N-Acetylcysteine Induces Apoptotic, Oxidative and Excitotoxic Neuronal Death in Mouse Cortical Cultures.

N-acetylcysteine (NAC) has been used as an antioxidant to prevent oxidative cell death. However, we found NAC itself to induce neuronal death in mouse cortical cultures. Therefore, the current study was performed to investigate the mechanism of neuronal death caused by NAC. Cell death was assessed by measuring lactate dehydrogenase efflux to bathing media after 24-48 h exposure to NAC. NAC (0.1-10 mM) induced neuronal death in a concentration- and exposure time-dependent manner. However, NAC did not injure astrocytes even at a concentration of 10 mM. Also, 10 mM NAC markedly attenuated oxidative astrocyte death induced by 0.5 mM diethyl maleate or 0.25 mM H2O2. The NMDA receptor antagonist MK-801 (10 µM) markedly attenuated the neuronal death caused by 10 mM NAC, while NBQX did not affect the neuronal death. Cycloheximide (a protein synthesis inhibitor, 0.1 µg/mL) and z-VAD-FMK (a caspase inhibitor, 100 µM) also significantly attenuated neuronal death. Apoptotic features such as chromatin condensation, nuclear fragmentation, and caspase 3 activation were observed 1 h after the NAC treatment. The neuronal death induced by 1 or 10 mM NAC was significantly attenuated by the treatment with 100 µM Trolox or 1 mM ascorbic acid. NAC induced the generation of intracellular reactive oxygen species (ROS), as measured by the fluorescent dye 2',7'-dichlorofluorescein diacetate. The ROS generation was almost completely abolished by treatment with Trolox or ascorbic acid. These findings demonstrate that NAC can cause oxidative, apoptotic, and excitotoxic neuronal death in mouse neuronal cultures.

Fluoxetine Induces Apoptotic and Oxidative Neuronal Death Associated with The Influx of Copper Ions in Cultured Neuronal Cells.

We examined the effect of fluoxetine, a selective serotonin reuptake inhibitor antidepressant, on neuronal viability in mouse cortical near-pure neuronal cultures. Addition of fluoxetine to the media for 24 hours induced neuronal death in a concentration-dependent manner. To delineate the mechanisms of fluoxetine-induced neuronal death, we investigated the effects of trolox, cycloheximide (CHX), BDNF, z-VAD-FMK, and various metal-chelators on fluoxetine-induced neuronal death. Neuronal death was assessed by MTT assay. The addition of 20 µM fluoxetine to the media for 24 hours induced 60-70% neuronal death, which was associated with the hallmarks of apoptosis, chromatin condensation and DNA laddering. Fluoxetine-induced death was significantly attenuated by CHX, BDNF, or z-VAD-FMK. Treatment with antioxidants, trolox and ascorbate, also markedly attenuated fluoxetine-induced death. Interestingly, some divalent cation chelators (EGTA, Ca-EDTA, and Zn-EDTA) also markedly attenuated the neurotoxicity. Fluoxetine-induced reactive oxygen species (ROS) generation was measured using the fluorescent dye 2',7'-dichlorofluorescin diacetate. Trolox and bathocuproine disulfonic acid (BCPS), a cell membrane impermeable copper ion chelator, markedly attenuated the ROS production and neuronal death. However, deferoxamine, an iron chelator, did not affect ROS generation or neurotoxicity. We examined the changes in intracellular copper concentration using a copper-selective fluorescent dye, Phen Green FL, which is quenched by free copper ions. Fluoxetine quenched the fluorescence in neuronal cells, and the quenching effect of fluoxetine was reversed by co-treatment with BCPS, however, not by deferoxamine. These findings demonstrate that fluoxetine could induce apoptotic and oxidative neuronal death associated with an influx of copper ions.

Effects of NADPH Oxidase Inhibitors and Mitochondria-Targeted Antioxidants on Amyloid ß1-42-Induced Neuronal Deaths in Mouse Mixed Cortical Cultures.

The Amyloid ß peptide (Aß) is a main component of senile plaques in Alzheimer's disease. Currently, NADPH oxidase (NOX) and mitochondria are considered as primary sources of ROS induced by Aß. However, the contribution of NOX and mitochondria to Aß-induced ROS generation has not been well defined. To delineate the relative involvement of NOX and mitochondria in Aß-induced ROS generation and neuronal death in mouse cortical cultures, we examined the effect of NOX inhibitors, apocynin and AEBSF, and the mitochondria-targeted antioxidants (MTAs), mitotempol and mitoquinone, on Aß-induced ROS generation and neuronal deaths. Cell death was assessed by measuring lactate dehydrogenase efflux in bathing media at 24 and 48 hrs after exposure to Aß1-42. Aß1-42 induced dose- and time-dependent neuronal deaths in cortical cultures. Treatment with 20 µM Aß1-42 markedly and continuously increased not only the DHE fluorescence (intracellular ROS signal), but also the DHR123 fluorescence (mitochondrial ROS signal) up to 8 hrs. Treatment with apocynin or AEBSF selectively suppressed the increase in DHE fluorescence, while treatment with mitotempol selectively suppressed the increase in DHR123 fluorescence. Each treatment with apocynin, AEBSF, mitotempol or mitoquinone significantly attenuated the Aß1-42-induced neuronal deaths. However, any combined treatment with apocynin/AEBSF and mitotempol/mitoquinone failed to show additive effects. These findings indicate that 20 µM Aß1-42 induces oxidative neuronal death via inducing mitochondrial ROS as well as NOX activation in mixed cortical cultures, but combined suppression of intracellular and mitochondrial ROS generation fail to show any additive neuroprotective effects against Aß neurotoxicity.

