1999

Apoptosis and necrosis in cerebrovascular disease.

Neuronal death following ischemic insults has been thought to reflect necrosis. However, recent evidence from several labs suggests that programmed cell death, leading to apoptosis, might additionally contribute to this death. We have used both in vitro and in vivo models to study the role of apoptosis in ischemic cell death. Some features of apoptosis (TUNEL staining, internucleosomal DNA fragmentation, sensitivity to cycloheximide) were observed following transient focal ischemia in rats. Brief transient focal ischemia was followed by delayed infarction more than 3 days later; this delayed infarction was sensitive to cycloheximide. A cycloheximide-sensitive component of neuronal cell death was also observed in cultured murine neocortical neurons deprived of oxygen-glucose in the presence of glutamate receptor antagonists. This presumed ischemic apoptosis was attenuated by caspase inhibitors, or by homozygous deletion of the bax gene. Neurons may undergo both apoptosis and necrosis after ischemic insults, and thus it may be therapeutically desirable to block both processes.

Animals↗
PubMed1999

Solid mesenchymal hamartoma of the liver in adult.

This paper presents an unusual solid mesenchymal hamartoma of the liver (MHL) in adult. A well defined solid mass in the left lobe of the liver was found in a 57-year-old female. Preoperative radiologic examinations demonstrated solid mass with multifocal calcifications abutting the gallbladder. By light microscopy, the lesion was composed of dense fibrous stroma with hyalinization, bile ducts and thick-walled vessels without hepatocytes. The solid and hyalinized mesenchymal component would suggest an unusual degenerative change representing a burnt-out MHL.

Female↗
PubMed1999

Attenuation of cortical neuronal apoptosis by gangliosides.

Addition of the natural gangliosides monosialoganglioside (GM1), disialoganglioside, trisialoganglioside, or tetrasialoganglioside in the range of 10 to 100 microM, but not asialoganglioside lacking the sialic acid moiety, attenuated cortical neuronal apoptosis induced by serum deprivation, ionomycin, or cyclosporin A but not by protein kinase inhibitors (staurosporine, genistein, lavendustin A, or herbimycin A). Coaddition of 100 nM wortmannin, a selective inhibitor of phosphatidylinositol 3-kinase, but not 1 microM Go6976, a selective protein kinase C inhibitor, blocked the neuroprotective effect of GM1. In contrast to its antiapoptotic effect, GM1 at up to 200 microM did not attenuate cortical neuronal necrosis induced by exposure to the excitotoxins N-methyl-D-aspartate or kainate. Furthermore, GM1 increased the necrosis induced by oxidative stress (addition of Fe(2+) or buthionine sulfoximine). These data suggest that neuroprotective effects of natural gangliosides may preferentially reflect reduction of neuronal apoptosis rather than necrosis, and be mediated through mechanisms involving activation of phosphatidylinositol 3-kinase.

Animals↗
PubMed1998

Extracellular acidity potentiates AMPA receptor-mediated cortical neuronal death.

The extracellular acidity that accompanies brain hypoxia-ischemia is known to reduce both NMDA and AMPA-kainate receptor-mediated currents and NMDA receptor-mediated neurotoxicity. Although a protective effect of acidic pH on AMPA-kainate receptor-mediated excitotoxicity has been assumed, such has not been demonstrated. Paradoxically, we found that lowering extracellular pH selectively increased AMPA-kainate receptor-mediated neurotoxicity in neocortical cell cultures, despite reducing peak elevations in intracellular free Ca2+. This injury potentiation may, at least in part, be related to a slowed recovery of intracellular Ca2+ homeostasis, observed after AMPA-kainate receptor activation, but not after NMDA receptor activation or exposure to high K+. The ability of acidic pH to selectively augment AMPA-kainate receptor-mediated excitotoxicity may contribute to the prominent role that these receptors play in selective neuronal death after transient global ischemia.

Acids↗
PubMed1998

Involvement of de novo ceramide biosynthesis in tumor necrosis factor-alpha/cycloheximide-induced cerebral endothelial cell death.

Cytokines, including tumor necrosis factor-alpha (TNF-alpha), may elicit cytotoxic response through the sphingomyelin-ceramide signal transduction pathway by activation of sphingomyelinases and the subsequent release of ceramide: the universal lipid second messenger. Treatment of bovine cerebral endothelial cells (BCECs) with TNF-alpha for 16 h followed by cycloheximide (CHX) for 6 h resulted in an increase in ceramide accumulation, DNA fragmentation, and cell death. Application of a cell permeable ceramide analogue C2 ceramide, but not the biologically inactive C2 dihydroceramide, also induced DNA laddering and BCEC death in a concentration- and time-dependent manner. TNF-alpha/CHX-mediated ceramide production apparently is not a result of sphingomyelin hydrolysis because sphingomyelin content does not decrease in this death paradigm. In addition, an acidic sphingomyelinase inhibitor, desipramine, had no effect on TNF-alpha/CHX-induced cell death. However, addition of fumonisin B1, a selective ceramide synthase inhibitor, attenuated TNF-alpha/CHX-induced intracellular ceramide elevation and BCEC death. Together, these findings suggest that ceramide plays at least a partial role in this paradigm of BCEC death. Our results show, for the first time, that ceramide derived from de novo synthesis is an alternative mechanism to sphingomyelin hydrolysis in the BCEC death process initiated by TNF-alpha/CHX.

