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Biomedical subjects

L Zheng

Publications and source records attributed to L Zheng.

At least 109 records · Page 6Linked to original sources
PubMed2000

Iterative optimal design of PET experiments for estimating beta-adrenergic receptor concentration.

To estimate in vivo myocardial beta-adrenergic receptor concentration with sufficient precision and to reduce the experimental complexities in positron emission tomography (PET), an iterative optimal design method is applied. An initial three-injection protocol, utilising [F-18]-labelled (R)- and (S)-fluorocarazolol and unlabelled (S)-fluorocarazolol, is optimised for ligand dosages and administration times to maximise the precision of all model parameters using the D-optimal criterion. Using this experimental protocol, PET data are collected in porcine studies, and model parameters are estimated. All model parameters are identified with satisfactory precision. The in vivo myocardial beta-receptor concentration is 7.5+/-0.6 pmol x ml(-1), which corresponds to the in vitro result of 10.1+/-1.3 pmol x ml(-1). With more accurate parameter values, a simplified two-injection protocol is optimally designed, utilising only radiolabelled and unlabelled (S)-fluorocarazolol, based on a new criterion to maximise the precision of the beta-receptor concentration. This revised optimum design predicts that the in vivo beta-receptor concentration can be estimated with good precision but reduced experiment complexity.

Adrenergic beta-Antagonists↗
PubMed2000

Independent evolution of Toll and related genes in insects and mammals.

Toll and Toll-related proteins play an important role in antibacterial innate immunity in insect, plants, and mammals. We present the first comprehensive phylogenetic analyses of Toll-related genes from both insects and mammals. Drosophila melanogaster contains Toll and a highly homologous gene, Tehao. The protein, Dm Tehao, comprises 795 amino acid residues and its cytoplasmic domain shares a striking 61% identity with Dm Toll. Two Toll homologues were found in another dipteran of medical importance, Anopheles gambiae, a vector for human malaria. One Toll-like gene each was identified from Aedes aegypti and Glossina palpalis palpalis, vectors for yellow fever and trypanosomiasis, respectively. Phylogenetic analyses revealed separate clustering of Toll and related proteins from insects and mammals, suggesting independent evolution of the Toll family of proteins and of innate immunity in arthropods and vertebrates. These results also provide new avenues to understanding the function of Toll proteins in insect innate immunity against bacteria, fungi, and protozoans.

Aedes↗
PubMed2000

Effect of region and dentin perfusion on bond strengths of resin-modified glass ionomer cements.

OBJECTIVES: The purpose of this study was to evaluate the hypothesis that regional differences and pulpal pressure would significantly affect bond strengths of resin-modified glass ionomer cements to dentin. METHODS: Twenty-six extracted caries-free human third molars were ground to expose middle dentin and were randomly divided into two groups for bonding: no pulpal pressure and pulpal pressure of 15cm H(2)O. Fuji II LC, Vitremer, or Photac-Fil Quick were applied to the previously pre-treated surfaces and light-cured as recommended by the manufacturers. After immersion in water at 37 degrees C for 24h, the teeth were sectioned to 0.7mm thick slabs, divided into pulp horn, center, and peripheral regions according to visual criteria, and trimmed along the bonded interface for microtensile bond test to a cross-sectional area of 1mm(2). The slabs were subjected to tensile forces and the data analyzed using ANOVA and Fisher's PLSD at the 95% level of confidence. RESULTS: For Fuji II LC, bond strengths to the pulp horn regions were significantly lower than those to the other regions independent of pulpal pressure (p<0.05). On the other hand, regional bond strengths were not observed for Vitremer and Photac-fil Quick 0.05). CONCLUSIONS: Pulpal pressure had a stronger influence on bond strengths and failure modes of resin-modified glass ionomers than regional differences of the substrate.

Analysis of Variance↗
PubMed2000

Effect of hydrostatic pressure on regional bond strengths of compomers to dentine.

