Biomedical subjects

T Zhang

Publications and source records attributed to T Zhang.

At least 37 records · Page 2Linked to original sources

PubMed2005

Effective diffusion coefficients of glucose in artificial biofilms.

A technique using horizontal attenuated total reflection (HATR) by Fourier transform infrared (FTIR) spectrometry was demonstrated for the determination of effective diffusion coefficient (De) of an inert solute in biofilm. Glucose was the selected solute, and agarose (1%) hydrogel films containing various concentrations of activated sludge biomass were used to simulate the biofilm. The agarose films were formed on the surface of an internal reflection crystal in contact with a bulk solution containing 0.5M glucose. Glucose molecules diffused through the film by concentration gradient, and the glucose concentration at the biofilm-crystal interface was measured over time by HATR-FTIR. Based on the glucose concentration and film thickness, the De of glucose was calculated according to the Fick's Law. Results showed that De of glucose in the biomass-free agarose films averaged 6.46 +/- 0.21 x 10(6) cm(2) s(-1), which is about 5% lower than the average reported De of glucose in water. The De of glucose decreased with increasing biomass concentration in the artificial biofilm. For the agarose films containing 0.45%, 0.90% and 1.80% of biomass, the De of glucose were lowered to 6.38 +/- 0.22 x 10(-6), 6.08 +/- 0.23 x 10(-6) and 5.62 +/- 0.17 x 10(4) cm(2) s(-1), respectively.

Biofilms↗

PubMed2005

Radiological studies reveal radial differences in the architecture of the polysaccharide capsule of Cryptococcus neoformans.

The polysaccharide capsule of the pathogenic fungus Cryptococcus neoformans is an important virulence factor, but relatively little is known about its architecture. We applied a combination of radiological, chemical, and serological methods to investigate the structure of this polysaccharide capsule. Exposure of C. neoformans cells to gamma radiation, dimethyl sulfoxide, or radiolabeled monoclonal antibody removed a significant part of the capsule. Short intervals of gamma irradiation removed the outer portion of the cryptococcal capsule without killing cells, which could subsequently repair their capsules. Survival analysis of irradiated wild-type, acapsular mutant, and complemented mutant strains demonstrated that the capsule contributed to radioprotection and had a linear attenuation coefficient higher than that of lead. The capsule portions remaining after dimethyl sulfoxide or gamma radiation treatment were comparable in size, 65 to 66 microm3, and retained immunoreactivity for a monoclonal antibody to glucuronoxylomannan. Simultaneous or sequential treatment of the cells with dimethyl sulfoxide and radiation removed the remaining capsule so that it was not visible by light microscopy. The capsule could be protected against radiation by either of the free radical scavengers ascorbic acid and sorbitol. Sugar composition analysis of polysaccharide removed from the outer and inner parts of the capsule revealed significant differences in glucuronic acid and xylose molar ratios, implying differences in the chemical structure of the constituent polysaccharides. Our results provide compelling evidence for the existence of two zones in the C. neoformans capsule that differ in susceptibility to dimethyl sulfoxide and radiation and, possibly, in packing and composition.

Antibodies, Monoclonal↗

PubMed2005

High-frequency signals (> 400 hz): a new window in electrophysiological analysis of the somatosensory system.

High-frequency signals (HFSs) between 400-1500 Hz in Magnetoencephalography (MEG) and Electroencephalography (EEG) provide a new window in electrophysiological analysis of the somatosensory system in humans and in other animals. The HFS in the primary somatosensory (SI) cortex precedes the conventional N20. In the swine model, they appear to be due to spiking in thalamocortical axonal terminals and in the soma and dendrites of cortical neurons. These spiking activities seem to activate slower conductances in the pyramidal cells in layers II-III and V, which give rise to N20. The HFS monitoring may be useful for separately evaluating the electrophysiology of the subcortical and cortical components of the somatosensory pathway.

Action Potentials↗

PubMed2005

Proteomic analysis of Rickettsia prowazekii.

