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Biomedical subjects

G Chen

Publications and source records attributed to G Chen.

At least 595 records · Page 33Linked to original sources
PubMed1997

[Deviation of size-exclusion chromatographic behavior of tryptophan on TOYOPEARL HW-40S column].

A deviation of size-exclusion chromatographic behavior of amino acids on TOYOPEARL HW-40S column is reported. On the column 18 amino acids were not eluted in the same fraction in the total volume, but separated into 5 fractions with tryptophan as the last one far behind the total volume. Interaction between tryptophan and the matrices was investigated under different conditions in order to elucidate the chemical nature of the deviation. It was found that addition of trifluoroacetic acid and sodium chloride of high concentration in mobile phase, dramatically increased the retention time of trypophan, while addition of acetonitrile, sodium chloride of lower concentration and the hydrogen bond breaker urea reduced the interaction. It is concluded that adsorption of tryptophan on TOYOPEARL HW-40S is basically due to the hydrophobic nature with limited influence of hydrogen bond and ionic interaction. The former factor can be eliminated by keeping acentonitrile concentration over 50% (V/V), while the latter two can be reduced to the minimum by adding 0.17mol/L sodium chloride and 3.51mol/L urea. The results not only lead to better understanding of size-exclusion chromatography of this matrices, but also help to apply hydrophobic chromatography of this matrices to the isolation of amino acids and peptides.

Amino Acids↗
PubMed1997

[Absorption spectra study for fullerene-doped in polystyrene film].

The absorption spectra of C60 and C70-doped in polystyrene film and in solution were studied. The experiment results showed that the positions of the absorption peaks for C60-doped in polystyrene film moved a little toward longer wavelength than in n-hexane, and regular solid material appeared while the ratio of C60-doped in the film increased; The absorption peaks for C70-doped in polystyrene film were almost in consistent with that in solution. We suggest that C60 molecules may be connected as "microcrystalline" in polystyrene film, while C70 may be exist as single molecule or particle less than C60 in it. The preliminary model for the growth of "microcrystslline" in polystyrene film has been proposed.

English Abstract↗
PubMed1997

[Determination of molybdenum in natural waters by direct current plasma atomic emission spectrometry with ion-exchange preconcentration].

A new method was developed for the determination of trace molybdenum in natural waters by direct current plasma atomic emission spectrometry after separating and preconcentrating with D301 anion exchange resin. Mo adsorbed on the resin column can be recovered quantitatively by using 20mL of 8mol/L HNO3 at a flow rate of 0.6mL/min with elution rate of (81.6 +/- 1.78)%. The behaviour of Mo on the resin has been discussed. Simulative water and natural water samples have been determined. It was found that the interference element Ca could be separated effectively from Mo; an enrichment factor of 50 was obtained for Mo in 1L water sample; the determination limit of Mo was improved to 0.5 microg/L and the recovery of 90-107% was obtained.

Analytic Sample Preparation Methods↗
PubMed1997

[IR and UV-vis spectra of nitrogen-doped fullerene].

Nitrogen-doped fullerene derivative's IR and UV-vis spectra are reported. Some of the C60 IR silent modes are activated due to nitrogen atom reducing C60 molecular symmetry. UV-vis spectrum indicates nitrogen is donor.

English Abstract↗
PubMed1997

A single copy of apolipoprotein B-48 is present on the human chylomicron remnant.

Individuals homozygous for the e2 allele encoding apolipoprotein E exhibit a remnant removal defect and accumulate substantial levels of intestinally derived particles containing apolipoprotein B-48 (apoB-48). Such lipoproteins were isolated from the plasma of E2/E2 individuals, and further purified by affinity chromatography using a polyclonal antibody specific for selective binding and removal of apoB-100-containing lipoproteins. The unbound lipoproteins, termed chylomicron remnants, were particles with average hydrated diameters of 31.2 nm as determined by dynamic light scattering. They contained apoB-48 and ApoE as their only protein components. The number of apoB-48 molecules on each lipoprotein was assessed by counting the number of antibody molecules bound to the surface of the chylomicron remnants, using either a monoclonal antibody specific for a single epitope on apoB-48 or a mixture of two such monoclonal antibodies specific for widely separated epitopes. The results of this analysis seem unambiguous: no more than one apoB-48 resides on the chylomicron remnant. Because apoB appears to be unable to transfer among lipoprotein particles, it may be inferred that nascent chylomicrons also contain a single copy of apoB-48.

Antibodies, Monoclonal↗
PubMed1997

[Analysis of genome-type, serovar and antibiotic susceptibility of Pseudomonas aeruginosa isolated in Beijing Hospital China in 1991 to 1993].

