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Biomedical subjects

W Ho

Publications and source records attributed to W Ho.

At least 73 records · Page 4Linked to original sources
PubMed2000

Human stem cells express substance P gene and its receptor.

We studied the expression of Substance P (SP) and its receptor in an established human stem cell line (TF-1) and primary stem cells derived from human placental cord blood (HPCB). Using reverse transcriptase polymerase chain reaction (RT-PCR) assay, SP mRNA is detected in both TF-1 cells and HPCB stem cells. Among the alpha, beta, gamma, and delta transcripts of the SP gene, only the beta, gamma, and delta transcripts are detectable in these cells. These RT-PCR-amplified transcripts are confirmed by Southern blot assay using a specific SP probe. Sequence analysis of the RT-PCR-amplified products transcribed from mRNA extracted from the HPCB stem cells also confirmed that these transcripts are identical to those found in human neurons. At the protein level, TF-1 cells produced endogenous SP as determined by an enzyme-linked immunosorbent assay (EIA). Capsaicin, a vanillyl fatty acid amide (ingredient of hot pepper), released SP from TF-1 cells. In addition, using RT nested-PCR analysis, we identified the presence of mRNA for neurokinin-1 receptor (NK-1R, the receptor for SP) in both TF-1 cells and HPCB stem cells, which was confirmed by Southern blot and DNA sequencing analysis. The demonstration that human stem cells express SP and its receptor support the notion that SP is biologically involved in the hematopoietic regulating network.

Capsaicin↗
PubMed1999

Single-bond formation and characterization with a scanning tunneling microscope

A scanning tunneling microscope (STM) was used to manipulate the bonding of a carbon monoxide (CO) molecule and to analyze the structure and vibrational properties of individual products. Individual iron (Fe) atoms were evaporated and coadsorbed with CO molecules on a silver (110) surface at 13 kelvin. A CO molecule was transferred from the surface to the STM tip and bonded with an Fe atom to form Fe(CO). A second CO molecule was similarly transferred and bonded with Fe(CO) to form Fe(CO)(2). Controlled bond formation and characterization at the single-bond level probe chemistry at the spatial limit.

Journal Article↗
PubMed1999

Human immunodeficiency virus infection of human placental cord blood CD34+AC133+ stem cells and their progeny.

The AC133 is a novel antigen selectively expressed on primitive CD34bright stem cells and is a valuable marker for the selection of long-term culture-initiating cells (LTC-ICs) and severe combined immunodeficiency (SCID)-repopulating cells. Human placental cord blood (HPCB) is a rich source of CD34+AC133+ cells. Since AC133 antibody is likely to be used as an alternative to CD34 for the selection of stem cells in transplant and gene therapy situations, we examined the susceptibility of HPCB-isolated CD34+AC133+ stem cells to infection with free and cell-associated HIV-1 in vitro. Freshly isolated HPCB CD34+AC133+ stem cells were not susceptible to HIV-1 infection as determined by PCR and reverse transcriptase assays. Inoculation with HIV-1 did not affect the viability and clonogenic ability of HPCB CD34+AC133+ cells. Although the highly purified HPCB CD34+AC133+ stem cells contained mRNA for CD4 and CXCR4 receptors, CD4 and CXCR4 proteins were not expressed on these cells. Similarly, CCR5 protein, the major macrophage-tropic HIV-1 coreceptor, was not expressed in freshly isolated HPCB CD34+AC133+ stem cells, although the transcript for CCR5 was identified in these cells. Expression of CD4, CXCR4, and CCR5 receptor proteins on the progeny derived from HPCB CD34+AC133+ stem cells was detected and correlated with susceptibility to HIV-1 infection in vitro. These findings suggest that freshly isolated HPCB CD34+AC133+ stem cells are not susceptible to HIV-1 infection and may not be a viral reservoir. These data have important implications for the use of AC133 antibody as a means of enriching for primitive hematopoietic stem cells from placental cord blood and in the design of stem cell or progenitor cell-based gene therapeutic strategies for perinatal HIV-1 infection.

AC133 Antigen↗
PubMed1999

Dynamic DNA hybridization on a chip using paramagnetic beads.

