PubMed Health⌕ Search

Biomedical subjects

Dawei Zhang

Publications and source records attributed to Dawei Zhang.

At least 19 recordsLinked to original sources
PubMed2006

Phenotypes and fed-batch fermentation of ubiquinone-overproducing fission yeast using ppt1 gene.

Ubiquinone (UQ), a component of the electron transfer system in many organisms, has been widely used for pharmaceuticals and cosmetics. In this study, we cloned and overexpressed the full-length ppt1 (MTppt1) gene, which encodes p-hydroxybenzoate:polyprenyltransferase and ERppt1 gene, which was modified to be localized on endoplasmic reticulum in fission yeast. The yeast MTppt1 and ERppt1 transgenic lines showed about 3.7 and 5.1 times increment in UQ content and the recombinant yeasts with a higher UQ level are more resistant to H(2)O(2), Cu(2+) and NaCl, and interestingly their growth was also faster than the wild type at lower temperature. For large-scale cultivation, the direct feedback control of glucose using an on-line ethanol concentration monitor for ubiquinone production of yeast ERppt1 by high-cell-density fermentation was investigated and the fermentation parameters (e.g., dissolved oxygen, pH, ethanol concentration, oxygen uptake rate, carbon dioxide evolution rate and respiration quotient) were also discussed. After 90 h cultures, the yeast dry cell weight reached 57 gl(-1) and the ubiquinone yield reached 23 mgl(-1). In addition, plasmid stability was maintained at high level throughout the fermentation.

Biomass↗
PubMed2006

Well-aligned arrays of CuO nanoplatelets.

This paper reports well-aligned arrays of CuO nanoplatelets synthesized through a hydrothermal route without template's assistance. The surface of well-aligned arrays of CuO nanoplatelets looks like a wall. These nanoplatelets, possessing four clear edges, are 50-80 nm in thickness, 150-250 nm in width, and 0.8-1.5 microm in length. Electron microscopic detection shows that the nanoplatelet grows along the [010] direction. The Ostwald ripening mechanism has been used to describe the growth of CuO nanoplatelets. In addition, the optic and electrochemical properties of as-obtained products have been discussed. And the arrays of CuO nanoplatelets exhibit the blue shift in UV-visible spectra, a slow capacity fading rate, and a relatively high Coulombic efficiency in charge-discharge process.

Journal Article↗
PubMed2006

High-content screening analysis of the p38 pathway: profiling of structurally related p38alpha kinase inhibitors using cell-based assays.

The complexity of the p38 mitogen-activated protein kinase (MAPK) signaling pathway presents challenges to understanding the efficacy of p38 inhibitors. Biochemical recombinant kinase assays and tumor necrosis factor alpha (TNFalpha) secretion assays are typically used to evaluate p38alpha inhibitors, but they do not provide insight into proximal intracellular events. Stimulation of the pathway evokes a cascade of phosphorylation events, accompanied by movement of molecules to different cellular compartments. Herein, we describe the profiling and potency comparison of a large set of p38alpha inhibitors with a pyrimidinone, imidazopyrimidine, or triazolopyrimidine core against biochemical recombinant p38alpha kinase activity, lipopolysaccharide (LPS)-mediated TNFalpha secretion by THP-1 cells, and a set of cellular imaging assays in SW1353 chondrocytes and baby hamster kidney cells. These pathway assays included p38 phosphorylation, MAPK-activated protein kinase 2 translocation, and heat shock protein (HSP) 27 phosphorylation. We established that HSP27 phosphorylation correlates well with LPS-induced TNFalpha secretion, validating our cellular imaging assays. We also found that the choice of cells and inducer can profoundly affect cellular potency results. High-content analysis may reveal signaling details, enriching our understanding of the mechanism of action of p38alpha inhibitors.

Animals↗
PubMed2005

Oltipraz-induced phase 2 enzyme response conserved in cells lacking mitochondrial DNA.

