Biomedical subjects

A Y Sun

Publications and source records attributed to A Y Sun.

At least 19 recordsLinked to original sources

PubMed2003

Prostaglandin E2 production in astrocytes: regulation by cytokines, extracellular ATP, and oxidative agents.

Upregulation and activation of phospholipases A2 (PLA2) and cyclooxygenases (COX) leading to prostaglandin E2(PGE2) production have been implicated in a number of neurodegenerative diseases. In this study, we investigated PGE2 production in primary rat astrocytes in response to agents that activate PLA2 including pro-inflammatory cytokines (IL-1beta, TNFalpha and IFNgamma), the P2 nucleotide receptor agonist ATP, and oxidants (H2O2 and menadione). Exposure of astrocytes to cytokines resulted in a time-dependent increase in PGE2 production that was marked by increased expression of secretory sPLA2 and COX-2, but not COX-1 and cytosolic cPLA2. Although astrocytes responded to ATP or phorbol ester (PMA) with increased cPLA2 phosphorylation and arachidonic acid release, ATP or PMA only caused a small increase in levels of PGE2. However, when astrocytes were first treated with cytokines, further exposure to ATP or PMA, but not H2O2 or menadione, markedly increased PGE2 production. These results suggest that ATP release during neuronal excitation or injury can enhance the inflammatory effects of cytokines on PGE2 production and may contribute to chronic inflammation seen in Alzheimer's disease.

Adenosine Triphosphate↗

PubMed2001

The C. elegans gon-2 gene encodes a putative TRP cation channel protein required for mitotic cell cycle progression.

The C. elegans gon-2 gene is required for the post-embryonic mitotic cell divisions of the gonadal precursor cells. A single major transcript of approximately 6.7 kb is derived from the gon-2 locus. This mRNA encodes a protein related to the TRP family of cation channels and has a high degree of similarity to several vertebrate genes, including melastatin. Mutant alleles of gon-2 affect evolutionarily conserved amino acid residues. Northern analyses suggest that gon-2 expression is not limited to gonadal tissues.

Alleles↗

PubMed2001

Oxidized lipoproteins, beta amyloid peptides and Alzheimer's disease.

Recent studies have provided strong evidence for the involvement of oxidative stress in the pathogenesis of Alzheimer's disease (AD) and beta-amyloid peptides (ABeta) have been implicated to play an important role in mediating these oxidative events. Lipoproteins (LP) in the brain are likely targets of oxidative insult and together enhance ABeta -mediated toxicity to neurons. We hypothesize that uptake of oxidized LP by neuron leads to an acceleration of the intracellular oxidative pathways and exacerbation of neuron cell death. In our previous studies, we demonstrated the ability of oxidized low-density LP from plasma to induce cell death in PC12 cells. In this study, a synthetic LP fraction was prepared using lipids extracted from rat brain and incubated with albumin and apoE. This brain lipid-derived LP (BLP) was subjected to oxidation by incubation with Fe(3+)and subsequently tested with primary cortical neurons in culture. To study uptake of the BLP, native and oxidized BLP containing apoE3 or apoE4 were labeled with [(14)C]cholesterol or the fluorescent probe 3,3-dioctadecylindo-carbocyanine (Di-I) prior to exposing to cultured neurons. Results showed that regardless of the labeling method, oxidized BLP were more effectively taken up by the neurons than the native BLP. Cell viability was assessed by assaying the release of lactate dehydrogenase (LDH) into the medium and by determining the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), an agent depicting mitochondrial activity. While exposure of neurons to oxidized BLP and aggregated ABeta (1-42) alone could result in MTT reduction (24%), greater reduction (40%) could be observed when oxidized LP was added together with ABeta. Neuronal cell death due to oxidized BLP could be ameliorated by resveratrol, a polyphenolic compound known for its antioxidant properties. Taken together, these results are in agreement with the notion that ABeta and oxidized BLP can synergistically enhance oxidative damage in neurons and antioxidants such as resveratrol can ameliorate these damages.

Journal Article↗

PubMed2001

Ethanol and oxidative stress.

