PubMed Health⌕ Search

Biomedical subjects

H W Chan

Publications and source records attributed to H W Chan.

At least 19 recordsLinked to original sources
PubMed2006

Glutathione peroxidase and glutathione reductase activities are partially responsible for determining the susceptibility of cells to oxidative stress.

Different cell types response differently to toxic insult. In a previous study, it was demonstrated that the C6 glioma cell is more sensitive to Cd induced oxidative stress than the HepG2 cells. To explain the difference between the two cell lines in their response to oxidative stress, it was hypothesized that the activity of glutathione metabolizing enzymes may be different. The objective of this study is to determine the activities of glutathione peroxidase (GPx) and glutathione reductase (GR) in the two cell lines and to explain how these differences may affect the susceptibility of the two cells to oxidative stress. In the HepG2 cells, the activity of GPx was 2.24+/-0.18 micromol/mg protein/min and that for GR was 5.63+/-0.58 micromol/mg protein/min. For the C6 glioma cells, GPx and GR activities were 1.29+/-0.14 and 1.07+/-0.11 micromol/mg protein/min, respectively. Using the kinetic equilibrium: K(eq)=([GSSG]x[NADPH]x[H(+)])/([GSH](2)x[NADP(+)]), and the GSH/GSSG previously published (HepG2: 2.6 and C6 glioma: 3.6), resting NADPH/NADP(+) for the cell lines were calculated. The results showed that NADPH/NADP(+) for HepG2 cells (17.8) is higher than that in the C6 glioma cells (10.8). These data supported the notion that the reducing power (NADPH/NADP(+)) in the HepG2 cells is higher than that in the C6 glioma cell and thus, the later would be more susceptible to oxidative stress. The results also suggested that besides GSH/GSSG, the activities of GPx and GR are important in predicting tissue redox state. Applying this hypothesis to animal tissues, the ratio of the activities of the two enzymes in mouse liver, cerebral cortex, hippocampus and cerebellum were measured. It was demonstrated that the activities of GPx and GR were different in the different tissues studied. The possible correlation between enzymatic activities and the redox state in the different tissues were discussed.

Animals↗
PubMed2004

Clinical profile and genetic basis of Brugada syndrome in the Chinese population.

OBJECTIVE: To study the clinical profile and genetic basis of Brugada syndrome in Chinese patients. DESIGN: Prospective observational study. SETTING: Seven regional public hospitals, Hong Kong. MAIN OUTCOME MEASURES: The clinical and follow-up data of 50 patients (47 men, 3 women; mean age, 53 years) were collected, and genetic data of 36 probands and eight family members of three genotyped probands were analysed. RESULTS: Eight patients survived sudden cardiac death (group A), 12 had syncope of unknown origin but no sudden death (group B), and 30 were asymptomatic before recognition of Brugada syndrome (group C). Programmed electrical stimulation induced sustained ventricular arrhythmias in 88% (7/8), 82% (9/11), and 27% (3/11) of patients in group A, group B, and group C, respectively. New arrhythmic events occurred in 50% (4/8) of patients in group A and 17% (2/12) of patients in group B after a mean follow-up period of 30 (standard deviation, 13) months and 25 (7) months, respectively. All group C patients remained asymptomatic during a mean follow-up period of 25 (standard deviation, 11) months. Five of 36 probands and three of eight family members who underwent genetic testing were found to have a mutation in their SCN5A gene. CONCLUSIONS: Chinese patients with Brugada syndrome who are symptomatic have a high likelihood of arrhythmia recurrence, whereas asymptomatic patients enjoy a good short-term prognosis. The prevalence of SCN5A mutation among probands is 14%. Thus, Chinese patients with Brugada syndrome share with their western counterparts similar clinical and genetic heterogeneity.

Adult↗
PubMed2004

Candidate genetic polymorphisms for asthma in Chinese schoolchildren from Hong Kong.

