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Y Huang

Publications and source records attributed to Y Huang.

At least 163 records · Page 9Linked to original sources
PubMed2001

Indium phosphide nanowires as building blocks for nanoscale electronic and optoelectronic devices.

Nanowires and nanotubes carry charge and excitons efficiently, and are therefore potentially ideal building blocks for nanoscale electronics and optoelectronics. Carbon nanotubes have already been exploited in devices such as field-effect and single-electron transistors, but the practical utility of nanotube components for building electronic circuits is limited, as it is not yet possible to selectively grow semiconducting or metallic nanotubes. Here we report the assembly of functional nanoscale devices from indium phosphide nanowires, the electrical properties of which are controlled by selective doping. Gate-voltage-dependent transport measurements demonstrate that the nanowires can be predictably synthesized as either n- or p-type. These doped nanowires function as nanoscale field-effect transistors, and can be assembled into crossed-wire p-n junctions that exhibit rectifying behaviour. Significantly, the p-n junctions emit light strongly and are perhaps the smallest light-emitting diodes that have yet been made. Finally, we show that electric-field-directed assembly can be used to create highly integrated device arrays from nanowire building blocks.

Journal Article↗
PubMed2001

Characterization of IFN-gamma regulation of the complement factor B gene in macrophages.

Complement factor B (Bf) is involved in the activation of the alternative complement cascade. Bf is induced by IFN-gamma; however, the mechanisms of Bf gene regulation have not been well characterized in general, and not in macrophages specifically. Northern analysis reveals that IFN-gamma induces a dose- and time-dependent increase in Bf mRNA expression in primary macrophages and macrophage cell lines. MH-S cells transfected with reporter constructs containing truncated regions of the Bf promoter reveal that IFN-gamma responsiveness lies between -154 and -53 bp on the Bf promoter. This region of the Bf promoter contains both an IFN-gamma-activation site (GAS) and an interferon-stimulated response element (ISRE). Site-directed mutagenesis of the GAS binding site or the ISRE binding site in this region of the Bf promoter partially inhibits IFN-gamma responsiveness. Mutagenesis of both the GAS and ISRE cis elements totally abrogates IFN-gamma responsiveness of the Bf promoter. Electrophoretic mobility shift assays reveal nuclear binding complexes involving both Bf-GAS and Bf-ISRE oligonucleotide sequences upon IFN-gamma stimulation. In competition assays, both Bf-GAS and Bf-ISRE oligonucleotides, but not mutant Bf-GAS nor mutant Bf-ISRE oligonucleotides, compete for the DNA binding. Supershift analysis reveals that Stat1-GAS and IRF-1-ISRE nuclear binding complexes contribute to induction of Bf by IFN-gamma. Western analysis confirms an IFN-gamma-stimulated increase in tyrosine phosphorylation of Stat1. These findings suggest that both GAS and ISRE cis binding sites have an additive effect on IFN-gamma-stimulated Bf gene expression and that both are required for full expression of Bf by IFN-gamma. Stat1 and IRF-1 take part in IFN-gamma-stimulated Bf gene induction in macrophages through their respective cis binding elements.

Animals↗
PubMed2001

Microdialysis studies of the middle ear distribution kinetics of amoxicillin in the awake chinchilla.

This work was performed to develop an experimental animal model for the study of antibiotic drug distribution into middle ear fluid (MEF) and to evaluate its relevance and significance to the clinical treatment of otitis media (OM). Chinchillas were assigned to normal or infected ear groups after Eustachian tube obstruction (ETO) or direct trans-bullar inoculation with type 3 Streptococcus pneumoniae. Following survival surgery to implant microdialysis (MD) probes in the jugular vein and middle ear (ME), amoxicillin was given intravenously (iv) as a bolus or infusion. Drug concentrations in blood and MEF were continuously monitored by microdialysis. The measured concentrations were corrected for probe recovery by simultaneous retrodialysis. Multiple MEF and blood sampling was also performed to validate the animal model and MD sampling technique. Bacterial infection was successfully induced 3-7 days after the inoculation, whereas the control group gave negative bacterial culture results. The beta-lactam antibiotic, amoxicillin, exhibited an elimination half-life of 0.33+/-0.23 h (n = 9) in chinchilla blood, 1.46+/-0.50 h (n = 5) and 1.75+/-0.84 h (n = 4) in MEF of normal and infected ears (p = 0.6), respectively. MEF-to-blood amoxicillin concentration ratios at steady state following iv infusion were 0.26+/-0.06 (n = 5) and 0.28+/-0.11 (n = 4) for normal and infected ears (p = 0.7), respectively. MD allows continuous monitoring of drug concentration-time profiles in blood and MEF in an awake chinchilla model. The concentrations measured by MD were validated by direct sampling. The ratio of the area under the curve (AUC) of drug concentration in MEF versus time to that in blood after iv bolus doses was less than unity, as was the steady-state concentration ratio following constant-rate iv infusion, suggesting an active transport mechanism was involved in the efflux of amoxicillin from the ME of chinchilla. The results of studies involving infected ears were not significantly different from those in normal ears in terms of amoxicillin distribution across the ME mucosal membrane after systemic administration.