OBJECTIVES: The aim of this study was to evaluate the effect of hydrostatic pressure on the regional bond strengths of compomers to dentine. METHODS: Thirty freshly extracted molars were ground flat to expose the dentine and randomly divided into two groups for bonding: no hydrostatic pressure and hydrostatic pressure of 15cm H(2)O. Xeno CF, Dyract AP and F 2000 were applied to dentine surfaces pretreated by the respective bonding systems following the manufactures' instructions, and then restored with Clearfil AP-X. After 24h storage in water, the teeth were sectioned into 0.7-mm thick slabs and visually divided into three regional subgroups: the region communicating with the pulp through dentinal tubules (pulp horn); the region between the pulp horns (center); and the region between the pulp horn and DEJ (periphery). The specimens were trimmed to a cross-sectional area of 1mm(2) and subjected to the micro-tensile bond test. The data were analyzed by one- and three-way ANOVA, and Fisher's PLSD (p<0.05). RESULTS: There were no significant regional differences of bond strengths for all the compomers tested (p>0.05). However, hydrostatic pressure significantly decreased the bond strength of F 2000 to all regions (p<0.05), while the bond strength of Dyract AP significantly decreased only at the pulp horn region (p<0.05). On the other hand, the bond strengths of Xeno CF seemed not to be affected by hydrostatic pressure (p>0.05). For Dyract AP and F 2000, the fracture modes were affected by hydrostatic pressure, while, for Xeno CF, there were no significant differences between the fracture modes with non- or positive hydrostatic pressure. SIGNIFICANCE: Simulated pulpal pressure of 15cm H(2)O had a greater influence on the bond strengths of compomers to dentine than did dentine regions. Therefore, when measuring the bond strengths of compomers to dentine under the simulated in vivo conditions, the wetness of the dentine surface, as well as the intrinsic properties of each material should be seriously considered.

Analysis of Variance↗
PubMed2000

Metabolism of the dorsal cochlear nucleus in rat brain slices.

In vitro brain slices of the cochlear nucleus have been used for electrophysiological and pharmacological studies. More information is needed about the extent to which the slice resembles in vivo tissue, since this affects the interpretation of results obtained from slices. In this study, some chemical parameters of the dorsal cochlear nucleus (DCN) in rat brain slices were measured and compared to the in vivo state. The activities of malate dehydrogenase and lactate dehydrogenase were reduced in some DCN layers of incubated slices compared to in vivo brain tissue. The activities of choline acetyltransferase and acetylcholinesterase were increased or unchanged in DCN layers of slices. Adenosine triphosphate (ATP) concentrations for in vivo rat DCN were similar to those of cerebellar cortex. Compared with in vivo values, ATP concentrations were decreased in the DCN of brain slices, especially in the deep layer. Vibratome-cut slices had lower ATP levels than chopper-cut slices. Compared with the in vivo data, there were large losses of aspartate, glutamate, glutamine, gamma-aminobutyrate and taurine from incubated slices. These amino acid changes within the slices correlated with the patterns of release from the slices.

Acetylcholinesterase↗
PubMed2000

Synthesis of [18F]fluoromethyl iodide, a synthetic precursor for fluoromethylation of radiopharmaceuticals.

[18F]fluoroiodomethane was labeled via nucleophilic substitution of diiodomethane with [18F]fluoride, and labeling conditions were optimized. The optimized labeling yield was 40 +/- 8% (decay-corrected). The synthesis and purification of [18F]fluoroiodomethane took 15 min. The reactions of [18F]fluoroiodomethane with amine, carboxylic acid, thiol and phenoxide groups produced fluoromethylated derivatives with various yields (12-95%). The results indicated that [18F]fluoroiodomethane is a valuable synthetic precursor for the introduction of an [18F]fluoromethyl group into radiopharmaceuticals.

Journal Article↗
PubMed2000

Sequence-specific transcriptional corepressor function for BRCA1 through a novel zinc finger protein, ZBRK1.

BRCA1 has been implicated in the transcriptional regulation of DNA damage-inducible genes that function in cell cycle arrest. To explore the mechanistic basis for this regulation, a novel human gene, ZBRK1, which encodes a 60 kDa protein with an N-terminal KRAB domain and eight central zinc fingers, was identified by virtue of its interaction with BRCA1 in vitro and in vivo. ZBRK1 binds to a specific sequence, GGGxxx CAGxxxTTT, within GADD45 intron 3 that supports the assembly of a nuclear complex minimally containing both ZBRK1 and BRCA1. ZBRK1 represses transcription through this recognition sequence in a BRCA1-dependent manner. These results thus reveal a novel corepressor function for BRCA1 and provide a mechanistic basis for the biological activity of BRCA1 through sequence-specific transcriptional regulation.