Oltipraz, a member of a class of 1,2-dithiolethiones, is a potent phase 2 enzyme inducing agent used as a cancer chemopreventive. In this study, we investigated regulation of the phase 2 enzyme response and protection against endogenous oxidative stress in lymphoblastic leukemic parental CEM cells and cells lacking mitochondrial DNA (mtDNA) (rho0) by oltipraz. Glutathione (GSH) levels (total and mitochondrial) and glutathione S-transferase (GST) activity were significantly increased after pretreatment with oltipraz in both parental (rho+) and rho0 cells, and both cell lines were resistant to mitochondrial oxidation, loss of mitochondrial membrane potential, and cell death in response to the GSH depleting agent diethylmaleate. These results show that the phase 2 enzyme response, by enhancing GSH-dependent systems involved in xenobiotic metabolism, blocks endogenous oxidative stress and cell death, and that this response is intact in cells lacking mtDNA.

Anticarcinogenic Agents↗
PubMed2005

Nitric oxide protects against mitochondrial permeabilization induced by glutathione depletion: role of S-nitrosylation?

Nitric oxide (NO) is known to mediate a multitude of biological effects including inhibition of respiration at cytochrome c oxidase (COX), formation of peroxynitrite (ONOO-) by reaction with mitochondrial superoxide (O2*-), and S-nitrosylation of proteins. In this study, we investigated pathways of NO metabolism in lymphoblastic leukemic CEM cells in response to glutathione (GSH) depletion. We found that NO blocked mitochondrial protein thiol oxidation, membrane permeabilization, and cell death. The effects of NO were: (1) independent of respiratory chain inhibition since protection was also observed in CEM cells lacking mitochondrial DNA (rho0) which do not possess a functional respiratory chain and (2) independent of ONOO- formation since nitrotyrosine (a marker for ONOO- formation) was not detected in extracts from cells treated with NO after GSH depletion. However, NO increased the level of mitochondrial protein S-nitrosylation (SNO) determined by the Biotin Switch assay and by the release of NO from mitochondrial fractions treated with mercuric chloride (which cleaves SNO bonds to release NO). In conclusion, these results indicate that NO blocks cell death after GSH depletion by preserving the redox status of mitochondrial protein thiols probably by a mechanism that involves S-nitrosylation of mitochondrial protein thiols.

Cell Death↗
PubMed2005

Three-dimensional vision with dual acousto-optic deflection encoding.

We report a new method of sensing a three-dimensional (3D) object surface with an arbitrary geometric shape. In this approach, the first-order beams diffracted from two acousto-optic deflectors (AODs) interfere with each other to form a spatial carrier that is used to encode the depth information from the 3D object surface. A direct digital synthesizer is utilized to control two AODs to generate sequentially spatial carriers with different spatial frequencies so that a modified temporal phase-unwrapping technique can be applied for decoding the shape information of the test surface. Preliminary experimental results are presented to demonstrate the effectiveness of this method.

Algorithms↗
PubMed2005

Conditional inactivation of presenilin 1 prevents amyloid accumulation and temporarily rescues contextual and spatial working memory impairments in amyloid precursor protein transgenic mice.