Animals↗
PubMed1998

Neuronal death in cultured murine cortical cells is induced by inhibition of GAPDH and triosephosphate isomerase.

Polyglutamine-containing proteins expressed in the CAG repeat diseases Huntington's disease and dentatorubralpallidoluyisian atrophy have recently been suggested to inhibit the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). To examine the consequences of GAPDH inhibition upon neuronal survival, we exposed murine neocortical cell cultures to the inhibitor of GAPDH and triosephosphate isomerase, alpha-monochlorohydrin. Cultures exposed to 6-15 mM alpha-monochlorohydrin for 48 h exhibited an increase in dihydroxyacetone phosphate and a decrease in neuronal ATP that was followed by progressive neuronal death; some glial death occurred at high drug concentrations. The neuronal death was characterized by cell body shrinkage and chromatin condensation and was sensitive to cycloheximide and to the caspase inhibitors Z-Val-Ala-Asp fluoromethylketone and tert-butoxycarbonyl-Asp fluoromethylketone. Neurons in striatal cell cultures were more vulnerable to death induced by exposure to alpha-monochlorohydrin, except that NADPH-diaphorase(+) neurons were selectively spared. Repeated addition of the glycolytic endpoint metabolite pyruvate to the bathing medium attenuated both the drop in neuronal ATP and the neuronal cell death.

Adenosine Triphosphate↗
PubMed1998

Enhancement of outward potassium current may participate in beta-amyloid peptide-induced cortical neuronal death.

In light of recent evidence implicating the upregulation of outward K+ current in mediating several forms of neuronal apoptosis, we tested the hypothesis that such an upregulation might specifically contribute to the pathogenesis of beta-amyloid peptide (A beta)-induced neuronal death. Exposure to A beta fragment 25-35 (20 microM) or 1-42 (20 microM) enhanced the delayed rectifier K+ current IK, shifting its activation voltage relationship toward hyperpolarized levels and increasing maximal conductance, but did not affect the transient K+ current IA or charybdotoxin-sensitive BK current. Reducing IK by adding the channel blocker tetraethylammonium (TEA, 5 mM) or raising extracellular K+ to 25 mM attenuated A beta-induced neuronal death, even in the presence of nifedipine or gadolinium to block associated increases in Ca2+ influx. The IA blocker 4-aminopyridine (4-AP, 5 mM) and the CI- channel blocker anthracene-9-carboxylic acid (ACA, 500 microM) were not neuroprotective. These data raise the intriguing possibility that manipulations aimed at reducing outward K+ current may provide an approach to reducing neuronal degeneration in patients with Alzheimer's disease.

Amyloid beta-Peptides↗
PubMed1998

Cortical tissue-specific accumulation of the root-specific ns-LTP transcripts in the bean (Phaseolus vulgaris) seedlings.

The characterization of a cDNA clone encoding non-specific lipid transfer protein (PvLTP, formerly named PVR3) in the roots of bean seedlings has been previously reported. In this study, we examined the temporal and spatial accumulation of PvLTP mRNA and the effect of the auxin naphthaleneacetic acid (NAA) on the accumulation of PvLTP mRNA during root development. In situ hybridization showed that accumulation of PvLTP mRNA is highly tissue-specific. Accumulation was detected in the cortical tissue, but not in other tissues of root, including the quiescent center and root cap. Within the cortical tissue, accumulation of PvLTP mRNA was developmentally regulated; accumulation of PvLTP mRNA was high in the cortical tissue of the proximal and ground meristem and declined as cortical tissue developed further. Since the appropriate distribution of auxin is an important factor responsible for the maintenance of root meristem organization. We examined effect of auxin on the accumulation of PvLTP mRNA in relation to the development of cortical tissue. In bean seedlings grown on medium supplemented with 5 microM NAA, morphological alternations, including radial root expansion and abnormal tissue organization in the root apical meristem, were observed. Only faint accumulation signals of PvLTP mRNA were observed in the cortical tissue of proximal meristem region, indicating that cortical tissue development was repressed by exogenous NAA. However, our results suggest that the change in accumulation of PvLTP mRNA is not direct regulatory effect but reflective effect of altered development of cortical tissue that was induced by exogenous NAA. The temporal and spatial accumulation of PvLTP mRNA indicates that PvLTP is a useful marker for the development of cortical tissue in the root tip in bean seedlings.

