Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 685 records · Page 38Linked to original sources

PubMed1999

[The investigation for lysozyme conformation changes in deuteromethanol solution by FT-Raman spectrometer].

Lysozyme conformation in deuteromethanol-deuteroxide solution has been studied by FT-Raman spectrometer. By using amide I mode in the Raman spectra and curve fitting method, information of Lysozyme's secondary structure is easily detected in details, and tertiary structure changes can be suggested by relative intensity changes of some bands. It is concluded that lysozyme conformation may be changed to loose structure with incrasing deuteromethanol concentration, and it seems like that increasing loose beta-sheet content lead to the gel's appearing in the solution.

Methanol↗

PubMed1999

[Pattern recognition applied to the Pu I even-parity energy level].

The partial least square (PLS)-back propagation network (BPN) method is applied to assigning the electronic configurations of Pu I even-parity levels and the assignments agree well with the experimental results. It is shown that PLS-BPN can be used as a tool to assign complicated spectral levels.

English Abstract↗

PubMed1999

[Studies on tailed metalloporphyrin coordination compounds. IX. Synthesis of tailed porphyrin with covalently linked phenylalanine and its fluorescence property].

A new tailed porphyrin with covalently linked phenylalanine 2 and its zinc complex 3 were synthesized. Intramolecular energy transfer (from singlet excited phenylalanine to porphyrin) was observed in compound 2 and 3. The influence of coordination chemistry factor on the fluorescence of porphyrin was also discussed.

Energy Transfer↗

PubMed1999

[A quantitative study on secondary structure of proteins by FT-Raman spectroscopy].

In this work, proteins have been scanned by FT-Raman spectrometer. Deconvolved spectra, second derivative or fourth derivative spectra were employed to determine positions of individual components. Curve-fitting procedures were carried out to amide I band of original spectra. The broad band was resolved into several components. The resolved band components were assigned to specific protein conformations. The areas of individual components are used to estimate the percentage of the relative secondary structure. Results are in reasonable agreement with data obtained by other methods.

Animals↗

PubMed1998

Determination of submicromolar concentrations of neurotransmitter amino acids by fluorescence detection using a modification of the 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate method for amino acid analysis.

A sensitive method for quantitatively determining submicromolar levels of neurotransmitter amino acids (e.g. Asp, Glu and gamma-aminobutyric acid) in microdialysates from brain and cerebrospinal fluids is reported. 6-Aminoquinolyl-N-hydroxy-succinimidyl carbamate (AQC) was employed as the derivatization reagent, followed by HPLC separation and fluorescence detection of the derivatives. The derivatization was conducted simply by mixing the AQC directly with the microdialysis samples. The reaction was complete within seconds after mixing at room temperature. Separation development optimizing the gradient profile, eluent pH and column temperature resulted in an excellent separation of the required amino acids in less than 30 min. Other resolved amino acids in the same profile include Gly, taurine, and Pro. Recoveries for the amino acids of interest spiked into high salt containing perfusion buffers were greater than 97%. The sensitivity of the method was increased by employing a 16-microliter flow cell in the detector and analyzing 20-microliter aliquots of the derivatization mixtures. With the optimized conditions, the detection limits were 3-7 nM (fmol/microliter). Typical reproducibility (%R.S.D.) for quantitation of these amino acids at submicromolar levels was approximately 2%. Excellent linearity (r2 > 0.999) was achieved over the range 0.2-20 microM. The low detection limits permitted the analysis of a number of different microdialysate samples including those from cerebrospinal fluid, as well as substantia nigra and hypothalamus from brain samples, even at basal levels where gamma-aminobutyric acid concentration may be < 50 nM. The excellent sensitivity made it easy to distinguish basal from stimulated levels of neurotransmitter amino acids, even from sample sizes as small as 10 microliters.

Aminoquinolines↗

PubMed1998

Preparation, Characterization, and Catalytic Properties of Polymer-Stabilized Ruthenium Colloids.

Poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium colloids were prepared by NaBH4 reduction at room temperature and characterized by transmission electron microscopy and x-ray photoelectron spectra. The average diameters of the colloids were 1.3-1.8 nm with final sigma = 0.4-0.7 nm with respect to the preparation conditions. The PVP-stabilized ruthenium colloids were used as catalysts in the hydrogenations of cyclooctene and n-heptene and the selective hydrogenation of citronellal to citronellol. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Molecular cloning and functional expression of a fifth-type alpha 2,3-sialyltransferase (mST3Gal V: GM3 synthase).

The cDNA encoding a new type of alpha 2,3-sialyltransferase (mST3Gal V) was cloned from mouse brain cDNA library by PCR-based cloning approach using a pair of degenerate primers deduced from the nucleotide sequence information of mouse ST3Gal III and IV. The predicted amino acid sequence of mST3Gal V showed 27.3% and 26.4% identity to mST3Gal III and IV, respectively. The recombinant soluble mST3Gal V fused with protein-A, which expressed in the culture media of COS-7 cells, showed activity toward lactosylceramide (LacCer), and synthesized GM3. The apparent Km value for LacCer was 9.3 microM. mST3Gal V did not exhibit any activity toward other substrates we tested in this study, including glycolipids, glycoproteins and disaccharides. The mST3Gal V cDNA transfected F28-7 cells, which express large amount of lactosylceramide and very small amount of GM3 at native stage, expressed a large amount of GM3. The ST3Gal V gene was strongly expressed in mouse brain and liver, which contained a large amount of ganglioside. The gene expression seemed to be coincident with ganglioside expression in mouse. Thus, we conclude that mST3Gal V is the fifth-type alpha 2,3-sialyltransferase carrying GM3 synthetic activity.

Amino Acid Sequence↗

PubMed1998

Galanin modulation of seizures and seizure modulation of hippocampal galanin in animal models of status epilepticus.

We examined the role of hippocampal galanin in an animal model of status epilepticus (SE). Control rats showed abundant galanin-immunoreactive (Gal-IR) fibers in the dentate hilus, whereas no Gal-IR neurons were observed. Three hours after the onset of self-sustaining SE (SSSE), induced either by intermittent stimulation of the perforant path for 30 min (PPS) or by injection of lithium and pilocarpine, Gal-IR fibers disappeared in the hilus and remained absent for up to 1 week afterward. Twelve hours after the induction of SE by PPS or 3 hr after pilocarpine administration, Gal-IR neurons appeared in the hilus; these neurons increased in number after 1 d and gradually declined 3 and 7 d later. Galanin concentration in the hippocampus, measured by ELISA, significantly decreased on the plateau of SSSE and increased 24 hr after PPS. Galanin (0.05 nmol) injected into the hilus prevented the induction of SSSE, and 0.5 nmol of galanin stopped established SSSE. These effects were attenuated by galanin receptor antagonists (M35 > M40 >/= M15). 2-Ala-galanin (5 nmol), a putative agonist of galanin type 2 receptors, prevented but was unable to stop SSSE. M35 facilitated the development of SSSE when given before PPS. We suggest that hippocampal galanin acts as an endogenous anticonvulsant via galanin receptors. SE-induced galanin depletion in the hippocampus may contribute to the maintenance of seizure activity, whereas the increase of galanin concentration and the appearance of galanin-immunoreactive neurons may favor the cessation of SSSE. The seizure-protecting action of galanin SSSE opens new perspectives in the treatment of SE.

Animals↗

PubMed1998

Re-expression of differentiated proteoglycan phenotype by dedifferentiated human chondrocytes during culture in alginate beads.