Accumulation of beta-amyloid (Abeta) peptides in the cerebral cortex is considered a key event in the pathogenesis of Alzheimer's disease (AD). Presenilin 1 (PS1) plays an essential role in the gamma-secretase cleavage of the amyloid precursor protein (APP) and the generation of Abeta peptides. Reduction of Abeta generation via the inhibition of gamma-secretase activity, therefore, has been proposed as a therapeutic approach for AD. In this study, we examined whether genetic inactivation of PS1 in postnatal forebrain-restricted conditional knock-out (PS1 cKO) mice can prevent the accumulation of Abeta peptides and ameliorate cognitive deficits exhibited by an amyloid mouse model that overexpresses human mutant APP. We found that conditional inactivation of PS1 in APP transgenic mice (PS1 cKO;APP Tg) effectively prevented the accumulation of Abeta peptides and formation of amyloid plaques and inflammatory responses, although it also caused an age-related accumulation of C-terminal fragments of APP. Short-term PS1 inactivation in young PS1 cKO;APP Tg mice rescued deficits in contextual fear conditioning and serial spatial reversal learning in a water maze, which were associated with APP Tg mice. Longer-term PS1 inactivation in older PS1 cKO;APP Tg mice, however, failed to rescue the contextual memory and hippocampal synaptic deficits and had a decreasing ameliorative effect on the spatial memory impairment. These results reveal that in vivo reduction of Abeta via the inactivation of PS1 effectively prevents amyloid-associated neuropathological changes and can, but only temporarily, improve cognitive impairments in APP transgenic mice.

Aging↗
PubMed2005

Antioxidants and trichostatin A synergistically protect against in vitro cytotoxicity of Ni2+ in human hepatoma cells.

The objective of this study was to investigate the separate and combined effects of antioxidants, trichostatin A (TSA) and their combination on the in vitro cytotoxicity of Ni2+ in human hepatoma cells. Cell viability, lactate dehydrogenase (LDH) release, and DNA fragmentation were measured as indicators of cell damage. Reactive oxygen species (ROS) generation and histone acetylation were also measured. The cytotoxicity of Ni2+ increased in a time- and dose-dependent manner. In the presence of 2 mM Ni2+, ROS generation increased 365% (p<0.05), while histone acetylation decreased 37% (p<0.05). Although antioxidants, ascorbic acid (AA, 0.5 or 1 mM), reduced glutathione (GSH, 100 or 200 microM) and N-acetyl-cysteine (NAC, 0.5 or 1 mM) strongly inhibited ROS generation, their effect on Ni2+-caused histone hypoacetylation was not so obvious. On the contrary, TSA (100 nM) showed no inhibition on ROS generation but significantly increased histone acetylation in both control and Ni2+-exposed cells. As expected, the combination of antioxidants and TSA possessed the activity of both diminishing ROS generation and increasing histone hypoacetylation caused by Ni2+. Further studies found that both antioxidants and TSA could diminish the cytotoxicity of Ni2+, and their combined effects obviously improved each of their protection roles, indicating that both ROS generation and histone hypoacetylation are involved in the cytotoxicity of Ni2+, and the combination of antioxidants and TSA may act as a useful strategy to protect against this cytotoxicity.

Acetylation↗
PubMed2005

Water-soluble antioxidants improve the antioxidant and anticancer activity of low concentrations of curcumin in human leukemia cells.

Curcumin (Cur) is a promising antioxidant and anticancer drug, but several recent studies indicate that Cur exerts its anticancer activity through promoting reactive oxygen species (ROS) generation. In the present study, concentration-dependent regulation of Cur on cell proliferation, viability and ROS generation, and effect of water-soluble antioxidants ascorbic acid (ASA), N-acetyl-cysteine (NAC) and reduced glutathione (GSH) on the antioxidant and anticancer activity of Cur were investigated in human myeloid leukemia cells (HL-60 cells). We found that although Cur concentration- and time-dependently decreased the proliferation and viability of cells, its effect on ROS generation (as indicated by the level of malondialdehyde, MDA) varied with its concentrations. I.e., low concentrations of Cur diminished the ROS generation, while high Cur promoted it. Combined with the opposite effect of 50 microM H2O2 on low or high Cur-induced MDA alteration, cell proliferation arrest and cell death, these results proved that low Cur exerted its anticancer activity through diminishing ROS generation in HL-60 cells, while high Cur through promoting ROS generation. Further studies showed that all water-soluble antioxidants ASA, NAC and GSH significantly enhanced both the antioxidant and the anticancer activity of low Cur. Considering that the extra accumulation of ROS is harmful to normal cells, the data presented here indicate that instead of using high doses, combining low doses of Cur with water-soluble antioxidants is a better strategy for us to improve the anticancer activity of Cur.

