Biomedical subjects
Publications and source records attributed to W Ho.
A novel method for preparing highly photoactive nano-sized TiO2 photocatalysts with anatase and brookite phases has been developed by hydrolysis of titanium tetraisoproproxide in pure water or a 1:1 EtOH-H2O solution under ultrasonic irradiation; the photocatalytic activity of TiO2 particles prepared by this method exceeded that of Degussa P25.
A carbon monoxide molecule (CO) was positioned with a scanning tunneling microscope (STM) at various distances from an oxygen atom (O) on the Ag(110) surface at 13 K. At the closest separation, carbon dioxide (CO(2)) production was induced by tunneling electrons. Direct reaction of a CO desorbed from the STM tip with an O atom on Ag(110) illustrates another catalytic oxidation mechanism. Inelastic electron tunneling spectroscopy with the STM was used to monitor the vibrations of CO in its different environment.
We examined how transient cerebral ischemia affects the mRNA expression, and the immunoreactive distribution, of the somatostatin type 2 (sst2) receptor in the adult rat hippocampus. Following reperfusion, sst2 mRNA levels increased significantly in the CA1 region by 3 h, and were also increased in the CA3 and CA4/hilus subfields at 6 and 12 h. At 24 h, however, sst2 receptor mRNA levels returned to baseline throughout the hippocampus. At the protein level, we found the regional immunoreactivity of the sst2a receptor was maintained, or slightly elevated, throughout the hippocampus at 6 h, but not different from control at 24 h. These results suggest that sst2 receptors maintain their normal distribution and prevalence in the post-ischemic hippocampus before the deterioration of the vulnerable CA1 neurons. Thus, they represent attractive targets for neuroprotective interventions.
We examined the gene expression responses of GABA-B R1A, R1B and R2 receptor subtypes in the hippocampus of perforant pathway-kindled rats at 24 h and 28 days after 15 consecutive daily stimulations. We found R1A expression, but not R1B expression, to be significantly induced in the dentate gyrus at 24 h. No change in the expression of R1A or R1B was observed at 28 days. R2 expression was induced throughout the hippocampus at 24 h, but also returned to control levels by 28 days. Thus, our results show that kindling induces a transient increase in GABA-B receptor mRNA in the hippocampus.
A combined experimental and theoretical study is presented for the C-D stretch mode excitation of acetylene isotopes, C2HD and C2D2, on Cu(100) via inelastic electron tunneling (IET) in a scanning tunneling microscope junction. The calculated IET images using density functional theory show that the measured signal from C2D2 derives from the antisymmetric stretch mode. Selection rules are derived and involve the constraint imposed by the IET image on the symmetry characters of the vibrational mode and the adsorbate-induced electron states at the Fermi level.
Rat pheochromocytoma PC12 cells have been widely used as a cell system for study of growth factor-stimulated cell functions. We report here that nerve growth factor (NGF) stimulated both chemotaxis (directional migration) and chemokinesis (random migration) of PC12 cells. Treatment with a MEK1/2-specific inhibitor (PD98059) or expression of a dominant negative variant of Ras differentially inhibited NGF-stimulated chemotaxis but not chemokinesis of PC12 cells. Priming of PC12 cells with NGF resulted in reduced extracellular signal-regulated kinase (ERK) activation and loss of chemotactic, but not chemokinetic, response. In addition, NGF stimulation of ERK is known to involve an early transient phase of activation followed by a late sustained phase of activation; in contrast, epidermal growth factor (EGF) elicits only early transient ERK activation. We observed that like NGF, EGF also stimulated both chemotaxis and chemokinesis, and treatment with PD98059 abolished the EGF-stimulated chemotaxis. Therefore, the early transient phase of ERK activation functioned in signaling chemotaxis; the late sustained phase of ERK activation did not seem to have an essential role. In addition, our results suggested that chemotactic signaling required a threshold level of ERK activation; at below threshold level of ERK activation, chemotaxis would not occur.
Toxic epidermal necrolysis syndrome is characterized by extensive skin rash with blisters and exfoliation similar to that of major burns. Current evidence suggests that toxic epidermal necrolysis syndrome is most likely due to cell-mediated immune response triggered by certain drugs. Recognition of the clinical situation which is similar to major burn has resulted in general agreement that these patients are best treated in a burns unit, where critical support and meticulous wound care can be carried out by experienced personnel. This represents a major step forward in the management of this condition. The 10 year experience of managing seven patients with severe toxic epidermal necrolysis in a tertiary burns centre in Hong Kong is presented and the controversies over classification and management of the disease are also discussed.
