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Biomedical subjects

K Chow

Publications and source records attributed to K Chow.

At least 19 recordsLinked to original sources
PubMed2004

Acute urinary retention: a review of the aetiology and management.

Acute retention of urine (AUR) is a common urological emergency characterised by a sudden inability to pass urine associated with lower abdominal pain. In recent years, the natural history and incidence of AUR has become better understood, however, further research into methods to prevent it and evaluation of the impact an episode of AUR has on the patient is required. This review provides an overview of the current management of AUR in men and the impact of the condition on patients' quality of life.

Abdominal Pain↗
PubMed2003

A stone farm: development of a method for simultaneous production of multiple calcium oxalate stones in vitro.

We have previously shown how individual calcium oxalate stones of about 1 cm can be grown in vitro. While this proved a design concept, it was severely limited as an experimental tool because of the time required to undertake comparative studies. Here we describe a development of this system in which six parallel pairs of stone generators are supplied with feed solutions generating a medium that is supersaturated with calcium oxalate. Twelve stones were grown simultaneously in aseptically prepared artificial urine over a period of 32 days from 100 mg to about 250 mg. Flow rates, pH and [Ca(2+)] were stable and reproducible over the course of the experiment. Sodium azide (0.02%) was included in the growth medium of six stones and caused a modest decrease in growth rate from 5.5 to 3.4 mg/day. The experimental design is such that this was readily detectable both visually and statistically ( p<0.001). This multiple stone growing system ("a stone farm") shows improved consistency and illustrates the statistical power of the technique. Azide has only a minor effect on the growth kinetics and can be used as an antibacterial agent in studies involving urinary macromolecules. The technique is suitable for practical and meaningful investigation of calcium oxalate stone formation in vitro.

Calcium Oxalate↗
PubMed2002

Do triglycerides modulate the effectiveness of clozapine?

We describe a case in which a patient's clinical response to clozapine appears to correlate positively with his serum triglyceride concentrations. We propose that the observed clinical response may partly be the result of the physical interaction of clozapine with the very low-density lipoproteins. We base this supposition on our previous in-vitro study showing that the plasma distribution of clozapine is significantly altered by increases in plasma triglyceride concentrations. Although this case only represents one patient, it highlights the possibility that serum lipids may be potential contributors to the clinical effectiveness of clozapine.

Adult↗
PubMed2001

Head and neck hypervascular lesions: embolization with ethylene vinyl alcohol copolymer--laboratory evaluation in Swine and clinical evaluation in humans.

PURPOSE: (a) To assess in swine long-term (12-month) histopathologic changes, particularly, those related to recanalization and angiotoxicity after endovascular delivery of ethylene vinyl alcohol copolymer (EVAC), and (b) to evaluate initial clinical experience in 18 patients with head and neck tumors and arteriovenous malformations. MATERIALS AND METHODS: Embolization with EVAC was performed in one rete each in five swine. After 12 months, an angiogram was obtained, and the contralateral rete was also embolized (acute). Swine were sacrificed and the retia harvested for pathologic examination. In the clinical study, 18 patients with tumors (n = 14), facial arteriovenous malformations (n = 3), and vertebral arteriovenous fistula (n = 1) underwent therapeutic embolization. The technical aspects of EVAC embolization, percentage of occlusion, and clinical complications were evaluated. RESULTS: Angiographic 12-month follow-up in swine revealed persistent occlusion of the embolized rete or retia. Histologic examination of the same rete showed vascular occlusion and moderate intraluminal foreign body giant cell reaction; the acutely embolized rete showed no endothelial denudation or angionecrosis. Clinical evaluation in patients revealed satisfactory penetration of lesion vasculature with EVAC when the microcatheter was advanced within 2 cm of a lesion or when percutaneous puncture was performed. There were two transient complications: one increase in a preexisting fifth nerve palsy and one increase in preexisting hemiparesis. CONCLUSION: EVAC is a promising liquid embolic material providing long-term occlusion of blood vessels.

Adolescent↗
PubMed2000

Magnetic field exposure enhances DNA repair through the induction of DnaK/J synthesis.

In contrast to the common impression that exposure to a magnetic field of low frequency causes mutations to organisms, we have demonstrated that a magnetic field can actually enhance the efficiency of DNA repair. Using Escherichia coli strain XL-1 Blue as the host and plasmid pUC8 that had been mutagenized by hydroxylamine as the vector for assessment, we found that bacterial transformants that had been exposed to a magnetic field of 50 Hz gave lower percentages of white colonies as compared to transformants that had not been exposed to the magnetic field. This result was indicative that the efficiency of DNA repair had been improved. The improvement was found to be mediated by the induced overproduction of heat shock proteins DnaK/J (Hsp70/40).

Bacterial Proteins↗
PubMed2000

MRI of Enterovirus 71 myelitis with monoplegia.

We report two boys diagnosed as having herpangina and hand-foot-mouth disease complicated by monoplegia during the outbreak enterovirus infection in Taiwan in 1998. Enterovirus 71 was identified in the stool and throat swab; neither polio nor Coxsackie viruses was identified. MRI showed unilateral lesions in the anterior horns of the spinal cord at T11-12 and C2-5. Although the MRI findings and sites of these lesions were similar to those of poliovirus-associated poliomyelitis, the virological data indicated that these boys were infected with enterovirus type 71.

