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Biomedical subjects

J Chan

Publications and source records attributed to J Chan.

At least 163 records · Page 9Linked to original sources
PubMed1996

Biosynthesis of human ficolin, an Escherichia coli-binding protein, by monocytes: comparison with the synthesis of two macrophage-specific proteins, C1q and the mannose receptor.

Ficolin is characterized by the presence of both collagen-like and fibrinogen-like sequences, and potentially has a similar overall structure as the complement protein C1q and the collectins. Previous studies have reported the presence of human ficolin mRNA predominantly in peripheral blood leucocytes. In the present study, the cellular origin of human ficolin was investigated in further detail. Preliminary studies using reverse transcriptase-polymerase chain reaction (RT-PCR) showed that ficolin mRNA was synthesized by U937 cells, a human monocyte cell line. This finding suggested that blood monocytes also normally synthesize human ficolin. Peripheral blood monocytes from adult human donors were harvested at serial time-points (0-20 hr) after adhesion to tissue culture plates, and total RNA was isolated and assayed for ficolin mRNA by RT-PCR. Ficolin mRNA was highly expressed in monocytes throughout the first 20 hr of adhesion. In contrast, C1q and mannose receptor mRNA were not detectable during the first 8 hr of adhesion, but were highly expressed by 20 hr. Cells were harvested at longer time intervals (1, 2, 4, 6 and 8 days) to determine whether ficolin expression was temporally regulated at later stages of monocyte differentiation. Ficolin mRNA levels decreased sharply from day 1 to day 6. In contrast, the levels of both C1q and mannose receptor mRNA showed no changing trend. These results are consistent with the absence of ficolin expression in many macrophage-rich tissues previously reported. The origin of ficolin from monocytes, together with its structural similarity to C1q and the collectins, raises the possibility that ficolin may be another plasma protein capable of binding to surface structures of micro-organisms. Escherichia coli was therefore incubated with human serum, and bound proteins, after elution with sugars, were analysed by Western blotting using an antiserum raised against a synthetic ficolin peptide. The antiserum identified a polypeptide of approximately 42000 MW, which is similar in size to that of ficolin as predicted from its cDNA-derived sequence.

Blotting, Western↗
PubMed1996

Isolation of microtubule-associated proteins from carrot cytoskeletons: a 120 kDa map decorates all four microtubule arrays and the nucleus.

A method for biochemically isolating microtubule-associated proteins (MAPs) from the detergent-extracted cytoskeletons of carrot suspension cells has been devised. The advantage of cytoskeletons is that filamentous proteins are enriched and separated from vacuolar contents. Depolymerization of cytoskeletal microtubules with calcium at 4 degrees C releases MAPs which are then isolated by association with taxol stabilized neurotubules. Stripped from microtubules (MTs) by salt, then dialysed, the resulting fraction contains a limited number of high molecular weight proteins. Turbidimetric assays demonstrate that this MAP fraction stimulates polymerization of tubulin at concentrations at which it does not self-assemble. By adding it to rhodamine-conjugated tubulin, the fraction can be seen to form radiating arrays of long filaments, unlike MTs induced by taxol. In the electron microscope, these arrays are seen to be composed of mainly single microtubules. Blot-affinity purified antibodies confirm that two of the proteins decorate cellular microtubules and fulfil the criteria for MAPs. Antibodies to an antigenically related triplet of proteins about 60-68 kDa (MAP 65) stain interphase, preprophase band, spindle and phragmoplast microtubules. Antibodies to the 120 kDa MAP also stain all of the MT arrays but labelling of the cortical MTs is more punctate and, unlike anti-MAP 65, the nuclear periphery is also stained. Both the anti-65 kDa and the anti-120 kDa antibodies stain cortical MTs in detergent-extracted, substrate-attached plasma membrane disks ('footprints'). Since the 120 kDa protein is detected at two surfaces (nucleus and plasma membrane) known to support MT growth in plants, it is hypothesized that it may function there in the attachment or nucleation of MTs.

