Biomedical subjects

H Chen

Publications and source records attributed to H Chen.

At least 181 records · Page 10Linked to original sources

PubMed2001

Human cutaneous fatty acid-binding protein induces metastasis by up-regulating the expression of vascular endothelial growth factor gene in rat Rama 37 model cells.

Human cutaneous fatty acid-binding protein (C-FABP) gene is capable of inducing the metastatic phenotype when overexpressed in nonmetastatic rat Rama 37 cells. However, the mechanism of how it induces metastasis is not clear. Northern and slot blot analyses revealed that expression of the endogenous vascular endothelial growth factor (VEGF) gene was increased by 3.8-5.2-fold in the C-FABP-transfected cells (pSV-CFABP-R37) and in their metastatic sublines (e.g., Met-1) when compared with that in the nonmetastatic control transfectant pSV-R37 cells generated by transfection of only plasmid DNA. Higher levels of VEGF immunoreactive protein were also secreted from the malignant C-FABP-expressing cells. Reverse transcription-PCR detected two VEGF transcript isoforms, VEGF(164) and VEGF(188), in both the nonmetastatic control transfectant pSV-R37 cells and the malignant metastatic Met-1 cells. Chick chorioallantoic membrane assays showed that the conditioned medium of the control pSV-R37 cells possessed only very weak angiogenic activity, whereas conditioned media from the metastatic C-FABP transfectants and their sublines were strongly angiogenic and could be inhibited by antibodies to VEGF. Transfection of VEGF(164) cDNA in an expression vector into nonmetastatic Rama 37 cells produced a cell clone (R37-VEGF-2) that expressed high levels of VEGF. Inoculation of R37-VEGF-2 cells into syngeneic Wistar Furth rats produced metastases in a significant number (Fisher's exact test, P < 0.01) of animals (18 of 31 animals), whereas the control, vector alone-transfected R37-PSV cells produced no metastases (0 of 30 animals). Immunocytochemical methods demonstrated a strong positive staining for VEGF and an increased microvessel density in the primary tumors produced from PSV-VEGF-2 cells in comparison with tumors produced from control transfectants. Immunocytochemical staining for factor VIII detected a 3.5-fold increase in microvessel density of the primary tumors produced by PSV-VEGF-2 cells when compared with that of the primary tumors developed from the control pSV-R37 cells. Therefore, we suggest that overexpression of the C-FABP gene in the original transfectants induces metastasis through up-regulation of expression of the VEGF gene in this rat Rama 37 model system, and thus VEGF may play a crucial role in this particular metastatic cascade.

Animals↗

PubMed2001

Unexpected signals in a system subject to kinetic proofreading.

When multivalent ligands attach to IgEs bound to the receptors with high affinity for IgE on mast cells, the receptors aggregate, tyrosines on the receptors become phosphorylated, and a variety of cellular responses are stimulated. Prior studies, confirmed here, demonstrated that the efficiency with which later events are generated from earlier ones is inversely related to the dissociation rate of the aggregating ligand. This finding suggests that the cellular responses are constrained by a "kinetic proofreading" regimen. We have now observed an apparent exception to this rule. Doses of the rapidly or slowly dissociating ligands that generated equivalent levels of tyrosine-phosphorylated receptors comparably stimulated a putatively distal event: transcription of the gene for monocyte chemoattractant protein 1. Possible explanations of this apparent anomaly were explored.

Animals↗

PubMed2001

Albumin thiolate anion is an intermediate in the formation of albumin-S-S-homocysteine.