Diagnosis, Differential↗
PubMed2000

Embolization with radiopaque microbeads of polyacrylonitrile hydrogel: evaluation in swine.

PURPOSE: To perform in vitro and in vivo studies of radiopaque microbeads of polyacrylonitrile (PAN) hydrogel to evaluate their characteristics as embolic material. MATERIALS AND METHODS: PAN microbeads were analyzed in vitro for swelling in different concentrations of contrast material and saline solution and injected through various microcatheters. In three nonsurvival swine, various organs were embolized with PAN microbeads. In eight survival swine, the rete mirabile was embolized with PAN microbeads or polyvinyl alcohol particles. Follow-up angiograms were obtained regularly, and histopathologic analysis was performed at 1 and 6 months. RESULTS: The microbeads were black with a regular shape and smooth surface. They were easily visible in the syringe and easy to inject through the microcatheters. When wet, their diameters increased by 40%. The microbeads were sufficiently radiopaque to be visible in all vascular territories. Vascular occlusion was not permanent, and even when embolization was adequate, some revascularization was detected at 3 months. The microbeads were intact and still radiopaque at 6 months. Histopathologic examination demonstrated variable inflammatory reactions and foreign-body giant cell reaction and no angionecrosis or hemorrhage. CONCLUSION: Because PAN microbeads are biocompatible, radiopaque, and easy to handle during embolization procedures, they have potential as a therapeutic embolic agent.

Acrylic Resins↗
PubMed2000

Endovascular treatment of dural sinus thrombosis with rheolytic thrombectomy and intra-arterial thrombolysis.

BACKGROUND AND PURPOSE: Cerebral venous thrombosis is a rare entity that can be difficult to manage. Intrasinus thrombolysis is an increasingly applied intervention, but this modality carries an increased risk of hemorrhage. We describe for the first time an option with a potentially lower incidence of intracranial bleeding, the combination of the AngioJet rheolytic thrombectomy catheter with intra-arterial thrombolysis, in 2 patients with extensive dural sinus thromboses, preexisting intracranial hemorrhage, and severe progressive neurological deficits despite heparin therapy. METHODS: Four procedures were performed in 2 patients with thromboses in the superior sagittal and transverse sinuses (right in 1 patient and bilateral in 1 patient) and cortical veins. Rheolytic thrombectomy was performed in the sigmoid, transverse, straight, and superior sagittal sinuses; this technique involves the use of the Bernoulli effect to create a vacuum that fragments and aspirates thrombus. For associated persistent cortical vein thromboses, low-dose intra-arterial thrombolysis was used. RESULTS: Both patients had excellent angiographic results with sinus reopening after rheolytic thrombectomy and cortical vein reopening after intra-arterial thrombolysis. Follow-up CT showed no change in 1 patient and increased preexisting intracranial hemorrhage in the other. One patient had a negative hypercoagulable workup, and the other patient had probable anti-phospholipid antibody syndrome. At 6 months, both patients had excellent clinical outcome with no neurological deficits except mild short-term memory loss in 1 patient. CONCLUSIONS: The combination of rheolytic thrombectomy with intra-arterial thrombolysis is a treatment modality that allows accelerated recanalization of occluded dural sinuses and cerebral veins with lower doses of thrombolytic agents.

Adult↗
PubMed1999

A role for perforin in downregulating T-cell responses during chronic viral infection.

Cytotoxic T cells secrete perforin to kill virus-infected cells. In this study we show that perforin also plays a role in immune regulation. Perforin-deficient (perf -/-) mice chronically infected with lymphocytic choriomeningitis virus (LCMV) contained greater numbers of antiviral T cells compared to persistently infected +/+ mice. The enhanced expansion was seen in both CD4 and CD8 T cells, but the most striking difference was in the numbers of LCMV-specific CD8 T cells present in infected perf -/- mice. Persistent LCMV infection of +/+ mice results in both deletion and anergy of antigen-specific CD8 T cells, and our results show that this peripheral "exhaustion" of activated CD8 T cells occurred less efficiently in perf -/- mice. This excessive accumulation of activated CD8 T cells resulted in immune-mediated damage in persistently infected perf -/- mice; approximately 50% of these mice died within 2 to 4 weeks, and mortality was fully reversed by in vivo depletion of CD8 T cells. This finding highlights an interesting dichotomy between the role of perforin in viral clearance and immunopathology; perforin-deficient CD8 T cells were unable to clear the LCMV infection but were capable of causing immune-mediated damage. Finally, this study shows that perforin also plays a role in regulating T-cell-mediated autoimmunity. Mice that were deficient in both perforin and Fas exhibited a striking acceleration of the spontaneous lymphoproliferative disease seen in Fas-deficient (lpr) mice. Taken together, these results show that the perforin-mediated pathway is involved in downregulating T-cell responses during chronic viral infection and autoimmunity and that perforin and Fas act independently as negative regulators of activated T cells.