Animals↗
PubMed1996

U.S. hospital mycobacteriology laboratories: status and comparison with state public health department laboratories.

In response to the resurgence of tuberculosis, the Centers for Disease Control and Prevention recommended the use of certain mycobacteriology laboratory methods to improve the accuracy of diagnosis and/or minimize times to complete specimen processing. A study to determine the extent to which these recommended methods were being used in hospital laboratories was needed. In 1992, a survey was mailed to infection control and laboratory personnel at 1,076 hospitals with > or = 100 beds to determine the mycobacterial laboratory services being performed, the methods being used, the number of specimens being processed, and the times to completion during 1991. In 1995, a 20% sample of hospital laboratories that responded to the initial questionnaire was resurveyed. Responses to the 1992 survey were received from personnel at 756 (70%) hospitals representing 750 laboratories. Among laboratories performing the services, the use of recommended methods was as follows: fluorochrome stain for acid-fast bacillus microscopy (47%); radiometric methods for primary culture (29%); rapid (radiometric methods, use of nucleic acid probes, high-performance liquid chromatography, or gas-liquid chromatography) methods for identification of Mycobacterium tuberculosis (59%); and radiometric methods for drug susceptibility testing (55%). Reported times to complete specimen processing were shortest for laboratories that used recommended methods and longest for hospitals that referred specimens to outside laboratories. Only 46% of surveyed laboratories performed at least the minimal number of mycobacterial cultures (20/week) deemed necessary to maintain competence. Among 145 laboratories that performed the services and were resurveyed in 1995, use of recommended techniques increased from 44 to 73% for acid-fast bacillus microscopy, from 27 to 37% for primary culture, from 59 to 88% for M. tuberculosis identification, and from 55 to 75% for drug susceptibility testing. These changes were associated with reductions in reported specimen turnaround times. Use of the methods recommended by the Centers for Disease Control and Prevention increased at the resurveyed hospital mycobacteriology laboratories between 1991 and 1995. However, continued efforts are needed to increase the use of recommended methods at moderate- and high-volume laboratories, encourage referral of specimens from low-volume laboratories, and transmit results rapidly from all laboratories.

Humans↗
PubMed1996

Long-term follow up of primary trabeculectomy for infantile glaucoma.

BACKGROUND: The treatment for infantile glaucoma is surgical. Treatment options include goniotomy, trabeculotomy, combined trabeculotomy-trabeculectomy, and trabeculectomy. METHODS: Patients who had a follow up of 5 years or longer after primary trabeculectomy were examined to determine the long term stability in infantile glaucoma. RESULTS: In eyes with primary infantile glaucoma 92.3% achieved control of their glaucoma with a single trabeculectomy; 100% achieved control with two trabeculectomies; 85.7% of eyes with secondary infantile glaucoma achieved control with a single trabeculectomy. There were no serious complications experienced in either group. CONCLUSION: Primary trabeculectomy is a safe and successful operation for infantile glaucoma.

Case-Control Studies↗
PubMed1996

Motor neuron disease in Hong Kong Chinese: epidemiology and clinical picture.

This study documents the clinical features, incidence and prevalence of motor neuron disease (MND) in Hong Kong Chinese. Patients with MND who were alive between 1989 and 1992 were recruited by retrieval of medical records from the four major hospitals in Hong Kong, and by referral of neurologists, neurosurgeons and medical consultants. Mortality statistics was provided by the Census and Statistics Department. A total of 84 cases were identified with a male preponderance of 1.98:1. The average annual period incidence was 0.31/100,000 and the point prevalence on December 31, 1992, was 0.95/100,000. The mean age at onset was 55.5 years (range 19-81) with a peak observed from 55 to 65 years. The clinical features are similar to other reported series of MND. The incidence and mortality of MND in Hong Kong are therefore lower than the worldwide figures of 2.0/100,000 and 1.5/ 100,000, respectively.