BACKGROUND: Polymorphisms in several genes have been associated with asthma, atopy and bronchial hyperresponsiveness in white and Japanese populations. In this study we tested for associations of 11 polymorphisms with wheeze and asthma in 10-year-old Chinese schoolchildren. METHODS: The subjects were 107 children who had wheeze in the last 12 months and 118 without wheeze in the last 12 months. They were randomly selected from 3110 children who took part in Phase II of the International Study of Asthma and Allergies in Childhood. These schoolchildren underwent questionnaire, spirometry and methacholine challenge testing. RESULTS: The A allele of the tumor necrosis factor-alpha (TNFA) G-308A polymorphism was significantly associated with wheeze in the last 12 months (odds ratio [OR] 2.1, P = 0.04) and current asthma (OR 2.6, P = 0.006). When stratified by gender, these associations were only seen in the female study participants. In girls, the OR for the TNFA-308A allele and wheeze in the last 12 months was 3.6 (P = 0.01) and for current asthma it was 6.0 (P = 0.0006). CONCLUSION: The A allele of the TNFA G-308A polymorphism was a risk factor for asthma-related phenotypes in girls but not boys.

Asian People↗
PubMed2000

Highly regioselective synthesis of 3,4-disubstituted 1H-pyrrole.

A highly regioselective method for the synthesis of 3, 4-disubstituted 1H-pyrroles has been developed employing the ipso-directing property of a trimethylsilyl group. As a key starting material in this study, the known 3,4-bis(trimethylsilyl)-1H-pyrrole (3), was protected with carefully chosen groups, namely tert-butoxycarbonyl, N,N-dimethylaminosulfonyl, p-toluenesulfonyl, and triisopropylsilyl. A highly regioselective monoiodination of these 1-protected pyrroles was achieved by reaction with iodine-silver trifluoroacetate at low temperatures. Subsequent palladium-catalyzed cross-coupling reactions afforded 1-protected-4-substituted 3-trimethylsilyl-1H-pyrroles, which again underwent further room-temperature ipso-iodination and palladium-catalyzed cross-coupling reactions to provide symmetrical and unsymmetrical 1-protected-3,4-disubstituted 1H-pyrroles. Deprotection of 1-(tert-butoxycarbonyl) and 1-(N, N-dimethylaminosulfonyl) groups was found to be nontrivial. The 1-(p-toluenesulfonyl) protecting group was eventually proved to be superior to other protection groups, because it was readily removed after stepwise ipso monoiodinations and palladium-catalyzed cross-coupling reactions.

Pyrroles↗
PubMed2000

Detection and characterization of a type IIA secretory phospholipase A2 inhibitory protein in human amniotic fluid.

Two types of phospholipase A2 (PLA2) inhibitory protein (PLIP-I, PLIP-II) were detected and isolated from human amniotic fluid by Sephacryl S300 gel filtration chromatography. The lower molecular weight-fraction (PLIP-II) was further purified by Sephadex G75 gel filtration and analyzed by SDS-PAGE. Its molecular weight was estimated to be approximately 18 kDa, and it was sensitive to heat treatment. Inhibition of phospholipase A2 (sPLA2 type IIA) by PLIP-II occurred in a dose-dependent manner (IC50 about 0.82/microm), and the effect was stronger on sPLA2 IIA than on pancreatic sPLA2 (IC50 about 3.11 microL). The ratio of the inhibitions of the sPLA2 IIA by PLIP-II remained consistent over an entire range of substrate concentrations. Furthermore, addition of excess Ca2+ at concentrations of up to 10 mm did not antagonize the inhibitory activity of PLIP-II.

Adult↗
PubMed1998

Molecular cloning, genomic characterization and expression of novel human alpha1A-adrenoceptor isoforms.

We have isolated and characterized from human prostate novel splice variants of the human alpha1A-adrenoceptor, several of which generate truncated products and one isoform, alpha(1A-4), which has the identical splice site as the three previously described isoforms. Long-PCR on human genomic DNA showed that the alpha(1A-4) exon is located between those encoding the alpha(1A-1) and alpha(1A-3) variants. CHO-K1 cells stably expressing alpha(1A-4) showed ligand binding properties similar to those of the other functional isoforms as well as agonist-stimulated inositol phosphate accumulation. Quantitative PCR analyses revealed that alpha(1A-4) is the most abundant isoform expressed in the prostate with high levels also detected in liver and heart.

Adrenergic alpha-Antagonists↗
PubMed1997

Relaxant actions of nonprostanoid prostacyclin mimetics on human pulmonary artery.