The proteoglycans (PGs) synthesised by normal human articular chondrocytes and a chondrocyte cell line cultured in monolayer and alginate beads were compared. Chondrocytes became dedifferentiated after serial subcultures in monolayer, exhibited a fibroblastic morphology and synthesised a large proportion of lower molecular weight, dermatan sulphate containing PGs. When transferred into alginate beads, the cells quickly regained their spherical shape and actively incorporated [3H]thymidine and [35S]sulphate during 70 days of culture. This resulted in a continuous increase in their DNA content and a rapid deposition of PGs for the first 25 days of culture, which then remained stable. Immediately after dedifferentiated chondrocytes were encapsulated into alginate beads, they began to synthesise a population of PGs with normal monomer size and an increased ability to form aggregates. The monomer size of newly synthesised PGs remained unchanged during extended periods of culture, but their ability to form aggregates and the ratios of chondroitin-6-sulphate to chondroitin-4-sulphate in their glycosaminoglycan chains gradually increased for the first 25 days before reaching normal values. Parallel experiments with HCS-2/8 cells, derived from a human chondrosarcoma, showed that they followed a similar pattern of development in alginate culture. The ability of their newly synthesised PGs to form aggregates increased with time and their sulphation pattern also gradually became normal. These results showed that culture in alginate promoted redifferentiation of dedifferentiated articular chondrocytes and assisted differentiation of HCS-2/8 chondrocytes. However, complete redifferentiation took a period of several weeks, after which synthesis of normal aggregating PGs was maintained.

Alginates↗

PubMed1998

Drug targeting using low density lipoprotein (LDL): physicochemical factors affecting drug loading into LDL particles.

Low density lipoprotein (LDL) has been found suitable as a targeting carrier for cytotoxic drugs. However, higher drug loading into LDL particles without disrupting their native integrity remains a major obstacle. The purpose of this study is to investigate the different physicochemical factors that may affect drug loading and to characterize LDL-drug conjugates. Doxorubicin (Dox) and 3', 5'-O-dipalmitoyl-5-iodo-2'-deoxyuridine (dpIUdR) were used as reference cytotoxic drugs. Drugs were loaded into LDL particles using the dry film method with or without surfactants, liposomal and the direct addition method. The effects of incubation temperature, time and stoichiometry of LDL-drug conjugates on drug loading were investigated. The LDL-drug conjugates were evaluated for their stability and characterized by differential scanning calorimetry (DSC), denatured gel (SDS-PAGE), and electron microscopy (EM). We have suitably incorporated 45+/-10 Dox and 150+/-25 dpIUdR molecules/LDL particle. A seven-fold increase in Dox incorporation was achieved with the liposomal preparation compared to the dry film method. A 4- to 6-h incubation at 37 degreesC was suitable to restore the native structure of LDL particles. No apo B fragmentation of LDL particles was noted on denatured gel. DSC studies showed no change in the Tm of the LDL and the LDL-drug conjugates. An increase in particle size of LDL-dpIUdR, not LDL-Dox was observed in EM compared to the native LDL which may be related to higher incorporation of dpIUdR. The results indicate that physicochemical factors significantly affect drug loading efficiency and may need to be considered to optimize drug incorporation into LDL particles.

Chromatography, High Pressure Liquid↗

PubMed1998

Patterns of status epilepticus-induced neuronal injury during development and long-term consequences.

The lithium-pilocarpine model of status epilepticus (SE) was used to study the type and distribution of seizure-induced neuronal injury in the rat and its consequences during development. Cell death was evaluated in hematoxylin- and eosin-stained sections and by electron microscopy. Damage to the CA1 neurons was maximal in the 2- and 3-week-old pups and decreased as a function of age. On the other hand, damage to the hilar and CA3 neurons was minimal in the 2-week-old rat pups but reached an adult-like pattern in the 3-week-old animals, and damage to amygdalar neurons increased progressively with age. The 3-week-old animals also demonstrated vulnerability of the dentate granule cells. To evaluate neuronal apoptosis, we used terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) stain, confocal fluorescence microscopy of ethidium bromide-stained sections, electron microscopy, and DNA electrophoresis. Neurons displaying all of those features of apoptotic death in response to SE were seen in the CA1 region of the 2-week-old pups and in the hilar border of the dentate granule cells of the 3-week-old animals. Some (3/11) of the animals that underwent SE at 2 weeks of age and most of the animals that underwent SE at 3 or 4 weeks of age (8/11 and 6/8, respectively) developed spontaneous seizures later in life; the latter showed SE-induced synaptic reorganization as demonstrated by Timm methodology. These results provide strong evidence for the vulnerability of the immature brain to seizure-induced damage, which bears features of both necrotic and apoptotic death and contributes to synaptic reorganization and the development of chronic epilepsy.