Dynamic DNA hybridization is presented as an approach to perform gene expression analysis. The method is advantageous because of its dynamic supplies of both DNA samples and probes. The approach was demonstrated on a microfluidic platform by incorporating paramagnetic beads as a transportable solid support. A glass chip was fabricated to allow simultaneous interrogation of eight DNA target samples by DNA probes. DNA targets were immobilized on beads via streptavidin-biotin conjugation or base pairing between oligonucleotide residues. The DNA/bead complex was introduced into the device in which hybridization took place with a complementary probe. The hybridized probe was then removed by heat denaturation to allow the DNA sample to be interrogated again by another probe with a different sequence of interest. A pneumatic pumping apparatus was constructed to transport DNA probes and other reagents into the microfluidic device while hydrostatic pumping was used for the introduction of paramagnetic beads with samples. After investigating three types of paramagnetic beads, we found Dynabeads Oligo(dT)25 best suited this application. Targets on the beads could be sequentially interrogated by probes for 12 times, and the hybridization signal was maintained within experimental variation. Demonstration of specific hybridization reactions in an array format was achieved using four synthesized DNA targets in duplicate and five probes in sequence, indicating the potential application of this approach to gene expression analysis.

Actins↗
PubMed1999

Nitric oxide participates in the recovery of normal jejunal epithelial ion transport following exposure to the superantigen, Staphylococcus aureus enterotoxin B.

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l -NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-alpha and IFN-gamma were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l -NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 microgram) treatment. However, Isc responses in l -NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-alpha and IFN-gamma in mice treated 24 h previously with l -NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l -NIL plus SEB and TNF-alpha- or IFN-gamma-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-alpha and IFN-gamma production.

Animals↗
PubMed1999

Inhibition of thymocyte positive selection by natural MHC: peptide ligands.

The 3A9 transgenic mouse line carries the rearranged TCR genes from a T cell hybridoma that recognizes hen egg lysozyme peptide 46-61 in the context of MHC class II Ak molecules. As expected, positive selection of immature 3A9 thymocytes to become mature CD4+ 8- T cells was efficient on the "selecting" CBA (H-2k) genetic background but not on the "non-selecting" C57BL/6 (H-2b) background. Surprisingly, positive selection was also inefficient on the CBA x C57BL/6 F1 background (H-2kb). We present evidence that expression of A(beta)b molecules on thymus epithelium (in conjunction with A(alpha)b or A(alpha)k molecules) inhibits the positive selection of 3A9 thymocytes mediated by A(alpha)k:A(beta)k complexes, in a process evocative of peptide antagonism of mature T cells.

Animals↗
PubMed1999

Decreased hippocampal expression, but not functionality, of GABA(B) receptors after transient cerebral ischemia in rats.

We have examined the effects of transient global ischemia on both the gene expression levels and the functionality of GABA(B) receptors in rat brain, using antisense in situ hybridization and electrophysiological evaluations. At the level of gene expression, no significant change in GABA(B) receptor expression was observed in any hippocampal subfield at either 6 or 12 h after challenge. At 24 h postchallenge, however, a significant decrease in GABA(B) receptor expression was observed in both the CA1 and CA3 subfields, whereas no change was observed in the dentate granule cell layer. Although expression in both the vulnerable CA1 and less vulnerable CA3 subfields was diminished at this time postchallenge, there was no significant difference in the degree of the diminished expression between these subfields. At the functional level, the dose-dependent ability of baclofen (1-100 microM) to inhibit an evoked excitatory postsynaptic potential (f-EPSP) in the CA1 subfield was evaluated at 24 h postischemia, in comparison with the dose-response observed in sham-operated subjects. No significant differences were observed in the efficacy of GABA(B) receptor-mediated inhibition of the elicited f-EPSP at any of the baclofen concentrations examined. These data demonstrate that although the mRNA expression levels for the GABA(B) receptor are diminished in both vulnerable and less vulnerable neurons of Ammon's horn at 24 h following transient global ischemia, the functionality of the GABA(B) receptor system is maintained at this time postchallenge.

Animals↗
PubMed1999

Altered expression levels of SEF-2 and p112 in the rat hippocampus after transient cerebral ischemia: identification by mRNA differential display.