Adult↗
PubMed1996

Oral health of Singapore adults.

In a study conducted by the Dental Division of the Ministry of Health in 1992, 3157 Singapore adults aged 20 to 65 years and over were interviewed on their knowledge, attitude and practice of dental care and given an examination. About 66% indicated they required dental treatment. Utilisation of dental services was low with 39% visiting the dentist at least once in 2 years. About 72% brushed their teeth morning and night. The dental examination showed that 79.2% had calculus, 92% needed prophylaxis and oral hygiene instruction and only 0.2% needed complex periodontal treatment. A large proportion (96.6%) of the sample was dentate. The mean DMFT was 10.7 and the mean number of decayed root for the dentate population was 0.2. The age-group 65 years and over had the highest percentage (63.6%) of persons wearing dentures and the age group 50-54 years had the highest percentage (54.2%) requiring dentures. This study has shown that oral health promotion for home and professional care should be stressed to the adult population, particularly the older age groups.

Adolescent↗
PubMed1996

Glucocorticoid increases rat apolipoprotein A-I promoter activity.

The observation that glucocorticoids increase the abundance of apolipoprotein A-I led us to a search for potential underlying mechanism(s). In this report, we show that the synthetic glucocorticoid, dexamethasone, injected into rats increases serum levels of apoA-I protein, hepatic mRNA and "run-on' transcription of the gene by 3-, 5-, and 2-fold, respectively. Results of transient transfection studies of the rat apoA-I promoter reveal that effects of dexamethasone are mediated by a cis-acting site B (-170 to -145). Dexamethasone treatment of hepatoma cells enhances the DNA binding activity of nuclear factors that bind this site. Unexpectedly, site B does not contain a consensus glucocorticoid receptor recognition motif nor binds to bacterially expressed glucocorticoid receptor. These results indicate that the actions of glucocorticoids on site B involve indirect mechanisms. Site B is comprised of a direct repeat of a nonanucleotide and mutation of either one abolishes the effect of glucocorticoid. Additionally, the transcriptional activity of site B in response to dexamethasone is amplified by a 5' sequence called site S (-186 to -171). Dexamethasone has no effect on site S in the absence of site B. In summary, our data show that dexamethasone increases rat apoA-I gene expression by an indirect mechanism.

Animals↗
PubMed1995

Glia-dependent neurotoxicity and neuroprotection in mesencephalic cultures.

Dopaminergic neurotoxicities of 6-hydroxydopamine (6-OHDA) and the lipopolysaccharide (LPS) were compared in rat mesencephalic cultures plated on poly-L-lysine or on glial monolayers. In the neuron-enriched cultures plated on polylysine, 6-OHDA killed 89% of the tyrosine hydroxylase (TH)-immunopositive neurons, but LPS was not neurotoxic. Conversely, in mixed neuron/glial cultures, 6-OHDA killed only 27% of the TH-immunopositive neurons while LPS killed 70%. The mixed neuronal/glial mesencephalic culture offers a better in vitro model for studying possible mechanisms involved in Parkinson's disease.

Animals↗
PubMed1995

Amygdala efferents form inhibitory-type synapses with a subpopulation of catecholaminergic neurons in the rat Nucleus tractus solitarius.