This article represents the proceedings of a workshop at the 2000 ISBRA Meeting in Yokohama, Japan. The chair was Albert Y. Sun. The presentations were (1) Ethanol-inducible cytochrome P-4502E1 in alcoholic liver disease, by Magnus Ingelman-Sundberg and Etienne Neve; (2) Regulation of NF-kappaB by ethanol, by H. Matsumoto, Y. Nishitani, Y. Minowa, and Y. Fukui; (3) Chronic ethanol consumption increases concentration of oxidized proteins in rat liver, by Shannon M. Bailey, Vinood B. Patel, and Carol C. Cunningham; (4) Antiphospholipids antibodies and oxidized modified low-density lipoprotein in chronic alcoholic patients, by Tomas Zima, Lenka Fialova, Ludmila Mikulikova, Ptr Popov, Ivan Malbohan, Marta Janebova, and Karel Nespor; and (5) Amelioration of ethanol-induced damage by polyphenols, by Albert Y. Sun and Grace Y. Sun.

Alcoholism↗

PubMed1999

Grape polyphenols protect neurodegenerative changes induced by chronic ethanol administration.

Increased oxidative stress in the brain due to chronic ethanol consumption is known to result in a number of neurodegenerative changes. This study was designed to test whether dietary supplementation of grape polyphenols (GP) can offer protection to the neurodegenerative changes resulting from chronic ethanol consumption. Sprague-Dawley rats were fed a Leiber-DeCarli liquid diet with ethanol or isocaloric amount of maltose, and with or without GP for 2 months. Chronic ethanol caused significant decreases in synaptosomal Na,K-ATPase (20.5%) and dopamine uptake (22.8%) activities compared with pair-fed controls. Although GP alone did not alter activities of these membrane-bound proteins, GP supplementation was able to completely protect the decrease in synaptic protein function elicited by chronic ethanol consumption.

Alcoholism↗

PubMed1999

Paraquat induced activation of transcription factor AP-1 and apoptosis in PC12 cells.

Drugs and certain environmental toxins may be responsible for the pathogenesis of Parkinson's disease. We have used paraquat as a model toxin for this study since paraquat has been shown to make its way to the nerve terminals and cause cell death of dopamine neurons by oxidative injury. We have shown by the electrophoretic mobility shift assay that paraquat, together with low concentrations of chelated iron (Fe++/DETAPAC), induced the activation of transcription factor AP-1 binding activity to DNA. Under similar conditions we also found by both a DNA laddering assay procedure and by terminal deoxynucleotidyl transferase assay (TUNEL assay) that paraquat also induces apoptotic cell death. Interestingly, both apoptotic cell death and AP-1/DNA binding activity induced by paraquat were blocked by cyclohexamide and genistein, indicating that both the AP-1/DNA binding activation and apoptosis induced by paraquat are closely related. Moreover, cells were also protected from paraquat toxicity in the presence of antioxidant defense enzymes SOD and catalase. The results support the hypothesis that oxidative stress may be contributing to the apoptotic cell death of dopaminergic neurons, leading to the manifestation of Parkinson's disease. Since paraquat was an important herbicide in the mid 20th Century, our results have the important implication that exposure to environmental toxins such as paraquat may induce Parkinson's disease.

Animals↗

PubMed1999

Dietary supplementation of grape polyphenols to rats ameliorates chronic ethanol-induced changes in hepatic morphology without altering changes in hepatic lipids.

