Biomedical subjects

B Chan

Publications and source records attributed to B Chan.

At least 19 recordsLinked to original sources

PubMed2002

The effect of chronic insulin delivery via the intraperitoneal versus the subcutaneous route on hepatic triglyceride secretion rate in streptozotocin diabetic rats.

Chronic intraperitoneal or subcutaneous insulin administration increases triglyceride secretion rate (TGSR) in normal rats. We wished to determine the effect of this treatment on TGSR and the hepatic lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) in diabetic rats. Streptozotocin-diabetic rats, untreated (D), diabetic rats treated with insulin (3 U/day for 21 days) intraperitoneally (IP) or subcutaneously (SC) and non-diabetic rats (N) were studied. TGSR was determined using Triton WR-1339. Fasting glucose and triglyceride levels, high in D, were normalized by insulin treatment regardless of route. Peripheral insulin levels were lowest in D and highest in SC, portal insulin levels were lowest in D and highest in IP. Non-esterified fatty acid levels were not elevated in D, presumably due to adipose tissue depletion. TGSR was reduced in D (P<0.05) and was normalized following insulin administration, regardless of route. ACC activity was normal, but FAS was decreased in D (P<0.05). ACC and FAS were normal in both IP and SC. Thus, in streptozotocin-diabetic rats, chronic intraperitoneal or subcutaneous insulin treatment increases TGSR and FAS activity from their low levels in insulin-deficient rats to levels equal to but not higher than those in normal rats.

Acetyl-CoA Carboxylase↗

PubMed2001

Identification of a novel receptor for B lymphocyte stimulator that is mutated in a mouse strain with severe B cell deficiency.

BLyS (also called BAFF, TALL-1, THANK, and zTNF4), a TNF superfamily member, binds two receptors, TACI and BCMA, and regulates humoral immune responses [1-7]. These two receptors also bind APRIL [7-10], another TNF superfamily member. The results from TACI(-/-) and BCMA(-/-) mice suggest the existence of additional receptor(s) for BLyS. The TACI knockout gives the paradoxical result of B cells being hyperresponsive, suggesting an inhibitory role for this receptor [11, 12], while BCMA null mice have no discernable phenotype [13]. Here we report the identification of a third BLyS receptor (BR3; BLyS receptor 3). This receptor is unique in that, in contrast to TACI and BCMA, BR3 only binds BLyS. Treatment of antigen-challenged mice with BR3-Fc inhibited antibody production, indicating an essential role for BLyS, but not APRIL, in this response. A critical role for BR3 in B cell ontogeny is underscored by our data showing that the BR3 gene had been inactivated by a discrete, approximately 4.7 kb gene insertion event that disrupted the 3' end of the BR3 gene in A/WySnJ mice, which lack peripheral B cells.

Amino Acid Sequence↗

PubMed2001

Consistency analysis of similarity between multiple alignments: prediction of protein function and fold structure from analysis of local sequence motifs.

A new method to analyze the similarity between multiply aligned protein motifs (blocks) was developed. It identifies sets of consistently aligned blocks. These are found to be protein regions of similar function and structure that appear in different contexts. For example, the Rossmann fold ligand-binding region is found similar to TIM barrel and methylase regions, various protein families are predicted to have a TIM-barrel fold and the structural relation between the ClpP protease and crotonase folds is identified from their sequence. Besides identifying local structure features, sequence similarity across short sequence-regions (less than 20 amino acid regions) also predicts structure similarity of whole domains (folds) a few hundred amino acid residues long. Most of these relations could not be identified by other advanced sequence-to-sequence or sequence-to-multiple alignments comparisons. We describe the method (termed CYRCA), present examples of our findings, and discuss their implications.

Adenosine Triphosphatases↗

PubMed2001

A study of demographic changes under sustained below-replacement fertility in Hong Kong SAR.