Age Factors↗

PubMed1998

Soluble fibronectin promotes migration of oral squamous-cell carcinoma cells.

We have shown that a fibronectin (FN) matrix is required for the organization of tenascin-C (TN-C) matrices by peritumor fibroblasts (PTF) cultured from tissue surrounding oral squamous-cell carcinoma (SCC). In the present study, we detected alternatively spliced FN containing both the EDA and EDB domains decorating the reactive stroma adjacent to the invading tumor nests in oral SCC biopsies. In vitro, PTF cells organized an extensive FN matrix rich in the EDA domain and containing a small amount of EDB. In contrast, normal human fibroblasts deposited a FN matrix which expressed only the EDA domain. PTF-conditioned medium (CM), shown to enhance migration of oral SCC cells on TN-C, was found to enhance their migration on FN and invasion of a reconstituted basement membrane. Addition of antibodies to FN to the PTF-CM inhibited SCC-cell migration on TN-C, and depletion of FN from the PTF-CM abolished its ability to induce migration or invasion by oral SCC cells, suggesting that FN promotes the migration and invasion of oral SCC cells. Western blots of the PTF-CM identified FN containing the EDA but not the EDB domain. When soluble FN was added to the control medium in the lower chamber of the Transwell system, SCC-cell migration increased significantly. These results demonstrate that both the EDA and the EDB domains of FN are expressed in the extracellular matrix of oral SCC in vivo and PTF in vitro and indicate that FN is the probable chemotactic factor in the PTF-conditioned medium.

Alternative Splicing↗

PubMed1998

[Reference value of urinary arsenic for nonoccupational exposed subjects in Henan].

Urinary arsenic levels of 2065 nonoccupational exposed subjects in Henan were determined by spectrophotometric analysis. The results showed: (1) The difference was not significant among Zhengzhou, Luoyang, Anyang, Xinyang and Shangqiu (0.01 < P < 0.025). (2) The difference was not significant among different ages(0.01 < P < 0.025) and between sexes(P > 0.05). (3) The distribution was positive skewness. The median of urinary arsenic was 17.8 micrograms/L. The arithmetic mean was 20.7 micrograms/L. The standard deviation was 15.2 micrograms/L. The geometric mean was 17.3 micrograms/L. (4) It is suggested that the reference upper limit value of urinary arsenic for nonoccupational exposed subjects in Henan in 56 micrograms/L.

Adolescent↗

PubMed1998

Constitutive and antibody-induced internalization of prostate-specific membrane antigen.

Prostate-specific membrane antigen (PSMA) is a cell surface glycoprotein expressed predominantly by prostate cancer cells. We have characterized four monoclonal antibodies that bind to the extracellular domain of PSMA (Liu et al., Cancer Res., 57: 3629-3634, 1997). Here we report that viable LNCaP cells internalize these antibodies. Laser scanning confocal microscopy reveals that the internalized antibodies accumulate in endosomes, and immunoelectron microscopy reveals that endocytosis of the PSMA-antibody complex occurs via clathrin-coated pits. In addition, a quantitative cell surface biotinylation assay demonstrates that PSMA is constitutively endocytosed in LNCaP cells and that anti-PSMA antibodies increase the rate of internalization of PSMA. These studies suggest that PSMA might function as a receptor mediating the internalization of a putative ligand. The availability of prostate-specific internalizing antibodies should aid the development of novel therapeutic methods to target the delivery of toxins, drugs, or short-range isotopes specifically to the interior of prostate cancer cells.

Antibodies, Monoclonal↗

PubMed1998

Chemiluminescence flow-through sensor for copper based on an anodic stripping voltammetric flow cell and an ion-exchange column with immobilized reagents.