The central nucleus of the amygdala (CNA) integrates visceral responses to stress partially through efferent projections to portions of the medial nuclei of the solitary tracts (mNTS) containing catecholaminergic neurons. To determine anatomical sites for CNA modulation of these neurons, immunoperoxidase detection of anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) was combined with immunogold-silver labeling of the catecholamine-synthesizing enzyme, tyrosine hydroxylase, in adult rat mNTS. From 350 anterogradely labeled terminals identified within the intermediate mNTS, 30% formed symmetric, inhibitory-type synapses and the remainder lacked recognized junctions as seen within a single plane of section. Of the terminals forming symmetric synapses, 16% were presynaptic to tyrosine hydroxylase immunoreactive dendrites and the remainder to unlabeled dendrites. The level of tyrosine hydroxylase immunoreactivity as assessed by density of gold-silver particles was significantly lower in dendrites receiving synaptic input from CNA efferents as compared with dendrites of the same sizes (2.0 microns 2 in mean area) which received synapses from unlabeled terminals or lacked recognizable synaptic inputs. When separately examined without regard to afferent input, the medium- and larger-sized dendrites having mean cross-sectional areas of 1-3 microns 2 also contained significantly less tyrosine hydroxylase immunoreactivity than small (< 1 micron 2) dendrites. These results suggest that CNA efferents to the mNTS inhibit non-catecholamine-containing neurons and a subpopulation of catecholaminergic neurons distinguished by their low levels of tyrosine hydroxylase. The findings also indicate that small, presumably more distal, dendrites in the intermediate mNTS may synthesize and/or release catecholamines.

Afferent Pathways↗
PubMed1995

MMK2, a novel alfalfa MAP kinase, specifically complements the yeast MPK1 function.

Mitogen-activated protein (MAP) kinases are serine/threonine protein kinases that are activated in response to a variety of stimuli. Here we report the isolation of an alfalfa cDNA encoding a functional MAP kinase, termed MMK2. The predicted amino acid sequence of MMK2 shares 65% identity with a previously identified alfalfa MAP kinase, termed MMK1. Both alfalfa cDNA clones encode functional kinases when expressed in bacteria, undergoing autophosphorylation and activation to phosphorylate myelin basic protein in vitro. However, only MMK2 was able to phosphorylate a 39 kDa protein from the detergent-resistant cytoskeleton of carrot cells. The distinctiveness of MMK2 was further shown by complementation analysis of three different MAP kinase-dependent yeast pathways; this revealed a highly specific replacement of the yeast MPK1(SLT2) kinase by MMK2, which was found to be dependent on activation by the upstream regulators of the pathway. These results establish the existence of MAP kinases with different characteristics in higher plants, suggesting the possibility that they could mediate different cellular responses.

Amino Acid Sequence↗
PubMed1995

Co-localization of angiotensin II and gamma-aminobutyric acid in axon terminals in the rat subfornical organ.

Angiotensin II (Ag II) and gamma-aminobutyric acid (GABA) in the subfornical organ have been implicated in drinking and cardiovascular responses to changes in circulating hormones. We combined immunogold silver labeling of Ag II with immunoperoxidase detection of GABA to determine whether there might be common cellular sites for their physiological actions in this circumventricular region. Electron microscopy showed that numerous terminals in central portions of the rat subfornical organ contained both Ag II and GABA immunoreactivity. These terminals as well as others exclusively labeled for AgII or GABA formed mainly symmetric, inhibitory type synapses with unlabeled dendrites. Immunogold-silver aggregates recognizing AgII were often detected near non-synaptic portions of the plasma membrane with or without apparent association with large dense core vesicles. In contrast, the GABA immunoperoxidase labeling was most intensely localized to membranes of small clear vesicles which were aggregated near the presynaptic junction. Our results indicate that in rat subfornical organ, neuronal AgII may modulate the inhibitory postsynaptic responses to GABA following release from single axon terminals.

Angiotensin II↗
PubMed1995

Induction of transforming growth factor beta 1 and its receptors during all-trans-retinoic acid (RA) treatment of RA-responsive human neuroblastoma cell lines.