An elevated concentration of plasma total homocysteine is an independent risk factor for cardiovascular disease. Greater than 80% of circulating homocysteine is covalently bound to plasma protein by disulfide bonds. It is known that albumin combines with cysteine in circulation to form albumin-Cys(34)-S-S-Cys. Studies are now presented to show that the formation of albumin-bound homocysteine proceeds through the generation of an albumin thiolate anion. Incubation of human plasma with l-(35)S-homocysteine results in the association of >90% of the protein-bound (35)S-homocysteine with albumin as shown by nonreduced SDS-polyacrylamide gel electrophoresis. Treatment of the complex with beta-mercaptoethanol results in near quantitative release of the bound l-(35)S-homocysteine, demonstrating that the binding of homocysteine to albumin is through a disulfide bond. Furthermore, using an in vitro model system to study the mechanisms of this disulfide bond formation, we show that homocysteine binds to albumin in two steps. In the first step homocysteine rapidly displaces cysteine from albumin-Cys(34)-S-S-Cys, forming albumin-Cys(34) thiolate anion and homocysteine-cysteine mixed disulfide. In the second step, albumin thiolate anion attacks homocysteine-cysteine mixed disulfide to yield primarily albumin-Cys(34)-S-S-Hcy and to a much lesser extent albumin-Cys(34)-S-S-Cys. The results clearly suggest that when reduced homocysteine enters circulation, it attacks albumin-Cys(34)-S-S-Cys to form albumin-Cys(34) thiolate anion, which in turn, reacts with homocysteine-cysteine mixed disulfide or homocystine to form albumin-bound homocysteine.

Albumins↗

PubMed2001

Familial thoracic aortic aneurysms and dissections: genetic heterogeneity with a major locus mapping to 5q13-14.

BACKGROUND: Aneurysms and dissections affecting the ascending aorta are associated primarily with degeneration of the aortic media, called medial necrosis. Families identified with dominant inheritance of thoracic aortic aneurysms and dissections (TAA/dissections) indicate that single gene mutations can cause medial necrosis in the absence of an associated syndrome. METHODS AND RESULTS: Fifteen families were identified with multiple members with TAAs/dissections. DNA from affected members from 2 of the families was used for a genome-wide search for the location of the defective gene by use of random polymorphic markers. The data were analyzed by the affected-pedigree-member method of linkage analysis. This analysis revealed 3 chromosomal loci with multiple markers demonstrating evidence of linkage to the phenotype. Linkage analysis using further markers in these regions and DNA from 15 families confirmed linkage of some of the families to 5q13-14. Genetic heterogeneity for the condition was confirmed by a heterogeneity test. Data from 9 families with the highest conditional probability of being linked to 5q were used to calculate the pairwise and multipoint logarithm of the odds (LOD) scores, with a maximum LOD of 4.74, with no recombination being obtained for the marker D5S2029. In 6 families, the phenotype was not linked to the 5q locus. CONCLUSIONS: A major locus for familial TAAs and dissections maps to 5q13-14, with the majority (9 of 15) of the families identified demonstrating evidence of linkage to this locus. The condition is genetically heterogeneous, with 6 families not demonstrating evidence of linkage to any loci previously associated with aneurysm formation.

Aortic Dissection↗

PubMed2001

Do medical school surgical rotations influence subspecialty choice?

BACKGROUND: A comprehensive exposure to general surgery is essential for medical students pursuing careers in surgery. Occasionally, students applying for surgical residency positions must choose a subspecialty field prior to starting their residency training. Often, this decision is heavily based on their experience on various surgical clerkships. MATERIALS AND METHODS: To determine if surgical clerkships influence subspecialty choice, we surveyed medical students who interviewed for general surgery training over a 2-year period at The Johns Hopkins Hospital. RESULTS: Of 211 surveys sent, 146 were returned (66%). The mean age of the students was 26 +/- 0 years with 21% being female. Students anticipating subspecialization in cardiothoracic, plastic, pediatric, and transplant surgery saw significantly more operations in their respective fields. Similar trends were seen in vascular surgery and surgical oncology. Despite the apparent differences in exposure to subspecialty operations, all students saw equal numbers of hernia repairs and laparoscopic cholecystectomies. CONCLUSIONS: While medical students pursuing careers in surgery have equal exposure to general surgery, their anticipated subspecialty field highly correlated with their operative exposure to that field. Thus, medical school surgical rotations appear to highly influence subspecialty choice.

Adult↗

PubMed2001

[A survey on blood lipid levels among newborns and healthy inhabitants in urban Shanghai from 1997 to 1999].