A novel chemiluminescence (CL) flow-through sensor based on immobilizing all the ingredients involved in the analytical reaction for the determination of copper is proposed. The analytical reagents including luminol and cyanide were coimmobilized permanently on an anion-exchange column, while the analyte copper was retained temporarily by electrochemical preconcentration on a gold electrode placed in an anodic stripping voltammetric flow cell. By injection of a volume of sodium hydroxide through the column with immobilized reagents, luminol and cyanide were eluted from the resins in alkaline aqueous solution and then reacted with copper stripped from the gold electrode to produce a CL signal, by means of which copper could be sensed. The sensor was not susceptible to interference by other metal ions associated with the CL reaction. The response to the concentration of copper was linear in the range of 0.01-10 micrograms/L and an extremely low detection limit of 8.0 x 10(-3) micrograms/L was achieved. A complete analysis could be performed in 4 min with a relative standard deviation of less than 8%. The column with immobilized reagents was readily prepared and could be reused over 200 times. The sensor was applied successfully to the determination of copper in human serum and natural water samples.

Chromatography, Ion Exchange↗

PubMed1998

A study of sexual behavior among rural residents of China.

OBJECTIVE: Although the recent spread of HIV/AIDS and other sexually transmitted diseases (STDs) in China has been associated with sexual activities, little information has been available about sexual behavior in rural areas with high HIV prevalence. Studies identifying high-risk sexual behaviors are needed to formulate effective prevention programs. METHODS: A cross-sectional study design was used to measure sexual activities using a two-stage cluster sampling method. A two-part anonymous questionnaire was used. Sensitive questions related to sexual behavior were administered using a tape recorder, earphones, and an answer sheet which did not include the text. RESULTS: In total, 1057 subjects were interviewed. Among 886 sexually active individuals, 7.8% had >1 sexual partner, 22.8% had premarital sex, 2.4% had anal intercourse, 4.1% had oral intercourse, and 2.3% had both anal and oral intercourse. Less than 2% reported past or current sexually transmitted diseases. Overall, 10.4% used condoms; only 11.2% for every sexual act. History of premarital and extramarital sex was higher in younger people. CONCLUSIONS: Sexual norms in rural China are changing rapidly and high-risk sexual behavior among young rural residents is increasing. Strategies to prevent HIV/AIDS should include education to promote delayed onset of sexual activity, safer sexual behavior, and condom use.

Adolescent↗

PubMed1998

Optimization of post-column photolysis and electrochemical detection for the liquid chromatographic determination of 3-nitro-L-tyrosine.

A new post-column photolysis technology has been developed based on the use of a low pressure, low temperature UV lamp and TiO2 coated knitted reaction coil. As a test case the developed technique was used for the determination of 3-nitro-L-tyrosine by liquid chromatography with electrochemical detection. Different photolysis lamps and reactor tubing lengths were evaluated in terms of their effect on the separation efficiency and/or photolysis efficiency. A detection limit of 0.5 nM (10 fmol) for 3-nitro-L-tyrosine was achieved under optimized conditions, with a linear correlation coefficient of R2 = 0.9898 over a concentration range of 2-100 microM. Pre-injection photolysis of 3-nitro-L-tyrosine indicated that dihydroxyphenylalanine is the main photolysis product. In general, use of the photoreactor prior to liquid chromatography is an excellent method for exploring photodegradation products of an analyte in conjunction with the full range of available liquid chromatography detectors.

Animals↗

PubMed1998

Comparison of detection methods for liquid chromatographic determination of 3-nitro-L-tyrosine.

A liquid chromatographic method has been developed for the determination of 3-nitro-L-tyrosine. Different detection methods, including UV, oxidative and redox electrochemistry, and postcolumn photolysis followed by electrochemical detection, have been optimized and compared in terms of analysis time, detection limit and dynamic range. It was demonstrated that liquid chromatography with postcolumn photolysis followed by electrochemical detection is the most effective method, with an analysis time of 5 min, detection limit of 0.01 pmol, and a linear dynamic range from 2 nM to 100 microM.

Animals↗