We analyzed the in vitro antibiotic susceptibility pattern and serovar for 192 strains of Pseudomonas aeruginosa isolated at Beijing Hospital(China) from October 1991 to October 1993. The frequency of resistant strains was high, more than 15%, for ceftazidime, cefsulodin, cefoperazone, aztreonam, gentamicin, tobramycin, tosufloxacin, ofloxacin and fosfomycin. The incidence of resistants against piperacillin and imipenem was significantly low. Among the 192 strains, 16 were designated as being multi-drug resistant strains(i.e.; resistant to more than 8 drugs out of 11 drugs), and all of the multi-drug resistant strains were isolated from inpatients. Predominant serovar of 192 strains were 60(31.3%) for G, 28(14.7%) for E, and 24(12.5%) for I. Multi-drug resistant strains have no characteristic serovar. Restriction enzyme SpeI digestion analysis(using pulse field electrophoresis) of P. aeruginosa-genome yielded several common patterns, and was shown to be useful for tracing the route of nosocomial infection. Further, isolates with closely related genome type, in which the size of one digested band was different, showed a different minimum inhibitory concentration of fosfomycin in one genome type or new quinolones in the other genome type. Analysis of genome type and antibiotic susceptibility pattern may exhibit the antibiotic resistant gene.

Anti-Bacterial Agents↗
PubMed1997

[Micro-particle image processing based on an artificial neuron network with fluid properties].

The form of macro-particle is a close successive region in two-valued micro-particle image, and the detection of microparticles is actually that of close successive regions. Accordign to this theory, this paper present a new technique for micro-particles detecting based on an artificial neuron network modeled on the diffusing behaviour of real visual system, which has fluid properties. The results of simulation on computer shew that this method is very effect.

Blood Cell Count↗
PubMed1997

[Double effects of arsenic trioxide (As2O3) on acute promyelocytic leukemic cell line].

OBJECTIVE: To investigate the effects of a wide range of concentrations of As2O3 on NB4 cells. METHODS: Cell morphology, cell-DNA content distribution, CD11b and CD33 antigens and nitroblue tetrazolium (NBT) reductions were evaluated in an APL cell line NB4 cells with or without As2O3 treatment. In addition, immunofluorescent analysis for APL marker molecule PML-RAR alpha was also performed. RESULTS: 1-2 mumol/L of As2O3 treated NB4 cells presented morphologically some features of apoptotic cells such as intact cell membrane, chromatin condensation and nuclear fragmentation. Sub-G1 cells, whose percentage presents concentration and time-dependency, were observed by flow cytometer. Otherwise, NB4 cells with the treatment of As2O3 at 0.1-0.25 mumol/L for a long time (10 days) have differentiation-related morphology, and their differentiation antigens CD11b and CD33 were also modulated to some extent. In addition, 0.1-2 mumol/L of As2O3 could rapidly and effectively modulate and degradate PML/PML-RAR alpha proteins. CONCLUSION: As2O3 had double effects (induction of apoptosis and imcomplete differentiation) on NB4 cells, which could associate with rapid modulation and degradation of PML/PML-RAR alpha proteins.

Antineoplastic Agents↗
PubMed1997

[Cloning and expression of a novel gene related to hypertension].

OBJECTIVE: To search and clone novel genes related to hypertension. METHODS: Using differential display, a RNA mapping method, we identified differentially expressed RNAs from cultured VSMCs of WKY and SHR. Down-expressed cDNAs of WKY were cloned. RESULTS: A novel cDNA (rHRG-1) obtained contained 4,160 bp nucleotides and an open reading frame which encoded 551 amino acid residues. Its molecular weight was 62,644. Northern blot analysis showed that the mRNA was expressed not only in VSMCs but in various rat tissues (heart, liver, brain, lung and kidney). Besides, the expression of rHRG-1 mRNA in various tissues (heart, liver, brain and kidney) of WKY rat was higher than that in those tissues of SHR. Semi-quantitative RT-PCR analysis showed that the expression of rHRG-1 mRNA was down-regulated by treating cells with angiotensin-II, endothelin-I or interleukin-I. VSMCs proliferation and hypertension-stimulating factor, but was up-regulated when treating cells with ANF, CGRP or adrenomedullin which could inhibit the proliferation of VSMCs and attenuate hypertension. These effects could be blocked or attenuated by corresponding antagonists or antibodies. CONCLUSION: The isolated novel rat cDNA (rHRG-1) is related to VSMCs proliferation or hypertension. It may antagonize the proliferation of VSMCs and may be involved in the formation of hypertension.

Amino Acid Sequence↗
PubMed1997

[The relationship between viral hepatitis and primary liver cancer in four areas of China].