Amino Acid Sequence↗
PubMed2000

Effects of high-potassium-induced depolarization on amino acid chemistry of the dorsal cochlear nucleus in rat brain slices.

High K+ was used to depolarize glia and neurons in order to study the effects on amino acid release from and concentrations within the dorsal cochlear nucleus (DCN) of brain slices. The release of glutamate, gamma-aminobutyrate (GABA) and glycine increased significantly during exposure to 50 mM K+, while glutamine and serine release decreased significantly during and/or after exposure, respectively. After 10 min of exposure to 50 mM K+, glutamine concentrations increased in all three layers of DCN slices, to more than 5 times the values in unexposed slices. In the presence of a glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC), glutamine concentrations in all layers did not increase as much during 50 mM K+. Similar but smaller changes occurred for serine. Mean ATP concentrations were lower in 50 mM K(+)-exposed slices compared to control. The results suggest that depolarization, such as during increased neural activity, can greatly affect amino acid metabolism in the cochlear nucleus.

Adenosine Triphosphate↗
PubMed2000

Endothelin-1 in stable bronchiectasis.

Endothelin (ET)-1 has been suggested to promote neutrophil adhesion to endothelium, migration to inflamed areas, and release of elastase. ET-1 might therefore play a role in the pathogenesis of bronchiectasis, a chronic inflammatory and infective airway disease which is still poorly understood. Thirty five patients with stable bronchiectasis (20 females, mean age+/-SD 49.1+/-15.0 yrs) and 18 control subjects (8 females, 49.4+/-11.3 yrs) were recruited prospectively. The ET-1 levels in serum and sputum were measured by commercially available enzyme linked immunosorbent assay (ELISA) kits. Patients with Pseudomonas aeruginosa in their sputum had a significantly higher serum level of ET-1 (median 25.8, interquartile range 13-43.9 pg x mL(-1)) than patients without P. aeruginosa (0, 0-10.5 pg x mL(-1); p=0.0004) and healthy control subjects (4.6, 0-16.3 pg x mL(-1); p=0.002). However, patients with and without P. aeruginosa infection had no significant difference in sputum ET-1 level (p=0.15). There was no correlation between serum or sputum ET-1 levels with the serum and sputum levels of the interleukin (IL)-1beta, IL-8 and tumour necrosis factor (TNF)-alpha; the number of bronchiectasis lung lobes; and spirometry. Serum ET-1 level correlated with 24 h sputum volume for the bronchiectasis patients (r=0.51, p=0.002). The results, therefore, suggest a significant pathogenic role for endothelin-1 among Pseudomonas aeruginosa-infected patients with bronchiectasis. Further studies should be performed to evaluate the clinico-pathological correlation and expression of endothelin-1 in bronchiectasis.

Bronchiectasis↗
PubMed2000

Up-regulation of circulating adhesion molecules in bronchiectasis.

Adhesion molecules are expressed on the surface of endothelial cells and leukocytes and are responsible for mediating the migration of intravascular leukocytes into inflamed tissue. Intensive recruitment of neutrophils into the airways occurs in bronchiectasis, although little is known about the role of adhesion molecules in this process. The authors, therefore, determined serum levels of E-selectin, intercellular adhesion molecule (ICAM)-1 and vascular adhesion molecule (VCAM)-1 in stable bronchiectasis patients (n=37) and healthy control subjects (n=17), and evaluated their relationship with clinical markers of disease severity in bronchiectasis. Serum levels of E-selectin, ICAM-1 and VCAM-1 in bronchiectasis patients were significantly higher than those in control subjects (p=0.02, <0.0001 and 0.0002 respectively). Both E-selectin and ICAM-1 levels were inversely related to forced expiratory volume in one second (FEV1)% predicted (r=-0.57, p<0.001; and r=-0.53, p=0.001 respectively), and FVC% predicted (r=-0.52, p=0.002; and r=-0.46, p=0.005). This was not the case for VCAM-1 levels. There was a correlation between serum ICAM-1 levels and 24 h sputum volume (r=0.34, p= 0.04). Serum E-selectin and ICAM-1, but not VCAM-1, levels showed correlation with the number of lung lobes affected by bronchiectasis (r=0.35, p=0.04 and r=0.34, p=0.04 respectively). These original observations strongly suggest that E-selectin, intercellular adhesion molecule-1 and Vascular adhesion molecule-1 could play a significant role in the pathogenesis of bronchiectasis.