Rickettsia prowazekii is an obligate intracellular gram-negative bacterium. Comparative proteomics study of a virulent strain (Breinl) versus an avirulent strain (Madrid E) was performed using an integrated liquid chromatography and mass spectrometer. About 30% of predicted proteins were detected and identified. Among the detected proteins, more than 30 proteins were of unknown function in both strains. Although several proteins were detected in only one strain, the overall distribution of detected proteins in different COGs (clusters of orthologs groups) was very similar between the two strains. Functional analysis of differentially expressed proteins, either qualitatively or quantitatively, may lead to the discovery of pathogenesis-related factors.

Bacterial Proteins↗

PubMed2005

Combination of boron and gadolinium compounds for neutron capture therapy. An in vitro study.

In neutron capture therapy, the therapeutic effect of the boron compound is based on alpha particles produced by the B(n, alpha) reaction while with the gadolinium compound the main radiation effect is from gamma rays derived from the Gd(n, gamma) reaction. The uptake and distribution within the tumor may be different among these compounds. Thus, the combination of the boron and gadolinium compounds may be beneficial for enhancing the radiation dose to the tumor. Chinese hamster fibroblast V79 cells were used. For the neutron targeting compounds, 10B (BSH) at 0, 5, 10, and 15 ppm, and 157Gd (Gd-BOPTA) at 0, 800, 1600, 2400, 3200, and 4800 ppm, were combined. The neutron irradiation was performed with thermal neutrons for 30 min. (neutron flux: 0.84 x 10(8) n/cm2/s in free air). The combination of the boron and gadolinium compounds showed an additive effect when the gadolinium concentration was lower than 1600 ppm. This additive effect decreased as a function of gadolinium concentration at 2400 ppm and resulted in no additive effect at more than 3200 ppm of gadolinium. In conclusion, the combination of the boron and gadolinium compounds can enhance the therapeutic effect with an optimum concentration ratio. When the gadolinium concentration is too high, it may weaken the boron neutron capture reaction due to the high cross-section of gadolinium compound against neutrons.

Animals↗

PubMed2005

Microbial characteristics of a methanogenic phenol-degrading sludge.

Microbial properties of a methanogenic granular phenol-degrading sludge were characterized using the 16S rRNA/DNA-based techniques, including polymerase chain reaction (PCR) amplification, cloning, DNA sequencing, and fluorescence in situ hybridization (FISH). The sludge was sampled from an upflow anaerobic sludge blanket reactor, which removed 98% of phenol (up to 1260 mg/l) in wastewater at 26 degrees C with 12 hours of hydraulic retention. Based on DNA analysis, the Eubacteria in the sludge was composed of 13 operational taxonomy units (OTUs). Two OTUs, one resembling Clostridium and the other remotely resembling Desulfotomaculum, were likely responsible for the conversion of phenol to benzoate, which was further degraded by five Syntrophus-resembling OTUs to acetate and H2/CO2; methanogens lastly converted acetate and H2/CO2 into methane. The role of six remaining OTUs remains unclear. Overall, the sludge was composed of 26 +/- 6% Eubacteria and 74 +/- 9% methanogens, of which 54 +/- 6% were acetotrophic Methanosaetaceae, 14 +/- 3% and 3 +/- 2% were hydrogenotrophic Methanomicrobiales and Methanobacteriaceae, respectively.

Bacteria↗

PubMed2004

Results of a technology demonstration project to compare rapid aquatic toxicity screening tests in the analysis of industrial effluents.

The results of a 'BioWise' demonstration project to assess the comparative sensitivity and practicality of seven new assays for the direct assessment of ecotoxicity in industrial effluents are presented. In addition the aim of the project was to validate the results of the new assays against benchmark data generated from non-proprietary, rapid, microplate screening assays using the regulatory species; freshwater crustacean Daphnia magna and green algae Selenastrum capricornutum, chosen in view of their environmental relevance. The new commercial test assays were: Daphnia magna, Selenastrum capricornutum and Thamnocephalus platyurus Toxkits supplied by Vickers Laboratories Ltd, containing dormant, immobilised life stages of the test species; GreenScreen EM, a yeast based assay for genotoxicity and general acute toxicity supplied by Gentronix Ltd; and CellSense a mediated, amperometric whole cell biosensor based on immobilised activated sludge and E. coli. 38 effluent samples supplied by members of SOCSA (Specialised Organic Chemicals Sector Association) were examined over a period of 13 months, in the project co-ordinated by the AstraZeneca Brixham Environmental Laboratory, and part funded by BioWise via the UK Government Department of Trade and Industry.