Carrier Proteins↗
PubMed1998

Oligodendrocytes from forebrain are highly vulnerable to AMPA/kainate receptor-mediated excitotoxicity.

Little is known of the molecular mechanisms that trigger oligodendrocyte death and demyelination in many acute central nervous system insults. Since oligodendrocytes express functional alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-type glutamate receptors, we examined the possibility that oligodendrocyte death can be mediated by glutamate receptor overactivation. Oligodendrocytes in primary cultures from mouse forebrain were selectively killed by low concentrations of AMPA, kainate or glutamate, or by deprivation of oxygen and glucose. This toxicity could be blocked by the AMPA/kainate receptor antagonist 6-nitro-7-sulfamoylbenzo(f)quinoxaline-2,3-dione (NBQX). In vivo, differentiated oligodendrocytes in subcortical white matter expressed AMPA receptors and were selectively injured by microstereotaxic injection of AMPA but not NMDA. These data suggest that oligodendrocytes share with neurons a high vulnerability to AMPA/kainate receptor-mediated death, a mechanism that may contribute to white matter injury in CNS disease.

Animals↗
PubMed1998

Conditioning heat stress reduces excitotoxic and apoptotic components of oxygen-glucose deprivation-induced neuronal death in vitro.

We investigated the effects of sublethal heat stress in murine cortical cell cultures exposed to combined oxygen and glucose deprivation. Pretreatment with sublethal heat stress mildly attenuated the widespread neuronal death induced a day later by 30-60 min of oxygen-glucose deprivation. Heat stress also blunted the increase in extracellular glutamate concentrations induced by the oxygen-glucose deprivation, as well as the neuronal death and 45Ca2+ uptake induced by exogenous addition of NMDA, although no reduction was seen in neuronal death caused by exogenous kainate or in NMDA-induced whole-cell currents. However, arguing against the idea that the neuroprotective effect of heat stress against neuronal death was exclusively due to reduction of excitotoxicity was the finding that heat stress also reduced the neuronal apoptosis induced by oxygen-glucose deprivation in the presence of glutamate antagonists. This antiapoptotic effect was specific in that heat stress did not reduce neuronal vulnerability to staurosporine-induced apoptosis. Whereas heat stress transiently suppressed protein synthesis, achieving comparable protein synthesis inhibition with cycloheximide did not reproduce the neuroprotective effects of heat stress. These studies suggest that a conditioning heat stress is able to attenuate both the excitotoxic and the apoptotic components of oxygen-glucose deprivation-induced neuronal death in vitro, by mechanisms independent of protein synthesis reduction.

Animals↗
PubMed1998

Antagonists for group I mGluRs attenuate excitotoxic neuronal death in cortical cultures.

Activation of ion channel-linked glutamate receptors, especially N-methyl-D-aspartate (NMDA) receptors, mediates the excitotoxic effects of glutamate upon central neurons. We examined the hypothesis that activation of group I metabotropic glutamate receptors (mGluRs) would increase NMDA receptor-mediated cortical neuronal death. Addition of the selective group I mGluR agonists, dihydroxyphenylglycine (DHPG) or trans-azetidine-2,4-dicarboxylic acid (t-ADA) potentiated NMDA-induced neuronal death, and application of the group I mGluR-selective antagonist, aminoindan-1,5-dicarboxylic acid (AIDA), as well as the non-selective antagonists methyl-4-carboxyphenylglycine (MCPG) or 4-carboxyphenylglycine (4CPG) reduced NMDA- and kainate-induced neuronal death in murine cortical cultures. The pro-excitotoxic effect of group I mGluR activation may be mediated largely by enhancement of glutamate release, as DHPG potentiated high potassium-stimulated glutamate release, and the protective effects of both AIDA and MCPG were abolished when NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptors were blocked immediately after toxic NMDA receptor overstimulation. The present data support the possibility that antagonizing group I mGluRs may be a useful strategy for attenuating excitotoxic neuronal death in certain disease states.

Animals↗
PubMed1998

Zinc and brain injury.

Zinc is an essential catalytic or structural element of many proteins, and a signaling messenger that is released by neural activity at many central excitatory synapses. Growing evidence suggests that zinc may also be a key mediator and modulator of the neuronal death associated with transient global ischemia and sustained seizures, as well as perhaps other neurological disease states. Manipulations aimed at reducing extracellular zinc accumulation, or cellular vulnerability to toxic zinc exposure, may provide a novel therapeutic approach toward ameliorating pathological neuronal death in these settings.

Brain↗