The total fertility in Hong Kong SAR fell continuously below replacement in the past two decades and reached a level of 0.98 in 1998. The rate in 1981 was close to replacement at 1.93. In this paper the theoretical outcomes of long-lasting below-replacement fertility are identified with a view to gaining some analytical insight into the situation, where the population is experiencing such a striking demographic trend. In the absence of migration, Hong Kong SAR will see its population start to decline between 2008 and 2038, if the future course of fertility falls within these 'bounds'. Concurrently, the aging of population will be reaching unprecedented proportions. Should fertility remain at the present below-replacement level, i.e. the worse-case scenario, the proportion of population aged 65 years or older would increase to 44 per cent, and those aged under 15 years would decrease to six per cent, by 2048. As a result, the potential labour supply (those aged 15-64 years) would dwindle to only 50 per cent of the population, suggesting that there would be less than one person potentially working to support one dependent (who is likely to be a person aged 65 years or older). The socio-economic consequences of population aging are discussed. By analysing net immigration in the demographic process in the past, the way in which replacement migration would help alleviate the problem of population decline and population aging is also discussed.

Adolescent↗

PubMed2001

Cell surface glypicans are low-affinity endostatin receptors.

Endostatin, a collagen XVIII fragment, is a potent anti-angiogenic protein. We sought to identify its endothelial cell surface receptor(s). Alkaline phosphatase- tagged endostatin bound endothelial cells revealing two binding affinities. Expression cloning identified glypican, a cell surface proteoglycan as the lower-affinity receptor. Biochemical and genetic studies indicated that glypicans' heparan sulfate glycosaminoglycans were critical for endostatin binding. Furthermore, endostatin selected a specific octasulfated hexasaccharide from a sequence in heparin. We have also demonstrated a role for endostatin in renal tubular cell branching morphogenesis and show that glypicans serve as low-affinity receptors for endostatin in these cells, as in endothelial cells. Finally, antisense experiments suggest the critical importance of glypicans in mediating endostatin activities.

3T3 Cells↗

PubMed2001

TACI-ligand interactions are required for T cell activation and collagen-induced arthritis in mice.

Interactions of the tumor necrosis factor superfamily members B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) with their receptors-transmembrane activator and CAML interactor (TACI) and B cell maturation molecule (BCMA)-on B cells play an important role in the humoral immune response. Whereas BCMA is restricted to B cells, TACI is also expressed on activated T cells; we show here that TACI-Fc blocks the activation of T cells in vitro and inhibits antigen-specific T cell activation and priming in vivo. In a mouse model for rheumatoid arthritis (RA), an autoimmune disease that involves both B and T cell components, TACI-Fc treatment substantially inhibited inflammation, bone and cartilage destruction and disease development. Thus, BLyS and/or APRIL are important not only for B cell function but for T cell-mediated immune responses. Inhibition of these ligands might have therapeutic benefits for autoimmune diseases, such as RA, that involve both B and T cells.

Animals↗

PubMed2001

Activation and accumulation of B cells in TACI-deficient mice.

The tumor necrosis factor (TNF)-related ligand B lymphocyte stimulator (BLyS) binds two TNF receptor family members, transmembrane activator and calcium-modulating and cyclophilin ligand interactor (TACI) and B cell maturation molecule (BCMA). Mice that are transgenic for BLyS show B cell accumulation, activation and autoimmune lupus-like nephritis. The existence of at least two distinct BLyS receptors raises the question of the relative contribution of each to B cell functions. We therefore generated mice that were deficient in TACI. TACI-/- mice showed increased B cell accumulation and marked splenomegaly. Isolated TACI-/- B cells hyperproliferated and produced increased amounts of immunoglobulins in vitro. In vivo antigen challenge resulted in enhanced antigen-specific antibody production. Thus, TACI may play an unexpected inhibitory role in B cell activation that helps maintain immunological homeostasis.

Animals↗

PubMed2001

Anti-IgE efficacy in murine asthma models is dependent on the method of allergen sensitization.