Acetylcysteine↗
PubMed2004

Employing oxygen-plasma posttreatment to improve the laser-induced damage threshold of ZrO2 films prepared by the electron-beam evaporation method.

ZrO2 films are deposited by the electron-beam evaporation method. Parts of the prepared samples are post-treated with oxygen plasma at the environment temperature. The laser-induced damage threshold (LIDT) of the films increases from 15.9 to 23.1 J/cm2 after treatment with oxygen plasma. Compared with that of the as-grown samples, significant reduction of the average microdefect density and absorption are found after oxygen-plasma posttreatment. These results indicate that the oxygen-plasma posttreatment technique is an effective and simple method for reducing the microdefect density and absorption to improve the LIDT.

Journal Article↗
PubMed2004

Synergistic killing of human leukemia cells by antioxidants and trichostatin A.

PURPOSE: Antioxidants and trichostatin A (TSA) are promising anticancer drugs, and are capable of enhancing the neoplastic toxicity of other chemicals that exert anticancer activity via different mechanisms. Since antioxidants and TSA (the specific inhibitor of histone deacetylase) are believed to combat cancer via different mechanisms, we sought to determine whether combining them would improve their anticancer activity in human leukemia cells (HL-60). MATERIALS AND METHODS: HL-60 cells were treated with antioxidants (ascorbic acid, AA and N-acetyl-cysteine, NAC), TSA or their combination, and cell proliferation arrest, lactate dehydrogenase (LDH) release and cell viability were measured as indicators of cell damage. Accumulation of reactive oxygen species (ROS) and the acetylation of histones were also measured. RESULTS: The cytotoxicity of AA, NAC and TSA increased in a time- and dose-dependent manner. AA (1, 2 and 4 mM) and NAC (0.2, 0.5 and 1 mM) were able to diminish ROS generation but showed no influence on histone acetylation in HL-60 cells. In contrast, TSA (20, 50, 100 and 200 nM) did not inhibit ROS generation but significantly increased histone acetylation, indicating a possible role for both scavenging ROS and increasing histone acetylation in the induction of cell death in HL-60 cells. This conclusion was further confirmed by the finding that the combination of antioxidant and TSA not only diminished ROS generation, but also increased histone acetylation, and hence showed greater cytotoxicity in HL-60 cells than either component alone. CONCLUSIONS: Our findings show that combining antioxidants and TSA can enhance their neoplastic toxicity at least in human leukemia HL-60 cells, providing a new approach to the design of chemotherapy strategies and the development of anticancer drugs.

Acetylation↗
PubMed2004

Involvement of histone hypoacetylation in Ni2+-induced bcl- 2 down-regulation and human hepatoma cell apoptosis.

Although induction of cell apoptosis is known to be involved in the cytotoxicity of Ni(2+), little research has been aimed at the mechanism of Ni(2+)-induced apoptosis. Recent studies showed that Ni(2+) induces histone hypoacetylation in different cell lines. Since histone hypoacetylation plays important roles in the control of cell cycle progress and apoptosis, we hypothesized that histone hypoacetylation may be an unrevealed pathway in Ni(2+)-induced apoptosis. To address this, effects of Ni(2+) on cell apoptosis, bcl- 2 gene expression and histone acetylation were examined in human hepatoma Hep3B cells. We found that Ni(2+) treatment resulted in cell proliferation arrest, the appearance of detached cells, condensed chromatin, apoptotic bodies and specific DNA fragmentation, indicating the occurrence of cell apoptosis. At the same time, Ni(2+) induced a significant decrease in bcl- 2 expression and histone acetylation; the decrease of histone H4 acetylation in nucleosomes associated with the bcl- 2 promoter region was also proven by a chromatin immunoprecipitation assay, indicating the involvement of histone hypoacetylation in Ni(2+)-induced bcl- 2 down-regulation. Further studies showed that increasing histone acetylation by either 100 nM of trichostatin A or over-expressing histone acetyltranferase p300 in Hep3B cells obviously attenuated the bcl- 2 down-regulation and cell apoptosis caused by Ni(2+). Considering the importance of bcl- 2 in determining cell survival and apoptosis, the data presented here suggest that histone hypoacetylation may represent one unrevealed pathway in Ni(2+)-induced cell apoptosis, where bcl- 2 is one of its targets.