Since its inception in 1990, the Hospital Authority (HA) has strongly supported the development and implementation of information systems both to improve the delivery of care and to make better information available to managers. This paper summarizes the progress to date and discusses current and future developments. Following the first two phases of the HA information technology strategy the basic infrastructural elements were laid in place. These included the foundation administrative and financial systems and databases; establishment of a wide area network linking all hospitals and clinics together; laboratory, radiology and pharmacy systems with access to results in the ward. A major push into clinical systems began in 1994 with the clinical management system (CMS), which established a clinical workstation for use in both ward and ambulatory settings. The CMS is now running at all major hospitals, and provides single logon access to almost all the electronically collected clinical data in the HA. The next phase of development is focussed on further support for clinical activities in the CMS. Key elements include the longitudinal electronic patient record (ePR), clinical order entry, generic support for clinical reports, broadening the scope to include allied health and the rehabilitative phase, clinical decision support, an improved clinical documentation framework, sharing of clinical information with other health care providers and a comprehensive data repository for analysis and reporting purposes.
BACKGROUND & AIMS: Marijuana and other cannabinoids are effective anti-emetics. Despite ongoing controversy over their usage, the receptor distribution and the site of the anti-emetic action of these compounds are not known. Our aim was to investigate whether the cannabinoid 1 receptor (CB1r) and endocannabinoids play a role in the anti-emetic action of cannabinoids. METHODS: Ferrets were given an emetic stimulus and the number of episodes of retching and vomiting were observed after administration of CB1r agonists and a CB1r antagonist. CB1r and fatty acid amide hydrolase (FAAH), which degrades endocannabinoids, were localized by immunohistochemistry. RESULTS: CB1r and FAAH were localized in the dorsal vagal complex, consisting of the area postrema, nucleus of the solitary tract, and the dorsal motor nucleus of the vagus in the brainstem. CB1r was found in the myenteric plexus of the stomach and duodenum. Activation of CB1r by the agonists (delta)(9)-tetrahydrocannabinol, WIN 55,212-2, and methanandamide inhibited emesis and their action was reversed by a selective CB1r antagonist, which alone had no effect, but potentiated vomiting in response to an emetic stimulus. CONCLUSIONS: CB1r mediates the anti-emetic action of cannabinoids in the dorsal vagal complex. Endocannabinoids are a novel neuroregulatory system involved in the control of emesis.
Single hydrogen atoms were imaged on the Cu(001) surface by scanning tunneling microscopy (STM). The vibrations of individual H and D atoms against the surface were excited and detected by inelastic electron tunneling spectroscopy (STM-IETS). Variable temperature measurements of H atom diffusion showed a transition from thermally activated diffusion to quantum tunneling at 60 K. Regimes of phonon-assisted and electron-limited quantum tunneling were observed. The thermal diffusion rate of D atoms varied over 7 orders of magnitude between 80 and 50 K with no transition to quantum tunneling down to a thermal hopping rate of 4x10(-7) s(-1).
PURPOSE: To compare meropenem, a carbapenem antibiotic, with ceftazidime for the empirical treatment of patients with febrile neutropenia. PATIENTS AND METHODS: A prospective, double-blind, randomized clinical trial was conducted at medical centers in North America and the Netherlands. A total of 411 cancer patients (196 treated with meropenem and 215 treated with ceftazidime), who had 471 episodes of fever, participated in the trial. For each neutropenic episode, patients were allocated at random to receive intravenous administration of meropenem (1 g every 8 hours) or ceftazidime (2 g every 8 hours). Treatment could be modified at any time. Key end points were clinical and bacteriologic outcomes, eradication of infecting organism, and adverse events. RESULTS: The rate of successful clinical response at the end of therapy was significantly higher for patients treated with meropenem than for those on ceftazidime for all episodes (54% v 44%, respectively) and for episodes of fever of unknown origin (62% v 46%, respectively), but differences between groups were not statistically significant for clinically defined or microbiologically defined infections. Meropenem was significantly more effective than ceftazidime in severely neutropenic (</= 100 cells/microliter) patients (55% v 43%, respectively), bone marrow transplant patients (73% v 27%, respectively), and patients given antibiotic prophylaxis before study entry (71% v 52%, respectively). Common adverse effects of meropenem and ceftazidime therapy were rash, diarrhea, and nausea and vomiting. CONCLUSION: Monotherapy with meropenem represents a suitable choice for initial empirical antibiotic therapy for febrile episodes in neutropenic cancer patients.
Inelastic electron tunneling spectroscopy and microscopy with a scanning tunneling microscope revealed two vibrational modes showing a decrease in conductance at +/-82.0 and +/-38.3 mV sample bias for single oxygen molecules chemisorbed on the fourfold hollow sites of Ag(110) surface at 13 K. The spatial distribution of the vibrational intensities exhibited pi(g)-orbital (perpendicular to surface) symmetry of O2 with the molecular axis along the [001] direction. These results are attributed to resonant inelastic electron tunneling.