BACKGROUND: Murine models used to delineate mechanisms and key mediators of asthma have yielded conflicting results and suggest that the dominant mechanism and mediators required for disease induction differ depending on the model and method of allergen sensitization used. OBJECTIVE: The goal of this study was to determine whether the mode of allergen sensitization influenced the role that IgE had in allergen-induced pulmonary eosinophilic inflammation. METHODS: Mice were exposed to dust mite extract in 2 models of allergic inflammation that differed in the method of sensitization. We compared sensitization by aerosol exposure with and without concomitant human respiratory syncytial virus infection with sensitization by means of systemic (intraperitoneal) exposure with adjuvant. After sensitization, animals were similarly challenged with aerosolized allergen. Animals were treated with anti-IgE mAb to deplete IgE and to determine its role in the induction of allergic inflammation and mucosa pathology in these models. RESULTS: Concomitant respiratory syncytial virus infection significantly enhanced allergen sensitization by aerosol exposure and exacerbated eosinophilic inflammation and airway mucosa pathology. Depletion of IgE in this model significantly reduced lung eosinophilic inflammation and airway mucosa pathology. However, in the model in which animals were sensitized by means of systemic allergen exposure with adjuvant, depletion of IgE had no ameliorative effect on lung inflammation or pathology. CONCLUSION: We demonstrated that the method of antigen sensitization can delineate the role of IgE in allergen-induced lung inflammation. In a murine model that more closely resembles ambient allergen exposure in human subjects, IgE had a critical role in the pathogenesis of allergic asthma and mucosa pathology. The results parallel the results reported with anti-IgE efficacy in allergic asthmatic human subjects.

Allergens↗

PubMed2001

Increased cell proliferation and associated expression of PDGFRbeta causing hypercellularity in patellar tendinosis.

OBJECTIVE: This study assessed cellularity in patellar tendinosis with respect to cell proliferation and the expression of platelet-derived growth factor receptor beta (PDGFRbeta). METHODS: Surgical samples were taken from 11 patients fulfilling criteria of patellar tendinosis and from 12 matched controls. Standard immunohistochemistry methods were used to detect expression of PDGFRbeta and proliferation cell nuclear antigen (PCNA). Results were analysed by computer-assisted microscopy. Tendon cells were isolated from nine tendinosis and eight control tissues for cell culture. RESULTS: Increased cellularity (P<0.001) was observed in tendinosis tissues compared with controls, and also a higher proliferative index (P:<0.001). Increased expression of PDGFRbeta was demonstrated (P<0.001). Cultured tendinosis cells showed a higher proliferation rate than controls (P<0.001). This was maintained when the cells were cultured under various conditions of serum supplementation (P<0.01). Tendinosis cells also showed a higher proliferation rate (P<0.01) in medium containing 10 ng/ml PDGF. CONCLUSION: Hypercellularity in patellar tendinosis is caused by increased cell proliferation and is associated with increased expression of PDGFRbeta.

Adolescent↗

PubMed2001

On-line detection of sleep-wake states and application to produce intermittent hypoxia only in sleep in rats.

Sleep-disordered breathing is associated with adverse clinical consequences such as daytime sleepiness and hypertension. The mechanisms behind these associations have been studied in animal models, especially rats, but intermittent stimuli such as hypoxia have been applied without reference to sleep-wake states. To determine mechanisms underlying the adverse physiological consequences of stimuli associated with sleep-disordered breathing requires criteria for detection of sleep-wake states on-line to trigger stimuli only in sleep. This study aimed to develop such a system for freely behaving rats. Twelve rats with implanted electroencephalogram and neck electromyogram electrodes were studied in the light and dark phases. Electroencephalogram frequencies in the high (20-30 Hz) and low (2-4 Hz) frequency bands distinguished non-rapid eye movement (REM) sleep, whereas neck electromyogram distinguished REM. Using these parameters in a simple algorithm led to detection accuracies of 94.5 +/- 1.0 (SE) % for wakefulness, 96.2 +/- 0.8% for non-REM sleep, and 92.3 +/- 1.6% for REM compared with blinded human judgment. The algorithm was then used to trigger hypoxic stimuli only in sleep. Because frequency and amplitude analysis is readily performed using a variety of commercial systems, incorporation of these parameters into such an algorithm will facilitate studies investigating mechanisms underlying the physiological consequences of sleep-related respiratory stimuli in a fashion that more effectively models clinical disorders.