Highly Ordered Microscale-Pyramidal-Structure-Arrayed Silicon Membranes for Filter Applications.

Microscale-pyramidal-structure-arrayed patterned silicon membranes are manufactured using semiconductor processes and potassium hydroxide (KOH) etching techniques for filter applications. The silicon nitride on silicon on the insulator wafer functions as a masking layer, and the roughness of the silicon (100) plane strongly depends on the etching temperature and KOH concentration. To fabricate the membrane filter, a series of dry and wet etching using 45 wt% KOH solutions at the constant temperature of 70 °C was performed. With the dry and wet etching, micro-pyramidal arrays with 300 µm top and 16-20 µm bottom opening sizes were created. The morphological structures were analyzed using scanning electron microscopy. The manufactured membranes were tested as optical directional filters and particle filters.

NADPH Oxidase Mediates ß-Amyloid Peptide-Induced Neuronal Death in Mouse Cortical Cultures.

ß-Amyloid peptide (Aß) is the main component of senile plaques in patients with Alzheimer's disease, and is known to be a main pathogenic factor of the disease. Recent evidence indicates that activation of NADPH oxidase (NOX) in microglia or astrocytes may be a source of Aß-induced reactive oxygen species (ROS). We investigated the role of neuronal NOX in Aß-induced neuronal death in mouse mixed cortical cultures. Cell death was assessed by measuring lactate dehydrogenase efflux to bathing media 24 or 48 hr after exposure to Aß25-35, a fragment of Aß with an equivalent neurotoxic effect. Aß25-35 induced neuronal death in concentration- and time- dependent manners with apoptotic features. Neuronal death was significantly attenuated, not only by anti-apoptotic drugs, such as z-VAD-fmk and cycloheximide, but also by antioxidants, such as trolox, ascorbic acid, and epigallocatethin gallate. We also demonstrated that treatment with 20 µM Aß25-35 increased fluorescent signals in mixed cortical cultures, but produced only weak signals in pure astrocyte cultures in the presence of 2',7'-dichlorofluorescin diacetate (DCF-DA), an indicator for intracellular ROS. Increased DCF-DA fluorescence was markedly inhibited, not only by trolox, but also by selective NOX inhibitors, such as apocynin and AEBSF. Western blot analyses revealed that Aß25-35 increased the expression of gp91phox, a main subunit of NOX in cells. The above antioxidants, apocynin, and AEBSF significantly attenuated neuronal death induced by Aß25-35. Furthermore, the gp91phox-specific siRNA-based knockdown of NOX significantly inhibited neuronal death. These results suggest that activation of neuronal NOX is involved in Aß25-35-induced neuronal death.

Neuroprotection by valproic Acid in mouse models of permanent and transient focal cerebral ischemia.

Valproic acid (VPA) is a well-known anti-epileptic and mood stabilizing drug. A growing number of reports demonstrate that VPA is neuroprotective against various insults. Despite intensive efforts to develop new therapeutics for stroke over the past two decades, all treatments have thus far failed to show clinical effect because of treatment-limiting side effects of the drugs. Therefore, a safety-validated drug like VPA would be an attractive candidate if it has neuroprotective effects against ischemic insults. The present study was undertaken to examine whether pre- and post-insult treatments with VPA protect against brain infarct and neurological deficits in mouse transient (tMCAO) and permanent middle cerebral artery occlusion (pMCAO) models. In the tMCAO (2 hr MCAO and 22 hr reperfusion) model, intraperitoneal injection of VPA (300 mg/kg, i.p.) 30 min prior to MCAO significantly reduced the infarct size and the neurological deficit. VPA treatment immediately after reperfusion significantly reduced the infarct size. The administration of VPA at 4 hr after reperfusion failed to reduce the infarct size and the neurological deficit. In the pMCAO model, treatment with VPA (300 mg/kg, i.p.) 30 min prior to MCAO significantly attenuated the infarct size, but did not affect the neurological deficit. Western blot analysis of acetylated H3 and H4 protein levels in extracts from the ischemic cortical area showed that treatment with VPA increased the expression of acetylated H3 and H4 at 2 hrs after MCAO. These results demonstrated that treatment with VPA prior to ischemia attenuated ischemic brain damage in both mice tMCAO and pMCAO models and treatment with VPA immediately after reperfusion reduced the infarct area in the tMCAO model. VPA could therefore be evaluated for clinical use in stroke patients.