A new mechanism for negative differential resistance (NDR) has been discovered and involves a single molecule in the junction of a scanning tunneling microscope. The NDR was observed at voltages corresponding to the vibrational energies of single pyrrolidine molecules on the (001) surface of copper at 9 K. This vibrationally mediated NDR contrasts with the previously known mechanisms which all involve the electronic states of the conducting media.
The novel dimer bis(7)-tacrine (1,7-N-Heptylene-bis-9,9'-amino-1,2,3, 4-tetrahydroacridine), which exhibits higher potency, selectivity and oral activity on acetylcholinesterase inhibition in vivo than tacrine, was evaluated for its ability to reverse AF64A-induced spatial memory impairment in rats using the Morris water maze. The intracerebroventricular injection of AF64A (3 nmol/side) resulted in a substantial increase in the escape latency to find the platform (F(1,7)=30.2, P<0.01). The observed impairment of spatial memory was paralleled by a 47% decrease in choline acetyltransferase activity in the hippocampus. Oral administration of bis(7)-tacrine (0.22-0.89 micromol/kg) dose-dependently reversed the AF64A-induced latency delay to the level of the saline control group (F(4,28)=7.45, P<0. 05). The present study provides additional evidence of bis(7)-tacrine as an ideal candidate for the palliative treatment of Alzheimer's disease.
Electrons from a scanning tunneling microscope were used to break a C-H bond in a single acetylene (HCCH) molecule adsorbed on Cu(001) at 9 K. The product ethynyl (CCH) was characterized by imaging, inelastic electron tunneling spectroscopy, and variable temperature measurements of the rotation rate. Significant changes in the vibrational spectra and bonding geometry accompanied HCCH dissociation. The ethynyl was further dehydrogenated to form dicarbon (CC). Dissociation studies of the isotopes HCCD and DCCD permitted unambiguous identification of the reaction products.
Three C-C chemokines inhibit human immunodeficiency virus (HIV) entry into macrophages: macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and regulated-upon activation, normal T-cell expressed and secreted (RANTES). We studied the ability of placental cord blood mononuclear cells (CBMC) to secrete these C-C chemokines in comparison to adult blood mononuclear cells (ABMC). CBMC had diminished ability to secrete RANTES, as determined by enzyme-linked immunosorbent assay. Secretion of MIP-1alpha and MIP-1beta were similar in CBMC and ABMC. Whereas MIP-1alpha and MIP-1beta secretion were comparable in monocytes and lymphocytes, RANTES was secreted primarily by lymphocytes. Flow cytometric analysis of RANTES expression showed diminished intracellular RANTES expression in cord blood lymphocytes (CBL) compared to adult (peripheral) blood lymphocytes (ABL). A subset analysis of RANTES-producing CBL and ABL demonstrated that RANTES was produced predominantly by CD8+/CD45RO+ cells. CBL had a reduced proportion of CD8+/CD45RO+ cells compared with ABL, which may account for the diminished RANTES secretion by CBMC. These results may be relevant to the pathogenesis of perinatal HIV infection. (Blood. 2000;95:715-718)
A scanning tunneling microscope (STM) operating at 9 K in ultrahigh vacuum was used to initiate a bimolecular reaction between isolated hydrogen sulfide and dicarbon molecules on the Cu(001) surface. The reaction products ethynyl (CCH) and sulfhydryl (SH) were identified by inelastic electron tunneling spectroscopy (STM-IETS) and by sequentially removing hydrogen atoms from an H2S molecule using energetic tunneling electrons. For comparison, the thermal diffusion and reaction of H2S and CC at 45 K and H2O and CC at 9 K were also observed.
The first outbreak of avian influenza A (H5N1) occurred among humans in Hong Kong in 1997. To estimate the risk of person-to-person transmission, a retrospective cohort study was conducted to compare the prevalence of H5N1 antibody among health care workers (HCWs) exposed to H5N1 case-patients with the prevalence among nonexposed HCWs. Information on H5N1 case-patient and poultry exposures and blood samples for H5N1-specific antibody testing were collected. Eight (3.7%) of 217 exposed and 2 (0.7%) of 309 nonexposed HCWs were H5N1 seropositive (P=.01). The difference remained significant after controlling for poultry exposure (P=.01). This study presents the first epidemiologic evidence that H5N1 viruses were transmitted from patients to HCWs. Human-to-human transmission of avian influenza may increase the chances for the emergence of a novel influenza virus with pandemic potential.