Acetylation↗
PubMed2004

Mutational analysis of ionizable residues proximal to the cytoplasmic interface of membrane spanning domain 3 of the multidrug resistance protein, MRP1 (ABCC1): glutamate 1204 is important for both the expression and catalytic activity of the transporter.

The multidrug resistance protein MRP1 is an ATP-dependent transporter of organic anions and chemotherapeutic agents. A significant number of ionizable amino acids are found in or proximal to the 17 transmembrane (TM) helices of MRP1, and we have investigated 6 of these at the cytoplasmic interface of TM13-17 for their role in MRP1 expression and transport activity. Opposite charge substitutions of TM13 Arg(1046) and TM15 Arg(1131) did not alter MRP1 expression nor did they substantially affect activity. In contrast, opposite charge substitutions of TM16 Arg(1202) and Glu(1204) reduced protein expression by >80%; however, MRP1 expression was not affected when Arg(1202) and Glu(1204) were replaced with neutral or same-charge residues. In addition, organic anion transport levels of the R1202L, R1202G, and R1202K mutants were comparable with wild-type MRP1. In contrast, organic anion transport by E1204L was substantially reduced, whereas transport by E1204D was comparable with wild-type MRP1, with the notable exception of GSH. Opposite charge substitutions of TM16 Arg(1197) and TM17 Arg(1249) did not affect MRP1 expression but substantially reduced transport. Mutants containing like-charge substitutions of Arg(1197) or Arg(1249) were also transport-inactive and no longer bound leukotriene C(4). In contrast, substrate binding by the transport-compromised E1204L mutant remained intact. Furthermore, vanadate-induced trapping of azido-ADP by E1204L was dramatically increased, indicating that this mutation may cause a partial uncoupling of the catalytic and transport activities of MRP1. Thus, Glu(1204) serves a dual role in membrane expression of MRP1 and a step in its catalytic cycle subsequent to initial substrate binding.

Adenosine Triphosphate↗
PubMed2004

Altered cortical synaptic morphology and impaired memory consolidation in forebrain- specific dominant-negative PAK transgenic mice.

Molecular and cellular mechanisms for memory consolidation in the cortex are poorly known. To study the relationships between synaptic structure and function in the cortex and consolidation of long-term memory, we have generated transgenic mice in which catalytic activity of PAK, a critical regulator of actin remodeling, is inhibited in the postnatal forebrain. Cortical neurons in these mice displayed fewer dendritic spines and an increased proportion of larger synapses compared to wild-type controls. These alterations in basal synaptic morphology correlated with enhanced mean synaptic strength and impaired bidirectional synaptic modifiability (enhanced LTP and reduced LTD) in the cortex. By contrast, spine morphology and synaptic plasticity were normal in the hippocampus of these mice. Importantly, these mice exhibited specific deficits in the consolidation phase of hippocampus-dependent memory. Thus, our results provide evidence for critical relationships between synaptic morphology and bidirectional modifiability of synaptic strength in the cortex and consolidation of long-term memory.

Analysis of Variance↗
PubMed2004

Loss of presenilin function causes impairments of memory and synaptic plasticity followed by age-dependent neurodegeneration.