Adult↗
PubMed2000

Human herpesvirus 8 (KSHV) contamination of peripheral blood and autograft products from multiple myeloma patients.

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), has recently been identified within the bone marrow dendritic cells of multiple myeloma (MM) patients. This virus contains homologues to human cytokines such as IL-6 that could potentially stimulate myeloma cell growth and contribute to disease pathogenesis. Since mobilization chemotherapy may increase circulating dendritic cell numbers, we searched for HHV-8 in peripheral blood mononuclear cells (PBMCs) before and after mobilization chemotherapy given to MM patients. Furthermore, we determined if autograft purging using the CEPRATE SC device would reduce the percentage of HHV-8 infected stem cell products. Only two of the 39 PBMC samples collected prior to mobilization chemotherapy contained PCR detectable virus, yet nine of 37 PBMCs collected on the first day of leukapheresis had detectable HHV-8 (P = 0.016). HHV-8 was more frequently identified in autograft products before vs after Ceprate SC selection (40% vs 15%, P = 0.016). Although the role HHV-8 plays in myeloma pathogenesis remains unclear, these results imply that mobilization chemotherapy increases the numbers of circulating HHV-8-infected dendritic cells within the peripheral blood. In addition, CD34 selection of autograft products in MM patients may reduce the reintroduction of virally infected cells following high-dose chemotherapy. Bone Marrow Transplantation (2000) 25, 153-160.

Antigens, CD34↗
PubMed2000

Microsatellite polymorphism in the Mediterranean fruit fly, Ceratitis capitata.

A total of forty-three simple sequence repeats (SSRs) were identified in the Mediterranean fruit fly (medfly) Ceratitis capitata. The most common SSR was the dinucleotide (TG)n/(CA)n occurring in thirty of the forty-three microsatellite loci. Polymorphism at ten dinucleotide markers was investigated in 122 flies from six natural populations sampled in the native and colonized areas. A very high level of allelic diversity was detected in the species range. An average of 13.6 alleles was found over all the ten loci indicating the informativeness of SSRs as genetic markers for the medfly. The distribution of microsatellite polymorphism in the species range reflects the medfly colonization history.

Animals↗
PubMed2000

Ciliary assessment in bronchiectasis.

Bronchiectasis is a common condition among the Oriental population and affected patients suffer from chronic sputum production punctuated by recurrent infective exacerbations. Cilia are minute structures present on the surface of respiratory and other epithelial cells that beat continuously to maintain a sterile mucosal surface in the respiratory tract. Patients with primary ciliary dyskinesia could potentially develop recurrent sinotrachrobronchitis, bronchiectasis, serous otitis media, hydrocephalus, and male infertility. The assessment of cilia has, however, received little attention until recently and generally involves elaborate methods that require complex and expensive technology. This brief article discusses application of the saccharine test, light microscopy assessment of ciliary beat, and transmission electron microscopy assessment of the ultrastructure of cilia. The rationale and indications for ciliary assessment are also listed along with illustrations showing ciliary structure, equipment required for sampling and assessment of cilia, and transmission electron micrographs of ciliary ultrastructural abnormalities.

Bronchiectasis↗
PubMed2000

Helicobacter pylori sero-prevalence in asthma.