Amoxicillin↗
PubMed2001

Analyses of [(18)F] altanserin bolus injection PET data. I: consideration of radiolabeled metabolites in baboons.

Positron emission tomography (PET) has been used to study serotonin 2A (5-HT(2A)) receptor binding in human brain using the 5-HT(2A) antagonist, [(18)F]altanserin. Previous analyses of bolus injection [(18)F]altanserin data provided 5-HT(2A) specific binding measures that were highly correlated with the in vitro distribution of 5-HT(2A) receptors and reflected decreased binding after ketanserin (5-HT(2A) antagonist) administration. These observations were made in the presence of a nonspecific tissue component that was consistent with blood-brain barrier (BBB) passage of radiolabeled metabolites (radiometabolites). In this work, we evaluated the in vivo kinetics of [(18)F]altanserin and two major radiometabolites of [(18)F]altanserin, focusing on the kinetics of free and nonspecifically-bound radioactivity. PET studies were performed in baboons after the bolus injection of [(18)F]altanserin or one of its major radiometabolites, either [(18)F]altanserinol or [(18)F]4-(4-fluorobenzoyl)piperidine, at baseline and after pharmacologic receptor blockade (blocking data). The cerebellar and blocking data were analyzed using either single (parent radiotracer) or dual (parent radiotracer and radiometabolites) input function methods. After bolus injection of either [(18)F]altanserin metabolite, radioactivity crossed the BBB and localized nonspecifically. The radio- metabolites were found to contribute to nonspecific "background" radioactivity that was similar in receptor-poor and receptor-rich regions. After bolus injection in baboons, two of the major radiometabolites of [(18)F]altanserin crossed the BBB and contributed to a fairly uniform background of nonspecific radioactivity. This uniformity suggests that conventional analyses are appropriate for human bolus injection [(18)F]altanserin PET data, although these methods may overestimate [(18)F]altanserin nonspecific binding.

Animals↗
PubMed2001

Analyses of [(18)F]altanserin bolus injection PET data. II: consideration of radiolabeled metabolites in humans.

Imaging serotonin-2A (5-HT(2A)) neuroreceptors with positron emission tomography (PET) and [(18)F]altanserin has been the focus of a series of PET studies, as [(18)F]altanserin is one of the most selective 5-HT(2A) antagonist radiotracers. Previous animal studies showed that radiolabeled metabolites (radiometabolites) of [(18)F]altanserin crossed the blood-brain barrier (BBB) to localize nonspecifically in brain, consistent with a constant radioactivity "background." In this work, we evaluated human bolus injection [(18)F]altanserin PET data with detailed consideration of the impact of BBB-permeable metabolites on the specific binding parameters. Data were quantified using either single (parent radiotracer), dual (parent radiotracer and radiometabolites), or no arterial input function(s) (cerebellum as reference tissue input function). A step-gradient high-performance liquid chromatography (HPLC) analysis provided distinct separation of [(18)F]altanserin and four radiolabeled components in plasma. After [(18)F]altanserin injection, the step-gradient data showed that the major BBB-permeable radiometabolites approached constant levels in plasma (>50 min), consistent with a constant metabolite "background." The single-input Logan graphical results were highly correlated with the dual-input results and its bias was fairly constant across regions and subjects, as similarly observed for a nongraphical reference tissue method. The most comprehensive and quantitatively valid analysis for bolus [(18)F]altanserin PET data was the dual-input method that specifically accounted for BBB-permeable metabolites, although the Logan analysis was preferred because it provided a good compromise between validity, sensitivity, and reliability of implementation. Further study is needed to better understand how the cerebellar kinetics of [(18)F]altanserin and its radiometabolites impact the reference tissue measures.

Adolescent↗
PubMed2001

Anaylsis of birefringence during wound healing and remodeling following alkali burns in rabbit cornea.