OBJECTIVE: To analyze the blood lipid levels among inhabitants of different ages in urban Shanghai by the end of 1990 and compare the results with those in 1970 s and 1980 s. METHODS: Venous blood samples were collected from 3647 persons undergoing annual health examination, including workers and staff members, employees, functionaries, and students of factories, governmental organizations, institutions, enterprises, and schools. Umbilical blood samples were collected from 88 newborns. Serum TC, TG, LDL-C, and HDL-C were determined. RESULTS: 3647 blood samples were collected in total. It is found that: (1) The levels of blood lipids increased along with the age. The levels of TC and LDL-C among females over their fifty were higher that those among the males in the same age groups. The level of TG among females over fifty was similar to that among the males in the same age groups. The levels of LDL-C were higher in families in all of the age groups than those in the males of the same ages. (2) In comparison to those in 1970 s the levels of TC and TG in 1990 s were significantly higher by 6.79% - 17.69% and 21.95% - 45.53% respectively, and the level of HDL-C decreased by 8.02% - 29.19%. (3) The percentage of persons over forty with their TC levels over the upper normal limit was much larger in 1990 s than in 1970 s (for TC 11.57% vs. 4.40% among males and 16.02% vs. 5.40% among females, for TG 21.83% vs. 5.20% among males and 13.32% vs. 5.70% among females). and (4) The percentage of persons with their TC/HDL-C >or= 4 and TG >or= 1.70 mmol/L was much larger among persons over forty than among persons under forty (20.74% vs. 10.99% among males and 13.32% vs. 2.05% among females). CONCLUSION: The mean serum TC, TG, and LDL-C levels increased and the HDL-C level decreased significantly among healthy inhabitants in urban Shanghai in 1990 s. Along with the rise of living standards of people, their mean lipid level increases too. Nutrition education is necessary.

Adolescent↗

PubMed2001

Quinazolines as cyclin dependent kinase inhibitors.

Quinazolines have been identified as inhibitors of CDK4/D1 and CDK2/E. Aspects of the SAR were investigated using solution-phase, parallel synthesis. An X-ray crystal structure was obtained of quinazoline 51 bound in CDK2 and key interactions within the ATP binding pocket are defined.

Binding, Competitive↗

PubMed2001

Effective volumetric lattice Boltzmann scheme.

An efficient fractional volumetric scheme is proposed for lattice Boltzmann method (LBM). By reducing the effective time step, the scheme possesses much better stability particularly for thermal LBM. The same accuracy and simplicity of the standard LBM are preserved for achieving the Navier-Stokes equation. Since the effective viscosity is reduced by the fraction factor p, the scheme becomes very effective for simulating high Reynolds number thermal flows.

Journal Article↗

PubMed2001

Separation and determination of flavonoids and other phenolic compounds in cranberry juice by high-performance liquid chromatography.

A HPLC method was developed for the separation and determination of flavonoid and phenolic antioxidants in cranberry juices. Free flavonoid and phenolic compounds were fractionated into neutral and acidic groups by means of a solid-phase extraction method, followed by subsequent HPLC separations. Combined flavonoids and phenolics were hydrolyzed by acid before HPLC analysis. This developed method provides a fast and high resolution of individual flavonoid and phenolic compounds. In cranberry fruit, flavonoids and phenolic acids exist predominantly in combined forms, such as glycosides and esters. A total of 400 mg of total flavonoids and phenolic compounds/l of sample was found in a freshly squeezed cranberry juice, which was distributed as about 44% of phenolic acids and 56% of flavonoids. Benzoic acid was the major phenolic compound. Major flavonoids in the freshly squeezed cranberry juice were quercetin and myricetin.

Chromatography, High Pressure Liquid↗

PubMed2001

Enhanced immune responses to viral epitopes by combining macrophage-inducible expression with multimeric display on a Salmonella vector.