The authors used mRNA differential display to identify genes whose expression levels are altered in the adult rat hippocampus 24 hours after global ischemia. At this time after challenge, the basic helix-loop-helix transcription factor, SEF-2, and the 26S proteasome complex subunit, p112, were identified as genes whose expression levels are decreased and increased, respectively, in the hippocampus. To determine the spatial and temporal patterns of expression change for each gene, the authors antisense in situ hybridization to paired brain sections of sham-operated and global ischemia-challenged rats at 6, 12, and 24 hours after reperfusion SEF-2 expression was not significantly altered from that of sham-operated controls in any hippocampal subfield at or before 12 hours after challenge. At 24 hours after ischemia, however, SEF-2 expression levels were significantly diminished in the vulnerable CA1 subfield, but not in the less vulnerable CA3 or dentate granule cell subfields. The proteasome p112 subunit gene displayed no change in expression levels at 6 hours after insult; however, an elevated expression was observed at 12 hours after challenge in the dentate granule cell subfield. By 24 hours after challenge, p112 expression was significantly elevated in both the CA1 and dentate granule cell subfields. These results demonstrate that a member of the basic helix-loop-helix family of transcription factors, SEF-2, and the major subunit of the 26S proteasome complex, p112, display altered gene expression in the hippocampus after transient cerebral ischemia.

Animals↗
PubMed1999

Medication errors in a pediatric emergency department.

OBJECTIVE: To initiate investigation into the medication errors that occur in a pediatric emergency department. These errors have the potential for significant morbidity and mortality, as well as costly litigation. METHODS: We conducted a retrospective chart review of all medication and intravenous fluid errors identified in a pediatric emergency department through incident reports filed over a 5-year period. An attempt was made to determine who was involved with the errors and what caused the errors. The patient outcomes were noted and classified according to clinical significance using previously published criteria. RESULTS: Thirty-three incident reports involving medication or intravenous fluid errors were analyzed. Most errors occurred on the evening and night shifts. Nurses were involved in 39% of reported errors; the nurse and emergency physician were jointly involved in 36%. The most common error was an incorrect dose of medication (35%) or incorrect medication given (30%). In one third of the cases, the family was not made aware of the error. In 12%, patients required additional treatment, and one was admitted to the hospital because of the error. There were no deaths. CONCLUSION: Incorrect recording of patient weights leading to an incorrect medication dose and failure to note drug allergy are common causes for medication errors in the pediatric emergency department. Incorrect drugs and i.v. fluids are given because of similar names and packaging. Many of the errors in the ED seem to be preventable.

Adolescent↗
PubMed1999

Hospital transformation and organisational learning.

Kwong Wah Hospital was founded by the charity organisation Tung Wah Group of Hospitals some 88 years ago, with management transfer to the Hong Kong Hospital Authority in 1991. Capitalizing both from the traditional caring culture of its founder, as well as opportunities in the new management environment, the hospital has scored remarkable successes in service quality, community partnership, organisational effectiveness, and staff development. Underpinning these transformations were Structure, Process, People, and Culture strategies. The learning imperative is heavily mandated or the success of each of these strands of development. Indeed, the embodiment of a learning organisation culture provides the impetus in sustaining the change momentum, towards achieving the Vision of becoming a 'Most Preferred Hospital' in Hong Kong.

Hong Kong↗
PubMed1998

Single-molecule vibrational spectroscopy and microscopy

Vibrational spectra for a single molecule adsorbed on a solid surface have been obtained with a scanning tunneling microscope (STM). Inelastic electron tunneling spectra for an isolated acetylene (C2H2) molecule adsorbed on the copper (100) surface showed an increase in the tunneling conductance at 358 millivolts, resulting from excitation of the C-H stretch mode. An isotopic shift to 266 millivolts was observed for deuterated acetylene (C2D2). Vibrational microscopy from spatial imaging of the inelastic tunneling channels yielded additional data to further distinguish and characterize the two isotopes. Single-molecule vibrational analysis should lead to better understanding and control of surface chemistry at the atomic level.

Journal Article↗
PubMed1998

Inducing and viewing the rotational motion of a single molecule

Tunneling electrons from the tip of a scanning tunneling microscope were used to induce and monitor the reversible rotation of single molecules of molecular oxygen among three equivalent orientations on the platinum(111) surface. Detailed studies of the rotation rates indicate a crossover from a single-electron process to a multielectron process below a threshold tunneling voltage. Values for the energy barrier to rotation and the vibrational relaxation rate of the molecule were obtained by comparing the experimental data with a theoretical model. The ability to induce the controlled motion of single molecules enhances our understanding of basic chemical processes on surfaces and may lead to useful single-molecule devices.