Increase in oxidative stress after chronic ethanol consumption can result in hepatic injury. Because polyphenolic compounds can offer antioxidant protection to the cardiovascular system, this study was designed to investigate whether dietary supplementation of polyphenols from grapes may ameliorate hepatic injury resulting from chronic ethanol consumption. Male Sprague-Dawley rats were administered the following diets for 2 mo: 1) Lieber-DeCarli (L-D) diet with isocaloric amount of maltose instead of ethanol (Basal), 2) the L-D diet with 50g/L ethanol (EtOH); 3) L-D diet with 50 mg/L of grape polyphenols (GP) and 4) ethanol diet with GP (EtOH + GP). Rats given EtOH or EtOH + GP diets had significantly more hepatic triacylglycerols (P < 0.0001) and lipid peroxidation products (P < 0.01) compared with those given the Basal and GP diets. In addition, ethanol ingestion also decreased significantly (P < 0.01) the proportion of 16:0 and increased 18:0 and 18:1 in hepatic phospholipids, suggesting a perturbation of the de novo fatty acid biosynthesis pathways. However, GP supplementation alone and GP added to the ethanol diet did not alter the lipid changes mediated by ethanol except for the levels of 22:6(n-3) which were significantly (P < 0.05) higher in the EtOH + GP group than in the EtOH group. Despite a lack of gross lipid changes, histologic assessment showed significantly (P < 0.05) less hepatic damage in the GP + EtOH group compared with the EtOH group. These results clearly distinguished ethanol-mediated changes in hepatic morphology from the changes in hepatic lipids and further demonstrated the ability of GP to ameliorate hepatic damage resulting from chronic ethanol consumption.

Animals↗

PubMed1998

Oxidized lipoproteins activate NF-kappaB binding activity and apoptosis in PC12 cells.

Oxidative stress in the central nervous system may cause oxidation of lipoproteins. The oxidized lipoproteins may in turn damage cellular and subcellular membranes and other biomolecules, leading to tissue injury and cell death. Recently, we have demonstrated that oxidized LDL and VLDL induced cell death in a dose-dependent manner. The present study examined the possible signal transduction cascade leading to cell death by oxLDL and oxVLDL in PC12 cells. Using the electrophoretic mobility shift assay, we found that both oxLDL and oxVLDL activated the binding of NF-kappaB to the consensus sequence in the promoter region of the target genes, followed by apopototic cell death. Resveratrol protects the cells from both the activation of NF-kappa-B/ DNA binding activity and apoptotic cell death. Results indicated that oxidized lipoproteins may serve as an oxidative mediator and may activate apoptosis through a nuclear signalling pathway contributing to the pathology in Alzheimer's disease.

Animals↗

PubMed1998

A novel thrombopoietin signaling defect in polycythemia vera platelets.

The pathogenesis of polycythemia vera (PV), a disease involving a multipotent hematopoietic progenitor cell, is unknown. Thrombopoietin (TPO) is a newly characterized hematopoietic growth factor which regulates the production of multipotent hematopoietic progenitor cells as well as platelets. To evaluate the possibility that an abnormality in TPO-mediated signal transduction might be involved in the pathogenesis of PV, we examined TPO-induced protein tyrosine phosphorylation using platelets as a surrogate model system. Platelets were isolated from the blood of patients with PV as well as from patients with other chronic myeloproliferative disorders and control subjects. Impaired TPO-mediated platelet protein tyrosine phosphorylation was a consistent observation in patients with PV as well as those with idiopathic myelofibrosis (IMF), in contrast to patients with essential thrombocytosis, chronic myelogenous leukemia, secondary erythrocytosis, iron deficiency anemia, hemochromatosis, or normal volunteers. Thrombin-mediated platelet protein tyrosine phosphorylation was intact in PV platelets as was expression of the appropriate tyrosine kinases and their cognate substrates. However, expression of the platelet TPO receptor, Mpl, as determined by immunoblotting, chemical crosslinking or flow cytometry was markedly reduced or absent in 34 of 34 PV patients and also in 13 of 14 IMF patients. Impaired TPO-induced protein tyrosine phosphorylation in PV and IMF platelets was uniformly associated with markedly reduced or absent expression of Mpl. We conclude that reduced expression of Mpl is a phenotypic characteristic of platelets from patients with PV and IMF. The abnormality appears to distinguish PV from other forms of erythrocytosis and may be involved in the platelet function defect associated with PV.

Blood Platelets↗

PubMed1998

Extracellular ATP-induced apoptosis in PC12 cells.