Animals↗
PubMed1998

Abnormal astrocyte development and neuronal death in mice lacking the epidermal growth factor receptor.

Stimulation of the epidermal growth factor receptor (EGF-R) produces numerous effects on central nervous system (CNS) cells in vitro including neuronal survival and differentiation, astrocyte proliferation and the proliferation of multipotent progenitors. However, the in vivo role of EGF-R is less well understood. In the present study, we demonstrate that EGF-R null mice generated on a 129Sv/J Swiss Black background undergo focal but massive degeneration the olfactory bulb, piriform cortex, neocortex, and thalamus between postnatal days 5 and 8 which is due, at least in part, to apoptosis. Some of the neuronal populations that degenerate do not normally express EGF-R, indicating an indirect mechanism of neuronal death. There were also delays in GFAP expression within the glia limitans and within structures outside the germinal zones in early postnatal ages. At or just prior to the onset of the degeneration, however, there was an increase in GFAP expression in these areas. The brains of EGF-R (-/-) animals were smaller but cytoarchitecturally normal at birth and neuronal populations appeared to be intact, including striatal GABAergic and midbrain dopaminergic neurons which have previously been shown to express EGF-R. Multipotent progenitors and astrocytes derived from EGF-R (-/-) mice were capable of proliferating in response to FGF-2. These data demonstrate that EGF-R expression is critical for the maintenance of large portions of the postnatal mouse forebrain as well as the normal development of astrocytes.

Animals↗
PubMed1996

Cortical gray matter volume deficit in patients with first-episode schizophrenia.

OBJECTIVE: A cortical gray matter deficit has been found in cross-sectional studies of patients with chronic schizophrenia. The purpose of this study was to examine whether this deficit is present early in the course of illness. METHOD: The authors measured cortical gray matter volume on magnetic resonance images acquired within 6 months of onset of illness from 22 patients with first-episode schizophrenia and 51 age-matched comparison subjects from the Stony Brook First Episode Study. RESULTS: A significant cortical gray matter deficit and lateral ventricular enlargement were found in schizophrenic patients relative to the comparison group. CONCLUSIONS: The presence of the cortical gray matter deficit close to onset of illness supports the role of preexisting structural brain deficits in the genesis of schizophrenia.

Adult↗
PubMed1995

Sixth plot of the carcinogenic potency database: results of animal bioassays published in the General Literature 1989 to 1990 and by the National Toxicology Program 1990 to 1993.

This paper presents two types of information from the Carcinogenic Potency Database (CPDB): (a) the sixth chronological plot of analyses of long-term carcinogenesis bioassays, and (b) an index to chemicals in all six plots, including a summary compendium of positivity and potency for each chemical (Appendix 14). The five earlier plots of the CPDB have appeared in this journal, beginning in 1984 (1-5). Including the plot in this paper, the CPDB reports results of 5002 experiments on 1230 chemicals. This paper includes bioassay results published in the general literature between January 1989 and December 1990, and in Technical Reports of the National Toxicology Program between January 1990 and June 1993. Analyses are included on 17 chemicals tested in nonhuman primates by the Laboratory of Chemical Pharmacology, National Cancer Institute. This plot presents results of 531 long-term, chronic experiments of 182 test compounds and includes the same information about each experiment in the same plot format as the earlier papers: the species and strain of test animal, the route and duration of compound administration, dose level and other aspects of experimental protocol, histopathology and tumor incidence, TD50 (carcinogenic potency) and its statistical significance, dose response, author's opinion about carcinogenicity, and literature citation. We refer the reader to the 1984 publications (1,6,7) for a detailed guide to the plot of the database, a complete description of the numerical index of carcinogenic potency, and a discussion of the sources of data, the rationale for the inclusion of particular experiments and particular target sites, and the conventions adopted in summarizing the literature. The six plots of the CPDB are to be used together since results of individual experiments that were published earlier are not repeated. Appendix 14 is designed to facilitate access to results on all chemicals. References to the published papers that are the source of experimental data are reported in each of the published plots. For readers using the CPDB extensively, a combined plot is available of all results from the six separate plot papers, ordered alphabetically by chemical; the combined plot in printed form or on computer tape or diskette is available from the first author. A SAS database is also available.

Animals↗
PubMed1994

Protein tyrosine phosphorylation in Mycobacterium tuberculosis.

Crude cell extracts from three strains of Mycobacterium tuberculosis were analyzed for the presence of proteins possessing phosphorylated tyrosine residues. A protein migrating at approximately 55 kDa was detected using an antiphosphotyrosine monoclonal antibody. In addition, less predominant bands were observed between 50 kDa and 60 kDa. That M. tuberculosis contains specific tyrosine phosphorylated proteins implies that M. tuberculosis has tyrosine kinase activity. Examination of other, non-pathogenic mycobacterium species yielded no major antiphosphotyrosine reactive proteins. This suggests that the antiphosphotyrosine reactive protein is specific to M. tuberculosis strains. These results provide evidence that M. tuberculosis contains an antiphosphotyrosine reactive protein.

Antibodies, Monoclonal↗