In this study, the immunogenicity of chimeric 987P fimbriae on a Salmonella vaccine strain was improved by optimizing fimbrial expression. The constitutive tetA promoter and the in vivo activated nirB and pagC promoters were evaluated for their use to express two epitopes of the transmissible gastroenteritis virus (TGEV) spike protein carried by fimbriae which were displayed on a Salmonella vaccine strain. Constructs with the pagC promoter were shown to drive increased expression of chimeric 987P fimbriae in macrophages as well as in Mg(2+)-poor media, mimicking a major environmental signal found in Salmonella-containing endocytic vacuoles of macrophages. Mice immunized orally with a Salmonella vaccine strain which expressed chimeric fimbriae from the pagC promoter elicited significantly higher mucosal and systemic immune responses to both the 987P fimbriae and the TGEV epitopes than mice immunized with the same strain hosting a tetA or nirB promoter-driven expression plasmid. Moreover, only the Salmonella vaccine strains harboring a plasmid with the pagC promoter, with or without an additional tetA promoter in tandem, elicited neutralizing antibodies to TGEV. This indicated that the pagC promoter can be used successfully to improve epitope-display by chimeric fimbriae on Salmonella vaccine strains for the induction of a desired immune response.

Animals↗

PubMed2001

Developmental expression of survivin during embryonic submandibular salivary gland development.

BACKGROUND: The regulation of programmed cell death is critical to developmental homeostasis and normal morphogenesis of embryonic tissues. Survivin, a member of the inhibitors of apoptosis protein (IAP) family primarily expressed in embryonic cells, is both an anti-apoptosis and a pro-survival factor. Since our previous studies have demonstrated the importance of apoptosis during embryonic submandibular salivary gland (SMG) development, we postulated that survivin is a likely mediator of SMG epithelial cell survival. RESULTS: We investigated the developmental expression of survivin in Pseudoglandular (approximately E14), Canalicular (approximately E15) and Terminal Bud (approximately E17) Stage SMGs. We report a significant 26% increase in transcript levels between the Canalicular and Terminal Bud Stages. Immunohistochemical studies demonstrate nuclear-localized survivin protein in epithelial cells bounding forming lumina in Canalicular and Terminal Bud Stage SMGs. CONCLUSIONS: Survivin is known to be a pro-survival and anti-apoptotic factor. Given that survivin translocation into the nucleus is required for the induction of entry into the cell cycle and the inhibition of apoptosis, our demonstration of nuclear-localized survivin protein in presumptive ductal and proacinar lumen-bounding cells suggests that survivin may be a key mediator of embryonic SMG epithelial cell survival.

Amino Acid Sequence↗

PubMed2001

Pulmonary hypoplasia in mice lacking tumor necrosis factor-alpha converting enzyme indicates an indispensable role for cell surface protein shedding during embryonic lung branching morphogenesis.

Many membrane-bound protein precursors, including cytokines and growth factors, are proteolytically shed to yield soluble intercellular regulatory ligands. The responsible protease, tumor necrosis factor-alpha converting enzyme (TACE/ADAM-17), is a transmembrane metalloprotease-disintegrin that cleaves multiple cell surface proteins, although it was initially identified for the enzymatic release of tumor necrosis factor-alpha (TNF-alpha). Mammalian lung growth and development are tightly controlled by cytokines and peptide growth factors. However, the biological function of the cell shedding mechanism during lung organogenesis is not understood. We therefore evaluated the role of TACE as a "sheddase" during lung morphogenesis by analyzing the developmental phenotypes of lungs in mice with an inactive TACE gene in both in vivo and ex vivo organ explant culture. Neonatal TACE-deficient mice had visible respiratory distress and their lungs failed to form normal saccular structures. These newborn mutant lungs had fewer peripheral epithelial sacs with deficient septation and thick-walled mesenchyme, resulting in reduced surface for gas exchange. At the canalicular stage of E16.5, the lungs of TACE mutant mice were impaired in branching morphogenesis, inhibited in epithelial cell proliferation and differentiation, and delayed in vasculogenesis. Embryonic TACE knockout mouse lungs (E12) branched poorly compared to wild-type lungs, when placed into serumless organ culture. Gene expression of both surfactant protein-C and aquaporin-5 were inhibited in cultured TACE-mutant embryonic lungs, indicating defects in both branching and peripheral epithelial cytodifferentiation in the absence of TACE protein. Furthermore, both the hypoplastic phenotype and the delayed cytodifferentiation in TACE-deficient lungs were rescued by exogenous addition of soluble stimulatory factors including either TNF-alpha or epidermal growth factor in embryonic lung culture. Thus, the impaired lung branching and maturation without TACE suggest a broad role for TACE in the processing of multiple membrane-anchored proteins, one or more of which is essential for normal lung morphogenesis. Taken together, our data indicate that the TACE-mediated proteolytic mechanism which enzymatically releases membrane-tethered proteins plays an indispensable role in lung morphogenesis, and its inactivation leads to abnormal lung development.

