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Biomedical subjects

H Gao

Publications and source records attributed to H Gao.

At least 91 records · Page 5Linked to original sources
PubMed2000

Experimental observation of further frequency upshift from dc to ac radiation converter with perpendicular dc magnetic field

A frequency upshift of a short microwave pulse is generated by the interaction between a relativistic underdense ionization front and a periodic electrostatic field with a perpendicular dc magnetic field. When the dc magnetic field is applied, further frequency upshift of 3 GHz is observed with respect to an unmagnetized case which has typically a GHz range. The radiation frequency depends on both the plasma density and the strength of the dc magnetic field, i.e., the plasma frequency and the cyclotron frequency. The frequency of the emitted radiation is in reasonable agreement with the theoretical values.

Journal Article↗
PubMed2000

Chloroquinoxaline sulfonamide (NSC 339004) is a topoisomerase IIalpha/beta poison.

Chloroquinoxaline sulfonamide (chlorosulfaquinoxaline, CQS, NSC 339004) is active against murine and human solid tumors. On the basis of its structural similarity to the topoisomerase IIbeta-specific drug XK469, CQS was tested and found to be both a topoisomerase-IIalpha and a topoisomerase-IIbeta poison. Topoisomerase II poisoning by CQS is essentially undetectable in assays using the common protein denaturant SDS, but easily detectable with strong chaotropic protein denaturants. The finding that detection of topoisomerase poisoning can be so dependent on the protein denaturant used in the assay has implications for drug discovery efforts and for our understanding of topoisomerase poisons.

Animals↗
PubMed2000

Evidence for valencelike quark-hadron duality

A newly obtained data sample of inclusive electron-nucleon scattering from both hydrogen and deuterium targets is analyzed. These JLab data span the nucleon resonance region up to four-momentum transfers of 5 (GeV/c)(2). The data are found to follow an average scaling curve. The inclusion of low-momentum transfer data yields a scaling curve resembling deep inelastic neutrino-nucleus scattering data, suggesting a sensitivity to valencelike structure only.

Journal Article↗
PubMed2000

Experimental verification of quark-hadron duality

A newly obtained sample of inclusive electron-nucleon scattering data has been analyzed for precision tests of quark-hadron duality. The data are in the nucleon resonance region, and span the range 0. 3<Q2<5.0 (GeV/c)(2). Duality is observed both in limited and extended regions around the prominent resonance enhancements. Higher twist contributions to the F2 structure function are found to be small on average, even in the low Q2 regime of approximately 0.5 (GeV/c)(2). Using duality, an average scaling curve is obtained. In all cases, duality appears to be a nontrivial property of the nucleon structure function.

Journal Article↗
PubMed2000

[Contrast test using three kinds of air-microorganism samplers LWC-I, CA6 and CA2 in public places].

A sampling experiment was conducted using three kinds of air-samplers, i.e. LWC-1, CA6 and CA2, on bacteria and fungus in the air under the same conditions and at the same time yet in three different public places. The results showed that there was no significant difference in the total number of bacteria and fungus colony forming units in the air in different public places using the above mentioned three air-samplers. In comparison, the LWC-1 air-sampler demonstrated a feature of small size, light weight, simple structure, and little noise, therefore, it was easy in carrying and requires no external power source. Such being the case, the LWC-1 air-sampler was more suitable for monitoring microorganism in the air in public places.

Air Microbiology↗
PubMed2000

How fast can cracks propagate?

We have performed atomic simulations of crack propagation along a weak interface joining two harmonic crystals. The simulations show that a mode II shear dominated crack can accelerate to the Rayleigh wave speed and then nucleate an intersonic daughter that travels at the longitudinal wave speed. This contradicts the general belief that a crack can travel no faster than the Rayleigh speed.

Journal Article↗
PubMed2000

Copper-transporting P-type adenosine triphosphatase (ATP7B) is associated with cisplatin resistance.