Recent work on a variety of normal and malignant cell lines has shown that induction and secretion of biologically active TGF-beta may occur after exposure to all-trans-retinoic acid (RA), coincident with decreased growth rate and/or differentiation. This study evaluates the expression and regulation of transforming growth factor beta (TGF-beta) and its receptors during RA-induced cell growth arrest and induction of differentiation in the RA-sensitive human neuroblastoma cell line SMS-KCNR and the RA-resistant neuroblastoma cell line SK-N-AS. RA treatment of SMS-KCNR cells results in a 40-fold increase in TGF-beta 1 mRNA after 4 days of RA, a dose-dependent increase in TGF-beta 1 secretion, an increase in types I (TBRI) and III (TBRIII) TGF-beta receptor proteins, and an increase in type II TGF-beta receptor (TBRII) mRNA coincident with RA-responsiveness of the cells. However, in the RA-resistant line SK-N-AS, TGF-beta 1 is constitutively secreted at levels that are unchanged after RA treatment, and although TBRI and TBRIII mRNA is expressed in untreated SK-N-AS cells, levels of TBRI and TBRIII protein and TBRII mRNA decrease after RA treatment. Thus, in RA-sensitive neuroblastoma cells, RA treatment may result in the induction of a negative autocrine TGF-beta 1 growth regulatory loop. These results suggest the hypothesis that: (a) induction of a TGF-beta 1 negative autocrine growth loop may be a necessary component for RA-responsiveness of neuroblastoma cells in vivo; and (b) the inability to induce or maintain this TGF-beta 1 negative autocrine growth loop may be a mechanism of RA resistance in neuroblastoma.

Base Sequence↗
PubMed1995

Rescue of synthetic measles virus minireplicons: measles genomic termini direct efficient expression and propagation of a reporter gene.

Measles virus (MV) mRNA transcription and replication are thought to be controlled by cis-acting sequence elements contained within the terminal MV genomic noncoding nucleotides. To validate these promoter and regulatory signal assignments, cDNAs were constructed allowing synthesis of RNAs corresponding to a MV genome in which all coding and intercistronic regions were replaced by the chloramphenicol acetyl transferase (CAT) coding sequence. Transcript production by T7 polymerase starting and ending precisely with the MV genome terminal residues was achieved by fusing the T7 polymerase promoter and the hepatitis delta virus genome ribozyme followed by tandem T7 polymerase termination sequences to the MV genomic 5' and 3' ends, respectively. Transfection of these negative polarity transcripts, mimicking natural defective interfering RNAs of the internal deletion type, into MV-infected 293 cells gave rise to CAT activity which could be serially transferred and massively amplified together with progeny helper virus in fresh cells. Transfer was blocked only by antibodies able to neutralize MV infectivity, indicating that the chimeric RNA not only was encapsidated, transcribed, and replicated, but also packaged into virions. Sequence analyses confirmed that both the expected chimeric antigenome and mRNA products were transcribed and replicated with fidelity during serial passage. Minor changes introduced in the transcription promoter markedly compromised function. This system now can be exploited to examine MV genomic cis-acting regulatory elements and extended to the development of full-length MV cDNAs.

Base Sequence↗
PubMed1995

Ultrastructural characterization of neurons recorded intracellularly in vivo and injected with lucifer yellow: advantages of immunogold-silver vs. immunoperoxidase labeling.

Immunoperoxidase labeling of lucifer yellow provides a sensitive method for morphological characterization of neurons recorded intracellularly in vitro or in vivo. However, the reaction product is often so dense that it obscures ultrastructural details necessary for the analysis of synaptic contacts onto individually filled neurons. In the present study, we describe a silver intensification procedure using 1 nm gold labeling of lucifer yellow as an optimal means for immunocytochemically identifying single physiologically characterized neurons at the ultrastructural level. Single neurons in the frontal cortex of anesthetized rats were impaled in vivo and filled with lucifer yellow. The brains were then perfused with an acrolein fixative. Single vibratome sections through the recording site were reacted with a rabbit antibody directed against lucifer yellow followed by goat anti-rabbit 1 nm gold-labeled IgG and silver intensified. For comparison, additional sections were processed for immunoperoxidase detection of lucifer yellow. Labeled sections were processed for light microscopy or embedded in plastic for electron microscopy. The immunogold-silver label as well as peroxidase reaction product of lucifer yellow was readily detected in cell bodies, proximal and distal dendrites, and spines. However, in contrast to immunoperoxidase, the immunogold-silver reaction did not obscure subcellular organelles. Most importantly, the synaptic junctions formed by afferents to the filled neuron were more easily identifiable following the immunogold-silver procedure. This clear visualization of postsynaptic densities is essential for examining synaptic circuitry between afferents and physiologically characterized neurons.