Algorithms↗

PubMed2001

Myopia in Singapore kindergarten children.

PURPOSE: The purpose of this study was to examine whether close-up work was related to myopia in Singapore kindergarten children. METHODS: One hundred twenty-eight children, ages 3 to 7 years, from a kindergarten in Singapore were examined by cycloplegic autorefraction. The parents also completed a questionnaire on the different types of close-up work activities each child was engaged in, socioeconomic status, and parental history of myopia. RESULTS: Myopic children spent 3.0 hours per day (median) on close-up work activity, while nonmyopic children spent 2.0 hours per day (median) on close-up work activity. The prevalence of myopia in the sample was 8.6%. CONCLUSION: Close-up work activity was not related to myopia in pre-school children.

Child↗

PubMed2000

Evolutionary coadaptation of the motif 2--acceptor stem interaction in the class II prolyl-tRNA synthetase system.

Known crystal structures of class II aminoacyl-tRNA synthetases complexed to their cognate tRNAs reveal that critical acceptor stem contacts are made by the variable loop connecting the beta-strands of motif 2 located within the catalytic core of class II synthetases. To identify potential acceptor stem contacts made by Escherichia coli prolyl-tRNA synthetase (ProRS), an enzyme of unknown structure, we performed cysteine-scanning mutagenesis in the motif 2 loop. We identified an arginine residue (R144) that was essential for tRNA aminoacylation but played no role in amino acid activation. Cross-linking experiments confirmed that the end of the tRNA(Pro) acceptor stem is proximal to this motif 2 loop residue. Previous work had shown that the tRNA(Pro) acceptor stem elements A73 and G72 (both strictly conserved among bacteria) are important recognition elements for E. coli ProRS. We carried out atomic group "mutagenesis" studies at these two positions of E. coli tRNA(Pro) and determined that major groove functional groups at A73 and G72 are critical for recognition by ProRS. Human tRNA(Pro), which lacks these elements, is not aminoacylated by the bacterial enzyme. An analysis of chimeric tRNA(Pro) constructs showed that, in addition to A73 and G72, transplantation of the E. coli tRNA(Pro) D-domain was necessary and sufficient to convert the human tRNA into a substrate for the bacterial synthetase. In contrast to the bacterial system, base-specific acceptor stem recognition does not appear to be used by human ProRS. Alanine-scanning mutagenesis revealed that motif 2 loop residues are not critical for tRNA aminoacylation activity of the human enzyme. Taken together, our results illustrate how synthetases and tRNAs have coadapted to changes in protein-acceptor stem recognition through evolution.

Adaptation, Biological↗

PubMed2000

FIZZ1, a novel cysteine-rich secreted protein associated with pulmonary inflammation, defines a new gene family.

Bronchoalveolar lavage fluid from mice with experimentally induced allergic pulmonary inflammation contains a novel 9.4 kDa cysteine-rich secreted protein, FIZZ1 (found in inflammatory zone). Murine (m) FIZZ1 is the founding member of a new gene family including two other murine genes expressed, respectively, in intestinal crypt epithelium and white adipose tissue, and two related human genes. In control mice, FIZZ1 mRNA and protein expression occur at low levels in a subset of bronchial epithelial cells and in non-neuronal cells adjacent to neurovascular bundles in the peribronchial stroma, and in the wall of the large and small bowel. During allergic pulmonary inflammation, mFIZZ1 expression markedly increases in hypertrophic, hyperplastic bronchial epithelium and appears in type II alveolar pneumocytes. In vitro, recombinant mFIZZ1 inhibits the nerve growth factor (NGF)-mediated survival of rat embryonic day 14 dorsal root ganglion (DRG) neurons and NGF-induced CGRP gene expression in adult rat DRG neurons. In vivo, FIZZ1 may modulate the function of neurons innervating the bronchial tree, thereby altering the local tissue response to allergic pulmonary inflammation.

Amino Acid Sequence↗

PubMed2000

Effects of humanized monoclonal antibody to rhesus CD11a in rhesus monkey cardiac allograft recipients.