The accumulation of cisplatin is decreased in many cisplatin-resistant cell lines, and an active efflux pump for cisplatin exists in some of them, but it has not yet been identified. In this study, we transfected the copper-transporting P-type ATPase cDNA (ATP7B) into human epidermoid carcinoma KB-3-1 cells. The transfectant, KB/WD cell line, which overexpressed the P-type ATPase, ATP7B, was resistant to both cisplatin (8.9-fold) and copper (2.0-fold). The accumulation of cisplatin in KB/WD cells was lower than in mock-transfected KB/CV cells, and the efflux of cisplatin from KB/WD cells was enhanced compared with KB/CV cells. KB/WD cells were sensitive to other heavy metals, such as antimony, arsenate, arsenite, cadmium, and cobalt. ATP7B was overexpressed in cisplatin-resistant prostate carcinoma PC-5 cells but not in the parental PC-3 cells and the revertant PC-5R cells. ATP7B may be involved in cisplatin resistance in some tumors.

Adenosine Triphosphatases↗
PubMed2000

Explanation for fracture spacing in layered materials

The spacing of opening-mode fractures in layered materials--such as certain sedimentary rocks and laminated engineering materials--is often proportional to the thickness of the fractured layer. Experimental studies of this phenomenon show that the spacing initially decreases as extensional strain increases in the direction perpendicular to the fractures. But at a certain ratio of spacing to layer thickness, no new fractures form and the additional strain is accommodated by further opening of existing fractures: the spacing then simply scales with layer thickness, which is called fracture saturation. This is in marked contrast to existing theories of fracture, such as the stress-transfer theory, which predict that spacing should decrease with increasing strain ad infinitum. Recently, two of us (T.B. and D.D.P.) have used a combination of numerical simulations and laboratory experiments to show that, with increasing applied stress, the normal stress acting between such fractures undergoes a transition from tensile to compressive, suggesting a cause for fracture saturation. Here we investigate the full stress distribution between such fractures, from which we derive an intuitive physical model of the process of fracture saturation. Such a model should find wide applicability, from geosciences to engineering.

Journal Article↗
PubMed2000

Effects of the protein tyrosine phosphatase CD45 on FcgammaRIIa signaling and neutrophil function.

OBJECTIVE: Neutrophil receptors for the Fc portion of IgG (FcgammaR) trigger immune responses following cross-linking by IgG-coated foreign particles or immune complexes. Membrane-associated CD45, a protein tyrosine phosphatase termed leukocyte common antigen, has been shown to be essential for antigen receptor kinase mediated signaling in lymphocytes, and we hypothesized that CD45 may play a similar role in FcgammaR-mediated signaling and immune function in human neutrophils. METHODS: The experimental approach was that of cell surface molecule ligation via cross-linking with specific antibodies. Antibody dependent cellular cytotoxicity (ADCC) was assessed using a single-cell plaque assay and IL-6 production measured using ELISA. Tyrosine phosphorylation levels were assessed with anti-phospho-tyrosine blots and F-actin polymerization by flow cytometry and confocal microscopy. RESULTS: Neutrophils pretreated with anti-CD45 had a reduced ability to perform ADCC compared to untreated neutrophils. FcgammaRIIa cross-linking resulted in significantly increased concentrations of secreted IL-6 compared to untreated neutrophils, and IL-6 production was further enhanced by cocross-linking CD45 with FcgammaRIIa. Cross-linking CD45 alone also induced IL-6 production. FcgammaRIIa cross-linking resulted in increased protein tyrosine phosphorylation and F-actin polymerization in neutrophils. Cocross-linking CD45 with FcgammaRIIa resulted in abrogation of FcgammaRIIa mediated tyrosine phosphorylation and F-actin polymerization. CONCLUSIONS: These data provide evidence that CD45 can regulate or enhance the stimulation and function of human neutrophils mediated through FcgammaR(s). In addition, CD45 ligation may play an essential role in cytokine induction pathways that lead to inflammatory reactions in vivo.

Actins↗
PubMed2000

Fabrication and photoelectric properties of self-assembled bilayer lipid membranes on conducting glass.

Supported bilayer lipid membranes (s-BLMs with and without the doping of fullerene C60) self-assembled on indium-tin oxide (ITO) glass were fabricated and characterized by cyclic voltammetry and electrochemical impedance spectroscopy using a three-electrode system. The photoelectric properties of the ITO supported planar lipid bilayers were studied. Light intensity of irradiation, bias voltage, and concentration of donors have been found to be limiting factors of the transmembrane photocurrent. The facilitation effect of C60 doping in s-BLMs on the photoinduced electron transfer across s-BLM is discussed. This novel self-assembled ITO/s-BLM system may provide a simple and mechanically stable model for the study of the photoelectric and photodynamic properties of biomembranes.