Studies in our laboratory indicate that extracellular ATP (ATP)o may induce cell death by reactive oxygen insults. We have also shown that the Ca(2+)-induced oxidative stress as elicited by ATP may lead to an activation of a specific AP-1 activity. Since early impairment of mitochondria constitutes a critical event of the apoptotic cell death, we have examined whether (ATP)o will affect mitochondrial damage and cell injury by using mitochondrial specific probes, dihydrorhodamine and 3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). We have found that (ATP)o induced cell death in a concentration dependent manner by MTT assay. The (ATP)o induced cell death correlated well with the reactive oxygen species (ROS) generation in mitochondria, since (ATP)o enhanced both cell death and ROS production and antioxidant blocked both of these processes. We found (ATP)o treatment led to apoptotic cell death by examining DNA laddering and the TUNEL assay. Interestingly, vitamin C and vitamin E combined treatment appeared to attenuate the (ATP)o-induced apoptosis. Results indicated that (ATP)o may cause oxidative damage of mitochondria leading to apoptotic cell death. Antioxidants may be useful in preventing apoptosis by preventing ROS formation in mitochondria.

Adenosine Triphosphate↗

PubMed1998

Oxidized lipoproteins may play a role in neuronal cell death in Alzheimer disease.

Oxidative stress in the central nervous system (CNS) may cause oxidation of lipoprotein particles. The oxidized lipoproteins may damage cellular and subcellular membranes, leading to tissue injury and cell death. Human low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) are oxidized by transition metal ions, such as Cu2+. Using PC 12 cells, we tested the cytotoxicity of oxidized LDL and VLDL. Cell death was increased in a dose-dependent manner. Antioxidants added to the incubation medium, such as vitamins E or C, or resveratrol showed some protection. Results indicated that oxidized lipoproteins may serve as an oxidative stressor, which may initiate the neuronal cell death leading to the manifestation of Alzheimer disease (AD).

Alzheimer Disease↗

PubMed1998

Protection of PC12 cells glutathione peroxidase in L-DOPA induced cytotoxicity.

L-DOPA may cause side-effects during the treatment of Parkinson's disease. We investigated the role of glutathione peroxidase (GSHPx) in cellular defense against L-DOPA cytotoxicity. A line of PC12 cells overexpressing GSHPx with plasmid pRc/CMV-GSHPx was established and stable transfectants overexpressing GSHPx were used for this study. GSHPx activity was found to be 1.5-fold higher in GSHPx-transfectants than in mock-controlled transfectants. Transfectants over expressing GSHPx were also significantly more resistant to exposure to either L-DOPA or t-butyl hydroperoxide than mock-transfected cells. Results suggested that L-DOPA may cause neuronal cell death by an oxidative pathway and GSHPx may play an important role in cellular defense against oxidative stress.

Animals↗

PubMed1998

Paraquat-induced cell death in PC12 cells.

Paraquat was taken up by PC12 cells in a carrier-mediated, saturable manner. When PC12 cells were permeabilized with digitonin (50 microg/ml) lipid peroxidation was observed after paraquat treatment in the presence of NADPH and chelated iron. The fact that lipid peroxidation preceded the appearance of LDH release provides positive evidence that lipid peroxidation may be one of the important factors leading to cytotoxicity of cells. Furthermore, the fact that addition of superoxide dismutase, catalase and promethazine efficiently blocked the malondialdehyde formation and attenuated the cell death indicated the involvement of reactive oxygen radicals in mediating the cytotoxicity induced by paraquat. Taken together the results present in vitro evidence that neurotoxicity of paraquat may be a consequence of cellular lipid peroxidation, which leads to cell death and may have great implications in assessing the risk of exposure to paraquat in Parkinson's disease.

Animals↗

PubMed1998

Activation of transcription factor AP-1 by extracellular ATP in PC12 cells.

We have previously shown that extracellular ATP caused cell death in PC12 cells through activation of its receptors. Oxidative stress has been implicated as a mechanism of cell death caused by extracellular ATP. In the present study we examined the possible signal transduction cascades leading to cell death by extracellular ATP. We found, using the electrophoretic mobility shift assay, that transcription factor AP-1 DNA binding activity was stimulated by extracellular ATP. Northern blot analysis showed that mRNA levels of c-fos, c-jun were elevated after treatment with ATP. The stimulation was receptor mediated, since it was blocked by the ATP receptor antagonist, suramin. The stimulated AP-1 binding was also blocked by the antioxidant N-acetyl-L-cysteine, indicating that reactive oxygen species generated following ATP stimulation were involved in the induction of AP-1 activity. It appears that both translational and posttranslational events contributed to the increased AP-1 DNA binding since cyclohexamide (a protein synthesis inhibitor), genistein (tyrosine kinase inhibitor) and staurosporine (PKC inhibitor) each partially blocked the AP-1 activation. Changes in AP-1 DNA binding activity may modulate expression of target genes involved in cell death pathways.