INTRODUCTION: Leukocyte function-associated antigen-1 (LFA-1, CD11a) monoclonal antibody (mAb) affects many leukocyte functions without cell depletion. We hypothesized that the use of a humanized, anti-rhesus modified LFA-1 mAb (H2C12) in rhesus monkeys would cause: (1) prolonged heart allograft survival, (2) inhibition of primary but not secondary antibody responses, and (3) minimal drug toxicity. METHODS AND RESULTS: Control (n=5) and H2C12-treated (n=7) (8-20 mg/kg i.v. on day -1 followed by 10 mg/kg/day) adult male rhesus recipients were inoculated with GP120 protein antigen on day -28 and -1 and grafted with heterotopic abdominal hearts (day 0). Donor-recipient pairs were equally MLR mismatched (4329.8+/-1124.1 CPM controls vs. 7289.0+/-1926.5 treated, P=NS). Mean heart allograft survival as evaluated by daily abdominal palpation was significantly prolonged in high dose recipients (23.0+/-2.6, n=4) vesus controls (8.2+/-1.3, n=5, P<0.02, Mann-Whitney U test). H2C12 treatment did not produce signs of cytokine release or toxicity, was nondepleting, but down-modulated PBL CD11a expression to 43.4+/-3.6% (n=4) of control levels (n=5) at day 7 as demonstrated by flow cytometry. It had no effect on postoperative Con A or MLR and did not prevent mAb clearance due to the rhesus-antihuman antibody response. The addition of mycophenolate mofitil prevented rhesus-antihuman antibody response with therapeutic H2C12 levels seen for >35 days. CONCLUSIONS: The use of this mAb to block CD11a had the benefit of being a well tolerated, highly targeted therapy. These are the first results showing that monotherapy with anti-leukocyte function-associated antigen-1 mAb prolonged survival of MLR mismatched allogenic cardiac grafts in primates.

Animals↗

PubMed2000

Microvascular reconstruction and tracheotomy are significant determinants of resource utilization in head and neck surgery.

BACKGROUND: Successful "critical pathway" design and implementation are dependent on appropriate patient stratification according to those factors that are primary determinants of resource utilization. OBJECTIVES: To test the validity of our previously reported critical pathway design and to determine whether tracheotomy and microvascular reconstruction (MR) are primary determinants of resource utilization. DESIGN: Cost-effectiveness analysis. SETTING: Tertiary referral academic institution. METHODS: Retrospective analysis of data from 133 head and neck surgery cases in which the treatment regimen was based on critical pathways over a 26-month period. OUTCOME MEASURES: Length of stay and total patient charges were used as indices of resource utilization. One-way analysis of variance and t tests were used for statistical analysis of significance. RESULTS: Ninety patients (67.7%) underwent MR; 43 (32. 3%) did not. Seventy-five patients (56.4%) underwent tracheotomy; 58 (43.6%) did not. Four patient groups were constructed in decreasing order of complexity as follows: group 1, patients who underwent both tracheotomy and MR (n = 58); group 2, patients who underwent MR alone (n = 32); group 3, patients who underwent tracheotomy alone (n = 17); and group 4, patients who did not undergo either procedure (n = 26). Both tracheotomy and MR were found to be independent determinants of resource utilization and were additive when both were present. The length of stay varied from 8.4 days (in patients who underwent both procedures) to 6.7 days (in patients who did not undergo either procedure), with intermediate values in cases in which only 1 procedure was performed. The total charges varied in a similar manner from a high of $33,371 to a low of $19,994. Subanalysis with respect to intensive care unit, ward, and operating room charges showed a similar stratification. CONCLUSION: Tracheotomy and MR are both significant determinants of charges and length of stay in head and neck surgery cases and must be considered in the design of strategies to promote efficient resource utilization.

Cost-Benefit Analysis↗

PubMed2000

Assessment of hemodynamic response during focal neural activity in human using bolus tracking, arterial spin labeling and BOLD techniques.