Electric Conductivity↗
PubMed2000

Differences in genotypes of Helicobacter pylori from different human populations.

DNA motifs at several informative loci in more than 500 strains of Helicobacter pylori from five continents were studied by PCR and sequencing to gain insights into the evolution of this gastric pathogen. Five types of deletion, insertion, and substitution motifs were found at the right end of the H. pylori cag pathogenicity island. Of the three most common motifs, type I predominated in Spaniards, native Peruvians, and Guatemalan Ladinos (mixed Amerindian-European ancestry) and also in native Africans and U.S. residents; type II predominated among Japanese and Chinese; and type III predominated in Indians from Calcutta. Sequences in the cagA gene and in vacAm1 type alleles of the vacuolating cytotoxin gene (vacA) of strains from native Peruvians were also more like those from Spaniards than those from Asians. These indications of relatedness of Latin American and Spanish strains, despite the closer genetic relatedness of Amerindian and Asian people themselves, lead us to suggest that H. pylori may have been brought to the New World by European conquerors and colonists about 500 years ago. This thinking, in turn, suggests that H. pylori infection might have become widespread in people quite recently in human evolution.

Amino Acid Isomerases↗
PubMed2000

Sequential inactivation of rdxA (HP0954) and frxA (HP0642) nitroreductase genes causes moderate and high-level metronidazole resistance in Helicobacter pylori.

Helicobacter pylori is a human-pathogenic bacterial species that is subdivided geographically, with different genotypes predominating in different parts of the world. Here we test and extend an earlier conclusion that metronidazole (Mtz) resistance is due to mutation in rdxA (HP0954), which encodes a nitroreductase that converts Mtz from prodrug to bactericidal agent. We found that (i) rdxA genes PCR amplified from 50 representative Mtz(r) strains from previously unstudied populations in Asia, South Africa, Europe, and the Americas could, in each case, transform Mtz(s) H. pylori to Mtz(r); (ii) Mtz(r) mutant derivatives of a cultured Mtz(s) strain resulted from mutation in rdxA; and (iii) transformation of Mtz(s) strains with rdxA-null alleles usually resulted in moderate level Mtz resistance (16 microg/ml). However, resistance to higher Mtz levels was common among clinical isolates, a result that implicates at least one additional gene. Expression in Escherichia coli of frxA (HP0642; flavin oxidoreductase), an rdxA paralog, made this normally resistant species Mtz(s), and frxA inactivation enhanced Mtz resistance in rdxA-deficient cells but had little effect on the Mtz susceptibility of rdxA(+) cells. Strains carrying frxA-null and rdxA-null alleles could mutate to even higher resistance, a result implicating one or more additional genes in residual Mtz susceptibility and hyperresistance. We conclude that most Mtz resistance in H. pylori depends on rdxA inactivation, that mutations in frxA can enhance resistance, and that genes that confer Mtz resistance without rdxA inactivation are rare or nonexistent in H. pylori populations.

Amino Acid Substitution↗
PubMed2000

Differential effects of furosemide on porcine bronchial arterial and airway smooth muscle.

Furosemide attenuates airway obstruction in asthmatic subjects when administered as an aerosol pretreatment. This protective effect of furosemide could be related to relaxation of bronchial smooth muscle or to increased bronchial blood flow. To determine whether furosemide dilates bronchial smooth muscle, isometric contractile responses in distal bronchi from young pigs were studied. In bronchial smooth muscle rings that were precontracted with 10(-5) M acetylcholine, significant relaxation occurred with 10(-8) to 3 x 10(-6) M isoproterenol but not with 10(-8) to 10(-3) M furosemide. In contrast, bronchial arteries that were precontracted with either 10(-4) M norepinephrine or 10(-8) M vasopressin significantly relaxed in response to 10(-4) to 3 x 10(-3) M and 10(-3) to 3 x 10(-3) M furosemide, respectively. We conclude that furosemide, under the described experimental conditions, relaxes airway vascular smooth muscle but not bronchial smooth muscle. These results are consistent with previous suggestions that inhaled furosemide increases blood flow to airway tissues (Gilbert IA, Lenner KA, Nelson JA, Wolin AD, and Fouke JM. J Appl Physiol 76: 409-415, 1994).

Animals↗
PubMed2000

Moderate metabolic acidosis and its effects on serum parameters in hemodialysis patients.

