Protective effects of fusidic acid against sodium nitroprusside-induced apoptosis in C6 glial cells.

Fusidic acid, a steroidal antibiotic, possesses antimicrobial, antioxidant, and anti-inflammatory properties, but the effect of fusidic acid against neurodegenerative disease-related cell death has not been studied. Here, we investigated the protective effects of fusidic acid on sodium nitroprusside (SNP)-induced toxicity in C6 glial cells. Fusidic acid (5-20 µM) prevented SNP (100 µM)-induced cell death dose dependently, and effectively attenuated SNP-induced generation of nitric oxide (NO), total reactive oxygen species (ROS), and peroxynitrite (ONOO). Fusidic acid (20 µM) pretreatment significantly suppressed SNP (100 µM)-induced apoptotic events, such as nuclear condensation and caspase-3 activation. In addition, fusidic acid effectively attenuated SNP-induced endoplasmic reticulum (ER) stress markers, such as GRP78, IRE1, ATF6, PERK, XBP1s, eIF2α, CHOP, and caspase-12. A specific adenosine monophosphate-activated protein kinase (AMPK) inhibitor, compound C (10 µM), reversed the preventive effects of fusidic acid against SNP-induced cytotoxicity, CHOP elevation, and caspase-3 activation. These results suggest that fusidic acid can protect C6 glial cells against cytotoxicity, through the regulation of AMPK pathway and apoptotic events.

Protective Effects of Alpha-Lipoic Acid on Glutamate-Induced Cytotoxicity in C6 Glioma Cells.

Glutamate-mediated cytotoxicity has been implicated in the pathogenesis of neurological diseases, including Parkinson's disease, Alzheimer's disease, and stroke. In this study, we investigated the protective effects of alpha-lipoic acid (ALA), a naturally occurring thiol antioxidant, on glutamate-induced cytotoxicity in cultured C6 astroglial cells. Exposure to high-dose glutamate (10 mM) caused oxidative stress and mitochondrial dysfunction through the elevation of reactive oxygen species, depletion of glutathione, and loss of the mitochondrial membrane potential (ΔΨm). Pretreatment with ALA (200 µM), however, significantly inhibited the glutamate-induced oxidative stress and mitochondrial dysfunction. ALA pretreatment dose-dependently suppressed glutamate-induced apoptotic events including altered nuclear morphology and activation of caspase-3. In addition, ALA significantly attenuated glutamate-induced endoplasmic reticulum (ER) stress markers; namely, glucose-regulated protein 78 (GRP78), activating transcription factor 6 (ATF6), protein kinase regulated by RNA (PKR)-like ER-associated kinase (PERK), eukaryotic translation initiation factor 2 alpha (eIF2α), inositol-requiring enzyme 1 (IRE1), CCAAT/enhancer binding protein homologous protein (CHOP), and caspase-12. We confirmed that CHOP and caspase-12 are key mediators of glutamate-induced ER stress. Furthermore, exposure of the cells to a caspase-12-specific inhibitor and CHOP small interfering RNAs (siRNAs) led to restoration of the ΔΨm that was damaged by glutamate treatment. These results suggest that ALA can effectively suppress oxidative stress, mitochondrial dysfunction, and ER stress in astroglial cells.

Protective Effects of Curcumin on Manganese-Induced BV-2 Microglial Cell Death.

Curcumin, a bioactive component in tumeric, has been shown to exert antioxidant, anti-inflammatory, anticarcinogenic, hepatoprotective, and neuroprotective effects, but the effects of curcumin against manganese (Mn)-mediated neurotoxicity have not been studied. This study examined the protective effects of curcumin on Mn-induced cytotoxicity in BV-2 microglial cells. Curcumin (0.1-10 µM) dose-dependently prevented Mn (250 µM)-induced cell death. Mn-induced mitochondria-related apoptotic characteristics, such as caspase-3 and -9 activation, cytochrome c release, Bax increase, and Bcl-2 decrease, were significantly suppressed by curcumin. In addition, curcumin significantly increased intracellular glutathione (GSH) and moderately potentiated superoxide dismutase (SOD), both which were diminished by Mn treatment. Curcumin pretreatment effectively suppressed Mn-induced upregulation of malondialdehyde (MDA), total reactive oxygen species (ROS). Moreover, curcumin markedly inhibited the Mn-induced mitochondrial membrane potential (MMP) loss. Furthermore, curcumin was able to induce heme oxygenase (HO)-1 expression. Curcumin-mediated inhibition of ROS, down-regulation of caspases, restoration of MMP, and recovery of cell viability were partially reversed by HO-1 inhibitor (SnPP). These results suggest the first evidence that curcumin can prevent Mn-induced microglial cell death through the induction of HO-1 and regulation of oxidative stress, mitochondrial dysfunction, and apoptotic events.