Journal Article↗
PubMed1997

Modulation of ATP-sensitive K+ channels in rabbit ventricular myocytes by adenosine A1 receptor activation.

The objective of the present study was to characterize the role of adenosine in the regulation of ATP-sensitive K (KATP) channel activity in isolated rabbit ventricular myocytes using the patch-clamp technique. In an outside-out patch exposed to guanosine 5'-triphosphate and ATP at the intracellular surface, external adenosine stimulated KATP channel activity. In an inside-out patch exposed to external adenosine, ATP reduced KATP channel activity and guanosine 5'-triphosphate stimulated KATP channel activity. Guanosine 5'-O-(3-thiotriphosphate) resulted in a gradual increase of KATP channel activity even in the absence of adenosine. When myocytes were preincubated with pertussis toxin or 8-cyclopentyl-1,3-dipropylxanthine, adenosine A1 receptor activation failed to activate the KATP channel. Analysis of the open and closed time distributions showed that adenosine A1 receptor activation increased burst duration and decreased interburst duration. In a dose-response relationship for ATP, adenosine A1 receptor activation shifted the half-maximal inhibition of the KATP channel from 70 to 241 microM.

Adenosine↗
PubMed1995

Synthesis and anti-HIV-1 activity of 4,5,6,7-tetrahydro-5-methylimidazo [4,5,1-jk][1,4]benzodiazepin-2(1H)-one (TIBO) derivatives. 3.

4,5,6,7-Tetrahydro-5-methylimidazo[4,5,1-jk][1,4]benzodiazepin-2 (1H)-ones (TIBO), 1, have been shown to significantly inhibit HIV-1 replication in vitro by interfering with the virus's reverse transcriptase enzyme. They have also demonstrated potential clinical efficacy in combating HIV-1, on the basis of a preliminary study. Our prior publications have discussed the discovery of this series of compounds and reported some preliminary chemical and biological studies around N-6 substitutions and 5-membered ring variations of 1. This manuscript describes our synthetic endeavors around 4, 5, and 7 mono- and disubstitutions of 1 and discusses related HIV-1 inhibitory structure-activity relationships. On the basis of inhibition of HIV-1's cytopathic effects in MT-4 cells, we found that 5-mono-Me-substituted analogues, the original substitution in the early lead compounds, and 7-mono-Me-substituted analogues of 1 were comparable as being consistently the most active compounds. Although generally less active, the 4,5,7-unsubstituted, 4-mono-substituted, cis- and trans-5,7-di-Me-substituted, and cis-4,5-di-Me-substituted analogues of 1 also exhibited some significant desired activity. The remaining trans-4,5-di-Me-substituted, cis- and trans-4,7-di-Me-substituted, and all 4,5-, 5,6-, 6,7-, and 7,8-fused disubstituted analogues of 1 possessed no noticeable desired activity.

Antiviral Agents↗
PubMed1995

Synthesis and anti-HIV-1 activity of 4,5,6,7-tetrahydro-5-methylimidazo-[4,5,1-jk][1,4]benzodiazepin- 2(1H)-one (TlBO) derivatives. 4.

In previous papers, we have described the discovery of a new series of compounds, 4,5,6,7-tetrahydro-5-methylimidazo[4,5,1-jk][1,4]benzodiazepin-2(1 H)- ones, TlBO (1 and 1a), with potent anti-HIV-1 activity and the synthesis of analogues to better define the structure-activity relationships (SAR) in terms of changes in substituents at the N-6 position and variations of the five-membered urea ring as well as the seven-membered diazepine ring. This paper describes the synthesis of TlBO analogues with various substitutents on the aromatic ring and their SAR in terms of anti-HIV-1 properties. Substituents on the 8-position furnished the most rewarding results and gave a large improvement in potency versus the parent compound. These included halogen, thiomethyl, and methyl. Analogues like 8-cyano, -methoxy, and -acetylene were equipotent, while 8-amino, -acetylamino, -dimethylamino, and -nitro were inactive (Table 1). Substituents at the 9-position tended to have little effect on activity, and 10-substituents decreased activity. The 8-chloro compound 6a with IC50 = 0.0043 microM is currently under clinical development.

Antiviral Agents↗