Mutations in presenilins are the major cause of familial Alzheimer's disease, but the pathogenic mechanism by which presenilin mutations cause memory loss and neurodegeneration remains unclear. Here we demonstrate that conditional double knockout mice lacking both presenilins in the postnatal forebrain exhibit impairments in hippocampal memory and synaptic plasticity. These deficits are associated with specific reductions in NMDA receptor-mediated responses and synaptic levels of NMDA receptors and alphaCaMKII. Furthermore, loss of presenilins causes reduced expression of CBP and CREB/CBP target genes, such as c-fos and BDNF. With increasing age, mutant mice develop striking neurodegeneration of the cerebral cortex and worsening impairments of memory and synaptic function. Neurodegeneration is accompanied by increased levels of the Cdk5 activator p25 and hyperphosphorylated tau. These results define essential roles and molecular targets of presenilins in synaptic plasticity, learning and memory, and neuronal survival in the adult cerebral cortex.

Activating Transcription Factor 1↗
PubMed2003

Molecular cloning and pharmacological characterization of rat multidrug resistance protein 1 (mrp1).

Multidrug resistance protein 1 (MRP1) transports a wide range of structurally diverse conjugated and nonconjugated organic anions and some peptides, including oxidized and reduced glutathione (GSH). The protein confers resistance to certain heavy metal oxyanions and a variety of natural product-type chemotherapeutic agents. Elevated levels of MRP1 have been detected in many human tumors, and the protein is a candidate therapeutic target for drug resistance reversing agents. Previously, we have shown that human MRP1 (hMRP1) and murine MRP1 (mMRP1) differ in their substrate specificity despite a high degree of structural conservation. Since rat models are widely used in the drug discovery and development stage, we have cloned and functionally characterized rat MRP1 (rMRP1). Like mMRP1 and in contrast to hMRP1, rMRP1 confers no, or very low, resistance to anthracyclines and transports the two estrogen conjugates, 17beta-estradiol-17-(beta-d-glucuronide) (E217betaG) and estrone 3-sulfate, relatively poorly. Mutational studies combined with vesicle transport assays identified several amino acids conserved between rat and mouse, but not hMRP1, that make major contributions to these differences in substrate specificity. Despite the fact that the rodent proteins transport E217betaG poorly and the GSH-stimulated transport of estrone 3-sulfate is low compared with hMRP1, site-directed mutagenesis studies indicate that different nonconserved amino acids are involved in the low efficiency with which each of the two estrogen conjugates is transported. Our studies also suggest that although rMRP1 and mMRP1 are 95% identical in primary structure, their substrate specificities may be influenced by amino acids that are not conserved between the two rodent proteins.

Amino Acid Sequence↗
PubMed2002

Receptors and signaling pathway underlying relaxations to isoprostanes in canine and porcine airway smooth muscle.

Using muscle bath techniques, we examined the inhibitory activities of several E- and F-ring isoprostanes in canine and porcine airway smooth muscle. 8-Isoprostaglandin E1 and 8-isoprostaglandin E2 (8-iso PGE2) reversed cholinergic tone in a concentration-dependent manner, whereas the F-ring isoprostanes were ineffective. Desensitization with 8-iso-PGE2 and PGE2 implicated isoprostane activity at the PGE2 receptor (EP). We found that the inhibitory E-ring isoprostane responses were significantly augmented by rolipram (a type IV phosphodiesterase inhibitor), while 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (a guanylate cyclase inhibitor) had no effect, suggesting a role for cAMP in isoprostane-mediated relaxations. 8-Iso-PGE2 did not reverse KCl tone, suggesting that voltage-dependent Ca2+ influx and myosin light chain kinase are not suppressed by isoprostanes. Patch-clamp studies showed marked suppression of K+ currents by 8-iso-PGE2. We conclude that E-ring isoprostanes exert PGE2 receptor-directed, cAMP-dependent relaxations in canine and porcine airway smooth muscle. This activity is not dependent on K+ channel activation or the direct inhibition of voltage-operated Ca2+ influx or myosin light chain kinase.

Animals↗