Melatonin Attenuates Manganese and Lipopolysaccharide-Induced Inflammatory Activation of BV2 Microglia.

Melatonin, a naturally occurring neurohormone in the pineal gland, has been shown to exert antioxidant and anti-inflammatory effects. This study examined the effects of melatonin on manganese (Mn) and/or lipopolysaccharide (LPS)-induced microglial activation. Melatonin (10 µM) inhibited Mn (100 µM) and/or LPS (0.5 µg/ml)-induced phagocytotic activity of activated BV2 microglia. It also inhibited the lipid peroxidation and intracellular reduced glutathione (GSH) depletion induced by Mn and/or LPS. Melatonin effectively suppressed the upregulation of interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) at both mRNA and protein levels in Mn and/or LPS-stimulated BV2 microglia. In addition, melatonin pretreatment attenuated Mn and/or LPS-induced degradation of IκB-α, nuclear translocation of nuclear factor-κB (NF-κB) and its activation, and the expressions of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) in BV2 microglial cells. These results suggest that melatonin can effectively modulate phagocytosis and expression of proinflammatory mediators, and can prevent neuroinflammatory disorders accompanied by microglial activation.

Protective effects of quercetin on dieldrin-induced endoplasmic reticulum stress and apoptosis in dopaminergic neuronal cells.

Dieldrin, an organochlorine pesticide still used in several developing countries, has been proposed as a risk factor for Parkinson's disease. Quercetin is one of the potent bioactive flavonoids present in numerous plants. In this study, we investigated the protective effects of quercetin on neurotoxicity induced by dieldrin in cultured dopaminergic SN4741 cells. Our initial experiments showed that quercetin (10-40 µM) dose dependently prevented dieldrin (20 µM)-induced cytotoxicity in SN4741 cells. Pretreatment for 1 h with quercetin before dieldrin application could significantly suppress dieldrin-induced apoptotic characteristics, including nuclear condensation, DNA fragmentation, and caspase-3/7 activation. Results showed that dieldrin-induced markers of endoplasmic reticulum (ER) stress response such as chaperone GRP78, heme oxygenase-1, and phosphorylation of the α subunit of eukaryotic initiation factor 2. In addition, dieldrin reduced antiapoptotic Bcl-2 expression, but significantly elevated a proapoptotic transcription factor CHOP. Furthermore, RNA interference to CHOP almost completely repressed dieldrin-induced apoptotic cell death. Interestingly, quercetin prevented the changes in dieldrin-induced ER stress markers. These results suggest that quercetin may suppress the ER stress-CHOP pathway and dieldrin-induced apoptosis in dopaminergic neurons.

Protective effects of N-acetylcysteine against monosodium glutamate-induced astrocytic cell death.

Monosodium glutamate (MSG) is a flavor enhancer, largely used in the food industry and it was reported to have excitotoxic effects. Higher amounts of MSG consumption have been related with increased risk of many diseases, including Chinese restaurant syndrome and metabolic syndromes in human. This study investigated the protective effects of N-acetylcysteine (NAC) on MSG-induced cytotoxicity in C6 astrocytic cells. MSG (20 mM)-induced reactive oxygen species (ROS) generation and apoptotic cell death were significantly attenuated by NAC (500 µM) pretreatment. NAC effectively inhibited the MSG-induced mitochondrial membrane potential (MMP) loss and intracellular reduced glutathione (GSH) depletion. In addition, NAC significantly attenuated MSG-induced endoplasmic reticulum (ER) stress markers, such as XBP1 splicing and CHOP, PERK, and GRP78 up-regulation. Furthermore, NAC prevented the changes of MSG-induced Bcl-2 expression level. These results suggest that NAC can protect C6 astrocytic cells against MSG-induced oxidative stress, mitochondrial dysfunction, and ER stress.

MicroRNA-205 directly regulates the tumor suppressor, interleukin-24, in human KB oral cancer cells.

MicroRNA (miRNA) is a form of small noncoding RNA that regulates the expression of genes either by inhibiting mRNA translation or by inducing its degradation. Small microRNA play important roles in regulating a large number of cellular processes, including development, proliferation and apoptosis. This study examined the biological functions of miR-205 as a tumor suppressor in KB oral cancer cells. The results showed that miR-205 expression was significantly lower in KB oral cancer cells than in human normal oral keratinocytes. Furthermore, the miR-205 over-expressed in KB oral cancer cells increased the cell cytotoxicity and induced apoptosis through the activation of caspase-3/-7. The transfection of miR-205 into KB oral cancer cells strongly induced IL-24, a well known cytokine that acts as a tumor suppressor in a range of tumor tissues. In addition, miR-205 targeted the IL-24 promoter directly to induce gene expression. Overall, miR-205 has significant therapeutic potential to turn on silenced tumor suppressor genes by targeting them with miRNA.