Asthma is a very common respiratory disease which is characterized by the presence of cytokine-mediated airway inflammation leading to smooth muscle contraction, oedema and progressive airway damage in some cases. In light of our recent finding of an increased sero-prevalence of Helicobacter pylori in bronchiectasis, we have determined serum levels of H. pylori-specific IgG in asthmatic and control subjects. Altogether 90 consecutive asthmatic [mean age +/- SD 42.6+/-16 years and 52 female (F)] and 97 healthy control subjects (mean age +/- SD 43.2+/-13.3 years and 51 female (F); P = 0.78 and 0.39 respectively) were recruited prospectively. H. pylori sero-prevalence was not significantly different between asthmatic and control subjects (P>0.05). Serum H. pylori IgG levels did not correlate with FEV1 % predicted, FVC % predicted or duration of asthma (P>0.05). Similar to the results of previously published sero-epidemiological studies, there was a weak correlation between serum H. pylori IgG with increasing age (r = 0.43, P = 0.004). Despite the sero-epidemiological association of H. pylori infection with many inflammatory conditions, our data showed no such association for middle age asthmatic patients with mild intermittent asthma in our locality.

Adult↗
PubMed2000

The BMP1 gene is essential for pathogenicity in the gray mold fungus Botrytis cinerea.

In Magnaporthe grisea, a well-conserved mitogen-activated protein (MAP) kinase gene, PMK1, is essential for fungal pathogenesis. In this study, we tested whether the same MAP kinase is essential for plant infection in the gray mold fungus Botrytis cinerea, a necrotrophic pathogen that employs infection mechanisms different from those of M. grisea. We used a polymerase chain reaction-based approach to isolate MAP kinase homologues from B. cinerea. The Botrytis MAP kinase required for pathogenesis (BMP) MAP kinase gene is highly homologous to the M. grisea PMK1. BMP1 is a single-copy gene. bmp1 gene replacement mutants produced normal conidia and mycelia but were reduced in growth rate on nutrient-rich medium. bmp1 mutants were nonpathogenic on carnation flowers and tomato leaves. Re-introduction of the wild-type BMP1 allele into the bmp1 mutant restored both normal growth rate and pathogenicity. Further studies indicated that conidia from bmp1 mutants germinated on plant surfaces but failed to penetrate and macerate plant tissues. bmp1 mutants also appeared to be defective in infecting through wounds. These results indicated that BMP1 is essential for plant infection in B. cinerea, and this MAP kinase pathway may be widely conserved in pathogenic fungi for regulating infection processes.

Amino Acid Sequence↗
PubMed2000

Cloning of the bovine immunodeficiency virus gag gene and development of a recombinant-protein-based enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay (ELISA) was established for the rapid detection of specific bovine immunodeficiency virus (BIV) antibodies in cattle, using recombinant Gag protein as an antigen. The gag coding region from BIV was cloned into an expression vector, pQE32, which expressed high levels of recombinant protein from Escherichia coli. The ELISA was standardized by a checkerboard titration against known BIV-positive and -negative sera from cattle and a monoclonal antibody to the Gag protein. A total of 139 cattle serum samples, from the diagnostic laboratory at Kansas State University, Manhattan, and from the Dairy Station, Louisiana State University, Baton Rouge, were compared by ELISA and immunoblot assays for the detection of BIV-specific antibodies. Of 26 cattle sera samples which tested positive using the immunoblot assay, 23 were positive by ELISA, thus establishing a strong correlation between the two tests. The sensitivity and specificity of ELISA relative to immunoblotting were 0.88 and 0.93, respectively. ELISA proved to be as specific as immunoblotting but was much less time-consuming and easier to perform.

Animals↗
PubMed2000

Genetic characterization of toxin A-negative, toxin B-positive Clostridium difficile isolates by PCR.

Toxin-specific enzyme immunoassays, cytotoxicity assays, and PCR were used to analyze 48 toxin A-negative, toxin B-positive Clostridium difficile isolates from various geographical sites around the world. All the isolates were negative by the TOX-A TEST and positive by the TOX A/B TEST. A deletion of approximately 1.7 kb was found at the 3' end of the toxA gene for all the isolates, similar to the deletion in toxinotype VIII strains (e.g., C. difficile serotype F 1470). Additional PCR analysis indicated that the toxin B encoded by these isolates contains sequence variations downstream of the active site compared to the sequence of reference strain VPI 10463. This variation may extend the glucosylation spectrum to Ras proteins, as observed previously for closely related lethal toxin from Clostridium sordellii and toxin B from toxin A-negative, toxin B-positive strain F 1470. Toxin A-negative, toxin B-positive isolates have recently been associated with disease in humans, and they may be more common than was previously supposed.

Bacterial Proteins↗