ADAM Proteins↗

PubMed2001

[Genotyping of multiple genetic alterations of intrahepatic cholangiocarcinoma].

OBJECTIVE: To provide genetic evidence for understanding the mechanism of oncogenesis of intrahepatic cholangiocarcinoma (ICC) by detecting the multiple genetic spectrums. METHODS: Twenty-two cases of paraffin-embedded ICC tissue sections were microdissected and genotyped by PCR-based DNA sequencing to detect the frequencies of loss of heterozygosity (LOH) of tumor suppressor genes APC, MCC, DCC, OGG1, p53, and RB1 and of point mutation of Ki-ras-2 oncogene. RESULTS: The genetic alteration rate was 68.8% for APC, 46.2% for DCC, 41.7% for OGG1, 37.5% for p53, 27.3% for Ki-ras-2, 22.2% for RB1, and 14.3% for MCC. CONCLUSION: ICC-related genetic spectrum is basically composed of APC, DCC, OGG1, p53, and Ki-ras-2. Multiple genetic alteration plays an important role in the carcinogenesis of ICC.

Adenomatous Polyposis Coli Protein↗

PubMed2001

Toxicity studies of Rhizoma Polygonati Odorati.

The toxicity of the water-soluble extract of Rhizoma Polygonati Odorati was studied in the present investigation, which included its acute toxicity, chronic toxicity, and genetic toxicity. The aqueous extract of Rhizoma Polygonati Odorati did not cause seriously abnormal signs or death to animals in the acute toxicity test and in the 6-month chronic toxicity test. Neither was genetic toxicity found in the Ames test, the micronucleus test of bone marrow and the sperm malformation test in mice.

Administration, Oral↗

PubMed2001

Hypoglycemic effects of aqueous extract of Rhizoma Polygonati Odorati in mice and rats.

Water soluble extract of Rhizoma Polygonati Odorati (RPO) was studied for its hypoglycemic effect in diabetic mice and rats. Results showed that RPO significantly lowered hyperglycemia caused by starch loading in both normal and diabetic mice. Four week's administration with RPO reduced fasting blood glucose, decreased glycosylated hemoglobin (GHb), and improved the glucose tolerance in diabetic mice. In diabetic rats complicated with hyperlipemia, RPO prevented and reduced both hyperglycemia and hypertriglyceridemia. The results support the view that RPO may influence glucose or carbohydrate metabolism of diabetic animals in many ways including inhibiting the activity of alpha-glucosidase in digestive canal, and improving the metabolism of glucose and triglyceride.

Animals↗

PubMed2001

Embryonic mouse submandibular salivary gland morphogenesis and the TNF/TNF-R1 signal transduction pathway.

TNF is a pleiotropic cytokine that modulates cell proliferation and apoptosis. The objective of the present study was to investigate the possible function(s) of the TNF/TNF-R1 signaling pathway in embryonic mouse submandibular salivary gland (SMG) morphogenesis. After characterizing in vivo mRNA and protein expression of various constituents of this pathway, we utilized in vitro experiments to investigate the phenotypic outcomes of enhanced and deficient ligand. The results of these experiments indicate that the TNF/TNF-R1 signal transduction pathway plays an important role in balancing cell proliferation and apoptosis during SMG duct and presumptive acini formation.