The use of synthetic inhibitors of metalloproteinases (SIMP) or medroxyprogesterone (MP) can prevent or significantly delay the ulceration of alkali-injured corneas by influencing collagen degradation. We have examined the remodeling of rabbit corneal stroma following alkali injury and have assessed the effect of SIMP and MP treatment. Following a defined alkali injury to the rabbit cornea, animals were divided into three subgroups, one group treated with topical beta-mercaptomethyl tripeptide (SIMP), one treated by subconjunctival injection of MP and one treated with a control solution. The corneal tissue was taken at 3 days, 1, 2, 3, 4, 9 and 26 weeks after alkali injury and prepared for light microscopy and transmission electron microscopy (TEM). A quantitative measurement of birefringence, in terms of the optical path difference (OPD), was made using a modified polarized microscopy technique based on the analysis of interference colours. The results showed that SIMP effectively prevented deep corneal ulceration. MP could delay the ulceration and the corneas treated with MP appeared to have better transparency than the other groups. There was a significant difference of the OPD between the anterior (5.8 +/-0.3 nm) and posterior (7.8 +/-0.4 nm) stroma of the normal cornea (P<0.001). The OPD values from the central corneas from alkali-injured eyes were generally lower than normal during the first 4 weeks and then gradually recovered to the normal level or above, except for the posterior stroma of the MP-treated eyes. We found that the OPD changes were very dependent on the presence of corneal lesions. The stroma near corneal ulceration, scar tissue, calcified stroma and the retro-corneal collagen layer showed a significant reduction of birefringence (lower OPD values). These OPD values remained much lower than normal up to the end of the experiment. TEM showed disrupted corneal stroma in all three groups, with thinner scar tissue in the MP group. The fibril diameters did not change significantly 3 days and 1 week after the alkali burns (27.1+/-2.3 nm in the control group, 27.3+/-2.2 nm in the SIMP group and 27.7+/-2.1 nm in the MP group) and there were no differences compared with 29.7+/-1.7 nm of the normal cornea (P>0.05). After 2 weeks of tissue remodeling, the fibril diameters in alkali-injured corneas showed a large variation (the range was between 11.5 and 80 nm) with a bimodal distribution, especially in the control group. The technique presented here for birefringence evaluation can provide an alternative way to monitor wound healing and tissue remodeling, both visually and quantitatively.

Animals↗
PubMed2001

Cloning, mapping, and characterization of a human homologue of the yeast longevity assurance gene LAG1.

We have identified LASS2, a previously unknown human homologue of the yeast longevity assurance gene LAG1. The LASS2 transcript is highly expressed in liver and kidney, which is very different from the expression of the previously identified human LAG1 homologue LAG1Hs-1. Radiation hybrid mapping studies indicated that LASS2 is located on chromosome 1q11. Yeast two-hybrid screening and glutathione S-transferase pull-down assays showed that the LASS2 protein interacts with several membrane-associated receptors or transporters. Furthermore, LASS2 protein was able to inhibit the colony formation of human hepatoma cells in vitro, which suggests that this gene may be involved in the regulation of cell growth.

Amino Acid Sequence↗
PubMed2001

A versatile framework for the design of ligand-dependent, transgene-specific transcription factors.

The ability to regulate transgene expression will be essential for the safety and efficacy of many gene therapies. Various ligand-dependent transcription factors, including steroid hormone receptors, have been modified to enable transgene-specific regulation. To minimize effects on cellular gene expression, chimeric steroid receptors have been constructed by replacing their native DNA binding domain (DBD) with a heterologous DBD, like that from the yeast transcription factor GAL4. This approach has limitations for human gene therapy, including the potential immunogenicity of the GAL4 domain and the inability to discriminate between different GAL4-linked transgenes in the same cell. To address this, we have constructed chimeric regulators containing the human estrogen receptor (ER) ligand binding domain (LBD) and a Cys(2)-His(2)-type zinc finger DBD. Cys(2)-His(2) zinc finger domains are common among human DNA binding proteins and can be engineered to selectively bind different DNA sequences. We demonstrate over 500-fold drug-dependent transgene induction with these chimeric regulators in vitro and the ability to regulate an adenovirus-delivered transgene in mice. Two chimeras containing different Cys(2)-His(2) domains displayed highly sequence-specific binding and regulation. Incorporating a point mutation in the ER LBD that ablates estrogen binding enables selective in vivo regulation with the clinically useful anti-estrogen tamoxifen. These Cys(2)-His(2)-ER LBD chimeras represent a versatile framework for creating transgene-specific regulators potentially useful for human gene therapy applications.