Acetylcysteine↗

PubMed1998

Paraquat-induced free radical reaction in mouse brain microsomes.

Paraquat has been implicated as an environmental toxin which may induce the syndrome of Parkinson's disease after exposure to this agent. However, the biochemical mechanism by which paraquat causes cell death and neurodegeneration has not been extensively studied. Paraquat was rapidly taken up by nerve terminals isolated from mouse cerebral cortices. It induced lipid peroxidation in a concentration dependent manner in the presence of NADPH and ferrous ion. The maximal stimulation effect was obtained at a paraquat concentration around 100 microM and the Km value for paraquat was 46.7 microM. The lipid peroxidation required microsomal enzymes. Antioxidants, such as superoxide dismutase, catalase and promethazine significantly inhibited paraquat-induced lipid peroxidation. Due to its structural similarity to the pyridinium compound MPP+ (N-methyl-4-phenyl pyridium ion), it may be taken up by dopamine neurons and cause lipid peroxidation and cell death resulting in the manifestation of Parkinsonian syndrome.

Animals↗

PubMed1998

Neuroprotective effects of poly (ADP-ribose) polymerase inhibitors in transient focal cerebral ischemia of rats.

AIM: To explore the role of poly (ADP-ribose) polymerase (PARP) in focal cerebral ischemia with reperfusion injury. METHODS: Male Wistar rats underwent 3.5-h of temporary middle cerebral artery occlusion by intraluminal suture. Infarction volume was showed with 2,3,5-triphenyltetrazolium chloride (TTC) staining and quantitated by image analysis system, neurologic scores were determined with a 0-5 grading scale. RESULTS: 3-Aminobenzamide (3-AB) 10 mg.kg-1 or nicotinamide (Nic) at 20 mg.kg-1 showed potent neuroprotective effects within 0-6 h, neurologic deficits were attenuated. With the increasing dose of PARP inhibitors, beneficial effects were compromised, particularly, administration of Nic 60 mg.kg-1 at the onset of reperfusion drastically accelerated brain damage. Phytomenadione, a selective inhibitor of mono (ADP-ribosyl) transferase, had little effect on infarction volume. CONCLUSION: Transient incomplete inhibition of PARP provides a neuroprotective effects against cerebral ischemia-reperfusion injury, with a relatively wide therapeutic window, whereas severe inhibition of this enzyme, especially in reperfusion phase, is detrimental.

ADP Ribose Transferases↗

PubMed1997

Amelioration of oxidative stress by antioxidants and resveratrol in PC12 cells.

The goal of this study was to investigate the effect of resveratrol, an active ingredient found in grapes and other plant products, in ameliorating oxidative stress. Oxidative stress was induced by addition of Fe2+ and t-butyl hydroperoxide to the cultured PC12 cell medium. Resveratrol, vitamins C and/or E, were added to the cell culture medium during oxidative stress. The combination of resveratrol and vitamins C and/or E was more effective in protecting the cell than was any of these three antioxidants alone.

Animals↗

PubMed1997

Ethanol-induced cell death by lipid peroxidation in PC12 cells.

Free radical generation is hypothesized to be the cause of alcohol-induced tissue injury. Using fluorescent cis-parinaric acid and TBARS, lipid peroxidation was shown to be increased in the presence of trace amounts of free ferrous ion in PC12 cells. This increase in lipid peroxidation was enhanced by ethanol in a dose dependent manner and also correlated with loss of cell viability, as measured by increased release of lactate dehydrogenase (LDH). Resveratrol, a potent antioxidant, had a protective effect against lipid peroxidation and cell death. These findings strongly suggest that ethanol-induced tissue injury and cell death is a free radical mediated process, and may be important in alcohol-related premature aging and other degenerative diseases.

Animals↗