The specific prostacyclin (IP) receptor agonist cicaprost relaxed human pulmonary artery preparations precontracted with phenylephrine [50% inhibitory concentration (IC50) approximately 0.6 nM], U-46619 (IC50 approximately 0.9 nM), and K+ (approximately 40% maximal relaxation); endothelium removal had little effect on relaxant activity. Ranking of relaxant potencies for prostacyclin and five of its analogs was 17 alpha, 20-dimethyl-delta 6,6a-6a-carba PGI1 (TEI-9063) > or = cicaprost > iloprost > prostacyclin > taprostene > benzodioxane prostacyclin > 15-deoxy-16 alpha-hydroxy-16 beta,20-dimethyl-delta 6,6a-6a-carba PGI1 (TEI-3356). The potency of the isocarbacyclin TEI-3356 may have been under-estimated because of its contractile (EP3 receptor agonist) activity. The potency ranking of four nonprostanoid prostacyclin mimetics was 3-[4-(4,5-diphenyl-2-oxazolyl)-5-oxazolyl]phenoxy] acetic acid (BMY 45778; IC50 approximately 2.5 nM) > > 2-[3-[2-(4, 5-diphenyl-2-oxazolyl)ethyl]phenoxy]acetic acid (BMY 42393) > octimibate > CU 23 (a novel diphenylindole). From IP receptor binding affinities obtained on human platelet membranes, it is suggested that the slightly shallower log concentration-response curves for BMY 45778, BMY 42393, and CU 23 may reflect the near-maximal receptor occupancy required for complete relaxation. A fifth nonprostanoid, CU 602, had much shallower log concentration-response curves than cicaprost against phenylephrine tone but not against U-46619 tone; this may indicate IP receptor partial agonism coupled with TP receptor antagonism. The relaxant actions of the nonprostanoid mimetics were more persistent than those of the prostacyclin analogs on washout of the organ bath; by the inhalation route, this type of compound may be retained within pulmonary tissue and thus afford greater pulmonary/systemic selectivity than currently used pulmonary vasodilators.

Acetates↗
PubMed1997

Domain organization and sequence relationship of killer cell inhibitory receptors.

Natural killer (NK) cells recognize class I HLA molecules via a family of related receptors composed of two or three Ig-like domains. Using neighbor-joining analysis of available sequences, groups of these receptors were identified that are likely to share specificity in HLA binding, which in some cases had been previously determined for individual group members. Subgroups or clades were further identified which did not appear to correlate with ligand binding, but instead reflect differences in the cytoplasmic region of the proteins. The Ig-like domains, which form the extracellular segment responsible for specificity of HLA recognition, were individually shown to be characteristic of specific groups of receptors, and do not appear to have been assorted between groups. Thus it does not appear that recombination of domains played a major role in generating diversity within regions of these proteins important for HLA binding. Finally, the Ig-like domains of KIR proteins are shown to be between 35-45% identical to those of CD89, a receptor for IgA on myeloid cells. This level of homology, combined with their shared localization on chromosome 19q13.4, suggests a common evolutionary origin.

Amino Acid Sequence↗
PubMed1997

Current views of direct angioplasty in acute myocardial infarct.

OBJECTIVE: The management strategies after acute myocardial infarction (AMI) have been evolving from simple supportive treatment to various protocols of thrombolytic therapies, and then to mechanical revascularization by balloon angioplasty in recent years. However, controversies still exist between which is the best treatment approach. METHODS: An extensive analysis was carried out in over 120 articles reported recently in the literature. RESULTS: Most reported series have shown that direct angioplasty is a feasible and safe option for the management of acute myocardial infarction. Large scale randomised studies comparing direct angioplasty versus thrombolytic therapy in acute myocardial infarction have also reported very favourable acute and long term outcomes by direct angioplasty as compared to thrombolytic therapy. The results are at least equivalent, if not better, by direct angioplasty. Acute results include better reperfusion rate of infarct related artery, less bleeding and stroke complications, shorter hospital stay, and most importantly, lower in-patient mortality (around 2% in direct PTCA group versus 6% in thrombolysis group) and less recurrent ischaemic event (around 10% in direct PTCA group versus 30% in thrombolysis group). Despite some delay in the commencement of treatment by direct angioplasty than thrombolytic therapy, the left ventricular function remains comparable in the two groups and the overall long term outcomes are very favourable with direct angioplasty. Specific indications for direct angioplasty include patients with cardiogenic shock after AMI and patients with contraindications to thrombolysis. No reflow phenomenon is still an issue of concern. It is in general contraindicated to use angioplasty after failure of thrombolysis. The cost implication is not far exceeding that of thrombolysis therapy. CONCLUSIONS: Direct angioplasty for acute myocardial infarction should be established as a treatment option if the circumstances allow. Planning should be carried out at the hospital and community level in order to make direct angioplasty a high priority treatment option for patients with acute myocardial infarction.