We screened the laboratory data of 50 chronic hemodialysis patients selected randomly over a 21-month period to generate 158 data points which identified two groups: (1) those with a predialysis total CO(2) concentration less than or equal to 19 mEq/l (data A; n = 57) and (2) those with a predialysis total CO(2) concentration greater than 19 mEq/l (data B; n = 101). Then, both groups were compared for the following parameters: predialysis blood urea nitrogen (BUN), serum phosphorus, uric acid, creatinine, and albumin concentrations, Kt/V, urea reduction ratio, normalized protein catabolic rate, dry weight, ultrafiltration, blood flow and dialysis flow rates, duration of dialysis treatment, and blood pressure. Group data A had significantly higher predialysis BUN, phosphorus, and uric acid concentrations than group data B. There were significant inverse correlations between predialysis serum bicarbonate and predialysis BUN, phosphorus, and uric acid concentrations. Although it is not clear what the long term side effects of moderate metabolic acidosis are, we recommend its correction.

Acidosis↗
PubMed2000

Studying the growth of cervical carcinoma nests and angiogenesis by immunostaining, quantitation and three-dimensional structural analysis.

OBJECTIVE: To analyze the relationship and mutual effect of the growth of cervical carcinoma nests and angiogenesis. STUDY DESIGN: Serial paraffin sections of cervical squamous carcinoma were stained in repeated order with hematoxylin-eosin (HE), immunostain for factor VIII-related antigen, type IV collagen and proliferating cell nuclear antigen (PCNA). Three-dimensional reconstructions were made, and the volumes of carcinoma nests, necrosis and microvessels were measured. RESULTS: Two types of cervical carcinoma nests were distinguished on the basis of their growth characteristics and vascularity (groups I and II). Group I nests: The carcinoma cells were proliferating actively, as determined by their morphology and PCNA staining. There were abundant microvessels. Some endothelial sprouts and cords penetrated the nests and then formed networks and new vessels. The volume ratio of microvessels, including sprouts and cords, to the nests was 0.6282:1. Group II nests: The center of these nests underwent necrosis. The peripheral cells were rather small, with no mitosis. The PCNA index was rather low; these nests grew very slowly. There were only a few surrounding microvessels with no endothelial sprouts or cords. The volume ratio of vessels to nest was 0.0657:1. CONCLUSION: Two types of cervical carcinoma nests show a close relationship and mutual effect of the growth of carcinoma nest and angiogenesis. Group I nests grow and develop well, with abundant microvessels. Thus, many tumor cells may be angiogenic and induce angiogenesis; growth of the nests seemed dependent on adequate neovascularization. Group II nests grow slowly, with a few microvessels; the center of the nests undergoes necrosis. The inadequate blood supply must be one of the important causes of necrosis. Considering that there must have been abundant neovascularization during their growth in the past, most of the microvessels must have been obliterated and then reabsorbed to make the remaining vessels so few.

Cell Nucleus↗
PubMed2000

Potentiation of BCNU anticancer activity by O6-benzylguanine: a study in vitro and in vivo.

O6-Alkylguanine-DNA alkyltransferase (O6-AGT), a constitutively expressed DNA repair protein, removes alkyl groups from the O6-position of guanine in DNA. Tumor cells with high O6-AGT activity are resistant to nitrosoureas and other agents that form toxic O6-alkyl adducts. We evaluated O6-benzylguanine (O6-BG) for its activity to inhibit O6-AGT and potentiate 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in O6-AGT-positive human gastric adenocarcinoma cell line, BGC-823 and its tumor xenograft. The sensitivity of BGC-823 cells to BCNU was increased by pretreatment for 2 hours with 1.5 to 6.0 microg/mL O6-benzylguanine. O6-benzylguanine (0.75-6.0 microg/mL) completely and rapidly suppressed the O6-AGT activity of cells for up to 12 hours. When given i.p. 2 hours before BCNU (25 mg/kg) to animals bearing s.c. tumors, O6-BG (90 mg/kg) produced a growth delay of 38.6 days in human gastric adenocarcinoma xenograft. Furthermore, O6-BG significantly inhibited the O6-AGT activity of tumor tissue and induced evident apoptosis. These results suggest that combination of O6-BG with BCNU may have a significant therapeutic effect in the treatment of mer + tumor.

Alkyl and Aryl Transferases↗