Animals↗

PubMed2004

The outer valance orbital electron densities of cyclopentane by binary (e,2e) spectroscopy.

The binding energy spectra and electron distributions in momentum space of the valence orbitals of cyclopentane (C(5)H(10)) are studied by Electron Momentum Spectroscopy (EMS) in a noncoplanar symmetric geometry. The impact energy was 1200 eV plus binding energy and energy resolution of the EMS spectrometer was 1.2 eV. The experimental momentum profiles of the outer valence orbitals are compared with the theoretical momentum distributions calculated using Hartree-Fock and density functional theory (DFT) methods. The shapes of the experimental momentum distributions are generally quite well described by both the Hartree-Fock and DFT calculations when the large and diffuse basis sets are used.

Journal Article↗

PubMed2004

Potential applications of nicotinic ligands in the laboratory and clinic.

The nicotinic acetylcholine receptor (nAChR) is a receptor, ion channel complex composed of five polypeptide subunits. There are many different nAChR subtypes constructed from a variety of different subunit combinations. This structural diversity contributes to the varied roles of nAChRs in the peripheral and central nervous system, and this diversity offers an excellent opportunity for chemists who are producing ligands. Subunit specific ligands could have wide and varied effects in the laboratory as experimental tools and in the clinic as therapeutic agents. Because presynaptic nAChRs have been shown to enhance the release of many neurotransmitters, new nicotinic ligands that potentiate nAChR activity would be very useful. Such ligands could enhance the release of various neurotransmitters during degenerative diseases that cause neurotransmitter systems to decrease their output. For example, boosting the release from cholinergic neurons would help patients with Alzheimer's disease, and boosting the release from dopaminergic neurons would help patients with Parkinson's disease.

Alzheimer Disease↗

PubMed2004

A heat inducible tyrosinase with distinct properties from Bacillus thuringiensis.

AIMS: The objective of this work was to purify the tyrosinase from Bacillusthuringiensis subsp. kurstaki (Bt) (CCTCC AB 90010) and study its enzymatic properties. METHODS AND RESULTS: A 'one-step' purification method was used in this work, which was an easy, high-yield purification method. Tyrosinase activity of this purity was measured under different conditions to study its kinetic characterizations. The optimum pH and thermal stability of this enzyme were also determined. The results revealed that the tyrosinase from Bt has distinct properties compared with those from other sources. CONCLUSIONS: A heat-inducible tyrosinase of a wild strain of Bt was identified and partially characterized. SIGNIFICANCE AND IMPACT OF THE STUDY: The distinct properties of Bt tyrosinase are important to the application of Bt as a biology pesticide.

Bacillus thuringiensis↗

PubMed2004

Evaluation of acute hematologic and long-term pulmonary toxicities of radioimmunotherapy of Cryptococcus neoformans infection in murine models.

We evaluated acute hematological and long-term pulmonary toxicity of radioimmunotherapy in murine models of Cryptococcus neoformans infection. Activities up to 250 microCi were well tolerated by healthy A/JCr mice for (213)Bi-18B7 and (188)Re-18B7 monoclonal antibodies. In infected mice, doses up to 150 microCi produced only transient toxicity. The lungs of treated mice had no evidence of radiation fibrosis.

Animals↗

PubMed2004

Anaerobic degradation of phenol in wastewater at ambient temperature.

Treating a synthetic wastewater containing phenol as the sole substrate at 26 degrees C, an upflow anaerobic sludge blanket reactor was able to remove over 98% of phenol up to 1,260 mg/l in wastewater with 12 h of hydraulic retention time, corresponding to 6.0 g-COD/(l x day). Results showed that benzoate was the key intermediate of phenol degradation. Conversion of benzoate to methane was suppressed by the presence of phenol. Based on DNA cloning analysis, the sludge was composed of five groups of microorganisms. Desulfotomaculum and Clostridium were likely responsible for the conversion of phenol to benzoate, which was further degraded by Syntrophus to acetate and H2/CO2. Methanogens lastly converted acetate and H2/CO2 to methane. The role of epsilon-Proteobacteria was, however, unclear.