Animals↗

PubMed2001

Difference between "proteinlike" and "nonproteinlike" heteropolymers.

Based on a simple two-dimensional (2D) hydrophobic-polar (H-P) lattice model, properties of amino acid chains are studied by enumeration and Monte-Carlo simulation methods. Among them some chains with large average energy gap (E(g);) are thought to be "proteinlike" while the others are "nonproteinlike." The large E(g); between the low excited conformations and the native conformation guarantees not only the thermodynamic stability of protein but also its fast-folding property. The phase transition from molten globule to the native conformation for the "proteinlike" polymer is found to be of first order, while that for the "nonproteinlike" polymer is not. Some properties of chains as a function of E(g); shows that the transition from "nonproteinlike" to "proteinlike" heteropolymers is continuous. The simulation of folding at different temperature indicates that the main reason why some polymers fold slowly to its native conformation is their low folding temperature which makes the effective energy barrier (E(b)/T(f)) much higher than "proteinlike" chains.

Amino Acid Sequence↗

PubMed2001

Transplantation of labeled periodontal ligament cells promotes regeneration of alveolar bone.

Regeneration of damaged periodontal tissues is mediated by periodontal cells, but a major sub-population comprises highly differentiated cells that do not renew. To overcome the loss of specialized cell types caused by disease, various therapeutic approaches including cell transplants have been developed to promote cell re-population in periodontal tissues. As previous transplantation studies used unlabeled cells, that are indistinguishable from host cells, it has been difficult to assess the contributions of transplanted cells to the healing processes. To track the fate and differentiation of rat periodontal cells transplanted into periodontal wounds, we used collagen-coated fluorescent beads as a permanent endocytosed marker, or cells constitutively expressing beta-galactosidase. We assessed osteogenic cell differentiation with immunohistochemical staining for osteopontin and bone sialoprotein. Cells were transplanted into periodontal wounds created in Sprague--Dawley male rats that are null for beta-galactosidase. Defects were allowed to heal spontaneously (controls), or were closed with collagen implants mixed with beta-galactosidase-positive (Lac-Z) periodontal cells, or closed with collagen implants mixed with periodontal cells loaded with fluorescent beads. Animals were killed at 1 and 2 weeks after surgery and tissues were prepared for morphometric assessment and immunostaining for osteopontin (OPN) and bone sialoprotein (BSP). Transplanted cells were easily distinguished by fluorescent beads or by beta-galactosidase-positive expression and were distributed throughout the regenerating periodontal ligament (PL) and alveolar bone. At 1 week after wounding, animals treated with beta-galactosidase-positive cells exhibited a slightly higher percentage of labeled cells in the PL compared with the fluorescent bead-labeled cell implant group (2% vs. 1% respectively; P > 0.2). At Week 2 percentages of labeled cells were slightly increased in the regenerating PL (approximately 3% for both groups, P > 0.2). In regenerating alveolar bone at 1 week, animals that were treated with beta-galactosidase-positive cells and fluorescent bead-loaded cells exhibited approximately 30% and 25% of labeled cells respectively. At 2 weeks after wounding there was an increase in the percentage of transplanted beta-galactosidase-positive cells (approximately 39% at week 2; P < 0.05), but not of transplanted cells with fluorescent beads (approximately 25% at week 2). In sites with transplanted cells there were higher percentages of OPN positive and BSP positive cells in nascent bone and more newly formed bone than in controls (>40%; P < 0.05). Transplantation of beta-galactosidase-positive cells or cells loaded with fluorescent beads is a useful method for assessing the fate and differentiation of periodontal cells in vivo. Fluorescent beads, however, are diluted at mitosis and this method underestimates the percentage of transplanted cells. As transplanted periodontal cells in both groups promoted regeneration of alveolar bone, cell transplantation could improve the restoration of periodontium destroyed by periodontitis.

Alveolar Bone Loss↗