The plant phenolic diterpene carnosol suppresses sodium nitroprusside-induced toxicity in c6 glial cells.

Carnosol, a naturally occurring bioactive phenolic diterpene originating from rosemary and sage, has been shown to exert antioxidant and anti-inflammatory effects. This study examined possible protective effects of carnosol on sodium nitroprusside (SNP)-induced cytotoxicity in C6 glial cells. Carnosol (1-10 microM) dose-dependently attenuated SNP (100 microM)-induced cell death and NO production. SNP-induced apoptotic characteristics, including DNA fragmentation, caspase-3 activation, and c-jun N-terminal protein kinase (JNK) phosphorylation, were significantly suppressed by carnosol (10 microM). In addition, carnosol pretreatment restored the level of reduced glutathione (GSH), which was diminished by SNP treatment. Although both SNP (100 microM) and carnosol (10 microM) stimulated the HO-1 expression time-dependently, SNP caused a temporal increase in HO-1 in early time periods (3-6 h) before cell death occurred. In contrast, carnosol induced the sustained expression of HO-1 until a late time point (24 h). The addition of 1 microM zinc protoporphyrin IX (ZnPP), a specific HO inhibitor, with SNP or carnosol further reduced cell viability. Also, the addition of ZnPP inhibited the protective effect of carnosol against SNP-induced cytotoxicity in C6 cells. These results suggest that carnosol possesses abilities to inhibit SNP-mediated glial cell death through modulation of apoptotic events and induction of HO-1 expression.

Nargenicin attenuates lipopolysaccharide-induced inflammatory responses in BV-2 cells.

Microglia activation has been considered as a major factor associated with neurodegenerative diseases. In this study, we investigated the inhibitory effects of nargenicin, a natural antibiotic from soil bacterium Nocardia, on lipopolysaccharide (LPS)-induced inflammatory activation of microglia. Nargenicin significantly attenuated LPS-induced nitric oxide production in BV-2 microglial cells. Furthermore, nargenicin effectively suppressed the upregulation of interleukin-1beta, tumor necrosis factor alpha, and inducible nitric oxide synthase at both mRNA and protein levels in LPS-stimulated BV-2 microglia. In addition, nargenicin blocked LPS-induced degradation of IkappaB-alpha, indicating that the initial molecular target of nargenicin is the transcription factor nuclear factor-kappaB. These results suggest that nargenicin should be evaluated as a therapeutic agent for inflammatory neurodegenerative diseases.

Rosmarinic acid protects human dopaminergic neuronal cells against hydrogen peroxide-induced apoptosis.

In this study, we investigated the protective effects of rosmarinic acid (RA) on H(2)O(2)-induced neurotoxicity in human dopaminergic cell line, SH-SY5Y. Results showed that RA significantly attenuated H(2)O(2)-induced reactive oxygen species (ROS) generation and apoptotic cell death. Rosmarinic acid effectively suppressed the up-regulation of Bax and down-regulation of Bcl-2. Furthermore, RA stimulated the antioxidant enzyme heme oxygenase-1 (HO-1). We also demonstrated that the HO-1 induction by RA was associated with the protein kinase A (PKA) and phosphatidylinositiol-3-kinase (PI3K) signaling pathways. These results suggest that RA can protect SH-SY5Y cells under oxidative stress conditions by regulating apoptotic process. Thus, RA should be clinically evaluated for the prevention of neurodegenerative diseases.

Modulation of parkin gene expression in noradrenergic neuronal cells.

Typical autosomal recessive juvenile Parkinsonism (AR-JP) is resulted from the loss of function mutation in the parkin gene. In an effort to learn more about the cell type-specific functional role of parkin, we used in vitro model such as locus coeruleus (LC) noradrenergic (NA) neuronal progenitor cell line, LC3541. Employing this in vitro model, we revealed that parkin plays a crucial role in phenotypic differentiation of NA neurons. Our results showed that parkin mRNA was expressed during the differentiation of NA neuronal progenitor cell line and that the level of the parkin mRNA was down-regulated by oxidative stress in the NA neuronal cells. Parkin protein overexpression in LC3541 cells induced expression of NA markers (TH, phox2a and DBH). Small interfering RNA (SiRNA) for parkin supressed NA differentiation and DBH expression. Preventing protein kinase A (PKA) activation with PKI attenuated expression of DBH in parkin overexpressed LC3541 cells. These findings suggest that the relative abundance of parkin enhances differentiation of NA phenotypes via a PKA-dependent pathway.