Animals↗
PubMed1995

Prospective study of cigarette smoking, alcohol use, and the risk of diabetes in men.

OBJECTIVE: To examine the association between smoking, alcohol consumption, and the incidence of non-insulin dependent diabetes mellitus in men of middle years and older. DESIGN: Cohort questionnaire study of men followed up for six years from 1986. SETTING: The health professionals' follow up study being conducted across the United States. SUBJECTS: 41,810 male health professionals aged 40-75 years and free of diabetes, cardiovascular disease, and cancer in 1986 and followed up for six years. MAIN OUTCOME MEASURE: Incidence of non-insulin dependent diabetes mellitus diagnosed in the six years. RESULTS: During 230,769 person years of follow up 509 men were newly diagnosed with diabetes. After controlling for known risk factors men who smoked 25 or more cigarettes daily had a relative risk of diabetes of 1.94 (95% confidence interval 1.25 to 3.03) compared with non-smokers. Men who consumed higher amounts of alcohol had a reduced risk of diabetes (P for trend < 0.001). Compared with abstainers men who drank 30.0-49.9 g of alcohol daily had a relative risk of diabetes of 0.61 (95% confidence interval 0.44 to 0.91). CONCLUSIONS: Cigarette smoking may be an independent, modifiable risk factor for non-insulin dependent diabetes mellitus. Moderate alcohol consumption among healthy people may be associated with increased insulin sensitivity and a reduced risk of diabetes.

Adult↗
PubMed1995

Transient acidosis induces delayed neurotoxicity in cultured hippocampal slices.

It remains unknown if tissue acidosis contributes to neuronal loss during cerebral ischemia. We report that brief intracellular acidification (pH 6.62) results in delayed neuronal loss in cultured hippocampal slices. Cell loss was located primarily in stratum pyramidale and the hilus suggesting that neurons were preferentially damaged. Removal of molecular oxygen greatly attenuated cell loss suggesting that generation of reactive oxygen species may underlie acidosis-induced toxicity. These data suggest that acidosis and incomplete anoxia contributes to the delayed neuronal loss in the ischemic penumbra.

Acidosis↗
PubMed1995

Neuropeptide Y and dynorphin-immunoreactive large dense-core vesicles are strategically localized for presynaptic modulation in the hippocampal formation and substantia nigra.

Neuropeptide Y (NPY) and dynorphin elicit regionally selective presynaptic modulation in the hippocampal formation and the pars reticulata of the substantia nigra, respectively. We examined potential anatomical substrates for their presynaptic modulation by determining the distribution and size of large (80-120 nm) dense-core vesicles (DCVs), organelles previously shown to be immunoreactive for each peptide. Throughout the hippocampal formation, NPY-immunoreactive DCVs were located primarily in axon terminals and were more sparingly distributed in dendrites. In comparison with other portions of the hippocampal formation, NPY-labeled DCVs were most abundant in axons and terminals of the CA1 region. The DCVs in the CA1 region of the hippocampus also more frequently had larger mean cross-sectional diameters when located along portions of the terminal in contact with unlabeled axons. In both the CA1 region of the hippocampus and the dentate gyrus, NPY-labeled DCVs in contact with portions of the axonal membrane apposed to astrocytes also were larger than those located more centrally in the axon terminal. Dynorphin-immunoreactive DCVs in axon terminals of the substantia nigra were significantly larger when found near portions of the axonal membrane in contact not only with other axons and astrocytic processes, but also occasionally with postsynaptic dendrites. The parallels between diameters of DCVs and known selectivity of NPY for presynaptic modulation in the CA1 region of the hippocampus suggest a direct correlation between the size and distribution of immunoreactive DCVs and their sites of exocytotic release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