Bacteria, Anaerobic↗

PubMed2003

Global nature of dilute-to-dense transition of granular flows in a 2D channel.

The dilute-to-dense transition of granular flow of particle size d(0) is studied experimentally in a two-dimensional channel (width D) with confined exit (width d). Our results show that with fixed d and D there is a maximum inflow rate Q(c) above which the flow changes from dilute to dense and the outflow rate drops abruptly from Q(c) to a dense rate Q(d). A rescaled critical rate q(c) is found to be a function of a scaling variable lambda only: q(c) approximately F(lambda), where lambda identical with d/d(0) d/D-d. This form of lambda suggests that the dilute-to-dense transition is a global property of the flow, unlike the jamming transition which depends only on d/d(0). Furthermore, the transition is found to occur when the area fraction of particles near the exit exceeds a critical value which is close to 0.65+/-0.03.

Journal Article↗

PubMed2003

Methanogen population in a marine biofilm corrosive to mild steel.

This study was conducted to analyze the methanogen population in a corrosive marine biofilm based on 16S rDNA analysis, using a PCR-cloning-sequencing approach. There were 80 methanogen clones developed from the PCR-amplified DNA extracted from the biofilm on the mild steel surface. All clones were categorized into one of five operational taxonomy units (OTUs). Two OTUs (comprising 57 clones) were affiliated with the acetotrophic Methanosaeta genus; the remaining three OTUs (23 clones) were affiliated with the hydrogenotrophic genera of Methanogenium, Methanoplanus and Methanocalculus. The hydrogenotrophic methanogens could directly cause metal corrosion through cathodic depolarization, whereas the acetotrophic methanogens grew syntrophically with corrosion-causing sulfate-reducing bacteria, as observed by fluorescent in situ hybridization, and thus contribute indirectly to metal corrosion.

Base Sequence↗

PubMed2003

Detrimental effects of cryopreservation of loach (Misgurnus fossilis) sperm on subsequent embryo development are reversed by incubating fertilised eggs in caffeine.

Cryopreservation can cause changes to the genetic material of cells, but the mechanism and significance of these changes are still unknown. It has been suggested that some damage to the sperm genome could be repaired by the DNA repair system of the oocyte after fertilisation. Caffeine has been reported to be an inhibitor of such repair processes. In this study the effect of caffeine on the repair system of Loach (Misgurnus fossilis) oocytes was investigated. Loach eggs were fertilised using cryopreserved sperm. Embryos derived from cryopreserved sperm were exposed to 2.6mM caffeine for 1h after fertilisation. The experiments were carried out using 32313 embryos from four females and eight males. Embryo survival was evaluated for 46 h until the hatching stage. Reduction in embryo survival after 20th stage is generally believed to result from the failure in the genome function of embryos. Cryopreservation of sperm significantly decreased embryo survival (53.4+/-2.8% compared to 68.4+/-2.8% of control) after the 20th stage. However, the addition of caffeine to the embryos derived from cryopreserved sperm, in contrast to our expectation, significantly increased survival of loach embryos (70.9+/-2.8% compared to 53.4+/-2.8% of embryos derived from cryopreserved sperm in the absence of caffeine). The effect of individual donors of sperm and eggs on overall embryo survival was also studied. Whilst no significant differences were observed between males, the effect of individual females on embryo survival was significant. The analysis of embryo survival at different developmental stages showed that embryo survival both before and after 20th stage decreased with embryo development. When fresh sperm were used the decline of embryo survival with development was more pronounced compared with those embryos derived from cryopreserved sperm. Possible explanations of these effects are presented.

Animals↗

PubMed2003

Arsenic trioxide induces apoptosis of rat hepatocellular carcinoma cells in vivo.