Taxol induces oxidative neuronal cell death by enhancing the activity of NADPH oxidase in mouse cortical cultures.

We examined the involvement of oxidative stress in neuronal cell death induced by taxol, a microtubule-stabilizing anti-cancer drug and investigated whether NADPH oxidase plays a role in taxol-induced neuronal cell death in mouse cortical cultures. Cell death was assessed by measuring lactate dehydrogenase in the bathing media after 24-h exposure to taxol. Taxol (30-1000 nM) induced the concentration-dependent neuronal death with apoptotic features. The neuronal death induced by taxol was significantly attenuated not only by anti-apoptotic drugs such as z-VAD-fmk and cycloheximide but also by antioxidants such as trolox, ascorbic acid and tempol. Vinblastine, a microtubule-depolymerizing anti-cancer drug, also induced neuronal death. The neuronal cell death induced by vinblastine was also attenuated by z-VAD-fmk, but not by antioxidants and NADPH oxidase inhibitors. Exposure the cortical cultures to taxol for 80 min formed neurite beadings visualized by fluorescence immunocytochemistry for tubulin. Treatment with either trolox or apocynin, an NADPH oxidase inhibitor, did not affect formation of the neurite beadings. RT-PCR and Western blot analysis revealed that exposure to taxol increased the expression of p47(phox) and gp91(phox) and induced translocation of the p47(phox) to the membrane in cortical cultures. Exposure to taxol markedly increased cellular 2,7-dichlorofluorescin diacetate fluorescence, an indicator for reactive oxygen species. Apocynin and trolox markedly inhibited the taxol-induced increase of the fluorescence. Moreover, treatment with NADPH oxidase inhibitors or suppression of gp91(phox) by siRNA significantly attenuated the taxol-induced neuronal death. These results indicate that taxol induces oxidative neuronal apoptosis by enhancing the activity of NADPH oxidase.

Inhibition of matrix metalloproteinase-9 attenuated neural progenitor cell migration after photothrombotic ischemia.

Recent studies have shown that neuroblasts migrate from the subventricular zone (SVZ) into the injured area after ischemic brain insults. However, it is not well understood which mechanism mediates this ectopic migration and which types of cells migrate into the damaged region from the SVZ. The present study was designed to investigate the characteristics of the migration of nestin-positive neural stem cells toward the region of ischemic injury after focal cortical ischemia. Nestin-eGFP transgenic mice were used to effectively model the migration of SVZ cells. Photothrombotic ischemia was induced by injection of rose bengal (30 mg/kg) and exposure to cold light. Migration of nestin-positive cells was examined using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and bromodeoxyuridine (BrdU) labeling. The number of nestin-positive cells was increased significantly in the peri-infarct area at 5 and 7 days after photothrombosis. A subset of nestin-positive cells was co-labeled with DiI or BrdU. Some of the nestin-positive cells co-expressed doublecortin (DCX) and only a few nestin-positive cells co-labeled with anti-epidermal growth factor receptor (EGFr) antibody. However, no nestin-positive cells were immunoreactive for glial fibrillary acidic protein (GFAP). The inhibition of matrix metalloproteinases (MMPs) using the MMP inhibitor, FN-439, decreased nestin-positive cells in the peri-infarct region at 7 days after photothrombosis. Although MMP-9 was not co-expressed in the nestin-positive cells in the peri-infarct cortex, MMP-9 did co-localize with GFAP-positive astrocytes. These results suggest that nestin-positive neural progenitor cells migrate into the peri-infarct cortex after photothrombotic ischemia and that MMP-9 is involved in the migration.

System L-amino acid transporters are differently expressed in rat astrocyte and C6 glioma cells.

The system L-amino acid transporter is a major nutrient transport system that is responsible for Na+-independent transport of neutral amino acids including several essential amino acids. We have compared and examined the expressions and functions of the system L-amino acid transporters in both rat astrocyte cultures and C6 glioma cells. The rat astrocyte cultures expressed the l-type amino acid transporter 2 (LAT2) with its subunit 4F2hc, whereas the l-type amino acid transporter 1 (LAT1) was not expressed in these cells. The C6 glioma cells expressed LAT1 but not LAT2 with 4F2hc. The [14C]l-leucine uptakes by the rat astrocyte cultures and C6 glioma cells were Na+-independent and were completely inhibited by the system l selective inhibitor, BCH. These results suggest that the transport of neutral amino acids including several essential amino acids into rat astrocyte cultures and C6 glioma cells are for the most part mediated by LAT2 and LAT1, respectively. Therefore, the rat astrocyte cultures and C6 glioma cells are excellent tools for examining the properties of LAT2 and LAT1, respectively. Moreover, the specific inhibition of LAT1 in cancer cells might be a new rationale for anti-cancer therapy.