Adenoviridae↗
PubMed2001

Effect of transforming growth factor-beta 2 on phagocytosis in cultured bovine trabecular meshwork cells.

The effect of transforming growth factor-beta 2 (TGF-beta 2) on phagocytosis in bovine trabecular meshwork cells in vitro was investigated. After the cultured bovine trabecular meshwork cells were treated with 0 ng/ml, 0.32 ng/ml, 1 ng/ml, 3.2 ng/ml TGF-beta 2 for 24 h, latex beads were added into the incubation medium, and the numbers of the latex beads in 20 adjacent cells were counted under a microscope 24 h later, after treatment with Wright's stain. Our results showed that the average numbers of the latex beads in the trabecular meshwork cells treated with TGF-beta 2 of different concentrations were 53.1 +/- 1.7 beads/cell, 56.4 +/- 2.9 beads/cell and 77.9 +/- 6.5 beads/cell respectively, in comparison with 45.5 +/- 3.3 beads/cell of the control group. TGF-beta 2 significantly increased the number of the latex beads phagocytosed by cultured bovine trabecular meshwork cells in a dose-dependent manner. TGF-beta 2 could promote the phagocytosis of bovine trabecular meshwork cells in vitro. It may be involved in the cellularity decrease of the trabecular meshwork in the patients of primary open angle glaucoma through promoting the phagocytosis of trabecular meshwork cells.

Animals↗
PubMed2001

Predator migration in response to prey density: what are the consequences?

A predator-prey metapopulation model with two identical patches and only migration of the predator is investigated. Local predator-prey interaction is described by the so-called Rosenzweig-MacArthur model, while the migration term of the predator is put in a nonlinear form, which is derived by extending the Holling time budget argument to migration. In particular, a dimensionless parameter theta is introduced to quantify the migration tendency of predators while they are handling their prey, which gives rise to a family of models connecting two extremes: predators have no inclination to migrate while handling prey (theta = 0) and standard diffusion (theta = 1). Various aspects of the model, including changes in the number and the stability of equilibria and limit cycles, are investigated. We then focus on the key question: "Does spatial structure lead to a substantial damping of the violent oscillations exhibited by many predator-prey models?". It is known that the answer is "yes" if one adopts standard diffusion (theta = 1). However, we present substantial evidence that the answer is "no" if one takes theta = 0. We conclude that the migration submodel is an important constituent of a spatial predator-prey model and that the issue deserves scrutiny, both experimentally and theoretically.

Animals↗
PubMed2001

Hybrids monosomal for human chromosome 5 reveal the presence of a spinal muscular atrophy (SMA) carrier with two SMN1 copies on one chromosome.

We have analyzed the survival motor neuron gene (SMN1) dosage in 100 parents of children with homozygous SMN1 deletions. Of these parents, 96 (96%) demonstrated the expected one-copy SMN1 carrier genotype. However, four parents (4%) were observed to have a normal two-copy SMN1 dosage. The presence of two intact SMN1 genes in the parent of an affected child indicates either the occurrence of a de novo mutation event or a situation in which one chromosome has two copies of SMN1, whereas the other is null. We have separated individual chromosomes from two of these parents with two-copy SMN1 dosage by somatic cell hybridization and have employed a modified quantitative dosage assay to provide direct evidence that one parent is a two-copy/ zero-copy SMN1 carrier, whereas the other parent had an affected child as the result of a de novo mutation. These findings are important for assessing the recurrence risk of parents of children with spinal muscular atrophy and for providing accurate family counseling.

Autoradiography↗
PubMed2001

A fast and efficient method for isolation of the BAC end.

As a new developmental vector system, the bacterial artificial chromosome (BAC) has been used widely in constructing genomic libraries and in generating transgenic animals. Isolation of the BAC insert end is useful to analyze the BAC clone. Here, we describe a fast and efficient method to obtain the BAC end by ligating the BAC fragments digested with Not I and another selected restriction enzyme into universal cloning vector, followed by determining the correct clones with HindIII digestion. Further DNA sequencing analysis verified the results mentioned above.

Chromosomes, Artificial, Bacterial↗
PubMed2001

Expression of adhesion molecules by human endothelial cells exposed to oxidized low density lipoprotein. Influences of degree of oxidation and location of oxidized LDL.