The aim of this work was to study the effect of arsenic trioxide (As2O3) on rat hepatocellular carcinoma (HCC), and investgate on the mechanisms of its antitumor effect. HCC was induced by chemocarcinogen diethylnitrosamine (DEN) in Wistar rats, that were then treated with As2O3 intraperitoneally in three different concentrations once a day for two weeks, and twice a week for another two weeks. The histological and ultrastructural changes in liver tissue were observed under microscope and electronic microscope on the 7th, 14th and 28th day after drug administration. The apoptosis and cellular dynamic parameters of tumor cells were observed by flow cytometry. The expression of bcl-2, bax, and proliferation cell nuclear antigen (PCNA) of rat liver cancer cells on the 7th day after drug administration was determined by using immunohistochemical technique. Treatment with As2O3 caused HCC cells death via both apoptotic and non-apoptotic mechanisms when the dose was high (5 mg.kg(-1)), while necrosis was rare and apoptosis was common when the dose was appropriate (1 mg.kg(-1)). This effect was obviously accompanied with accumulation of cells in G2/M phases (G2/M restriction). Many apoptotic cells were also found in G2/M phases. The expression intensity of bcl-2 or bax varied depending on the dose administrated. Downregulation of bcl-2/bax was observed, accompanied with upregulation of apoptosis. However, the ratio of bcl-2/bax and the percentage of apoptosis were not the utmost when the dose administered was the highest. In conclusion, these data demonstrate that As2O3 induces apoptosis of rat HCC cells, and it is closely associated with G2/M restriction when apoptosis reaches the top. Apoptosis can be observed in all three phases of cell cycle, but it is more common in G2/M phase when the dose is appropriate. It is suggested that arsenic trioxide may be an atypical cell cycle specific agent. Apoptosis of tumor cells is closely associated with down-regulation of the ratio of bcl-2/bax, but that may not be the only dominant factor.

Animals↗

PubMed2003

Exogenous nitric oxide induces apoptosis in Toxoplasma gondii tachyzoites via a calcium signal transduction pathway.

The mechanism by which nitric oxide (NO)-dependent cytotoxicity acts against Toxoplasma gondii tachyzoites is poorly understood. An NO donor, sodium nitroprusside (SNP), was used to induce death in T. gondii tachyzoites in vitro as a model for investigating (i) whether NO is capable of inducing apoptosis-like death in tachyzoites and (ii) whether a calcium signal transduction pathway is involved. Exposure to 2 mM SNP resulted in a pattern of tachyzoite death that shares many features with metazoan apoptosis and it may involve a calcium signal transduction pathway. Motility and cell survival in these parasites showed a gradual decline with increasing levels of SNP. Features common to metazoan apoptosis are observed after exposure to 2 mM SNP. Ethylene glycol bis-(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA), Verapamil and bis-(o-aminophenoxy) ethane-N,N,N',N'-tetra-acetic acid/acetoxymethyl ester (BAPTA/AM) partially increased the cell survival concomitant with decreased [Ca2+]i in cells exposed to SNP. An NO scavenger (N-acetylcysteine), the analogue of SNP (devoid of NO), inhibited the rate of apoptosis after SNP treatment compared with SNP treatment without scavenger, but alone did not induce apoptosis. Taken together, the results indicate that SNP is capable of inducing apoptosis in T. gondii tachyzoites via a calcium signal transduction pathway.

Animals↗

PubMed2002

Inheritance and fine mapping of fertility restoration for cytoplasmic male sterility in Gossypium hirsutum L.

Genetics of CMS fertility restoration was presented through the analysis of classic genetics and molecular markers. Based on F(2) segregation of the crosses between CMS and the restoring lines, the testcrosses and F(1) x F(1) populations, together with RAPD and SSR mapping, one dominant gene was identified to control the CMS fertility restoration in cotton. The strategy of genotype representation analysis (GRA) was put forward to screen the markers linked with the Rf(1) locus. Using 1,025 random decamer primers and 282 pairs of SSR primers, two RAPD and three SSR markers were identified to be closely linked to the Rf(1) gene. Among the five markers, three were co-dominantly inherited. Additionally, based on the analysis of monosomic and telesomic lines with one SSR maker, the Rf(1) locus could be located on the long arm of chromosome 4. The molecular markers available here are helpful in the development of the elite restoring lines in cotton by marker-assisted selection.

Chromosome Mapping↗