To investigate the relationship between hepatitis B, C and G and primary liver cancer (PLC), both population-based and hospital-based case-control studies were conducted in four areas of China. The prevlence rates of HBsAg in 359 pairs of PLC cases and controls were 66.3% and 23.4% (OR = 6.60, PAR = 55.5%), respectively; the prevalence of anti-HCV in 340 pairs of PLC cases and controls were 17.9% and 6.5% (OR = 3.31, PAR = 12.4%), respectively. When both markers were positive, the OR was higher than their multiple effect of HBsAg and anti-HCV. In the Haimen Case-control study, serum HGV-RNA was detected in 11 of the 50 PLC cases, compared to 5 of the 50 controls matched with age and sex (P > 0.05). These data suggested that HBV might have played a more important role than HCV and HGV in the development of PLC in China.

Case-Control Studies↗
PubMed1996

The product of the ATM gene is a 370-kDa nuclear phosphoprotein.

Neuronal degeneration, gonadal abnormalities, and immune deficiency are some of the major manifestations of the hereditary disease ataxia telangiectasia, which is caused by mutations in a single gene, designated ATM. Here we show that the product of the ATM gene is a 370-kDa nuclear phosphoprotein. Because ATM knockout mice recapitulate the clinical symptoms of the human disease, we have examined ATM gene expression in mice. In mouse embryos at gestation day 13.5, ATM mRNA is expressed ubiquitously, with high levels detected in the nervous system and lung. Elevated ATM mRNA levels were also found in the thymus of mouse embryos at gestation day 18.5, a time when V(D)J recombination is occurring. In adult mice, ATM protein was detected in all tissues examined and was present at elevated levels in the testis, spleen, and thymus. The ATM expression pattern and the nuclear localization of the ATM protein are consistent with the proposed function of ATM in the activation of cell cycle checkpoints, DNA repair, and genetic recombination.

Adult↗
PubMed1996

Integration of the SV40 promoter/enhancer sequences in an anchorage-independent clonal subline of SV40-infected human keratinocytes.

Long-term cultures of SV40-infected human keratinocytes contain integrated, but structurally altered copies of the viral sequences. The presence of these sequences is required for expression of properties associated with the transformed phenotype including immortalization. The integrated viral sequences in an anchorage-independent line of viral-transformed human keratinocytes have been found to be contained on two BamHI fragments of about 6.9 and 5.2 kb. In the larger fragment the viral sequences were present as two tandemly repeated subgenomic fragments containing the viral origin/promoter region with nucleotide alterations that affect enhancer function, the origin of replication and T antigen binding site 1. The viral early gene promoter in one integrant gave rise to an unspliced fusion transcript comprised of a short portion of the viral early gene leader sequence and the flanking human sequences. The smaller fragment consisted of full-length SV40 containing a nine-nucleotide insertion in the C-terminal portion of the SV40 T antigen, a region involved in the regulation of viral host range.

Antigens, Polyomavirus Transforming↗
PubMed1996

Disappearance of body fat in normal rats induced by adenovirus-mediated leptin gene therapy.

Sustained hyperleptinemia of 8 ng/ml was induced for 28 days in normal Wistar rats by infusing a recombinant adenovirus containing the rat leptin cDNA (AdCMV-leptin). Hyperleptinemic rats exhibited a 30-50% reduction in food intake and gained only 22 g over the experimental period versus 115-132 g in control animals that received saline infusions or a recombinant virus containing the beta-galactosidase gene (AdCMV-beta Gal). Body fat was absent in hyperleptinemic rats, whereas control rats pair-fed to the hyperleptinemic rats retained approximately 50% body fat. Further, plasma triglycerides and insulin levels were significantly lower in hyperleptinemic versus pair-fed controls, while fatty acid and glucose levels were similar in the two groups, suggestive of enhanced insulin sensitivity in the hyperleptinemic animals. Thus, despite equivalent reductions in food intake and weight gain in hyperleptinemic and pair-fed animals, identifiable fat tissue was completely ablated only in the former group, raising the possibility of a specific lipoatrophic activity for leptin.

Adenoviridae↗
PubMed1996

Clinical value of proton magnetic resonance spectroscopy for differentiating recurrent or residual brain tumor from delayed cerebral necrosis.