In this study, the hemodynamic response and changes in oxidative metabolism during functional activation were measured using three functional magnetic resonance imaging (fMRI) techniques: the blood oxygenation level-dependent (BOLD) technique, flow-sensitive alternating inversion recovery (FAIR), and bolus tracking (BT) of an MR contrast agent. With these three techniques we independently determined changes in BOLD signal, relative cerebral blood flow (rCBF), and cerebral blood volume (rCBV) associated with brain activation in eight healthy volunteers. In the motor cortex, the BOLD signal increased by 1.8 +/- 0.5%, rCBF by 36.3 +/- 8.2% (FAIR), and 35.1 +/- 8.6% (BT), and rCBV by 19.4 +/- 4.1% (BT) in response to simultaneous bilateral finger tapping. In the visual cortex, BOLD signal increased by 2.6 +/- 0.5%, rCBF by 38.5% +/- 7.6 (FAIR), and 36.9 +/- 8.8% (BT), and rCBV by 18.8 +/- 2.8% (BT) during flickering checkerboard stimulation. Comparing the experimentally measured rCBV with the calculated rCBV using Grubb's power-law relation, we conclude that the use of power-law relationship results in systematic underestimate of rCBV.

Adult↗

PubMed2000

A mixed-penalty biphasic finite element formulation incorporating viscous fluids and material interfaces.

The fluid viscosity term of the fluid phase constitutive equation and the interface boundary conditions between biphasic, solid and fluid domains have been incorporated into a mixed-penalty finite element formulation of the linear biphasic theory for hydrated soft tissue. The finite element code can now model a single-phase viscous incompressible fluid, or a single-phase elastic solid, as limiting cases of a biphasic material. Interface boundary conditions allow the solution of problems involving combinations of biphasic, fluid and solid regions. To incorporate these conditions, the volume-weighted mixture velocity is introduced as a degree of freedom at interface nodes so that the kinematic continuity conditions are satisfied by conventional finite element assembly techniques. Results comparing our numerical method with an independent, analytic solution for the problem of Couette flow over rigid and deformable porous biphasic layers show that the finite element code accurately predicts the viscous fluid flows and deformation in the porous biphasic region. Thus, the analysis can be used to model the interface between synovial fluid and articular cartilage in diarthrodial joints. This is an important step toward modeling and understanding the mechanisms of joint lubrication and another step toward fully modeling the in vivo behavior of a diarthrodial joint.

Biomechanical Phenomena↗

PubMed2000

A multi-mutant herpes simplex virus vector has minimal cytotoxic effects on the distribution of filamentous actin, alpha-actinin 2 and a glutamate receptor in differentiated PC12 cells.

To develop effective gene therapy techniques that target populations of neurons in the spinal cord, suitable vectors must be developed that will undergo efficient, retrograde transport from an appropriate peripheral site and will not be cytotoxic. Our previous work (LeVatte et al, 1998a) has demonstrated that a replication defective herpes simplex virus vector 14Hdelta3vhsZ, that has been substantially detoxified, is retrogradely transported from peripheral sites and can infect large numbers of the targeted spinal neurons. We plan to develop targeted gene therapy approaches designed to modulate the excitatory glutamatergic methyl-D-aspartate (NMDA) receptor in spinal cord neurons as a means of ameliorating a form of episodic high blood pressure that occurs after spinal cord injury. In this report, we demonstrate that, in differentiated PC12 cells, a neuronal-like cell line, the virus vector does not appear to alter aspects of the cytoskeletal architecture important to the proper distribution of the NMDA receptor. In turn, the distribution of endogenous NMDA receptor 1 subunit protein (NMDAR1) or a transfected NMDAR1-green fluorescent fusion protein was also found to be unaltered after vector infection. However, whereas endogenous NMDAR1 distribution was maintained, vector infection did tend to reduce the level of its expression. This drop in endogenous NMDAR1 expression coincided with the expression of the HSV immediate early genes ICP0 and ICP27 over the first 24-48 h. These results indicate that the 14Hdelta3vhsZ herpes simplex virus vector is suitable to use in future strategies to alter the level of gene expression in targeted populations of spinal cord neurons.

Actin Cytoskeleton↗