The main objective of this study was to determine the influence of the degree of low density lipoprotein (LDL) oxidation and the location of oxidized LDL (oxLDL) on expression of adhesion molecules on endothelial cells (EC). OxLDL preparations 1-4 with different degrees of oxidative modification were studied. All preparations of oxLDL, after addition to the medium, stimulated the expression of intercellular adhesion molecule-1 (ICAM-1) by human umbilical vein endothelial cells (HUVEC) as determined by cell-ELISA. Concentration-dependent studies examining ICAM-1 expression by HUVEC showed that the minimal concentration of oxLDL which significantly stimulated ICAM-1 expression was 5 microg/ml, suggesting that the predicted physiological concentration of oxLDL in plasma may be not high enough to elicit a substantial increase of ICAM-1 expression in EC. In contrast, very small amounts (0.15 microg/well) of oxLDL-3 and 4, the more heavily oxidized LDL preparations, stimulated effectively ICAM-1 expression by HUVEC when located below the endothelial cell monolayer by immobilizing to type I collagen. The results suggest that the increased expression of ICAM-1 induced by accumulated oxLDL may be one of the mechanisms by which oxLDL contributes to atherogenesis.

Cells, Cultured↗
PubMed2001

Oxidized LDL differentially regulates MMP-1 and TIMP-1 expression in vascular endothelial cells.

We have reported recently that oxidized low-density lipoprotein (oxLDL) stimulates matrix metalloproteinase-1 (MMP-1) expression in human vascular endothelial cells. The present study was conducted to examine the effect of oxLDL on expression of Tissue inhibitor of metalloproteinase-1 (TIMP-1), an endogenous inhibitor of MMPs, in human vascular endothelial cells. Our enzyme-linked immunosorbent assay and Northern blot analysis showed that oxLDL inhibited TIMP-1 secretion and expression by human umbilical vein endothelial cells. In contrast, PMA stimulated TIMP-1 expression and secretion. Both oxLDL and PMA increased MMP-1 expression and secretion significantly as previously reported. Inhibition by oxLDL of TIMP-1 expression was also observed in human aortic endothelial cells. Collagenase activity as detected by an enzymatic activity assay demonstrated, as expected, an increase in collagenase activity in the culture medium from oxLDL-treated cells as compared with that from untreated cells. The presented data indicates that oxLDL differentially regulates TIMP-1 and MMP-1 expression, whereas PMA coordinately regulates TIMP-1 and MMP-1 in vascular endothelial cells. The lack of coordination in the secretion of MMP-1 and TIMP-1 induced by oxLDL leads to an increased collagen-degrading activity that may contribute to destabilization of atherosclerotic plaques.

Cells, Cultured↗
PubMed2001

Kinetics of hydroxyapatite precipitation at pH 10 to 11.

The mechanism and kinetics of hydroxyapatite (HAP) precipitation from aqueous solution at the conditions of pH 10-11 and at calcium ion concentrations of more than 0.5 mol/l were investigated. The results show that the reaction undergoes the following process: transferring from octacalcium phosphate (OCP) to amorphous calcium phosphate (ACP) rapidly, and then from ACP to calcium-deficient hydroxyapatite (DAP) and HAP. DAP was the non-stoichiometric material that ACP converts to HAP. Reaction temperature greatly affects the reaction rate of the conversion from ACP to HAP. It takes about 24 h to form pure-phase HAP at 25 degrees C while it takes only 5 min at 60 degrees C. The temperature also has a great deal of influence on the particle size and morphology of precipitated hydroxyapatite. The reaction of transformation from ACP to DAP was second order and the activation energy was 95 kJ/mol (22.7 kCal/mol) and therefore it was inferred that the conversion reaction was a surface control process.

Calcium Phosphates↗
PubMed2001

Automatic evaluation of arterial diameter variation from vascular echographic images.

An automatic procedure for accurate arterial diameter evaluation from B-mode images obtained by diagnostic ultrasound systems is presented. It is used for measuring brachial artery dilation following reactive hyperemia induced by forearm ischemia, which is an appropriate parameter to study endothelial function in humans. B-mode images obtained from the diagnostic ultrasound system are acquired on a personal computer as grey intensity fields (pixels). A completely automatic algorithm is then applied and the artery walls are identified by two discrete sets of points. Artery diameter is evaluated by parabolic least-square approximation. The accuracy and extensive range of applicability of the diameter evaluation procedure were demonstrated both by preliminary analytic test cases and in vivo analyses. Reproducibility of the diameter estimate was assessed by in vivo measurements. The proposed procedure permits fast and accurate analysis of large amounts of data, because it requires no action by the operator. It thus represents a valuable tool for assessment of endothelium-dependent vasodilation, especially in large, multicentric clinical trials.

Adult↗