PURPOSE: Delayed cerebral necrosis (DN) is a significant risk for brain tumor patients treated with high-dose irradiation. Although differentiating DN from tumor progression is an important clinical question, the distinction cannot be made reliably by conventional imaging techniques. We undertook a pilot study to assess the ability of proton magnetic resonance spectroscopy (1H MRS) to differentiate prospectively between DN or recurrent/residual tumor in a series of children treated for primary brain tumors with high-dose irradiation. METHODS AND MATERIALS: Twelve children (ages 3-16 years), who had clinical and MR imaging (MRI) changes that suggested a diagnosis of either DN or progressive/recurrent brain tumor, underwent localized 1H MRS prior to planned biopsy, resection, or other confirmatory histological procedure. Prospective 1H MRS interpretations were based on comparison of spectral peak patterns and quantitative peak area values from normalized spectra: a marked depression of the intracellular metabolite peaks from choline, creatine, and N-acetyl compounds was hypothesized to indicate DN, and median-to-high choline with easily visible creatine metabolite peaks was labeled progressive/recurrent tumor. Subsequent histological studies identified the brain lesion as DN or recurrent/residual tumor. RESULTS: The patient series included five cases of DN and seven recurrent/residual tumor cases, based on histology. The MRS criteria prospectively identified five out of seven patients with active tumor, and four out of five patients with histologically proven DN correctly. Discriminant analysis suggested that the primary diagnostic information for differentiating DN from tumor lay in the normalized MRS peak areas for choline and creatine compounds. CONCLUSIONS: Magnetic resonance spectroscopy shows promising sensitivity and selectivity for differentiating DN from recurrent/progressive brain tumor. A novel diagnostic index based on peak areas for choline and creatine compounds may provide a simple discriminant for differentiating DN from recurrent or residual primary brain tumors.

Adolescent↗
PubMed1996

Multiple NPY receptors coexist in pre- and postsynaptic sites: inhibition of GABA release in isolated self-innervating SCN neurons.

Although NPY has been shown to influence the action of many transmitters in the brain, modulation of GABA, the primary inhibitory transmitter, has not been detected with electrophysiology. Using whole-cell patch-clamp recording, we found that NPY has a large modulatory effect on GABAergic neurons of the suprachiasmatic nucleus (SCN) that act as the circadian clock in the mammalian brain. NPY, acting at both Y1- and Y2-like receptors, reduced the frequency of spontaneous miniature inhibitory postsynaptic currents while having little effect on the postsynaptic GABA receptors, suggesting a presynaptic mechanism of NPY action. In single self-innervating neurons, application of either Y1 or Y2 agonists to the same neuron significantly inhibited the evoked autaptic GABA release. The use of single-neuron microcultures has allowed the demonstration that a single peptide, NPY, has two different receptors coded for by different genes in the same axon terminal. The Y1 and Y2 agonists also inhibited whole-cell calcium currents when applied to the same neuron, indicating a coexistence of Y1- and Y2-like receptors in the postsynaptic cell body. The self-innervating cell model we use here may be applicable generally for discriminating presynaptic versus postsynaptic actions of other neurotransmitters and neuromodulators and locating their subtype receptors.

Animals↗
PubMed1996

Activated function of the pyruvate dehydrogenase phosphatase through Ca2+-facilitated binding to the inner lipoyl domain of the dihydrolipoyl acetyltransferase.

Micromolar Ca2+ facilitates approximately 10-fold enhancement of pyruvate dehydrogenase phosphatase (PDP) activity by aiding the association of PDP with the dihydrolipoyl acetyltransferase (E2) component. Connected by linker regions, E2 consists of two lipoyl domains, the NH2-lipoyl domain (L1) and the interior lipoyl domain (L2), and a pyruvate dehydrogenase component binding domain surrounding a 60-mer inner core. Using recombinant constructs of L1 or L2, E2-enhanced PDP activity was markedly decreased by L2 but not by L1, effectively competing with intact E2 in Ca2+-dependent binding of PDP (half-maximal reduction at 2.0 microM L2 versus 6.7 microM E2 subunit). Using L2 fused to glutathione S-transferase resulted in direct Ca2+-dependent binding of PDP to L2 (Kd, approximately 1.7 microM L2). Affinity-bound glutathione S-transferase-L2 was used to purify PDP to homogeneity by selective binding and elution by Ca2+ chelation. The large activity enhancement of PDP by E2 was eliminated by enzymatic removal of lipoates from E2 and restored by their enzymatic reintroduction. The critical role of the L2 lipoate is not in binding of PDP to E2, since PDP was still bound by delipoylated L2, and delipoylated L2 inhibited E2-enhanced PDP activity, although lipoylated L2 was more effective in each of these tests. Thus, pyruvate dehydrogenase complex activity is increased by enhanced availability of PDP to its E2-bound, phosphorylated pyruvate dehydrogenase substrate as a consequence of the Ca2+-facilitated interchange of PDP among the mobile L2 domains and an essential (undetermined) step engaging the L2 lipoate.

Acetyltransferases↗