Angioplasty, Balloon, Coronary↗
PubMed1997

Stent thrombosis with different types of intracoronary stents: is it still a problem?

OBJECTIVE: The reported results of intracoronary stenting with Palmaz-Schatz stents using the low dose anticoagulation protocol have been encouraging and no stent thrombosis was observed. The effectiveness of such method extending to the use of other types of stents was therefore evaluated in this study. METHODS: All patients followed the anticoagulation protocol (heparin and warfarin) using non-heparin-coated stents. From September 1995, 92 patients received intracoronary stenting (69 men, 23 women, mean age 60.9 years). Altogether 117 stents were implanted in 99 target arteries and 106 lesions. RESULTS: A total of 50.4% of the stents were bare stents (stents without protective sheaths). Both coil stents and slotted tubular stents were used. Stenting was performed without the guidance of intravascular ultrasonography and high-pressure poststenting inflation was used in only 24.0% of patients with less than optimal angiographic results. The mean (+/- SD) coronary minimum luminal diameter changed from 0.63 +/- 0.39 mm to 3.12 +/- 0.48 mm immediately after stenting. Both stent thrombosis rate and femoral bleeding complication rate remained at 0%. Four bare stents could not be deployed in the first instance but without sequels. No morbidity nor mortality was recorded. The mean hospital stay remained at a mean of 4.5 days. All patients (100%) were followed up regularly. The mean (+/- SD) clinical follow-up period was 229 +/- 173 days. Clinical symptoms improved in all patients. CONCLUSIONS: These findings further support that the method is safe and stent thrombosis was not observed. Post-stenting recoil was more with coil stents. Dislodgment and potential risk of embolization could not be underestimated with bare stents. The restenosis rate between different types of stents remains to be determined.

Aged↗
PubMed1996

Amino acid substitutions at position 97 in HLA-A2 segregate cytolysis from cytokine release in MART-1/Melan-A peptide AAGIGILTV-specific cytotoxic T lymphocytes.

CD8+ T lymphocytes recognize antigenic peptides presented by major histocompatibility complex (MHC) class I molecules. Individual peptide termini appear to be fixed at the C- and N-terminal ends. In contrast, central peptide side chains residues may point in different directions and exhibit limited flexibility, dependent on the MHC class I structural variation. For instance, position 97 in HLA-A201 has been shown to shift individual peptide species into different coordinations, one oriented towards the peptide N terminus, or more towards the C-terminal end. The conformational shape of such non-anchor peptide residues may affect the affinity of MHC/peptide/TCR interaction, resulting in quantitative, or qualitative different T cell effector functions. To characterize the impact of different amino acid residues occupying position 97 in HLA-A2 on peptide binding and presentation to CTL, we generated a panel of mutated HLA-A2 molecules containing either M, K, T, V, G, Q, W, P or H at position 97. The HLA-A0201 presented melanoma-associated MART-1/Melan-A derived peptide AAGIGILTV was employed to assess the impact of such position-97 mutations on HLA-A2 in peptide binding measured in an HLA-A2 reconstitution assay and presentation to AAGIGILTV-specific polyclonal or clonal T lymphocytes as measured by cytotoxicity, or interferon (IFN)-gamma and granulocyte/ macrophage colony-stimulating factor (GM-CSF) secretion. The high-affinity AAGIGILTV peptide bound to all position-97 mutants, albeit with differential efficiencies, and elicited specific release of IFN-gamma and GM-CSF by CTL. CTL responses were triggered only by the HLA-A2 wild type, by HLA-A2-H97 (histidine position 97 mutant), and HLA-A2-W97. The HLA-A2-M97 presenting molecule elicited enhanced cytokine release and CTL effector functions by polyclonal and by clonal effector T cells. These results indicate that MHC class I-bound peptides can trigger specific cytokine release by effector T cells independently of their ability to induce cytolysis. We conclude that relatively minor changes in the MHC class I peptide binding groove, including substitutions at position 97, can affect recognition by antigen-specific T cells. Mutant MHC class I molecules, such as those described here, may act as partial peptide antagonists and could be useful for inducing T lymphocytes with qualitatively different effector functions.

Amino Acid Sequence↗